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Aspen Tech Handbook: A Technical Aide for Chemical Engineering Process Design Students
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Contents
For information on the contents of any section, read the opening paragraph of that section, or use the alphabetical index in the back of the handbook for easier searching.
Chapter
Title
Page
1
Computer Management
2
2
Multicomponent Flash Drums
6
3
Generating Graphs in Aspen
10
4
Modeling Distillation Columns
13
5
Modeling Reactors
20
6
Using RateFrac for Rate-Based Simulations
22
7
Putting Everything Together
26
8
Using Aspen Icarus for your Cost Estimate
34
9
Using Aspen Pinch For Your Heat Integration
39
Appendix A
Thermodynamic Property Tree
47
Appendix B
References
48
Appendix C
Index
49
Note: The makers of the AspenTech, Inc.’s Aspen Plus simulation engine have no affiliation with this tutorial. This tutorial was produced for educational purposes and any distribution of this material without the expressed written consent of Cornell University is strictly prohibited. Possible side effects of using this software include: blurred vision, self-induced hair loss, hours of frustration, and the realization that you probably never need to use activity coefficients again. Please consult your physician before operating the simulation engine.
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Preface to the Manual
Over the last several years, we have introduced modern Chemical Engineering software to the Unit Operations and Design Courses. Even more recently, we have introduced AspenPlus simulation to the Separations Course and we hope this "downward" integration will continue. The value to the senior courses has been enormous and many graduates have expressed that knowing something about these computer techniques has been helpful in their jobs. Unfortunately, as the programs get more able to predict real processes and equipment, they become more complicated. The "Help" manuals are not easy (although they are complete) and step-by-step tutorials are non-existent. Keep in mind that we are being provided with several hundred thousand dollars worth of software and licenses for a tiny fraction of the normal price. While Aspen does provide technical service, we cannot expect them to answer our specific questions overnight. In the spring of '01, Brock Tuczynski was a TA for Separations and wrote a very nice tutorial for getting started with Aspen. I had written several sets of instructions for solving various problems with Aspen and Icarus and, over the years, we had assembled lots of specific but unorganized answers to questions. Over the summer of '03, Josh Banke and Meghan Cuddihy put together this tutorial. They edited Brock's original work, tied together all we had and wrote many new sections. They have tried to make this into a comprehensive user's guide to the Aspen and Icarus software and have added quite a bit of material about the computer lab organization and setup that I hope you will find useful. Good luck as you become more proficient with the simulations and remember that these are difficult and complicated programs to use. Patience is important. One last piece of advice: the fundamentals of Chemical Engineering are the most important tools you have. I have seen many, many flash drums that were not adiabatic, columns with a reflux ratio below the minimum( try a McCabe-Thiele Diagram for starters), and overall material balances that were not right. Start every problem with a sketch, a material balance and a heat balance and you will spend a lot less time trying to get yo ur process to converge. Ken Ackley
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Chapter 1: Computer Management The purpose of this chapter is mainly to demonstrate how to setup a shared folder on the computer lab network, how to optionally set up one from your home, as well as to discuss some of the more pertinent issues regarding managing and securing the integrity of your computer that are useful to know. Windows XP File Sharing Windows XP lets you share a computer's disks and folders with other computers on the network, using a method called Simple File Sharing. If a disk or folder is shared, everyone with whom you give permissions to the file may access it from the network. This can be useful for several reasons: a shared folder will make it easy for all members of the group to access any saved Process Design or UO files; it obviates a need for writing files to discs or other data transfer media; and it can ward off any answer predators, who might want access to your Aspen or Icarus files. Probably the simplest method for going about this is to share and set permissions on a folder in your account on the Instruct Domain. Here is a brief explanation of how to do that. o Note: The computers in the computer lab in Olin Hall should have Windows XP Professional, if not the latest operating system, installed and running, so we will try to base our example on that assumption. In our example, we've used Windows Explorer to browse to the directory of the My Documents folder, which should be located on the desktop. o In the right-hand pane, right-click, select New and then Folder, and enter the name Shared Folder (or whatever you feel comfortable naming it). o Note: For maximum compatibility with all versions of Windows, use 1-12 characters. o Now, you should specify sharing options for the folder you have created. To do this, rightclick the folder and select Sharing and Security. o On the Sharing tab, select Share this folder and enter a share name. You can add a comment that describes the share on other computers on the same network. o Leave the User limit alone. On XP professional, the maximum limit is 10. o You should probably set some password permissions, so that only you or your group members can access it. To do this: o Click Permissions. Notice that, by default, the group Everyone has Full Control. This means that all users can read, write, and even delete files. That's not what we want at all! o Click Add, and then choose Object Types. Un-check Built-in security principles and Groups, because we only want to see Users. Click OK. o Choose Advanced, and click Find Now. Click on the users who should have access to this share. This should include your group partners and you. You can repeat this to add additional users. When you are done, click OK. o You should be back at the Permissions List. By default, the newly-added users have read-only access. You may want them to have read/write access, meaning each user who logs in can alter files as well as read them, so tick the Change box. You should repeat this for each user as you see fit. A powerful alternative is to set up a share at home, if you don’t want to worry about being in the lab to access the shared folder. This way, you and your partners can telecommute and can exchange ideas and work without being physically present. You would just need to drop your work on the shared folder and it would be accessible by all members of your group. But this method has some issues with compatibility that need to be taken into account first. • Important! Making Sure You Can Set Up a Shared Folder at Home The process for setting up a shared folder that is accessible from another connection is not necessarily easy. There are a few requirements that need to be met first. Before setting up a shared folder that can be easily accessed from home, either you need to be on the Resnet Domain, or you should have a direct connection to the internet with what is called a static IP given to you by your internet service provider. Being on Resnet automatically allows you to access your computer easily from home, but if you live off campus, and want to set up a share that you can access from outside home, you will need to make sure you have a static IP. Your IP address is essentially the identifying address that your computer uses to interact with the internet, and, as the name suggests, a static IP address is one that doesn’t change. If you are not sure whether you have a static IP or its counterpart, a dynamic DHCP-based address, there is a way to check.
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o First you need to know what your IP is, if you don’t already know it. There are a number of ways to go about this. One way is to hit the Start button, then click the Run button. Type in “cmd” and hit enter. This should bring up what is called a command prompt or a dos prompt. o At the prompt, type in “ipconfig,” and the result should be a listing of numbers, but the one you will need to actually take note of will be the number labeled by “IP Address.” Keep this prompt open. To make IP address changes from within a script, you can use Win2K's multipurpose Net Shell (Netsh) command. This command provides several functions that relate to viewing and changing IP addressing on a Win2K system. For example, to switch from DHCP to static IP, enter the following command: netsh interface ip set address "[connection name]" static [ip address] [netmask] [gateway] [metric] o Netmask is the subnet mask (e.g. 255.255.255.0) associated with the IP address, gateway is the default gateway on the command prompt, and metric is the numerical difference between the IP and the default gateway. For example, to change to the static IP address 192.168.0.4, mask 255.255.255.0, and gateway 192.168.0.1 (metric 3), you would type: netsh interface ip set address "local area connection" static 192.168.0.4 255.255.255.0 192.168.0.1 3 o If you still have access to the internet, then your ISP supplied you with a static IP but if you no longer have access to the internet, then you don’t have a static IP. To switch back to DHCP-based addressing, you need to merely enter into the command prompt: netsh interface ip set address "" dhcp If you do not have Resnet or a static IP it isn’t the end of the world. You have 3-4 members per group, so there is a good chance that someone in the group has a direct internet connection with a static IP. But let’s be optimistic, and assume your apartment has viable access. Windows XP Home Edition’s Simple File Sharing Windows XP lets you share a computer's disks and folders with other computers on the network, using a method called Simple File Sharing, and it really is simple. If a disk or folder is shared, everyone on the network can access it. There are no user permissions and no passwords. Because sharing in this way is so wide open, Windows XP tries to protect you from some potential security risks. • Just a small note: Windows XP Professional has a much more powerful way to control the sharing of files, so if you have it or have access to it, I recommend it over the Home Edition. It’s a little more complicated, but you will worry less about who is rummaging through your computer and who isn’t. However, since your computer more likely has the home edition installed on it, here is a short how-to for setting up a shared folder with XP Home. o Right click the disk or folder that you want to share and select Sharing and Security. The disk or folder that you share, along with all of the folders that it contains, will be accessible by other network users.
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o Note: If you're sharing an entire disk, Windows XP gives a warning. What’s implied in the warning is that it's better to share a specific folder, since only that folder (and its subfolders) will be accessible by others, and the rest of the disk will be inaccessible. Click where indicated if you want to go ahead and share the entire disk. This screen doesn't appear if you're sharing a folder. o The first time that you set up sharing, Windows XP displays a warning, urging you to use the Network Setup Wizard for safety. Click where indicated to either run the Wizard or to share files without running the wizard. o Note: The Wizard automatically enables the Internet Connection Firewall (ICF) to prevent other Internet users from accessing your shared disks and folders. Enabling ICF is a good idea if you connect directly to the Internet through a dial-up, DSL, or cable modem. But it's a terrible idea if you connect to the Internet through your LAN, using a software or hardware router, since it will block File and Printer Sharing. o XP should display another warning. If you want ICF enabled, select Use the wizard to enable file sharing. Otherwise, select Just enable file sharing.
o Having successfully run the Wizard's obstacle course, you may now specify a Share name, which users on other networked computers will use to access this disk or folder. o By default, users on other computers have full access: they can read, write, and delete shared files. If you only want them to be able to read files, un-check Allow network users to change my files. o Warning: If a user has full access, deleting a file doesn't put it in the Recycle Bin. Once it's deleted, it's gone for good. Also, if you don’t have an Antivirus program, there is a good chance to pick up a virus accidentally from one of the computers in the lab. We strongly urge you to never run Aspen without an updated anti-virus agent, and, as a corollary, update your virus definitions frequently. o To access your shared folder, you have a couple of options. You can either memorize your IP address, typing “\\” followed by the IP into the address bar in Internet Explorer, or you can map it as a network drive. To map a network drive, open My Computer, click Tools, and select Map Network Drive .
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Specify an unused drive letter and enter the network path for the share (ie. In the format of \\“Computer Name”\“ Folder Name” or \\“IP Address”). Once it has a drive letter, you access it just like a disk on the same computer. o Check Reconnect at logon, so that the mapping will happen automatically every time you start your computer. Otherwise, you'll have to map it manually every time. Click Finish. The mapped drive is connected and appears in a new window. It should also be available in My Computer as a drive.
One Method for Protecting Your Shared Files Hiding Them Most likely, the “safety” afforded by Simple File Sharing is not enough for you. It’s not incredibly safe for both your computer and your files, as people would be able to add files to your shared folder willy-nilly. One answer is to create a hidden share by adding a dollar sign ('$') to the end of the share name. A hidden share doesn't appear in My Network Places or Network Neighborhood on any of the networked computers. Only people who know the share name should be able to access it. o To create a hidden share, right click the disk or folder and select Sharing and Security. Specify a share name that ends with a dollar sign. Once again, use 1-12 characters (1-11 before the dollar sign). o Here we labeled the share Design$, but if you think anyone you don’t want to give access is clever enough to guess a name like Design$, use a more secure name, like a combination of letters and numbers. o To access your folder, either map the hidden folder as a network drive like before, or type in your IP address, followed by the name of the share. (For example, \\192.168.0.4\Design$).
One last point that we can never stress enough is to make sure that, if you share a folder at home, you constantly protect your computer from viruses and worms. If you already have an anti-virus program, such as Symantec Anti-Virus, this should be quite sufficient for protective means. However if you don’t have it, you can download it from the CIT website: http://www.cit.cornell.edu/services/nav/. You only need to enter your netid and your password. Make sure you update your virus definitions every two or three weeks.
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Chapter 2: Aspen Plus Simulation Engine Multi-Component Flash Drums The purpose of this chapter will be to (re-)introduce you to the vile world of Aspen. It first goes step -by-step through the basics of Aspen, then specifies an important piece of equipment you should need to know how to model in Aspen, and covers how to perform a sensitivity analysis. The sensitivity analysis is instrumental in observing how process performance changes with varied operating conditions. Problem Statement: A flash chamber operating 80oC (176oF) and 500kPa (72.5 psia) is separating 1000 kg/hr (2204 lb/hr) of a feed that is 10 mol% Ethane, 5% Propane, 15% n-Butane, 10% n-Pentane, 12% iso-Pentane, 8% n-Hexane, 30% Heptane and 10% Nonane. What are the product compositions and flow rates? Feed conditions are the same as that of the flash chamber. (Example taken from http://chemeng.stanford.edu/~charles/cheme120/Lectures/Lecture6-BubbleDew.ppt) Solution Methodology: • The Basics (This section is a step-by-step process for those who have never used Aspen): Starting Up: First we shall discuss how to open Aspen. o Click on the button, then click on and . o This will bring up the Aspen startup screen. If this is the first simulation you have ever made, choose to create a Template, click OK, and then select . The purpose of this is to have all default settings in English Units. Click OK.
• Setting up your flowsheet: First you need to select the piece(s) of equipment you desire. o To get to flash drums click on the Separators tab on the bottom of the screen. Then click the down arrow next to the picture labeled Flash2. Some choices of drums come up; select the top right by clicking on it. o Note: When you hold the cursor over each directory like “Flash 2” or Flash 3”, an explanation appears under it. All the selections in a given directory are exactly the same program and only LOOK different so that your flow diagram can look the way you want it. o Now click the mouse in the middle of the screen, and the drum should appear. Right clicking stops you from placing drums on the screen.
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o To name the piece of equipment, left click on each piece(s) of equipment, right click and then select Rename Block. An easier alternative is to hold CTRL and type M. Type in an 8 character name for your unit, such as FLASHDRM for example. o Note: If you don’t want names to be shown on the flowsheet, click on the name, hold CTRL and type H. o Next you will need to connect streams, which is done by first clicking on the Material Streams tab at the bottom right of the screen. For the feed, click and hold away from the feed side of the drum and pull the mouse to connect with the Red feed arrow of the drum (it’s on the left side). o For the exiting streams, click and hold the arrow on the top of the drum and pull the stream off the drum and release. Follow the same procedure for the red arrow on the bottom of the drum. Name streams using the same method as for naming the drum. o Note: Holding the mouse over the colored arrows, blue or red, will tell you the purpose of that stream (feed, tops, bottoms, etc) For your reference, our flowsheet is shown in the diagram above. o Click the (Next) button in the middle of the top of the screen. Click OK to proceed to the next step • Setting Properties o To add a title, type it in the Title block that appears then click . o Note: It’s often more useful to have results with components in the form of mole fractions instead of mole flow rates. To do this, under the Setup folder, simply go to Report Options, then the Stream tab, and choose Mole under Fraction Basis. o Now you need to add all of your components. Simply type in the name if you know it, or you can search for it using the Find button and typing in either a component formula or name. Unfortunately, you might have a little trouble finding iso-Pentane, since Aspen has its own conventions for carbon chains with branching. To locate it, use Find, and type in butane, or search using its formula. The component with a name of 2(or 3)-Methyl-Butane fits the description of iso-Pentane, so press the Add button to add it to the list of components. Continue adding all components in our column and press Close. o Note: You can rename the components by changing their Component ID, and choosing Rename at the screen that pops up. When you are done, click . Choosing an Appropriate Thermodynamic Property: o Now, you need to choose an appropriate thermodynamic property for the specific separation. Doing this can often be confusing, but don’t stress over it. Located in Appendix A is the very handy Thermodynamic Decision Tree. It gives you numerous options for deciding on a calculation method. Just start from the first branching (polar vs. nonpolar) and continue along it. o Note: For most problems that you face in your college career, you will rarely have to worry about your system having an electrolyte or not having available interaction parameters. It is probably best to just assume that Aspen has the interaction parameters, unless you are dealing with a very complex system or one that has little research associated with it. Our system has a number of nonpolar components, so start from there, and continue on. o Note: Here are some tips from Aspen on choosing a Thermodynamic system when you really don’t know what to use: 1. If you have a mixture of liquids that separate into two or three layers or if the liquids are non-ideal use an activity-based system. NRTL-RK, according to Aspen, is the one to pick if you have no real data to check your selection with. 2. If there is a dissolved gas in the liquid phase (as from sparging a gas into your reactor, etc) designate that gas as a Henry’s Component. 3. For all other systems, as a selection of last resort, use RK-SOAVE. This is an equation of state model. For this sp ecific operation, I chose to use PENG-ROB, because it fits our “thermodynamic path.” PENG-ROB is usually a good choice if you have a system with a several hydrocarbons. With water in your system, things can get complicated. If water will separate out as a third immiscible phase, don’t worry about it; but, if water is miscible (ie. water and ethanol), you will need to use a polar calculation method, such as NRTL-RK. o Important Note: The only real way to tell whether you have selected the proper system is to compare a T-x-y or x-y diagram generated by Aspen with REAL DATA. We cannot stress this point enough. If you have a relatively simple system, or one that has been researched thoroughly, you can probably get real data from numerous sources. This includes one of your professors, the infamous Perry’s Chemical Engineer’s Handbook, other library resources, etc. Click when you are done. o Enter the stream data and conditions for the feed stream (Temperature, pressure, flowrate, and composition). For having the composition in terms of mole fractions, you must select Mole-Frac from the menu on the right. Click . o Set the Temperature and Pressure of your Flash Drum, and again click on . Click OK to run the simulation, sit back and let the machine do the work. o To view your results click on the button towards the upper right of the Control Panel that should now be up. o Click on and then you can scroll down to see the results. o Note: Any time you change conditions and want to run again you must Reinitialize the process before running. This is done by clicking the button that looks like . o In order to print your results, you can print your data table summary onto the flowsheet by clicking on the Stream Table button. o Assuming you have input the data correctly, you should have results similar to the data shown on the next page:
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These results are pretty close to what you would obtain using a Depriester Chart, so let’s move on. • Performing a sensitivity analysis: If you wanted to determine how a component (say Ethane) in one of your output streams (let’s use the Vapor stream) is affected by the temperature, you could perform a sensitivity analysis showing how the flash changes while varying temperature. Methodology: o Click on the Data Browser button : o Open the Model Analysis Tools “folder”. Then click on Sensitivity. o Create a new sensitivity object by clicking on the button. Name it something you will recognize or just keep the default S -1 name given to you. o Then, under the define tab, create a new “Flowsheet Variable” by clicking on the New button. Create a name and specify what kind of variable it will be. Here we named it ETHVAP. o Note: Think of the flowsheet variable as that which is watched as Aspen performs its calculations, so it would likely be either mole fraction of Ethane in the liquid or vapor streams. o This might be a little confusing at first, so, as an example, look at our example in the diagram to the right: o Under the Vary tab, you are now asked to input conditions for the “Manipulated Variable,” which is the item Aspen changes while it performs its iterative calculations. This should be what you want to increment so that you obtain a change in the flowsheet variable, which will be the block variables temperature or pressure. o Choose a range of values over which the temperature will be changing. If you are performing an simulation where you want to show all the results in a range, merely choosing a range both above and below the initial guess, then narrowing the range down can be quite useful. I recommend using 100 to 300 as the temperature range to look at, and incrementing by 1. Again, if you are a little unsure of what this screen should look like, to the right is an example.
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o o o o
Under the Tabulate tab, type in a column number, and enter the name of the Flowsheet Variable that you wish to evaluate. Click the Next button to run the sensitivity simulation. To view the results click on the Check Results button on the control panel, once the calculations have been completed. Click on the Model Analysis Tools folder, then Sensitivity, and S -1 (or whatever you named the object) and then you can scroll down to see the results. If you want to graph the results, it is recommended that you highlight the data, copy (CTRL-C) the data then paste (CTRL-V) it into Excel or another database program. You should be able to graph it quite easily from that point on. o Note: To highlight a whole column of data, merely left-click on the column’s label box. This should select all data below it. If you want to highlight all columns in one click, just click the blank box in the top left corner of the Summary table. This is usually located next to the Status column.
As always make sure your answer makes sense. If your distillation column consists of 7 trays, and operates between -50oF at the top and 700oF at the bottom, you probably should take a closer look at your column. This ends the first chapter on using Aspen. From here on, the manual will no longer be written in a step-by-step -by-step fashion, mostly because we feel you do not need to be led by the hand through the entire process. If there are potentially confusing instances, we will try to accommodate by including a visual aide. However, the main purpose for this manual is more geared to hopefully providing useful hints on managing the rather confusing simulation tool we refer to as Aspen.
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Chapter 3: Aspen Plus Simulation Engine Generating Graphs in Aspen Now might be a good time to demonstrate how to use Aspen to create and edit pure component, binary and tertiary system property graphs. It’s a pretty useful tool to use if you need to give your manager hard-to-find physical property data for your system, or if you want to evaluate your system’s temperature and composition data before you perform a simulation. Pure Component Systems: Problem Statement: Assume you are running an experiment using a simple pure substance (>99.9%), such as methanol (g) at 68oF, and you require a few bits of information. You have found out through your various reference sources or your employer that, at atmospheric pressure, methanol boils at 65oC (149oF), so you will be required to heat your stream of methanol (obviously without exposure to air). However, your experiment requires you to gather some information, for purposes of data verification, about methanol over the change in temperature from 68oF to 165oF. This includes documenting the constant volume heat capacity, the change in Gibb’s Free Energy and Enthalpy, and density over the specified range; as such, you will need to use Aspen to graph these physical properties of methanol. Solution Methodology: First you need to input the components and specify which thermodynamic system you are going to use. o Much like in the previous chapter, open either a new template or blank document in Aspen, and then add a piece of equipment, including the streams. o Open the data browser, click on the Components folder, and then go to the Specifications tab. Add all component(s) to the system. In our case, this is merely methanol. o Choose the thermodynamic system you will be working with by using the Thermodynamic Decision Tree, located in Appendix A. To input and edit your choice, click on the Properties folder. Then, click on the Specifications tab, and choose the system from those listed under Base Method. Here I chose UNIQUAC, but you could also choose NRTL, or WILSON. UNIQUAC usually provides a reasonable amount of accuracy, but the only way to be completely sure of a correct choice is comparison to real data. Now we need to actually make the graphs. o Click on the Tools button located on the toolbar at the top of the screen. Click on Analysis and choose the option of Property. Then choose Pure. o When the Pure Component Properties Analysis Screen pops up, you need to choose the property you wish to analyze. From the problem statement, you are asked to plot constant volume heat capacity, t he change in Gibb’s Free Energy and Enthalpy, and density over the given range. The screen might look something like this:
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Hit the Go button to plot the results of your analysis. With the plot done, you now have a couple of options. o If you are satisfied with your plot, you can perform another plot analysis using a different property, or you could edit the way the graph looks by playing around with the Plot Wizard. Optional: If you want to edit the plot: o Close the plot, and click on the Plot Wizard button on the analysis results screen. Click Next, then choose the plot type (there is probably only 1 or 2 options) and go to the next screen. o Select the data you wish to plot and click the > button to add data from the left column, < to remove data from the right column. o On this screen you are also given the option to change the units that are displayed. o On the next screen you can alter the title of the graph, and you can alter the title of the axes (Usually you would like to have the axis display the units, so do not remove %Unit%). o You can also change the type of gridlines that are present on the graph by changing the Grid Type or Line Type selections. When you are finished, click the Finish button. Our plot is shown in the diagram below. o With the editing done, you can print the new plot, and repeat the process to create plots for the remaining properties asked for.
∆
o Note: With each type of Aspen graph, you will be presented more editing options when you right-click on the diagram. You can Zoom in or Zoom out, change the color scheme, etc. However, since these options are mostly for aesthetic purposes, I haven’t covered them. Binary Systems: Problem Statement: Now assume that you are running a similar experiment, however you now have a mixture of Methanol, and n-Butane (50-50 mixture), and you wish to obtain an xy, Txy, and KVL diagram of your system. Solution Methodology: o First you need to add n-Butane to your components list, and make any necessary changes to your thermodynamic system, if any. Remember this is done by going to the “Properties” folder, then hitting “Specifications”, and changing your Base Method. o Note: Whenever you make a modification to the current system, make sure you make any pertinent changes, especially if you are adding a complex component, or if your system is no longer at a low pressure, etc. Some other possible modifications could include adding Henry’s components, electrolytes, petroleum free-water method calculations, etc if you were dealing with the appropriate binary mixtures. o Click on Tools, then click on Analysis and Property. Under “Property” you should have the choice of Pure and Binary. Here instead choose “Binary.”
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o When the Binary Analysis screen pops up, go the Analysis Type option, and you should have the choices of Txy, Pxy, and Gibb’s Free
Energy of Mixing. Choose Txy. o Make sure you are operating at Atmospheric Pressure, and that
your property options (Base Method, Henry’s Components, etc), range and number of points/increments are how you like it. o When you are done click Go. o The plot should pop up, and it should look like the diagram to the right: o You can either edit the plot or go on to the next chart. In any case, go to the Binary Analysis Results window created along with the plot, and choose Plot Wizard. o If you want to edit the current plot, you would select the Txy type of plot. You would now have the same options for editing a plot as you would in a pure component situation. After making your diagram look the way you want it to, plot the new graph. o The other option is to choose either the xy or KVL type of diagram. When you choose either of these, you enter the plot -editing pages, which have already been discussed. When you are done editing, you can plot each graph. Tertiary Systems: Problem Statement: Now assume that you are running a similar experiment, however, this time, some of the methanol in your system is actually ethanol (30-20 and 50 butane mixture), and you need to generate a ternary diagram of the system. Solution Methodology: o Again, add the new component to your system and make the necessary changes to your thermodynamic system, if any. o Click on Tools, then on Analysis and then Property. Under Property you should have the choice of Pure, Binary and Residue with the addition of a third component. Here instead choose Residue. o When the Residue Analysis screen pops up, check to make sure that all of the options chosen are correct. Make changes as needed and select the number of curves you wish to generate. When you are done click Go. o The plot should pop up, and, depending on the number of curves you chose, it should look something like this:
I think the diagram looks fine the way it is. There isn’t much in the way of editing options, other than the ability to add a legend, and modify the axis labels, so your graphing task should be complete.
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Chapter 4: Aspen Plus Simulation Engine Modeling Distillation Columns Distillation columns will be the major units of your overall process flowsheet. Setting up a column is very similar to that of flash drums, but optimizing becomes much more complex. To guide you through some of the more useful simulation techniques, we’ll walk you through a quick example. Problem Statement: It’s your first assignment at your new job at the AMC ® Refinery, and you’ve been assigned to design a series of columns to remove propane. Propane tends to build up in reactor units downstream, and it is also saleable. For these reasons, you will need to first design a column to remove ethane, so that the saleable propane only contains 1% ethane. Next, your depropanizer column needs to remove 99% of the propane. You are given the following information about your stream, which enters your process at 100oF and 250 psia: Component Ethane Propane i-Butane n-Butane i-Pentane Total:
lb/hr 1,804
lbmol/hr 60 277 277 497 13 1,124
12,214 16,100 28,887 938 59,943
Mole % 5% 25% 25% 44% 1% 100
Solution Methodology: The following instructions will guide you through the early steps of designing your deethanizer. o Add a column by selecting the Column tab at the bottom of the screen. RadFrac is the most common method we use to model our columns, so click on the arrow next to RadFrac and select your favorite picture of a distillation column. Your selection really doesn’t affect the way Aspen does its calculations. o However, note: If your column does not have a reboiler or condenser, pick the picture that most closely represents your column. o Place the column on your flow sheet and name it. Now add your material streams and name them. Feed, Tops and Bottoms or some variant of them usually works. Remember if you are ever unsure of what a stream on the block (your column) represents, hold the mouse over the red or blue arrow and Aspen will tell you.
o Click Next and then click OK to go to the Data Browser. o Another hint: By now, you should realize that whenever tabs display
, it means you need to enter more information before
moving onto the next step. Once those nasty red symbols turn into encouraging blue checks , you can press to proceed to the next step. If you have entered all information and need to go back to something else, feel free to pick the section you desire on the left bar of the screen. You can also navigate backwards and forwards by clicking on the appropriate arrow: .
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o Supply a title if you wish. o Add your two components, remembering that if you can’t type in the name of the component, you can search for it using the find options. As always, the next step is to choose a thermodynamic system from the Thermodynamic System Tree. We are going to use PENG-ROB for our example, and choose it under Property method, as shown at right. o Next, in the Streams Data Browser, enter the conditions and flow rates of your feed stream (Remember: Make sure that all of the components add up or else you will get horrendous errors later on! We suggest using mole fraction because it is easier to make sure that the total is what it should be, since it should always be 1.) o In the Blocks Data Browser, choose a number of stages, condenser, distillate rate , and reflux ratio. o Note: The condenser counts as the first stage, and the reboiler counts as the last stage.
o For a good starting point on column properties, use the FACT Method. The FACT Method will estimate the number of trays and reflux ratio, based on the relative volatilities of components you want to separate, providing an excellent starting point. To refresh your memory, the number of actual distillation trays is: Product Purity # of actual trays
<95% 17/(a-1)
< 98% 19/(a-1)
< 99% 22/(a-1)
+/- 0.5 2.5
+/- 0.15 6
99.5% 25/(a-1)
And the reflux ratio is: Value of a-1 R/D
>1 1
o Using FACT to start from, the relative volatility, a, estimated by the vapor pressure ratio of ethane and propane, is approximately 4. This indicates that our reflux ratio should be around 1. Next, we recommend using Figure 19-19 in the GPSA Handbook to get a more precise starting set of conditions, which, for a deethanizer, is 30 stages, a reflux ratio of 1.5. We also chose a distillate rate of 60 lbmol/h, since we are rejecting approximately that amount of ethane. o Now specify where the feed(s) enter the column. If you are feeding to the bottom of a column (below the lowest tray) you must change the Stage Convention from Above -Stage (the default) to On-Stage. We’ll choose to feed at tray 15. o Specify the column and/or condenser pressure. Setting only the condenser pressure is fine. o Note: Make sure the units you are using are correct. Most of the time you will be dealing with absolute pressure, so if you tell the column that it is operating at 10 inches of water it will treat the system as a vacuum. In other words just make sure you are using absolute pressure (unless the units on the right say psig or barg). o The condenser pressure dictates the column pressure, as well as the temperature of the condenser. You typically want to choose a condenser pressure to be the vapor pressure of the component you want to remove at around 20o greater than your cooling temperature. o Looking at Figure 23-20 in the GPSA Handbook, the vapor pressure of ethane at 120oF is over 1000 psia! If we were to set the condenser pressure that high, too much of the heavier components would vaporize. The separation we are making is mostly between ethane and propane. The vapor pressure of propane at 120oF is around 250 psia. Therefore we want to pick a pressure that is reasonably inbetween these two pressures. We’ll try running at 425 psia, and now the column should be ready to Run. Our results are pictured to the right: o Our separation converges, always a good starting point. We are removing 35% of ethane, but only losing 3% of
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propane out the tops. But let’s see if a couple changes can improve this separation to our target point. o We can try changing several things to improve our column: reflux ratio, distillate rate, number of trays, and feed tray. • Optimizing reflux ratio: o A good place to start our analysis is with the reflux ratio. We want to find the smallest rate that satisfies our design spec of 99% recovery of propane in the tops. We’ll do this by performing a Sensitivity Analysis. o Remember that this is done by first selecting the Model Analysis Tools folder, then selecting the Sensitivity Analysis folder and pressing New to define a new variable. It’s fine to call this S -1. o Next, define the flowsheet variable of interest; again, this is the variable which you are observing while another variable is varied. We’ll define two: ETH as the molar flow rate of ethane in the tops, and PROP, the amount of propane in the tops (just to keep track). o A Variable Definition window should pop up that looks like this:
% Recovery
o Again, if the variable of interest is a block variable (temp, pressure, heat duties) select Blocks on the left and then choose the Type, Block, and Variable. For Stream, blocks follow the same procedure but select Streams on the left and then select the Type, Stream, and Component. o Similarly, in the Vary tab, choose your manipulated variable. Select what you wish to vary by selecting the variable from the pull-down menus on the left (molar reflux ratio is MOLE-RR). o Now either create a list of values for your variable or pick a range and a number of points or increments. We’ll vary the reflux ratio from 1 to 10, incrementing by 0.25. o If you wish to have more than one variable select the Variable Number pull-down menu and select New. Repeat the process above until you have all of your variables. o Note: The more variables or points you have significantly increases the amount of time it takes to run the simulation so choose wisely. o In the Tabulate menu, for each column write a number and then type in the name of your variable. o Reminder: Instead of typing in the name, you can select % Component Recovery the variable from a list. First right click in the variable space and then select Variable List. Double click on the vs Reflux Ratio variable you want to tabulate then close the Defined 100 Variable List window. Right click again in the variable 90 space and paste your variable name. 80 o Make sure you have reinitialized by clicking then click 70 to run your simulation. 60 o To view the results of the sensitivity analysis, in the results 50 browser menu select Model Analysis Tools, Sensitivity, S -1 40 (if this is what you named it), and finally . Ethane 30 o A table of your results should now appear. You can either Propane 20 scroll down the list in Aspen or select and copy the desired 10 columns and view them in Excel. The latter is useful if you wish to plot your results for visual comparison. 0
0
Shown to the right is a plot of the % recovery of Ethane and Propane in the tops vs. the Reflux Ratio:
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2
4
6 8 Reflux Ratio
10
12
% Recovery
o It looks like we might have a tough time recovering a lot of ethane with a low reflux ratio. o Note: we have to reject at least 80% of the ethane to meet our 1% ethane in propane spec. The graph indicates that above 8 there isn’t much change in ethane recovery when increasing the reflux ratio. We’ll set it at 8 for now and see if after we change some other specs we can lower it a bit. • Optimizing distillate rate: o Increasing the distillate rate is not helping us very much – for every increase, we are letting at least as much propane into the tops as ethane. o We should keep the distillate rate at just over 60, and see what else we can change to improve our process. With the distillate rate at 61 lbmol/hr, 96% of ethane is rejected out the tops.
% Component Recovery In The Tops vs Distillate Rate 100 90 80 70 60 Ethane 50 Propane 40 30 20 10 pr 0 58
60
62
64
66
68
70
72
74
o Lastly, we’ll try to find the best number of trays and feed tray. This is done by running a design spec on the feed tray for several different sized columns. In doing so, we found that increasing to 35 total trays and feeding on tray 10 gave the best separation (results below), and also allowed us to decrease our reflux ratio to 5.75:
76
Distillate Rate (lbmol/hr)
o The ethane rejected is around 98%, and we are only losing 1% of the propane – Not bad! Since our overall goal is propane recovery downstream, and the ethane in the bottoms is around 0.4% of the propane in the bottoms, we should be safe with these numbers, but… o Note also that the tops temperature is 52oF, which will require very expensive refrigeration. To increase the tops temperature, we can adjust the column pressure, reflux ratio, and distillate rate. o First, we ran a design spec on the reflux ratio to obtain an ethane molar flow rate in the bottoms of 2.7 lbmol/hr (approximately 1% of propane). This gave us a reflux ratio of 2.2. o Though we rejected our desired amount of ethane, the tops temperature was still too low. To try and increase the temperature, we increased the condenser pressure to 460 psi. This caused more ethane to leave through the bottoms. o Lastly, we incrementally increased the distillate rate until the amount of ethane in the bottoms was nominal. The more total moles you let out the tops, the more ethane will be rejected through the tops. The tops temperature ended up at 113.5oF:
o Originally, we used the FACT Method to calculate our reflux ratio to be around 1, but we ended up with a reflux ratio of 2.2. The vapor pressures of ethane and propane are so different that a ends up being huge, which means that it should be an easy separation with a low reflux ratio. Instead, we’re seeing a hard separation, and needing to use a higher reflux ratio. This is probably because there is so little ethane in the feed that the separation is actually more like a stripping column than a distillation column. o The message from this is that FACT is a good place to start from, but you will still need to be aware of the specific circumstances of what you are trying to model.
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o Next, we will design a depropanizer to remove the saleable propane from the deethanizer’s bottoms stream. The composition of the bottoms stream is: Component Ethane Propane i-Butane n-Butane i-Pentane Total:
lb/hr 34 12,078 16,093 28,887 938 58,030
lbmol/hr 1.1 273.9 277 497 13 1,062
Mole % 0.1 25.7 26 46.8 1.4 100
o We will design the column in the same way as we did before, in a separate file, and later we will join them together. o We will start with 35 trays, and feed on tray 15. We’ll set the reflux ratio to 3, the distillate rate to 275, and the condenser pressure to 200 psia, which is the approximate vapor pressure of propane at 120oF. The results from this initial simulation are:
o These results are very good for an initial simulation. We’re recovering 94.5% of the propane, and the tops are 94% pure. Let’s see if we can improve the purity of the tops to less than 1% impure.
Since the overheads of this column will be a lot greater than the overheads of the deethanizer, there shouldn’t be any problems with a low reflux ratio. Let’s try to find RD. • Finding RD: In the beginning stages of process design, you are not expected to know anything definitive about number of trays, reflux ratio, heat duties, etc. You can tentatively set RD to RMIN + 10%. We’ll try playing with some Design Specs to find RD. o The minimum reflux ratio can be estimated by increasing the number of trays dramatically, and changing the feed stage to get the best separation. Note the reflux ratio required for the best separation, and repeat until increasing trays does not change the reflux ratio. This will be your RMIN. o To perform this analysis, go to Design Spec under Flowsheeting Options in the Data Browser. o We’ll define two specs, setting the mass flow rate of propane in the tops and bottoms to our desired separation. o We’ll then vary the reflux ratio (our example will choose 1 to 10) and the distillate rate (we’ll try 274 to 350 lbmol/hr), and increase the number of trays until the reflux ratio satisfying our specs does not get any smaller. Our best results are shown in the Results Summary to the right: o With 600 trays, feeding on stage 100, our reflux ratio is 3. RD is then approximately 3.3. o Plugging in 3.3 as the reflux ratio, our stream results are (right): o These results are excellent – 98.9% recovery of propane, and 97.8% purity. We can try improving these results by performing a Sensitivity Analysis on distillate rate, feed tray, and total number of trays. o After checking out feed tray and number of trays, we get the best results with 35 trays, feeding on tray 11. o Lastly, we will try doing a Design Spec, to see if we could improve our results. Our two specs will be 99% recovery of propane in the tops, and 99% molar purity of the tops. We’ll vary our distillate rate and reflux ratio from 273 to 350, and 1 to 10, respectively. Here are the results:
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With a distillate rate of 274 lbmol/hr and a reflux ratio of 4.2, we have obtained our design specs! • Connecting Columns: o Now that we’ve optimized our two columns, where the feed of the 2nd is the product of the 1st, it is very easy to connect them. All you have to do is select the picture of one column, copy it, and paste it onto the other flowsheet:
o Next, right-click on one stream, we’ll Reconnect Destination of BOTDEETH to DEPROP. Arrows should show up on various locations where you can reconnect the stream to. We will reconnect it to the feed of DEPROP, the depropanizer. We can then delete PROPFEED:
o You may then reinitialize and run the simulation; Aspen may ask you for a new feed stage for the second column. Enter the same stage you had been operating at previously. In addition, you might need to add a heat exchanger or pump in case what you took from the first column is too hot or cold for what you designed for the feed of the second column or the pressure of the second feed doesn’t match the pressure of the first bottoms product. Here are the results of the combined columns:
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o The two columns now produce saleable propane with 99% purity. We can finally call this chapter to a fond end. We realize this is your first time attempt to model distillation columns. It's quite a lot of information to take in, but once you have read through and perhaps tried running this example yourself, you can officially call yourself an Aspen Guru.
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Chapter 5: Aspen Plus Simulation Engine Modeling Reactors Eventually, all components of your design process will need to be modeled in Aspen so that a cost estimate in Icarus can be evaluated; this includes your reactor, too. In many cases you will not be able to model your reactor at all, but it still needs to be represented in Aspen. The simplest way of representing a reactor is by using RStoic type reactor. It is a reactor that separates components and performs reactions based on chemical stoichiometry. The main purpose for this chapter, therefore, will be to give you an introduction to the “black boxes” of Aspen. These are for stating material “x” goes into your device, and “x” (or “y,” in the case of reactors) comes out, and for having your equipment (simple reactors, mixers, splitters, and various solid separators) represented in Aspen. Each can usually be adequately modeled in Aspen, but for your design needs, you don’t need to worry about it, nor should you immediately have enough information to perform such a task. For right now, let’s work with a reactor. RStoic Type Reactor You would usually use RStoic if the kinetics of the reaction are unknown. The only real requirements are that you know the stoichiometry of the reaction and the reaction’s percent molar conversion. RStoic can model reactions occurring simultaneously or sequentially and can determine selectivity and perform heat of reaction calculations. However, it is always recommended that hand-calculations of these are done before modeling, since there is no real basis for comparison. Let’s start with an example. Let’s assume you were in one of the Tuesday ethanol plant design groups and you needed to model your reactor. The typical ethanol reactor operates according to the reaction:
C6H12O6 → 2(CH 3CH2OH) + 2(CO2 ) Assuming that you found in several journal papers or patents with verified documentation that the typical molar extent of reaction for an ethanol plant was 99.5% you should be able to model this reaction in Aspen. (I am making this number up for this example. If you are in a Tuesday group, you will need to find this number or more pertinent information yourself) Solution Methodology: o Open Aspen, select the Reactors tab and place an RStoic reactor on the flowsheet. Connect all required streams (there should be 2), and open the data browser.
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o Add a title if you like, change the report options (Setup à Report Options à Stream Tab) so that you have both molar flow and mass flow reported, and then add your components (there are 3: Ethanol, CO 2 and “Dextrose”). If you were dealing with a whole system, there would obviously be more components but these are the only ones pertinent to our little example. o Select your base thermodynamic method. I chose UNIQUAC, but it isn’t really too important for this example. o Specify the conditions of the feed stream. In this case we can assume that the feed is at normal conditions (68oF, 1 atm), and that the flow rate is 150 lbmol/hr. Under the composition, there is only one component in the feed (Dextrose), so enter it as a 100%. o Next, you should be in the block options. Specify the temperature and pressure at which the reactor should be operating. You may again find, in a paper or journal, a typical temperature that the microorganism facilitating in the reaction operates best around is usually 95-98oF; In that case, let’s use 98oF as our reactor temperature. For the sake of having a number, let’s use 2 atm for the pressure.
o You next need to specify the reaction. You create a reaction by clicking on the New button in the Reactions tab; if the reactor had multiple reactions occurring within, you create an item for each reaction. If the reactions occur in series you would need to check the box below the New button. o You need to now edit the stoichiometry of each reaction that is involved, and this means selecting each reactant or product, and supplying a reaction coefficient. Products have a positive coefficient, but reactants will be negative since they are being used up. (ie: dextrose = -1, ethanol = 2). o The final step is to specify the Molar Extent of Reaction or Fractional Conversion. Either works. The screen could look something like the diagram to the right: o Run the simulation. • Optional : Finding the Heat of Reaction o You might need to specify the heat of reaction so that the heat duty can be accurately transferred to Aspen Pinch or Icarus. o The best way of doing this is either to have Aspen calculate the value (by going to the “Heat of Reaction” tab, selecting “Calculate heat of reaction” and input the reference component), or to perform the calculations by hand and enter the resulting value by selecting “Specify heat of reaction” and inputting it. Here is a little rundown of the requirements for each type of reactor. For Design class you probably should just stick to either RStoic or REquil, and realize that no professor in Design class will seriously expect you to completely model all aspects of your reactor in ASPEN. Reactor RStoic
Conditions/Restrictions o Reaction stoichiometry known; o Reaction kinetics are not important or known; o Conversion is known.
RYield
o Unknown stoichiometry or kinetics; o Yield distributions known.
REquil
o Stoichiometry known; o Some or all reactions reach equilibrium; o OK for one- or two-phase reactors.
o Mass & energy balances (balance); o Equilibrium constants for reactions (Keq).
RCSTR
o Reaction kinetics known; o Contents of the reactor have same properties as outlet stream (Assumes perfect mixing); o Specify temperature or heat duty, calculates the other.
o Mass & energy balances (balance).
Plug
RBatch
o o o o o o
Output (Tab) o Mass & energy balances (balance); o Compositions of outlet stream (phase equilibrium); o Heats of reaction (reactions); o Product selectivities (selectivities). o Mass & energy balances (balance); o Compositions of outlet stream (phase equilibrium); o Outlet component weight distribution factors (weight distribution); o Pseudocomponent results (pseudocomponent breakdown).
Reaction kinetics known; Cooling stream (cocurrent and countercurrent) optional; Rate-based kinetics only. Reaction kinetics known; Rate-based kinetics only; Specify stop criteria.
o Mass & energy balances (balance); o Polymer distributions (distributions). o Mass & energy balances (balance); o Polymer distributions (distributions).
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Chapter 6: Aspen Plus Simulation Engine Using RateFrac for Rate-Based Simulations The purpose of this chapter is to get you acquainted with a new and powerful Aspen tool for systems such with rate-based models such as extractive and azeotropic distillation columns, absorbers and strippers, called RateFrac. We will run through a fairly thorough example, and we will try to give some useful hints for designing your absorber or stripper. RateFrac is a rate-based nonequilibrium model for simulating many types of multistage vapor-liquid operations and simulates actual tray and packed columns, rather than the idealized representation of equilibrium stages. This is a relatively new item in your Aspen arsenal, so understanding how to fully use it can be complicated, but it shouldn’t be completely unfamiliar territory. Problem Statement: Let’s assume first that we have a packed tower absorber and acetone in a stream of air is being absorbed by water. The acetone composition in the inlet air entering at the bottom of the column is 3 mol%, and in the outlet gas leaving the top of the column it should be at most 0.5 mol%. The total entering gas flow rate is 15,000 mol/h, and the pure water inlet flow rate is 45,000 mol/h. You will need to find the outlet acetone composition in the water. The column specifications are as described below: Temperature and Pressure: 68oF, 14.7 psia Diameter: 1.5 ft Height: 7 ft
Solution Methodology: First we need to set up our example simulation. o First of all, open a blank simulation in Aspen. Under the Columns subdirectory, place a RATEFRAC column on the flowsheet. Pressing the arrow next to the RateFrac block will give you a list of icons you can use to represent the column. Choose any icon, but it is recommended that you choose a picture that most accurately represents your desired piece of equipment. o Next attach all required Material Streams: this includes 2 inlet streams, one tops stream and one bottoms stream. If you have a more complicated system you could have to add side product, free water distillate, or pseudo streams. o Note: You are able to move the head of the stream arrow by clicking on it, and dragging it along the edge of the piece of equipment to another location. o Once the flow sheet connectivity is complete, click Next.
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o Under the Setup folder, you can give your model a title, but more importantly you can change the output options for your results to a mole fraction basis. o Note: Remember this is done by going to the Setup folder à Report Options folder à Stream tab and de-checking mole in Flow Basis and checking it in Fraction Basis. Once you are done, click the Next button. o Enter your components. There should be 3 in this example: Air, Acetone, and Water. Usually you will need to Find your components in Aspen’s directory, but you can merely enter these names and the correct item should appear. Click Next when you are done. o Under the Base Method option, enter the Thermodynamic Method you will be using to evaluate the properties of your components. Again, if you are unsure at any time what your property method is, don’t hesitate to use the Thermodynamic Method Tree located in Appendix A. In our example, we will be using NRTL. Click Next. If the Binary Interaction screen appears, just ignore it, click Next again and choose to Go to Next required input step. o On the stream property sheets for each inlet streams, fill in the required fields according to the problem statement, including temperature, pressure, flow rate, and composition. While inputting your values, remember that the molar flow rate is in metric units, and not the English Unit lbmol . Also, in order to enter your compositions in terms of mole fractions, you will need to change the composition basis from MoleFlow to Mole-Frac. o Note: In the inlet vapor stream sheet, if you were given vapor fraction and one other property, instead of both temperature and pressure, you can enter the percent vapor fraction under the missing property. Now, we need to specify information for our Absorber. This includes specifying numbers of “segments,” defining packing types and sizes, and entering column dimensions. o Once you are done, click Next and the input sheet for your Block, the absorption column, should appear. Here you will need to enter the number of segments. o Note: Aspen, for the purpose of easing calculations in evaluating heat and mass transfer rates between contact phases, divides columns into segments; in a packed bed column, these get translated into segments of packing, or a series of trays in a trayed column. More segments usually mean more accuracy, but usually you should stick to one segment per foot or two of packing. In our example, we will use 10 segments, but feel free to use more if it will be more accurate. o You will also need to select the Condenser and Reboiler type. However, since we are modeling an absorber, select the None option for both the condenser and reboiler, and click Next. o Note: Because of this, the Operating Specifications at the bottom of the screen should have both condenser and reboiler duty set at 0, which is what we want. o Next, you will need to enter the pressure, which, as stated in the problem, is 14.7 psia for the first segment. The first segment is the first segment from the top, so first change the view to Top/Bottom if it isn’t already chosen, and enter our pressure as the Top Segment Pressure. When you are done, click Next. o You should be at the Tray Specs object manager screen. Since we are using a packed tower instead of a trayed tower, you can skip this step by simply going to the folder in the data browser. Now, click the New button, and enter the starting segment number (ie. 1) and click OK. o Input the number of the last segment, which in our example is 10, under Ending Segment. Since the packing type was not specified in the problem, you are free to pick any type. We have chosen 1 in. Plastic Pall Rings, but if you wish to have a basis for comparison, there is a listing of information on various packing types in Figures 19-23 and 19-24 of the GPSA Handbook. o Next, we need to input an initial packing height that will be used to calculate our gas and liquid concentrations. This is given in the problem statement as being 7 ft, so when you are done, click Next. o On the next screen, enter the diameter given in the problem statement of 1.5 ft and click Next. o Note: If we were given the percent flooding instead of the column diameter in the problem statement, we could have Aspen calculate the diameter for us by selecting Use calculated diameter. The only requirements are inputting the percent flooding, the number of the bottom segment, and an initial estimate for the diameter. o On the Material Streams screen, you need to specify where the segments the feed and outlet streams are located. Since this is an absorber, the feed and outlet streams all leave either the top (Segment 1) of the column or the bottom (Segment 11) of it, with the gas entering from the bottom and the liquid from the top. o Note: Notice that the number 11 was stated for the bottom segment. This is because the default convention for stream location is Above Segment. You can make it so that the bottom segment is 10 by changing the convention to On Segment as shown to the left. o You have entered all the information Aspen needs, so Run the simulation by clicking Next and hitting OK at the Required Input Complete screen. o You can access your results by clicking on the shown on the next page:
button and choosing the Streams folder. They should look something like the picture
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Unfortunately, our resulting acetone composition in the exiting gas stream doesn’t meet the requirement set by the problem statement of 0.5 mol%. There are a couple of things you can do to correct this. • Change a non-numeric estimate or a variable • Create a Design Spec Changing a Non-Numeric Estimate or a Variable The first option is probably the easiest to do if you have a result that is very close to what you want and you weren’t looking for an answer with a high degree of error tolerance. Though, as a warning, this does not always work to benefit you, so try it only when your results are very close to the spec. If this is not the case, do not attempt at all, since this will be very tedious and potentially unreliable. In our case, this would be a good option, since we have at least one non-numeric variable, that being our type of packing. Any one of the options associated with it could be altered to theoretically give us a better answer; this includes size, type, and material. One possible solution is to change the Pall Rings from Plastic to Metal material. This results in an acetone composition of 0.4 mol% which satisfies the problem statement. But, for the sake of getting more accurate results, let’s try a Design Spec. Creating a Design Spec Creating a design spec for a RateFrac model is practically the same as creating one for a distillation column, so this should be a refresher course for those with distillation experience, or those who have already read Chapter 4. Our wish here is to vary the packing height in the column in order to obtain the desired mole fraction of acetone in the gas outlet stream. o Reopen the data browser and choose the Flowsheeting Options folder and then open the Design Specs folder. o Create a new design spec by clicking the New button on Object Manager Screen that pops up. Click OK to keep the name of DS -1, or change it if you are the discerning type. o Now we have to create a flowsheet variable, which will be the mole fraction of acetone leaving the column in the gas outlet stream. So, click on New, and name it something easily remembered, like ACETON and select OK. On the Variable Definition form, select the category All (or Streams), and fill out the required fields under Reference and click Next. o Under the Spec tab, enter the name of the variable just created, and enter under Target the value of the variable, which is 0.005. Finally, set the error Tolerance, which is the allowable difference between the spec and the target, and it is necessary to stop iteration. Here, we set the tolerance to 0.0001, though you don’t have to adhere to that number. o Under the Vary tab, you will need to specify t he manipulated variable, which, in our case, is the height of packing. Choose Block-Var, then name of your block ABSORBER, and the type of variable that Aspen is changing. In this case, since we are varying the total height of the packing, select HTPACK as the variable. o Note: Don’t get discouraged while looking through this giant list of strangely labeled manipulated variables. Remember that, if you are confused, you can highlight the variable and look at the dialogue box at the bottom of the browser to obtain a description of what each represents. o In the ID1 field enter the column number, which should be 1, and in ID2 enter the starting segment number, which should also be 1. o Next, choose a range for the upper and lower limits for your manipulated variable. A reasonable set of values for Aspen to iterate between is 30 (ft) as your upper limit and 1 (ft) as your lower limit. o Reinitialize and Run your simulation. You can view your results by clicking on Results Summary, then choosing the Streams folder to obtain the resulting stream compositions, or you can click on the Convergence folder to obtain your new packing height. This information should be listed under Variable Value as having a value of 8.06 ft of packing material if everything was done per our instructions. Notice that this is not the actual height of the absorber. You would need to account for the area above and below the equipment.
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• Optional: Modeling Reactions Within Your Absorber Some design groups might have system that incorporates a stripping or absorbing column with one or more reactions occurring inside the model. If you have time and feel the need to have your process as detailed as possible, you might want to model the reactions occurring within your piece of equipment. Reactions are introduced to Aspen in a similar manner as they are in Reactors (Chapter 7). o After you have finished entering your packing material specifications, click on the Reactions sub-directory located below it. If you are unable to find this, look at the picture below. o Enter the starting segment and the ending segment, then, since we haven’t entered the reaction yet, create a new Reaction ID by choosing New from the pull down menu. Again, you can give the reaction a name, but its default should be R-1.
o Under the Reactions main directory, click on the newly created R-1 reaction. You will need to specify the stoichiometry of the reaction. So, simply click on New, and select the reaction type that fits your reaction. o Note: Usually you will be dealing with an equilibrium or conversion reaction, but a salt precipitation is not out of the question. In that specific case, select the precipitating salt from the list, then hit OK. o Now you need to fill out the stoichiometry form. Kinetic/Equilibrium/Conversion type reactions should yield virtually the exact same form as the one in the previous chapter, but if you are dealing with a Salt Precipitation, you merely need to specify the two reacting agents, and their stoichiometric coefficients, that precipitate out the salt. o With your Reaction sheet filled out, merely Run your simulation, and Aspen should model all reactions, as well as create your column. This concludes our discussion on RateFrac columns. We hope that it has been helpful in modeling any absorber or stripper that you have in your design process, or, say, if you are furiously writing up your Stripping column report for UO Lab one or two days before it is due because you were unable to figure out how to get this part to run. In such situations, keep telling yourself “It’s not me, it’s ASPEN’s fault.” That always made my group feel a whole lot better.
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Chapter 7: Aspen Plus Simulation Engine Putting the Pieces Together This will be our final chapter dealing solely with Aspen Plus, and as such, we have decided to give an example that tries to pull together most of the work and information gleaned from the previous chapters into one. We will try to show you how to model an entire process, which you could hopefully translate to your own work. Remember that your system might be a little more rigorous than ours, or not have the exact same pieces of equipment, but it isn’t impossible to model it if you take what you have learned here and try to adapt it to your own specifications. Problem Statement: In the process pictured below, we have a stream of natural gas at 400 psig and 110oF. This stream contains numerous saleable propane, butane, and C5+ (pentanes and above), as well as a large percentage of methane, all of which could be sold at a higher price in its purified liquid state. To extract these, we first cool our feed to -20oF by heat exchanging with our cold residue gas, and then with propane refrigerant, thereby causing condensation of the heavier hydrocarbons. The feed is then introduced to the bottom of an absorber, where chilled lean oil (nonane) is introduced at the top. The lean oil will absorb the heavier hydrocarbons from the gas. The methane-rich Residue Gas can then be resold at a higher price than purchased. The lean oil and hydrocarbons leave the bottom of the absorber, and are introduced to the top of a stripping column, where some propane and lighter hydrocarbons are removed by a vapor stream created by a reboiler. The stripper tops are recycled back and mixed with the feed, whereas the stripper bottoms are then fed into a depropanizer, where saleable propane is removed in the tops. The bottoms are then sent to a debutanizer, where saleable butane is removed. We could, later on in our process, remove any excess nonane from our process with another distillation column and recycle it back to the absorber, but let’s just stick with what we have now. Our goal in this example is to recover more than 85% of the propane in the feed. Its product stream can contain at most 1 mol% ethane.
Solution Methodology: You may realize that you probably don’t have enough information to completely design this system. The absorption/stripping column can be pretty challenging, because, aside from not knowing the column dimensions, you also do not know the flowrates of the absorbing oil or the distillate rate in the stripping column. One of the best suggestions we can give is to use the GPSA Handbook, and find initial estimates for your specific column. Listed below are some good estimates for the first two columns. Absorption and Stripping Column Specifications: (Partially suggested by the GPSA Handbook Fig. 19-20) Absorber Height: 23 ft. Stripper Height: 15 ft. Diameter: 36 in. Diameter: 18 in. Packing: 2 in. Plastic Pall Rings Packing: 1 ½ in Plastic Pall Rings • Setting Up Your Absorber:
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First, let’s setup our flowsheet. Our recommendation is to input one piece of equipment at a time, instead of putting in every piece all at once. It is easier to try to figure out why your column dries up with one column than with 4. Without going into details because this should be somewhat obvious, column optimization is also much easier separately. So, we are only initially going to deal with our first main column, the absorber, and not worry about the recycle or the stripper. However, since there is a recycle, it wouldn’t hurt to add a stream mixer before the feed, as shown below in our flowsheet. Trust me, it will save you time in the long run, when you have actually added the recycle stream.
Next, you need to setup the specifications for your column in the Data Browser (If you are confused on how to do this, or are unsure, see Chapter 7 for details on setting up your absorber column). o Enter all of the components into the component setup page, realizing that, if you are entering iso-Hexane you would need to Find using “Methyl -Pentane.” Make sure to also add n-Nonane. o Enter the Thermodynamic Property Method you will be using. o Note: As well as the recommended Thermodynamic Property Tree, an index of most common abbreviations for the models is given in the online help. However, the list is not complete. A complete list of abbreviations is given in the online manuals, accessible by going to Start -> Programs -> AspenTech AES 11.1 -> Aspen AES 11.1 Documentation. Look for the pdf file Physical Property Methods and Models. This manual will have details of the parameter names and the models. o Enter your stream specifications. Remember that both nonane and feed streams will be at 400 psig and -20oF. We don’t know what our flowrate of nonane will be, but we can take a fairly educated initial guess by using the suggested L/G ratio in the GPSA Handbook Fig. 19-19, and scaling it up for this process. A good starting guess for the mass flowrate of the nonane would be 1,600 lb/hr (this is a number we arbitrarily chose), but, as this number will be overridden later on, try not to marry yourself to any initial guess made. o Note: If you are unsure of the volumetric flowrate of your gas, you can find a pretty reliable online weight, flowrate and volume converter for crude oil, its products, and various hydrocarbons at http://www.processassociates.com/process/basics/oil_vw.htm, or one of many other online unit conversion websites. You could alternatively use Perry’s Chemical Handbook, but using a conversion calculator, such as the one on the website, will save you precious time. o Now you need to enter the number of segments and the conditions for your Reboiler and Condenser (you have neither, so choose None for both). More segments usually translate into more precision, but make your preliminary guess. We are using 10 as our number. o Important Note: From the problem statement, we are missing two important pieces of information: the column pressure, and the flowrate of our absorbing oil, Nonane. Since we are trying to optimize our system, while remaining within the specifications set by the problem, we will first need to choose one of these two variables to keep constant, while we optimize the column via the other variable. In our example, we chose to set the pressure to be our constant, and, later on, tried to find the “best” flowrate of nonane to obtain a desired percentage of our component(s) retained. o So, first you will need to enter the pressure at the top segment, which can often be tricky. If you use a pressure higher than that of your feed streams, your segments could dry up because there isn’t enough driving force into the column, which will give you severe errors, or stop calculations entirely. o Note: Since this wasn’t really stated in the problem, we are going to set some goals for the amount of some components in our packed columns. That said, we will arbitrarily try to achieve a minimum of 95% recovery of propane in the absorber, and between 85 – 90% in the stripper, so that when it gets to the DePropanizer, it has more than enough room to achieve the purity specification, and still maintain 85% recovery.
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o Shown below is a diagram of how some important components will be retained in our absorbing oil when we vary the pressure of the column (We created this using a Sensitivity Analysis after completing our first run, so don’t worry about where this came from right now). o Note: I have only shown the effects on Methane, Ethane and Propane, since we are attempting to retain most of our propane, while getting rid of most of our lighter hydrocarbons. Our heavier hydrocarbons, you will find later on, should have an even better retention rate than propane (near 99%), so, for now, we will mainly be concerned with these three components.
% Component Retained
% Component Retained vs. Column Pressure 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
Methane Ethane Propane
0
100
200
300
400
Column Pressure (psig) For now, let’s assume that the added benefits to our separation gained from using a lower pressure won’t change too dramatically upon changing the flowrate of our absorbing oil. You may notice that, with a column pressure greater than 80 psig, there is no appreciable loss in propane, however a significant amount of our lower weight hydrocarbons are removed. For our current flowrate of nonane (1,600 lb/hr), at 80 psig, we have removed 95.3% of the methane and 48.5% of the ethane, while still retaining 99.4% of our propane. This is a pretty good number to use. o Next, you need to enter your Packing S pecifications, Col umn Diameter, and Feed Locations (remember to use On Segment convention). o Now enter any specifications for the mixer. This includes the stream pressure and temperature conditions. After you are done, Run your simulation. Your results should look something like those shown below.
We have successfully removed a fair amount of the methane and nitrogen, but some of the other components that we wanted to remove (ethane and carbon dioxide) are still present in relatively large amounts.
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We will minimize this by now running a sensitivity analysis on the flow rate of our absorbing oil, but you could take a possibly more difficult path by creating a design spec and solving for the flow rate of a specific component. The latter is potentially more complicated because you have the risk of going crazy from running your design spec and finding it doesn’t work, or it doesn’t get the separation you want, etc. You may take either path, however, we specifically chose to use a sensitivity analysis on the flowrate of nonane because we can see easily see how many components change with varying the nonane flowrate. (For more information on performing a Sensitivity Analysis, see Chapter 2) o Firstly, and always remember to do this before you run your simulation, Reinitialize. You will find out that if you don’t reinitialize you will get fatal errors, and Aspen will terminate its calculations. You probably won’t realize this at first, but if change your input and then run your fairly complicated simulation, Aspen will freak out! You will, at the very least, see warnings everywhere. o Next, go to your Model Analysis Tools folder and then Sensitivity Analysis. Under the Define tab, create a flowsheet variable and input the information for the first component you want to look at; here, you will want to find the “Mole Flow” of Methane in TOSTRIP. When you are done, repeat this for the other two components we were looking at earlier (Ethane and Propane). o Under the Vary tab, you want to input the information for the Mass flowrate of Nonane. I would recommend varying the flowrate from 500-4,000, incrementing by 100. Finally under the Tabulate tab, enter the name of each variable and the order you want their spreadsheet column to appear as. Run the simulation. Our results are shown in the plot to below.
% Component Retained
% Component Retained vs Nonane Flowrate 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
500
Methane Ethane Propane
1000 1500 2000 2500 Flowrate of Nonane (lb/hr)
3000
o By using a flowrate of Nonane of 1,000 lb/hr, we will retain 95.2% of our propane, 36.6% of the ethane, and 3.4% of the methane. Using this new flowrate, run the simulation once more as a check. We have managed to optimize this column just by varying the pressure of the column and the flowrate of the absorber oil. If you want to try varying another aspect of this column (number of segments, packing type, temperature or pressure of the feed, etc) go for it. You might very well achieve a better separation. Using the new chosen flowrate, our results are as follows:
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With your work on the absorber ostensibly completed, you will need to add your second piece of equipment, the stripping column. However, since you need the feed going to both columns at 400 psi, you will require the addition of a pump as well. So, go back to your flowsheet, and attach a Pump (found under Pressure Changers item directory) to the absorber bottoms, then add another RateFrac column to the stream coming from the pump. The diagram on the next page is a visual description. o Note: In the final design, it is probably a good idea to add a pressure changer to the Residual Gas Stream, which exits at 80 psig. Repressurizing your residual gas (or adding a multi-stage mixed-propellant cascade refrigeration unit) will cause it to condense, thus making your methane saleable as well as yielding a 600-fold decrease in volume and making it easy to transport .
% Component Retained
o Reopen the browser and add the setup information to the Pump block. This will really only include the discharge pressure of 400 psig. o Now you need to set up the stripping column. This should be very similar to the manner in which you set up the absorber, except that you now have to include a Reboiler when you get to the Setup page. This also means that, if you have 10 segments, the Ending Segment is now 9. o Note: Instead of using 10 segments, I recommend you try using 5 % Component Retained vs Column – 7. I speak from experience when I say that you will probably Pressure for Initial Distillate Rate of 1.75 receive errors otherwise. I am not trying to dissuade you from 100% using 10, merely saying that it happened when I ran my column. o You have to assign it an Operating Specification, such as distillate 90% flow rate, boilup ratio, reboiler duty, etc, so that it can minimize the 80% number of variables. I personally think that using the Distillate 70% Flow Rate makes it easier to find out later on how large your 60% recycle stream has to be in order to achieve your specifications. A Ethane 50% good initial estimate for your distillate flow rate should be around Propane the size of the molar flow rate of the amount of impurities you are 40% Iso-Butane trying to remove (Methane, Ethane, CO2, N2), so try using a molar 30% distillate rate of 1.75 lbmol/hr. 20% o Again, here we don’t know the column pressure. Shown to the right 10% is a sensitivity analysis plot for % of component retained in the 0% bottoms vs. column pressure. According to the chart, the optimum 0 100 200 300 400 pressure to operate at would be approximately 30 psi, since the Column Pressure (psi) minimum ethane composition occurs there. o Reinitialize, and run your simulation. Hopefully your results match ours below.
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If you re-Run your simulation, you should obtain a bottoms stream fairly free of ethane that yields approximately 85% recovery. One thing to take note of is that the higher the distillate rate you use, the less room the depropanizer has to meet the recovery specification. While the value we used, D = 2.38, was on the higher end of this operating range, this was OK since our depropanizer does a very good job of separating out our propane from our butanes. The final results for our absorber and stripping column with recycle are shown below.
% Component Retained in Bottoms vs Molar Distillate Rate 100% 90%
% Component Retained
While we do manage to remove a lot of the ethane bottoms stream, we also remove more propane than our spec allows. For right now, this is fine, since we will be recycling the stripper vapor back to the feed. So, now connect the STRIPVAP stream to the mixer, reinitialize and run the simulation. The results you obtain are ok, but still do not manage to meet the specifications that we were hoping for. To find the best separation possible, try running a Sensitivity Analysis comparing component molar flow rates to distillate rates. If you do, you should find that the best operating range for your distillate flow rate is between a flow rate of 1.99 to 2.4 lbmol/hr. Our diagram is shown to the right.
80% 70% Methane
60%
Ethane Propane
50%
Iso-Butane
40% 30% 20% 10% 0% 1
1.25
1.5 1.75 2 2.25 Molar Distillate Rate (lbmol/hr)
2.5
To produce saleable propane and butanes, we’ll now need to introduce and design in Aspen the two remaining columns: the DePropanizer and the DeButanizer.
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• DePropanizer o The feed into this column will be the bottoms from the stripper: Component Ethane Propane iso-Butane n-Butane iso-Pentane n-Pentane iso-Hexane n-Hextane n-Heptane CO2 n-Nonane Total
lb/hr 0.43 49.16 17.46 35.00 4.35 14.50 1.73 10.39 6.04 0.017 999.9
lbmol/hr 0.0144 1.1158 .3004 .6022 .0603 .2009 .0201 0.1206 0.0603 .0004 7.7960 10.2914
Mole % 0.14 10.84 2.92 5.85 0.59 1.95 0.20 1.17 0.59 0.004 75.75 100
o You should be decently familiar with how to set up a distillation column in Aspen, so we won’t walk you through the basics. Refer back to Chapter 5 to navigate yourself through the simulation. o After inputting the feed rates, we’ll use the depropanizer in Chapter 5 as a start to simulating this column. We’ll start with 35 trays, feeding on tray 11, with a reflux ratio of 4.2 and distillate rate of 1.3 lbmol/hr. o While running this column, stages below the feed started to dry up, so we lowered the condenser pressure slowly until our column converged at 160 psia. Our first converging run produces the following results: o All of the propane is removed out the tops, but the purity is not at 99% yet. o We tried lowering the distillate rate, and lowering the condenser pressure if the column dried up. While doing this, we maintained total recovery of propane, while increasing the purity of the tops to over 98.7%. We ended up with a condenser pressure of 140 psia (below).
We cannot really improve this separation, since ethane will come out with propane, and and the molar flowrate of ethane is 1.29% of that of propane, we won’t ever reach a 99% purity level in the tops. Lastly, decreasing the size of the column to 30 trays and continuing to feed at tray 16 results in the same level of recovery and purity. • Debutanizer Next, we desire to recover as much of the butanes as possible from the bottoms of the depropanizer, with at least 97% purity. o We’ll start the column with 30 trays, feeding at tray 15, and setting our reflux ratio to 1.5. and distillate rate to 0.91 lbmol/hr. We set the condenser pressure to 100 psia, which is the vapor pressure of iso-Butane at 120oF. o The results from our initial run are shown on the next page.
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o Here we see that we’ve recovered 100% of the butanes, and the purity of the stream is over 99%. Excellent results for the first shot. o We’ll try to make the column a little smaller, by running a Sensitivity Analysis on reflux ratio, and feed tray for several column sizes.
o We were able to decrease the reflux ratio to 0.9, and use 25 total trays, while feeding on tray 9:
Our final results for the debutanizer are almost 100% recovery of iso-Butane, 99.8% recovery of n-butane, and a stream purity of 99%. When you are modeling your process and you find that nothing seems to work, just try making slight adjustments, perhaps in error tolerance, or increment size. Mastery of ASPEN comes in time, but also understand that small things like that have, in reality, major consequences on how ASPEN operates. Fiddling with, or, as I like to call it, “fine-tuning,” can mean the difference in getting severe ASPEN errors on the first iteration and seeing your 7 column system with 3 recycles converge in 4 iterations. If you are still stuck, possibly consider modifying your process slightly. This could include adding a small purge stream, to aid in convergence, or specifying the data associated with a stream. Wow, wasn’t that fun? Sorry for the blatant sarcasm (we thought it would introduce an element of levity), but I am sure you will have as much fun with this example as we did. Recycle streams are easily the worst possible curveballs you will have thrown at you, and to conquer that is seriously quite an accomplishment. We have only worked on a simple case here, but, much like all chemical engineering courses, it is our wish that you are able to adapt what you have learned here to your personal situation. Now that you, hopefully, have overcome the challenge of Aspen, you will need to create a project cost estimate with the help of Aspen Icarus Process Evaluator.
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Chapter 8: Icarus Process Evaluator (IPE) Mapping ISBL and OSBL Once you’ve got your process design down, your manager will probably want to know something about cost. Aspen Icarus provides a more precise cost estimation than that of the FACT Method, and can be used to price everything from your columns, reactors, and other process equipment (ISBL), to the pavement on your parking lot, and fire hydrants on the road (OSBL). It works in a similar fashion as FACT method, by pro-rating each item and area, but does so in a more detailed manner. In evaluating your process, you’re going to need to report ISBL and OSBL. ISBL (Inside Battery Limit) facilities are comprised of major purchased equipment costs, and the costs associated with that equipment. OSBL (Outside Battery Limit) facilities include storage tanks, shipping for feedstock and product, cooling water, steam, fire water, instrument air, flare stack, environmental treating, and other facilities (FACT description). Appraising ISBL and OSBL is done through Aspen Icarus Project Evaluator. Before you begin, the first thing you will need to do is to fix your simulation so that it will import correctly into Icarus. It’s not the simplest thing to remember, but it really should be done to ensure your Aspen file will be properly detailed and analyzed by Icarus. Fixing an Aspen Simulation to Work in Icarus: o With your Aspen Simulation open, go to File à Import, and first change the file type to Templates (*.apt). You will need to open a file located under C:/Program Files/Aspen Tech/Aspen Plus 11.1/GUI/ Templates/Simulations/ called Aspen IPE Stream Properties.apt. o Now go to your Data Browser, open the Components folder, and then open the Specifications subfolder. Click on the Databanks tab, and highlight all of the fields on the right. o Click the button. Reinitialize and Run. This should allow you to properly import your working Aspen files. Now you will need to send your project to Icarus and map your equipment. Mapping ISBL: o Once you have your Aspen Plus file fixed to import, go to File à Send to à Aspen Icarus. On the left-hand side of the screen, you should see the following tabs: o Select the first tab, Project Basis View. In the Basis for Capital Costs folder, click on General Specs. o There is a field labeled Project Type, which indicates what type of a project this is (addition/new). For a plant addition (i.e. for U.O. Labs) change Grass Roots/Clear Field to Inside Plant Addition. o Now, select the center tab, Process View, and left click your design. Select Map to turn it into an Icarus component. You may also click on to map all items. o For columns, when you reach the Project Component Map Preview screen, check out the Configuration option box. This lists ten different configurations (use the arrows to scroll up and down – it only looks like it has two options) to choose from. The detailed descriptions are on page 4-30 of the Icarus manual. o Important Note: Make sure you choose a configuration that does NOT have a split condenser or you will run into problems later on. o You can also add extra equipment to the blocks you are mapping by selecting New Mapping. Click OK to map. o To add extra pumps or peripheral equipment, on the left-hand side of the screen, click on the third tab, Project View. Right-click on the main process area, and Add Project Component. The equipment that is of concern to you at this point is listed under Process Equipment. o Once added, right-click on each item and click Size. o Enter any required input; this includes known flow rates, pressure head required, etc. o Click on (or Run à Evaluation Project) and Evaluate All Items. o Select the area you are dealing with, and on the right side, select List. It should look something like the image to the right. o Right-click on each item and choose Size to view the sizing information Icarus obtained from Aspen. o You can also right-click on each item and choose Item Report to view the sizing and cost data. You can also select multiple items at once to view multiple reports. Go ahead and fix anything that doesn’t look right. o Clicking the Results tab will reveal your overall capital and utilities costs.
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Once you’re confident that you have correctly mapped your ISBL components, you can move on to OSBL. A lot of OSBL tends to be projectspecific, so be careful with sizing. Most importantly, make sure whatever you tell Icarus, as well as what Icarus tells you, makes sense. Mapping OSBL: Icarus is a good tool for estimating the cost of OSBL within your facility. You have probably already used the FACT method to calculate costs of OSBL, and you might find that the numbers are fairly similar. Understand that although Icarus may be more exact with their calculations (FACT only uses percentages of one cost to estimate another), it is also just an estimation based on sizing. For example, it will estimate the size of water facilities, or amount of wiring, based on the area of your plant. Before adding OSBL facilities, note that the following elements are sized with a default value, and will need to be resized: • Utilities (except for Electricity) o These are read from the PROJSUM.ICS reports file. Within the Results tab click on the Project Summary tab (it may be hidden if the middle window isn’t expanded enough – its tab should be next to Executive Summary):
• Area Sizing/Pipe lengths: o Area sizing is needed for infrastructure sizing, and pipe lengths are needed for flare headers, process lines, steam lines, condensate returns, etc. o Note: To proceed with these sizes, adjust your VISIO diagram to scale for the now known equipment sizes. o When your scale is under control, you should be able to read area sizes and your pipe rack with a ruler. In Icarus, Areas refer to objects that contain particular types of mapped equipment, not necessarily areas of your plant. o Piping and wiring lengths are calculated from the center of an Area so be sure that the sizing and type of area specified is accurate. o The number and size of each type of storage tank should have been calculated previously. o The wastewater treatment and settling pond sizes are also calculated depending on what your process requires. • What you do NOT need to add: o On the left-hand side of the screen, click on the Project Basis tab. In the Basis for Capital Costs folder, click on General Specs. There is a field labeled Project Type, where you can indicate if this is a type of plant addition or a brand-new project. You should choose Grass roots/Clear field, which indicates that this is a new project. • Icarus automatically adds certain components, which you do not have any control over, so do NOT add these components:
Project Type Grass roots/Clear field
MAIN Substation Transformers, Switchgears
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Components Included UNIT Control MCC*, SW Operator Center, Transformer Control Center
• Adding OSBL: o On right side of screen, click the Projects tab and the + sign next to Additional Project Components. o Double-click on either inch-pound or metric and a window similar to the one shown below should open in the right-hand window:
o Note: Each is considered an “Area” by Icarus. You can either drag the entire area to your project in the left-hand window, or expand the area and drag certain components. o You might want to create/drag areas for storage, wastewater, main process, and plant area (as big as the whole plant for parking, buildings, roads, etc). o Once you’ve dragged over the components you need, double-click on them in the left-hand window (Project View) to see their default sizes, and make necessary adjustments to their size or Number of identical units (number you wish to purchase). Check the cost, because some items are too project-specific for IPE to calculate, and you may need to research a cost and add it in. Some OSBL facilities to consider: Water • Raw water treating
• De-Aerator
(Make up for BFW + process water + cooling tower) x 1.1 Clarification and/or silica removal may be required if city water is not the raw water source. Boiler feed water (BFW comprises all steam demand – non-recovered condensate or process steam) x 1.1. Demineralization required All water going to steam generators
Electric Power • Incoming power switch yard • Motor control centers.
Total electric power load All electric motors in facility. One or more for process And one or more for OSBL • Un-interruptible Power Sufficient for all instrument and shut down systems and emergency lighting (say 5 kW minimum) • Emergency Generator Say 50 kW minimum Air System (Instrument Air and Yard Air) • Typically air is available to the consumer at 90 psig. Suggest minimum 300 scfm • Compressor(s) Usually two at 100%; one motor and one turbine drive • Air Dryer Usually one sized for 100% + spare • Air Receiver 5 minutes of capacity going from 90 to 60 psig. Fuel Gas • Incoming gas metering station • Fuel gas supply drum (5 minutes of capacity going from 60 psig to 45 psig with main supply source not flowing) • Fuel gas collection drum if process makes useable fuel gas
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Fire Fighting Facilities • Central Fire Pumps • • • • • • •
Central Fire Water Tank Ring Mains Hydrants and monitors Breathing Apparatus Fire Truck Foam inventory Fire Station
200-psig discharge pressure minimum. 1 motor, 1 turbine and 1 diesel minimum) Eight hours at maximum capacity of one fire pump Size for 1500 gpm flow or 8 inch diameter minimum Sufficient to attack the fire from at least two locations (Should have some sort of fire fighting truck. May need full size engine)
Aqueous Effluent Treating Plant • This is very much a function of the plant and the types of aqueous effluents. • As a minimum, require a collection tank, and aerated bio-digester followed by polishing tank or pond and land farm for sludge disposal. If you can hook up to the municipal sanitary sewer, so much the better, if not then you need a separate sanitary waste treating plant. . Flare System • Flare line (s) • Flare Drum (s) • Flare Stack (s) (minimum height 150 feet) • Flare drum pump out pumps Roads, Bridges, Fences, Parking Lots • Should be around 1 – 2 % of total installed cost dependent upon plant size Raw Material Receipt and Product Shipping • Rail siding • Truck loading bays • Pipeline Connection • Warehouse Maintenance Equipment • Cranes • Trucks • Other Vehicles • Welding Machines • Other Special Equipment • Hand Tools Buildings • Central Control Building\ • Product Loading System Control Building • Dispatcher’s Office • Gate House • First Aid • Fire House • Admin Building • Maintenance Machine Shop • Spare Parts Store House These services can be combined in one or more buildings depending upon plant size Spare Parts Commissioning and Start Up Insurance Spares
1% of all equipment and materials Percent of equipment capital cost Fired Heaters @ 10% Heat Exchangers @ 4 % Pumps and Compressors @15% Columns, Vessels, Reactors @ 1%
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Invested Spares
Fire and Safety Equipment @ 14% Instruments @ 10% Electrical @ 13% 25% of major critical un-spared equipment such as compressors and high pressure pumps
Storage Tanks The sizing of storage tanks is a function of the amount of material that is likely to flow in or out of them in a given time period. Feedstock. If a storage tank is expected to receive one lot of feedstock equivalent to 20 rail cars of 25,000 gallons capacity per car, then the tank must be able to receive at least 500,000 gallons of material. Since it would make no sense to run the tank totally empty or totally full, tanks are specified for a "working capacity. This "working capacity" is then multiplied by say 120% to give the actual size of the tank. So for 500,000 gallons of working capacity we would specify a 600,000-gallon tank for this service. Continuing this example, the plant would have at least two 600,000-gallon tanks in the feed system. One tank would be receiving feedstock, and the other would be providing feedstock to the process. If the feedstock delivery method is somewhat erratic, or it more or less tank cars might make up a shipment, then there may be need for further tankage. For added flexibility you might also choose to have three 400,000-gallon tanks rather than two 600,000-gallon tanks. All incoming feedstock is usually tested for quality assurance purposes, either by random samples or by testing a tank of received product. If your feedstock is being delivered by pipeline then it is common to run to a tank and then into the process. You would most likely fill the tank one-day, test it the next and release it for processing on the third. This suggests that you should have three tanks each with say 120% of one day's capacity. Product Product storage is a function of testing policy and shipment size. It is industry practice to run a full lab test on a tank before it is released for shipment. Typically samples are taken from the top, middle and bottom of the tank and are tested both individually and as a composite sample. That means that the tank must have no flow in or out from the time the samples are taken. Any product produced in that period must go to another tank(s). There must be enough tankage for supplying the maximum sized product shipment, plus testing a full tank, plus rundown capacity for product. In lieu of a witty comment, look at this amusing Dilbert anecdote with the full knowledge that we are nearing the end.
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Chapter 9: Aspen Pinch An Introduction to Aspen Pinch While tackling the issue of Heat Integration throughout Design, your main objective is to arrange your process to provide the most economically efficient heat transfer. Once you’ve optimized your design of reactors, separation units and recycles, you have a fixed system of material and energy balances from which you can design a heat exchanger network. Then cooling and heating requirements left over from this scheme must be satisfied by utilities. When designing a heat integration scheme, you should balance two economic factors: operating cost and capital cost. Operating cost is calculated from minimizing utilities, and capital cost is calculated from minimizing the number of heat exchangers. Though you may design an intricate heat exchanger network that minimizes utilities, your capital costs will skyrocket purchasing all those exchangers. Alternatively, with few exchangers and low capital cost, you will have a lot of utility to make up for, and thus your operating cost will soar. Pinch Technology calculations assist the process engineer in achieving the balance by choosing the best streams matches for streams to exchange. Pinch Technology uses thermal data from streams involved in heat integration to assist in designing an efficient network. The first step in heat integration is to define hot and cold streams. “Hot” streams are streams that need to be cooled, and “Cold” streams are streams that need to be heated. Let’s step back and work through a simple example. Problem Statement: Consider the following scheme, with three columns, a reactor, and a mixer and use Aspen Pinch to optimize your heat integration:
Solution Methodology: o First, we’ll develop a stream table that will display the data needed to solve the heat integration problem. o Note: The names for streams that you choose in your flowsheet are not Stream Type going to be the same names that Aspen Pinch chooses. We can easily see that one hot stream is the Reactor Effluent, and two cold R1 Effluent HOT streams are B1 Feed and B2 Bottoms. B1 Feed COLD o In addition, utility is also consumed for each reboiler and condenser, so we B2 Bottoms COLD must include those items in our stream table. B1 Condenser HOT o As you might remember from Chapter 3, you can obtain the heat capacity B1 Reboiler COLD of each element at various temperatures by doing a Property Analysis. For B2 Condenser HOT each stream, we used a weighted average of each stream’s Cp at T 1 and T 2, B2 Reboiler COLD then averaged the two for an average heat capacity. B3 Condenser HOT o The enthalpy of each stream also can be taken from Aspen, subtracting the B3 Reboiler COLD enthalpy of each stream at its initial temperature from its final temperature. o Our completed stream table is shown to the right. Now, we are going to show how performing your heat integration by hand compares to using Aspen Pinch.
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T1 (oF) 200 100 160 135 150 140 160 140 170
T2 (oF) 140 145 200 135 150 140 160 140 170
dH (MMBtu/Hr) -4.12 1.46 4.32 -3.3 5.8 -28.4 28.4 -39.7 35.6
Performing your manual calculations: • Selecting DTmin: As you hopefully remember from Thermo, you cannot transfer heat from one stream to another if the hot stream is at a temperature lower than the cold stream, because there needs to be some driving force. The driving force, DTmin, must be chosen to minimize heat exchange area, and maximize energy recovery. For example, large DT min will ensure a large driving force, and thus a smaller exchanger, but it will lower heat recovery. Typically, DTmin will be between 15 and 30oC. The temperature difference between hot and cold streams at any enthalpy must always have this DTmin to ensure minimal capital cost. For our example, we will use 20oF. • Creating composite curves: Once you have compiled a stream table similar to the one above, it is time to create a composite curve , which is an enthalpy-temperature diagram that compiles the enthalpy changes of hot and cold streams at each temperature. o A composite curve is constructed by graphing each stream as a line, with temperature on the y -axis, and enthalpy on the x-axis. o Start with the stream with the lowest temperatures and zero enthalpy and graph the temperature and enthalpy changes of that stream. Then move on to the next -highest temperature range in your stream table. You will probably find that multiple streams fall within one temperature change interval. In this case, add the streams:
(http://www.cheresources.com/pinchtech4.shtml ) o To make heat transfer possible, the hot and cold streams cannot cross. The graphs should indicate a minimum temperature difference, where the two curves approach each other most closely. The temperatures (one hot, one cold) at which this occurs are called the Pinch Temperature. o Shift your curve horizontally so that at the pinch temperature the DT is the DTmin that you selected earlier. The Pinch Point is the point at which there are the most restrictions in the design of the heat exchanger network. o Drawing horizontal lines across your curves indicates the maximum amount of enthalpy that can be recovered at that t emperature. o The overhangs that occur at the end of the two curves are considered the minimum hot and cold utility. This is the amount of heat that cannot be recovered through internal exchange, and must be provided through external utilities. o The composite curves for our example are shown in the diagram below, where our DTmin is 20oF, leaving us with a pinch temperature around 130oF.
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Your process will probably be a lot more complicated than our example, so hopefully you will have plenty of heat exchange opportunities, and will you not have such high minimum hot and cold utilities! Now that you understand the basics behind Pinch technology, you can move on to designing a heat exchanger network. • A Note on Pinch Technology: Now you can consider where you can design your heat exchangers, and this is where the Pinch Method comes into consideration. Pinch Technology sets up three simple rules to obey for an “optimum” heat exchanger network. The pinch point splits hot and cold streams into two groups: those above the pinch, and those below the pinch. These two groups are considered two separate energy balances. The streams above the pinch require hot utility, and those below the pinch require cold utility. Therefore, the first rule of Pinch Technology is: 1. No heat transfer across the pinch. (See Aspen Pinch’s Training Course Lecture 2 for across pinch diagrams) If the two stream groups (above and below the pinch) are considered separately, you can see that exchanging across the pinch increases utility requirements:
Heat donated from above the pinch to below the pinch, requires utility to add heat above the pinch…
…and utility to remove excess heat below the pinch
The second and third rules of Pinch Technology are: 2. No external heating below the Pinch. 3. No external cooling above the Pinch. Sometimes it is okay to exchange heat across the pinch; it may give you a lower capital cost to do so, outweighing the operational cost you save in a complex heat exchanger network. If you choose to do so, here’s how: o Exchanging hot utility above the pinch with cold utility below the pinch. o Using hot utilities below the pinch. o Using cold utilities above the pinch. Experiment with different combinations of heat exchanger networks to see what gives you the lowest capital and operational costs.
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• Designing a Heat Exchanger Network: Grid Diagrams o Create a Grid Diagram by drawing horizontal lines to represent each stream, like the figure above. Convention dictates that red lines (on top) represent hot streams, and blue lines (on bottom) represent cold streams. Next to each line, indicate the lower temperature on the right, and the higher temperature on the left. As a visual aid, in our example we’ve represented reboilers and condensers as a small line. With a couple general steps, it will be easy to design a heat exchanger network. o First, let’s work above the pinch. Start at the pinch temperature, and look at streams going into the pinch (HOT streams). o Work with the largest stream first. In our example, it is R1 Effluent. Remember that there are different pinch temperatures for above and below the pinch, ½ DTmin from the pinch T in each direction. o When picking streams to match, you must follow a Cp rule: CpIN = CpOUT, This basically indicates that the heat capacity of the stream heading into the pinch must be less than the heat capacity of the stream paired with it (heading out of the pinch). o Note: Streams heading OUT of the pinch can be paired with any stream that follows the Cp rule, with any stream that does not reach the pinch, or with utility (this won’t violate Rules 2 & 3). If you are confused by this, check out Aspen Pinch’s Training Course Lecture 3 for some more detailed graphs. o Once you’ve matched your stream, check it off, and subtract the utility used from the stream you matched it with. Move on to the next biggest, and repeat the same steps until you’ve matched all streams going into the pinch. o Once all hot streams have been matched, place heaters on all cold streams that you have extra utility. o Next, move to streams above the pinch. Follow the same steps, starting with the largest streams heading into the pinch (these should be cold streams now), and move outward. Lastly, place coolers on all hot streams that have extra utility left over. o Note: If you run into problems, such as more hot streams below the pinch or more cold streams above the pinch than you can match, you can experiment with splitting streams. Again, see Aspen Pinch’s Training Course Lecture 3 for more information if you are stuck. Using Aspen Pinch o First you need to open Aspen Pinch (Located by going to Start > Programs > AspenTech > Aspen Engineering Suite > Aspen Pinch 11.1 > Aspen Pinch 11.1). Next, you need to create a Base Directory. Give it a name you will easily remember. o Next, right-click on the folder (your base directory name) on the left hand side of the screen, and select New. Name your new case. o To import your flowsheet, click File > Import > Aspen Plus. Find your flowsheet and press OK. o The “Data Extraction Options” window should pop up. The default selections should be okay, so select OK. Pinch will then begin to extract streams and units, so sit back and give it a few minutes. o When it is done, a stream table should appear that looks like this:
o You’ll
probably notice that Pinch renames your streams according to its own conventions. As Pinch’s manual states: The stream names Aspen Pinch creates are derived from the Aspen Plus block names. The stream name could just be the Aspen Plus name (for heaters/coolers). The letters FD or PR might be added to the end, depending on whether the stream is a feed or a product. If heat is associated with the Aspen Plus block, the word HEAT might be added. Distillation columns use the Aspen Plus column name, with COND and REB added for the condenser and reboiler respectively. If you want to replace the stream name, use the Editing Data Extraction Information dialog box. o Now is a good time to take a look at the Stream Table and acquaint yourself with Aspen’s names. You may also notice streams that Pinch did not consider, for example preheating feed before a column.
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o When you close the “Editing Data Extraction Information” window, you should be asked if you want to add streams. If so, select Yes. • Adding Streams: o In the “Add Stream” window that pops up (shown to the right), name the stream that you would like to add. o Under Supply, select what stream you are referring to. The stream data should appear. o In Target, select the stream again, and change the target temperature. o Hit Calculate Duty and after it is calculated, select OK. o You can add more streams in this manner, or select Finish if you are done. • Grid Diagram: In the toolbar, select Tools > Network Design. It should then prompt you for a DTmin. Enter your value (here we are using 20oF), and select OK. A grid diagram should pop up:
This is Pinch’s version of the diagram we constructed manually earlier. It indicates all of the stream’s names on the left hand side, and their supply and target temperatures on the left and right of each stream, respectively. Note that the hot and cold Pinch temperatures are indicated on the top and bottom of the diagram. Here, the hot pinch is 139.9oF, and the cold is 119.9oF. You can also obtain this graph by clicking . • Creating Composite Curves To create a composite curve in Aspen Pinch, go to Tools > Targeting, or click . Here you should see a diagram that looks like the diagram to the right:
• Obtaining a Report on Minimum Hot and Cold Utilities To obtain your minimum hot and cold utilities, go to Targets > Report > Targeting. Your report should look like the diagram below:
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The pinch temperature is reported as 129.9oF, and the minimum hot and cold utilities are 73.2 and 70.7 MMBtu/hr, respectively. • Entering Utility Data o In the toolbar, select Data > Utilities > General Data (or click on the Case Manager toolbar, and select Utility Data from the Create New Data window). Here, you want to enter what you will use for Hot and Cold Utilities (Cooling Water, Saturated Steam, etc). In Type, you can right-click and select List to see a list of possible utility types. o You will probably have been given, or decided upon amongst groups, standardized values for these utilities, but as guidelines, you should use air for cooling, and steam for heating. The cooling air temperature should be summer ambient temperatures (an average temperature, not the hottest day in history!), and cooling water temperature should be 5-7o below summer ambient temperature. For pressurized steam, you will have the choice of high, medium, and low pressure steam. High pressure steam should be is supersaturated at 600psig, and should be used to power drivers. Medium and low pressure steam is saturated at 150 and 50 psig, respectively. o When deciding on pricing for steam, consider low pressure steam to have the same heating value as fuel. Therefore for every $/Btu fuel costs, low pressure steam will cost the same. Medium pressure steam should be priced $1/Btu greater than low pressure steam, and high $2/Btu greater. o To enter additional data, right-click on a cell and select Insert Record. Once you’ve entered your data, Save and close the Utility Data window. • Creating a HEN (Heat Exchanger Network) o Press to go back to your Grid Diagram. Now you should see streams added for your hot and cold utilities. o To add heat exchangers between streams, right-click on a stream and select Heat Exchanger. You can do the same with your utility streams, symbolizing utility exchangers. o Create another report, and see how close to the minimum hot and cold utilities you have gotten. Overall example: Problem Statement: Here is a simple scheme with a reactor, a separator, and a distillation column:
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Stream
Type
T1 (oF)
T2 (oF)
RX EFFLUENT RX FEED FRAC FEED FRAC BOTTOMS REBOILER
HOT COLD COLD HOT COLD
500 100 100 300 300
100 600 250 100 320
MCp (MMBtu/HrR) 0.12 0.13 .13 .06 .6
dH (MMBtu/Hr) 50 50 20 12 12
o We imported this stream table in to Aspen Pinch, the same as you would add streams (Data > Streams). Then we were able to construct a composite diagram in Pinch, and obtain minimum hot and cold utilities of 23.7 and 3.7 MMBtu/Hr, respectively. (Remember to find these utilities, while composite diagram is up: Targets > Report > Targeting).
Minimum hot utility (23.7 MMBtu/Hr)
Minimum cold utility (3.7 MMBtu/Hr)
o In the composite diagram, you can see that the pinch temperature is at 110oF (also in Target Report). It is also clear that the minimum cold utility is much smaller than the minimum hot utility.
o In the Pinch grid diagram, above, we have represented each of the five streams, as well as a cooling and heating stream. In this case, starting above the pinch, the biggest hot stream is RX Effluent. Thus we will pair it with a cold stream going out of the pinch (above the pinch), so either RX Feed, or Frac Feed. Since RX Feed has a bigger Cp value, we will pair the two streams.
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• Note: By right-clicking on a stream on the grid diagram, and selecting More Information > Duty, you can see the heat duty of the stream on the side of the pinch you are clicking on. o Next, we will subtract 47.5 MMBtu/Hr (RX Effluent) from 50 MMBtu/Hr (RX Feed), leaving 0.3 MMBtu/Hr with RX Feed. RX Effluent can be checked off. o Let’s move on to Frac Bot, which is the next hot stream heading into the pinch. This can be paired with Frac Feed, which has 20 MMBtu/Hr above the pinch, paired with Frac Bot’s 10.8 MMBtu/Hr. We can now check off Frac Bot, and leave 9.2 MMBtu/Hr with Frac Feed. Since both hot streams above the pinch are paired with cold streams, and since there aren’t any cold streams below the pinch, we have to leave the rest up to utility. Therefore we saved a total of 58.3 MMBtu in hot utility. o Since we originally had 62 MMBtu/Hr in hot streams to cool, and 82 MMBtu/Hr in cold streams to heat, we now only have 3.7 MMBtu/Hr (62 – 58.3) in cold utility, and 23.7 (82 – 58.3) in hot utility. We have achieved our minimum utilities! • A Noteworthy Comparison: Manual vs. Aspen Calculations If you try to use both manual calculations and Aspen Pinch in constructing a Heat Exchanger Network, you might notice some differences. Students have noticed that Aspen Pinch might import values incorrectly, so be sure to double check the numbers and make necessary corrections. Also make sure to add any streams Pinch might not have considered. Many different Heat Integration schemes can result from each process, so just play around while following the rules and try to find the best results for your design. • Note: More extensive resources for Pinch Technology can be found at www.cheresources.com/pinchtech1.shtml and www.heatintegration.com. This concludes our final chapter in this tutorial for Aspen Pinch. Our hope is that this tutorial has been useful in your UO and Design classes, that your burdens have been lightened somewhat by having this reference. Please don’t let the little goblins in your head tell you to burn things. Use that fire inside to make a better distillation column, with side streams, a recycle, a fully optimized pre-feed heat exchanger, and a partridge in a pear tree.
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Appendix A: Thermodynamic Property Tree
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Appendix B: References 1)
Aspen Technology Inc, Aspen Plus: Unit Operations Models. Cambridge, 2000
2)
Aspen Technology Inc, Aspen Plus: Aspen Plus User Guide. Cambridge, 2000
3)
Aspen Technology Inc, Aspen Plus: Physical Property Methods and Models. Cambridge, 2000
4)
Aspen Technology Inc, Getting Started Modeling Petroleum Processes. Cambridge, 2000
5)
McCabe, Smith and Harriott, Unit Operations of Chemical Engineering, 5th Edition. McGraw-Hill Publishing, New York, 1993
6)
Perry, et al, Perry’s Chemical Engineer’s Handbook, 7th Edition. McGraw-Hill Publishing, New York, 1997
7)
Gas Processors Suppliers Association, Engineering Data Book, Volumes I and II, 11th Edition. Tulsa OK, 1998
Recommended Websites: 1)
Stanford Chemical Engineering Department, Website, http://chemeng.stanford.edu/~charles/cheme120/Lectures/Lecture6BubbleDew.ppt
2)
Brigitte McNames, Design Procedure for an Absorption Unit on the Aspen Plus Software. Website, http://www.sdsmt.edu/mse/chem-che/chemE/nsfproj/aspen/absorber.pdf
3)
Heat Integration – Pinch Technology Software, Webpage, http://www.heatintegration.com
4)
Chemical Engineering Resources Webpage, http://www.cheresources.com/pinchtech1.shtml
5)
United Feature Syndicate, Inc., Dilbert Comic Strip Webpage, http://www.dilbert.com
6)
Process Associates Website, http://www.processassociates.com/process/basics/oil_vw.htm
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Index Fuel Gas, 39
A Absorber Reactions Within, 28 Simulation of, 26, 29 Aspen Pinch, 42, 45 Adding Streams, 46 AddingUtility Data, 47
G Graphs, 13 Grass Roots/Clear Field, 37 Grid Diagram Construction Aspen Pinch, 46 Manually, 45
RD, 20 Reactions, 24, 28 Reactors, 23 Reboiler, 16, 17 REquil, 24 Residue Analysis, 15 RMIN, 20 RStoic, 23, 24
S B Binary Systems, 14
C Components Graphing, 13 Composite Curve Construction Aspen Pinch, 46 Manually, 43 Condenser, 16, 17 Condenser Pressure, 17 Connecting Columns, 21 Cp rule, 45
D Design Specification Distillation Column, 20 Design Specification Distillation Column. Design Specification Reactor, 27 Distillation Column Optimization of, 18, 19, 21 Simulation of, 16 DTmin, 43
E Electric Power, 39 Ending Segment, 26
F FACT Method, 37 Feedstock Storage, 41 File Sharing, 5, 6, 8 Fractional Conversion, 24
H Heat Exchanger Network Aspen Pinch, 47 Manually, 45 Heat Integration, 42 Heat of Reaction, 24 Hidden Share, 8
I Icarus, 37 Add Project Component, 37 Adding OSBL, 39 Area Sizing, 38 Configuration of Columns, 37 ISBL, 37
M Mapping ISBL, 37 Minimum Hot and Cold Utilities, 43
Sensitivity Analysis Distillation Column, 18 Shipping, 40 Sizing Air System, 39 Buildings, 40 Fire Fighting Facilities, 40 Flare System, 40 Pipe Lengths, 38 Product Storage, 41 Reactors, 40 Settling Pond, 38 Storage Tanks, 38, 41 Wastewater Treatment, 38 Water, 39 Sizing Equipment FACT Method, 17 Icarus, 37 Static IP, 5
T Tertiary Systems, 15 Thermodynamic System, 13 Top Segment Pressure, 26 Tray Specs, 26
O OSBL, 37
P
U
Pinch Point, 43 Pinch Technology, 42 Pinch Temperature, 43 Plot Wizard, 14 Pure Component Properties Analysis, 13
R RadFrac, 16 Rate-Based Simulations, 25 RateFrac, 25
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Utilities Aspen Pinch, 46 Heat Integration, 42 Icarus, 38
