Aspen Plus. Getting Started Modeling Processes with Electrolytes

Transcription

1 Aspen Plus Getting Started Modeling Processes with Electrolytes

2 Version Number: V8.4 November 2013 Copyright(c) by Aspen Technology, Inc. All rights reserved. Aspen Plus, aspenone, the aspen leaf logo and Plantelligence and Enterprise Optimization are trademarks or registered trademarks of Aspen Technology, Inc., Burlington, MA. All other brand and product names are trademarks or registered trademarks of their respective companies. This software includes NIST Standard Reference Database 103b: NIST Thermodata Engine Version 7.1 This document is intended as a guide to using AspenTech's software. This documentation contains AspenTech proprietary and confidential information and may not be disclosed, used, or copied without the prior consent of AspenTech or as set forth in the applicable license agreement. Users are solely responsible for the proper use of the software and the application of the results obtained. Although AspenTech has tested the software and reviewed the documentation, the sole warranty for the software may be found in the applicable license agreement between AspenTech and the user. ASPENTECH MAKES NO WARRANTY OR REPRESENTATION, EITHER EXPRESSED OR IMPLIED, WITH RESPECT TO THIS DOCUMENTATION, ITS QUALITY, PERFORMANCE, MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE. Aspen Technology, Inc. 200 Wheeler Road Burlington, MA USA Phone:(1)(781) Toll Free:(1)(888) URL:

3 Contents WhoShouldReadthisGuide...1 IntroducingAspenPlus...3 WhyUseElectrolyteSimulation?...3 WhatisanAspenPlusElectrolyteModel?...3 SessionsinthisBook...4 UsingBackupFiles...5 RelatedDocumentation...5 TechnicalSupport...5 1ModelingElectrolyteChemistry...7 ElectrolyteChemistryFlowsheet...7 StartingAspenPlus...8 ToStartAspenPlus...8 ToSpecifytheTemplatefortheNewRun...8 SpecifyingComponents...9 ToRenameH2OtoWater...10 TheElectrolyteWizard...10 ToRemoveSaltsfromtheSolutionChemistry...12 ExaminingGeneratedChemistry...14 ToExaminetheGeneratedChemistry...14 ToViewaParticularReaction...14 ToViewtheEquilibriumConstantsfortheSaltReactions...16 SelectingElectrolytePropertyModels...17 EntertheSimulationEnvironment...18 DrawingtheGraphicalSimulationFlowsheet...19 SpecifyingTitle,StreamProperties,andGlobalOptions...20 ToSpecifyFlowsonaMoleBasisforthisSimulation...20 ReviewingReportOptions...21 EnteringStreamData...21 SpecifyingtheFlashBlock...22 SpecifyingAdditionalStreamProperties...22 ToSpecifyAdditionalProperties...22 RunningtheSimulation...23 ExaminingSimulationResults...24 RunningElectrolytesinEO...25 ViewingEOElectrolyteResults...27 ExitingAspenPlus ModelingaSourWaterStripper...31 SourWaterStripperFlowsheet...31 StartingAspenPlus...32 ToStartAspenPlus...32 Contents iii

4 ToSelecttheTemplateOption...33 ToSpecifytheTemplatefortheNewRun...33 SpecifyingComponents...33 TheElectrolyteWizard...33 ToRemoveNH2COO-FormationfromtheSolutionChemistry...34 ToRemovetheSaltsfromtheSolutionChemistry...35 ExaminingGeneratedChemistry...36 ToExaminetheGeneratedChemistry...37 ToViewtheGeneratedChemistry...37 DrawingtheGraphicalSimulationFlowsheet...39 SpecifyingTitle,StreamProperties,andGlobalOptions...40 ToReviewtheReportOptionsSpecifiedintheSelectedTemplate...41 EnteringStreamData...41 SpecifyingtheRadFracBlock...43 To Review the Types of Specifications that You Can Make for RadFrac ToSpecifythatthisColumnOperatesIsobaricallyat15psia...44 ToDefinetheFirstDesignSpecification...45 ToDefineAnotherDesignSpecification...46 ToDefinetheFirstManipulatedVariable...46 ToDefinetheSecondManipulatedVariable...47 ToChangetheReport...47 RunningtheSimulation...48 ExaminingSimulationResults...48 ToViewRadFracResults...49 ToViewDesignSpecificationResults...49 ToViewVaryResults...50 ToViewCompositionProfiles...50 ToViewtheseResults...51 ConvertingtoTrueComponents...53 ToTellAspenPlustoUsetheTrueComponentApproach...53 To Revise the RadFrac Design Specification to Apply to the Apparent CompositionofNH RunningtheTrueComponentSimulation...55 ToViewSelectedResultsoftheTrueComponentSimulation...55 ExitingAspenPlus...56 iv Contents

5 Who Should Read this Guide ThisguideissuitableforAspenPlususerswhowanttostartmodeling electrolytes. Users should be familiar with the procedures covered in Aspen Plus Getting Started Building and Running a Process Model before starting these examples. Who Should Read this Guide 1

6 2 Who Should Read this Guide

7 Introducing Aspen Plus You can easily model all types of electrolyte systems with Aspen Plus, including systems with strong electrolytes, weak electrolytes, salt precipitation, and even mixed solvents. The two sessions in this book- Modeling Electrolyte Chemistry and Modeling a Sour Water Stripper- introduce you to simulating electrolyte systems with Aspen Plus by guiding you through two simulations. Getting Started Modeling Processes with Electrolytes assumes that you have an installed copy of the Aspen Plus software. Why Use Electrolyte Simulation? A rigorous treatment of electrolytes is needed to model many industrial systems. With the Aspen Plus electrolyte capabilities, you can model: Sourwatersolutions WatercontainingdissolvedH 2 S,NH 3,CO 2,HCN, sometimes with additional solvents. Aqueous amines for gas sweetening Water containing DGA, MEA, DEA, ormdeafortheremovalofh 2 SandCO 2. Aqueousacidsorbases HCl,HBr,H 2 SO 4,H 3 PO 4,HNO 3,HF,NaOH,KOH, and others, in aqueous solution, sometimes with additional solvents. Saltsolutions NaCl,KCl,Na 2 SO 4,CaSO 4,CaCO 3 insolution,sometimes with participation. WhatisanAspenPlus Electrolyte Model? InAspenPlus,anelectrolytesystemisdefinedasoneinwhichsomeofthe molecular species dissociate partially or completely into ions in a liquid solvent, and/or some of the molecular species precipitate as salts. These dissociation and precipitation reactions occur fast enough that the reactions Introducing Aspen Plus 3

8 can be considered to be at chemical equilibrium. The liquid phase equilibrium reactions that describe this behavior are referred to as the solution chemistry. In Aspen Plus, solution chemistry is often referred to simply as Chemistry. Solution chemistry has a major impact on the simulation of electrolyte systems. For nonelectrolyte systems, chemical reactions generally occur only in reactors. In Aspen Plus, all unit operation models can handle electrolyte reactions. Solution chemistry also impacts physical property calculations and phase equilibrium calculations. The presence of ions in the liquid phase causes highly nonideal thermodynamic behavior. Aspen Plus provides specialized thermodynamic models and built-in data to represent the nonideal behavior of liquid phase components in order to get accurate results. Sessions in this Book The two sessions in the book illustrate the following concepts: Typesofelectrolytecomponents o Solvents o Solutes o Ions o Salts Typesofreactionsinelectrolytesolutionchemistry o Complete dissociation o Partial dissociation(equilibrium reaction) o Salt precipitation(equilibrium reaction) AutomaticChemistrygeneration Recommendedphysicalpropertymethodsforelectrolytes Methodsforcalculatingandreportingelectrolytesystems o True component approach o Apparent component approach Useofstreamproperties(PropertySets)forelectrolytes 4 Introducing Aspen Plus

9 Followthestepsinthischapter Tolearnhowto 1 Modeling Electrolyte Chemistry Define electrolyte components. Use automatic chemistry generation. Examine Chemistry data. View electrolyte databank parameters. Use the true component modeling approach. 2 Modeling a Sour Water Stripper Modify the generated Chemistry. Use the apparent component approach for electrolytes. Convert from apparent component approach to true component approach. Using Backup Files We recommend that you perform all sessions sequentially, because Chapter 2 assumes you are familiar with the concepts presented in Chapter 1. Aspen Plus provides backup files containing all problem specifications and resultsforeachtutorialsession.youcanusethebackupfilestocheckyour results. Related Documentation Title Aspen Plus Getting Started Building and Running a Process Model Aspen Plus Getting Started Modeling Processes with Solids Aspen Plus Getting Started Using Equation Oriented Modeling Aspen Plus Getting Started Customizing Unit Operation Models Aspen Engineering Suite Installation Manual Aspen Plus Help Content Tutorials covering basic use of Aspen Plus. A prerequisite for the other Getting Started guides Tutorials covering the Aspen Plus features designed to handle solids Tutorials covering the use of equation-oriented models in Aspen Plus Tutorials covering the development of custom unit operation models in Aspen Plus Instructions for installing Aspen Plus and other Aspen Engineering Suite products Procedures for using Aspen Plus Technical Support AspenTech customers with a valid license and software maintenance agreement can register to access the online AspenTech Support Center at: Introducing Aspen Plus 5

10 ThisWebsupportsiteallowsyouto: Accesscurrentproductdocumentation Searchfortechtips,solutionsandfrequentlyaskedquestions(FAQs) Searchforanddownloadapplicationexamples Searchforanddownloadservicepacksandproductupdates Submitandtracktechnicalissues Sendsuggestions Reportproductdefects Reviewlistsofknowndeficienciesanddefects Registered users can also subscribe to our Technical Support e-bulletins. These e-bulletins are used to alert users to important technical support information such as: Technicaladvisories Productupdatesandreleases Customer support is also available by phone, fax, and . The most up-todate contact information is available at the AspenTech Support Center at 6 Introducing Aspen Plus

11 1 Modeling Electrolyte Chemistry In this simulation mix and flash two feed streams containing aqueous electrolytes. You will: Defineelectrolytecomponents. UsetheElectrolytesExpertSystem. ExamineChemistrydata. Viewelectrolytesdatabankparameters. Usethetruecomponentsmodelingapproach. Allow about 45 minutes to do this simulation. Electrolyte Chemistry Flowsheet The process flow diagram and operating conditions for this simulation are shown in the process diagram below: Electrolyte Chemistry. Two feed streams, one containing water and HCl, the other water and NaOH, arefedtoamixer.themixeroutletisflashedtoevaporatewaterandcause NaCltoprecipitate.UsetheMIXERmodelforthemixerandtheFLASH2 model for the flash. 1 Modeling Electrolyte Chemistry 7

12 HCL VAPOR Temp = 25 C Pres = 1 bar 10 kmol/hr H2O 1 kmol/hr HCL NAOH MIX MIXED FLASH Isobaric Molar vapor fraction = 0.75 Temp = 25 C Pres = 1 bar 10 kmol/hr H2O 1.1 kmol /hr NAOH MIXER Isobaric Adiabatic FLASH2 LIQUID Electrolyte Chemistry Starting Aspen Plus To Start Aspen Plus 1 From your desktop, select Start and then select Programs. 2 Select AspenTech Process Modeling <version> Aspen Plus Aspen Plus <version>. TheStartUsingAspenPluswindowappearsinthemainwindow.On thispage,aspenplusdisplayslinksforcommandsandcasessothatyou can quickly enter information or make a selection before proceeding. In this simulation, start a new case using an Aspen Plus template. 3 ClickNewontheStartUsingAspenPluswindow. TheNewdialogboxappears.Usethisdialogboxtospecifythetemplate for the new run. With the template, Aspen Plus automatically sets various defaults appropriate to your application. ToSpecifytheTemplatefortheNewRun 1 UnderInstalledTemplatesinthepanelontheleftsideoftheNew dialog box, click Electrolytes. Then click the Electrolytes with Metric Units template. Information for unit sets, property method, etc. that were pre-defined in thetemplateisshownontherightside,inthepreviewfield. 8 1 Modeling Electrolyte Chemistry

13 2 Click Create to apply this template. IttakesafewsecondsforAspenPlustoapplytheseoptions. TheAspenPlusmainwindowisnowactive. Specifying Components OntheHometaboftheribbon,inRunMode,Analysisisselected,whichis appropriate for this simulation. The Components- Specifications Selection sheet appears in the work space. Theapparent(orbase)componentsforthissimulationareH 2 O,HCl,and NaOH. Because you chose an electrolytes template, water already appears on the sheet. 1 SpecifytheremainingcomponentsbyenteringHCLandNAOHonthe nexttworowsofthecomponentidcolumn. Aspen Plus automatically fills in the rest of the data for these components. 1 Modeling Electrolyte Chemistry 9

14 ToRenameH2OtoWater 1 InthefirstComponentIDfield,selectthetextH2Oandreplaceitwith WATER. 2 Press Enter. TheAspenPlusdialogboxappears,askingifyouwishtorenamethe component. 3 Click Rename. The Electrolyte Wizard UsetheElectrolyteWizardtodefinetheionicspeciesandsaltsthatcanbe generated from the base components entered on the Components- Specifications Selection sheet, and to generate the reactions that occur among these components in the liquid phase. 1 Click Elec Wizard. The Electrolyte Wizard dialog box appears. Use this wizard for defining automatic chemistry generation. Below the list of steps, the Select chemistry databank and reference state section shows the wizard's source of reaction data. 2 From the Electrolytes Wizard dialog box, click Next>. Base Components and Reactions Generation Options appears. There isasetofoptionsforhydrogeniontype.thedefaultishydroniumion H3O+,butHydrogenionH+isalsoavailable.AspenPluscantreat acidicspeciesaseitherh + orh 3 O +.However,useofH 3 O + isstrongly recommended,becausethepresenceofh 3 O + inthesolutionchemistryis better able to represent the phase and chemical equilibrium of almost all electrolyte systems. 3 Click to move all components in the Available components column to the Selected components column Modeling Electrolyte Chemistry

15 4 Click Next> to continue. Generated Species and Reactions appears. Aspen Plus generates all possible ionic and salt species and reactions for theh 2 O-NaOH-HClsystem. In the Reactions section, different style arrows denote the following reaction types: <===> Denotes ionic equilibrium or salt precipitation ---> Denotes complete dissociation In this example, three types of reactions are generated: ionic equilibrium, complete dissociation, and salt precipitation. The dissociation of water and the dissociation of HCl are equilibrium reactions. NaCl precipitation/dissolution is also an equilibrium reaction. In contrast,naohdissociatescompletelyandirreversiblyintona + andoh. 1 Modeling Electrolyte Chemistry 11

16 To Remove Salts from the Solution Chemistry In this simulation, the NaOH and the NaOH*W salts are not relevant. Remove these unnecessary species and their reactions. 5 From the Salts list, select NaOH(S) and NaOH*W(S). 6 Click Remove. Nowthatyouhaveremovedthesesaltsfromthesystem,AspenPlus automatically removes all reactions involving NaOH(S) and NaOH*W(S) from the Reactions list. Note:Anytimeyouknowthatareactioncanbeneglectedbecauseof expected process conditions, remove it from the solution chemistry to decrease the execution time required for your simulation. 7 Next to Set up with property method, select ENRTL-RK. 8 Click Next> to accept the remaining generated species and reactions. Simulation Approach appears, allowing you to choose between the true component approach and the apparent component approach. 9 Select the True component approach option Modeling Electrolyte Chemistry

17 When you use the true component approach, Aspen Plus solves the equations describing solution chemistry simultaneously with the unit operation equations. The unit operations deal directly with the ions and salts formed by solution chemistry. In addition, the true component approach defines how Aspen Plus reports the simulation results. Results are reported in terms of the ions, salts, and molecular components that are actually present, not in terms of the original base components. For example, the generated chemistry for this system specifies that NaOH fullydissociatesintona + andoh.ifyouchoosethetruecomponent approach,aspenpluswillreportnaohflowintermsofna + flowandoh flow,notintermsofthenaohbasecomponentflow.youcanrequestthat composition and flows also be reported in terms of the apparent(base) components. You will do this later in this simulation. 10ClickNext>tomovetothenextstep. Note: If the Update Parameters dialog box appears, click Yes to update the parameters. Summary appears, providing Aspen Plus electrolytes expert system information. 11ClickFinishtoclosethedialogbox. On the Components- Specifications Selection sheet, Aspen Plus has now added the generated electrolyte components. Since all components are databank components, Aspen Plus automatically retrieves all relevant physical property parameters. Note that the salt NACL(S) is identified as type Solid. 12 Click to continue. The Henry Comps- Global Selection sheet appears. The Electrolyte Wizardhasalreadyfilledinthissheet.Usethissheettoseewhich components have been declared as Henry's Law components by the Electrolytes Wizard. If you had additional Henry's Law components in your 1 Modeling Electrolyte Chemistry 13

18 simulation(suchasnitrogenandoxygen),youwouldaddthemtothelist on this sheet. Examining Generated Chemistry In the previous step, the Aspen Plus Electrolyte Expert System automatically generated the chemistry definition for your simulation and named it GLOBAL. To Examine the Generated Chemistry 1 From the Navigation Pane, select the Chemistry folder. 2 From the Chemistry folder, select GLOBAL. The GLOBAL Chemistry sheet appears: To View a Particular Reaction 1 Click1intheReactionstoichiometrygridandthenclickEdit. The Equilibrium Reaction Stoichiometry dialog box appears, with the data for the selected reaction Modeling Electrolyte Chemistry

19 The first equilibrium ionic reaction shown is for water dissociation. 2 Close the dialog box by clicking Close. View the other reactions following the same steps. 3 Click the Equilibrium Constants tab. The optional equilibrium constant coefficients have been automatically retrieved from the Aspen Plus reactions database. The first equilibrium ionic reaction is for HCL dissociation. There are no equilibrium constant coefficients for this reaction. Instead of calculating the equilibrium constant directly, Aspen Plus will calculate the chemical equilibrium from the Gibbs free energy of the participating components. The Aspen Plus reactions database contains over 600 reactions, which cover virtually all common electrolyte applications. 4 Click to the right of the Equilibrium reaction field to select another equilibrium reaction and view the equilibrium constants. 1 Modeling Electrolyte Chemistry 15

20 To View the Equilibrium Constants for the Salt Reactions The reaction for NACL(S) precipitation and its equilibrium constant coefficients are also available on this sheet. 1 For the Equilibrium constants for option, select Salt. 2 If you had additional salt dissolution reactions you could click and toviewthem,butsincethereisonlyonesalt,these buttons are unavailable. For the complete dissociation reaction of NaOH, no constants are shown. Since this is a complete dissociation reaction, it does not require an equilibrium constant. If you had your own equilibrium constant coefficients, you would enter them directly on this sheet. If you had additional reactions to include, you wouldenterthemonthechemistrysheetandthenperhapsadd equilibrium data here Modeling Electrolyte Chemistry

21 Selecting Electrolyte Property Models TheMethods-Specifications Globalsheetisusedtoenterthe thermodynamic methods used to calculate the properties used in the simulation. 1 From the Navigation Pane, open the Methods folder and select Specifications. The Methods- Specifications Global sheet appears. The Electrolyte Wizard has already completed this sheet: The Unsymmetric Electrolyte-NRTL activity coefficient model, ENRTL-RK, is the recommended option set for simulations with electrolytes. ENRTL-RK calculates liquid phase properties from the Electrolyte-NRTL activity coefficient model. Vapor phase properties are calculated from the Redlich- Kwong equation of state. ENRTL-RK can represent aqueous and aqueous/organic electrolyte systems over the entire range of electrolyte concentrations with a single set of binary interaction parameters. In the absence of electrolytes, the model reduces to the standard NRTL model. Aspen Plus contains a databank of binary interaction parameters between water and over 600 electrolyte ion pairs. If the binary interaction parameters between any solvent and an electrolyte ion pair are missing from the databank, and you do not provide values, Aspen Plus provides reasonable default values. 2 Click to continue. The Binary Interaction- HENRY-1(T-DEPENDENT) Input sheet appears. 1 Modeling Electrolyte Chemistry 17

22 UsethissheettoviewtheHenry'sLawparametersretrievedbythe electrolytes expert system. If you had your own Henry's Law parameters, youwouldenterthemonthissheet. 3 Click to continue. The Binary Interaction- VLCLK-1(T-DEPENDENT) Input sheet appears. Use this sheet to view the Clarke density parameters retrieved by the electrolytes expert system. If you had your own Clarke density parameters, you would enter them on this sheet. 4 From the Navigation Pane, select the Methods Parameters Electrolyte Pair folder. The Electrolyte Pair sheets define the electrolyte pair parameters: GMELCC, GMELCD, GMELCE, GMELCN, GMENCC, GMENCD, GMENCE, and GMENCN.Ifyouhadyourownpairparameters,youwouldenterthemon these sheets. 5 Click several times to look at all the electrolyte pair input sheets. Correct representation of physical properties is essential to process modeling. For many simulations, the only physical property specification that you must provide is the selection of a property method. Because the Aspen Plus electrolytes database has data for all components and pairs in this simulation, you don't need to provide any optional specifications or data. Now that the Components and Methods specifications are complete, completetherestoftheflowsheetspecificationsinthesamewayasfor nonelectrolytes. There are no stream or block restrictions in using Aspen Plus electrolytes. You can use all Aspen Plus unit operation models in an electrolytes simulation. Enter the Simulation Environment 1 Click to continue. The Properties Input Complete dialog box appears: The Required Properties Input Complete message appears on the left side ofthestatusbar. Aspen Plus can run the properties calculation if you select the Run Properties Analysis/Setup option in the Required Properties Input Complete dialog box. 2 Select Go to Simulation environment and click OK. -or- Click the Simulation bar on the Navigation Pane to enter the Simulation environment Modeling Electrolyte Chemistry

23 Drawing the Graphical Simulation Flowsheet Nowyouwillbegintobuildtheprocessflowsheet.Sinceyouwillenteryour own block and stream IDs, turn off the default options to automatically assign block IDs and stream IDs. 1 From the ribbon, click File. Click Options. The Options dialog box appears. 2 SelectFlowsheetfromthepanelontheleftsideofthedialogbox. 3 Clear the Automatically Assign Block Name with Prefix and Automatically Assign Stream Name with Prefix check boxes under Stream and unit operation labels. 4 ClickApplyandthenOKtoapplythechangesandclosethedialogbox. 5 PlaceaMixerblock,aFlash2block,andfivematerialstreamstocreate the graphical simulation flowsheet as follows: 1 Modeling Electrolyte Chemistry 19

24 6 From the Navigation Pane, expand the Setup folder, then click the Specifications form. Specifying Title, Stream Properties, and Global Options The Setup- Specifications Global sheet displays defaults which Aspen Plus uses for other sheets. Usethissheettogiveyoursimulationatitle,andtoreviewthestream properties and global options that were set when you selected the Electrolytes with Metric Units template. Itisalwaysgoodpracticetoenteratitleforthesimulation. 1 In the Title field, enter Getting Started with Electrolytes- Simulation 1. 2 Press Enter from the keyboard. The Electrolytes with Metric Units template sets the following global defaults for electrolytes applications: TheInputdataandOutputresultsfieldsaresettoMETCBARunits (Metric units with temperature in degrees Centigrade and pressure in bars) TheFlowbasisfieldissettoMassforallflowinputs. In this simulation, we actually want to use a mole-flow basis. ToSpecifyFlowsonaMoleBasisforthis Simulation In the Flow basis field, click and select Mole Modeling Electrolyte Chemistry

25 Reviewing Report Options To review the report options specified in the selected template: 1 From the Navigation Pane, select the Setup Report Options form. 2 ClicktheStreamtab. Based on the Electrolytes with Metric Units template, Aspen Plus displays the following defaults for calculating and reporting stream properties: o FlowBasis:MoleandMass.AspenPluswillreportthecomponent flowratesonamoleandmassflowbasis.aspenpluswillnotreport composition on a fraction basis or a standard liquid volume flow basis. o Stream Format: ELEC_M. Aspen Plus formats the Stream Summary sheet for electrolytes using Metric units. You will return to this sheet and specify stream properties later in this simulation. 3 Click on the Quick Access Toolbar. Entering Stream Data The HCL(MATERIAL)- Input Mixed sheet appears. Aspen Plus requires two thermodynamic specifications and enough information to calculate the flow rate of each component. 1 OntheHCL(MATERIAL)-Input Mixedsheet,enterthefollowing: Parameter Value Temperature Pressure WATER flow value HCL flow value 25 C 1 bar 10 kmol/hr 1 kmol/hr Youenteredtheflowspecificationsforthisstreamintermsofthebase components(the apparent components). Although you are using the true component approach in this simulation, Aspen Plus can accept stream specifications in terms of the apparent components as well as the true components. Aspen Plus converts the apparent component flow specifications to true component specifications. 2 Click to continue. The NAOH(MATERIAL)- Input Mixed sheet appears. 3 Enter the following data: Parameter Temperature Pressure WATER flow value NAOH flow value Value 25 C 1 bar 10 kmol/hr 1.1 kmol/hr 4 Click to continue. 1 Modeling Electrolyte Chemistry 21

26 Specifying the Flash Block The FLASH(Flash2)- Input Specifications sheet appears. For this simulation, specify the pressure drop and vapor fraction. 1 In the Flash Type field, click beside the first input field, select Vapor Fraction. 2 InthePressurefield,enter0(indicatingthereisnopressuredrop). 3 IntheVaporfractionfiled,enter Click to continue. The Required Input Complete dialog box appears informing you that all requiredinputiscompleteandaskingifyouwanttorunthesimulation. Before running the simulation, request that certain optional properties be included in the stream report. 5 Click Cancel to close the dialog box without running the simulation. Specifying Additional Stream Properties By default, the only component properties that Aspen Plus calculates and reports for this simulation are component mass flows. Since you are using the true component approach, the component flows will be in terms of the components actually present at equilibrium, not the apparent(base) components. To Specify Additional Properties 1 From the Navigation Pane, select the Setup folder and then select Report Options. 2 SelecttheStreamtab. OntheSetup-ReportOptions Streamsheet,youspecifythestream properties to be calculated and reported. For this simulation, request that component mass fractions be calculated and reported. 3 Under Fraction basis, select the Mass check box. You can also define additional stream properties to be calculated and reported, using Aspen Plus property sets. Aspen Plus provides a number of built-inpropertysetsbasedontherunmodeyouselected.youcanalso define your own property sets. In this simulation, you will use a built-in propertysettoreportthebubblepointofeachstream,andasecondbuiltin property set to report the mass fractions of the apparent components in each stream. 4 Click Property Sets. The Property Sets dialog box appears. 5 From the Available property sets column, select TBUBBLE and WXAPP Modeling Electrolyte Chemistry

27 6 Click to move the selected property sets to the Selected property sets column. 7 Click Close. 8 Click to continue. Running the Simulation The Required Input Complete dialog box appears. 1 ClickOKtorunthesimulation. The Control Panel appears. As the run proceeds, status messages appear in the Control Panel. AspenPlushasaspecialdatabankitsearchesonlywhenyouusethe ENRTL-RK option set, as in this simulation. Some physical property parameters in this databank may be different from the parameters in the standard non-electrolyte databanks. The values of the physical property parameters in the special databank were determined to provide a better fit for electrolyte systems, and are not generally applicable. When values are retrieved from this special databank, Aspen Plus generates messages in the Control Panel to inform you what properties are retrieved for which components. 2 UsetheverticalscrollbartotherightoftheControlPanelwindowtosee the messages. When the calculations finish, the message Results Available appears on theleftsideofthestatusbar. 3 Close the Economic Analysis dialog box. Examine the results of your run. 1 Modeling Electrolyte Chemistry 23

28 Examining Simulation Results 1 In the Control Panel, click Check Status. The Results Summary- Run Status Status sheet appears, indicating that the simulation completed normally. 2 OntheHometaboftheribbon,inSummary,clickStreamSummary. The Results Summary- Streams Material sheet appears. 3 Reviewtheresultsonthissheet. Use the horizontal and vertical scrollbars to review results that are off the screen. Since you selected the True Component approach, results for Mass Flow andmassfracareintermsoftruecomponents. Although you specified the flow rates in terms of the apparent components (1kmol/hrHCland10kmol/hrH 2 O),AspenPluscalculatedtheflowrates ofthetruecomponents.instreamhcl,thereisonlyatraceofmolecular HCLremaining.VirtuallyalloftheHClisdissociatedintoH 3 O + andcl. SincetheHCldissociationconsumesamoleofwater,theoverallH 2 Oflow rateisreducedfrom180kg/hr(10kmol/hr)to162kg/hr(9kmol/hr). You also specified stream NAOH in terms of apparent components(1.1 kmol/hrnaohand10kmol/hrh 2 O).NaOHdissociatescompletelyintoNa + andoh.thisisreflectedbythecompletedisappearanceofmolecular NaOH in this stream. StreamHCLandStreamNAOHareaddedtogetherinblockMIXtoform Stream MIXED. Because water dissociation is included as one of the electrolytereactions,mixallowsh3o + andoh - torecombinetoform water. The heat of this reaction raises the temperature of Stream MIXED from 25 ºC(the temperature of both inlets) to 58.6 ºC. This demonstrates that the heat of electrolyte reactions(including the heat of mixing) is automatically included in Aspen Plus electrolytes calculations. Stream MIXED feeds into a Flash2 block where water is boiled off. Because ions and precipitated salts are nonvolatile, Stream VAPOR only contains 24 1 Modeling Electrolyte Chemistry

29 pure water. As the ions are concentrated in Stream LIQUID, the solubility limit of NaCl in water is exceeded, causing 30 kg/hr of molecular NaCl(S) to precipitate. Examine the bubble temperature for stream MIXED and stream LIQUID. Stream MIXED is subsaturated in NACL and stream LIQUID is saturated with NACL. Aspen Plus correctly calculates the bubble point of LIQUID (109 C)asgreaterthanthebubblepointofMIXED(103 C),whichis greaterthantheboilingpointofpurewaterat1bar(99.6 C). Compare the apparent mass fractions for the liquid phase with the true component mass fractions in stream LIQUID. Even though stream LIQUID has precipitated NaCl(S), the apparent mass fraction of NaCl(S) is zero because Aspen Plus does not consider precipitated salts to be apparent components.theapparentmassfractionsoftheionsna +,H 3 O +,OH,and Cl arealsozero.precipitatedsaltsandionscanonlybetruecomponents. Since the precipitated NaCl(S) is not an apparent component, it is represented in the apparent component approach in terms of the original speciesthatcombinedtoformnacl(s):naoh,andhcl.thisiswhythe apparent component basis mass fraction of NaOH is even though the true component basis mass fraction of NAOH is zero. You have now viewed the most relevant results for an electrolytes simulation. 4 This simulation has other results sheets. Use the Navigation Pane to view them, if you choose. Running Electrolytes in EO This topic assumes that you are familiar with running simulations in Equation Oriented mode. If you are unfamiliar with EO, you can either skip this section, or refer to Getting Started Using Equation Oriented Modeling. 1 ClickontheControlPaneltomakeittheactivewindow. Note:IftheControlPanelhasnotbeenopenedintheworkspace,onthe Hometaboftheribbon,inRun,clickControlPanel. 2 ClickthepaneShowEOControltoseeoptionsrelatedtoEOcontrols. The Equation-Oriented Synchronization Status is SM: Results Available.ThismessageindicatesthatyoucanmoveontoEO calculation. 3 Ontheribbon,clicktheEquationOrientedtab.InRunControls,click the arrow beside the input field of Method and then select Equation Oriented. Aspen Plus builds the EO flowsheet and initializes the EO variable values from the SM solution. The following Warnings(or similar ones) are displayed during EO synchronization: * WARNING WHILE INITIALIZING UNIT OPERATIONS BLOCK: "FLASH" (MODEL: "FLASH2") SMALLEST LIQUID MOLE FRACTION OF 1.11E-27 IS LESS THAN THE COMPOSITION TOLERANCE OF 1.00E-15 THIS MAY RESULT IN LOSS OF ACCURACY OF THE SOLUTION. REDUCE THE EO-OPTION FOR THE COMPOSITION TOLERANCE. 1 Modeling Electrolyte Chemistry 25

30 * WARNING WHILE INITIALIZING UNIT OPERATIONS BLOCK: "MIX" (MODEL: "MIXER") SMALLEST LIQUID MOLE FRACTION OF 2.44E-28 IS LESS THAN THE COMPOSITION TOLERANCE OF 1.00E-15 THIS MAY RESULT IN LOSS OF ACCURACY OF THE SOLUTION. REDUCE THE EO-OPTION FOR THE COMPOSITION TOLERANCE. * WARNING WHILE INITIALIZING STREAM BLOCK: "NAOH" SMALLEST LIQUID MOLE FRACTION OF 1.61E-17 IS LESS THAN THE COMPOSITION TOLERANCE OF 1.00E-15 THIS MAY RESULT IN LOSS OF ACCURACY OF THE SOLUTION. REDUCE THE EO-OPTION FOR THE COMPOSITION TOLERANCE. * WARNING WHILE INITIALIZING STREAM BLOCK: "HCL" SMALLEST LIQUID MOLE FRACTION OF 7.89E-18 IS LESS THAN THE COMPOSITION TOLERANCE OF 1.00E-15 THIS MAY RESULT IN LOSS OF ACCURACY OF THE SOLUTION. REDUCE THE EO-OPTION FOR THE COMPOSITION TOLERANCE. To prevent numerical difficulties in the equilibrium equations, liquid compositions of exactly zero are not permitted. When EO is synchronized, allionicandvolatilecomponentsthathaveamolefractionofzeroare reset to the EO Composition tolerance. If this is unacceptable, these components can be removed from EO calculations by specification of Model Comps. EO solution of an electrolyte simulation using the true approach also requires a smoothing of liquid compositions as they approach zero. The smoothed mole fractions are the raw mole fractions after passing through a smoothing equation. Smoothing ensures that the liquid compositions remain positive during physical property evaluations. The smoothing tolerance is defined by the EO option Comp-Tol. The Warning messages above were triggered by streams/blocks that have one or more liquid mole fractions below the smoothing tolerance. When the EO problem is solved, compositions less than the composition tolerance should be considered suspect. If it is important to calculate these compositions as accurately as possible, the composition tolerance should be decreased(in this case to 1.e-27 or smaller). Alternatively, if compositions less that the composition tolerance are unimportant, the solution can be accepted as is. In addition, components with very low concentrations are dropped in EO to simplify the problem. In this case, the HCL component(which is almost entirely dissociated into ions) gets dropped. For this example, we do not want any components to get dropped. For this example, you will solve the problem as is, modify the composition tolerance and option to remove components, and re-solve the problem. 4 Click to solve the EO simulation. Like all EO Options, the composition tolerance can be specified at the global level, the hierarchy level, or the block level. For this example, you willspecifyitatthegloballevel. 5 From the Navigation Pane, select EO Configuration EO Options. The EO Configuration- EO Options Global sheet appears Modeling Electrolyte Chemistry

31 6 In the Remove Components field, select Never. 7 Click Additional Options. The Additional Options dialog box appears. 8 Enter1E-28intheComp-tolfield. 9 Close the Additional Options dialog box. 10Ontheribbon,inRunControls,click,thenclickOKtoreinitializethe EO simulation with the new options. This is required to restore the dropped components. 11 Click to solve the EO simulation with the modified composition tolerance. The simulation solves without warnings. Viewing EO Electrolyte Results When using the true component approach with electrolytes, some additional EOvariablesarecreated.YoucanfindtheseontheEOgridforanyblockor stream. 1 OntheNavigationPane,clickEOConfiguration EOVariablesto display the EO grid. 2 ScrolldowntobringupthestreamresultsforstreamNAOH. 1 Modeling Electrolyte Chemistry 27

32 NAOH.BLK.LIQ_WATER is the smoothed liquid mole fraction for water. NAOH.BLK.LIQ_RAW_WATER is the raw liquid mole fraction for water. Since its value( ) is greater than the composition tolerance, the smoothed valueandtherawvalueareequal. *.BLK.LIQ_HCL is the smoothed liquid mole fraction for HCl. *.BLK.LIQ_RAW_HCL is the raw liquid mole fraction for HCl. Since its value is less than the composition tolerance, the smoothed value and the raw value are not equal. The value is actually slightly negative because it is difficult to convergeonsuchasmallconcentration;thisisthekindofproblemthatthe smoothing algorithm is designed to alleviate. *.BLK.LIQ_H3O+_LOG_ACT is the logarithm of the activity coefficient of H 3 O +.Liquidphaseactivitycoefficientsareusedintheevaluationof Chemistry equilibrium constants. *.BLK.LOG_KEQ_1 is the log of the equilibrium constant for Chemistry reaction number 1. Chemistry reactions are numbered, with equilibrium reactions occurring first, dissociation reactions second, and salt precipitation reactions last. *.BLK.EXT_1 is the extent of reaction for Chemistry reaction number 1. *.BLK.TRUE_NA+isthetruecomponentmolefractionofNa + afterallofthe streams are mixed together. Since these are the results for a single, liquid phasestream,ithasthesamevalueasblk.na Modeling Electrolyte Chemistry

33 Exiting Aspen Plus 1 Fromtheribbon,selectFileandthenselectExit. The Aspen Plus dialog box appears. 2 ClickNo. or ClickYesifyouwanttosavetherun,andenteraRunIDwhenprompted. This simulation(using the apparent approach) is delivered as backup file GSG_Electrolytes\elec1 in the Aspen Plus Examples Library. Use this backup file to check your results. 1 Modeling Electrolyte Chemistry 29

34 30 1 Modeling Electrolyte Chemistry

35 2ModelingaSourWater Stripper Inthissimulation,useadistillationcolumntostripNH 3 andh 2 Sfromasour water feed stream. You will: ModifythegeneratedChemistry. Usetheapparentcomponentapproachforelectrolytes. Defineastreamproperty(PropertySet). Convertthesimulationfromtheapparentapproachtothetrueapproach. Allow about 45 minutes to do this simulation. Sour Water Stripper Flowsheet The process flow diagram and operating conditions for this simulation are shown in the Process Diagram: Sour Water Stripper. Two feed streams, one containingsourwater,theothersteam,arefedtoastrippertoremoveco 2, H 2 S,andNH 3 fromthesourwater.useradfractosimulatethestripper. 2 Modeling a Sour Water Stripper 31

36 Temperature = 190 F Pressure = 15 psi Total flow = 10,000 lb/hr Mass fraction H2S = Mass fraction NH3 = Mass fraction CO2 = Mass fraction H2O = SOURWAT Above Stage 3 VAPOR 9 Theoretical stages + condenser Pressure = 15 psi Estimated molar reflux ratio = 25 saturated vapor distillate Condenser temperature = 190 F STEAM On Stage 10 Pressure = 15 psi Saturated vapor Estimated H2O flow rate = 2,000 lb/hr BOTTOMS 5.0 ppm NH3 Process Diagram: Sour Water Stripper The specifications for the column are: 10theoreticalstagestotal(includesoneforthecondenser). Distillateproductassaturatedvapor(partialcondenser). Initialestimateformolarrefluxratio=25. Noreboiler. FeedstreamSOURWATabovestage3. FeedstreamSTEAMonstage10. Columnpressureof15psia(isobaric). VarytherefluxratioandstreamSTEAMfeedratetoachieveabottoms productwith5ppm(mass)ofnh3andacondensertemperatureof190 F. Starting Aspen Plus To Start Aspen Plus 1 From your desktop, select Start and then select Programs. 2 Select AspenTech Process Modeling <version> Aspen Plus Aspen Plus <version>. The Start Using Aspen Plus window appears in the main window. Aspen Plusdisplayslinksforcommandsandcasessothatyoucanquicklyenter information or make a selection before proceeding. In this simulation, startanewcaseusinganaspenplustemplate Modeling a Sour Water Stripper

37 To Select the Template Option 1 ClickNew. The New dialog box appears. 2 UsetheNewdialogboxtospecifythetemplateforthenewrun.Aspen Plus uses the template you choose to automatically set various defaults appropriate to your application. ToSpecifytheTemplatefortheNewRun 1 Click Electrolytes on the left pane to view the templates for Electrolytes. 2 Select the Electrolytes with English Units template. 3 Click Create. ItwilltakeafewsecondsforAspenPlustoapplythetemplate. Specifying Components The Components- Specifications Selection sheet appears. Theapparent(orbase)componentsforthissimulationareH 2 O,NH 3,H 2 S, andco 2.Becauseyouchoseanelectrolytestemplate,wateralreadyappears on the sheet. 1 Enter the following components in addition to the predefined H2O: Component Component name NH3 H2S CO2 Ammonia Hydrogen-Sulfide Carbon-Dioxide Note: Click Yes if the Update Parameters dialog box appears. 2 Click Elec Wizard. The Electrolyte Wizard dialog box appears. The Electrolyte Wizard UsetheElectrolyteWizarddialogboxtodefinetheionicspeciesthatcanbe generated from the base components you specified on the Components- Specifications Selection sheet, and to generate the reactions that occur among these components in the liquid phase. 1 On the Electrolyte Wizard dialog box, click Next>. 2 Click to move all components in the Available components column to the Selected components column. 3 Click Next> to continue. Generated Species and Reaction appears. 4 Next to Set up with property method, select ENRTL-RK. 2 Modeling a Sour Water Stripper 33

38 AspenPlusgeneratesallpossibleionicspeciesandreactionsfortheH 2 O- NH 3 -H 2 S-CO 2 system. In the generated Reactions list, the following arrows denote different reaction types: o <===>: Denotes ionic equilibrium and salt precipitation o --->: Denotes complete dissociation For this simulation, you know that ammonium carbamate formation can be neglected. To Remove NH2COO- Formation from the Solution Chemistry 5 Select NH2COO in the Aqueous species list. 6 Click Remove. NowthatyouhaveremovedNH 2 COO fromtheaqueousspecieslist, AspenPlusautomaticallyremovesallreactionsinvolvingNH 2 COO from the Reactions list. The salts are also not relevant Modeling a Sour Water Stripper

39 To Remove the Salts from the Solution Chemistry 7 Select NH4HS(S) and NH4HCO3(S) from the Salts list. 8 Click Remove. Note:Anytimeyouknowthatareactioncanbeneglectedbecauseof expected process conditions, remove it from the solution chemistry to decrease the execution time required for your simulation. In this example, only ionic equilibrium reactions are generated. The remaining six generated reactions represent partial dissociation of water, partialdissociationofh 2 StoHS ands 2,partialdissociationofCO 2 to HCO 3 andco 3 2,andpartialdissociationofNH 3 tonh Click Next> to accept the generated species and reactions. Simulation Approach appears, allowing you to choose between the true species approach and the apparent component approach. For this simulation, use the apparent component approach. When you use the apparent component approach, Aspen Plus solves the equations describing solution chemistry as part of the physical property calculations. Aspen Plus modifies the physical properties of the apparent components to account for the reactions described by the solution chemistry. The ions and precipitated salts are not seen by the unit operation models. The apparent component approach also defines how Aspen Plus reports simulation results. The component flow rates for ions are not reported. Instead, Aspen Plus reports the component flow rates of the apparent components as if no dissociation occurred. Forexample,thegeneratedChemistryforthissystemspecifiesthatH 2 S partiallydissociatesintohs - ands -2.Ifyouchoosetheapparent component approach, Aspen Plus will report a value for the mole flow rate ofh2sthatincludesmolecularh 2 S,HS -,ands Select the Apparent component approach option. 11ClickNext>tomovetothenextstep. Note: If the Update Parameters dialog box appears, click Yes to update the parameters. Summary appears, providing Aspen Plus electrolytes expert system information. 2 Modeling a Sour Water Stripper 35

40 12ClickFinishtoclosethedialogbox. On the Components- Specifications Selection sheet, Aspen Plus has now added the generated electrolyte components. Since all components are databank components, Aspen Plus automatically retrieves all relevant physical property parameters. Examining Generated Chemistry In the previous step, the Aspen Plus Electrolyte Wizard automatically generated a set of Henry components, and generated the chemistry definition for your simulation and named it GLOBAL. To Examine the Generated Henry Components 1 Click. The Henry Comps- GLOBAL Selection sheet appears. The light gases CO2,H2S,andNH3haveallbeenaddedasHenrycomponents Modeling a Sour Water Stripper

41 To Examine the Generated Chemistry 1 From the Navigation Pane, select the Chemistry folder. 2 FromtheChemistryfolder,selecttheGLOBAL Inputform. The GLOBAL- Input Chemistry sheet appears. To View the Generated Chemistry 1 SelectaReactionandclickEdit. The Equilibrium Reaction Stoichiometry dialog box appears, with the data for the selected reaction that was generated by the Electrolytes Wizard. 2 Closethedialogboxandviewtheotherreactionsusingthesamesteps. 3 Click the Equilibrium Constants tab. Select the various reactions in the Equilibrium reaction field. All six reactions have equilibrium constants that have been retrieved from the Aspen Plus reactions database. 4 From the Navigation Pane, select the Methods folder and then select Specifications. The Methods- Specifications Global sheet appears. The Electrolyte Wizard has already completed this sheet: 2 Modeling a Sour Water Stripper 37

42 5 EnsurethattheUsetruecomponentscheckboxiscleared. 6 Click to continue. The Binary Interaction sheet appears for the binary parameters HENRY-1. UsethissheettoviewtheHenry'sLawparametersretrievedbythe electrolytes expert system. If you had your own Henry's Law parameters, youcouldenterthemonthissheet. 7 Click to continue. The Binary Interaction sheet appears for the binary parameters NRTL-1. Use this sheet to view the molecule-molecule interaction parameters retrieved by the electrolytes expert system. If you had your own molecule-molecule interaction parameters, you could enter them on this sheet. 8 From the Navigation Pane, select the Electrolyte Pair folder under Methods Parameters. The Electrolyte Pair object manager define the electrolyte pair parameters: GMELCC, GMELCD, GMELCE, GMELCN, GMENCC, GMENCD, GMENCEandGMENCN.Ifyouhadyourownpairparameters,youcould enter them on these sheets. 9 Use ortheexpandtheelectrolytepairfolderonthenavigationpaneto view each electrolyte pair input sheet. 10 Click to continue. The Properties Input Complete dialog box appears: 38 2 Modeling a Sour Water Stripper

43 Correct representation of physical properties is essential to process modeling. For many simulations, the only physical property specification thatyoumustprovideistheselectionofapropertymethod.thisdialog box shows that the Aspen Plus physical property system has many optional capabilities to increase the accuracy of the physical property calculations. Because the Aspen Plus electrolytes database has data for all components andpairsinthissystem,youdon'tneedtoprovideanyoptional specifications or data. Now that the components and properties specifications are complete, complete the rest of the flowsheet specifications in the Simulation environment. Use all Aspen Plus unit operation models in an electrolytes simulation. 11 Select Go to Simulation environment and click OK. Drawing the Graphical Simulation Flowsheet In this simulation, begin to build the process flowsheet. Since you will enter yourownblockandstreamids,turnoffthedefaultoptionswhich automatically assign these IDs. 1 Fromtheribbon,clickFile Options. The Options dialog box appears. 2 ClickFlowsheetfromthepaneontheleft. 3 Clear the check boxes in front of Automatically assign block name with prefix and Automatically assign stream name with prefix. 2 Modeling a Sour Water Stripper 39

44 4 ClickApplyandthenOKtoapplythechangesandclosethedialogbox. 5 Place a RadFrac block and streams to create the graphical simulation flowsheet as follows: Note that the distillate stream is connected to the Vapor Distillate port. 6 GototheSetup-Specifications Globalsheet. Specifying Title, Stream Properties, and Global Options The Setup- Specifications Global sheet displays default Aspen Plus settings and units used for other sheets. Usethissheettogiveyoursimulationatitle,andtoreviewthestream properties and global options that were set when you selected the Electrolytes with English Units template Modeling a Sour Water Stripper

45 The Electrolytes with English Units application type sets the following global defaults for electrolytes applications: ENGunits(Englishunits). MassFlowbasisforallflowinputs. Itisalwaysgoodpracticetoenteratitleforthesimulation. In the Title field, enter Getting Started with Electrolytes- Simulation 2. To Review the Report Options Specified in the Selected Template 1 From the Navigation Pane, select the Setup Report Options form. 2 Select the Stream sheet. Aspen Plus displays the following defaults for calculating and reporting stream properties taken from the Electrolytes with English Units template: o FlowbasisofMass:AspenPluswillreportthecomponentflowrateson amassflowbasis. o ELEC_E Stream Format: Aspen Plus formats the Stream Summary sheet for electrolytes. 3 Click tomovetothenextrequiredinputsheet. Entering Stream Data The SOURWAT(MATERIAL)- Input Mixed sheet appears. Aspen Plus requires two thermodynamic specifications and enough information to calculate the molar flow rate of each component. 1 Enter the following data: Field Temperature Value 190 F 2 Modeling a Sour Water Stripper 41

46 Field Value Pressure 15 psia Total flow Mass lb/hr 2 In the Composition field, click and select Mass-Frac. 3 Enter the following mass fraction values: Component Value H2O NH H2S CO Click to continue. The STEAM(MATERIAL)- Input Mixed sheet appears. 5 In the Temperature field, click and select Vapor Fraction. 6 Enter the following data: Field Value Vapor fraction 1 Pressure 15 psia Composition Mass-Flow H2O Mass flow value 2000 lb/hr 42 2 Modeling a Sour Water Stripper

47 7 Click to continue. Specifying the RadFrac Block The B1(RadFrac)- Setup Configuration sheet appears. To Review the Types of Specifications that YouCanMakeforRadFrac 1 On the B1 Specifications- Setup Configuration sheet, enter the following: Field Value Number of stages 10(9 theoretical stages and condenser) Condenser Reboiler Partial-Vapor None 2 In the Operating specifications section, at the Reflux ratio field, select Moleandspecify25astheinitialestimateforrefluxratio.Theother operating specification is disabled because you can only choose one specification when Reboiler is None. 3 Thesheetiscomplete: 2 Modeling a Sour Water Stripper 43

48 4 Click to continue. TheB1(RadFrac)-Setup Streamssheetappears.Usethissheetto describe how the streams are connected to the RadFrac block. 5 FortheSOURWATfeedstream,enter3intheStagefieldandAbove- Stage in the Convention field. 6 FortheSTEAMfeedstream,enter10intheStagefieldandOn-Stagein the Convention field. Because stream VAPOR is connected to the vapor distillate port, Aspen Plus automatically assigns stream VAPOR as a vapor phase product from stage 1. Similarly, Aspen Plus assigns stream BOTTOMS as a liquid phase productfromstage10.thestreamssheetdoesnotallowflow specifications for distillate product or bottoms product streams. 7 Click to continue. The Pressure sheet appears. To Specify that this Column Operates Isobarically at 15 psia 1 IntheStage1/Condenserpressurefield,enter15psia. 2 Click to continue. The Required Input Complete dialog box appears, indicating that all required input specifications have been entered: 44 2 Modeling a Sour Water Stripper

49 3 ClickCanceltoclosethedialogbox. You can now enter optional specifications. These specifications include setting up two design specifications. The first will be a concentration of 5 ppmnh3inbottoms,andthesecondwillbeacondensertemperatureof 190 F. To Define the First Design Specification 1 Click the Blocks B1 Specifications Design Specifications form from the Navigation Pane. The B1 Specifications Design Specifications object manager appears. 2 ClickNew. The B1 Specifications Design Specifications- 1 Specifications sheet appears. 3 In the Type field, click and select Mass purity. 4 IntheTargetfield,enterthevalue5E-6. 5 Click to continue. The B1 Specifications Design Specifications- 1 Components sheet appears. Use this sheet to specify where this specification is to be applied, and what component and phase it applies to. 6 In the Components area, from the Available components column, select NH3(ammonia) and click. 7 Click to continue. The B1 Specifications Design Specifications- 1 Feed/Product Streams sheet appears. 8 From the Available streams column, select BOTTOMS and click. The B1 Specifications Design Specifications- 1 form is complete: 2 Modeling a Sour Water Stripper 45

50 To Define Another Design Specification 1 From the Navigation Pane, select the Design Specifications folder again. The B1 Specifications Design Specifications object manager appears. 2 ClickNew. The new B1 Specifications Design Specifications- 2 Specifications sheet appears. 3 In the Type field, select Stage temperature. 4 IntheTargetfield,enter190F. 5 IntheStagefield,enter1. 6 Click to continue. The B1 Vary object manager appears. Define two manipulated variables to meet the two design specifications. In thissimulationkeepfreethesteamfeedrateandtherefluxratio specifications provided on the B1 Specifications- Setup sheet. Aspen Plus adjuststhesteamfeedrateandrefluxratiotoachievethenh 3 bottoms concentration specification and the condenser temperature specification. To Define the First Manipulated Variable 1 ClickNewandthenclickOK. The B1 Specifications Vary- 1 Specifications sheet appears. Onthissheet,specifywhichinputvariablesyouwanttokeepfreeinorder to meet the design specifications you provide. 2 IntheTypefield,selectFeedrate. 3 IntheStreamnamefield,selectSTEAM. 4 IntheLowerboundfield,enter50lbmol/hr. 5 IntheUpperboundfield,enter200lbmol/hr. On the STEAM(MATERIAL) form you specified a Mass-Flow for stream STEAM.However,whenyouselectthevariabletypeFeedrateonthe Varyform,AspenPlusassumestheFeedratetobeonamolebasis.In 46 2 Modeling a Sour Water Stripper

51 thiscase,varyingthefeedrateonamolebasisfrom50-200(lbmol/hr)is equivalent to varying the Mass flow from (lb/hr). To Define the Second Manipulated Variable 1 FromtheNavigationPane,clicktheB1 Specifications Varyfolder again. 2 ClickNew. 3 IntheTypefield,selectRefluxratio. 4 IntheLowerboundfield,enter15. 5 IntheUpperboundfield,enter50. AswithFeedrate,AspenPlusalwaysvariestherefluxratioonamole basis,evenifyouspecifyamassrefluxratioontheb1specifications- Setup form. 6 Click to continue. The Required Input Complete dialog box appears, indicating that all required specifications are complete. 7 Click Cancel. By default, Aspen Plus displays results only for stages that have feeds, products, heaters, or a maximum or minimum flow, and for the stages immediately above and below those stages. Modify the default stage report so that results are reported for all stages. To Change the Report 1 FromtheNavigationPane,selectBlocks B1 Analysis Report. The B1 Analysis- B1.Report Property Options sheet appears. 2 Click the Profile Options tab. 3 OntheProfileOptionssheet,intheStagestobeincludedinreport section, select All Stages. By default, Aspen Plus reports only temperature, pressure, total mole flows, enthalpy, mole fractions and K-values for the selected trays. 2 Modeling a Sour Water Stripper 47

52 Request that additional properties be reported by selecting additional property sets on the Properties sheet. Specify that Aspen Plus report ph and true component mole fractions using two built-in Property Sets. 4 Click the Properties tab. 5 IntheDefinedpropertysetscolumn,selectPHandXTRUEandclick to move the selected property sets into the Selected property sets column. Running the Simulation 1 Click to continue. The Required Input Complete dialog box appears. 2 ClickOKtorunthesimulation. The Control Panel appears. Astherunproceeds,messagesappearintheControlPanel.Ittakesafew moments for Aspen Plus to process input specifications and perform the simulation. As in simulation 1, Aspen Plus displays messages indicating that some properties have been retrieved from a special databank. When the calculations finish, the message Results Available appears in the leftsideofthestatusbaratthebottomofthemainwindow. 3 When the message Results Available appears in the status bar, click CheckStatustoviewtheresultsofyourrun. Examining Simulation Results Aspen Plus generates many results for this simulation. Examine any results thatareofinteresttoyou.thisexampleguidesyouthroughareviewofsome of the simulation results Modeling a Sour Water Stripper

53 To View RadFrac Results 1 In the workspace, click the Main Flowsheet tab. 2 On the flowsheet, select the RadFrac block. 3 Click the right mouse button and select Results. The B1(RadFrac)- Results Summary sheet appears. This sheet reports the flows, temperatures, and duties for the top and bottom stage of the column. 4 ClickthetabsontheB1(RadFrac)-Resultsformtoviewmoreresults. TheBalancesheetappears.Theblockisinmassbalance,butisnotin enthalpy balance, because heat is being removed from the RadFrac block inthecondenser.theenthalpywouldhavebalancedifyouhadassigneda heat stream to the condenser duty. AsummaryoftheresultsofthedesignspecificationsislocatedontheB1 Specifications Design Specifications Results sheet. This sheet reportsthespecifiedvaluesandthefinalvaluesforallofthedesign specifications. To View Design Specification Results 1 FromtheNavigationPane,selecttheBlocks B1 Specifications Design Specifications folder. 2 Click the Results tab to view the Design Specification results. 2 Modeling a Sour Water Stripper 49

54 Asummaryoftheresultsofthemanipulatedvariablesislocatedonthe B1 Specifications Vary Results sheet. This sheet reports the specified bounds and the final values for all manipulated variables. To View Vary Results 1 FromtheNavigationPane,selecttheBlocks B1 Specifications Vary folder. 2 ClicktheResultstabtoviewtheVaryresults. The B1(RadFrac)- Profiles Compositions sheet lists the mole fractions of each component for every stage. Since you chose the apparent component approach for this simulation, only the apparent components are reported. The exact values that the vary determines may vary slightly depending on the convergence path. To View Composition Profiles 1 FromtheNavigationPane,selecttheBlocks B1 Profilesform. 2 Click the Compositions tab to view the results. 3 In the View field, click and select Liquid Modeling a Sour Water Stripper

55 The B1(RadFrac)- Profiles Properties sheet reports the actual composition of molecular components and ions. To View these Results 1 ClickthePropertiestab.Youmayneedtoclickthearrows atthe rightendoftherowoftabstoreachit. ConsidertheresultsforStage1.ThetruecompositionofNH3andNH4+ sumto onstage1.thisvalueisslightlydifferentfromthe apparent mole fraction of NH3 reported on the Compositions sheet: This slight difference is caused by the solution chemistry. 2 Modeling a Sour Water Stripper 51

56 Ingeneral,thetotalnumberofmolesisnotconservedbysolution chemistry. In this simulation, the fourth equilibrium reaction consumes 3 moles of reactants and generates two moles of products: CO2 2 HCO H 2O H 3O 3 The total number moles on an apparent component basis will be different fromthetotalnumberofmolesonatruecomponentbasis.thusx NH3 (apparentbasis)isnotexactlyequaltox NH3 (truebasis)+x NH4+ (true basis). TheliquidcompositionofapparentNH3onstage1is: X NH3 = Select the Compositions sheet. 3 IntheViewfield,selectVapor. ThevaporcompositionofapparentNH3onstage1is: Y NH3 = Fromthesetwovalues,youcancalculateaK-valueforNH3onstage1: K=Y NH3 /X NH3 = Select the K-Values sheet. TheK-valueforNH3onstage1is5.35.Theseresultsdemonstratethat when you use apparent components, Aspen Plus also reports the K-values calculated by RadFrac(or any flash) on an apparent basis Modeling a Sour Water Stripper

57 Converting to True Components Choosing between the true component approach and the apparent component is a matter of personal preference. For all simulations, the simulation results should be equivalent. To demonstrate this, you will convert this simulation from the apparent component approach to the true component approach. To convert the simulation to the true component approach, you must tell AspenPlustousethetruecomponentapproach,andyoumustadaptthe Design Specification in the RadFrac block(5 ppm mass apparent NH3 in the bottoms). ToTellAspenPlustoUsetheTrue Component Approach 1 Click the Properties bar on the Navigation Pane to enter the Properties environment. 2 From the Navigation Pane, click Methods Specifications. 3 OntheMethods-Specifications Globalsheet,selectthecheckbox next to Use true components. For the RadFrac block, you entered a desired specification of 5.0 ppm (mass) of apparent NH3 in the bottoms. However, this specification is incorrect for the true component approach, because a significant portion oftheapparentnh3ispresentasnh4 +. To Revise the RadFrac Design Specification to Apply to the Apparent Composition of NH3 1 Click the Simulation bar on the Navigation Pane to enter the Simulation environment. Click the Main Flowsheet tab in the workspace. 2 On the flowsheet, right-click on the RadFrac block and select Input. 3 From the Navigation Pane, under the Specifications folder, select the Design Specifications folder. The Design Specifications object manager appears. 4 SelectDesignSpecID1,andclickEdit. The B1 Specifications Design Specifications- 1 Specifications sheet appears. Modify Design Specification 1 to specify a stream property for the apparent mass fraction of NH3. 5 In the Type field, click and select Property value. 6 IntheTargetfield,enter5E-6. 7 InthePropertysetfield,clicktherightmousebuttonandselectNew. 8 IntheNewItemdialogbox,enterXNH3APPasthenewpropertyset name. 9 ClickOK. 2 Modeling a Sour Water Stripper 53

58 10 Click the Feed/Product Streams tab. 11 In the Available streams column, select BOTTOMS and click to move the stream to the Selected stream column. 12 From the Navigation Pane, click Property Sets XNH3APP. The Property Sets- XNH3APP Properties sheet appears. Aspen Plus usesthispropertysettocalculatetheapparentmassfractionofnh3in the liquid phase. 13 Click Search. 14 In the Search Physical Properties dialog box, enter apparent component mass fraction in the box under 1 Type physical property youwanttofindandthenclicksearch. 15 Click Search. The system searches for valid physical properties and displays them in the fieldunder2clickoneormorepropertiesyouwant,andthenclick Add. 16 Select Apparent component mass fraction(alias WXAPP) from the search results. 17 Click Add. The system adds the selected physical property and displays it in the field under3clickoktoaccepttheselection. 18ClickOK. 19 Select the Qualifiers sheet. 20 In the Phase field, click and select Liquid. 21 In the Component field, click and select NH3. 22 Click to continue. The Required Properties Input Complete dialog box appears Modeling a Sour Water Stripper