Supercritical CO2 Power Cycle Symposium May 24-25, 2011 Boulder Colorado

“Gas Turbine Engine Exhaust Waste Heat Recovery Navy Shipboard Module Development” Di Bella, Francis A. Concepts ETI, Inc., d.b.a. Concepts NREC 217 Billings Farm Road White River Junction, VT 05001-9486 [email protected]

Abstract Concepts NREC (Wilder, VT, and Woburn, MA) is collaborating with the Maine Maritime Academy (Castine, ME) and their principal consultant, Thermoelectric Power Systems LLC, to address a need as expressed in a recent Small Business Research Innovation (SBIR) request for proposal offered by the Navy for an increase in the power output from the prime mover propulsion systems aboard naval vessels. A power recovery system must be able to improve the power output of the prime mover by 20% while also considering the effects that transient power demand from the prime mover have on the waste heat flow rate and temperature, which may consequently affect the fatigue integrity of the heat exchangers and stability of the turbomachinery subsystems. The complexity of using steam heat recovery systems, as well as the lower expected cycle efficiencies, temperature limitations, toxicity, material compatibilities, and/or costs of organic fluids in Rankine cycle power systems, precludes their consideration as a solution to power improvement for this application in naval vessels. The power improvement system must also comply with the space constraints inherent with onboard marine vessel power plants, as well as the interest to be economical with respect to the cost of the power recovery system compared to the fuel that can be saved per naval exercise. Concepts NREC (CN) will perform a feasibility analysis on a Brayton cycle-based, supercritical carbon dioxide (SCO2) system to recover waste heat from a Rolls-Royce MT-30 gas turbine used in marine applications. The analysis will also consider the integration of one or more thermoelectric generator (TEG) systems within the S-CO2 cycle in order to further increase the power recovery. The use of an auxiliary combustion system to provide thermal stability within the power recovery system during the transient power demands, required of the vessel’s prime mover propulsion system, will also be considered. The use of TEG systems within the heat engine bottoming cycle takes advantage of the temperature differences between the cycle components that are a consequence of the second law of thermodynamics. The TEG systems use this temperature difference to generate electric power directly and without “moving parts” and effectively increase the cycle efficiency to almost the limit of the Carnot Efficiency for the SCO2 heat engine cycle. CN’s preliminary feasibility analysis has indicated a power improvement over the MT-30 gas turbine engine of from 20%, for the simple S-CO2 waste heat recovery system, to as high as 24% when the TEG systems are included. The supercritical CO2 cycle has been promoted in several Department of Energy (DOE) project studies as an efficient prime mover system using high temperature heat sources as may be available, for example, from nuclear energy as the heat source. A waste heat recovery application of the CO2 supercritical cycle that will be prepared by CN integrates the TEG work done by Maine Maritime Academy (MMA) and will culminate in the sizing of the major components, concluding with an engineering cost analysis to determine the Simple Payback for the system and ultimate cost per kWe ($/kWe).

1. Project Background: State-of-the-Art Supercritical CO2 Systems for Power Generation There has been renewed interest in the recovery and conversion to electric power of waste heat from fuel-fired prime movers. Waste heat recovery system efficiencies have improved due to the development of new materials, advanced controls, and improved CFD analysis to produce more advanced and efficient turbomachinery, as well as direct energy conversion devices. This renewed interest is also due to the recent hike and instability of fossil fuel prices, which has also increased the general interest to improve the efficiency of prime movers. The conversion of wasted heat from the prime movers to generate electric or mechanical power has long been considered a viable means of improving the energy efficiency of a prime mover. The collaboration of CN and the MMA brings together CN’s experiences with waste heat recovery power systems and advanced turbomachinery design with MMA’s recent

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Supercritical CO2 Power Cycle Symposium May 24-25, 2011 Boulder Colorado research and laboratory testing of thermoelectric power generation devices for heat recovery from gas turbine exhaust1. Historical considerations of the value of a supercritical Brayton cycle-based power generation system can be found in detailed technical reports from the 1960s through the 1980s. Seminal among these were studies by Feher (1967) [1] and Kines (1984) [2]. The technical results indicated Brayton supercritical systems using CO2 as the working fluid had many thermodynamic advantages over other working fluids and were able to generate higher efficiencies than the more conventional Rankine cycle-based systems by enabling operation at the higher temperatures available from nuclear reactors. A typical state point diagram for the S-CO2 cycle on a P-h diagram is shown in Figure 1. The principal difficulty at the time was material compatibility with the high operating inlet turbine temperatures and pressures. However, the conclusions were explicit in their declaration that a supercritical CO2 cycle can be technically viable and could achieve higher thermal efficiencies compared to the more conventional Rankine cycle steam cycles of that era. These conclusions are particularly relevant to the present proposal, in that the proposed use of supercritical CO2 for waste heat recovery from engine exhaust gases that are less than 900°F (480°C) will eliminate the concerns of material failure due to high-temperature operation.

Figure 1. A typical supercritical CO2 heat engine process using the Brayton Cycle The previous S-CO2 symposium on the development and application of supercritical CO2 (S-CO2) power systems was hosted by Rensselaer Polytechnic Institute (Troy, NY) in April of 2009. During this symposium, projects under study by private subcontractors, as well as several National Labs (e.g., Knolls Atomic Power Laboratory [KAPL] and Bettis Laboratory with funding by the Department of Energy’s Office of Nuclear Energy and the DOE’s Office of Fossil Energy’s Advanced Turbine Systems programs; NASA; and the Naval Reactors Program) were highlighted. The objective of these funded programs is the advancement of applying a viable supercritical CO2 cycle in nuclear and solar applications. The presentations described the effectiveness of supercritical CO2 cycles for high-temperature (not waste heat) power generation, particularly as they may be used with Light Water Reactors (LWR) and Breeder Water Reactors (BWR). These systems identify cycle efficiencies between 40% and 50%, but with operating turbine inlet temperatures of 1000°F and operating pressures of 3500 psia as being common, as shown in Figure 1. Advances in the analysis and design of turbomachinery, materials compatibility with hightemperature CO2 heat exchanger development, and controls technology were cited as reducing the risks associated with material fatigue and the operation and maintenance of multistage turbines and compressors. The reasons for the almost universal choice of carbon dioxide as the fluid2 continue to be based on: 1.

The moderate magnitude of its critical point (1080 psia, 88°F) which enables it to operate completely above the critical point with typical coolant temperatures

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Maine Maritime Academy continues to develop and test TEG devices integrated with exhaust gas waste heat, heat exchangers in a program supported by the Office of Naval Research and the American Bureau of Shipping. 2 Many analyses have been conducted to confirm CO2 as the best fluid for supercritical operation compared to ammonia, helium, sulfur dioxide, xenon, hexafluorobenzene, perfluorobenzene, and even water.

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Supercritical CO2 Power Cycle Symposium May 24-25, 2011 Boulder Colorado 2. 3. 4. 5. 6.

Its chemical and thermal stability at high operating temperatures; much higher than the 600°F turbine inlet temperatures that CN and MMA are proposing here for the combined TEG-S CO2 waste heat recovery system The accuracy and sufficient knowledge of the thermodynamic properties at or near the critical point, compared to other less common industrial fluids Its ability to be highly regenerative and require less compressive power, which contributes to its relatively high cycle efficiency Non-toxicity of the fluid and its abundance (to the point where it is subject to sequestration). Its low cost

The innovative suggestion for the Navy SBIR project is the study of the feasibility of using one or more thermoelectric systems integrated within the S-CO2 cycle where the temperature differences are causing significant second law entropy losses. Figure 2 identifies four viable integration sites along with the preliminary analysis estimates of the power that can be generated from the temperature differences at these points in the cycle. The power improvement for the MT-30 is increased to 24% if all of these TEG’s are utilized. A typical Rankine cycle system using an organic-based refrigerant (i.e., R245fa or R113), working with the same heat source temperature, could achieve only approximately 15 to 17% efficiency. As illustrated in Figure 2, a simple Brayton cycle-based, supercritical CO2 system can achieve the necessary 20% improvement in the power output from the MT-30 gas turbine. However, the second law of efficiency of this cycle can be further improved by utilizing thermoelectric generator elements to recover energy, using only the temperature difference between various components of the Brayton cycle, as well as the temperature difference between the exhaust gas that exits the primary exhaust gas heat exchanger and the ambient. For example, a TEG # 1 is placed as part of the regenerator, TEG #2 is placed in the hottest end of the super heater heat exchanger, TEG #3 is placed at the stack discharge of the waste heat, heat exchanger, and TEG #4 is used as the CO2 Cooler. In order to do this, it was assumed that the heat exchanger could be mechanically designed to have the TEG devices attached to the heat transfer surfaces in a manner that allows the devices to operate individually at different source and sink temperatures that continue to incrementally step down, even as the sensible temperature of the heat source and heat sink are changing. The amount of temperature change between the hot (or cold) heat source (or heat sink) and the temperature of the TEG hot (or cold) surface is dependent upon the heat transfer coefficients between the fluid and the TEG surface. As illustrated in Figure 2, an additional power improvement of 5% of the MT-30 power output, or approximately 1520 kW, is recoverable according to CN’s preliminary feasibility analysis of TEG elements integrated within the S-CO2 system. The additional power from the supercritical CO2 and from one or more of the TEG systems options will affect the net weight per kWe and net volume per kWe, characteristics that must be determined from the analysis performed in Phase I. As shown in Figure 2, the system also features the use of an auxiliary-fired combustor system that can increase the heat recovery and/or control the exhaust temperature to ensure that auxiliary power is always available to stabilize the turbomachinery performance even as the prime mover’s power output is fluctuating. The controllable limits of the auxiliary combustion system must be evaluated when integrated with the prime mover and S-CO2 waste heat recovery as a coupled power delivery system. The inclusion of an auxiliary combustion system is also the first step in planning the Phase II developmental testing of the combined TEG S-CO2 system. The auxiliary combustion system can be used in Phase II in lieu of the availability of a prime mover providing the exhaust waste heat. CN’s efforts in Phase I of the project will focus on the thermodynamic modeling of the supercritical CO2 cycle and on conducting a feasibility analysis of an advanced design for a TEG-heat exchanger that integrates thermal electric generator modules with sufficient surface area to enable the necessary heat transfer required for one or more of the TEG systems found by CN’s analysis to benefit the S-CO2 cycle. CN’s effort will also include the conceptualized design of an S-CO2 compressor, turbine, and generator using a single drive shaft that enables a compact, modular package, similar to that shown in Figure 3. This arrangement is intended to also reduce bearings, seals, and gearbox drives, reducing the operation and maintenance costs as well as facilitating installation in the confined spaces of the engine room. The inclusion of an auxiliary combustion system adds heat energy input to the cycle in the event that the prime mover is either unavailable or at a part-load demand.

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Supercritical CO2 Power Cycle Symposium May 24-25, 2011 Boulder Colorado

Figure 2. One of the goals of the project is to be able to design a compressor-turbine-generator module that can use a single, common drive shaft and be packaged to reduce installation space and cost. The use of the auxiliary combustion system also enables the supercritical heat exchanger to maintain relatively constant pressure and material temperatures, and thus minimizes the thermal or mechanical fatigue of the heat exchanger. The project will also consider the use of bio-derived fuels for the auxiliary combustion system to further increase its economic viability. The feasibility analysis for the turbine-generator-compressor and the heat exchangers will be of sufficient design to enable the cost per kWe for the TEG-Heat Exchanger to be estimated so that the cost may be used in CN’s economic analysis of the value of the combined power recovery system to the vessel’s energy costs. A description of the state-of-the-art TEG technology and how it was thermodynamically modeled with the S-CO2 cycle by CN to obtain the results (illustrated in Figure 1) is provided in the next section.

1. State-of-the-Art of Thermoelectric Generator (TEG) Systems

Figure 3. Seebeck Effect creating voltage potential

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STTR Solicitation NAVY N103-229: Concepts ETI, Inc., d.b.a. Concepts NREC (Wilder, VT) “Gas Turbine Engine Exhaust Waste Heat Recovery Shipboard Module Development”

 

0.26

Cp, exhaust =

BTU/LBm/R

Mass Flow Rate, Lbm/sec= 250

Rolls-Royce MT-30 Gas Turbine

Water Cooled TEG

1.2E+08 BTU/Hr. = kWt 574

Prime Mover Waste Heat

CASE 1

TEG # 3

Texhaust,in (F)= 860

35999

TEG Performance Param

335

TEG #1

250 Texhaust, out (F)

50

4 Aux-Fuel Supply

F, Pinch Point

TEG #2-Super Heater

AUX.-COMBUSTOR SYSTEM OPTION

5

Kw,in/m^2= 10 Thot,K= 484 Tcold,K= 418 % DT,hot surface= 10.0% % DT,cold surface= 10.0% Z*, [units: 1/K]= 0.025 Z*Tavg 1.5 Thermal Eff.= 3.0% TEG Power (kWe)= 29

TEG #1 Combined with Regen. HX TEG Hot Surface

TEG #3

10 10 722 429 499 301 10.0% 10.0% 10.0% 10.0% 0.025 0.025 2.3 2.5 4.00% 7.8% 683 451 TOTAL kWe=

3 7

CO2 COMPRESSOR-TURBINE-GENERATOR

0.8

Regen. Effec.=

QTEG/QTotal= 0.25

BASELINE S-CO2 SYSTEM without TEG SY 5717 kWe at 16% Base Cycle Eff. Carnot Eff.= 49% 2nd Law Eff.= TOTAL COMBINED TEG plus CO2 SUPERC 7237 kWe at 20% Combined Cycle Carnot Eff.= 46% 2nd Law Eff.= a 26.6% Improve. in S-CO

2

TEG Cold Surface 1 0.96 =Gen. Eff.

6 1 Electric Power Gen. Twater, out = 75 F Identifies Integrated TEG on S-CO2 TEG #4 CO2 Cooler Water Cooled, CO2 Cooler with TEG - Cooler Option

CO2 Compressor - Turbine -Gen. Package Comp. Eff.= 0.85 0.85 Turbine Thermal EFF. Pres. Ratio= 2.75 0.96 Turbine-Comp. Mech. Eff. Comp. Pwr.[kWe] 5253 Tur.= 11456 kWm Net MT-30 Power Improvement WITHOUT TEG= Net MT-30 Power Improvement WITH TEG= FLUID: Carbon Dioxide MOLE. WT. 44.01 1 2

19% 24%

CYCLE STATE POINT PROPERTIES {NOTE: Only "Boxed" Cells in RED text are Inputs}

P [psia] 1300 3575 T [F] 100 166 F Twater, in = 60 Water Flowrate= 161693 GPM h [Btu/Lbm] 137.64 149.65 Dt,pinch,cooler= 25 F s [Btu/Lbm/R] 0.331 0.33 k= Cp/Cv 1.39 1.35 MxCp)exhaust/MCO2= 0.210 MASS FLOWRATE with TEG= 309.00 LBm/sec. FLOWRATE wo/TEG= 315.88 LBm/sec.

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4

5

6

7

Ideal Pressure ratio

3575 285 209.8 0.42 1.33

3575 418 260.1 0.48 1.31

3575 600 317.85 0.544 1.24

1300 425 282.70

1300 218 222

wo/Regeneration =

1.62

1.42

COMBINED TEG-CO2 SUPER CRITICAL BRAYTON CYCLE WITH TEG-REGENERATION

Figure 4. Conceptualized design of an S-CO2 compressor, turbine, and generator

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TEG #2

Supercritical CO2 Power Cycle Symposium May 24-25, 2011 Boulder Colorado . Thermoelectric generators utilize a phenomenon known as the thermoelectric effect to generate an electric potential, and hence an electric current, across an external resistance load. The thermoelectric effect has been traditionally named after Thomas Johann Seebeck, who in the early 1800s, along with several contemporaries including Jean Peltier and Hans Oersted, observed various effects of temperature and magnetism on the junctions of dissimilar metals. The Seebeck Effect is the phenomenon wherein a voltage potential is created when the junction of two dissimilar materials is exposed to two different hot and cold temperatures as shown in Figure 4. Although Seebeck’s exploratory experimentation was conducted in the early 1800s, the first formal explanation of the Seebeck Effect3 based on contemporary materials science was only first formulated in the early 1900s. The Seebeck Effect was not considered seriously for waste heat, direct energy conversion until after the discovery of semiconductors and subsequent developmental research on these materials starting in the 1950s. The resultant use of precise solid-state physics formulations provided a more formal understanding of the irreversible thermodynamics explanation of the Seebeck Effect. The dissimilar materials are now actually more accurately described as being p-type or n-type semiconductor materials (i.e., a sink or a source of electrons). This research and the advent of advanced materials development during the late 20th century has led to manufacturing of TEG devices that have higher efficiencies. Figure 4 illustrates a single-stage thermoelectric device [3]. State-of-the-art TEGs are commercially available and provide electric power generation without any mechanical moving parts. They therefore have found applications in powering electrical devices in remote, not easily serviced locations, where heat sources are available at large temperature differences. The researchers at the MMA, CN’s project collaborator for the Phase I STTR, have used TEG devices from Hi-Z Technology, Inc. (http://www.hi-z.com/profile.php). There are numerous other suppliers, notably Global Thermoelectric (www.globalte.com). The developmental objective of research into better TEG materials is to increase the Figure of Merit (Z) for the p-type and n-type materials. The Figure of Merit is defined as: Z= (αn +αp)2/[ (ρλ)n 1/2 +(ρλ)p 1/2]2 Where: α, ρ, and λ are the Seebeck Coefficient [volt/oK], electrical resistivity [ohm-cm]; and thermal conductivity [watt/(cm-oK] of the materials. The theoretical efficiency of the device is dependent upon these parameters which are not usually favoring a high Figure of Merit because the values of electrical resistivity and thermal conductivity tend to oppose each other; that is, when conductivity is low for a material, the electrical resistivity is high, resulting in compromised Figures of Merit. Also of great importance to the efficiency of the TEG device is the temperature differential that must be maintained across the hot and cold material surfaces. The thermal efficiency of the TEG device is defined as the amount of electrical power (watts) that can be generated for an input of thermal energy. The expression for the theoretical efficiency of a TEG device is given as follows, Angrist, p. 138 [4]: ηmax = (Mopt -1) (ΔT/Th)/ (Mopt +Tc/Th); where: Mopt = (1 +Z ΔTavg)1/2 It can be easily shown that high efficiencies are possible when the product Z ΔTavg is high, and that the temperature difference between Th and Tc is large. The product of the Figure of Merit (Z) for common Seebeck materials and the average temperature difference across the hot and cold surfaces (ΔTavg) have typical values of 0.5 to 1. Current research goals are to improve this modified Figure of Merit to attain values of 4. The power densities for common TEG materials are typically 6 to 10 kWe/m2 with the research objectives to attain values of power density of 15 to 20 kW/m2. Using these basic relationships for a TEG device operating across a temperature difference, CN has calculated the efficiency for TEG devices that can be situated where there are temperature differences across several components in a supercritical CO2 system.

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The reverse phenomenon, called the Peltier Effect, is the production of a hot and cold junction with the administration of a voltage potential across two conductors. The Peltier Effect is the basis of thermoelectric refrigerators.

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Supercritical CO2 Power Cycle Symposium May 24-25, 2011 Boulder Colorado TEG Performance Parameters TEG #1

Kw,in/m^2= 10 Thot,K= 484 Tcold,K= 418 % DT,hot surface= 10.0% % DT,cold surface= 10.0% Z*, [units: 1/K]= 0.025 Z*Tavg 1.5 Thermal Eff.= 3.0% TEG Power (kWe)= 29

TEG #2

TEG #3

TEG #4

10 10 10 722 429 372 499 301 293 10.0% 10.0% 10.0% 10.0% 10.0% 10.0% 0.025 0.025 0.025 2.3 2.5 0.9 4.00% 7.8% 1.5% 683 451 356 TOTAL kWe= 1520

CO2 COMPRESSOR-TURBINE-GENERATOR PACKAGE BASELINE S-CO2 SYSTEM without TEG SYSTEM= 5717 kWe at 16% Base Cycle Eff. Carnot Eff.= 49% 2nd Law Eff.= 32% TOTAL COMBINED TEG plus CO2 SUPERCRITICAL SYSTEM 7237 kWe at 20% Combined Cycle Eff. Carnot Eff.= 46% 2nd Law Eff.= 43% a 26.6% Improve. in S-CO2 Cycle Eff. Net MT-30 Power Improvement WITHOUT TEG= Net MT-30 Power Improvement WITH TEG=

19% 24%

Figure 5. Thermoelectric generator performance specifications used in CN’s preliminary cycle analysis The major assumptions used in the preliminary analysis included the use of the product of Figure of Merits (Z) x Tavg for the four TEG systems that varied from 0.5 to 3.0, resulting in power theoretical efficiencies from 0.5 % to 9 %. The TEG efficiency is also dependent on the location of the systems within the CO2 cycle, which in turn, determines the actual hot and cold cycle fluid temperatures. A more precise thermodynamic analysis will include a finite difference approach to determining the exact temperature difference across the multiple TEG elements that populate the surfaces of the heat exchangers. The many small, individually wired TEG elements will need to be mechanically integrated into the heat transfer surfaces of the heat exchangers in order to provide a large enough contact surface area to provide the necessary heat exchange between the hot and cold TEG surfaces. However, the packaging of sufficient surface area within a small volume package, suitable for use within the confined spaces of the shipboard engine room, is similar to the construction of a compact surface heat exchanger that easily provides surface densities 100 to 200 ft2/ft3.

2. Statement of Work Summary The engineering effort that is planned is summarized in this section. The goals of the proposed project include the complete thermodynamic analysis of the integrated TEG and supercritical CO2 system with an MT-30 gas turbine. The results of this analysis will be the selection of the operating state points for the supercritical CO2 cycle to produce the maximum power while considering the physical constraints of utilizing an integrated waste heat recovery system in Navy shipboard service, as well as the constraint imposed by the maximum acceptable back pressure on the gas turbine. In addition to completing the thermodynamic analysis for the combined TEGsupercritical CO2 system, CN will complete a preliminary design of the CO2 compressor-turbine-generator as a modular package that can fit alongside the MT-30 engine room aboard the marine vessel. The preliminary design will be in sufficient detail to enable CN to determine a size and cost estimate for the turbomachinery-electric generator systems. A preliminary design of the waste heat recovery super heater and regenerator heat exchangers will also be completed in Phase I. These heat exchangers will require the mechanical integration of the TEG systems within the heat exchanger so as to provide the maximum temperature difference between the hot and cold surfaces within the TEG, while also fitting the necessary TEG hot and cold surfaces within a heat exchanger volume that conforms to the MT-30 footprint. Mr. Travis Wallace and his company, Thermoelectric Power Systems LLC, have already started the research required to integrate TEG systems into waste heat recovery exchangers. Mr. Wallace will continue this research as the principal consultant-researcher by implementing the goals for the heat exchanger development. He will work with MMA Professors Paul Wlodkowski and Peter Sarnacki, and will use

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Supercritical CO2 Power Cycle Symposium May 24-25, 2011 Boulder Colorado MMA’s research facilities. Thermoelectric Power Systems LLC will be the manufacturer of the advanced heat exchangers that are developed and demonstrated in Phase II of the project. Concepts NREC (CN) is a recognized leader in the analysis, design, and manufacturing of turbomachinery. CN is the Principal Investigator for the project. An economic analysis of the viability of the combined TEG S-CO2 system for waste heat recovery on shipboard for the Navy will be completed using cost estimates of the major TEG-S CO2 components, TEG-heat exchangers provided by the MMA team, and compressor-turbine-generator costs from CN. CN engineering staff, combined, have over 40 years of experience in the analysis, design, prototype fabrication, and testing of waste heat recovery systems. These waste heat recovery systems utilized exhaust gas heat from diesel engines to generate electric power in the 30 kWe to 100 kWe range. Two such applications date from the late 1970s into the 1980s, when interest in the U.S. was focused on energy conservation and increased energy efficiencies due to the recent oil embargo. CN, MMA, and Thermoelectric Power Systems LLC will use the results of Phase I to determine a viable development plan for fabricating and testing a prototype system that combines the TEG technology with the supercritical CO2 thermodynamic cycle in Phase II and the commercialization of the waste heat recovery system in Phase III of the project. The collaboration of work by CN and the MMA researchers includes: A. (By CN) The determination of the optimum design state points for the supercritical CO2 cycle (S-CO2), the selection of one or more integration sites within the S-CO2 for a TEG-Heat Exchanger, and the determination of a specification for an auxiliary combustion system fueled with bio-fuels. B. (By MMA and TPS) The conceptualized mechanical design of an exhaust gas waste heat exchanger integrated with TEG devices so as to provide sufficient surface area within a compact heat exchanger. C. (By CN) The conceptualization of a CO2 compressor-turbine-generator package that is driven on one shaft so as to reduce size, number of bearings, shaft seals, and gearboxes, and thus decreases the cost of Operation and Maintenance ($O&M). D. (By CN and MMA) An economic analysis will be performed with estimated costs for the TEG-Heat exchangers by MMA and the packaged, single-shaft CO2 compressor-turbine-generator by CN to determine a Simple Payback of the S-CO2 system with respect to fuel savings and/or the value of increased range for the naval vessel during mission exercises. As of the writing of this paper, the engineering work has only just begun on the Army SBIR award. Much more conclusive results will be reported at the Symposium in May, 2011.

References 1. Feher, E. G., “The Supercritical Thermodynamic Power Cycle”, Douglas Paper No. 4348, presented to the 2. 3. 4. 5.

IECEC, Miami Beach, Florida, August 13-17, 1967. Kines, M. A., “Carbon Dioxide Flooding,” D. Reidel Publishing, Holland, 1984. Angrist, S. W., “Direct Energy Conversion,” 2nd edition, 1971, p.141. Angrist, S. W., “Direct Energy Conversion,” 2nd edition, 1971, p.138. Angrist, S. W., “Direct Energy Conversion” and U.S. Dept. of Energy Report: A Science-Based Approach to Development of TEG materials for Transportation Applications,” August 2007.

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