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Table of Contents Getting Started with ChemCAD * What is ChemCAD? * Special Features about ChemCAD * About this Tutorial * Accessing ChemCAD at UT *
Getting Started Right Away: Two Simple Simulations * Combustion of 3-Methyl-1-Pentene * Create a job name and file * Establish the engineering units system * Add unit operations to the flow sheet * Connect the unit operations with streams * Build the chemical component list * Select K-value and enthalpy thermodynamic models * Specify feeds (and cut streams) properties * Press OK to continue * Specify equipment parameters * Run the simulator * View the output * Save the simulation * The Simulated Haber Process * Creating a Job Name and File * Establishing the Engineering Units System * Adding Unit Operations to the Flowsheet *
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Connecting the unit operations with streams * Building the Chemical Component List * Selecting K-value and Enthalpy Models * Specified Feeds (and Cut Streams) * Specifying Equipment Parameters * Running the Simulator * Viewing the Output *
Using Other Real or Quasi-Real Unit-Operations * Component Separator * Compressor and Expander * Divider * Fired Heater * Heat Exchanger * Mixer * Liquid Pump (PUMP) * Shortcut Distillation * Stoichiometric Reactor * Valve * Flash *
Using the Controller * Introduction * How to use the controller * Controlling Streams * Example 1 * Example 2 *
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Example 3 * Example 4 * Unit Operation Regulation * Example 5 * Example 6 * Example 7 *
File Management * ChemCAD File Management Commands * Start a New Job * Load a Job * Copy a Job * Delete a Job * Rename a Job * Import a Job * Export a Job * Create a Backup Job (another job case) * Load a Case * Copy a Case * Delete a Case * Rename a Case * View or Edit Case Notes * Switch Directories * View or Edit Job Record * Windows Equivalent Commands * New *
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Open * Close * Save * Save As * Exit *
Getting Started with ChemCAD
What is ChemCAD? ChemCAD is a chemical engineering process simulation software package. This program enables the user to design Process Flowsheet Diagrams (PFD), and regulate and edit virtually every aspect about it including feed compositions and equipment parameters. More complicated functions of this program include pipe sizing, pricing, establishing crude assays, and formulating control strategies. One will find that the chief advantage in using this program or any other type of process simulation software is the avoidance of the nuisance of having to perform countless series of tedious and often repetitive calculations.
Special Features about ChemCAD To use this program, extensive knowledge of the undergraduate chemical engineering course-work is useful but certainly not necessary. While this program is complicated, with practice, anyone can use and master it. The overall effect of any slight change in the PFD, its equipment or a feed composition can easily and expediently be determined to allow the user to optimize the chemical process with less haste. This version of the program operates in windows. As such, many features commonly associated with windows operations make this program user-friendly. These features include, but are not limited to the use of pointing & clicking with the mouse, scrolling and scroll down menus, and "Help" paragraphs. One will find that by simply pointing and clicking to the object or icon of interest, usually, the desired manipulation of the PFD, will be made readily available to the user. File management can be tricky. For this reason it is prudent to pay special attention to one’s actions and commands in this program so as not to have to risk loosing work when trying to recall a previous version of the case study. In this program it is not necessary to completely "fill out" (with data) any "screen" with the information requested. In certain cases, most "blanks" will remain empty. Actually, the program runs bests when the "blanks" remain empty and the system’s defaults are used. Some "blanks" are for customized or special operating conditions and are unimportant for most instances and general operating conditions. The primary use for these types of blanks are to override any assumptions or operating procedures or
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algorithms that the program uses or is known to do. Many parts of this program can be effectively and most easily used by just controlling the mouse. In this program, the left mouse button tells the computer to select and/or "Enter." The right mouse button tells the computer to deselect, go back, or "Escape." ChemCAD is a valuable tool to any chemical engineer for reasons other than process simulation. Other features included in this and many other process simulators are vast databanks containing the physical properties of thousands of chemicals, various thermodynamic and equilibrium packages for more accurate modeling, and equipment (theoretical and actual) sizing and cost analysis subroutines.
About this Tutorial The bold-faced type in this tutorial represents commands or information to type. Each bold-faced word, in some way, corresponds to an action for the reader of this tutorial to undertake. This tutorial is for the version of the software package leased by the Chemical and Environmental Engineering Department at the University of Toledo and may or may not be applicable in its entirety to other later, previous, or alternate versions of ChemCAD. This tutorial is limited to describing only the relatively simpler functions of ChemCAD. To learn about more complicated functions of the program, a more comprehensive user's guide can be found in the student chemical engineering lounge along the shelf but, there is no substitution to good ole’ fashion trial & error practice.
Accessing ChemCAD at UT l l l l l l l l l l l l
Log in to any computer in the engineering college. Hit the Start icon. Go to the Programs menu Go to the ChemCAD for Windows Menu Select ChemCAD for Windows Wait while the program loads Ignore the prompt that instructs you to insert the ChemCAD installation disk. Hit Cancel Ignore the Job Accounting Information box prompt. Hit Cancel. Go to the Control Menu Go to New Job Give your new job a name Happy Simulating!
Getting Started Right Away: Two Simple Simulations
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Combustion of 3-Methyl-1-Pentene Plan: Use ChemCAD to mix, heat, and react two streams to completely combust 3-Methyl-1-Pentene without a recycle. The feed stream variables are given below. The reaction in the reactor is 1C6H12 + 9O2 goes to 6H2O + 6CO 2; everything else is inert. The mixed stream fed to the reactor must be 250°F and at a pressure of 300 pounds per square inch (absolute). The conversion of the hydrocarbon is 75%. Also assume there is a 30psi drop in the heat exchanger. The reactor operates adiabatically. Feed Streams Stream 1 Stream 2 Stream Name Air Fuel lbmole/hr flow rate 2000 100 Temperature (°F) 100 125 Pressure (psi) 200 300 Molar % Nitrogen 79 0 Molar % Oxygen 21 0 Molar % 3-Methyl-1Pentene 0 45 Molar % Helium 0 55 Molar % Water 0 0 Molar % Carbon Dioxide 0 0 Total % 100 100 After having named your new job, ignore the "Job Accounting Information" prompt and press the cancel icon. You should see a white screen with pull-down menus and icons across the top and scroll bars across the bottom and right side. The following is a list of the steps one must take to successfully create a process simulation. 1. Create a job name and file 2. 3. 4. 5. 6. 7. 8. 9. 10.
Establish the engineering units system Add unit operations to the flow sheet Connect the unit operations with streams Build the chemical component list Select K-value and enthalpy thermodynamic models Specify feeds (and cut streams) properties Specify equipment parameters Run the simulator View the output
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11. Make sure the output is sound and logical 12. Save the simulation
Create a job name and file Follow the instructions given in Accessing ChemCAD at UT section above. Establish the engineering units system Access the pull-down menu entitles EngUnits. Go to Reset Current Units Go to ENGLISH By double clicking on the name of any unit you wish to change, under the "Current Units…" submenu, you can select your new unit. For this simulation, make sure the units that you will be using, as listed above, are the ones that the program indicated that it will be using. Press the OK icon to confirm your changes. Add unit operations to the flow sheet With the mouse, click where it reads Edit FlowSheet. This is along the pull-down menu on the top of the screen. Observe that the pull-down menu choices have now changed. Click where it reads Simulate FlowSheet to view the other pull-down menu selection. For now, click Edit FlowSheet to view the editing. Click on UnitOps. Click on Add UnitOps. Here are all of the program’s unit operations. By using the down arrow key, you can scroll down to see more.
Note: There is an important convention worth noting that ChemCAD uses with regards to feeds and products. While feed streams or product streams are not actually physical pieces of equipment, they still need to be represented on the process flow sheet diagram for the program to run. This can be accomplished by selecting Feed or Product in the unit operations selection menu. Scroll to "Feed" and double click on it with the left mouse button. Don’t be intimated by the complexity of the unit operations as you scroll down the page! With the funny looking cursor, place the feed on the left of the screen. This takes you back to adding new unit operations. Add another feed. Place it under the first feed. Notice that ChemCAD gives the unit a number.
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In a similar fashion add a Mixer. Use Mixer #1 or #4. Place the Mixer to the right of the feeds. In a similar fashion add a Pump. Place the Pump to the right of the Mixer. In a similar fashion add a Heat Exchanger. Place the Heat Exchanger to the right of the Pump. In a similar fashion add a Heat Exchanger. Use Heat Exchanger #1 or #2. Place the Heat Exchanger to the right of the Pump. In a similar fashion add a (Stoichiometric) Stoich. Reactor. This is the simplest type of reactor. Use Stoich Reactor #2. Place the Stoich. Reactor to the right of the Pump. Finally, add a Product icon to the right of the reactor. There should be seven unit operations represented on the flow sheet. Connect the unit operations with streams After having placed the product icon on the page, you may have to click the Right Mouse Button to take change the cursor from the funny-shaped vessel to the normal looking arrow. Go to the Streams Pull Down menu.
Go to Add Streams. Notice the cursor now looks like a pipe. With the Left Mouse Button, connect the outlets of the feed icons to the inlets of the Mixer. You will see that a unit operation is ready to be connected to another when a colored arrow emerges from the inlet or outlet of that unit operation. Note: When moving the end of the represented stream around, expect to see the colored arrow pointing to the input with which the stream will connect. This indicator will tell you exactly which input the stream will connect. No connection will be made unless the outline is visible. Note: You can goose-leg the stream lines by clicking the left mouse button away from any input (in the absence of the previously mentioned indicator). Sometimes, in order to make your PFD look orderly and presentable, it may be necessary to goose-leg your streams. To remove an undesired elbow in your goose-legged stream, simply press the Right mouse button immediately after you hit the left mouse button to make the elbow in the first place. In a similar manner, connect the mixer to the Pump. In a similar manner, connect the Pump to the Heat Exchanger. In a similar manner, connect the Heat Exchanger to the Stoich. Reactor. Finally, connect the reactor to the Product. The program will then tell you that there are no available inlets in view. Your PFD should look like this.
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Build the chemical component list Note: The next few steps involve specifying the list of chemical components associated with your process. Remember that this list must include not only the components in your feed streams but also the components in your product stream and ALL intermediate streams. You can select a component either by its ChemCAD ID number, formula, or name. Database searching is dynamic; the highlight is adjusted each time you type a character in the input field. You can also move the cursor with the up and down arrow keys. The F1 key displays a list of all formulae and names associated with the highlighted component. Press the Enter key to transfer the highlighted component to the list of selected components. With the mouse, click where it reads Simulate FlowSheet to view the other pull-down menu selection. The program will ask you if you want to save your updates. Click Yes. Go to the Components pull-down menu. Go to Component List. The Program will then ask you if you wish to copy a component list form another job or case. Click NO. Choose to select the components by synonym. This option should appear in the lower left lower right hand corner of the component list box. The Program will take a moment to reorganize the list. Type nitrogen or at least enough of it to get the nitrogen selected highlighted. When it is highlighted, press Enter to place Nitrogen on the component list. Ignore the Component ID number. The program will refer to the chemical by its ordinal placement on the component list. Note: The program refers to chemicals not by name, but by their ordinal position, i.e. 1, 2, 3, … etc
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position on the component list. The Component ID number is not relevant to normal operations or calculations by the program. In a similar manner, type oxygen or at least enough of it to get the oxygen, O 2, highlighted. When it is highlighted, press Enter to place oxygen on the component list. In the same manner, and in this order add the following chemicals to the list: 3-Methyl-1-Pentene Helium-3 Water Carbon Dioxide When you have added these six chemicals in the order listed in the tutorial, your component list should look like the following: 46 Nitrogen 47 Oxygen 1352 3-Methyl-1-Pentene 551 Helium-3 62 Water 49 Carbon Dioxide With the options in the left hand corner, one can change or edit or you component list. Click the OK icon when you are done creating your list. Select K-value and enthalpy thermodynamic models Note: This step involves selecting mathematical models used by ChemCAD for calculating various chemical properties. ChemCAD uses an Expert System to make initial selections for K values and Enthalpy models. However, you should override these selections if, in your opinion, there are more suitable models for your system. Go to the Thermo pull-down menu. Go to Expert Input the minimum and maximum temperatures and pressures for the system. For this case example, use the following: T Min 100
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BIP means binary interactive parameter. Leave the BIP data threshold at 0.5000. The text on the screen should say, "Selected K = SRK and H = SRK. This is good. SRK is the name if a thermodynamic model. It stands for Soave Redlich Kwong. Press the left mouse button on the OK icon to continue. The next screen enables you to override the assumptions and models used with the temperature and pressure data and component. Press the left mouse button on the OK icon to continue. Specify feeds (and cut streams) properties This step involves specifying feed and cut stream properties. Cut streams are recycle streams, which form loops in your flowsheet. Mathematically, these loops force the simulator to use an iterative process for solving mass and energy balances. Since you don’t have any recycle streams you have no loops in your flowsheet and the simulator can solve mass and energy balances for all streams and equipment in a single pass. Go to the Streams pull down Menu. Select Feed Streams From the information at the beginning of this chapter enter "AIR" for the name of stream 1 and "Fuel" for the name of stream 2. Note: Just as in any Windows-based program, you can select the data field with which you wish to type information with the mouse. First, with the mouse, point to the data entry space you wish to fill. Second, press the left mouse button to place a character cursor in the data entry space. Since you will be typing, it may be easier to use the arrow keys, to go from data field to data field. Finally, type the data and repeat the first step of this note to enter data in another data field. These lines require you to enter the temperature, absolute pressure, vapor fraction, and enthalpy of the streams. In reality as in this program, if one knows the composition of a system, one must enter two of the four quantities since the Gibbs’ phase rule states that only two are independent. ChemCAD calculates the remaining quantities from the thermodynamic model chosen for the simulation. If more than two are entered, only the 2 from the highest two lines will be used; the rest of the data will be discarded and recalculated. From the information at the beginning of this chapter enter the temperatures and pressures of both feed streams. Note: In ChemCAD, there are several ways to describe the composition of a stream. Three such ways are as follows: (A) You can enter the molar flow rate of each component, whereby the total flow rate of the stream will be calculated for you in moles/time; (B) You can enter the weight percentage of each component and enter the total flow rate in mass/time separately; (C) You can enter the molar percentage of each component and enter the total flow rate in moles/time separately. In this tutorial, we will use the
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third method to describe the feed rates. With the mouse, go to where it reads "Comp Flow Units." With the left mouse button click twice on the yellow text to the right to find another menu. Click again with the left mouse button on where it reads "Mole Frac." Do the same for both streams. Enter 2000 in the data entry space labeled "Total Flow" for stream #1. Enter 100 in the data entry space labeled "Total Flow" for stream #2. Enter the rest of the relevant feed data. When you are done. The Stream data page should look like this: Quantity
Stream 1
Stream 2
Label
Air
Fuel
Temperature
100
125
Pressure
200
300
Total Flow Rate Units
Lbmol/h
Lbmol/h
Total Flow Rate
2000
100
Component Flow Units
Mole fraction
Mole fraction
Nitrogen
0.79
Oxygen
0.21
Vapor mole Fraction Enthalpy
3-Methyl-1-Pentene
0.45
Helium-3
0.55
Water Carbon Dioxide Note: The sum of the molar fractions must be equal to 1.0000. Fortunately, if this is not the case, each entry will be normalized. Normalization means mathematically that the computer takes each entry and divides it by the sum of every entry. For example, suppose there was a stream of four components with the first component being 10%, the second, 20%; the third, 30%; and the forth 40%. By entering (1,2,3,4), (2,4,6,8), (10,20,30,40), or (501,1002,1503,2004) for the molar fractions, ChemCAD would understand each of the four sets of molar fractions as (.1,.2,.3,.4), which adds up to 1.0000. Likewise, suppose a stream was 1/33 of component A, 2/33 of component B, 9/33 of component C, 10/33 of component D, and 11/33 of Component E. In other words, this stream is 1 part A, 2 parts B, 9 parts C, 10 parts D, and 11 parts E. It would be suitable to enter 1,2,9,10,11 for molar fractions for the molar
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components of A,B,C,D,E in that order since the computer will normalize the data entries. Press OK to continue Specify equipment parameters With your mouse, click on the stream mixer. Stream Mixer: For this piece of equipment, the screen could be left empty and the simulation would still work perfectly. Put the cursor in the data field at the top entry bank and press the F1 key to read why. Leaving the data field on the highest line of this screen, in this case, sets the pressure of the mixed stream to the lower or lowest stream pressure entering the mixer. Press OK to continue With your mouse, click on the pump. Set the OutPut Pressure to 330Psia Take time to view the other data entry fields that you can set with this unit operation. Press OK to continue. Heat Exchanger: Click on the heat exchanger. Enter 30.0 for the "pressure drop" in the heat exchanger. Only One blank, from "Temp Out" to "Delta T." needs to be entered. If more than one data entry blank is entered, than only the information from the highest blank will be used and the rest of the information will be discarded. Enter 250°F for the data entry field that reads "Temp out." This regulates the temperature of the stream that leaves the heat exchangers. Press OK to continue. Stoichiometric Reactor: The stoichiometric reactor is the simplest type of reactor to use in ChemCAD. Notice how it can be set to being an isothermal, adiabatic, or heat duty reactor. If it is not already, set it to "Adiabatic" with the left mouse button by placing the cursor and clicking on the set of parenthesis before the word "adiabatic". The "Key Component," is the component that can not fully react. For example, if you were to read that, in some process, "Methanol is 90% reacted in a single-pass conversion," then methanol would be the key component. In our case, the hydrocarbon is the key component. Enter 3-Methyl-1Pentene as the key component. Enter 0.75 for the data field that says Frac. Conversion because only 75% of the 3-Methyl-1Pentene will react. Note: Only when creating the component list of the process simulation is it important to know the ChemCAD ID. number of a specific chemical. Otherwise, in any other part of the program, a specific chemical is referred to by its ordinal number as it appears on the component list. You can press F5 to view the component list. Enter the stoichiometric coefficients for each component using the guide from the proceeding note.
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Note: Coefficients are negative if they are reactants, positive if they are products and zero if they are inert. Coefficients do not have to be integers. If any stoichiometric coefficient data entry field is left empty, the program assumes that that component is inert. Set the component stoichiometric coefficients as listed for the following reasons: Component Coefficient Reason 1 0 Nitrogen is inert 2 -9 9 moles Oxygen react 3 -1 1 mole of Methyl-1Pentene reacts 4 0 Helium is inert 5 6 6 moles Water are produced 6 6 6 moles Carbon Dioxide are produced Press OK to continue. Ignore the warning message that the heat of formation data is missing. Run the simulator Note: In this program, "to run the simulator," is synonymous with (in more general computer terms) "to compile." Go to the Run pull down menu. Go to Steady-State Go to Run All. Note: the entire simulation can be ran by simply pressing F8. Ignore the warning messages. Congratulations: You have completed your first simulation! View the output After a short delay, the monitor should stop flashing notes. Those flashing notes were indications of the computations which were being worked and iterated. More complicated flowsheets with more complicated unit operations and especially those with multiple recycles could take hours to compile. This one should have taken only a couple seconds. Did it work? To find out, go to the "Output" menu with the mouse and press the left mouse button to select it. Then, with the left mouse button click on "Reports". Under "Report Menu," Go to "Calculate and Give Results" by clicking on it with the left mouse button. After a short delay you should be able to see a white report. You can scroll down the report with the arrow keys. Under "Flowsheet Summary," you can see each piece of equipment listed and the streams
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that go into and out from those unit operations. Under "Stream Connections," you can see what each stream connects. The blanks represent products or feeds that, of course, have no numerical designation. Go to the "Overall Mass Balance." Look at the totals. Note how the total moles in are not equal to the total moles out. Likewise note how the total pounds in is equal, or about equal to the total pounds out. The reason as to why the mass in may not be exactly equal the mass out is because the computer tolerance of the calculations is to plus or minus .1% of the actual value. The tolerance can be adjusted. Save the simulation Do the following to save your work: Close the file, not ChemCAD. This can be done under the control pulldown menu. Notice that when you do this. The Pulldown menus change. Go to "Jobs menu" Go to "Export jobs" Select the job that you wish to save. Select the destination to which you wish to save your file. Note: In ChemCAD terms, "export jobs," means to save work onto a disk. "Import jobs," means to recall work from a disk.
The Simulated Haber Process Plan: Use ChemCAD to mix, heat, and react two streams to produce ammonia without a recycle. (The recycle and an explanation about the mathematics of a recycle will be introduced in chapter 5 as an annex of chapter 4.) The feed stream variables are given below. The reaction in the reactor is N2 + 3H2 goes to 2NH3. The mixed stream fed to the reactor must be heated to at least 1550 K. Assume that the single-pass fractional conversion of N2 is .40. Also assume there is a 2000 Pa drop in the heat exchanger. To do this simulation, set the PFD (structurally) exactly like the PFD from Chapter 2 but allow room to add other unit operations. Feed Streams Stream 1 Stream 2 Stream Name Nitrogen Hydrogen kmol/hr flow rate 15 45 Temperature (K) 300 400 Pressure (Pa) 150,000 250,000 Molar % Hydrogen 000 100 Molar % Nitrogen 100 000
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Total % 100 100 This example exposes the user to more parts of ChemCAD than previously shown. For the person just beginning to use this program, it would be wise to pay special attention to all of the options in a scroll down menus, not just the one you specifically need. The reason for this is simply to obtain a better familiarity of the locations of specific commands for later, other, more complicated projects. Creating a Job Name and File Go to {Control Menu; Jobs & Cases; New Job} and choose and enter the name of the job that you are working on. Expect to see the screen go blank for a moment after you press enter. Note: It is recommended by the author of this tutorial that you assign the name of the job to the name of the principal product, or an abbreviation thereunto, of your chemical process. For instance, if the main product of your process simulation is Di-Isopropylbenzene, perhaps DIPB would be an appropriate name for that particular job. Establishing the Engineering Units System Go to { Eng Units; Reset Current Job}. From here you should see the "Profiles menu." Select "SI" with the left mouse button. Adding Unit Operations to the Flowsheet Go to {Edit Flowsheet Flowsheet Menu (labeled "Flsht"); Unit Opss; Unit Op.'s; Add Units}. From left to right, using the entire width of the screen, place two feed icons (facing right), one mixer, one heat exchanger, and one stoichiometric reactor and one product icon in that order. This PFD should almost perfectly resemble the PFD generated in chapter 2. Proceed to Connecting the unit operations with streams. Connecting the unit operations with streams Go to {Flowsheet Menu (labeled "Flsht"); Streams; Add Streams}. In this order, with the left mouse button, connect the feeds to the mixer, the mixer to the heat exchanger, the heat exchanger to the stoichiometric reactor, and the stoichiometric reactor to the product. Proceed to the next section. Building the Chemical Component List Go to {Component Menu; component list}. And in this order, add hydrogen (#1), nitrogen (#46), and ammonia (#63). Your list should appear as follows: 1 Hydrogen 46 Nitrogen 63 Ammonia
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Proceed to the next section. Selecting K-value and Enthalpy Models Go to {Thermo Menu; expert}. Enter 400 K and 800 K for the temperature values and 100,000 Pa and 200,000 Pa for the pressure values. Leave the "Bip data threshold" at 0.5000. Simultaneously hit the CTRL key and the Enter key to save this data. The text on the screen should say, "Selected K = SRK and H = SRK. This is good. SRK is the name of a thermodynamic model. It is an acronym for Soave Redlich Kwong. Specified Feeds (and Cut Streams) Go to {Simulate Flowsheet; Streams; Feed Streams}. In the streams data entry page, make it so that the data stream information input corresponds to the stream properties at the beginning of this chapter. No ammonia enters this process. Specifying Equipment Parameters Select the unit ops by clicking on them and then specify the relevant information Regulating the Heater: Place the pressure drop at 2000 Pa and the Temp out at 1550 K. For the stoichiometric reactor, keep it adiabatic. The key component is 2. The fractional conversion is 0.4. And the stoichiometric coefficients are [-3,-1,2]. Running the Simulator Press F8 to run the simulation Viewing the Output Go to {Output; Report; Calculate and Give Results}.
Using Other Real or Quasi-Real Unit-Operations Thus far in the tutorial, the unit op.'s that have been introduced were the feeds & products, the heat exchanger, the stoichiometric reactor, the mixer, and the divider. Chapters 7 through 10 of the official user’s guide intensively discuss the unit op.'s of this program. Though minor errors in that text have been discovered, it remains a useful guide none-the-less. This chapter is an index to using some of the more common, but less complicated unit operations of ChemCAD. To write a complete description of every unit operation that ChemCAD has to offer would be a monumental task. Such an effort has already been done in the mentioned chapters of the user's guide and can be seen by using the help options. This chapter serves as a "get you going" chapter. The main purpose of this chapter is to list various unit operations and describe how to use them. The first part of the description of the unit operation will be a brief description of the module. The second part will be a list describing the minimal amount of information needed to be specified to operate that module. In this case, "minimal," means without the other functions of ChemCAD. These other functions
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include pricing, rating, and sizing. Any other parts of the module description will be other relevant information about the unit operation. It should also be noted that the most efficient way to go about reading this chapter is to look at the unit operation's parameter specification page while reading this chapter. This can be done by (1) placing the unit operation on the PFD, (2) going to {Unit Op.'s Input; Select Unit}, and (3) selecting the unit with which you are reading. Review: By now, you know that to successfully use unit a operation in ChemCAD, you have to (1) place its icon on the PFD, (2) connect its inputs and outputs with flow streams, (3) specify its equipment parameters. Note: When entering equipment parameters and specifications, pay special attention to the green text. The data entry field next to the green text usually must be completed with the relevant information about the specific unit operation. If any of the "minimal" data entry fields are not completed, an error message will be shown and the simulation will not compile. The simulation can work with warning messages but not error messages.
Component Separator The component separator module simulates separation without actual distillation. It is a fictitious, abstract piece of equipment used to be able to take the place of columns without having to go through the rigors of actually setting up a distillation column. It can be used by: 1. Specifying one of the following regarding the top product: temperature; bubble point temperature; dew point temperature; user specified degrees of subcooling; or user specified degrees of superheat 2. Specifying one of the following regarding the bottom product: temperature; bubble point temperature; dew point temperature; user specified degrees of subcooling; or user specified degrees of superheat 3. Specifying the "Split Basis" 4. Specifying the "Split Destination" (Top or Bottom) 5. Specifying the "Split Fractions or Mole Flowrates" There is something here that should be clarified. At step #5, suppose you are specifying the split fractions. You are not telling the computer the composition of the top or bottom stream. You are telling the computer what fraction of "Component No. X" will go to the top or bottom stream. If the "Split Destination" was set to the bottom and if you were to enter a .92 for Component No. 7, that would mean that 92% of component No. 7 would exit through the bottom of the column while the remaining 8% would go through the top.
Compressor and Expander The compressor or expander module simulates an isentropic or polytropic compressor or expander
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operation. Output pressure, pressure ratio (P out / P in) or actual work required or generated by the compressor or expander may be specified. Either module can be used by: 1. Specifying the "Mode of Operation" 2. Specifying the "Type" of compressor or expander 3. Specifying the output pressure, labeled, "Pressure out" or the Pressure ratio
Divider The divider splits a stream into two or more streams, each having the same pressure, temperature, and composition but different flow rates. If a stream was a road, the divider would be a fork in it. It can be used by: 1. Specifying what the "Split (is) based on" 2. Specifying what "Flow rate units" to use 3. Assigning a flow ratio to each of the output streams
Fired Heater The fired heater calculates the fuel usage required to heat a process stream to a specific temperature. The heating value of the of the fuel gas can be provided by the user or a default value or 900.0 Btu/Scf is used. It can be used by: 1. Entering the required temperature of the exiting stream 2. Entering any optional information in the "Optional Input" data field
Heat Exchanger The heat exchanger module can be used to simulate an exchanger with one or two input streams. For one input stream, the exchanger serves as a heater or cooler. If the exchanger has two input streams, more complicated operational modes are available. It can be used as a heater or cooler by: 1. Selecting the icon that has one input and one output. 2. Entering only 1 of the 6 "Specs" on the left column on page #1; The heat exchanger will not work if more than one spec is entered.
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It can be used as a heat exchanger by: 1. Selecting the icon that has two inputs and two outputs. 2. Entering only one of the 15 "Specs" on the left column on page #1; The heat exchanger will not work if more than one spec is entered.
Mixer The mixer module mixes several input streams and performs an adiabatic flash calculation at the output pressure of the mixer. If there is more than one output on the icon, the mixer also serves as a phase generator. It can be used by: 1. Not specifying any data upon specifying equipment parameters. If this is the case, the output pressure will take the value of the lowest pressure of any of its input streams. 2. Otherwise, you could specify a desired output pressure.
Liquid Pump (PUMP) The liquid pump is used to increase the pressure of a liquid stream. Either the outlet pressure or the pressure increase may be specified. In either case, the required work is calculated. It can be used by either entering the desired output pressure of the outlet stream, or the pressure increase of it.
Shortcut Distillation The shortcut distillation module simulates a simple distillation column with one input and two product streams (distillate and bottom). Both rating and design cases are provided. It can be used by: 1. Selecting the mode 2. Selecting the condenser type 3. Entering the number of the light key component 4. Entering the number of the heavy key component 5. Entering the heavy key split 6. Entering any addition information that is specific to the mode with which you are using Note: If the light key component has a lower boiling point than the heavy key component, the tower will not work.
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Stoichiometric Reactor The stoichiometric reactor module simulates a reactor given a set of stoichiometric factors, key component and fraction of conversion. The reactor can be set as adiabatic, isothermal, or with certain heat removal or addition. If the specified conversion causes any reactant flow in the output stream to go negative, the conversion will be reduced so that the flow rate of the limiting reactant becomes zero in the output. It can be used by: 1. Specifying the "thermal mode": adiabatic, isothermal or heat duty 2. Identifying the "Key Component" 3. Entering the fraction of conversion 4. Entering the stoichiometric coefficients using ChemCAD's convention
Valve The valve module does an adiabatic flash calculation of its input stream. Output pressure, dew point temperature, pressure drop, or bubble point temperature can be specified. In case of specifying dew point or bubble point temperature, the module will first determine its corresponding pressure, then perform the adiabatic flash calculation. The valve module will also serve as a phase separator if more that one output stream is specified. It can be used by entering either the output pressure, dew point temperature, pressure drop, or bubble point temperature.
Flash The Flash Tank operates by entering 2 of the following variables: Outlet Temperature, Outlet Pressure, exiting vapor fraction, or Heat duty. ChemCAD will calculate the other two variables.
Using the Controller Introduction The controller module is placed in the flowsheet between other unit operation modules and has the following two modes: Feed forward mode: This mode allows you to pass the calculated stream or equipment information to a specified equipment. For example, the feed forward controller can be used to send the calculated work from an expander to a compressor as available work, or to pass the heat duty from a heat exchanger to a reboiler of a distillation column. Feedback controller: This mode allows you to adjust an equipment variable until a specified condition is achieved. For example, you can adjust the stream flow rate by varying the split fraction of a divider to
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meet the heat duty of a heat exchanger which accepts the adjusted stream as the input. Any stream variable or equipment variable can be controlled or adjusted with the controller. Physically, the controller is an abstract unit operation in ChemCAD that doesn't represent any physical piece of hardware. As it will be shown, its use in ChemCAD is to make so user has to perform less calculations manually and to help make obsolete trial and error derivations of solutions. It works by examining one process variable in a Stream Or Piece of Equipment (SOPE). It will regulate that process variable in a SOPE until the specifications of another (or that same one) process variable in a SOPE is within the tolerance of its desired result. While this may seem confusing, the seven examples provided in this chapter and the two examples provided in the official user's guide will draw some light on the subject. All seven examples will use the controller in the feedback controller mode. The controller operates in either mode identically. The first four examples will use the controller to regulate process streams and the last three examples will use it to regulate unit operations.
How to use the controller The first four examples will use the same structural PFD and the same feeds. Set up the following PFD to have two feeds that connect into a mixer. Connect the mixer to a controller (stream #3) and the controller to a product icon (stream #4). Enter the following data for the stream variables. The numbers to the right of the chemical components are their ChemCAD chemical ID numbers. Assume no pressure drop across the mixer. Get to the equipment specification page of the controller before continuing. Feed Streams Stream 1 Stream 2 Stream Name Air Fuel lbmole/hr flow rate 100 100 Temperature (°F) 50 500 Pressure (psi) 16 16 Molar % Argon (98) 01.00 0 Molar % Nitrogen (46) 78.50 11.14 Molar % Oxygen (47) 19.50 0 Molar % N-Octane (12) 0 87.67 Molar % Water (62) 01.00 01.19 Total % 100 100 Mentally, separate the first page into 8 parts as shown below. The first three parts are on the left column, the last five are on the right.
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Part Region Part I. The "Mode:" selection section in the upper left column Part II. The green text in the left middle of the column Part III. The yellow text in the lower left column Part IV. The "Input for Measured Object:" section Part V. The "Operator" in the middle of the right column Part VI. The "Type" section under Part V. Part VII. "Constant" and "units" in the lower right column Part VIII. The "Type" section under Part VII Now mentally assign the information in Part IV as Variable A; the information from Part VI as Variable B; the information from Part VII as Constant C and the information in Part VIII as Variable D. The controller operates by adjusting the variable specified in Part II. until: Variable A [some operator +,-,/,*] Variable B equals Constant C, or... Variable A [some operator +,-,/,*] Variable B equals Variable D. This is to say that either C or D can be specified, not both. More generally: The controller operates by adjusting the variable specified in Part II until: some scalar times Variable A [some operator +,-,/,*] some scalar times Variable B equals Constant C, or... some scalar times Variable A [some operator +,-,/,*] some scalar times Variable B equals some scalar times Variable D. Algebraically: Adjust the specified variable in Part II until: aA operated on bB equals to C or dD where a, b, C, and d are constants and
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A, B, and D are process variables in a stream or piece of equipment. þ See figure 1000 at the end of this chapter.
Controlling Streams Example 1 Use the controller in the given PFD to adjust the air stream so that it has four times the total mass flow rate as the fuel stream. Keep the fuel stream at a flow rate of 100 lbmole/hr. Note: At most times while using ChemCAD by pressing the F4 key, you can view the PFD and return to the screen that you were using. There are several ways to go about solving this problem. We will solve this problem by adjusting the mass of the air flow, stream #1, until the mass flow of the mixed stream, stream #3, is five times the mass flow of the fuel flow, stream #2. 1. Adjust the controller so it is in the "Feed-backward" mode. 2. In Part II, the part where we specify what variables get adjusted, enter 1 in the "Stream No." data entry field. This will tell the program that there is something about stream #1 that we want to adjust. Place the cursor in the data entry field to the right of where it reads "Variable No." in Part II. 3. Press the F9 key to find the number of the process variable that you wish to specify. There should be an untitled scroll-down menu at page labeled "VARIABLE NUMBER CHECK." Make sure that "process stream" is highlighted on this page. 4. Press the Ctrl key and the Enter key to access the variable number reference page. 5. As you can see by scrolling down once, the variable number we want is #6. As shown, this variable number represents the total mass rate. Press the right mouse button to return to the controller specification page. Enter 6 in the "Variable No." data entry field in Part II. 6. Part III is for the regulation and adjustment of convergence and iteration process of the controller. It usually can be ignored. Skip it for now. If adjustments need to be made in the mathematical procedure that the controller uses, it can be done from Part III. 7. Part IV will be where we tell the program to measure the flow rate of the mixed stream, which is stream #3. Using a slightly different convention as in Part II, place the asterisk in the parentheses before the word "stream." Type a 3 for the number to represent stream #3. Since we know that the variable number is 6, enter it in the data entry field to the right of the word variable. Leave the scale blank. The scale represents the scalar. Its default is 1. 8. We don't need an operator for Part V. Having no operator in Part V negates the data entered in Part VI. Leave the operator to read "No operator." 9. In this example, we have no need for a constant because we only want that four times as much air than fuel enters, mass-wise. Skip part VII.
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10. For Part VIII, since we know that the mixed stream must have five times the mass flow rate as the fuel stream, enter the following data in the following places for the following reasons: Place Data Reason Type: Stream It is a stream that we are evaluating. Number 2 In Part VIII, we are evaluating stream #2. Variable 6 We want to monitor total mass flow rate. Scale 5 5 times the mass flow rate of Stream #2, equals stream number three. 11. Simultaneously hit the Ctrl key and the Enter key to save this data and continue. 12. Run the simulator. 13. View the output. The mass flow rate (in lb/hr) of the stream #1, the air, is 41392.7031. The mass flow rate of stream #2, the fuel, is 10348.1455. Stream #1 is about four times stream number #2. Our simulation worked. 14. Conceptually, we adjusted the mass flow rate of stream #2 until the mass flow rate of stream number 3 was five times that of stream number #1. For this example. The information in Parts IV and VIII could have been switched because of the commutative property of equality which states if A=B then B=A. In our case, algebraically, A=dD. Example 2 Before starting example 2, reset the total molar flow in Stream #1, the air feed, back to 100, from 1436.7267. This can be done at {Streams Input; Feed Streams}. Use the controller in the given PFD to adjust the molar flow rate of the air stream so in the mixed stream, there is 10.0 times more oxygen on a molar bases than there is octane. Note: Adjusting the total molar flow rate of a stream is essentially the same as adjust the total mass flow rate of stream. 1. Part I: Make certain that the controller is in the "Feed-backward" mode. 2. Part II: Since we will be adjusting stream #1, type 1 in the data entry field to the right of the "Stream No." 3. Press F9 and then simultaneously hit the Ctrl and the Enter key to find out what the total molar flow rate variable number is. As seen without having to scroll, it is 5. Type 5 in the data entry field to the right of the "Variable No." 4. Skip Part III. 5. Part IV: We want to examine the molar flow rate of the octane in the fuel stream. Be sure that the asterisk is in the parentheses before the word "Stream." Enter 2 for the stream "number."
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6. Press F5 to recall what component number octane and oxygen are on the component list. Remember, the component number is the same as the sequence number. 7. Since we want to examine the molar flow rate of the octane, press F9 and then simultaneously hit the Ctrl and the Enter key to find out what the component molar flow rate variable number is. 8. The mole variable number convention for "mole flow rate of the ith component," is -(i). If N-Octane is the 4th component in your chemical list, enter "-4" in the data entry field to the right of the "Variable" in Part IV. 9. Part V: We don't need an operator in this simulation. Retain the setting, "No operator." 10. Part VI: Having no operator in Part V negates the data entered in Part VI. Having left the operator to read "No operator," skip Part VI. 11. In this example, we have no need for a constant because we only require that there is 10.0 times as much of one component in stream #3 as there is of another component in stream #3, on a molar basis. Skip part VII. 12. Part VIII: Since we know that there must be 10.0 times as much octane in the mixed stream as there is oxygen in it, on a molar basis, enter the following data in the following places for the following reasons: Place Data Reason Type: Stream It is a stream that we are evaluating. Number 3 In Part VIII, we are evaluating stream #3. Variable -3 The negative digit because of the convention and the 3 is for if it was the molar flow rate of the 3rd component we wanted to measure. Scale 10 We want 10 times the molar flow rate of oxygen to equal that of the octane. 14. Run the simulator. 15. View the output. The total molar flow rate (in lbmol/hr) of the stream #1, the air, is 44.9592. The mass flow rate of stream #2, the fuel, remains 100. Stream #1 is about four times stream number #2. In the mixed stream there is about 87.67 lbmol/hr of octane and 8.767 lbmol/hr of oxygen. 16. Conceptually, we adjusted the mass flow rate of stream #2 until the molar flow rate of the octane in stream #3 was 10.0 times that of the molar flow rate of the oxygen in stream #3. 17. Another way to have completed this simulation would have been to type -603 and -604 instead of -3 and -4. This would have adjusted the molar fraction of the ith component rather than the molar flow rate of the ith component. Those two conventions are not always interchangeable. Example 3 Before starting example 2, reset the total molar flow in Stream #1, the air feed, back to 100, from 44.9592. This can be done at {Streams Input; Feed Streams}.
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Use the controller in the given PFD to adjust the molar flow rate of the fuel feed stream so the mixed stream is 345° F. 1. Part I: Make certain that the controller is in the "Feed-backward" mode. 2. Part II: Since we will be adjusting stream #2, type 2 in the data entry field to the right of the "Stream No." 3. Press F9 and then simultaneously hit the Ctrl and the Enter key to find out what the total molar flow rate variable number is. As seen without having to scroll, it is 5. Type 5 in the data entry field to the right of the "Variable No." 4. Skip Part III. 5. Part IV: Since we want to examine the temperature of the stream #3, be sure that the asterisk is in the parentheses before the word "Stream." Enter 3 for the stream "number." 6. Since we want to examine the temperature in stream #3, press F9 and then simultaneously hit the Ctrl and the Enter key to find out what the variable number for temperature is. It is 1. Type 1 in the data entry field to the right of the "Variable." 8. Part V: We don't need an operator in this simulation. Retain the setting, "No operator." 9. Part VI: Having no operator in Part V negates the data entered in Part VI. Having left the operator to read "No operator," skip Part VI. 10. Part VII: This time we do have a constant. Enter 345 to the right of in the "constant" data entry field. 11. Reset the units with the left mouse button so it reads temperature. Because the program is set to English units, it will understand the 345 to be in Fahrenheit.
12. Part VIII: Since you can only enter information in Part VII or Part VIII, not both, skip Part VIII. 13. Run the simulator. It may not converge on the first attempt. Try running it a few times. It should work. 14. View the output. The temperature of the stream #3 is 344.3354. The molar flow rate of stream #2, the fuel, is reduced to 22.3226. Stream #1 remains at 100 lbmol/hr. Example 4 Before starting example 4, reset the total molar flow in Stream #2, the fuel feed, back to 100. This can be done at {Streams Input; Feed Streams}. Use the controller in the given PFD to adjust the molar flow rate of the air stream so that 5 times the molar flow rate of the Argon in the air stream plus 10 times the molar flow rate of the nitrogen in fuel stream equals 25 times the molar flow rate of the oxygen in the mixed stream.
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1. Part I: Make certain that the controller is in the "Feed-backward" mode. 2. Part II: Since we will be adjusting stream #1, type 1 in the data entry field to the right of the "Stream No." 3. Press F9 and then simultaneously hit the Ctrl and the Enter key to find out what the total molar flow rate variable number is. As seen without having to scroll, it is 5. Type 5 in the data entry field to the right of the "Variable No." 4. Skip Part III. 5. Part IV: Here, we want to examine the molar flow rate of the Argon in the air stream. Be sure that the asterisk is in the parentheses before the word "Stream." Enter 1 for the stream "number." 6. Press F5 to recall the component numbers. Remember, the component number is the same as the sequence number. 7. Since we want to examine the molar flow rate of the Argon, press F9 and then simultaneously hit the Ctrl and the Enter key to find out what the component molar flow rate variable number is. 8. The molar variable number convention for "mole flow rate of the ith component," is -(i). If Argon is the 1st component in your chemical list, enter "-1" in the data entry field to the right of the "Variable" in Part IV. 9. Since we want to use 5 times the molar flow rate of the Argon in the air for the computation, enter 5 for the scale in Part IV. 10. Part V: With the left mouse button, select "Add" for the operator setting. 11. Part IV: Here, we want to examine the molar flow rate of the nitrogen in the fuel stream. Be sure that the asterisk is in the parentheses before the word "Stream." Enter 2 for the stream "number." 12. Press F5 to recall the component numbers. Remember, the component number is the same as the sequence number. 13. Since we want to examine the molar flow rate of the nitrogen, press F9 and then simultaneously hit the Ctrl and the Enter key to find out what the component molar flow rate variable number is if you don't remember it. 14. The molar variable number convention for "mass flow rate of the ith component," is -(i). If Nitrogen is the 2nd component in your chemical list, enter "-2" in the data entry field to the right of the "Variable" in Part VI. 15. Since we want to use 10 times the molar flow rate of the nitrogen in the fuel stream for the computation, enter 10 for the scale in Part VI. 16. In this example, we have no need for a constant because all of the numbers given in the problem statement were scales, 5, 10 and 25. Skip part VII. Make sure the data entry field for it is empty.
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17. Part VIII: Since we know that the sum of the 10 times the molar flow rate of the nitrogen in the fuel and 5 times the molar flow rate of the argon in the air equals 25 times the oxygen in the mixed stream, enter the following data in the following places for the following reasons: Place Data Reason Type: Stream It is a stream that we are evaluating. Number 3 In Part VIII, we are evaluating stream #3. Variable -3 The negative digit because of the convention and the 3 for if it was the molar flow rate of the 3rd component we wanted to measure. Scale 25 We want 25 times the molar flow rate of oxygen to equal that of the octane. 18. Run the simulator. It may not converge on the first attempt. Try running it a few times. It should work. 19. View the output. The argon in the air stream, had component flow rate of .5350. 5 times that is 2.675. The nitrogen in the fuel stream had a molar flow rate of 32.2986. 10 times that is 322.986. The oxygen in the mixed stream had a molar flow rate of 13.0239. 25 times that is 325.5975. 2.675 + 322.986 = 325.661, which is extremely similar to 325.5975. This simulation worked. The fuel stream gets fed at a rate of 100.0000 lbmol/hr and the air stream gets fed at a rate of 74.6328 lbmol/hr.
Unit Operation Regulation In the next three examples, we will be controlling unit operations with the controller. Examples 5-6 will use the same PFD. As noted in the prior examples, be sure that before you start the simulator, you return the feed streams and the equipment to it original settings. Upon completing the next four examples, pay attention to the similarities in procedure that exist between controlling a feed and controlling a unit operation. Example 5 Connect a feed to a stream divider. Have one of the outputs of the stream divider connect to a heater and the other to a mixer. Have the output of the heater connect with the other input of the mixer. Connect the output of the mixer to a controller which will connect to a product stream. There should be six streams in all. To follow this tutorial, make sure that the stream that connects the divider and the mixer is #4. Label the other streams, in order, as they go from the feed to the product. The feed stream properties are given below. They are the same as the Stream #1 from the previous examples. Make sure the unit operations are numbered accordingly. Feed Streams Stream 1 Unit Operation Number Stream Name Air Divider 3 lbmole/hr flow rate 100 Heater 4 Temperature (°F) 50 Mixer 1
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Pressure (psi) 16 Controller 2 Molar % Argon (98) 01.00 Molar % Nitrogen (46) 78.50 Molar % Oxygen (47) 19.50 Molar % N-Octane (12) 0 Molar % Water (62) 01.00 Total % 100 Set the divider so that equal amounts of the feed stream leave both outputs. Set the heater to have the exit stream be at 1000° F. Make sure that the divider is set to "split base on" Flow ratio and the flow rate units are lbmol/hr. ratio Use the controller in this PFD to regulate the divider so that the product stream is 500° F.
1. Make sure the feed and unit operation specifications are as listed on your PFD. 2. Part I: Make certain that the controller is in the "Feed-backward" mode. 3. Part II: Since we will be adjusting the divider, enter 3 for the "Equip No." 4. Press the F9 key to find out what the variable number we will need. 5. With the left mouse button, select the highlighted text. Upon seeing the list of all of the unit operations (except the controller), select the "divider". 6. Once the divider appears on the "Variable Number Check," simultaneously hit the Ctrl and the Enter key. 7. If your stream #3 emerges from the higher part of the divider, your variable number is 3. If your stream #3 emerges from the lower part of the divider, your variable number is 4. 8. Enter your variable number. 9. Skip Part III. 10. Part IV: Enter stream #5 variable #1 for temperature and leave the scale data entry field empty. 11. Skip Parts V and VI.
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12. Part VII: Enter 500 for the "Constant" and make sure the "Units" for it read "Temperature". 13. Skip Part VIII. 14. Run the Simulator 15. View the output: The temperature of streams #5 and #6 are about 499.9499°F. Close enough. The flow ratios should be about .8607 and 1.000, or some non-zero scalar times those two. Example 6 Using the same PFD as in Example 5, and the same initial conditions, use the controller to regulate the heater so that the product stream is 800° F. 1. Make sure the feed and unit operation specifications are as listed on your PFD. 2. Part I: Make certain that the controller is in the "Feed-backward" mode. 3. Part II: Since we will be adjusting the heater, enter 4 for the "Equip No." 4. Press the F9 key to find out what the variable number we will need. 5. With the left mouse button, select the highlighted text. Upon seeing the list of all of the unit operations (except the controller), select the "heat exchanger". 6. Once the heat exchanger appears on the "Variable Number Check," simultaneously hit the Ctrl and the Enter key. 7. Variable number 4 is T1 out. 8. Enter 4 for the variable number. 9. Skip Part III. 10. Part IV: Enter stream #5, variable #1 for temperature and leave the scale data entry field empty. 11. Skip Parts V and VI. 12. Part VII: Enter 800 for the "Constant" and make sure the "Units" for it read "Temperature". 13. Skip Part VIII. 14. Run the Simulator 15. View the output: The temperature of the product is about 800° F. The temperature of the stream leaving the heat exchanger is about 1495.8° F. This simulation worked. Example 7 Problem Statement:
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A stream that is 24% molar N2 and 76% molar H2 that has a pressure of 750,000 Pa and a temperature of 100 K flows at rate of 100 kmol/Hr. This stream will go through a parallel series of three stoichiometric reactors that will react N2 + 3H2 to make 2NH3. Assume that in the reactors, the single-pass fractional conversion of the nitrogen is 20%. The product exiting the third reactor must have a temperature of 873 K. However, the heat duties of all three reactors must be exactly the same. Use three controllers to design three reactors that can perform this task. Find out how much energy must be added or removed from each reactor in MJ/h to accomplish this. 1. Set up a chain of unit operations in the following order: Feed, Reactor, Reactor, Controller, Reactor, Controller, Controller, and Product. There should be seven streams in all. Make sure the stream numbers go in order. 2. Create and name a new job. Change the Engineering units to SI. 3. Establish the thermodynamic model, the component list, and the feed stream specifications. 4. For each of the three reactors, change their thermal mode to heat duty. Enter the component number for nitrogen as the key component number. Enter the Fractional Conversion of 0.2, and enter the stoichiometric coefficients. 5. The last controller will be used to regulate the heat duty of the first reactor to make sure the stream passing the last controller is 873 Kelvin. Make sure it is in feed- backward mode. In Part II, Enter 1 for its equipment number to be adjusted and 4 for the variable number for heat duty of the stoichiometric reactor. 6. In Part III, set the iterations to 999. 7. In Part IV, have the measure object be stream #6, and variable 1 for temperature. 8. In Part VIII, set it the constant to 873 and the units to temperature. 9. Leave all other data entry fields blank. 10. The middle controller will set the third reactor's heat duty equal to that of the second reactor's heat duty. (The first controller will set the second reactor's heat duty equal to that of the first reactor's heat duty.) Enter 4 for the Equipment number to be adjusted and 4 for the variable number in Part II of the middle controller. 11. In Part III, set the number of iterations to 999. 12. In Part IV, set the object to be measured to equipment #4, variable number 4. 13. In Part VIII, set the object to be measured to equipment #2, variable number 4. 14. Leave all other data entry fields blank 15. The first controller will set the second reactor's heat duty equal to that of the first reactor's heat duty. Recall that the first reactor's heat duty has already been controlled by the temperature of the product stream. Enter 2 for the equipment number to be adjusted and 4 for the variable number in Part II of the first controller.
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16. In Part III, set the number of iterations to 999. 17. In Part IV, set the object to be measured to equipment #2, variable number 4. 18. In Part VIII, set the object to be measured to equipment #1, variable number 4. 19. Leave all other data entry fields blank. 20. Run the simulator. It may take you up to ten times for it to work. If there is still an error, go back and make sure you entered the data correctly. 21. View the output. If you correctly simulated this constrained process, you should find that reactor must add about 320.4 MJ/hr of energy for this process to work.
File Management Anything file management procedure that can be done using Windows, can also be done using ChemCAD, but differently. This chapter will serve as an index to using the file management commands in ChemCAD. The first part of the chapter is a "how-to" list, A though O, of the ChemCAD file management commands. The second part of the chapter is a list of the Windows file management commands and the sequence of ChemCAD commands needed to perform the Windows equivalent commands. Special attention should be paid to the italicized notes of this chapter. There are four. This chapter will use the bracket-semicolon notation introduced in chapter 3.
ChemCAD File Management Commands Start a New Job 1. Go to {Control Menu; Jobs & Cases; New Job}. Choose and enter the name of the new job with which you will do work. 2. The monitor will go blank at this point. A moment later, the main working screen will appear with a blank PFD and the job name and the case name will take the title of the name you entered. Load a Job 1. Go to {Control Menu; Jobs & Cases; Load Job}. Choose the job with which you will do work. Note: The only jobs that can be loaded and worked on are those that have been imported or the generic job "NEWJOB." To import a job from a diskette or the U-drive, see "Import Job" in this chapter. Copy a Job
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1. Go to {Control Menu; Jobs & Cases; Job Management; Copy}. Choose the job with which you wish to copy. 2. Enter the new name of the newly copied job. Delete a Job 1. Go to {Control Menu; Jobs & Cases; Job Management; Delete}. Choose the job that you want to delete. 2. There is a safeguard against accidental deletion. To confirm the deletion, enter the name of the job that you wish to delete. Rename a Job 1. Go to {Control Menu; Jobs & Cases; Job Management; Rename}. Choose the job that you want to rename. 2. Enter the new name of the job. Import a Job 1. Go to {Control Menu; Jobs & Cases; Job Management; Import Job}. 2. Enter the directory and/or drive from where you want to import a job. If you want to import a job from the A drive, for instance, type "A:". 3. Choose the job with which you wish to import. 4. Importing a job and loading a job are not synonymous. An imported job must be loaded in order to do work on that job. Note: To some, the words "import" and "export", as they would apply to computer terminology, may mean a file transfer. This is NOT the case. When a job gets imported, it means it is copied to the directory C:\User. Likewise when a job gets exported, it is saved to the target location. Note: Exported jobs can be written over if you are trying to export a job onto a drive that already has a job of that same name. Imported jobs can't be written over like so. This is the reason why you shouldn't use the job named "NEWJOB." The program always has a job named "NEWJOB" in the C:\USER file directory. Export a Job 1. Go to {Control Menu; Jobs & Cases; Job Management; Export Job}. 2. Choose the job with which you wish to export. 3. Enter the directory and/or drive from where you want to export the job. If you want to export a job from the U drive, for instance, type "U:".
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Create a Backup Job (another job case) 1. Go to {Control Menu; Backup Job}. 2. Optional: If you plan on having multiple cases within a job, you will want to rename each case as you create them. To do this, see L. Rename a Case. Load a Case 1. Go to {Control Menu; Jobs & Cases; Case Studies; Load Case}. 2. Choose the case with which you wish to do work. 3. The monitor will go blank at this point. A moment later, the main working screen will appear with a blank PFD and the job name and the new case name appear on the top of the screen. Copy a Case 1. Go to {Control Menu; Jobs & Cases; Case Studies; Copy Case}. 2. Choose the case with which you wish to copy. 3. Enter the name of the newly copied job. Delete a Case 1. Go to {Control Menu; Jobs & Cases; Case Studies; Delete Case}. Choose the case that you want to delete. 2. There is a safeguard against accidental deletion. To confirm the deletion, enter the name of the case that you wish to delete. Rename a Case 1. Go to {Control Menu; Jobs & Cases; Case Studies; Rename}. Choose the case with which you wish to rename. 2. Enter the new name of the case. View or Edit Case Notes 1. Go to {Control Menu; Jobs & Cases; Case Studies; Edit}. 2. Select the case with which you want to view or edit notes. Switch Directories 1. Go to {Control Menu; Jobs & Cases; Switch Directories}. 2. Specify the new drive and/or directory.
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View or Edit Job Record 1. Go to {Control Menu; Jobs & Cases; Job Management; Edit}. Choose the job of which you wish to view or edit the record. 2. Enter the relevant information. 3. Simultaneously hit the Ctrl key and the Enter key to save the data. Note: Keeping case notes and job records are optional.
Windows Equivalent Commands New 1. For a new job: New Job 2. For a new case: Backup Job, then Rename the Case Open 1. If the job hasn't yet been imported, Import Job 2. Load Job Close There is always a job loaded on the program, even if it is NEWJOB. The only was to close a job is to open another one. Save Every time you finish making adjustments to the PFD, the program saves the PFD. In ChemCAD, there is no need for a specific "save" command. Save As 1. To "Save as" a separate job: Copy the Job 2. To "Save as" a separate case: Backup Job, then rename or copy the case labeled "BACKUP." 3. To "Save as" in a new drive or directory: Export Job Exit 1. Go to {Control Menu; Quit}. 2. Or push Alt+X.
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Note: Unlike exiting in a windows based program, there is no screen that has you confirm your decision to exit the program. As long as you do not log off the computer, the C: drive should remain intact for when you immediately return to the program at that point. If you accidentally log off or if the computer crashers, push the 1 key for crash recovery after you enter your password. The C: drive should remain intact for when you immediately return to the program at that point.
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