䔀唀刀伀倀䔀䄀一 䴀䄀匀吀䔀刀匀 䤀 一 䌀䰀䔀䄀一 䘀伀匀匀䤀 䰀 䄀一䐀 䄀䰀吀䔀刀一䄀吀䤀 嘀䔀 䘀唀䔀䰀匀 䔀一䔀刀䜀夀
吀攀愀洀眀漀爀 欀 戀礀 猀 琀 甀搀攀渀琀 猀 漀昀 䬀䤀 䌀 䤀 渀渀漀䔀渀攀爀 最礀 䴀⸀ 匀挀⸀ 倀爀 漀最爀 愀洀Ⰰ 漀渀
匀唀匀吀䄀䤀一䄀䈀䰀䔀 䔀一䔀刀䜀夀 䜀氀 椀 眀椀 挀 攀 ㈀ 㔀
Sustainable Energy
Gliwice 2015
Sustainable Energy Editor: Dhanush Basavakumar
Contributors: Alessandro Pan Dagmara Pokwiczał Dhanush Basavakumar Maciej Olszewski Krzysztof Trzepizur Magdalena Maj Magdalena Trzcionka Maria Kolmer Milan Zlatkovikj Paweł Rodak Przemysław Maziarka Szymon Dulik Viktor Kadek
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Foreword Energy is indispensable for continued human development and economic growth. Providing adequate, affordable energy is essential for improving human welfare, and raising living standards world-wide. The strategy for sustainable development aims to promote harmony among human beings and between humanity and nature. KIC InnoEnergy is the European company dedicated to promoting innovation, entrepreneurship and education in the sustainable energy field by bringing together academics, businesses and research institutes. The goal of the organization is to make a positive impact on sustainable energy in Europe. We would like to thank KIC InnoEnergy, which has been the force behind this conference. The organisation has helped us in overcoming problems. We are greatly indebted to this organisation, which has been of immense value and has played a major role in bringing this conference to a successful completion. The satisfaction and euphoria that accomplished the successful completion of any task would be incomplete without the people who made it possible, whose constant guidance and encouragement crowned out effort with success. On behalf of students of KIC InnoEnergy M.Sc. Program in Clean Fossil and Alternative Fuels Energy I would like to thank all the people who made this conference possible. Our heartfelt thanks to Dr. Krzysztof Pikon, Program Director of M.Sc. Clean Fossil and Alternative Fuels Energy in Silesian University of Technology for the encouragement and facilities provided to carry out this conference in our college. We would like to place on record our deep sense of gratitude to Magdalena Bogacka, Katarzyna Piecha, and Joanna Mehlich for the help and encouragement. We take this opportunity to express our gratitude and respect to all the reviewers, Dr. Karol Sztekler, Dr. Krzysztof Pikon, Dr. Sylwester Kalisz, Dr. Arkadiusz Ryfa, and Dr. Adam Klimanek for their valuable guidance. We wish to express sincere thanks to OŚIE organisation, for extending necessary assistance without which this conference would not have been possible.
Thanking you, Dhanush Basavakumar
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Table of contents Emission analysis of biomass boiler for domestic use ............................................................................................ 7 Catalytic cracking in fluidized bed reactor as a method of plastic wastes utilization ........................................... 19 Future of Energy Technologies ............................................................................................................................. 27 Use of Bacillus Megaterium in solubilization of phosphorus from incineration plant .......................................... 37 Cost of producing electricity ................................................................................................................................. 47 Analysis of CCS process in post-combustion technology ..................................................................................... 59 Impact of SCNR DeNOx installations on coal combustion by-products quality ................................................... 73 Renewable energy from biomass – vineyard prunings .......................................................................................... 81 The perspectives of thermal utilization of municipal solid waste (MSW) in the city of Gliwice. ........................ 87 Energy Storage Technologies ............................................................................................................................... 97
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Emission analysis of biomass boiler for domestic use Alessandro Pan Politecnico di Torino
Abstract This work has the objective of analyzing and studying the emissions of a biomass boiler with the nominal output of 25 kW, to be used for domestic heating. The aim is as well to study a new type of wood pellet and state the levels of its emissions. Particular attention will be given to dust, nitrogen oxides and carbon monoxide. The work will be structured as follows: an overview on Italian and European regulations on emissions, a description of materials and methods used and, in the end, the conclusions obtained. This work has been done with the group “Systems for Energy and Environment” from Politecnico di Torino, in a project financed by the Piedmont region
1. Regulations The analysis of emissions from boilers with power output under 500 kW concerns two groups of laws: the first defining structure of the boilers and the second about the emission limits. Regarding the structure and requirements of boilers should be named two norms, both valid on European level:
UNI EN 303-5, regarding boilers with solid fuel with nominal power output under 500 kW EN 12809:2001, regarding residential boilers with solid fuels with power output under 50 kW
Emissions of biomass boilers are regulated at the Italian level by the D. Lgs 152/2006, but every single region can make regulations stricter: for example, minimum level of dust emissions for boilers of 35 kW output is 200 mg/Nm3 at a national level but only 30 mg/Nm3 in the Piedmont region. In Northern Italy, as well as in many other densely populated regions, there is a huge problem with air pollution, especially regarding suspended particles. Because of this, it may happen that in particularly critical situation biomass boilers might be prohibited in a certain region or for a certain time. In our case the analysed boiler has got a nominal output of 25 kW, and thus does not have to take account of the regulations: both on regional and national account the minimum power considered is 35 kW; in Germany, for example, a regulation exists for all boilers over 4 kW and thus regards almost all domestic plants. It must be remembered that according to regulations the emissions must be expressed on dry exhaust gases with 11% of oxygen at normal conditions (0 °C, 1 atm). This is very important as in biomass combustion the variation of air excess and thus of oxygen is very significant.
2. Materials and methods 2.1. Measuring tools To measure the emissions of the boiler has been used the TESTO 380, an instrument that allows to measure continuously the instant value of the concentration of dust, CO and O2. It is possible to measure other values as well, such as flue gas temperature and gas humidity. Single measures of NOx can be made, with a special probe. The measuring system is composed by two different instruments, as can be seen in figure 1: the total dust analyzer, with a probe for particulate matter, and the combustion analyser TESTO 330-2 LL V3, which is a command center to analyse the values of combustion products.
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Fig. 1. TESTO 380 used during the dust measuring: it is possible to notice the exhaust probe inserted in the flue gas duct and the combustion analyser The probe for particulate matter is composed as well by a rotating diluter made in ceramic, that mixes a part of the raw gas with clean air, with the aim of having a cleaner gas incoming in the central analyser, without dirtying problems in the pipe and in the sensor. The temperature remains around 80°C to avoid condensation of dangerous compounds. Oxygen is measured with a lambda probe; continuous measuring of dust is, instead, more complicated. In laboratory tests, dust is measured through a gravimetric analysis: this consists in letting a known airflow pass through a filter and later weigh the mass that has been deposited on it. This measurement has got a high accuracy, but the big inconvenient is that it can’t be taken in a continuous way [1]. This instrument is based on the same gravimetric principle, but is able to measure values in a continuous way: exhaust gases are let pass into a nozzle and later impact on an oscillating quartz plate. The frequency of the oscillation is a function of the mass on the plate; in this way it is possible to calculate the mass and (since the amount of air is known) the original concentration. The accuracy of the instrument is 0.1 mg/m3, which is much more than the minimum resolution demanded by the law [2].
2.2. Fuel The types of fuels derived from biomass are defined in the European standard EN 14961. In general, the fuel must contain standard values that change according to the origin of biomass, in such a way it’s possible to have the best accuracy. Thus, have to be measured the values of:
Calorific value Humidity Ash Nitrogen Sulphur Chlorine
The compounds named make combustion less ideal and thus make it more complicated from the exhaust treatment point of view. Thus, all these values (except from the calorific value) should be as low as possible. Humidity is twice damaging: it makes the fuel heavier (and thus more complicated to move and to store) and makes the process less effective, since some heat is used to vaporize the water in the fuel with no useful effect. Two types of fuel have been used, to make a comparison between them: an innovative woodchip, object of this study, and a well-known standard wood pellet.
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The alternative fuel that will be analysed is an innovative type of woodchip, obtained by chipping the fuel in small pieces of about 1 cm of length (Figure 2); the classic production system that is widely carried out is standard wood chips, but with bigger dimensions. Standard pellet is usually imported in Italy, since there are very little possibilities of having a competitive production of this good, mainly because of the territory: mountains are too steep to use big machineries, and thus the production costs are much higher. This innovative woodchip, instead, can have a good local production which is actually almost not used by residential heating, but only by big plants, since quality of wood is lower. This fuel has been produced by two firms specialized in wood in the province of Torino, mainly by chestnut wood and has the following properties:
Humidity around double as the one of standard pellet Calorific value about half as much of pellet Density slightly less than a half of pellet
Fig. 2. Innovative woodchip
Fig. 3. Standard pellet
The fuel we used to compare the woodchip’s emissions is common wood pellet with well-known characteristics (Figure 3), with a low level of dust and humidity; it is of category EN plus A1 (the best possible) and produced in Austria by the company Binderholz. It has the following properties [3]:
Species of wood: spruce fir Humidity: 5.2% in weight Calorific value: 17.86 MJ/kg Dust at 850°C: 0.19% Density: 710 kg/m3
2.3. Plant The plant was located inside a container and is composed by these fundamental parts, most of which can be seen in figure 4:
A boiler with nominal power output of 25 kW, developed from Pelletstar boiler by the Austrian firm Herz. Compared to the original version, it has some differences in the combustion chamber and in the time interval between the charging of the fuel.
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A puffer of 1250 liters of capacity, connected to the boiler with a three way valve. Its aim is to absorb the rapid increases or decreases in the power output of the boiler, typical for any kind of wood boiler: if the boiler was directly connected to the fan coils, it would be much more difficult to have a constant power output. The overall efficiency of the plant is as well improved. During steady state working, this puffer has a temperature around 75 °C. Two fan coils connected to the puffer, to emit the power to the environment, that start working when the puffer reaches its standard temperature. A fuel extraction auger, bigger than in the pellet version, to avoid problems of extraction and transport data from the rougher fuel, thus more difficult to handle. This is driven by an electric motor which rotates at a constant speed for a certain time, and then stops. Depending on the thermal load to be supplied it is automatically altered the rotation time and the pause between two rotations, so as to have a loading more or less frequent and/or more or less in quantity. A deposit of fuel of about 200 kg of capacity, in order to guarantee sufficient autonomy in the case of a real use for domestic heating. There are systems that prevent the formation of so-called "bridges", which block the loading of the fuel and stop the working boiler. Network of pipes and pumps with temperature and flow rate sensors.
3. Experimental data
Fig. 4. Plant overview: it is possible to notice the boiler, the puffer and the measuring tool. The sensors are connected to a computer that registers the data with intervals of 2 minutes The data reported here were collected during the month of June 2015 at one of the firms involved in the project. As anticipated, the discussion will focus primarily on the issues of:
Total suspended particles (TSP) Nitrogen oxides (NOx) Carbon monoxide (CO)
These are in fact the main pollutants resulting from the combustion of biomass. The correlation between these values will be analyzed, to understand how they are related and possibly figure out how to adjust the combustion optimally. Tests were carried out at full load and partial load (35% of the nominal power) to study the differences in the behavior of the system.
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3.1. Nitrogen oxides The nitrogen oxides or NOx are produced by virtually all combustion processes, either from the biomass or from other sources of energy. They are in fact the result of the oxidation of nitrogen, always involved in the combustion processes because of its presence in ambient air. Their formation has some main causes:
Nitrogen in the air: in normal ambient air it is present with a percentage of 79%. In addition to this, biomass combustion requires excess air to have the complete oxidation of all components. Nitrogen in the fuel High combustion temperature
In our case, the wood used is mainly chestnut for innovative woodchip, and conifer in the case standard pellets, it is therefore supposed that the amount of nitrogen in the fuel is negligible. The parameters on which one can study the case are the air excess and the flue gas temperature.
The excess air is significant since the size and chemical composition of the fuel are not constant. In case combustion happened with air in stoichiometric proportions, this would lead to a defect in the combustion air and therefore production of carbon monoxide and other unburnt compounds, clearly more harmful than NOx. The temperature of the flue is equally important, since the reaction of NOx formation is the more accentuated the more the combustion temperature is high.
The measurement was made through the TESTO 380 with a specific probe for the measurement of nitrogen oxides. Unfortunately, the probe was not able to measure the NOx continuously (while it is possible with the dust). Significant data in the various conditions of operation were chosen, so as to cover both the full load and the partial load. The measurement of Total Nitrogen Oxides (NOx) is made via a direct measurement of the nitrogen monoxide (NO) and a subsequent addition of a quantity "theoretical" of nitrogen dioxide (NO2). This amount was set at 5% of the total value of NO measured directly; this value is in accordance with the legislation of Piedmont (Piedmont Regional Plan for heating and improvement of air quality). As can be seen from Figures 5 and 6 on the next page, oxygen in the flue gas (and therefore excess air) and temperature are closely related: the temperature increases and thus the amount of oxygen decreases. In figure 6 it is possible to distinguish two well-defined areas: on the right, side at full load (at higher temperature) and on the left, at partial load (at lower temperature). This fact could be understood even better with the data of the temperature in the combustion chamber as a function of the temperature. Unfortunately, this data was not possible to be downloaded from the machine instantaneously, and was only possible to be read on the display. At full load the temperature fluctuates around 630°C, while at partial load it is reduced to approximately 430°C, because of constant leakages and greater time interval that elapses between the one load and the other. From these graphs it can be seen how the NOx concentration increases with increasing temperature and with decreasing oxygen (which is itself connected to the temperature in combustion chamber). This makes these data trustable as it is what expected from theory.
3.2
Total Suspended Particles
The suspended particles are probably the most critical emission factor in the biomass plants and, as mentioned previously, is what makes its use problematic within densely populated and polluted areas. Their presence is due to multiple causes [4]:
The finer particles (<1 μm) usually originate from processes that take place at high temperatures and/or so-called "secondary" formation processes between gas and particles. These particles carry inorganic, organic and semi-volatile compounds. The coarser particles (> 1 μm) are generated from mechanical processes such as erosion, corrosion and abrasion of materials. The ultra-fine particles (<0.1μm) are abundant in number, but they constitute only a small part of total dust.
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Fig. 5. Nitrogen oxides compared to the amount of oxygen in the flue gas. Notice how the concentration is lower when the air excess is higher.
Fig. 6. Nitrogen oxides compared to the flue gas temperature. The correlation in the case is directly proportional.
In the analyzed case the main amount of particles will be made up of particles of larger size, but still the instrument will measure the amount of total dust (in mg/Nm3), regardless of the aerodynamic diameter.
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The ashes are present to a greater extent within the cortex and the less noble parts of the tree, but are also a result of a fine powder created during the cutting of the wood and present in the fuel. This wood powder, when loaded in the combustion chamber, does not burn and is directly sucked in the flue gases from the boiler, and then discharged to the chimney. Precisely for this reason, the results obtained by us are not entirely comparable to those which could conceivably obtain the combustion of the commercial product when will be marketed: the fuel was sieved only in some cases, while when production will be started these operations will be performed automatically before the packaging. The measuring instrument is able to detect concentrations of total dust in continuous, with a resolution of 5 seconds. From the data used have been removed the data taken at the very beginning of each measurement: we noticed that for the first 15 seconds the instrument showed data that made no sense with the later measurements and thus decided not to consider this transient state. In addition to this, tests were used only when all single measurements were always positive. In some cases the sensor detected negative data; it was assumed that this error is due to sudden mass variations detected by the oscillator that weighs dust. All data shown are those detected by the instrument upstream of corrections; the instrument in fact subtracts a certain amount from the "raw" value. This amount is proportional to the value resulting from a statistical parameter that concerns the uncertainty in the measurement, and calculated to be around 1.75; in this discussion is given the figure of 40 mg/Nm3, but the correct figure would be slightly less than 23 mg/Nm3. For avoidance of doubt in the interpretation we have chosen to reason only on raw data, both in the case of innovative woodchip and of standard pellet. As described in the section concerning the installation, the boiler is fed through an auger that performs a specified number of rounds each time interval established. At the time of loading, the oxygen in the room is used for burning fuel, so that its content is lowered; combustion continues while the amount of oxygen tends to rise until new fuel is loaded. Considering this, we can explain the cyclical fluctuation, like oxygen. As in the previous graph, the fluctuations in the concentration of CO often occur at the same time as those of the dust; the oscillations of the carbon monoxide, however, are much more marked. This can be explained with the cycles of loading and burning of the fuel.
Fig. 7. Dispersion of all the values obtained for tests at full load for woodchip. The average value is 40.1 mg/Nm3 Looking at figure 7, it’s possible to compare all the tests done and see their progress in a single representation. It can be noticed how some tests are markedly more stable than others, recording all or most of their values within a
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very narrow range; on the other hand some tests (e.g. the first) have values extremely oscillating who seem never to reach stability. In some tests the concentrations have very big changes in values; it’s supposed to be due to transients of the sensor or operation error. On average, the value of 40.1 mg/Nm3 can be considered as an attendible data, although, to have even more precise measurements, tests with more controlled fuel than that used in the case study should be made.
3.3. General Results It is possible to notice in all measurements similar patterns of the different species:
The powders and carbon monoxide fluctuated, and have peak values at similar moments. The flue gas temperature is almost constant, with slight variations around its average value; however, it is highly dependent on the load and the fuel. Oxygen has an average oscillating trend, more pronounced in full load working in innovative woodchip than in the other cases.
The temperature of the flue gas is closely connected to the load, and is therefore possible to distinguish two fundamental cases:
At full load the temperature in the combustion chamber is around 630°C, while the flue gas temperature is 115°C; At partial load both values are reduced, with the temperature in the combustion chamber around 430°C and that of the flue gas at 70°C.
These values are shown in figure 8, in which the plotted points represent the average values of the valid measurements, both for the nominal load that for the partial load. It can also be noticed a close relationship between the temperature increase and the lowering of the amount of oxygen. This is understandable, given that, at partial load, the loading cycles are much longer and therefore combustion in its latter stages has a high excess air. Besides full and partial load, there are also data about the cleaning of the burner (with the green dot): the burner has to be cleaned cyclically, and this cleaning takes place by stopping the combustion and letting the air flow through the burner to clean it from ashes and other unburnt compounds. While the temperature and dust have average values in both the case at partial and at full load, the oxygen in the flue gas increases very much (since the combustion is almost stopped), as well as the CO, that has peaks above the 10 g/Nm3 while in the standard running it has values around 200-400 mg/Nm3. These data about the cleaning of the burner were measured only once and therefore are not very reliable, but they give an idea of the orders of magnitude during the cleaning of the boiler and how these operations may influence the actual average emissions during the actual operation. The carbon monoxide is shown in figure 9 in a logarithmic graph in order to submit the average values of the measurement carried out during the cleaning of the burner. Its value is almost two orders of magnitude greater than the emissions during nominal load. Comparing figures 9 and 10, emissions of TSP and carbon monoxide are higher in partial load running; they are directly proportional, how was stated observing the data from single tests.
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Fig. 8. Average values for different tests at full and partial load. The load influences very much the amount of oxygen in the flue gas; it is possible to notice that with partial load there is a greater dispersion of the values
Fig. 9. Average values of dust compared to carbon monoxide. During the cleaning of the burner the concentration of CO reaches very high levels, compared to the standard running
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Fig. 10. Average values of dust and oxygen concentration; load concerns oxygen amount but not necessarily dust emissions .
3.4
Comparison between standard and innovative woodchip, at full load
In order to be able to reason in a clearer way, it is useful to make a comparison between the emissions of innovative woodchip, about which it has been written so far, with the emission of standard pellet in standard running conditions. To have a comparison with "the best possible fuel" from the point of view of emissions, it has been chosen the best possible competitor: we tested an Austrian pellet of quality ENplus-A1, the highest standard. More accurate data can be read in detail in "fuel used." The differences in the characteristics of combustion are imaginable, and can be seen in figure 11:
Dust emissions of the pellets are 40% lower. The reasons are both the different composition of the wood and the absence of dust in the fuel, which is much more dense and compact. The emissions of carbon monoxide have a reduction almost identical to that of the powders. The amount of oxygen is slightly lower, by approximately 12%, the result of better combustion which therefore needs less excess air. The temperature of the fumes is higher as the temperature in the combustion chamber rises from 600°C to almost 750°C.
Fig. 11. Comparison hystogram between NG and standard pellet. The innovative woodchip’s values are normalised to 1
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4. Conclusions Emissions are measured in line with what could be expected from a fuel of this type: they are higher than the "competitor" fuel, but not to an extent to be too different. In Italy there is no limit emissions for biomass boilers with under 35 kW. If it were adopted in the future the same limit that now applies to boilers of power above 35 kW, these devices would respect it. In the analysis were used only the raw data and not the corrected data given by the instrument, that have a much lower value; since we don’t know how is the formula to achieve this corrections, all the calculations have been done on the raw data. The measuring tool used by us uses a method derived from the gravimetric system, which therefore makes the data very reliable; an interesting analysis to validate the data would be to do the same testing with another instrument that works with a different principle in parallel, and observe if there is any difference. The fuel used can be considered representative enough of the commercial fuel that will be marketed, with the difference that it contains a higher level of powder, that in the large-scale production will be eliminated. Once the production process will be initiated on a larger scale, from the fuel so treated it is conceivable to expect values of lower emissions of CO and dust. The plant has been arranged so as to represent as closely as possible to a domestic plant, which is the destination of this type of boiler. The combustion of the standard pellet compared to the innovative woodchip is much better both from the point of view of the powders of the carbon monoxide: the pellet has reached the great diffusion that has today precisely because it is easy to burn, very low values of ashes and moisture. In addition, standard pellet has a density about three times higher, with the added benefit of a higher calorific value: the result is that, a hypothetical system powered with woodchips needs a storage volume six times bigger. It should be noted, however, that the current state of the Italian production chain of wood pellet is very costly from the energetic point of view: as anticipated, almost all the fuel used is imported from European countries or even outside Europe, with an amount of emissions from transportation not negligible at all. In light of these facts, but beyond the discussion of this thesis, the more emissions achieved during combustion of innovative woodchip are one price to be paid to prevent the introduction of other pollutants during production and transportation in places far away from end users.
References [1] [2] [3] [4]
http://www.minambiente.it/pagina/principi-di-misura-degli-inquinanti Informative booklet of Testo 380 Technical informations on Binderholz pellet packaging http://bioenergyfvg.uniud.it/fileadmin/documenti/Corso_energie_rinnovabili/Le_emissioni_nella_combustione _di_biomasse.pdf
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Catalytic cracking in fluidized bed reactor as a method of plastic wastes utilization Dagmara Pokwiczał, Przemysław Maziarka , Maciej Olszewski. University of Science and Technology in Kraków
Abstract Due to increasing amount of plastic wastes coming from different sources there is a need to implement various technologies, which are to recycle plastic wastes and allow to decrease landfilling. There are several already implemented technologies, but still not for a scale exceeding landfilling of that type of wastes. In this paper authors focus on a catalytic cracking carried out in fluidized bed reactor as a method of plastic wastes utilization. The test stand was built by students in a laboratory with money from Rector’s Grant AGH no. 52 from 2015.
1. Introduction Over the past years, countries in the European Union recorded economic growth. Due to that growth production of different goods is increasing. That causes higher demand for sources through which products can be obtained. In most industrial processes not only goods are produced, but also a waste. Additionally, every product has its own lifetime. That means after its lifetime useful product becomes a waste. Due to these facts it can be stated that economic growth indirectly contributes to increasing amount of waste. Modern economies that approach to the problem consciously try to reverse this trend. Most often this is done through increasing production efficiency and waste management. A large role here also takes public awareness of a need for recycling and not producing excessive amounts of waste. The significant consumption has made people to look for solutions leading to decrease of landfilled wastes. In Poland there are around 4 billion tonnes of wastes landfilled and that number increases by 145 million tonnes every year [1]. In most commonly used division, there are two general groups of waste. The first of them is industrial waste from production of goods and services. The second is the waste associated with households. According to data from Eurostat [2], the EU countries generated in 2012 approximately 2500 million tonnes of waste, of which 91% were industrial waste, and municipal 9%. Two the biggest groups producing industrial waste are mining industry (29%) and building industry (31% of industrial waste). Municipal waste takes 9% of all waste what is 213 million tonnes of waste. Municipal waste due to the diversity of their origin are much harder to manage. In Poland there are similar trends in terms of waste structure. In 2014 industrial waste amounted to 123 million of tonnes (92.3%), municipal waste amounted to 10.3 million of tonnes (7.7%) [3]. Of all the waste generated, most mineral waste arises which, by their nature, restrained applications [4]. In case of organic waste, the situation is different. Their amount is far smaller than inorganic waste and there is much greater possibility of their management. Waste of major importance in this group is biodegradable waste (biogas, fertilizers), paper waste (recycling) and also plastic waste. The last of the mentioned groups is characterized by the highest potential of chemical processing and energy.
2. Characterization of plastic waste It was estimated that in 2012 had been produced around 25.2 million tonnes of plastic wastes on the European market [4]. European Union takes second place in terms of world plastics production [3]. According to Association of Plastics Manufacturers “Plastics Europe” about 75 % of plastics is produced in following European countries: Germany, France, Netherlands, Spain and also in Poland [4]. Plastic waste consists of organic compounds which are mostly long chained and aromatic hydrocarbons like paraffins, naphthenes, aromatics and in lower amounts olefins [10]. Due to plastics origin they can be divide into two groups: industrial waste and municipal waste. Those two groups have different properties and the way of their management is also different [5]. Industrial plastic wastes are from plastic manufacturing and industrial processing. They are rather low contaminated. Industry of plastic manufacture causes plastic wastes, but they are mostly reused within the factories [6]. Municipal plastic wastes are collected from households. Typical composition of that type
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of plastic wastes is PE, PP, PS, PVC [4]. The ratio of present types of plastic is usually three parts of PE, one part PP and one part PS [4]. Major of plastic sources are from packages (at the level of 30% of municipal waste by volume). Particularly noteworthy is the fact that these are the compounds that are an important source of hydrogen (3%-15% by mass. H) [7], with high calorific value at the level of 45 MJ/kg [6]. Below structures of most common compounds are presented.
Fig. 1. Polyethylene
Fig. 2. Polypropylene
Fig. 3. Polyvinyl chloride
Methods of plastic waste management Taking into account the waste management models, there are three solutions: recycling, energy recovery and landfilling. Averaged data on waste plastics in Europe is 26.3% of waste recycled, 35.6% directed to energy recovery, while the remaining 38.1 % of the waste was sent to landfill waste [4]. In countries with a ban on landfilling of plastics ( Policy “zero plastic landfill” ), recycling ranges from 25 to 35%, landfilling only a few percent, while the remaining part is the recovery of energy from waste [2]. In Poland in 2012, 25 % of waste was recycled, 13 % of waste was designated to energy recovery and 62 % of waste remaining was landfilled [3]. Since 2016, Poland will start implementation of „Zero plastic landfill” policy. That means the gradual introduction of a landfill ban in favor of recycling and energy recovery. Figure presented below shows data on the management of plastic waste in the EU and Poland.
Fig. 4. The share of waste management in 2012 in a) EU b) Poland [1] Due to increasing demand, urbanization, a rising standard of living, there are more plastic products manufactured, as well as already launched on the market [9]. In Poland and also in the entire Europe, there are plenty of solid, organic wastes which can be transformed into different forms of energy. In Europe the largest share of plastics production are polymers of ethylene (PE). Other, smaller shares are polymers from propylene (PP), polyvinyl chloride (PCV), polystyrene (PS) and polyethylene terephthalate (PET). As there is a significant social development all over the world, there is also higher demand of energy. Conventional sources cause high environmental pollution, so due to that fact new, clean, alternative sources are sought. Plenty of surveys has confirmed the possibility of exploiting of solid plastic wastes as an energy sources with high calorific values. It is also an approach leading to improvement of environment condition, since Poland and many countries of Europe has to face the problem of significant emission of CO 2 and many pollutants. Methods of plastic
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wastes utilization, as well as of obtaining valuable fuels by recovery of hydrocarbons are under research and development all over the world. On the market there are already implemented technologies for utilizing waste [9]. From the available technologies on the market for energy recovery from waste made of plastic thermal processing plays a crucial role. The most widely used method of waste utilization with energy recovery is their combustion. It takes place in specially prepared incineration plants. Energy coming from that process is converted to the heat for municipal residents and to electricity. Another thermal process is thermal cracking. It is a process of thermal decomposition of material in oxygen-free atmosphere. This process is aimed at a partial tear of long hydrocarbon chains of which are composed of polymers [10]. Owing to thermal cracking, in the process we obtain shorter hydrocarbons as liquid and gas fractions. Thermal cracking products are not high quality due to wide range of hydrocarbons present in these products. Due to that fact, they can be used in narrow range of valuable sources, for instance in production of engine fuels [11]. Furthermore thermal cracking is usually carried out in temperatures higher than 500 °C [11, 12]. Due to high temperature process is very energy consuming and therefore rather uneconomic.
3. Catalytic cracking Catalytic cracking is a continuation of approach to processing waste plastics. Catalytic cracking of plastic wastes is also the process of interests of many researchers as well as companies dealing with plastic waste management. The difference between thermal cracking and catalytic cracking is usage of catalyst. Due to use of catalyst we can receive product which is in field of our interest. This is all owing to presence of selective catalyst which direct reaction of decomposition to obtain desirable products. Furthermore in catalytic cracking application of selective catalyst allows to carry out the process in lower temperature what decrease the cost. Under catalytic conditions the cracking process may be carried out at the temperature of 300 °C up to 500°C [12, 13, 14]. Increasing catalyst/plastic waste ratio we can lower the process temperature. According to the Y. Ishihara and others [15], in pyrolysis of polypropylene when the catalyst/plastics ratio was 6 to obtain the liquid yield of 46 % the temperature was kept at the level of 220°C. In catalytic cracking application of selective catalyst allows to carry out the process in lower temperature what decrease the cost [11]. According to the current research results in case of plastic wastes utilization mostly aromatics and naphthenes are formed [5]. As a product we receive gas fraction and liquid fraction.
Tab. 1. Product composition of polypropylene cracking over silica-alumina at 477 °C (wt.%) [6]
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Applied catalysts vary with the desirable products we want to obtain. There are used fluid cracking catalysts (FCC), which have been found as ones causing high efficiency in plastic pyrolysis. The most known are zeolite-based catalyst with high activity and selectivity and alumina-silicate catalysts [5]. There are also so called reforming catalysts, which are based on transition metals supported on silica-alumina. Metal sites catalyze hydrogenation and dehydrogenation reaction, while acidic sites catalyze isomerization reactions. Well known catalyst from that group is Pt:SiO2-Al2O3 with about 0.5 wt. % Pt [6]. There might be also activated carbon used. In industry dealing with catalytic cracking mostly fluidized bed reactors are used. This is due to their high efficiency compared to fixed bed reactors. The type of bed is very important as the efficiency of process and its selectivity depends on contact surface [10]. The products which are obtained in process of catalytic cracking are usually further exploited. Liquid fraction is used as a fuel or an additive to fuels. Gas fraction as it contains significant amount of hydrogen is a source of hydrogen intended for refining processes [10].
4. Experimental As a material of bed quartz sand was chosen, which was derived by company producing sand for industrial fluidized bed reactors. There was sieving process applied to divide bed into four class of grain fractions: 0.1-0.2 mm; 0.2-0.315 mm; 0.315-0.4mm; 0.4-0.5mm. Containers with sand fractions are presented on the picture below.
Fig. 5. Selected grain fractions of the material of the fluidized bed The feedstock were plastic wastes such as: offcuts of bottles, caps, bumpers, foils and granules from ready recycled plastics. Firstly, that was ground in a rotary mill. Plastic particles were separated into fractions. All plastics used in the experiment are shown in the table presented below. Tab. 2. Characterization of waste materials
Type of plastic
Form
Colour
Origin
% wt. H
PE/PP
Offcuts
Various
Caps
14,4%
PP+EPDM
Offcuts
Black
Bumpers
12,9%
PET
Offcuts
Various
Bottles
4,5%
PE
Offcuts
Green
Foil
14,4%
PE HD
Granulate
Blue
No data
14,4%
EVA
Granulate
Orange
No data
9,8%
There is research being done about the most suitable catalyst. It is planned to apply commercial catalysts available on the market used in processes of cracking. Under consideration are taken alumina-silicate catalysts such as zeolites, since they have relatively big specific surface area.
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Apparatus Before the reactor was built, there was made a mathematical model of fluidization process. Using that model velocity of a carrier gas was calculated, as well as raw material, and bed's grain size. Below is presented the scheme of equipment used to carry out the process of catalytic plastics cracking.
Fig. 6. Scheme of installation of catalytic plastic wastes cracking (1-inert gas cylinder, 2-gas pressure regulator, 3-carrier gas heater, 4-tubular furnace, 5-vessel for sieved bed’s material, 6-reactor with a grid, 7- vessel lowering velocity of the gas, 8-thermocouple, 9-sample vessel/feeder, 10-solid particle separator,11-cooler, 12-liquid fraction container, 13-gas flow measure, 14-gas vent to chromatograph/combustion)
The process begins with the fluidizing gas inlet (1). As an inert gas argon was used. The gas goes through pressure regulator (2) to gas heater (3), where is heated up to 400°C. The next element of the installation is a vessel which is to collect any particles which may be sieved through grid placed at the bottom of the reactor, when the gas will not be provided into the system after the process (5). After that gas is conveyed into the reactor (6). The reactor is filled with a bed with proper diameter of particles, which start to fluidize, while gas is flowing through the bed. At the bottom of the reactor is placed a grid made from precious metal. It is to prevent the bed to fall out of the reactor. The reactor is placed in the RST 33P furnace (4). RST 33P is continuous furnace with ceramic liner. In the following furnace there is a possibility of five-zone temperature control. In the furnace there is only the reactor and thermocouple. At the top of the reactor is placed a vessel which role is to decrease particles velocity and prevent elutriation (7). That vessel has three connections. Through first one raw material is dosed owing to gravity force from feed tank (9). During the process was observed a transport of fine particles of the reactor. Despite lack of those fine particles at the beginning of the process, they were created because of attrition and abrasion of bed’s particles. Due to that fact a cyclone had to be added (10). Sedimentation of fine particles could increase flow resistance and that would lead to occlusion of the installation. Gas going out from the vessel (7) goes to cyclone (10). Hot, post-process gas contains liquid and gas hydrocarbons. To separate them cooler was added (11). At the end of the cooler, a tank for liquid fraction was installed (12). After that part post-process gas goes to rotameter (13) and then to chromatograph or to part where it can be combusted (14). Below is presented the photo of installation. At that moment gas heater was not added yet.
Fig. 7. Installation of catalytic plastics cracking in the laboratory at AGH.
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The reactor, cyclone, tanks and cooler were made of boro-silicate glass by experienced glass technician. The installation has a high tightness after applying grease on connecting sockets and by applying clamps to the connectors. During installation’s operation occurred one problem. The operating temperature was not enough to carry out sufficient process. This is due to fact, that the only heat source was RST 33P furnace, which can heat up to 600°C, but only in case of fixed bed. When gas flows through reactor it is cooled down to temperature around 200°C. This is why gas heater was installed. Unfortunately, due to lack of gas-tightness of the system first model of gas heater did not operate properly. Another model of it is under development. Both models were designed to obtain operating temperature at the level of 300-500°C. Due to too low operating temperature the process has not been carried out in the way of obtaining products of catalytic cracking. The laboratory test stand was built by students owing to Rector’s Grant AGH no. 52 from 2015.
5. Conclusions Since the problem of waste management affects not only companies dealing with it but also the environment and the society, it is important to search for new ways of facing that problem. There are already technologies that replace traditional landfilling. Applying these technologies has not only the advantage of getting rid of plastic wastes in more harmless way. Innovative approach which is application of catalytic cracking can also allow to gain valuable fuels (hydrocarbons of the desirable range), since plastics are characterized by high calorific values. The possibility of obtaining gas and liquid fractions in addition to economic benefits, also gives us the chance to obtain fuels in different way than by direct processing of crude oil. Application of fluidized bed reactor allows to uniform heating, so that the process run uniformly within the reactor. Application of the gas-tight heater in the presented system will allow to carry out the process fully. After establishing the test procedure the research will be focused on proper selection of catalyst, since it is the key factor to gain the most valuable products with high efficiency.
References [1] Małgorzata Grodzińska-Jurczak, Management of industrial and municipal wastes in Poland, Wydawnictwo, Miejsce i rok wydania [2] EUROSTAT Database, http://ec.europa.eu/eurostat/data/database [3] Praca zbiorowa - General Statistic Office of Poland – GUS, Envirorment 2015, Statistical information and elaboration, Warszawa, 2015 [4] Association of Plastics Manufacturers “Plastics Europe”: Production analysis, demand and recover of plastics in Europe, Warsaw 2014 [5] A.G. Buekens, H. Huang, Catalytic plastics cracking for recovery of gasoline-range hydrocarbons from municipal plastic wastes, Elsevier; Resources, Conservation and Recycling 23(1998) 163-181 [6] Autor niezany, Recykling materiałów polimerowych w Polsce, tworzywa.com.pl, 21.11.2015, http://tworzywa.com.pl/Wiadomości/Recykling-materiałów-w-Polsce-20936.html; [7] Chuanwei Zhuo, Yiannis A. Levendis: Upcycling Waste Plastics into Carbon Nanomaterials: A Review, Journal of Applied Polymer Science, 10.1002/app.39931, 2013 [8] Paweł Wójcik, Odzysk odpadów z tworzyw sztucznych, Środowisko i odpady, nr 4 (70)/11, 2011 [9] Joanna Radziewicz, Problemy gospodarki odpadami w Polsce, Ekologia i środowisko, nr 42, 2014 [10] Surygała J. - Ropa naftowa: właściwości, przetwarzanie, produkty, Vademecum rafinera, Warszawa, Wydawnictwa Naukowo-Techniczne, 2006 [11] J. Sokołowski, M Marczewski, G. Rokicki, Thermal-catalytic recycling of polyolefins and polystyrene, internal elaboration,University of Science and Technology in Warsaw, Faculty of Chemistry, Warsaw, 2010
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[12] Dezhen Chen, Lijie Yin, Huan Wang, Pinjing He, Pyrolysis technologies for municipal solid waste, A review, Elsevier, Waste Management 34, 2466-2486, 2014 [13] Luis Noreña, Julia Aguilar, Violeta Mugica, Mirella Gutiérrez and Miguel Torres: Materials and Methods for the Chemical Catalytic Cracking of Plastic Waste, Material Recycling - Trends and Perspectives, ISBN: 978-953-51-0327-1, 2012 [14] S.K. Kimuti, A.M. Muumbo, I.K. Chebii: An experimental study on catalytic cracking of polyethylene and engine oils, Research Journal of applied Sciences, Engineering and Technology, 2013 [15] Yumiko Ishihara, Hidesaburo Nanbu, Katsuhiko Saido and others Mechanism of gas formation in catalytic decomposition of polypropylene, Fuel, Volume 72, Issue 8, August 1993, Pages 1115-1119
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Future of Energy Technologies Dhanush Basavakumar Silesian University of technology
Abstract In the future, mankind will be forced to research and develop alternative energy sources. Our current rate of fossil fuel usage will lead to an energy crisis within this century. In order to survive the energy crisis many companies in the energy industry are inventing new ways to extract energy from renewable sources. While the rate of development is slow, mainstream awareness and government pressures are growing. This article is about the future of energy technologies.
1. Introduction The use of renewable energy sources, such as solar, wind and hydraulic energies, is very old; they have been used since many centuries before our time and their applications continued throughout history and until the "industrial revolution", at which time, due to the low price of petroleum, they were abandoned. During recent years, due to the increase in fossil fuel prices and the environmental problems caused by the use of conventional fuels, we are reverting back to renewable energy sources. Renewable energies are inexhaustible, clean and they can be used in a decentralised way (they can be used in the same place as they are produced).
2. Energy Technologies 2.1. The Spherical Sun Power Generator
Fig. 1. Spherical Sun Power Generator
Fig. 2. The modular collector
German Architect Andre Broessel believes he has a solution that can “squeeze more juice out of the sun”, even during the night hours and in low-light regions. His company Rawlemon has created a spherical sun power generator prototype called the beta ray. His technology will combine spherical geometry principles with a dual axis tracking system, allowing twice the yield of a conventional solar panel in a much smaller surface area. The futuristic design is fully rotational and is suitable for inclined surfaces, walls of buildings, and anywhere with access to the sky. It can even be used as an electric car charging station. The beta ray comes with a hybrid collector to convert daily electricity and thermal energy at the same time. While reducing the silicon cell area to 25% with the equivalent power output by using our ultra-transmission Ball Lens point focusing concentrator, it operates at efficiency levels of nearly 57% in hybrid mode. At night time the Ball Lens can transform into a high-power lamp to illuminate your location, simply by using a few LED’s. The station is designed for off grid conditions as well as to supplement buildings [1].
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Fig. 3. Working of the Spherical Sun Power generator
Fig. 4. Suitability for conventional CPV and thermal power plants.
Fig. 5. Suitability for solar hybrid power plants with Rawlemon technologies
thermal power plants Spherical Sun Power
2.2. Harvesting Solar Energy from space Generator Since 2008, the Japanese Space Agency (JAXA) has been working to develop technologies to transmit electricity wirelessly. The goal of the Space Solar Power Systems (SSPS), is to be able to transmit energy from orbiting solar panels by 2030 [2]. Mitsubishi Heavy Industries, Ltd. (MHI) successfully conducted a ground demonstration test of “wireless power transmission”, a technology that will serve as the basis for the SSPS [3]. In the test, 10 kilowatts of electricity was successfully transmitted via a microwave unit. Power reception was confirmed at a receiver located 500 meters away. LED lights on the receiver confirmed the transmission. This marks a new milestone in transmission distance and power load (enough to power a set of conventional kitchen appliances). The test also confirmed the success of the advanced control system technology that is used to direct the microwave beam so that it stays on target. The new test results promise to lead to way to terrestrial applications like the SSPS, and will hopefully eliminate the need for traditional cable connections. Potentially, a solar battery in orbit (36,000 kilometres above earth) could generate power which would then be transmitted to earth via microwave/laser, without relying on cables. JAXA anticipates that this new technology could become a mainstay energy source that will simultaneously solve both environmental and energy issues on Earth.
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Fig. 6. Concept photo of harvesting solar energy from space
Fig. 8. Wireless power transmission confirmation of MHI experiment
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Fig. 7. Prototype for transmitting wireless power by MHI
Fig. 9. Concept photo of energy wave receiver on the Earth
2.3. Goodyear’s Electricity-Generating Tire Concept
Fig. 10. Concept photos of BH-03 tyre developed by Goodyear As awesome as electric vehicles are, range remains their limiting factor. At the Geneva International Auto Show, Goodyear unveiled a new concept tire called the BH03. Goodyear’s new tire looks radical and could potentially generate electricity for electric cars by converting the friction heat of the tire on the road. Regenerative braking, which captures energy otherwise lost as heat and returns it to the battery. And engineers have considered other ways of capturing energy from things like the rebound and compression of shock absorbers. Goodyear sees an opportunity to squeeze a little juice out of the tires. The idea behind the BH-03 concept is to capture energy in two ways. First, Goodyear thinks it can take advantage of piezoelectricity, the electric charge that builds up in certain materials as they’re squeezed or pressed. Tires are
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constantly being deformed as they spin, so engineers are planning to put it into good use. Piezoelectric materials (quartz, some ceramics, and a few kinds of salt) are used in things like electric cigarette lighters, electric guitar pickups and the fuses in rocket-propelled grenades. Another idea is creating electricity through thermoelectricity, converting variations in temperature into electric voltage. Whether they’re sitting in the sun or spinning on the road, tires generate heat. Goodyear is looking to use thermoelectric materials (like bismuth telluride and tin selenide), to generate electricity from the difference between the hottest and coolest parts of the rubber. Again, the challenge is incorporating those materials without sacrificing elasticity and durability. To send energy to the battery engineers could use a connection running from the tire to the hub and on to the battery. Or they could transfer energy with an induction current. [4]
2.4. Flying Wind Farms The thought of swarms of kite-like airborne turbines spinning at high altitudes sending power down via nano-tube cable tethers to generate power is exciting. This could very well be a true picture of future power harvesters according to NASA. [5] TWIND is a prototype planned by Italian start-up. It has a pair of balloons at 2,600 feet. The open sails move antagonistically so while one moves downwind the other moves upwind. This movement spins a turbine to generate power. The option of offshore flying wind turbines is also being explored to solve the airspace competition issue. At higher altitudes, wind has more power and velocity and is more consistently predictable. As power generated goes up because of higher wind resistance proportional to the cube of relative velocity, more power can be generated. That works out to be some 8 – 27 times the power produced at ground level. The tethers can haul in the kites/balloons housing the turbines during storms or for general maintenance work. Less pollution is an advantage, as well as the fact that it will not take up much ground space for installation. [6]
Fig. 10. Concept photos of flying wind turbine developed by TWIND
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2.5. Power from two energy sources Fujitsu Develops Hybrid Energy Harvesting Device for Generating Electricity from Heat and Light. Alternative sources of energy are clean and green but the catch is they generate less energy compared to fossil fuels. So now the scientists are trying to use different sources of alternative energy at the same place and same time to generate power. Attempts are being made to combine two forms of external energy sources such as light and heat or light and vibration to generate external energy so that enough energy can be collected for practical use. Fujitsu Laboratories have now succeeded in using hybrid energy sources to generate power. Fujitsu Laboratories are working extensively in this regard, and to generate electricity both from heat and light, they are creating a new hybrid energy harvesting device. Energy harvesting is the procedure used in accumulating energy from the environment. Later on that energy is transformed into electricity. Fujitsu is not doing something innovative. Work in this field was done by scientists earlier too. But hybrid energy could only be generated by combining separate devices and that proved costly so it was commercially unviable. Now Fujitsu laboratories confirm that two separate devices are not needed to generate electricity from a hybrid source. Production cost was reduced by using organic materials for creating hybrid device. The new technology is showing promise to convert energy from the environment to electricity. The device from Fujitsu Laboratories is just a one-piece device that catches energy from the most common form of energy available for large scale use. An organic material of high efficiency that can generate power from both photovoltaic and thermoelectric mode has been developed by Fujitsu Laboratories. This organic material can make power both from heat in thermoelectric mode and indoor lighting in photovoltaic mode. The production cost is very low because of the organic materials and the processing costs are very low. The device can be made to work as a thermoelectric generator or photovoltaic cell by changing the electrical circuit connecting P-type and N-type semiconductors. For Fujitsu Laboratories, combining two different sources of generating energy to produce power is just the beginning. They want to make this technology more efficient so that by combining two sources of producing energy, hybrid equipment can be made to work better. [7]
Fig. 11. Single device featuring operation in both photovoltaic mode (left) and thermoelectric mode (right).
Fig. 12. Prototype hybrid generating device manufactured on flexible substrate
2.6. Solar Wind Power As the world discovers new ways to meet its growing energy needs, energy generated from Sun, which is better known as solar power and energy generated from wind called the wind power are being considered as a means of generating power. Though these two sources of energy have attracted the scientists for a very long time, they are not able to decide, which of these two is better source to generate power. Now scientists are looking at a third option as well. Scientists at Washington State University have now combined solar power and wind power to produce enormous energy called the solar wind power, which will satisfy all energy requirements of human kind.
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The satellite launched to tap solar wind power, instead of working like a wind mill, where a blade attached to the turbine is physically rotated to generate electricity, would use charged copper wire for capturing electrons zooming away from the sun at several hundred kilometres per second. The scientists say that whereas the entire energy generated from solar wind will not be able to reach the planet for consumption as a lot of energy generated by the satellite has to be pumped back to copper wire to create the electron-harvesting magnetic field, yet the amount that reaches earth is more than sufficient to fulfil the needs of entire human race, irrespective of the environment condition. The team of scientists at Washington State University hopes that it can generate 1 billion billion gigawatts of power by using a massive 8,400-kilometer-wide solar sail to harvest the power in solar wind. According to the team at Washington State University, 1000 homes can be lit by generating enough power for them with the help of 300 meters of copper wire, which is attached to a twometer-wide receiver and a 10-meter sail. One billion gigawatts of power could also be generated by a satellite having 1,000-meter cable with a sail 8,400 kilometres across, which are placed at roughly the same orbit. But despite the fact that Solar wind power will solve almost all the problems that we were to face in future due to power generating resources getting exhausted, it has some disadvantages as well. The distance between the satellite and earth will be so huge that as the laser beam travels millions of miles, it makes even the tightest laser beam spread out and lose most of the energy. To solve this problem, a more focused laser is needed.
2.7. Electricity from Algae Cells With the help of photosynthesis plants convert light energy to chemical energy. This chemical energy is stored in the bonds of sugars they use for food. Photosynthesis happens inside a chloroplast. Chloroplasts are considered as the cellular powerhouses that make sugars and impart leaves and algae a green hue. During photosynthesis water is split into oxygen, protons and electrons. When sunrays fall on the leaves and reach the chloroplast, electrons get excited and attain higher energy level. These excited electrons are caught by proteins. The electrons are passed through a series of proteins. These proteins utilize more of the electrons’ energy to synthesize sugars until the entire electron’s energy is exhausted. Now researchers at Stanford are inspired by a new idea. They intercepted the electrons just after they had been excited by light and were at their highest energy levels. They put the gold electrodes inside the chloroplasts of algae cells, and tapped the electrons to create a tiny electrical current. It may be the beginning of the production of “high efficiency” bioelectricity. This will be a clean and green source of energy but minus carbon dioxide. The Stanford research team created an exclusive, ultra-sharp gold nano electrode for this project. They inserted the electrodes inside the algal cell membranes. The cell remains alive throughout the whole process. When cells start the photosynthesis, the electrodes attract electrons and produce tiny electric current. The by-products of such electricity production are protons and oxygen. Researchers explained that they were able to extract just one picoampere from each cell. This quantity is so little that they would require a trillion cells photosynthesizing for one hour just to get the same amount of energy in an AA battery. Another drawback of such an experiment is that the cells die after an hour. It might be the small trickles in the membrane around the electrode could be killing the cells. Or cells may be dying because they’re not storing the energy for their own vital functions necessary to sustain life. To attain commercial viability researchers have to overcome these hurdles. They should go for a plant with larger chloroplasts for a larger collecting area. For such experiment they will also need a bigger electrode that could tap more electrons. With a longer-surviving plant and superior collecting ability, they could harness more electricity in terms of power. [9]
2.8. Car fuel from Carbon Dioxide If a car is running smoothly on the road and its consuming carbon dioxide from air as fuel instead of petrol, what a dream world that would be. Researchers from the South West are working on a £1.4 million project to turn the above dream into a reality. This car of future will consume one of the root causes of greenhouse effect. What a greener world that would be. Scientists and engineers from many universities will combine their efforts to produce
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that dream car running on carbon dioxide. The University of Bath is leading the research. They are joined by the University of the West of England and members from the University of Bristol. Scientists say the current processes rely on using separate technology to capture and utilize the CO2 , which makes the process very inefficient. By combining the processes the efficiency can be improved and the energy required to drive the CO2 reduction is minimized. Currently the project is trying to develop porous materials. Porous materials are helpful in absorbing the gas from the air. Carbon dioxide causes global warming but scientists are converting it into chemicals that can be used to make car fuel or plastics. They are utilizing the solar power for their experiments. The researchers are visualizing a future where their porous materials are the main components of a factory’s chimneys. These porous materials would be absorbing carbon dioxide pollutants from the air, reducing the effects of climate change. When this project will be completed it will mean that new kinds of fuels can be produced from old ‘carbon emissions’ that are generated from factories, plants and even cars themselves. The idea of ‘recycling’ carbon emitted from the fossil fuels, is not new. But people are warming up towards this idea now. The project, funded by the Engineering & Physical Sciences Research Council (EPSRC), is in its nascent phase but the researchers predict the new technology could make a real difference in the fight against climate change. The project is part of Research Councils UK (RCUK) cross-Council programme ‘Nanoscience: through Engineering to Application’. [10]
2.9. Artificial Leaf for Hydrogen production Scientists are quite optimistic that hydrogen will emerge as the fuel of the future and the world would be driven by ‘hydrogen economy’. The only by product of hydrogen fuel is water vapour. By using hydrogen fuel we can reduce the harmful effects of greenhouse gases. Currently many research labs are engaged in duplicating the phenomenon of photosynthesis to produce hydrogen fuel. What fascinates the scientists is the splitting of water into hydrogen and oxygen by using solar energy. A vast majority of scientists all over the world believe that we can get rid of our dependence on fossil fuels by breaking water into its components. Even some automobile companies such as Toyota are promoting hydrogen fuelled cars. But till now the use of hydrogen as fuel is not cost effective. Scientists are trying to develop a design that would be an artificial leaf but its function would be almost similar to natural leaf. Like a real leaf, the lab designed leaf too utilizes solar energy and water to produce hydrogen. In biology this process performed by green leaves is known as photosynthesis. Their methodology would take inspiration from chemistry and biology of natural leaves. The above mentioned project is being carried out at State Key Lab of Matrix Composites at Shanghai Jiaotong University, Shanghai, China. Researchers decided to duplicate the natural design and development of a blueprint for artificial leaf like structures. They christened their creation as the “Artificial Inorganic Leaf” (AIL). They also used titanium dioxide (TiO2), as a photo-catalyst for hydrogen production. Researchers used the native plant of China, known as Anemone vitifolia for their experiments. They infiltrated the leaves of Anemone vitifolia with titanium dioxide in a two-step process. They depended on advanced spectroscopic techniques to confirm the exact structural features in the leaf. These structural features helps in trapping the light energy of the sun. They replicated the same features in new TiO2 structure. It is found that the AIL are eight times more active for hydrogen production than TiO2. But it is true only when AIL has not been “biotemplated” in that fashion. Another plus point in favour of AILs is their activity is three times more in comparison with commercial photo-catalysts. The researchers also inserted the nanoparticles of platinum. It is a known fact that platinum along with the nitrogen increases the artificial leaves by an additional factor of ten. Their results may represent an important first step towards the design of novel artificial solar energy transduction systems based on natural paradigms, particularly based on exploring and mimicking the structural design. Nature still has much to teach us, and human ingenuity can modify the principles of natural systems for enhanced utility. [11]
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2.10. Electricity from Human power Princeton University engineers have developed a device that may change the way that we power many of our smaller gadgets and devices. By using out natural body movement, they have created a small chip that will actually capture and harness that natural energy to create enough energy to power up things such as a cell phone, pacemaker and many other small devices that are electronic. The chip is actually a combination of rubber and ceramic nanoribbons. When the chip is flexed, it generates electrical energy. Think of rubber soled shoes that have this chip embedded into them and every time a step is taken, energy is created and stored. Just the normal walking around inside the office during a normal work day would be enough to keep that cell phone powered every day. An application that has pacemaker users excited is the fact that this chip could be placed in proximity of the lungs and it would create natural power for their pacemakers. Currently, the only way to replace the battery is to go through another surgery, but the natural motion of the lungs would create enough movement to continuously power the device via this chip. Finally, only one surgery would be needed and unless there was actually a problem with the pacemaker itself, there would no longer be the need to go under the knife again. This technology is an incredible development in that it can have so many different applications. The engineers at Princeton were able to combine the materials in a way that created an electric charge when pressure is applied to the chip. It actually converts about 80% of the mechanical energy into electrical energy. In the case of the pacemaker, this means a constant power source as the lungs would obviously continuously apply the pressure that was needed to create the energy. Additionally, the new power chip is pretty much ready to go in regards to being an implant device. Because of the materials that it is made up of, the body should readily accept it without fear of rejection. When we think of how many varieties of medical devices that are available and require power sources, this is a truly amazing invention. While it would appear that the technology itself is very futuristic, once it is able to be mass produced, it is probably reasonable to assume that the chips will not actually be all that expensive because of the materials that are being used in its construction. They may be a bit pricey when they first hit the market, but as they become more widely used and available, that price tag should come down. Similar technology has already been introduced in other products, but nothing that has the flexibility of this product. Human power is nothing new, but to be able to have medical devices implanted that require nothing more than normal breathing or walking is quite amazing.[12]
Fig. 12. Piece of silicone rubber imprinted with super-thin material that generates electricity when flexed
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3. Conclusion The technologies described in this article can help to create a more secure and sustainable energy system. To achieve this potential will require that the public and private sectors carry out extensive research, development, and demonstration of many of these technologies within the next decade. To make the necessary advances, industry and the government must adopt a portfolio approach to developing and deploying new technologies. Mixed strategies are required to ensure staged development and deployment within a particular mode of production as well as progress in a mix of approaches. A number of barriers are likely to delay deployment, especially given that many new sources of energy will be more expensive than current sources are. Policy and regulations, however, can help overcome some of these obstacles. Global leaders have long been interested in improving the energy system, although most efforts have been piecemeal.
References [1] [2] [3] [4] [5] [6]
http://www.rawlemon.com/collections/beta-ray http://global.jaxa.jp/article/interview/vol53/index_e.html http://www.mhi-global.com/news/story/1503121879.html http://www.cnet.com/news/heat-gathering-concept-tire-charges-electric-cars-on-the-go/ http://www.nasa.gov/topics/technology/features/capturingwind.html www.popsci.com/technology/article/2010-12/nano-tethered-flying-wind-turbines-inspire-new-nasastudy [7] http://www.fujitsu.com/global/about/resources/news/press-releases/2010/1209-01.html [8] www.popsci.com/science/article/2010-10/solar-wind-could-replace-solar-wind-renewable-energysource [9] http://news.stanford.edu/news/2010/april/electric-current-plants-041310.html [10] https://www.ucl.ac.uk/news/news-articles/1003/10032902 [11] http://www.eurekalert.org/pub_releases/2010-03/acs-bf031010.php [12] https://www.princeton.edu/main/news/archive/S26/47/03A23/index.xml?section=topstories
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Use of Bacillus Megaterium in solubilization of phosphorus from incineration plant Krzysztof Trzepizur1, Szymon Dulik2. 1 2
AGH University of Science and Technology New Chemical Synthesis Institute Inorganic Division “IChN” in Gliwice
Abstract Sewage sludge produced by sewage treatment plant can be a very generous source of phosphorus. Due to present level of phosporites and apatites excavation insufficiency it is crucial to find another source of that element. Present work is analysis of future prospects of using ashes, which are the products from sewage sludge incineration, as an alternative source of phosphorus and application of biotechnological methods in fertilizers production. Experimental section is devoted to use of Bacillus megaterium culture of bacteria to biotechnological solubilisation of phosphorus present in ash, produced as a product of incineration of sewage sludge from Łyna sewage treatment plant. Results shows, that higher yields can be obtained using higher concentrated medium for feeding. Influence of mixing type was also considered if it has influence on a results of solubilisation.
1. Introduction Phosphorus plays significant role in plant fertilization process. This is one of the three most important macroelements needed to existence of every organism. Because of that, it is a necessity of supplying of that element, what is strongly connected with intensive production of phosphoric fertilizers. The main resources used in production are phosphorites and apatites. The result of phosphoric acid production, which is the main semiproduct in phosphoric fertilizer production, is harmful for environment, due to phosphogypsium production, which is used only in small, 5% extent [1]. There are two possible ways to improve phosphorus management in industry. First of them is addition of strict amount of fertilizers to reduce losses. Second method is to reuse phosphorus compounds from renewable sources. From technical point of view there are plenty of alternative phosphorus sources. It can be for example wastes from slaughterhouses, sewage treatment plants, manure etc. The biggest concern in that sources is, that all of the phosphorus content is in inassimilable form. One of the most important advantage of using emulsion fertilizers is its ability to produce them from more contaminated raw products. This is why there is a possibility of waste usage, obviously which have desired components. Important matter is, that fertilizer needs to contain digestible forms of nutrient. From phosphorus fertilizers point of view, useful resources are wastes such as slaughterhouse by-products, after breeding materials, sewage treatment substances or other agricultural wastes. Additives like mud are beneficial for that kind of fertilizers due to decrease of suspension stabilizing agents needed. In nature there are plenty of microorganisms which collects micro or macroelements in inassimilable form, and converts them into assimilable one. One of the most known case is so called diazotrophy, which is convertion of free nitrogen present in air. Trichodesmium, which live in tropical and subtropical zones are responsible for 60-80 Tg of nitrogen bonding per year [2]. That kind of microorganisms are often in symbiosis with plants and introduces nitrogen directly to soil. There are also microorganisms which converts nitrogen in different forms in sewage treatment. Bacteria from Nitrosomonas and Nitrobacter are responsible for that operation. This type of methods are needs continuous supply of external carbon source in form of methanol or acetic acid [3]. Bacteria take also part in solubilisation of potassium. Mechanism of that process is production of organic acids, which are responsible for potassium solubilisation. In lithosphere potassium content is 2.6% [4]. It appears mainly in inassimilable form if minerals like muscovite, orthoclase, biotite etc. Authors of that concept assumed direct injection of microorganisms into soil. Problems with process are on stage of commercialization, due to difficulty of usage.
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There is a similar situation in case of phosphorus. The main issue in phosphorus fertilization is phosphorus in inassimilable form for plants. This element is present in organic and inorganic form. Plant cells are capable of collect phosphorus in various form, but the most often one is ionic form of HPO42- and H2PO4- [5]. In soil phosphorus is available mostly in form of calcium phosphates, like hydroxyapatite, which is not suitable for plants [6]. Only 0.1 % of phosphorus is assimilable [7]. This is one of the main problem of current phosphorus development. In soil there is also present organic compounds of that element, but its amount is strongly dependent on type of soil. Content of organic phosphorus usually varies between 30-50%, but there are also a cases with content at levels 5 or 95% [5]. Organic forms are also inassimilable and this fact also causes need of conversion to anions or small particle organic compounds. However, there are gram-negative bacteria, which contributes to solubilisation of calcium phosphates like fluoroapatite. It was stated, that it is possible in way of synthesis of 2-ketogluconic acid from glucose, in way of two-stage oxidation [6]. Product is relatively strong acid, with pKa =2.6.
1.1. Phosphorus recovery Sharma et al proposed three possible ways of insoluble phosphorus compound solubilisation. First is releasing of organic acids anions, siderophores, protons, hydroxyl ions and carbon dioxide. There is also possibility of biochemical mineralization, which is done by substrate degradation [7]. Phosphorus solubilisation in inorganic form is done mainly with participation of organic acids with decreased pH. There is a possibility of chelation of cations bounded with acid part containing phosphorus. Organic acids are competing with phosphorus in adsorption process in soil and creates complexes with metals, which are bounded with phosphorus in form of insoluble salts. However, it was proofed, that fungus T. Harzianum T-22 dissolves insoluble phosphorus compounds without organic acids. Altomare et al. [8] did research of that process and they did not observe any presence of organic acids in this organisms and it was stated, that in that case this mechanism is not dominating one. One of interesting discovery was a process of oxonium cation releasing process as a result of ammonium ion assimilation by microorganism’s cells. Parks et al. [9] prove, that in Pseudomonas bacteria case solubilisation of phosphorus were conducted without organic acids presence. That phenomenon was explained by descripted mechanism. In soil there are also organic phosphorus compounds, which may be degraded to assimilable forms by microorganisms. This process is done by enzymes called phosphatases, which causing hydrolysis of esters and phosphoric anhydrides [10]. Municipal and industrial sewages could be also important source of phosphorus. It was estimated, that every citizen introduced into sewage 2,5g of phosphorus daily [11]. Poliphosphates and phosphorus bonded in organic compounds is hydrolysed to phosphate ions right after injection to sewage installation. Due to significant amount of phosphorus in sewage there are methods under development, which main objective is recovery of that element. Usually it is done by precipitation with Iron (III) or aluminium sulphate and Iron (III) chloride. This method is relatively easy, but precipitated phosphorus is hard to assimilate by plants. There are also developed process, which uses CaO for crystallization of calcium phosphate (DHV Crystalactor, Kurita). Also, there exist biological process of phosphorus removing, called BPR-PHOSTRIP [11]. In that method, phosphorus is used in bacteria’s own metabolism, simultaneously accumulating bigger amounts of that element. Also methods, which uses sewage treatment incineration ashes were under scientists’ examination. Franz [12] checked possibility of phosphorus production in form of calcium hydrophosphate. Proposed method was leaching using sulphuric acid with acid/solid ratio equal to 2. The main disadvantage of that process was leaching alongside with phosphorus also toxic metals. In order to remove them, second stage of process was applied, purification using chelating ion exchange resin, and after that precipitation of calcium hydrophosphate with calcium milk. Author reported similar quality parameters to conventional fertilizer of that type [12].
1.2. Bacillus megaterium characteristics Bacillus megaterium is gram-positive bacteria, which creates resting forms [13], which metabolic processes are the main issue in that paper, are very common in soils, sea water, residues, as well as in food. This bacteria are used in industry from around 50 years. They take part in processes of synthesis of penicillins, vitamin B12,
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pirogronians and other complex chemical compounds [14]. This bacteria is able to produce weak organic acids. Due to this fact, that bacteria was chosen to production of phosphorus fertilizer.
Fig. 2. Megaterium, next to E. coli. Volume off B. megaterium cell is 100 times bigger. White line determines 2 μm length. Photo taken from [14]. Researches described in that paper were done in order to plan and overcome possible difficulties during maintenance of higher scale run attempts for colloidal fertilizer production. Two parameters taken into consideration were composition of medium in which process was maintained and what type of mixing is more suitable for proper aeration of a mixture and ashes’ particles distribution.
2. Experiment performance 2.1. Microorganisms For microbiological solubilisation of phosphorus Bacillus megaterium bacteria, delivered by division of inorganic chemical technology and mineral fertilizers from Wrocław University of Technology was used. Before insertion to reaction mix they were kept in 5 degree Celsius temperature. Bacteria mix contained both resting and vegetative forms, what can be easily seen on the figure.
Fig. 3. Megaterium in bacteria suspension before implementation, magnified 640x
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2.2. Raw material The raw material used was ash created during incineration of waste sludge taken from Łyna sewage treatment plant located in Olsztyn. Ashes before usage were grinded in IChN. Phosphorus content in ash: P2O5 total: 24.73% weight P2O5 soluble in ammonium citrate: 7.30% by mass P2O5 soluble in water: below limit of quantification
2.3. Analytical methods All methods of phosphates determination were applied according to WE 2003/2003 regulation by European Parliament. In delivered ashes all of forms of phosphates were determined, so that total, assimilable and water soluble, in P2O5%. Content of total phosphorus was determined using ICP-OES technique using CID detector with extended spetra. Phosphorus soluble in water and soluble in neutral ammonium citrate was determined using mass method accordin to PN-EN 15959:2011 norm. Extent of solubilisation was examined by changes of water soluble phosphorus concentration inf P 2O5%. That was done by spectrophotometric method with usage of phosphomolibdenium method and Jenway 6300 spectrophotometer. Oxygen content was measured using CX-501 multifunction meter, with thermocouple and oxygen probe connected. Results are presented as a ratio of dissolved oxygen and maximum amount of oxygen dissolved in water at temperature T. The same multifunction meter was used to check pH of reaction mixture.
2.4. Preparation of reaction mixture Dry ash from incineration plant before insertion to reaction mix was grinded to desired size. After milling sample was taken in order to determine various forms of phosphorus content. All of the nutrient taken were analytical grade. Culture medium, which was an environment for microorganisms raising was prepared by adding nutrients to demineralised water. Two types of medium was prepared; one of them was ten times more concentrated. Before process it was necessary to sterilise medium, it was done by keeping solution in 100 degree Celsius in 15 minutes. Culture medium composition is presented in table 1. In every run extent of the process was measured according to pH measurement. pH gave a sense about changes of organic acids concentration in mixture. Decrease of that value is a sign, that bacteria involved in solubilisation were active and started producing organic acids, which were responsible for phosphorus solubilisation. pH of culture medium was establish at the level of 6.24, so there is no possibility of increasing acidity by adding culture medium. Due to the fact, that Bacillus Megaterium are aerobic organism, oxygen content in reaction mixture was determined. In order to determine, if additional type of mixing was done or not, run 2 and 4 were equipped with additional air inlet. Another advantage of that solution was observation whether it is beneficial to have better oxygenation of reaction mixture or not. In case of run 1 and 3, no additional source of oxygen was present. Also, at the end of each runs, phosphorus content in taken samples was analysed. In case of run 3 and 4 additional phosphorus analyses were done in order to observe changes in amount of phosphorus soluble in water.
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Tab. 1. Composition of breeding medium 1st and 2nd run 3rd and 4th run concentration [g/l] concentration [g/l] 10 100
Ingredient Glucose (NH4)2SO4
0.5
5
NaCl
0.2
2
MgSO4·7H2O
0.1
1
KCl
0.2
2
MnSO4·H2O
0.002
0.02
FeSO4·7H2O
0.002
0.02
Yeast extract
0.5
5
Ca3(PO4)2
2.5
25
Parameters of a processes are collected in table 2. Tab. 2. Run characteristics
Mixing type
Number of revolutions Air volumetric flow rate Volume Mass of ash Bacteria injection Daily feeding Average temperature of process
1 Mechanical blade rotor
3 Mechanical blade rotor
140 rpm
2 Mechanical blade rotor with additional air injection 140 rpm
140 rpm
4 Mechanical blade rotor with additional air injection 140 rpm
nd
75 l/h
nd
75 l/h
1500ml 45g 113ml 150ml 35,3
750ml 22,5g 75ml 75ml 33,3
1500ml 45g 113ml 150ml 34,4
750ml 22,5g 75ml 75ml 33,3
3. Results and discussion 3.1. Influence of nutrient concentration on solubilisation Runs 1 and 3 were taken into consideration, due to similar way of mixing, heating and maintenance. The only difference was composition of nutrient medium, in case of run 3, all nutrients had 10 times bigger concentration except calcium phosphate, due to possibility of adjusting phosphorus content. pH data are presented on graph below.
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Fig. 4. Changes in pH, comparison between run 1 and 3 As it can be seen, we can observe common trend, that run 1 has slightly bigger pH during almost every step of the process. After fifth day of experiment more acidic was run 1. That fact may be caused by a fact, that during last days of bacteria action there were insufficient amount of nutrient, what caused process backward to solubilisation and, therefore, increase of acidity. The bigger differences can be observed in comparison of phosphorus content in both runs. Analyses done after experiments indicates, that in first run soluble phosphorus was at the level 0.149%, while in third 0.22%. This means, that increasing amount of nutrient ten times we were able to achieve 47% bigger amount of soluble phosphorus in a samples. Also micrographic analysis shows (figure) that replication of bacteria in more concentrated medium was more intensive and thanks to that, process was more efficient
Fig. 5. Comparison between run 1 and 3, during 3 day of experiment, magnified 640x
3.2. Comparison between two practical mix design As it was mentioned before, Bacillus megaterium are aerobic bacteria; they need oxygen in order to grow and act properly. Idea at this stage of experiment was to determine if additional air injection is necessary to improve process. Additional inlet could be beneficial thanks to two facts: more efficient Bacillus megaterium action, as well as better mixing efficiency and, thanks to that, more uniform distribution of ash particles. In order to have representative results all of runs were taken into account. Air was injected using small pipe fixed at the bottom of the reactor with multiple outlet, in order to keep uniform distribution of the air inside reaction mix. Results are shown at the figure below:
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Fig. 6. pH changes comparison together for all runs pH changes were done in almost the same extent in every run. However, runs 2 and 4 exhibits slightly lower values at the initial stages. This could be treated as a signal, that solubilisation is boosted by additional dissolved oxygen in mix. Unfortunately, comparing run 3 and 4 from phosphates point of view, the trend is completely reversed as on figure:
Fig. 7. Changes of phosphorus concentration, run 3 and 4, together with trendline of changes That behaviour of process can be an effect of non-uniform distribution of ash and, despite a fact, that more organic acids were present, they have not reached ash particles. However results may differ from expectations, objective of bigger oxygen content in mix was achieved as it is shown on figure 7. As it can be seen, oxygen presence was bigger in run with additional oxygenation across almost whole process. However, in fifth day of experiment dissolved oxygen amount in run 3 started rising up to achieving 100% saturation. That fact, connected with no significant changes of phosphate concentration can be treated as a signal, that process was stopped. Another observation done during all of the attempts was, that run 2 and 4 had no deposits at the bottom of the reactor, which may be beneficial from solubilisation point of view after optimisation of a process.
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Fig. 8. Dissolved oxygen in run 3 and 4
4. Conclusions The aim of that work was to see if the ashes, which are the products from sludge incineration sewage treatment plants, are a good raw materials to fertilizer production and how the composition of medium and presence of additional air inlet influences process of solubilisation. Done researches presented, that ashes taken from Łyna plant are a beneficial source of phosphorus. When it comes to determination of a supplementation way for Bacillus Megaterium colony and results of solubilisation during whole process, it is obvious, that the higher concentration of all nutrients tends to higher efficiency of bacteria’s maintained process. It should be also noted, that during that researches we were not determine which of the nutrient is the most important one, however, increase of population observed in reaction mixture gives an information, that increased amount of glucose is the key value in order to get efficient replication of bacteria. The factor, which should be included in next researches should be daily addition of medium, in order to determine how the mixture should be enriched to achieve satisfactory results. According to the results and graphs presented above it cannot be unequivocally stated whether additional oxygenation is beneficial or not in solubilisation of sewage treatment incineration ashes. This is caused by a fact that differences between concentrations in two runs were not big enough to talk about general trend, difference may be caused by errors of chemical analysis of examined specie. From particle distribution point of view it is good to have additional air inlet at the bottom in order to prevent bigger-sized particles settling.
References [1] [2] [3] [4] [5] [6] [7] [8]
[9]
Fuleihan, N. F. Procedia Engineering 2012, 46, 195-205. Bergman, B.; Sandh, G.; Lin, S.; Larsson, J.; Carpenter, E. J. FEMS Microbiol. Rev. 2013, 37, 286-302. Makuch, A. PhD thesis, Politechnika Gdańska, KTH, 2009 Saeid, A.; Labuda, M.; Chojnacka, K.; Górecki, H. Waste Biomass Valor. 2014, 5, 265-272 Behera, B. C.; Singdevsachan, S. K.; Mishra, R. R.; Dutta, S. K.; Thatoi, H. N. Biocatal. Agric. Biotechnol. 2014, 3, 97-110. Goldstein, A. H.; Braverman, K.; Osorio, N. FEMS Microbiol. Ecol. 1999, 30, 295-300. Sayyed, R. Z.; Trivedi, M. H.; Gobi, T. A. SpringerPlus [online] 2013, 2 http://www.springerplus.com/content/2/1/587 (access 25th of November 2015) Altomare C, Norvell WA, Borjkman T, Harman GE (1999) Solubilization of phosphates and micronutrients by the plant growth promoting and biocontrol fungus Trichoderma harzianum Rifai 1295–22. Appl Environ Microbiol 65:2926-2933 Parks EJ, Olson GJ, Brinckman FE, Baldi F (1990) Characterization by high performance liquid chromatography (HPLC) of the solubilization of phosphorus in iron ore by a fungus. J Ind Microbiol Biotechnol 5:183-189
Sustainable Energy [10] Bielińska, E. J. Acta Agrophysica, Rozprawy i Monografie 2005, 3, 63-74. [11] https://suw.biblos.pk.edu.pl/resources/i1/i6/i3/i9/i0/r16390/HudziakG_GlowneKierunki.pdf (access 25th of November 2015) [12] M. Franz, Phosphate fertilizer from sewage sludge ash (SSA) Waste Management, Volume 28, Issue 10, 1809-1818 [13] Behera, B. C.; Singdevsachan, S. K.; Mishra, R. R.; Dutta, S. K.; Thatoi, H. N. Biocatal. Agric. Biotechnol. 2014, 3, 97-110. [14] Goldstein, A. H.; Braverman, K.; Osorio, N. FEMS Microbiol. Ecol. 1999, 30, 295-300 [15] Vary, P. S.; Biedendieck, R.; Fuerch, T.; Meinhardt, F.; Rohde, M.; Deckwer, W.-D.; Jahn, D. Appl. Microbiol. Biotechnol. 2007, 76, 957-967.
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Cost of producing electricity Magdalena Maj Silesian University of Technology,
Abstract This article is devoted to power production costs and discusses the impact of different factors on it. The attempt was made to look at those issues both from technical and economic point of view. There were taken efforts to find answers for such questions as: what exactly is included in the electricity price? What is the most expensive component of producing energy? And how does it look in different types of sources? How does the world think energy sector should be developed? What are the global efforts for environment and climate protection? How does energy market look in Poland?
1. Introduction Process of producing electricity is highly complicated. People from energy sector should be educated in both areas, the one concerning energy market as well as in the issue of producing electricity. Even engineers are consumers, all of the people, who have access to electricity, are consumers of energy. Each month the bill for energy has to be paid. It is worth knowing what is included in the price and how it can be changed depending on some factors.
2. Producing electricity 2.1. Components of costs of producing electricity People should be aware how many functions and processes are being managed in companies that produce electricity. The most significant are: production processes – maintenance installations – monitoring the operations; supplying of basic raw materials for energy production (fuel or energy input, water, chemical manufacturer for desulfurizer, demineralization, and others); supplying with an auxiliary machinery and materials, including those for renovations, facility equipment, tools, work protection measures, and others; internal quality control; sales – invoicing and recovery; maintenance custom service – including complaints; marketing; planning renovations and investments; planning strategy and strengthen; renovation processes; financial and accounting processes; stuff services; OSH management; public relations and internal communications; services of lawyers; administrative work; management; telephone communications, tele - video, inter/intra – net; collect and process data;
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internal and external transport; property protection; cleanliness and order maintenance.
We can also divide costs into some categories like: variables and fixed. Variables are those that vary in proportion to the production. Fixed are those that don’t change with the amount of electricity used. The changing of the quantity of production involves changing in variable costs. Often, especially in small changes in production, it is assumed that variable cost is proportional to the production volume – constant unit variable cost. However, in reality variable costs are rising. Fixed cost is not a function of production. Fixed costs have to be considered in specific range of time, e.g. labor cost in a short period of time is seen as fixed cost and in a longer period at least part of this cost can be considered as a variable cost. Another way of dividing costs is to direct and indirect. Indirect cost is cost that can be attached uniquely to the process of producing specific product and its part (unit product) or to provision of specific service. Direct cost is named as cost that is borne by the undertaking but it cannot be attached uniquely to the process of production of unit product or to provision of specific service. The way of dividing costs is shown in the table below. Tab. 1. Dividing costs Fixed
Variable
constant; considered in the range of time; e.g. payment can be treated as a fixed cost in short time as well as V in long time
V=f(P); usually if the small change of production it is assumption that V is proportional to the production but in real life V increase with the production
Indirect
Direct
If it is needed to consider costs of producing electricity and compare those among different sources it should be calculated unit cost which refers to the amount of production. It can be calculated total unit cost or unit cost for variable or fixed costs. Equation given below shows how to do it: Variable unit cost =
𝐕𝐚𝐫𝐢𝐚𝐛𝐥𝐞 𝐜𝐨𝐬𝐭 𝐏𝐫𝐨𝐝𝐮𝐜𝐭𝐢𝐨𝐧
In production process also an important term is marginal cost defined below. Marginal cost - it is the cost which has to be paid to increase the production by one. Marginal cost is equal to marginal variable cost. If the variable cost per unit is constant it is equal to the marginal cost.
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Indirect
Direct
Tab. 2. Fixed and variable costs in Energy companies Fixed
Variable
• • • •
• • • •
•
cost of labour fixed part of waste storage cost of process and sanitary water cost of materials and spare parts for renovations cost of repair services depreciation in the part related to productive installation others… (e.g. license)
• • • • •
Fixed cost of labour employees except for service and technical supervisors cost of external legal services and debt collection taxes and local payments depreciation in the part not related to productive installation others…
• •
•
cost of fuel and other basic sources cost of transporting fuel and other basic sources variable part of cost waste storage cost of using the environment – emission of dust, SO2, NOX, CO2 cost of draining technical sewage
2.2. Development costs based on ARE data On the basis of study of ARE SA [3], charts and tables were done showing the structure of variable and fixed costs and also unit variable and fixed costs of electricity based on the following costs dividing: Tab. 3. Costs dividing by ARE Fixed
Variable
• depreciation • other costs of core activities • materials (costs of materials which quantity does not depend on the volume of production) • labour costs
• • •
cost of fuel (including costs of purchasing, transporting the fuel, loading) cost of using the environment – emission of dust, SO2, NOx, CO2 other costs (materials cost except for fuel which quantity depend on the volume of production, including water and chemicals )
Renovation costs were distinguished from the fixed costs. In this study supportive departments costs, levies (and other duties) and other costs of core of activities were summed up and presented in one position as other costs.
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Fig. 1. Variable cost structure of electricity, reserve capacity and system services in power plants and CHP
In the structure of variable cost of electricity, reserve capacity and system services predominant component is fuel (together with purchasing costs), being about 90% of variable costs, especially in the case of biomass power plant and combined heat and power plant being even 98.57%. For hard coal and lignite power plants cost of fuel stands for respectively 94.32% and 89.37% of summary variable costs.
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Fig. 2. Components of variable cost per unit for electricity, reserve capacity and system services in power plants and CHP
Unit variable cost of electricity, reserve capacity and system services reaches the value of 69.81 EUR/MWh for biomass CHP and power plants with fuel cost of 68.81 EUR/MWh. The minimum value of unit variable cost has wind power with power higher than 10 MW, it is in total 0.95 EUR/MWh.
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Fig. 3. Fixed cost structure of electricity, reserve capacity and system services in power plants and CHP
In the structure of fixed costs of electricity, reserve capacity and system services predominant component is depreciation, being in the case of wind power plant with the power higher than 10 MW equal to 60.71% of costs, whereas materials for such kind of power plants is at the rate of 1.29% of fixed costs. Depreciation for lignite and hard coal power plant is 24.53% and 32.98% of costs, respectively.
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Fig. 4. Components of fixed cost per unit for electricity, reserve capacity and system services in power plants and CHP
Unit fixed cost of electricity, reserve capacity and system services has the maximum value of 53.86 EUR/MWh, with depreciation cost of 32.69 EUR/MWh for wind power plants with capacity higher than 10 MW. The lowest value of unit fixed cost of electricity, reserve capacity and system services have lignite and hard coal power plants equal to 11.29 EUR/MWh and 12.05 EUR/MWh, respectively with depreciation cost of 4.55 EUR/MWh and 4.41 EUR/MWh.
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Fig. 5. Cost of producing electricity per unit
Total unit cost of electricity, reserve capacity and system services is the highest for power plants and combined heat and power plants for biomass; hard coal and lignite power plants are characterized by, the lowest value of unit cost of producing electricity. [3]
2.3. Coal power plants in the energy market In free market, power price is set by variable cost of marginal plants. In Germany, the marginal plants are fueled by hard coal (in off peak) or gas (in peak).
Fig. 6. Generation cost curve
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As a result, the power price should be driven by coal, gas and CO2 price. In Poland about 75% of electricity is produced in coal power plants thanks to the price of producing, as it was shown before, and thanks to having natural resources (however, nowadays progressively more coal is imported). Combustion of fossil fuels involves lots of emissions, mostly of SOx, NOx, CO2, dust, CO. It is common opinion that CO2 gas is responsible for called greenhouse effect which in turn, some say, is linked to the global temperature increase.
Tab. 4. Example components structure of fossil fuels – hard coal and lignite. coal
lignite
coal - modern power plant
gC
0.624
0.25
0.624
gH
0.04
0.02
0.04
gN
0.04
0.05
0.04
gO
0.04
0.03
0.04
gS
0.006
0.01
0.006
P
0.15
0.2
0.15
W
0.1
0.44
0.1
LHV
GJ/t
24.6
9.2
24.6
efficiency
%
36.7
35.3
45
CO2 emission factor
tons of CO2/MWh
0.91
1.02
0.74
People of the world decided to handle the problem of greenhouse effect. The beginning of actions is assign to agreeing UN Framework Convention on Climate Change (UNFCCC) from Rio in 1992 and later at the Conference of Parties (CoP) when 160 countries make an approach called “cap - and - trade”. This is marked – based approach that put price on greenhouse effect gases. In UNFCCC nowadays there are six trading exchanges: the Chicago Climate Exchange, NASDAQ OMX Commodities Europe, European Climate Exchange, European Climate Exchange, Commodity Exchange Bratislava, PowerNext and the European Energy Exchange. The European Union Emissions Trading System (EU ETS) was launched in 2005 and set an obligation to purchase allowances for CO2 emission for energy – intensive industries and company’s electricity generations after using allocated pool of free CO2 allowances. In the table below it is shown how carbon dioxide price influence the cost of producing power in energy companies and there was also made a comparison with some other costs.
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Tab. 5. Effect of CO2 allowance on the price of electricity coal
lignite
coal - modern power plant
Salary
3.34
3.34
0.89
Fuel (with transport)
31.53
18.21
25.43
Auxiliary raw materials
1.40
1.27
1.13
Repair and maintenance
2.64
2.64
2.20
Use environment
0.48
0.48
0.48
Local taxes
0.33
0.77
1.54
Other costs
2.38
2.38
2.38
Subtotal
42.10
29.09
34.05
Depreciation
1.38
3.22
6.44
Sum 1
43.47
32.31
40.49
CO2 7 EUR/t
6.31
7.05
5.09
Sum 2
49.78
39.36
45.58
CO2 20 EUR/t
18.02
20.15
14.54
Sum 2
61.50
52.45
55.03
CO2 35 EUR/t
31.54
35.26
25.44
Sum 2
75.02
67.57
65.93
2.4. About COP21 During days from the 30th of November to 11th of December 2015 COP21 – “Conference of the Parties” was held in Paris. It was a summit of UN devoted to the issue of climate. The summit should result in a new version of the global agreement concerning counter greenhouse gas emission and signing of a new agreement making reference to the famous Kyoto Treaty from the year 1997. It was the first international settlement fixing reducing carbon dioxide emission. Signatories decided to decrease it by at least 5.2% by 2012, looking at the level of 1990. It is known now, that agreements were not respected. In fact, global emission from the 1990, which was about 17 mld tons, has been doubled which is shown on the picture below. [2]
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Fig. 7. CO2 emissions
In COP21 all the 195 countries which were participating in the conference have signed an agreement and 188 of them also an individual commitments on climate protection. Obligations concern limiting the average global temperature increase to 2 °C (maybe tending to 1.5°C) above pre-industrialization levels. Single states (or groups) have their own goal. The agreement stipulates, that each country will have called: nationally determined contributions (NDCs), while globally this is to give it a controlled increase in the average global temperature. Before arrangements will come into force everything must to be verified and finally arrangements must be ratified by at least 55 countries, where global emissions are at least 55% of the world. However, here it should be noted, that the ratification of the Kyoto Treaty – signed in 1997, it took eight years… While the level of global greenhouse was completely different and as a leader arose China, which has not signed Kyoto Treaty at all.
3. Conclusions In the near future, the world will have to deal with problems relating to changes in the energy sector. Some sources should be replaced either because they may strongly affect the environment or their resources are not inexhaustible. And there is still an open question what techniques or fuels should be developed and used in the future. There are lots of factors that should be taken into consideration, mostly the money and environment protection issues. Balancing those two is a real challenge. This situation creates many opportunities for scientists and business people related to energy. Those have to remember to think about future generations, that should live on Earth with conditions not worse than the present one and make decisions and actions that are indeed significant, not those which just can satisfy public opinion but also can make some real improvements.
References [1] http://www.cop21paris.org/; [2] http://www.europarl.europa.eu; [3] Hanna Mikołajuk, Janusz Smardz, Włodzimierz Liszyk, Mariusz Sowa, Dorota Zaborska and others, SYTUACJA FINANSOWA PRZEDSIĘBIORSTW ENERGETYKI w 2014 roku, DANE ZAGREGOWANE, Warszawa, lipiec 2015.
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Analysis of CCS process in post-combustion technology Magdalena Trzcionka University of Technology in Częstochowa
Abstract There is an increasing growth of CO2 concentration in earth’s atmosphere, which is one of the greenhouse gases leading to progressive climate change. Poland is committed to adhere to the climate and energy package about the aspiration to decrease the harmful production of CO2. It is worth mentioning that most power plants do not hold proper installation, which could decrease the emission of CO 2 into the atmosphere. The implementation of new technologies is costly and requires time. In the near future it is forecasted that companies, which use the old technologies, will hold high liability costs. Carbon, capture and storage of CO2, also known as CCS, consists of CO2 separation, transportation and storage in a harmless manner for the environment. Energy industry consistently contributes to the increase of concentration of CO2, so scientists search for solutions that will limit the emission of this harmful gas into the atmosphere. The aim of the article is to introduce the problem of the reduction CO2 emission into the atmosphere by its capture from exhaust gases by chemical absorption process. The first phase of the CCS process, called absorption allows to describe the amount of the energy which is needed to execute of captured CO2 with the use of MEA solution and ammonia. In a geometrical model of the absorber there were covered 2 phases-liquid and gaseous (fumes). The designed CFD model of absorption implemented analysis of floating conditions in the column. The modelling program was Ansys Fluent. In the simulation section following parameters were taken into account: analysis of temperature of flue gases, mass fraction of CO2, mass fraction of MEA for process effectiveness and efficiency of the capture CO2. [1]
1. Introduction This chapter develops a framework of development of carbon capture and storage (CCS). It presents types of CCS technologies and includes issues about CCS. It is based on a review of the literature about post-combustion, pre combustion and oxy-fuel. The most known methods of CO2 reduction in power industry and other industrial areas are: to increase power industry efficiency of all production process, replace the fossil-fuel power plants by renewable sources, to implement CCS technologies –capture CO2 from fossil fuels in power plants and storage underground or in the seabed. The questions concerning CCS were extensively regulated in a CCS directive, which is a part of climate-energetics package. Coal is the cheapest and most richly presented fossil fuel. Unfortunately in a combustion process, uttermost amounts of greenhouse gases are emitted which are the main reason of acid rain phenomenon. There are three main methods to reduce CO2 emission: ultra super-critical power plants, renewable resources, capture CO 2: pre-combustion, oxyfuel, post combustion capture (PCC). CO2 is a major greenhouse gas that is responsible for global warming. The capture of carbon dioxide from a flue gases goes down with a MEA monoethanolamine.
Fig. 1. The classification of post combustion CO2 technologies [2].
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Fig. 1 presents the different types of post combustion technology. In this article, the chemical absorption is considered with the use monoethanolamine (MEA) as a solvent. The simplified CCS installation is shown in Fig. 2. The installation consists of absorber, desorber, power plant, scrubber, flue gas cooler and heat exchanger. Desulphurized exhaust fumes are sent to the absorber column, where they contact the concentration based on MEA aqueous amine solution in a chemical compounds which absorbs CO2. MEA is the chemical solvent used for CO2 absorption due to its good reactivity and low cost. Cleared fumes leave the column and go to the desorber to which device is provided heat which enables the release of gaseous CO2. Obtained in that way, the gaseous stream in the installation is directed to the chimney and industrial process will be stored and economically used. The solution deprived from CO2 goes back to an absorber column in an absorption process where it once again contacts with the fumes and absorbs CO2. Then, the whole cycle repeats. The absorber column is made of filled porous material which provides the effective absorption process of CO2. [2]
Fig. 2. Post combustion capture process [3].
2. Research in the field of CCS technology in Poland. The strategic Research Programme of Advanced Technologies
From the previous couple of years the Institute of Chemical Processing of Coal in Zabrze has been working on questions about removal of CO2 from industrial flue gases. In the Institute which holds proper research and apparatus, scientists analyze technological process of producing energy and research about capturing CO 2 using absorption method in amine solution. The tasks are realized within The Strategic Research Programme of Advanced Technologies. The work is conducted by the scientific group and conducts complex tests of liquid sorbents and the whole absorption process for different solutions. Within 2010-2012, there was launched a laboratory workstation of CO2 removal with flow intensity of gas in the inlet equal to 5 m3/h and another workbench of removal CO2 with the use of the absorption method with the set flow intensity of gas equal to 100 m3/h. Obtained knowledge and experience enables the creation of a real test on a real object The scientists with
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the Partners from Tauron Company decided to build an installation of coal block and conduct tests. In Fig.4 there is a scheme of amine absorption installation that was developed as a result of their cooperation. The intake of flue gases is 200m3/h and enables removal of about 50kg/h CO2 which gives about 1.2 tonne CO2 released per day [4].
Fig.3. Scheme of an amine absorption installation developed in Institute for chemical processing and coal in Zabrze [5]
The experimental apparatus which is in the Institute of Chemical Processing of Coal in Zabrze is presented in Fig.4
Fig. 4. Post-combustion CO2 capture laboratory installation [4]
3. Model definition Numerical model of absorber is a two-dimensional axi-symmetrical computer fluid dynamics model of the CO 2 capture process. Nominal stream in a column for a gas is 5
𝑚3 ℎ
and for a liquid is 0.05
𝑚3 ℎ
. The dimensions of the
column are: 1.5 m of height, diameter: 0.01m and the height of porous zone is 1.2 m. Filling of a column was obtained with the use of Rashing rings. In a model, gas is passes at the bottom, then it flows through porous zone and is received at the top of a column. A liquid is passed at the top, and then falls down according to the gravity [5]. The Fig. 5 presents the whole model absorber and desorber.
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Fig. 5. Absorber and desorber [5]
Simulation of CO2 capture-results The goal of simulation was to model the flow of the absorption process in the absorber column. The real model for the simulation is a CCS pilot installation installed in an Institute for Chemical Processing of Coal in Zabrze. The simulation was held for the 5 first cases with different amount of CO2 at the inlet of the absorber with the following condition: Q(gas)=var; L(liguid)=const, so ratio the L/Q=var. For the two others it was settled that: Q=var; L=var so L/Q=const. The results of different parameters such as: gas temperature, MEA, CO2 content and efficiency of CO2 capture were taken from the program Ansys Fluent. In the first case it was established that:
𝑄1−𝐶𝑂2<𝑄2−𝐶𝑂2<𝑄3−𝐶𝑂2 <𝑄4−𝐶𝑂2<𝑄5−𝐶𝑂2 where:
𝑄1−𝐶𝑂2 =0.00144 [kg/s]; 𝑄2−𝐶𝑂2=0.00157 [kg/s] 𝑄3−𝐶𝑂2=0.00196 [kg/s] 𝑄4−𝐶𝑂2=0.00215 [kg/s] 𝑄5−𝐶𝑂2=0.00241 [kg/s]
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313
L= const
L/Q=var
Temperature of gas [K]
311
309
Q1
Q
Q2 Q3
307
Q4 Q5
305
303 0
0.2
0.4
0.6
0.8
1
1.2
axial coordinate [m]
Fig. 6. Axial distribution of gas temperature for varying L/Q In Fig.6 is shown the gas temperature in function of L/Q=var (ratio of mass liquid flow and mass content of CO2 in a flue gases). From the graph it can be seen that inlet temperature is on 303 K and in the outlet of absorber is on 312 K. For all cases the temperature increases along the absorber, because there are hold intensive chemical reactions between 𝐶𝑀𝐸𝐴 and 𝐶𝐶𝑂2 , reaction is exothermic.
Fig. 7. Axial distribution of mass fraction of CO2 as a function for varying L/Q
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Fig. 7. presents the changes of CO2 mass fraction along the absorber. Such parameters like temperature and MEA content influence on the CO2 change. According to the graph when gas enters to the absorber at the bottom the amount of CO2 is constant and after it gets into the porous zone starts to decrease cause it is absorbed my MEA solvent. The temperature increases too because chemical reactions occur.
Fig. 8. Axial distribution of mass fraction of MEA for varying L/Q
Fig. 8 shows that molar fraction of reagent MEA. The MEA content increases when the amount of CO2 decreases along the absorber which has a positive effect on CO2 capture. MEA solvents are generally considered to be potentially good absorbents for CO2 absorption due to their fast CO2 absorption rate. More MEA concentration is in the top part of absorber and its value decreases from top to bottom, then rest of MEA capture CO2 and creates two different compounds MEAH and MEACO2 which don’t take part in capture process. From the Fig.6 it is observed that the temperature of gas influences on MEA due to given heat reactions are faster and CO2 is better absorbed by MEA. The Fig. 7 and Fig. 8 collect the molar fraction of reagents CO2 and MEA. The MEA content increases when the amount of CO2 decreases along the absorber.
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Fig. 9. Axial distribution of reaction rate for varying L/Q
The Fig. 9 shows the results of the reaction rate of both phases (liquid and gas phase). In the beginning the state is steady cause everything is constant and after it starts to change so it reach the transient state. Rate constant coefficients increases in first phase which is connected with the increase of removal CO2 by MEA solvent. Reaction rate as it enters the porous zone achieves the maximum value. After 1.2 [m] it reaches the liquid source which makes the reaction slower cause the MEA solution is higher and CO2 is lower. The reaction rate is dependent from CO2 and MEA and as it was observed is high when both concentrations are high.
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Fig.10. Efficiency versus capture in flue gases
Fig. 10. presents the efficiency changes within given amount of gas. When the amount of gas increases, the efficiency decreases. Below there are presented the graphs for the second case, when ration of L/Q is constant. In the second case it was established that: 𝑄6−𝐶𝑂2 <𝑄3−𝐶𝑂2 <𝑄7−𝐶𝑂2 𝑄6−𝐶𝑂2 = 0.00144 [kg/s] 𝑄7−𝐶𝑂2 =0.002434 [kg/s]
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L/Q=const
Fig. 11. Axial distribution of gas temperature for L/Q=const. The Fig. 11 presents the profiles of temperatures of gas phase. The temperature increases for both cases. It can be seen that gas temperatures have influence of MEA loading. The numerical model is sensitive to that factor change in the inlet of absorber.
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L/Q=const.
Fig. 12. Axial distribution of mass fraction of CO2 for L/Q=const.
L/Q=const.
Fig. 13. Axial distribution of mass fraction of MEA for L/Q=const.
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With the increase of the L/Q ratio the mass fraction of MEA in a porous zone of absorber increases and efficiency of CO2 capture increases too.
L/Q=const.
Fig. 14. Axial distribution of solvent lean loading for L/Q=const.
L/Q=const.
Fig. 15. Axial distribution of reaction rate for L/Q=const.
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Fig. 16. Efficiency versus capture in flue gases In a Fig. 16 are shown the results of simulation of experiment which presents the influence of L/Q for capture efficiency of CO2 . In a one case the amount of gas is different but the amount of liquid is constant so the ratio of L/Q is varied. In the second case the amount of gas and liquid are different so the ratio of L/Q is constant. The capture efficiency is a key element of CCS installation .For the first case it was observed that with the increase of the flue gases in the inlet the efficiency decreases. For the smallest Q gas =0.0014 [kg/s] the efficiency is the highest. As it is observed the amount of the Q gas increases, so the efficiency increase linearly so the Q gas is inversely proportional to efficiency. On the efficiency influence parameters like liquid temperature in the inlet, lean loading of CO2 which increase the efficiency. It was observed that efficiency decrease with the amount of lean loading CO2 in the inlet and increase with the higher ratio of L/Q. For a smaller value of L/Q the drop efficiency is more rapid and then decreases the amount of pure sorbent MEA. In a consequence MEA is faster consumed with the drop of liquid and as a result the efficiency is lower and reaction rate is slower.
4. Conclusion In the article the analysis of the CO2 capture in the model was shown. The goal of the system is to capture CO2 with a given efficiency, based on CFD model, in the absorber, the simulation for steady states was held. The evaluation of the parameters like amount of CO2, amount of MEA and reaction rate was conducted. In real conditions the knowledge of given parameters enable for estimation of power plant efficiency. Efficiency increase has a positive effect in decreasing of emission of CO2 in flue gases and reduction of fuel consumption. Analysing the results it can be observed that with the increase of the liquid to gas ratio (L/Q) the efficiency increases in a range of these analyzed values. With the increase of ratio L/G, when L/G is const. the efficiency of absorber decreases. High costs of the facility and implementing CCS technology generates a lot of interest, because that way people contribute to protect the environment and prevent greenhouse effect.
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References [1] Spigarelli, B. P. & Kawatra, S. K. Opportunities and challenges in carbon dioxide capture. Journal of CO2 Utilization 1, 69–87 (Elsevier Ltd., 2013). [2] Wang, M., Lawal, A., Stephenson, P., Sidders, J. & Ramshaw, C. Post-combustion CO2 capture with chemical absorption: A state-of-the-art review. Chemical Engineering Research and Design 89, 1609– 1624 (Institution of Chemical Engineers, 2011). [3] http://www.captureready.com/EN/Channels/Research/showDetail2.asp?objID=29 [4] dr inż. L. Więcław-Solny, dr hab. inż. M. Ś. prof. nadzw. Absorpcyjne usuwanie CO 2 ze spalin kotłowych. 8 (2011). [5] Asendrych, D., Niegodajew, P. & Drobniak, S. CFD Modelling of CO 2 Capture in a Packed Bed by Chemical Absorption. Chemical and Process Engineering 34, 269–282 (2013).
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Impact of SCNR DeNOx installations on coal combustion byproducts quality Maria Kolmer Silesian University of Technology
Abstract Application of SNCR installations in large combustion coal power plants results in unreacted reagent remaining in flue gas as ammonia slip. The presence of ammonia has several negative impacts on the boilers operation. One of the concerns is the ammonia contamination in combustion products (especially in fly ash). In result by-products lose on their commercial value and have to be stored. In this work, we investigated different factors, which have impact on ammonia content in fly ash and looked for correlations between them. The discussion was based on measurements from two boilers. We examined relations between amount of injected urea, ammonia slip and ammonia content in fly ash and we investigated impact of boilers load on them. The discussion was concluded by the scope of the future work.
1. Introduction The Industrial European Directive requires significant reduction in NOx emissions from coal-fired boilers in large combustion power plants. This necessitates the use of ammonia or urea injection, such as in Selective Catalytic Reduction (SCR) or Selective Non-Catalytic Reduction (SNCR) technologies. To obtain required level of NOx emission under operational conditions, the amount of a reagent, that needs to be injected, is much higher than theoretically predicted from a simple stoichiometric ratio. This leaves a large portion of the unreacted reagent remaining in the flue gas as ammonia slip, what has several negative impacts on boilers operation. Ammonia has a detectable odour at the level of 5 ppm and poses a health concern at levels higher than 25 ppm. Particularly ammonia causes a stack plume visibility problem due to the formation of ammonium chlorides and ammonium bisulphate. Moreover, ammonia-sulphur salts can plug, foul, and corrode a downstream equipment such as air heaters, ducts and fans. [1] The sinks for the NH3-slip in a typical boiler are presented on the figure 1.
Fig. 1. Sinks for NH3-slip in the boiler [2] The amount of unreacted ammonia is normally maintained at levels that do not create operating problems or pollutant emission issues. Typically the level of slip varies for different power plants from 2 to 10 ppm. [3] Other issue related to the presence of ammonia is a decrease of coal combustion by-products quality. Especially the fly ash, which contains up to 80% of the ammonia slip, is the main product affected by the ammonia (figure 1). The presence of ammonium salts on the ash particles is a serious obstacle during the fly ash utilization into a concrete. In this case ammonia does not influence strength properties of the concrete, but it causes specific unpleasant odour [4]. Because of odour concerns, the fly ash recipients require low ammonia content, in Poland we can encounter maximum acceptable values at the levels of 50, 80 or 100 mg/kg.
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Coal combustion by-products contaminated with NH3 lose on their commercial value and have to be stored, what is a loss for every power plant. In consequence, it is important to examine factors and understand processes which have impact on ammonia content in combustion by-products. In this work relation between ammonia slip, ammonia content in fly ash and amount of injected urea are analysed on the example of two boilers, type: BP1150. The technology used for NOx emissions reduction in the boilers is Selective Non-Catalytic Reduction.
2. Input data The measurements, which were carried out during the operation of boilers, include:
Ammonia slip in flue gas, Flow rate and concentration of injected urea, Ammonia content in fly ash.
The values of ammonia slip were measured with 10 min intervals in flue gas ducts before the air preheater. A daily average of those values is used in the further calculations. Ammonia content in fly ash (figure 2. and figure 3) was measured in the laboratory as a daily average from three samples collected from an electrostatic precipitator each day. Flow rate and concentration of injected urea were measured in the power plants with 10 min intervals. The amount of urea used in the calculations is a daily average of those measurements, calculated as urea of 100% concentration (with the assumption, that density of urea solution is equal to 1 kg/dm3). Input data were complemented by measurements of boilers load and the elemental analysis of fuel. Data used in the calculations were collected from 43 days in case of first boiler and from 79 days in the case of second boiler.
Significant changes in NH3 content
Fig. 2. NH3 content in the fly ash, first boiler (B1)
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Fig. 3. NH3 content in fly ash, second boiler (B2) Graphs show that for each boiler, we observe significant changes in ammonia content (more than 20 mg/kg) and high ammonia contamination (close to the limit of commercial usefulness).
3. Analysis of ammonia content in fly ash in terms of selected factors 3.1. Mass of daily injected urea The first investigated factor, which has an impact on ammonia content in fly ash, is mass of injected urea. The daily amount of injected reagent calculated, as of urea of 100% concentration, is given by: 𝑚urea,100% = 𝐹urea ∙
𝑆urea 100
∙ 𝛿 ∙ 𝑡 [𝑘𝑔]
(3.1)
where: 𝑚urea,100% - daily mass of urea of 100% concentration [kg], 𝐹urea – average urea solution flow rate[dm3/min], 𝑆𝑢𝑟𝑒𝑎 –concentration of urea solution[%weight], 𝛿 - density of urea solution, 𝛿 = 1 kg/dm3, 𝑡 - time, t=1440 min. The advantage of reagent mass as an indicator of ammonia contamination in fly ash is simplicity of calculation and high accuracy of measurements of the urea flow rate. Graphs presented in figure 4 and figure 5 show obtained result.
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Fig. 4. Relation between NH3 content in fly ash and mass of reagent, B1
Fig. 5. Relation between NH3 content in fly ash and mass of reagent, B2 The increase of ammonia content in fly ash with mass of injected urea is observed for both boilers. Moreover the slope of trend lines is similar, what indicates that the correlation between those two values exists. We also observe higher usage of the reagent in case of second boiler.
3.2. Ratio of urea to fly ash mass flow Ammonia content in fly ash depends not only on injected urea, but also on the amount of fly ash. Those both quantities are taken into consideration in the second investigated factor, in the form of ratio (
𝑭𝐮𝐫𝐞𝐚,𝟏𝟎𝟎% 𝒎̇𝒂𝒔𝒉
). The
analysis starts with determination of daily average mass flow of ash given by: 𝑚̇𝑎𝑠ℎ = 𝑧𝑎 ∙ 𝑎 ∙ 𝛽
𝑘𝑔
[ ]
where: 𝑚̇𝑎𝑠ℎ – mass flow of fly ash [kg/s], 𝑧𝑎 – ash content in the fuel (from the proximate analysis) [%], 𝑎 – fly ash coefficient, a=0.85, 𝛽 – mass flow of fuel [kg/s].
𝑠
(3.2.)
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The mass flow of fuel is calculated with the assumption of the power plant net efficiency equal to 39% in the case of the first boiler and 41% in the case of second boiler: 𝑵
𝜷 = 𝑾 𝒆𝒍∙𝜼 𝒅
𝒌𝒈
[𝒔]
(3.3)
where: 𝑊𝑑 – lower calorific value[kJ/kg], 𝜂 – efficiency, 𝑁𝑒𝑙 – net power [MWel]. In the next step the daily average of fuel and urea mass flow are calculated. Determining the mean value is necessary in order to compare the ratio
𝐅𝐮𝐫𝐞𝐚,𝟏𝟎𝟎% 𝐦̇𝐚𝐬𝐡
with daily measured ammonia content in fly ash. Results are
showed in figure 5 and figure 6.
Fig. 5. Ammonia contamination in fly ash in the function of ratio:
Fig. 6. Ammonia contamination in fly ash in the function of ratio:
𝑭𝒖𝒓𝒆𝒂 𝟏𝟎𝟎% 𝒎̇𝒂𝒔𝒉
, B1
𝑭𝒖𝒓𝒆𝒂 𝟏𝟎𝟎% 𝒎̇𝒂𝒔𝒉
, B2
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The presented relation combines all measured parameters: ash content in the fuel, reagent flow rate, ammonia content in fly ash and indirectly the daily load of the boiler (through fuel mass flow). We observe that points in the graphs are highly dispersed, what is also indicated by low value of coefficient of determination R 2. However, slopes of the trend lines are similar for both boilers.
4. The impact of boilers load on relation between injected urea and ammonia slip In order to study impact of boilers load on investigated quantities, measurements data were classified. The classification was on the basis of produced net power in the power plant. In the first case boilers worked with small load (less than 280 MWel) and in the second case net power was higher than 280 MWel. Measured value of ammonia slip has the form of volume concentration in flue gas. In order to precisely determine relation between injected urea and unreacted ammonia, the value of reagent flow rate is dived by the average volumetric flow of flue gas (
𝑭𝐮𝐫𝐞𝐚,𝟏𝟎𝟎% 𝑽̇
). In the result daily load of boiler is taken into consideration. The volumetric
flow rate of reagent is measured in the power plant .The volume of flue gas is given by:
𝑽̇ = 𝒗𝒔 ∙ 𝜷 [Nm3/s]
(3.4)
where: 𝑉̇ – volume flow of flue gas [Nm3/s], 𝑣𝑠 – specific volume of flue gas calculated from the elemental analysis of fuel [Nm3 / kg fuel], 𝛽 – mass flow of fuel [kg/s].
Results of calculations are presented on the graphs in the figures 7-4.4, regarding to the produced net power.
Fig. 7. Relation between ammonia slip and injected reagent, net power > 280 MWel, B1
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Fig. 8. Relation between ammonia slip and injected reagent, net power < 280 MWel, B1
Fig. 9. Relation between ammonia slip and injected reagent, net power > 280 MWel, B2
Fig. 10. Relation between ammonia slip and injected reagent, net power < 280 MWel, B2
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Graphs indicate, that during the boiler operation with high load, amount of ammonia slip increases proportionally to the urea flow rate. When boilers work with low load, we observe lower grow of ammonia slip due to increase in urea injection, what is indicated by almost flat trend lines.
5. Conclusions In this work we briefly discussed the impact of SNCR installation on the quality of combustion by-products in large coal fired power plants. Our discussion is based on two examples of boilers. We investigated relations between injected urea, ammonia slip and ammonia content in fly ash. From obtained results we concluded, that there are correlations between examined quantities. However, graphs indicate, that ammonia contamination in ash is different for each of boiler. We also observe large dispersion of points in the plots. This indicates that daily averages of ash samples and boilers parameters have significant impact on the quality of obtained results and can lead to too general conclusions. Processes, which take a place during the NOx reduction reactions are very complex. In order to fully examine the correlation between amount of injected urea, NH3-slip and NH3 content in fly ash other factors, like flue gas temperature, quality of coal grinding and the position of urea injection nozzles should be taken into consideration. However, the biggest impact on quality of obtained results have the measurements inaccuracy of ammonia content in fly ash and the fact, that during tests boilers were working with different loads. The scope of the future work includes more complex analysis, based on measurements with samples collected after two hours stable work of a boiler. The study should be expanded by the calculation of reagent utilization factor and efficiency of NOx reduction. The complete analysis should also include the measurements of ammonia content in bottom ash and in gypsum.
Acknowledgements The author acknowledges the company SBB ENERGY S.A. for providing all necessary materials and assistance.
References [1] Environmental Protection Agency [Online, date of the access: 20.11. 2015] http://www3.epa.gov/ttncatc1/dir1/c_allchs.pdf [2] Dirk Porbatzkl, Jurgen Brandenstein, Impact of DeNOx – DeSOx installations on CCP quality, Conference Proceedings, Copenhagen 2010 [3] James E. Staudt, Measuring Ammonia Slip from Post Combustion NOx Reduction Systems, ICAC Forum 2000 [4] G.F. Brendel, J.E. Bonetti, Investigation of Ammonia Adsorption on Fly Ash due to Installation of Selective Catalytic Reduction Systems, Final report, November 2000
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Renewable energy from biomass – vineyard prunings Milan Zlatkovikj Silesian University of Technology, e mail:
[email protected]
Abstract. Every year, after the pruning of the vineyard, there are big amounts of vineyard prunings, which have high energy value, and until now, minimal use. To maximize the energy value of the prunings, it is recommended to make briquettes from them. The result is homogeneous fuel with increased heating value. Most often briquettes are used in the winter period for heating purposes. With effective use of briquettes for heating, the use of wood and electrical energy for heating purposes will be largely reduced. Grape is grown everywhere throughout the world, so there are many opportunities for use of vineyard waste and collaboration in this area, for the purpose of developing effective technologies for use of this waste for generating heat and electricity. The aim of this paperwork is to intensify the importance of using renewable energy sources from biomass, to analyze the potential and completely utilize it. With successful implementation, the heat requirements will be satisfied long term.
1. Introduction Energy consumption rises on world level continuously. In the sametime, the fossil fuels reserves are getting lower. These two facts show us that we must work on finding new sources of energy for the future if we want to continue our technological development. Energy and fuels influence every aspect of our live. The price of energy is not only in our bills for electricity, heating and fuel for vehicles. In every product we buy, such as food, clothes, decorations, gifts etc. 30% of the price is for energy consumed in the production process. So it’s quite obvious that cheaper energy will introduce cheaper products from the markets for the consumers, and that’s something that everyone would happily accept. In the meantime, during the generation of energy, we should also consider its impact on the environment. We already evidence the impact of industrialization in some countries or particular cities in the world. Adding to this, that in many countries the economic development and industrialization of the country is put ahead of environmental protection, the situation gets even worse. The technologies currently used for energy conversion and use are available on the market for a long time and are proven and reliable. One of the areas of research in energy engineering is to continue the use of this method, with reduced impact on the environment – filtering systems, more efficient process, and some other methods. This would help to continue their use, and lower their impact on the environment, but it won’t help with their prolonged use. Fossil fuels are in big supply, there are data for proven reserves throughout the world, and everyday there are new data for new proven reserves, but they are limited. The dependency on fossil fuels is huge, so this period should be used to generate solutions for other types of fuels. The use of renewable energies is on the rise - solar, hydro, wave, wind, biomass, geothermal and other. However some of these technologies are new and unconventional, so they will need some time to prove their efficiency and reliability in use. This should not be a discouraging fact, because, even the use of fossil fuels needed a lot of time to get to today’s degree of efficient use. Taking into consideration that today we live in highly developed technological society, resources evaluation and monitoring is far easier than in the beginning of the industrial age, when with the use of coal, started the era of fossil fuels. So every available opportunity for new source of energy that is renewable and eco-friendly should be supported as much as possible, in all the aspects of the process of development. Energy from biomass is one of the renewable energies. It’s very high growing sector, and it’s predicted this growth to continue in the future, even with higher intensity. In order to reduce emissions in the energy sector, sustainably produced energy from biomass will have an important role, with primary biomass demand increasing three-fold until year 2050. It is predicted that electricity generated from biomass energy will increase 10 times. Use in industry will increase rapidly because of replacing coal with biomass in high-temperature applications. The only reduction in use, will still be a positive one, because the reduction is estimated to be in the primitive use of biomass in developing countries. [1]
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2. Biomass share in energy consumption Biomass is the oldest source of energy that humans use to gain heat. The first use of biomass is burning wood in the caves to gain heat. Although long time passed from that period, in many developing countries this type of biomass is the main energy supply for cooking and heating. Biomass is used all-over the world, but in different ways. In the developing countries it is largely used and it causes deforestation (destroying of forests) and it’s used in inefficient way. In more developed countries in northern Europe and North America, source of biomass is agricultural waste, waste of trees, waste of food-processing factories and other types of waste. Generally is used in plants to gain electricity and heat, and this improves the efficiency and reduces the emissions of combustion. Biomass energy takes around 10% from (50EJ) of world total primary energy supply today [1]. Most of this is consumed in developing countries for cooking and heating, using very inefficient open fires or simple cook stoves with big impact on health and environment with smoke pollution and deforestation. Biomass energy in the developed countries is in smaller supply, but is growing steadily and continuously. Another contribution from this energy source, is that it is used in different areas of energy consumption – household heating, industry, electricity generation and biofuels. In 2012 biomass energy is used for: Tab. 1. Use of biomass in 2012[1] Use of biomass Amount (EJ) Heating and cooking in primitive way
≈ 35.67
Modern heating in households
5
Use in industry
8
Generating electricity
1.33 (370 TWh)
Total
50
Many proven technologies for generating heat and power from biomass exist on the market. This include: solid wood heating installations, biogas digesters for power generation, large-scale biomass gasification plants for heat and power, co-firing biomass with coal in existing coal-fired power plants can be an important option to achieve short-team emission reductions and increase the sustainable use of existing assets. In some cases, the use of biomass energy is cost competitive on the market, for example for heating. In most of the cases of the use of biomass, economy subsidies are required to cover the difference between the price of biomass energy and fossil fuel generated electricity and power. These subsidies help can be justified by the environmental, energy security and socio-economic advantages associated with sustainable energy from biomass. In the near future, significant growth is predicted in the biomass sector. Global biomass energy production in the world is expected to rise from 370 TWh in 2012 to 560 TWh in 2018[1]. In the heating sector constant growth of 3% per year is expected and to reach 16 EJ in 2018, mostly because of the European Union targets set for 2020[1]. Biomass sources are wood and wood waste (from cutting and processing wood), waste from agriculture, industrial plants, waste from food processing processes, communal waste and many others. For some of these technologies there are developed technologies for utilization of the sources energy. Some of them are proven and are used, fulfilling both criteria for economic competitiveness on the market and ecological. For some of the possible resources, the conducted studies show that their use might not fulfil some of the criteria, so they can’t be regarded as a reliable long-term future source of energy. There are certain numbers of possible sources that are in the evaluation phase. Taking into consideration, that most of the energy installations require mayor financial investments, the evaluation process takes period of several years evaluation of the source, its potential, its advantages and disadvantages, and its possibility for being placed in the energy market. One of the sources that have huge energy potential, and is not yet evaluated completely and appropriately used are vineyard prunings. Grapes is one of the oldest plants that the human grow. The earliest archaeological evidence of
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growing grapes and producing wine from them is from 8000 years ago, in Georgia. Although its beginning is mainly in the Mediterranean region and other warm regions, today grape-wine is grown on every continent, except Antarctica. Most of the produced grape is used for producing wine. Other uses are as fresh fruit for eating, dried fruit, fresh and concentrated juice, distilled liquors, grapeseed oils and ethanol production. The world biggest producers are China, Italy, US, Spain, France, Turkey, Chile, Argentina, India and Iran. The production of grape increases in Asia and South America, and decreases in Europe. Although its primary and most effective use is in producing wine, there is possibility to increase the effectiveness of the grape plant (vineyard) by using the wastes that is created in the process of growing the grapes. Pruning is a critical component of the grape production system. It’s an activity that increases the productivity of the vineyard greatly. Shortly, pruning is an activity that is done once per year, it consists of removing two-year old canes, allowing new canes to grow, and with that the productivity is increased. With this activity, a high quantity of biomass is generated. This waste is in form of prunings, most similar to tiny tree branches. They have high calorific value, and that is why it is interesting for further exploration. The amount of gathered biomass from vineyards depends on several factors. Most important ones are air humidity, type of culture (plant), age of plant, biological characteristics, sizing of the plants and climate. Biomass gathered from prunings varies within certain limits. In most of the articles related to this area, the amount of biomass gathered from vineyard prunings is 4-8 t/ha [4]. As stated previously, there is big number of factors that influence this amount, and that explains the big difference between the minimum and maximum obtained quantity per 1ha. With all the new regulations for effective use of energy and reducing emissions from fossil fuels, alternative fuels are very popular, in high demand and in intensive development. The process of gathering the biomass from vineyard prunings consists of several phases. Prunings are cut from the plant, harvested from the vineyard, and then transported to a remote site where they are to be treated and conversed in the most useful way. The prunings can be used for producing solid, liquid and gas fuels. They can be used for generating heat and electricity. Until now, they are generally used in a few ineffective ways to generate heat. For the possibility of obtaining electricity from power plants with small capacity, there are several undergoing projects and evaluations. Calorific value from prunings vary, depending on its chemical composition and percent of moisture. However, this value is from 15 MJ/kg up to 19 MJ/kg [4], which is high calorific value for agricultural waste product.
3. Evaluation of the energy potential from vineyard prunings The use of renewable energy throughout the world varies largely. This applies also for the regulations for protection of the environment and the air in the urban areas. For these regulations, developed European countries have the highest requirements and the highest restrictions of hazardous emissions. Countries, members of the European Union, are required to have 20% renewable energy in primary energy consumption by the year 2020. Also the regulations for the allowed level of sulphur and nitric oxides emissions are getting lower and lower, with high goals set for the future. Three of the world biggest producing grape countries are in Europe – Italy, France and Spain, and in all other countries with adequate climate, grape is grown on large land areas and used for producing wines, so the interest for this source of energy is big. For the purpose of evaluation of the possibilities of this source of energy, the project EuroPruning is created [2]. The aim of this project is to enable an extensive utilization of the agricultural prunings for energy in Europe. The main task is to develop new and improved logistics for pruning residues. Logistics include harvesting, transport and storage of agricultural prunings (fruit tree, vineyards, olive grove prunings and branches from up-rooted trees). There is huge potential for energy generation from prunings. The potential of prunings in EU27 countries is estimated to 25.2 Mt/yearly [2]. One big advantage of this source is its reliability. Prunings are obtained from trees and vineyards. These are long-term growing agricultural cultures, so the variation in the land area they cover is very small in comparison to other agricultural plants. The huge potential of this source is not utilized by now, because of several constraints related to its utilization, from which the logistics is the most important one. The project should influence this process in many areas. New machinery for harvesting and on-site pre-treatment of the prunings will be developed. This machinery should fill a technology gap – specified machinery that will be applicable for different type of vineyard plants. The development of this machinery and its presence on the market, will be able to reduce costs and pre-treat the biomass, so that the product is compatible with standard transport means. During storage, biomass can change their properties due to biochemical processes. Therefore, optimization
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of the logistic for the biofuel quality is a must. Practical solution how to carry out the open air storage will be provided in order to ensure the quality of the product to be sufficient for the bioenergy market. Innovations for the transport process are also planned. Finally, taking into consideration that many of the biggest grape producing countries in the world, are not part of the EU, the potential for use is much higher. Some of these countries are still considered as developing (in Asia and South America) so the use of this source can replace the primitive use of biomass (most often wood) for cooking and heating purposes. With this the pollution and health effects will be largely reduced, and the efficiency improved. Beside the energy potential, there are also other aspects that should be considered in the evaluation of the fuel, such as: transport ability, market price, convenience for storage, workmanship and combustion, as some of the most important. Prunings harvested from the vineyard have low bulk density. With moisture content 35-38 %, bulk density is around 180 kg/m3. When they are chopped in small pieces with length 2-3 cm, the bulk density increases to 300 kg/m3 [4]. If they are used for the production of bio-pellets or briquettes, the transport process for this type of fuel, is already proven on the market. It’s easy to distribute them to petrol stations and bigger malls. At the moment, their market price is higher than currently available fossil fuels. However, the growing interest in renewable and sustainable energy, supported with subsidies and innovation projects, should help that this type of energy is market competitive. Utilizing this fuel source, will help in the struggle against unemployment. The process of generating energy from this source contains several phases, so new work places will be created. The growing interest in this area, will also help engineers and researchers to make scientific contribution. In some of the undergoing evaluation projects for this source, some combustion tests are made. Although the results vary, depending on the installation used, in general they satisfy the law limits regarding emissions from combustion.
3.1. Evaluation of the process of generating energy from vineyard prunings The process of generating energy from vineyard waste is similar to the other types of agricultural waste (wheat waste for example). The process starts with the pruning activity done on the vineyards and fruit trees. This activity can be done manually (workers) and with use of machines. Depending on the region, land area, available technology and other factors, one of this two options is selected. After the pruning process, the prunings are in the vineyard area, and are harvested with the use of machinery. Most often used machine for this purpose is tractor with attached baller or comminuter. There are ballers for gathering balles in square and round shape, and the comminuter can be with a big bag or built-in dumping bin. The prunings are either gathered in the form of round or square balle, or chopped into small short pieces by the comminuter. Depending on the machine used for harvesting, the transport from the field to the storage location can be done by the tractor, if there is a built-in dumping bin, or by trucks. On figure 1 is shown the sequence of operations in the process. All this operations are energy consuming (mostly fuel for the used machinery), and their efficiency influences the overall effectiveness of the process greatly. Optimization of logistics in this sector is crucial. Improvements in the harvesting process are the most important. There is big room for improvement in this process, because until now there are not any specialised tools and machines produced for this purpose. The available tools now are just adjusted from some other sector (wood industry – choppers, straw gathering – ballers). With the increase of use of this source, the demand for specialised machinery will increase. Until now, because of the importance of the agricultural sector in the country in Italy, most of the mechanisation for this process is produced there. During the transportation process, the prunings are transported from the field to the storage location. The storage of the biomass is one of the most important aspects. When biomass is harvested from the field it contains high percentage of moisture, so some period in open air storage is required for it to dry, and increase its calorific value. In figure 2 the change of moisture content throughout the year is shown. After the storage, depending on the final use there are two options for energy production from it. It can be used in the process of manufacturing pellets and briquettes, or transported directly to plant for combustion for generating heat or steam for production of electricity. Depending on the gathered quantity, and the market requirement it can be used for district heating, industrial use, household heating and generating electricity. Most of the tests run until now, are run on small and medium sized boilers, for producing hot water and steam.
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Fig. 1. Process of generating energy from vineyard prunings [2]
Fig. 2. Humidity of vineyard prunings in open air storage throughout the year [5]
4. Energy potential from vineyard prunings in Republic of Macedonia According to official data from organisations, in Macedonia there are 26000 ha of land area planted with grapes [3]. Taking the minimal amount for calculation (4t/ha), we obtain minimal quantity of 104,000 tons of vineyards prunings. For a small country like Macedonia, this is significant number. This is agricultural waste with high calorific value, and good combustion characteristics, so it is convenient for use for the purpose of generating heat. Utilizing its whole potential can have significant impact in the energy market in the country. It can largely increase the primary energy use from biomass. With developing and implementing an efficient way of utilizing prunings, the heat demand in the country can be satisfied long term.
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Taking into consideration that Macedonia have small percent of installed and used renewable energy, this source of energy can be beneficial in several ways. Using the waste from vineyards can be a replacement for the most common biomass curently used – wood for household heating. Wood is used for household heating in old and ineffective stoves, and improvements in this sector are necessary. The last few years the price of wood increases, and the heating in general gets more expensive. There are not many offers currently on the market for heating, so this source have big potential. Also, the wine producing sector have some problems in the last years, mainly with the price of grape, that is declining, and the production costs rise. Utilizing the waste will mean more revenue for vineyard and winery owners. In the town of Negotino (around 15000 inhabitants), there are around 4500 ha planted with grapes. There are several wineries that work in this region. Up by now, there are not some significant projects for utilizing the waste from vineyards and wineries. Taking into consideration that there are problems with the price of grapes several years ago, and there is stagnation in this sector, utilizing the waste will help the farmers to make additional income. The energy used in the industry in this region is generated from fossil fuels. Utilizing the prunings and other waste that can be obtained from grapes growing and it’s processing, the percent of renewable energy used in the region, would significantly increase. This would be beneficial to the whole region, increasing both the economy and the environmental protection.
5. Conclusions The demand for new ecological fuels is higher than ever before. Having an energy source that is both renewable and ecological, is a guarantee that the heat demands will be satisfied long term. Vineyard prunings have these two qualities that makes them very interesting for further research. There are many undergoing projects (EuroPruning, reports on national level for biomass source. that give satisfactory results in the key areas for the fuel. High calorific source of energy, available worldwide in high quantities, gives huge potential for long term use of this fuel. This source would be perfect solution in many developing countries in southern Asia and South America, which have big land areas planted with grapes. With the huge potential, and the growing interest in this sector, research work will intensify in the coming period. Innovations are expected in the used mechanisation, transport, storage, and combustion process.
References [1] https://www.iea.org/topics/renewables/subtopics/bioenergy/ [2] http://www.europruning.eu/ [3] Славе Арменски, Обновливи – одржливи извори на енергија, Македонија, 2012 (English title Renewable and sustainable energy sources, author Dr. Slave Armenski) [4] Производство на брикети и пелети – Д-р Славе Арменски, Д-р Доне Ташевски, Д-р Љубица Каракашева (English title – Production of pellets and briquettes, Authors Dr. Slave Armenski, Dr. Done Tashevski, Dr. Ljubica Karakasheva) [5] Recovery of vineyards pruning residues in an agro-energetic chain – Cavalaglio G., Cotana S. – University of Perugia – Biomass Research Centre
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The perspectives of thermal utilization of municipal solid waste (MSW) in the city of Gliwice. Paweł Rodak Silesian University of Technology
Abstract The purpose of this article is to discuss the idea of the thermal utilization of municipal solid waste (MSW) in the city of Gliwice, in the already existing district heating plant PEC Gliwice. The article focuses on the analysis of greenhouse gases emission related to the thermal utilization of waste instead of stockpiling the MSW on the landfill sites. Currently the only technique used for municipal waste management in this city is the stockpiling. In such case the thermal potential of the waste being disposed is lost and also waste stockpiling poses different threats to the environment. These threats are related to the unwanted emission of biogas to the atmosphere, the possibility of underground water pollution and the nuisances of the landfill site such as smell and the landscape degradation. The thermal utilization of municipal waste is common technique used worldwide. If the incineration of waste is conducted in a proper way, it is both environmentally friendly, concerning the emission of greenhouse gases, and beneficial, because the chemical energy of waste is used to provide heat and/or electric energy for the community.
1. Introduction Municipal Solid Waste (MSW) is waste generated in households, public institutions, commercial institutions, businesses. It includes primarily used paper, cans, bottles, plastic, food leftovers, garden wastes and several other items [1]. The city of Gliwice is 4th the largest city in Silesian region (based on the number of citizens) with the population of 181 thousands of people [2]. It produces around 71 thousand tonnes of MSW annually, which is equal to 394 kg of MSW per 1 citizen [3]. About 53 % of all these wastes are disposed on the stockpiles outside the city of Gliwice and about 47% on one city’s stockpile occupying the area of 51,5 ha in a depression after clay pit [2]. There is no incineration plant for municipal waste. Graph shows the average composition of MSW from the city of Gliwice.
Fig. 1. The example composition of MSW from Gliwice [3].
Not surprisingly, some of the MSW produced in the city is separated and recycled, however this process is still far from perfection, when it comes to Gliwice. Overall about 30% of MSW is recycled, which consists of about 9% of MSW separated before being reclaimed, and the rest being separated from the mixed MSW [3]. If the MSW was to be incinerated, it shouldn’t contain certain items like used batteries for instance. Generally, waste
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incineration should be a part of overall waste management strategy, but not on the expense of waste reduction or recycling. MSW which would be potentially incinerated cannot be fully controlled, so it is the responsibility of the public to separate the waste in a proper way and the city government to provide the education and infrastructure allowing the mindful waste management in the city.
2. Thermal utilization of MSW Thermal utilization (or incineration) of MSW is the oxidation of the combustible materials contained in the MSW. As the result of incineration, flue-gases are formed, which contain the chemical energy of the MSW in the form of heat, which can be simply used for district heating or for the production of electric energy. The objective of waste incineration is to reduce their volume and hazard, whilst capturing and destroying potentially harmful substances that are, or maybe released during incineration. The process requires high temperature in order to make sure, that the MSW is combusted completely. In fully oxidative incineration similarly like in coal combustion, the main components of flue gas are water vapour, nitrogen, carbon dioxide and oxygen. Depending on the specific composition of the MSW, there are also smaller amounts of: CO, HCl, HF, HBr, HI, NOx, SO 2, VOCs, PCDD/F, PCBs and heavy metal compounds. Depending on the combustion temperatures, volatile heavy metals and inorganic compounds can be completely or partially evaporated. These substances are transferred into the flue gas and fly-ash within the flue gas. In MSW incinerators bottom ash is about 10% by volume or 30% by weight of input MSW. The proportions vary for different MSW and incineration process design [5]. As it has been mentioned before, there is no incineration plant in Gliwice yet. However, one idea is to accommodate the already existing WR-25 stoker boilers in district heating plant of Gliwice (PEC Gliwice) for waste incineration. The boilers are fuelled with hard coal. If some of MSW produced by the city was incinerated in these boilers, it would lead to:
Smaller dependency on fossil fuels, in this case, on hard coal. Hard coal used in PEC Gliwice is very easily accessible, due to the fact that PEC Gliwice is nearby the Sośnica coal mine (KWK Sośnica) and connected by the conveyor. Nevertheless, the prices of coal are not stable and also there are some political issues in mining industry, which does not make the future of this fuel predictable. Lower expenses on the waste landfill sites maintenance. Currently, the city spends 5.65% of its budget on the Municipal Economy and Environmental Protection, which is equal to 76.693 million PLN (~18.045 million EUR / 1 EUR=4.25 PLN) [2]. Lower greenhouse gases emission from Gliwice. This is related to two different effects. First of all, the more MSW is incinerated instead of stockpiling, the less biogas would be produced from the landfill site. This is positive, as the biogas emitted from the unit of MSW has much greater Global Warming Potential (GWP) than the CO2 (GWP CO2 = 1) produced as the result of incineration of MSW unit. Biogas emitted from the MSW is mainly CH4, which has GWP of 56 (over 20 years) [6]. Apart from that, significant part of MSW originates from plants, which means, that it is basically biomass, which is threated as renewable energy source. Therefore, if instead of hard coal, the biomass is combusted, the emission of CO2 decreases, as the carbon dioxide originating from biomass has been absorbed by the plants from the atmosphere in the process of photosynthesis.
MSW is much different fuel comparing to hard coal. It is not as consistent, when it comes to its composition. The waste collection and pre-treatment systems applied can have great impact on the type and nature of MSW provided to the incineration. Provision for the separate collection of various fractions of household waste can have great influence over the average composition of MSW for incineration. For instance, the separate collection of batteries can largely reduce mercury inputs to the process. As it has been mentioned before, waste incinerators have limited control over the precise content of the received waste. This results in the need for the installation to be flexible both on the combustion stage and the flue-gas cleaning stages.
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For incineration there can be distinguished two types of fuel coming from MSW: I. II.
Mixed MSW (Non pre-treated) [5]. RDF – Refuse Derived Fuel, which is produced as the result of shredding and dehydrating technology, after the removal of non-combustible materials such as glass and metals from the MSW. It consists mostly of paper, plastic and cloth, which have relatively high calorific value [5].
RDF can be produced through a number of different processes [13]:
Separation at source Sorting or mechanical separation Size reduction (shredding, chipping and milling) Separation and screening Blending Drying or pelletising Packaging Storage
Usually, waste material is freed of all recyclable materials, such as metals, the inert (non-combustible) fraction such as glass and fraction like food or garden wastes containing high moisture and ash content. These wet organic materials can then undergo further treatment: compositing, anaerobic digestion or can be used as soil conditioner for landfill restoration [13]. Contribution of the major components RDF may be as in the following graph [8].
Fig. 2. Composition of major components of RDF [8]. In can be noticed, that RDF composition is too high extent of biogenic origin. As it has been mentioned before, the incineration of bio fraction of fuel is considered as zero emission concerning the emission of CO2. For RDF about 50% of element C within this fuel originates from plants [10].
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The table shows the comparison of three fuels: mixed MSW, RDF and hard coal. Tab. 1. The comparison of mixed MSW, RDF and hard coal. Parameter
mixed MSW [5]
RDF [7, 8]
Hard coal [7]
Calorific value (upper), MJ/kg
7-15
13-22
21-32
Moisture, %
15-40
11-34
3-10
Ash, %
20-35
10-22
5-10
Carbon, % d.s.
18-40
35-50
75-85
Hydrogen, % d.s.
1-5
-
-
Nitrogen, % d.s.
0.2-1.5
-
-
Oxygen, % d.s.
15-22
-
-
Suphur, % d.s.
0.1-0.5
-
-
Fluorine, % d.s.
0.1-0.035
-
-
Chlorine, % d.s.
0.1-1
-
-
Bromine, % d.s.
-
-
-
Iodine, % d.s.
-
-
-
100-2000
-
-
1-15
-
-
Copper, mg/kg d.s.
200-700
-
-
Zink, mg/kg d.s.
400-1400
-
-
Mercury, mg/kg d.s.
1-5
-
-
Thallium, mg/kg d.s.
<0.1
-
-
Manganese, mg/kg d.s.
250
-
-
Vanadium, mg/kg d.s.
4-11
-
-
Nickel, mg/kg d.s.
30-50
-
-
Cobalt, mg/kg d.s.
3-10
-
-
Arsenic, mg/kg d.s.
2-5
-
-
Chrome, mg/kg d.s.
40-200
-
-
Selenium, mg/kg d.s.
0.21-15
-
-
PCB, mg/kg d.s.
0.2-0.4
-
-
PCDD/PCDF ng I-TE/kg
50-250
-
-
Lead, mg/kg d.s. Cadmium, mg/kg d.s.
If we compare mixed MSW and RDF with hard coal, it is possible to see, that waste fuel has much higher moisture and ash content. Also, the calorific value is significantly smaller, so more waste fuel is required in order to obtain the same amount of energy as from hard coal. Another issue related to waste incineration in already existing installation such as WR-25 stoker boiler from PEC Gliwice is the handling of the fuel fed to the boiler. In PEC Gliwice the fuel is transported to the boiler from the storage site by conveyor and then to the container, from which the fuel can fall gravitationally onto the moving grate. There is a question how to transport the MSW from the storage site, to the container. In waste incineration plants this is often accomplished by the cranes, which is impossible to be done in PEC Gliwice. In order to make it possible to transport the MSW by the conveyor, the MSW would have to be shredded and dried, which means, that the best fuel for this purpose would be RDF. Incineration of mixed MSW, without any pre-treatment could appear to be impossible with the use of infrastructure provided by PEC Gliwice. Therefore in this article, the use of RDF derived from city’s MSW will be considered.
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Last, but not least, co-combustion of waste with coal, faces strict limitation from the legislation in Poland. It is possible to co-combust at most just 1% of waste in fuel mixture. In order to make it possible to co-combust larger amounts of waste it is required that, the legislation changed. Such limitation could be reasonable from the perspective of the incineration of non-pretreated MSW. When it comes to RDF it is very good fuel, according to its calorific value, moisture and ash content. It does not contain significant amount of hazardous materials, which can be found in mixed MSW. Therefore greater amount of waste in the form of RDF could be co-incinerated with coal. The good example is Finland, where co-combustion of waste fuels is widespread among district heating plants of small size (~20 MWth) relying on grate combustion technology, similar as in PEC Gliwice. The amount of RDF co-combusted is usually 10-30% of the fuel mass flow to the boiler [13]. Nevertheless, when considering co-combustion of waste fuel, several threats need to be considered [14]:
Higher heat load and wear of industrial installations Higher chlorine corrosion; more frequent maintenance is required Worse emission factors of flue gas comparing to combustion of conventional fuels
3. The incineration of RDF in PEC Gliwice WR-25 boilers, as the method of reducing greenhouse gases emission WR-25 boiler – stoker boiler designed for district heating plants, with the heating capacity of 29.2 MW (25 Gcal, on output) equipped in mechanical moving grate. Its nominal efficiency is equal to 78%. As it has been mentioned before, incineration of MSW leads to the reduction of greenhouse gases emission by avoiding the emission of biogas from stockpiled MSW and as the result of the combustion of biomass within MSW instead of fossil fuel. For the purpose of this analysis 4 scenarios have been chosen: 1) 2) 3) 4)
WR-25 boilers in PEC Gliwice are fed with fuel: 0% RDF, 100% COAL (by weight) WR-25 boilers in PEC Gliwice are fed with fuel: 5% RDF, 95% COAL (by weight) WR-25 boilers in PEC Gliwice are fed with fuel: 10% RDF, 90% COAL (by weight) WR-25 boilers in PEC Gliwice are fed with fuel: 20% RDF, 80% COAL (by weight)
The assumptions:
There are four WR-25 boilers, they operate with full heating capacity of 29.2 MW for the time equal to 6 months (180 days) annually. The combustion process is complete, all element C within the fuel goes to CO2. The boilers work with their nominal efficiency of 78%. The biomass content in RDF is 50%, which means that 50% of CO2 produced as a result of the RDF combustion comes from biomass [10]. RDF has calorific value of 17.5 MJ/kg and 40% of element C (as fired), the hard coal has calorific value of 26 MJ/kg and 80 % of element C (as fired). The biogas emitted from the stockpiled MSW is equal to 250 m3n/tonneMSW (116 kgCH4/tonneMSW + 172 kgCO2/tonneMSW) assuming that the biogas composition is: 65% CH4, 35% CO2 [11]. GWPCH4 = 56, meaning that one tonne of emitted CH4 is equal to 56 tonnes of emitted CO2, when it comes to global warming potential.
The analysed parameters:
The emission of greenhouse gases represented as the CO2 equivalent (CO2eq) and as the number of average car CO2 emission (ncar) per year: 1 average car = 4.7 tonneCO2/year [12] The amount of each fuel required.
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The amount of waste utilized (by weight and by percent of MSW produced in the city).
4. Results The graph showing the annual CO2 emission from boilers for different scenarios.
Fig. 3. CO2 emission from boilers The graph showing the annual CO2eq emission from incinerated MSW if stockpiled. The result was calculated as follows: tonnes CO2eq = tonnes CO2 from biogas emitted by incinerated MSW if stockpiled + tonnes CH4 * GWP CH4 from biogas emitted by incinerated MSW if stockpiled
Fig. 4. Avoided CO2eq emission
The graph showing the annual emissions of CO2 equivalent (CO2eq) for different scenarios. It combines previous two results. The CO2eq was calculated as follows: tonnes CO2eq = (tonnes CO2 emission from boilers)/year – (tonnes avoided emission of CO2 and CH4 from stockpiled MSW)/year = (tonnes CO2 emission from boilers)/year - (tonnes CO2 from biogas emitted by
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incinerated MSW if stockpiled + tonnes CH4 * GWP CH4 from biogas emitted by incinerated MSW if stockpiled)/year
Fig. 5. Combined CO2eq emission The table showing the annual CO2 equivalent (CO2eq) for different scenarios represented as the number of average car CO2 emission (ncar) per year. Tab. 2. CO2eq represented as number of average cars CO2 emission
ncar
Scenario 1
Scenario 2
Scenario 3
Scenario 4
11 892
6 412
766
-11 054
The table showing the amounts of each fuel required for different scenarios in tonnes. Tab. 3. The amount of each fuel required for different scenarios COAL [tonnes]
RDF [tonnes]
COAL + RDF [tonnes]
Scenario 1
69 864
0
69 864
Scenario 2
66 371
3 551
69 922
Scenario 3
62 878
7 223
70 100
Scenario 4
55 891
14 950
70 842
The table showing the amount of MSW utilized by incineration in different scenarios by weight and by percent of the total MSW produced in the city of Gliwice annually.
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Tab. 4. The amount of MSW utilized by incineration for different scenarios MSW utilized [tonnes]
total MSW produced [tonnes]
MSW utilized [%]
Scenario 1
0
71 000
0%
Scenario 2
3 551
71 000
5%
Scenario 3
7 223
71 000
10%
Scenario 4
14 950
71 000
21%
5. Conclusions The idea of MSW incineration in the form of RDF in PEC Gliwice heating plant is promising, but also very challenging. The challenges to overcome are related to the need for proper infrastructure needed for the transformation of mixed non-pretreated MSW into RDF, which could be then provided for the WR-25 boilers in the heating plant. Another challenges are connected with the accommodation of flue-gas treatment process to the new fuel, which has different composition and behaviour comparing to hard coal. What is more, it is required, that the most hazardous components of MSW, such as used batteries, would not make their way into the boilers. It would be the most favourable, if any hazardous materials or materials, which can to be recycled would be separated on the level of individual people or organizations, rather than separated from mixed MSW.
When it comes to the scenarios analysed in this article, it is possible to see, that waste incineration leads to:
significant decrease in greenhouse gases emission; for scenario 4, the CO2eq emission value was negative, which indicates, that the avoided greenhouse gases emission of biogas from stockpiled MSW was much greater, that the greenhouse gases emission related to the incineration of both hard coal and RDF combined; to put it into perspective, in scenario 4 the avoided emission was equal to the removal of 11 054 average cars from the roads, when it comes to the emission of CO2 the amount of MSW, which could be incinerated in PEC Gliwice is the significant part of the whole MSW produced by the city of Gliwice, ranging from 5% for scenario 1 to 21% for scenario 4, although the share of RDF in the fuel mix provided for the boilers was not very high (the original fuel (hard coal) remains the dominant in the mix) lower expenditures on hard coal fuel, which means, that the price changes of hard coal have lower impact on the cost of heat production in the city, because part of the energy would come from MSW
References [1] Environmental Protection Agency (EPA) [2015-11-15], http://tinyurl.com/petb8ao [2] RAPORT O STIANIE MIASTA GLIWICE – dane na koniec roku 2014 [2015-11-14], https://gliwice.eu/sites/default/files/imce/uzupe_nienie_raportu_za_rok_2014.pdf [3] Plan gospodarki odpadami dla województwa śląskiego 2014 [2015-11-14], http://bip.slaskie.pl/dokumenty/2012/08/29/1346244652.pdf [4] PLAN GOSPODARKI ODPADAMI DLA MIASTA GLIWICE [2015-11-14], http://tinyurl.com/nl5jxky [5] Reference Document on the Best Available Techniques for Waste Incineration, August 2006 [2015-1115], http://eippcb.jrc.ec.europa.eu/reference/BREF/wi_bref_0806.pdf
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[6] United Nations Framework Convention on Climate Change [2015-11-15], http://unfccc.int/ghg_data/items/3825.php [7] National Energy Technology Laboratory, U.S. Department of Energy [2015-11-15], http://www.netl.doe.gov/File%20Library/Research/Coal/energy%20systems/gasification/gasifipedia/pro duction-refuse-derived-fuel-chapter12.pdf [8] Scientific References COSMOS [2015-11-15], http://www.srcosmos.gr/srcosmos/showpub.aspx?aa=11180 [9] PEC Gliwice [2015-11-15], http://www.pec.gliwice.pl/news/4/18/Informacja-publiczna.html [10] Laboratory of Solid Waste Disposal Engineering [2015-11-15], http://wastegr2er.eng.hokudai.ac.jp/home/IWWG-ARB/presentation/PDF/s4/4-5.pdf [11] Innowacyjny projekt ponadnarodowy PI-PWP-Model Regionalnego Centrum Kompetencji Technologicznych Green-Job [2015-11-15], http://green.radom.zdz.kielce.pl/epodrecznik/ucz/mod5/p44.htm [12] Environmental Protection Agency (EPA) [2015-11-29], http://www3.epa.gov/otaq/climate/documents/420f14040a.pdf [13] European Commission – Directorate General Environment, Refuse Derived Fuel, Current Practice and Perspectives (B4-3040/2000/306517/MAR/E3) [2015-12-10], http://ec.europa.eu/environment/waste/studies/pdf/rdf.pdf [14] Przemysłowe współspalanie odpadów [2015-12-10], http://ekotechnologie.org/5-pwo.html
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Energy Storage Technologies Viktor Kadek
Silesian University of Technology
Abstract In today’s world, there is a stronger and bigger need for using renewable sources of energy. Unfortunately, most of these sources are more or less unstable and intermittent. As we cannot predict output of solar, wind or other green sources, the only way how to use them as a reliable part of grid power is to use energy storage technologies. These technologies allow us to store extra energy produced during peak-off hours and use it during higher demand hours. The purpose of this article is to give a brief overview about currently most used energy storage technologies around the world.
1. Introduction “A next-generation smart grid without energy storage is like a computer without a hard drive: severely limited.” - Katie Fehrenbacher, GigaOm
On any regular day, energy companies have to plan how much energy to generate and distribute onto the electrical grid. They try to predict what customers will do based on historical trends and data, primarily by referencing usage on the same day of the previous year. Then they modify those estimates relative to the current weather forecast for the following day using complex formulas that create demand profiles for a given city or region. This is a very challenging issue. The job of the grid is to deliver electricity to every customer at exact voltage and frequency. With these predictive models being the norm for operations, it sets utilities up to create more or less energy than is needed on any given day - a potential recipe for problems. Some energy production technologies can be turned on and off rather quickly - for example, disconnecting a solar panel from the grid. But other power production methods, like fossil fuel or nuclear power plants, take a long time to turn on and off, at a considerable cost. Making sure the right amount of energy is being distributed to end-users is critical to our grid infrastructure - too much energy can wreak havoc on electronics, too little results in brownouts and disruptions to service. As long as there has been an electrical grid, companies have sought ways to safely and efficiently store energy so that it can be consumed on demand, output can be precisely controlled, and the exact frequency of the energy distributed can be tightly regulated. Today, a wide array of technologies has been developed and deployed to ensure that the grid can meet our everyday energy needs - from scalable banks of advanced chemistry batteries and magnetic flywheels, to pumped hydro-power and compressed air storage. Perhaps most importantly, energy storage is also resource neutral, and allows us to use electricity from any power source more efficiently. Whether the energy produced comes from a coal power plant or a field of wind turbines, energy storage technologies capture that energy to be used on demand when it is needed most. Our investment in energy storage evolves with our grid, creating long-term benefit and reliability for years to come. These diverse technologies have been providing these capabilities to the grid for decades, and as we continue to modernize and create a more intelligent grid infrastructure together with wider and wider usage of renewable sources, energy storage will play an increasingly vital role in delivering the energies of tomorrow [1].
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2. Energy Storage Technologies Since the invention of electricity, we have discovered various effective methods to store that energy for use on demand. Over the last century, the energy storage industry has continued to evolve and adapt to changing energy requirements and advances in technology. Energy storage systems provide a wide array of technological approaches to managing our power supply in order to create a more resilient energy infrastructure and bring cost savings to utilities and consumers. To help understand the diverse approaches currently being deployed around the world, we have divided them into six main categories [1]:
Solid State Batteries - a range of electrochemical storage solutions, including advanced chemistry batteries and capacitors, Flow Batteries - batteries where the energy is stored directly in the electrolyte solution for longer cycle life, and quick response times, Flywheels - mechanical devices that use rotational energy to deliver instantaneous electricity, Compressed Air Energy Storage - utilizing compressed air to create a potent energy reserve, Thermal - capturing heat and cold to create energy on demand, Pumped Hydro-Power - creating large-scale reservoirs of energy with water.
3. Solid State Batteries Alessandro Volta is credited with the invention of the first battery in 1800, and along with it the entire field of electrochemistry. On its most basic level, a battery is a device consisting of one or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. Electrolytes allow ions to move between the electrodes and terminals, which allows current to flow out of the battery to perform work [1]. Solid-state batteries hold the promise of providing energy storage with high specific energy and high power density, yet with far less safety and temperature stability issues relative to those associated with conventional liquid or gel-based lithium-ion batteries. Solid-state batteries are envisioned to be useful for a vast range of energy storage applications, from powering automobiles, stationary storage and load-levelling of renewably generated energy, and powering the wide range of electronics that have become so pervasive in our lives [2]. Advances in technology and materials have greatly increased the reliability and output of modern battery systems, and economies of scale have dramatically reduced the associated cost. Continued innovation has created new technologies like electrochemical capacitors that can be charged and discharged simultaneously and instantly, and provide an almost unlimited operational lifespan [1].
3.1. Electrochemical Capacitors Electrochemical capacitors (ECs) – sometimes referred to as “electric double-layer” capacitors (also called supercapacitors or ultra-capacitors because of their extraordinarily high capacitance density). The phrase “double-layer” refers to their physically storing electrical charge at a surface-electrolyte interface of high-surface-area carbon electrodes. There are two types of ECs, symmetric and asymmetric, with different properties suitable for different applications. ECs first appeared on the market in 1978 as farad-sized devices to provide computer memory backup power. Markets and applications for electrochemical capacitors are growing rapidly and applications related to electricity grid will be part of that growth. [2] [3] A simple EC can be constructed by inserting two conducting rods in a beaker of salt water. During charging, charge separation occurs at each liquid-solid interface and potential builds up between the rods. Solvated ions in the electrolyte are rapidly attracted to the solid surface by an equal but opposite charge in the solid. These two parallel regions of charge are the source of the term “double layer.” This process in effect creates two capacitors, connected in series by the electrolyte that stay charged after the circuit is opened. Because the surface area of activated carbon
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electrode material can be thousands of square meters per gram, a 5000-farad EC (a million times the capacitance offered by typical electrostatic or electrolytic capacitors) can be small enough to be handheld.
Fig. 9. Scheme of double layer capacitors [1]. This very high capacitance comes at a cost: The operating voltage of an EC cannot exceed the potential at which the electrolyte undergoes chemical reactions (typically 1 to 3 V per cell). For high-voltage applications, EC cells, like batteries, can be series-connected. One of the most important advantages of batteries over ECs is that for a given volume, they can store 3 to 30 times more charge. However, ECs can deliver hundreds to many thousands of times the power of a similar-sized battery. In addition, the highly reversible electrostatic charge storage in ECs does not produce the changes in volume that usually accompany the redox reactions of the active masses in batteries [3]. There are two types of ECs: those with symmetric designs, where both positive and negative electrodes are made of the same high-surface-area carbon and asymmetric designs with different materials for the two electrodes, one high-surface-area carbon and the other a higher capacity battery-like electrode. Symmetric ECs have specific energy values up to ~6 Wh/kg and higher power performance than asymmetric capacitors where designs having specific energy values approach 20 Wh/kg. Because of their high power, long cycle life, good reliability, and other characteristics, the market and applications for ECs have been steadily increasing. There are dozens of manufacturers and more are entering the market because of market growth. Applications range from portable electronics and medical devices to heavy hybrid and other transportation uses. ECs are better suited than batteries for applications requiring high cycle life and charge or discharge times of 1 second or less. The largest barrier to market growth has been the lack of understanding of the technology and the applications for which it is best suited. Aqueous electrolyte asymmetric EC technology offers opportunities to achieve exceptionally low-cost bulk energy storage. There are difference requirements for energy storage in different electricity grid-related applications from voltage support and load following to integration of wind generation and time-shifting. Symmetric ECs have response times on the order of 1 second and are well-suited for short duration high-power applications related to both grid regulation and frequency regulation. Asymmetric ECs are better suited for grid energy storage applications that have long duration, for instance, charge-at-night/use-during-the-day storage (i.e., bulk energy storage). Some asymmetric EC products have been optimized for ~5 hour charge with ~5 hour discharge. Advantages of ECs in these applications include long cycle life, good efficiency, low life-cycle costs, and adequate energy density.
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3.2. Lithium Ion Batteries (LI-ION) In 1991 Sony and Asahi Kasei released the first commercial lithium-ion battery. The first batteries were used for consumer products and now building on the success of these lithium-ion (Li-ion) batteries, many companies are developing larger-format cells for use in energy-storage applications. Many also expect there to be significant synergies with the emergence of electric vehicles (EVs) powered by Li-ion batteries. The flexibility of Li-ion technology in EV applications, from small high-power batteries for power buffering in hybrids, to medium-power batteries providing both electric-only range and power buffering in plug-in hybrids, to high-energy batteries in electric-only vehicles, has similar value in energy storage. Li-ion batteries have been deployed in a wide range of energy-storage applications, ranging from energy-type batteries of a few kilowatt-hours in residential systems with rooftop photovoltaic arrays to multi-megawatt containerized batteries for the provision of grid ancillary services [1]. These batteries are mostly used for rather local storing of solar or wind energy at time of night or increased demand. Although the Li-Ion batteries were not fundamentally designed for grid storage, using new materials can make them enough safe and economic efficient for using as energy storage for grid. Some energy companies (e.g. Tesla) have already announced a new lithium battery for households.
Fig. 10 Power density vs. energy density of various energy storage systems [5].
Powerwall by Tesla The Powerwall is a rechargeable lithium-ion battery product manufactured by Tesla Motors for home use. It stores electricity for domestic consumption, load shifting, and backup power. The Powerwall has two different models, each using different generic cell chemistries. One model is optimized for daily cycling, such as for an off-grid situation; the other for being a backup battery. Tesla uses proprietary technology for packaging and cooling the cells in packs with liquid coolant. Elon Musk, the chairman, CEO and product architect of the Tesla company, promised not to start patent infringement lawsuits against anyone who, in good faith, used Tesla's technology for Powerwalls as he had promised with Tesla cars. The daily cycle 7 kWh battery uses nickel-manganese-cobalt chemistry and can be cycled 5000 times. The 10 kWh battery uses a nickelcobalt-aluminium cathode, like the Tesla Model S, is for weekly or emergency use and has a cycle life of 1000– 1500 cycles. It includes a DC to DC converter to sit between a home's existing solar panels, and the home's existing DC to AC inverter. The Powerwall was originally announced at the April 30, 2015 product launch with power
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output of 2 kW steady and 3.3 kW peak, but Musk said at the June 2015 Tesla shareholders meeting that this would be more than doubled to 5 kW steady with 7 kW peak, with no increase in price. He also announced that Powerwall deliveries would be prioritized to partners who minimize the cost to the end user, with a Powerwall installation price of US$500 [4].
Fig. 11. Possible usage of household grid with Tesla Powerwall [6]
4. Flow batteries A flow battery is a type of rechargeable battery where recharge ability is provided by two chemical components dissolved in liquids contained within the system and most commonly separated by a membrane. This technology is akin to both a fuel cell and a battery - where liquid energy sources are tapped to create electricity and are able to be recharged within the same system. One of the biggest advantages of flow batteries is that they can be almost instantly recharged by replacing the electrolyte liquid, while simultaneously recovering the spent material for re-energization. Different classes of flow cells (batteries) have been developed, including redox, hybrid and membraneless. The fundamental difference between conventional batteries and flow cells is that energy is stored as the electrode material in conventional batteries but as the electrolyte in flow cells. Redox flow batteries (RFB) represent one class of electrochemical energy storage devices. The name “redox” refers to chemical reduction and oxidation reactions employed in the RFB to store energy in liquid electrolyte solutions which flow through a battery of electrochemical cells during charge and discharge. During discharge, an electron is released via an oxidation reaction from a high chemical potential state on the negative or anode side of the battery. The electron moves through an external circuit to do useful work. Finally, the electron is accepted via a reduction reaction at a lower chemical potential state on the positive or cathode side of the battery. The direction of the current and the chemical reactions are reversed during charging. The total difference in chemical potential between the chemical states of the active elements on the two sides of the battery determines the electromotive force (emf or voltage) generated in each cell of the battery. The voltage developed by the RFB is specific to the chemical species involved in the reactions and the number of cells that are connected in series. The current developed by the battery is determined by the number of atoms or molecules of the active chemical species that are reacted within the cells as a function of time. The power delivered by the RFB
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is the product of the total current and total voltage developed in the electrochemical cells. The amount of energy stored in the RFB is determined by the total amount of active chemical species available in the volume of electrolyte solution present in the system. Redox flow batteries offer an economical, low vulnerability means to store electrical energy at grid scale. Redox flow batteries also offer greater flexibility to independently tailor power rating and energy rating for a given application than other electrochemical means for storing electrical energy. Redox flow batteries are suitable for energy storage applications with power ratings from 10’s of kW to 10’s of MW and storage durations of 2 to 10 hours.
Fig. 12. A schematic of an upgraded vanadium redox battery [7].
5. Flywheels A flywheel is a rotating mechanical device that is used to store rotational energy that can be called up instantaneously. At the most basic level, a flywheel contains a spinning mass in its center that is driven by a motor - and when energy is needed, the spinning force drives a device similar to a turbine to produce electricity, slowing the rate of rotation. A flywheel is recharged by using the motor to increase its rotational speed once again. Flywheel technology has many beneficial properties that enable us to improve our current electric grid. A flywheel is able to capture energy from intermittent energy sources over time, and deliver a continuous supply of uninterrupted power to the grid. Flywheels also are able to respond to grid signals instantly, delivering frequency regulation and electricity quality improvements. Flywheels are traditionally made of steel and rotate on conventional bearings; these are generally limited to a revolution rate of a few thousand RPM. Modern flywheels are made of carbon fiber materials, stored in vacuums to reduce drag, and employ magnetic bearings, enabling them to revolve at speeds up to 60,000 RPM [1].
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5.1. FESS Flywheel energy storage systems (FESS) use electric energy input which is stored in the form of kinetic energy. Kinetic energy can be described as “energy of motion,” in this case the motion of a spinning mass, called a rotor. The rotor spins in a nearly frictionless enclosure. When short-term backup power is required because utility power fluctuates or is lost, the inertia allows the rotor to continue spinning and the resulting kinetic energy is converted to electricity. Most modern high-speed flywheel energy storage systems consist of a massive rotating cylinder (a rim attached to a shaft) that is supported on a stator by magnetically levitated bearings. To maintain efficiency, the flywheel system is operated in a vacuum to reduce drag. The flywheel is connected to a motor-generator that interacts with the utility grid through advanced power electronics. Some of the key advantages of flywheel energy storage are low maintenance, long life (some flywheels are capable of well over 100,000 full depth of discharge cycles and the newest configurations are capable of even more than that, greater than 175,000 full depth of discharge cycles), and negligible environmental impact. Flywheels can bridge the gap between short-term ridethrough power and long-term energy storage with excellent cyclic and load following characteristics. Typically, users of high-speed flywheels must choose between two types of rims: solid steel or carbon composite. The choice of rim material will determine the system cost, weight, size, and performance. Composite rims are both lighter and stronger than steel, which means that they can achieve much higher rotational speeds. The amount of energy that can be stored in a flywheel is a function of the square of the RPM making higher rotational speeds desirable. Currently, high-power flywheels are used in many aerospace and UPS applications. Today 2 kW/6 kWh systems are being used in telecommunications applications. For utility-scale storage a ‘flywheel farm’ approach can be used to store megawatts of electricity for applications needing minutes of discharge duration.
Fig. 13. A scheme of FESS [1] FESS are especially well-suited to several applications including electric service power quality and reliability, ride-through while gen-sets start-up for longer term backup, area regulation, fast area regulation and frequency response. FESS may also be valuable as a subsystem in hybrid vehicles that stop and start frequently as a component of track-side or on-board regenerative braking systems [1]. Conversely, flywheels with magnetic bearings and high vacuum can maintain 97% mechanical efficiency, and 85% round trip efficiency.
5.2. Flywheels as a grid energy storage Flywheels energy storage system has a wide usage in transportation (automotive, railway, raily electrification), in uninterruptible power supplies (costs of fully installed FESS is $330 per kilowatt and the maintenance is 50% cheaper in comparison with batteries), in laboratories, in aircraft launcher systems, spacecraft energy storage, in wind turbines for absorbing fluctuations in the power output and last but not least, they can be used as a grid power storage. There are several flywheel energy storage systems for grid power storage built in USA, the biggest are 20 MW plant in Stephentown and 20 MW plant in Hazle, both constructed an operated by Beacon Power [8].
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Fig. 14. FESS plant in Hazle, NY [8]
5.3. Comparison to Batteries Flywheels are not as adversely affected by temperature changes, can operate at a much wider temperature range, and are not subject to many of the common failures of chemical rechargeable batteries. They are also less potentially damaging to the environment, being largely made of inert or benign materials. Another advantage of flywheels is that by a simple measurement of the rotation speed it is possible to know the exact amount of energy stored. Unlike most batteries which only operate for a finite period (for example roughly 36 months in the case of lithium ion polymer batteries), a flywheel potentially has an indefinite working lifespan. Flywheels built as part of James Watt steam engines have been continuously working for more than two hundred years. Working examples of ancient flywheels used mainly in milling and pottery can be found in many locations in Africa, Asia, and Europe. Most modern batteries are typically a sealed device that needs minimal maintenance throughout its service life. Magnetic bearing flywheels in a vacuum enclosure, such as the NASA model depicted above, do not need any bearing maintenance and are therefore superior to batteries both in terms of total lifetime and energy storage capacity. Flywheel systems with mechanical bearings will have a limited lifespan due to wear. The arrangement of batteries can be designed to a wide variety of configurations, whereas a flywheel at a minimum must occupy a square surface area. Where space is a constraint for the application of energy storage (e.g. under trains in tunnels) the flywheel may not be a valid application.
6. Compressed Air Energy Storage (CAES) Compressed air energy storage (CAES) is a way to store energy generated at one time for use at another time. At utility scale, energy generated during periods of low energy demand (off-peak) can be released to meet higher demand (peak load) periods. Since the 1870's, CAES systems have been deployed to provide effective, on-demand energy for cities and industries. While many smaller applications exist, the first utility-scale CAES system was put in place in the 1970's with over 290 MW nameplate capacity. CAES offers the potential for small-scale, on-site energy storage solutions as well as larger installations that can provide immense energy reserves for the grid. CAES plants are largely equivalent to pumped-hydro power plants in terms of their applications, output and storage capacity. But, instead of pumping water from a lower to an upper pond during periods of excess power, in a CAES plant, ambient air is compressed and stored under pressure in an underground cavern. When electricity is required, the pressurized air is heated and expanded in an expansion turbine driving a generator for power production [1].
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The special thing about compressed air storage is that the air heats up strongly when being compressed from atmospheric pressure to a storage pressure of approx. 70 bar. Standard multistage air compressors use inter and after coolers to reduce discharge temperatures to 149/177°C and cavern injection air temperature reduced to 43/49°C. The heat of compression therefore is extracted during the compression process or removed by an intermediate cooler. The loss of this heat energy then has be compensated for during the expansion turbine power generation phase by heating the high pressure air in combustors using natural gas fuel, or alternatively using the heat of a combustion gas turbine exhaust in a recuperator to heat the incoming air before the expansion cycle. Alternatively, the heat of compression can be thermally stored before entering the cavern and used for adiabatic expansion extracting heat from the thermal storage system [1].
Figure 15: Basic CAES scheme [9]
6.1. Diabatic CAES Method The only two existing CAES plants in Huntorf, Germany, and in McIntosh, Alabama, USA, as well as all the new plants being planned in the foreseeable future are based on the diabatic method. In principle, these plants are essentially just conventional gas turbines, but where the compression of the combustion air is separated from and independent to the actual gas turbine process. This gives rise to the two main benefits of this method. Because the compression stage normally uses up about 2/3 of the turbine capacity, the CAES turbine – unhindered by the compression work – can generate 3 times the output for the same natural gas input. This reduces the specific gas consumption and slashes the associated CO2emissions by around 40 to 60%, depending on whether the waste heat is used to warm up the air in a recuperator. The power-to-power efficiency is approx. 42% without, and 55% with waste heat utilization. Instead of compressing the air with valuable gas, lower cost excess energy can be used during off peak periods or excess wind energy that cannot meet the daily demand cycle. The aforementioned plants both use single-shaft machines where the compressor-motor/ generator-gas turbine are both located on the same shaft and are coupled via a gear box. In current planning of CAES plants, the motorcompressor unit and the turbine-generator unit will be mechanically decoupled. This makes it possible to expand the plant modularly with respect to the permissible input power and the output power. Using conventional gas turbine exhaust heat energy for the purposes of heating the high pressure air before expansion in an air bottoming cycle allows for CAES plants of variable sizes based on cavern storage volume and pressure.
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6.2. Adiabatic Method A much higher efficiency of up to 70% can be achieved if the heat of compression is recovered and used to reheat the compressed air during turbine operations because there is no longer any need to burn extra natural gas to warm up the decompressed air. An international consortium headed by the German energy company RWE is currently working on the development of the necessary components and the heat storage. The pilot plant is scheduled to start operations in 2018. Thermal oil and molten salt storage is being investigated in the US [1].
6.3. Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) Advanced-adiabatic compressed air energy storage (AA-CAES) is an evolution of traditional CAES, designed to deliver higher efficiencies via a zero-carbon process. Operation is similar to traditional CAES in that energy is stored by compressing air with turbo machinery and storing in an underground cavern. The difference lies in the treatment of the heat of compression. Since it is not possible to process and store compressed air at the very high temperatures reached during compression, the heat must be removed prior to storage. Traditional CAES essentially dumps the heat into the atmosphere, therefore requiring a second injection of heat prior to re-expansion. AA-CAES instead aims to remove the heat and store it separately, then re-inject the heat at the expansion stage. This has potential to substantially increase the round-trip efficiency of the process. One possible means is to heat-exchange the compressed air with oil, which can be stored in an insulated aboveground vat. If the compression process takes place in several stages (e.g., using multiple compressors) with heatexchange occurring between each stage, the oil could be kept to a safe temperature for storage (e.g., below 600K). A variation of this scheme is to modify the design of wind turbines so as to compress air directly using a mechanical link. In theory, skipping the conversion to and from electricity should improve efficiency and lower costs. A further variation is to store the compressed air in inflatable underwater ‘bags’. This could provide an alternative to the requirement for a storage cavern and would allow air to be stored and retrieved at constant pressure, which could improve operating characteristics. A number of AA-CAES schemes have been proposed, but none have yet made it past the design stage; however, this may be about to change. In 2010, an international consortium headed by German electrical utility RWE announced plans to construct a new AA-CAES plant in Germany. They aim to achieve efficiencies in excess of 70% - the demonstration plant is due to go on stream in the middle of the decade [1].
Fig. 16. ADELE - an AA-CAES with thermal storage project by RWE [10]
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6.4. Isothermal CAES Isothermal compressed air energy storage (CAES) is an emerging technology which attempts to overcome some of the limitations of traditional (diabatic or adiabatic) CAES. Traditional CAES uses turbo machinery to compress air to around 70 bar before storage. In the absence of intercooling the air would heat up to around 900K, making it impossible (or prohibitively expensive) to process and store the gas. Instead the air undergoes successive stages of compression and heat-exchange to achieve a lower final temperature close to ambient. In Advanced-Adiabatic CAES the heat of compression is stored separately and fed back into the compressed gas upon expansion, thereby removing the need to reheat with natural gas. Controlling the pressure-volume (P-V) curve during compression and expansion is the key to efficient CAES. Roughly speaking, the closer the P-V curve resembles an isotherm, the less energy is wasted in the process. Rather than employing numerous stages to compress, cool, heat and expand the air, isothermal CAES technologies attempt to achieve true isothermal compression and expansion in site, yielding improved round-trip efficiency and lower capital costs. In principle it also negates the need to store the heat of compression by some secondary means (e.g., oil). Isothermal CAES is technologically challenging since it requires heat to be removed continuously from the air during the compression cycle and added continuously during expansion to maintain an isothermal process. Heat transfer occurs at a rate proportional to the temperature gradient multiplied by surface area of contact; therefore, to transfer heat at a high rate with a minimal temperature difference one requires a very large surface area of contact. Although there are currently no commercial Isothermal CAES implementations, several possible solutions have been proposed based upon reciprocating machinery. One method is to spray fine droplets of water inside the piston during compression. The high surface area of the water droplets coupled with the high heat capacity of water relative to air means that the temperature stays approximately constant within the piston – the water is removed and either discarded or stored and the cycle repeats. A similar process occurs during expansion. The companies developing Isothermal CAES quote a potential round-trip efficiency of 70-80%. The technology compresses and expands gas near-isothermally over a wide pressure range, namely from atmospheric pressure to a maximum of about 170 bar. This large operating pressure range, along with the isothermal gas expansion (allowing for recovery of heat not achieved with adiabatic expansion), achieves a ~7x reduction in storage cost as compared to classical CAES in vessels [1].
6.5. Storage Options Independent of the selected method, very large storages are required because of the low storage density. Preferable locations are in artificially constructed salt caverns in deep salt formations. Salt caverns are characterised by several positive properties: high flexibility, no pressure losses within the storage, no reaction with the oxygen in the air and the salt host rock. If no suitable salt formations are present, it is also possible to use natural aquifers – however, tests have to be carried out first to determine whether the oxygen reacts with the rock and with any microorganisms in the aquifer rock formation, which could lead to oxygen depletion or the blockage of the pore spaces in the reservoir. Depleted natural gas fields are also being investigated for compressed air storage; in addition to the depletion and blockage issues mentioned above, the mixing of residual hydrocarbons with compressed air will have to be considered. CAES power plants are a realistic alternative to pumped-hydro power plants. The capital expenditure and operational expenditure for the already operating diabatic plants are competitive [1].
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7. Thermal Energy Storage How much energy is stored in a coffee thermos? How about in a tray of ice cubes? Thermal energy storage technologies allow us to temporarily reserve energy produced in the form of heat or cold for use at a different time. Take for example modern solar thermal power plants, which produce all of their energy when the sun is shining during the day. The excess energy produced during peak sunlight is often stored in these facilities - in the form of molten salt or other materials - and can be used into the evening to generate steam to drive a turbine to produce electricity. Alternatively, a facility can use 'off-peak' electricity rates which are lower at night to produce ice, which can be incorporated into a building's cooling system to lower demand for energy during the day. A well designed thermos or cooler can storage energy effectively throughout the day, in the same way thermal energy storage is an effective resource at capturing and storing energy on a temporary basis to be used at a later time.
7.1. Pumped Heat Electrical Storage (PHES) In Pumped Heat Electrical Storage (PHES), electricity is used to drive a storage engine connected to two large thermal stores. To store electricity, the electrical energy drives a heat pump, which pumps heat from the “cold store” to the “hot store” (similar to the operation of a refrigerator). To recover the energy, the heat pump is reversed to become a heat engine. The engine takes heat from the hot store, delivers waste heat to the cold store, and produces mechanical work. When recovering electricity, the heat engine drives a generator. PHES requires the following elements: two low cost (usually steel) tanks filled with mineral particulate (gravelsized particles of crushed rock) and a means of efficiently compressing and expanding gas. A closed circuit filled with the working gas connects the two stores, the compressor and the expander. A monatomic gas such as argon is ideal as the working gas as it heat/cools much more than air for the same pressure increase/drop - this in turn significantly reduces the storage cost. The process proceeds as follows: the argon, at ambient pressure and temperature (top left limb of the circuit on the diagram), enters the compressor (diagram shows a rotating compressor symbol - all equipment is in fact reciprocating). The compressor is driven by a motor/ generator (top) using the electricity that needs to be stored (yellow arrows at top). The argon is compressed to 12 bar, +500°C. It enters the top of the hot storage vessel and flows slowly (typically less than 0.3m/s) through the particulate, heating the particulate and cooling the gas. As the particulate heats up, a hot front moves down the tank (at approximately 1m/hour). At the bottom of the tank, the argon exits, still at nearly 12 bar but now at ambient temperature. It then enters the expander (bottom) and is expanded back to ambient pressure, cooling to minus -160°C. The argon then enters the bottom of the cold vessel and flows slowly up, cooling the particulate and itself being warmed. It leaves the top of the tank back at ambient pressure and temperature. To recover the power (i.e. discharge), the gas flow (and all arrows on the diagram) is simply reversed. Argon at ambient temperature and pressure enters the cold tank and flows slowly down through it, warming the particulate and itself becoming cold. It leaves the bottom of the tank at -160°C and enters the compressor. It is compressed to 12 bar, heating back up to ambient temperature. It then enters the bottom of the hot tank. It flows up, cooling the particulate and itself being warmed to +500°C. The hot pressurized gas then enters the expander where it gives up its energy producing work, which drives the motor/generator. The expected AC to AC round trip efficiency is 75-80%. PHES can address markets that require response times in the region of minutes upwards. The system uses gravel as the storage medium, so it offers a very low cost storage solution. There are no potential supply constraints on any of the materials used in this system. Plant size is expected to be in the range of 2-5 MW per unit. Grouping of units can provide GW-sized installations. This covers all markets currently addressed by pumped hydro and a number of others that are suitable for local distribution, for example, voltage support. Technology is in development stage and commercial systems are due in 2014 [11].
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Fig. 17. PHES scheme [11]
7.2. Hydrogen Energy Storage Electricity can be converted into hydrogen by electrolysis. The hydrogen can be then stored and eventually reelectrified. The round trip efficiency today is as low as 30 to 40% but could increase up to 50% if more efficient technologies are developed. Despite this low efficiency the interest in hydrogen energy storage is growing due to the much higher storage capacity compared to batteries (small scale) or pumped hydro and CAES (large scale).
7.2.1. Hydrogen Production Alkaline electrolysis is a mature technology for large systems, whereas PEM (Proton Exchange Membrane) electrolyzers are more flexible and can be used for small decentralized solutions. The conversion efficiency for both technologies is about 65%~70% (lower heating value). High temperature electrolyzers are currently under development and could represent a very efficient alternative to PEM and alkaline systems, with efficiencies up to 90%.
7.2.2. Hydrogen Storage Small amounts of hydrogen (up to a few MWh) can be stored in pressurized vessels at 100~300 bar or liquefied at 20.3K. Alternatively, solid metal hydrides or nanotubes can store hydrogen with a very high density. Very large amounts of hydrogen can be stored in man-made underground salt caverns of up to 500,000 m3 at 200 bar, corresponding to a storage capacity of 167 GWh hydrogen (100 GWh electricity). In this way, longer periods of flaws or of excess wind / PV energy production can be leveled. Even balancing seasonal variations might be possible.
7.2.3. Hydrogen Re-Electrification Hydrogen can be re-electrified in fuel cells with efficiencies up to 50%, or alternatively burned in combined cycle gas power plants (efficiencies as high as 60%).
7.2.4. Other Uses of Hydrogen Because of the limited round trip efficiency, direct uses of green hydrogen are under development, e.g. as feedstock for the chemical and the petrochemical industry, as fuel for future fuel cell cars or blending with natural gas of up to 5 to 15% in natural gas pipelines. Electrolytic hydrogen can also be used for the production of synthetic liquid fuels from biomass, thereby increasing significantly the efficiency of the biomass utilization.
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7.2.5. Deployment Status Several European and American companies offer integrated hydrogen solutions for the supply of electric power to small isolated sites or islands. Demonstration projects have been performed since 2000 in Europe and the USA and commercial products are available. Large scale hydrogen storage in salt cavern is standard technology. To date there are two full size hydrogen caverns in operation in Texas, USA, a third one is under construction, three older caverns are operating at Teesside, UK.
Fig. 18. Scheme of Electricity - Hydrogen cycle [12]
7.3. Liquid Air Energy Storage (LAES) Liquid Air Energy Storage (LAES) uses electricity to cool air until it liquefies, stores the liquid air in a tank, brings the liquid air back to a gaseous state (by exposure to ambient air or with waste heat from an industrial process) and uses that gas to turn a turbine and generate electricity. LAES systems use off the shelf components with long lifetimes (30 years +), resulting in low technology risk. Liquid Air Energy Storage (LAES) is sometimes referred to as Cryogenic Energy Storage (CES). The word “cryogenic” refers to the production of very low temperatures. LAES/CES is a long duration, large scale energy storage technology that can be located at the point of demand. The working fluid is liquefied air or liquid nitrogen (~78% of air). LAES systems share performance characteristics with pumped hydro and can harness industrial low-grade waste heat/waste cold from co-located processes. Size extends from around 5MW to hundreds of MWs and, with capacity and energy being de-coupled, the systems are very well suited to long duration applications. Although novel at a system level, the LAES process uses components and sub-systems that are mature technologies available from major OEMs. The technology draws heavily on established processes from the power generation and industrial gas sectors, with known costs, performance and life cycles all ensuring a low technology risk. LAES involves three core processes:
Stage 1: Charging the system
The charging system is an air liquefier, which uses electrical energy to draw air from the surrounding environment, clean it and then cool the air to sub zero temperatures until the air liquefies. 700 litres of ambient air become 1 litre of liquid air.
Stage 2. Energy Store
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The liquid air is stored in an insulated tank at low pressure, which functions as the energy store. This equipment is already globally deployed for bulk storage of liquid nitrogen, oxygen and LNG. The tanks used within industry have the potential to hold GWh of stored energy.
Stage 3. Power Recovery
When power is required, liquid air is drawn from the tank(s) and pumped to high pressure. The air is evaporated and superheated to ambient temperature. This produces a high-pressure gas, which is then used to drive a turbine. LAES plants can provide large-scale, long-duration energy storage, with hundreds of MWs output. LAES systems can use industrial waste heat/cold from applications such as thermal generation plants, steel mills and LNG terminals to improve system efficiency. LAES uses existing and mature components with proven long-life times (30 years +), performance, operational costs [1].
8. Pumped Hydro-Power Gravity is a powerful, inescapable force that surrounds us at all times - and it also underpins one of the most established energy storage technologies, pumped hydro-power. Currently the most common type of energy storage is pumped hydroelectric facilities, and we have employed this utility-scale gravity storage technology for the better part of the last century in the United States and around the world. A hydroelectric dam relies on water cascading down through a turbine to create electricity to be used on the grid. In order to store energy for use at a later time, there are a number of different projects that use pumps to elevate water into a retained pool behind a dam - creating an on-demand energy source that can be unleashed rapidly. When more energy is needed on the grid, that pool is opened up to run through turbines and produce electricity. But the material that is raised to a higher elevation doesn't have to be water. Companies are currently creating gravitational systems that move gravel up the side of a hill and use the same underpinning principle - when energy is needed, the gravel is released and the weight drives a mechanical system that drives a turbine and generates electricity. Because of the immense scale achieved through these applications, this is the most common type of grid-level energy storage based on megawatts installed today.
8.1. Pumped Hydroelectric Storage Pumped hydroelectric storage facilities store energy in the form of water in an upper reservoir, pumped from another reservoir at a lower elevation. During periods of high electricity demand, power is generated by releasing the stored water through turbines in the same manner as a conventional hydropower station. During periods of low demand (usually nights or weekends when electricity is also lower cost), the upper reservoir is recharged by using lower-cost electricity from the grid to pump the water back to the upper reservoir. Reversible pump-turbine/motorgenerator assemblies can act as both pumps and turbines. Pumped storage stations are unlike traditional hydroelectric stations in that they are a net consumer of electricity, due to hydraulic and electrical losses incurred in the cycle of pumping from lower to upper reservoirs. However, these plants are typically highly efficient (roundtrip efficiencies reaching greater than 80%) and can prove very beneficial in terms of balancing load within the overall power system. Pumped-storage facilities can be very economical due to peak and off-peak price differentials and their potential to provide critical ancillary grid services. Pumped storage hydroelectric projects have been providing energy storage capacity and transmission grid ancillary benefits in the United States and Europe since the 1920s. Today, the pumped-storage projects operating in Europe provide more than 44 GW. In 2009, the world’s pumped hydroelectric storage generating capacity was over 100 GW. Pumped storage hydropower can provide energy-balancing, stability, storage capacity, and ancillary grid services such as network frequency control and reserves. This is due to the ability of pumped storage plants, like other hydroelectric plants, to respond to potentially large electrical load changes within seconds. Pumped storage historically has been used to balance load on a system, enabling large nuclear or thermal generating sources to operate at peak efficiencies. A pumped storage project would typically be designed to have 6 to 20 hours of
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hydraulic reservoir storage for operation at. By increasing plant capacity in terms of size and number of units, hydroelectric pumped storage generation can be concentrated and shaped to match periods of highest demand, when it has the greatest value. Pumped storage projects also provide ancillary benefits such as firming capacity and reserves reactive power, black start capability, and spinning reserve. In the generating mode, the turbinegenerators can respond very quickly to frequency deviations just as conventional hydro generators can, thus adding to the overall balancing and stability of the grid. In both turbine and pump modes, generator-motor excitation can be varied to contribute to reactive power load and stabilize voltage. When neither generating nor pumping, the machines can be also operated in synchronous condenser mode, or can be operated to provide spinning reserve, providing the ability to quickly pick up load or balance excess generation. Grid-scale pumped storage can provide this type of load-balancing benefit for time spans ranging from seconds to hours with the digitally controlled turbine governors and large water reservoirs for bulk energy storage. The existing 38 pumped hydroelectric facilities can store just over 2 percent of the country’s electrical generating capacity. That share is small compared with Europe’s (nearly 5%) and Japan’s (about 10%). But the industry plans to build reservoirs close to existing power plants. Enough projects are being considered to double capacity [1].
Fig. 19. Scheme of PHS [13]
9. Conclusions To use intermittent renewable energy sources a proper way to store produced energy is essential. Energy storage is providing essential services along the whole energy chain: balancing demand and supply, managing transmission and distribution grids, promoting demand side management, contributing to competitive and secure electricity supply. There are many technologies to store energy, some of them are widely used (Pumped Hydro Storage), some of them are still in a development phase. Technologies with biggest capacities (Compressed Air Energy Storage, Pumped Hydro Storage) are used for energy management (provides capacity supply and reduction of transmission and distribution losses) and have operating range from hours to days. Unfortunately, these technologies are highly dependent on geographical attributes of the country. For providing bridging power (emergency reserves and dispatching of load) mainly high energy density batteries are used with operating range from few minutes to one or two hours. In battery field, there is still lot of space for innovation and development, the advantage is they are not dependent on geographical attributes, however, they can contain toxic materials and can be also very temperature dependent. Third group of energy storage technologies are technologies which provides power quality improvements and their main purpose is frequency and voltage regulations with operating range from seconds to few minutes. These are for example flywheels, ultra-capacitors, batteries.
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There are still many technologies being developed and we should focus on these technologies more and more, since they are essential for turning renewables into stable and reliable part of a modern electricity grid. The diversity of possible energy storage solutions enables a high stability of future energy systems and is the key for a clean, stable and decarbonised energy.
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