Thermodynamics and HYSYS - Cours en Ligne Chimie ParisTech
Contents
1. Chloroform _ 583 617 285 388 4571 081 12163 Immiscible 629 221 Seal 396 209 4293 937 12 163 Individual Pair 1289 218 1137 062 1332312 12 163 62226 371 5642 370 109 634 12 163 Unknowns Only 1522574 1430 040 2414 426 1863 905 o s258 197751 120524 e2208 ooon _AlLBiaies Reset Params l R 1 98721 gt cal gmol K Delete Name Stripper Property Pkg NATL J The interaction parameters for each binary pair will be displayed You can overwrite any value or use one of the estimation methods Note that the K Kj rule does not apply to Activity Model interaction parameters The UNIFAC UNIquac group Functional Activity Coefficient method is a group contribution technique using the UNIQUAC model as the starting point to estimate binary coefficients This however should be a last solution as it is preferable to try and find values estimated from experimental data Thermodynamics and HYSYS 15 Estimation Methods When using Activity Models HYSYS provides three interaction parameter estimation methods Select the estimation method by choosing one of the radio buttons in the Coeff Estimation window The options are e UNIFAC VLE e UNIFAC LLE e Immiscible You can then invoke the estimation by selecting one of the available cells For UNIFAC methods the options are e Individual Pair calculates the parameter2. for the thermodynamic model The xy phase diagrams on the next page figures 1 and 2 illustrate the homogeneous behaviour when no parameters are available and the heterogeneous azeotropic behaviour when properly fitted parameters are used The majority of the default interaction parameters for activity coefficient models in HYSYS have been regressed based on VLE data from DECHEMA Chemistry Data Services 19 20 20 Thermodynamics and HYSYS Fig 1 Interaction Parameters set to 0 x y Plot for di i P Ether and H2O 0 8000 0 6000 0 4000 0 2000 y Mol Fraction of di i P Ether 0 0 0 2 0 4 0 6 0 8 1 0 x Mol Fraction of di i P Ether Fig 2 Using the Default HYSYS Interaction Parameters x y Plot for di i P Ether and H2O 0 8000 0 6000 0 4000 y Mol Fraction of di i P Ether 0 2000 0 0 0 2 0 4 0 6 0 8 1 0 x Mol Fraction of di i P Ether Thermodynamics and HYSYS 21 Exercise 2 Phenol H20 Binary This binary shows the importance of ensuring that properly fitted interaction parameters for the conditions of your simulation are used The default parameters for the Phenol H20 system have been regressed from the DECHEMA Chemistry data series and provide very accurate vapour liquid equilibrium since the original data source was in this format However the Phenol Water system is also shown to exhibit liquid liquid behaviour A set of
3. 8 25 Thermodynamics and HYSYS Fig 5 Without Regressed CC6 H20 Interaction Parameters Fig 6 With Regressed CC6 H20 Interaction Parameters
4. CC6 and H20 Using this data and the regression capabilities within DISTIL an AEA Technology Engineering Software conceptual design and thermodynamic regression product you can obtain new interaction parameters The temperature dependent B j parameters are to be left at 0 and the alpha term is to be set to 0 2 for the CC6 H20 To implement these parameters proceed with the steps on the following page CO Ot Thermodynamics and HYSYS 25 Return to the Basis Environment by pressing the Enter Basis Environment button Open the Fluid Package view and move to the Binary Coeffs tab Enter the data in the Aj matrix as shown here H20 3719 395 286 977 4843 376 _ _3589 973 33395 5645 254 Benzene _Cyclohexane Select the Alpha C radio button Enter a CC6 H20 alpha value of 0 2 Close the Fluid Package view Return to the Simulation Environment Open the stream Benzene CC6 H20 How many phases are now present What are the compositions The figures on the following page figures 5 and 6 clearly show the behaviour of the ternary system Without the regressed CC6 H20 binary the thermodynamic property package incorrectly predicts the system to be miscible at higher CC6 concentrations This prediction is correct given properly regressed CC6 H2O parameters References 1 Schreinemakers F A H Z Phys Chem 35 459 1900 2 Hill A E and Malisoff W M J Am Chem Soc 48 1926 91
5. NIFAC is a handy tool to give initial estimates for activity coefficient models Nevertheless keep in mind the following Group contribution methods are always approximate and they are not substitutions for experimental data UNIFAC was designed using relatively low molecular weight condensable components thus high boilers may not be well represented using temperatures between 0 150 C and data at modest pressures Thermodynamics and HYSYS e Generally UNIFAC does not provide good predictions for the dilute region Choosing an Activity Model Again some general guidelines to consider e Margules or van Laar generally chosen if computation speed is a consideration With the computers we have today this is usually not an issue May also be chosen if some preliminary work has been done using one of these models e Wilson generally chosen if the system does not exhibit phase splitting e NRTL or UNIQUAC generally chosen if the system exhibits phase splitting e General NRTL should only be used if an abundant amount of data over a wide temperature range was used to define its parameters Otherwise it will provide the same modelling power as NRTL Exploring with the Simulation Proper use of thermodynamic property package parameters is key to successfully simulating any chemical process Effects of pressure and temperature can drastically alter the accuracy of a simulation given missing parameters or parameters fitted
6. Thermodynamics and HYSYS 2000 AEA Technology plc All Rights Reserved 1 Chem 2_5 pdf 2 Thermodynamics and HYSYS Thermodynamics and HYSYS Workshop One of the main assets of HYSYS is its strong thermodynamic foundation Not only can you use a wide variety of internal property packages you can use tabular capabilities to override specific property calculations for more accuracy over a narrow range Or you can use the functionality provided through OLE to interact with externally constructed property packages The built in property packages in HYSYS provide accurate thermodynamic physical and transport property predictions for hydrocarbon non hydrocarbon petrochemical and chemical fluids The database consists of an excess of 1500 components and over 16000 fitted binary coefficients If a library component cannot be found within the database a comprehensive selection of estimation methods is available for creating fully defined hypothetical components HYSYS also contains a regression package within the tabular feature Experimental pure component data which HYSYS provides for over 1000 components can be used as input to the regression package Alternatively you can supplement the existing data or supply a set of your own data The regression package will fit the input data to one of the numerous mathematical expressions available in HYSYS This will allow you to obtain simulation results for specific thermophysical pro
7. able Extended and General NRTL The Extended and General NRTL models are variations of the NRTL model simple NRTL with a complex temperature dependency for the aj and aj terms Apply either model to systems The general NRTL model is particularly susceptible to inaccuracies if the model is used outside of the intended range Care must be taken to ensure that you are operating within the bounds of the model No interaction between non condensable component pairs is taken into account in the VLE calculations Thermodynamics and HYSYS 11 e with a wide boiling point range between components e where you require simultaneous solution of VLE and LLE and there exists a wide boiling range or concentration range between components Extreme caution must be exercised when extrapolating beyond the temperature and pressure ranges used in regression of parameters Due to the larger number of parameters used in fitting inaccurate results can be obtained outside the original bounds Chien Null Chien Null is an empirical model designed to allow you to mix and match models which were created using different methods and combined into a multicomponent expression The Chien Null model provides a consistent framework for applying existing activity models on a binary by binary basis In this manner Chien Null allows you to select the best activity model for each pair in the case For example Chien Null can allow the user to have a b
8. bition PR Chemical Systems Activity Models PRSV HF Alkylation PRSV NRTL Contact Hyprotech TEG Dehydration with PR Contact Hyprotech Aromatics Thermodynamics and HYSYS 5 and HYSYS 5 Equations of State For oil gas and petrochemical applications the Peng Robinson EOS PR is generally the recommended property package HYSYS currently offers the enhanced Peng Robinson PR and Soave Redlich Kwong SRK equations of state In addition HYSYS offers several methods which are modifications of these property packages including PRSV Zudkevitch Joffee ZJ and Kabadi Danner KD Lee Kesler Plocker LKP is an adaptation of the Lee Kesler equations for mixtures which itself was modified from the BWR equation Of these the Peng Robinson equation of state supports the widest range of operating conditions and the greatest variety of systems The Peng Robinson and Soave Redlich Kwong equations of state EOS generate all required equilibrium and thermodynamic properties directly Although the forms of these EOS methods are common with other commercial simulators they have been significantly enhanced by Hyprotech to extend their range of applicability e The Peng Robinson property package options are PR Sour PR and PRSV e Soave Redlich Kwong equation of state options are the SRK Sour SRK KD and ZJ For the Chemical industry due to the common occurrence of highly non ideal systems the PRSV EOS may be considered I
9. efore care must be exercised when simulating LLE as almost all the default interaction parameters for the activity coefficient models in HYSYS are for VLE Thermodynamics and HYSYS 23 Fig 3 Using the Default VLE Interaction Parameters x y Plot for H2O and Phenol 0 6000 0 4000 y Mol Fraction of H2O 0 2000 0 0000 4 00 02 04 06 08 10 x Mol Fraction of H20 Fig 4 Using the Fitted LLE Optimizied Interaction Parameters x y Plot for H2O and Phenol 1 000 sses 6 6 oo 7 0 8000 0 6000 0 4000 y Mol Fraction of H2O 0 2000 0 0000 44 o0 02 04 06 08 10 x Mol Fraction of H2O 23 24 24 Thermodynamics and HYSYS Exercise 3 Benzene Cyclohexane H20 Ternary This example again illustrates the importance of having interaction parameters and also discusses how the user can obtain parameters from regression To illustrate the principles do the following 1 Open the case Ternary hsc 2 Enter the following stream conditions for Benzene CC6 H20 Conditions Temperature 25 C Pressure l atm Composition Benzene 20 mole H20 20 mole CC6 60 mole How many phases are present __ To provide a more precise simulation the missing CC6 H20 interaction parameter has to be obtained Fortunately some data is available at 25 C giving the liquid liquid equilibrium between
10. for different conditions HYSYS is user friendly in allowing quick viewing and changing of the particular parameters associated with any of the property packages Additionally the user is able to quickly check the results of one set of parameters and compare against another 17 18 Thermodynamics and HYSYS E Exercise 1 Di iso Propyl Ether H20 Binary This example effectively demonstrates the need for having interaction parameters Do the following 1 Open case DIIPE hsc 2 Enter the following conditions for stream DITPE H20 Conditions Vapour Fraction 0 0 Pressure latm Molar Flow 1 kgmole h 1 lbmole hr Composition di i P Ether 50 mole H20 50 mole What phases are present 3 Close the stream view and press the Enter Basis Environment button 4 Select the Binary Coeffs tab of the Fluid Package Notice that the interaction parameters for the binary are both set to 0 0 5 Press the Reset Params button to recall the default NRTL activity coefficient model interaction parameters Close the Fluid Package view Return to the simulation environment by pressing the Return to Simulation Environment button 8 Open the stream view by double clicking on the stream DIIPE H20 What phases are now present What is the composition of each Thermodynamics and HYSYS 19 Clearly it can be seen how important it is to have interaction parameters
11. he NRTL equation called the alpha term or non randomness parameter represents the inverse of the coordination number of molecule i surrounded by molecules j Since liquids usually have a coordination number between 3 and 6 you might expect the alpha parameter between 0 17 and 0 33 The van Laar equation implemented in HYSYS has two parameters with linear temperature dependency thus making it a four parameter model In HYSYS the equation is empirically extended and therefore its use should be avoided when handling multicomponent mixtures Wilson The Wilson equation proposed by Grant M Wilson in 1964 was the first activity coefficient equation that used the local composition model to derive the Gibbs Excess energy expression It offers a thermodynamically consistent approach to predicting multi component behaviour from regressed binary equilibrium data e Although the Wilson equation is more complex and requires more CPU time than either the van Laar or Margules equations it can represent almost all non ideal liquid solutions satisfactorily except electrolytes and solutions exhibiting limited miscibility LLE or VLLE e It performs an excellent job of predicting ternary equilibrium using parameters regressed from binary data only e It will give similar results to the Margules and van Laar equations for weak non ideal systems but consistently outperforms them for increasingly non ideal systems e It cann
12. inary defined using NRTL another using Margules and another using van Laar and combine them to perform a three component calculation mixing three different thermodynamic models The Chien Null model allows 3 sets of coefficients for each component pair accessible via the A B and C coefficient matrices The Thermodynamics appendix in the HYSYS User Manual provides more information on Property Packages Equations of State and Activity Models and the equations for each Henry s Law Henry s Law cannot be selected explicitly as a property method in HYSYS However HYSYS will use Henry s Law when an activity model is selected and non condensable components are included within the component list HYSYS considers the following components non condensable Methane Ethane Ethylene Acetylene Hydrogen Helium Argon Nitrogen Oxygen NO H2S CO2 and CO 11 Thermodynamics and HYSYS The extended Henry s Law equation in HYSYS is used to model dilute solute solvent interactions Non condensable components are defined as those components that have critical temperatures below the system temperature Activity Model Vapour Phase Options There are several methods available for calculating the Vapour Phase in conjunction with the selected liquid activity model The choice will depend on specific considerations of your system Ideal The ideal gas law can be used to model the vapour phase This model is approp
13. interaction parameters can be obtained from sources such as DECHEMA and entered into HYSYS The following example illustrates the poor LLE prediction than can be produced by comparing the results using default interaction parameters and specially regressed LLE parameters 1 Open the case Phenolh2o hsc 2 Enter the following conditions for stream Phenol H20 Conditions Temperature 40 C Pressure latm Molar Flow 1 kgmole h 1 lbmole hr Composition Phenol 25 mole H20 75 mole What phase s are present 21 22 22 Thermodynamics and HYSYS To provide a better prediction for LLE at 40 C 105 F the following Aj interaction parameters are to be entered To enter the parameters do the following 1 Close the stream view and press the Enter Basis Environment button 2 Ensure the Fluid Package view is open and select the Binary Coeffs tab 3 Enter the Ajj interaction parameters as shown here Phenol H20 Phenol 3891 142 H20 EGA Select the Alpha C j radio button Enter an Alpha j 0 2 Close the Fluid Package view BIr a Ui e Return to the simulation environment by pressing the Return to Simulation Environment button 8 Open the stream view for Phenol H20 What phase s are present now What are the compositions The figures on the following page figures 3 and 4 show the difference between the two sets ofinteraction parameters Ther
14. ity Model e Enter new interaction parameters for a property package e Check multiphase behaviour of a stream e Understand the importance of properly regressed binary coefficients 4 Thermodynamics and HYSYS Thermodynamics and HYSYS Selecting Property Packages The property packages available in HYSYS allow you to predict properties of mixtures ranging from well defined light hydrocarbon systems to complex oil mixtures and highly non ideal non electrolytic chemical systems HYSYS provides enhanced equations of state PR and PRSV for rigorous treatment of hydrocarbon systems semi empirical and vapour pressure models for the heavier hydrocarbon systems steam correlations for accurate steam property predictions and activity coefficient models for chemical systems All of these equations have their own inherent limitations and you are encouraged to become more familiar with the application of each equation The following table lists some typical systems and recommended correlations Type of System Recommended Property Package TEG Dehydration PR Sour Water PR Sour PR Cryogenic Gas Processing PR PRSV Air Separation PR PRSV Atm Crude Towers PR PR Options GS Vacuum Towers PR PR Options GS lt 10mm Hg Braun K10 Esso K Ethylene Towers Lee Kesler Plocker High H Systems PR ZJ or GS see T P limits Reservoir Systems PR PR Options Steam Systems Steam Package CS or GS Hydrate Inhi
15. modynamics and HYSYS 7 and HYSYS 7 The following table briefly summarizes recommended activity coefficient models for different applications refer to the bulleted reference guide below Application Margules van Laar Wilson NRTL UNIQUAC Binary Systems A A A A A Multicomponent LA LA A A A Systems Azeotropic Systems A A A A A Liquid Liquid A A N A A A Equilibria Dilute Systems A A A Self Associating A A A Systems Polymers N A N A N A N A A Extrapolation 2 2 G G G e A Applicable e N A Not Applicable e Questionable G Good e LA Limited Application 8 Thermodynamics and HYSYS Thermodynamics and HYSYS The Margules equation should not be used for extrapolation beyond the range over which the energy parameters have been fitted The van Laar equation performs poorly for dilute systems and CANNOT represent many common systems such as alcohol hydrocarbon mixtures with acceptable accuracy Overview of Models Margules One of the earliest activity coefficient expressions was proposed by Margules at the end of the 19th century e The Margules equation was the first Gibbs excess energy representation developed e The equation does not have any theoretical basis but is useful for quick estimates and data interpolation e In its simplest form it has just one adjustable parameter and can represent mixtures which feature symmetric activi
16. nsity The numbers appearing in the matrix are initially calculated by HYSYS but you have the option of overwriting any library value Thermodynamics and HYSYS 13 Binary Coefficients For the Property Packages which do include binary coefficients the Binary Coefficients tab contains a matrix which lists the interaction parameters for each component pair Depending on the property method chosen different estimation methods may be available and a different view may be shown You have the option of overwriting any library value Equation of State Interaction Parameters The Equation of State Interaction Parameters group appears as follows on the Binary Coeffs tab when an EOS is the selected property package Fluid Package Stripper OP x Equation of State Interaction Parameters Chloroform Toluene 0 00000 0 00000 0 00000 0 00000 0 50000 0 00000 0 00000 0 50000 0 00000 0 31560 0 00000 0 00000 0 00000 001200 d 0 00000 0 19320 0 31560 0 01200 pa 0 19320 Treatment of Interaction Coefficients Unavailable from the Library Estimate HC HC 7 Set Non HC HC to 0 0 C Set llto 0 0 Reset Parameters N Prop Pkg Parameters Binary Coeffs StabTest Runs Tabular Notes Delete Name Stripper Property Pkg E Sour PR For all EOS parameters except PRSV Ky Kj so when you change the val
17. onal assistance it is best to contact Hyprotech s Technical Support department Basic Data Activity coefficient models are empirical by nature and the quality of their prediction depends on the quality and range of data used to determine the parameters Some important things you should be aware of in HYSYS The parameters built in HYSYS were fitted at 1 atm wherever possible or were fitted using isothermal data which would produce pressures closest to 1 atm They are good for a first design but always look for experimental data closer to the region you are working in to confirm your results The values in the HYSYS component database are defined for VLE only hence the LLE prediction may not be very good and additional fitting is necessary Data used in the determination of built in interaction parameters very rarely goes below 0 01 mole fraction and extrapolating into the ppm or ppb region can be risky Again because the interaction parameters were calculated at modest pressures usually 1 atm they may be inadequate for processes at high pressures Check the accuracy of the model for azeotropic systems Additional fitting may be required to match the azeotrope with acceptable accuracy Check not only for the temperature but for the composition as well If three phase behaviour is suspected additional fitting of the parameters may be required to reliably reproduce the VLLE equilibrium conditions UNIFAC or no UNIFAC U
18. ot predict liquid liquid phase splitting and therefore should only be used on problems where demixing is not an issue Our experience shows that the Wilson equation can be extrapolated with reasonable confidence to other operating regions with the same set of regressed energy parameters NRTL The NRTL Non Random Two Liquid equation proposed by Renon and Prausnitz in 1968 is an extension of the original Wilson equation It uses statistical mechanics and the liquid cell theory to represent the liquid structure These concepts combined with Wilson s local composition model produce an equation capable of representing VLE LLE and VLLE phase behaviour Like the Wilson equation the NRTL model is thermodynamically consistent and can be applied to ternary and higher order systems using parameters regressed from binary equilibrium data The NRTL model has an accuracy comparable to the Wilson equation for VLE systems e The NRTL combines the advantages of the Wilson and van Laar equations 10 Thermodynamics and HYSYS e Itis not extremely CPU intensive e It can represent LLE quite well e However because of the mathematical structure of the NRTL equation it can produce erroneous multiple miscibility gaps The NRTL equation in HYSYS contains five adjustable parameters temperature dependent and independent for fitting per binary pair UNIQUAC The UNIQUAC UNIversal QUAsi Chemical equation proposed by Abrams and Prausnit
19. perties that closely match your experimental data However there are cases when the parameters calculated by HYSYS are not accurate enough or cases when the models used by HYSYS do not predict the correct behaviour of some liquid liquid mixtures azeotropic mixtures For those cases it is recommended to use another of Hyprotech s products DISTIL This powerful simulation program provides an environment for exploration of thermodynamic model behaviour proper determination and tuning of interaction parameters and physical properties as well as alternative designs for distillation systems Thermodynamics and HYSYS 3 and HYSYS 3 Proper use of thermodynamic property package parameters is key to successfully simulating any chemical process Effects of pressure and temperature can drastically alter the accuracy of a simulation given missing parameters or parameters fitted for different conditions HYSYS is user friendly by allowing quick viewing and changing of the particular parameters associated with any of the property packages In addition you are able to quickly check the results of one set of parameters and compare those results with another set In this module you will explore the thermodynamic packages of HYSYS and the proper use of their thermodynamic parameters Learning Objectives Once you have completed this module you will be able to e Select an appropriate Property Package e Understand the validity of each Activ
20. riate for low pressures and for a vapour phase with little intermolecular interaction The model is the default vapour phase fugacity calculation method for activity coefficient models Peng Robinson SRK or RK To model non idealities in the vapour phase the PR SRK or RK options can be used in conjunction with an activity model e PR and SRK vapour phase models handle the same types of situations as the PR and SRK equations of state e When selecting one of these three models ensure that the binary interaction parameters used for the activity model remain applicable with the chosen vapour model e For applications with compressors and turbines PR or SRK will be superior to the RK or Ideal vapour model Virial The Virial option enables you to better model vapour phase fugacities of systems displaying strong vapour phase interactions Typically this occurs in systems containing carboxylic acids or compounds that have the tendency to form stable H bonds in the vapour phase Care should be exercised in HYSYS contains temperature dependent coefficients for carboxylic choosing PR SRK RV or Virial 7 3 a os to ensure binary coefficients acids You can overwrite these by changing the Association ij or have been regressed with the Solvation ii coefficients from the default values corresponding vapour phase model This option is restricted to systems where the density is moderate typically less than one half the critical de
21. s For every component i in the mixture the condition of thermodynamics equilibrium is given by the equality between the fugacities of the liquid phase and vapour phase This feature gives the flexibility to use separate thermodynamic models for the liquid and gas phases so the fugacities for each phase have different forms In this approach an equation of state is used for predicting the vapour fugacity coefficients normally ideal gas assumption or the Redlich Kwong Peng Robinson or SRK equations of state although a Virial equation of state is available for specific applications e an activity coefficient model is used for the liquid phase Although there is considerable research being conducted to extend equation of state applications into the chemical industry e g PRSV equation the state of the art of property predictions for chemical systems is still governed mainly by Activity Models Activity coefficients are fudge factors applied to the ideal solution hypothesis Raoult s Law in its simplest form to allow the development of models which actually represent real data Although they are fudge factors activity coefficients have an exact thermodynamic meaning as the ratio of the fugacity coefficient of a component in a mixture at P and T and the fugacity coefficient of the pure component at the same P and T Consequently more caution should be exercised when selecting these models for your simulation Ther
22. s for the selected component pair Aj and Aj The existing values in the matrix are overwritten e Unknowns Only calculates the activity parameters for all the unknown pairs If you delete the contents of cells or if HYSYS does not provide default values you can use this option All Binaries recalculates all the binaries of the matrix If you had changed some of the original HYSYS values you could use this to have HYSYS re estimate the entire matrix When the All Binaries button is used HYSYS does not return the original library values Estimation values will be returned using the selected UNIFAC method To return to the original library values you must select a new property method and then re select the original property method For the Immiscible method the options are e Row in Cim pair estimates the parameters such that the row component j is immiscible in the column component i e Cim in Row pair estimates parameters such that the column component j is immiscible in the row component i Allin Row estimates parameters such that both components are mutually immiscible In Module 1 you chose the NRTL Activity Model then select the UNIFAC VLE estimation method default before pressing the Unknowns Only cell 15 16 Thermodynamics and HYSYS Which Activity Coefficient Model Should I Use This is a tough question to answer but some guidelines are provided If you require additi
23. t is a two fold modification of the PR equation of state that extends the application of the original PR method for highly non ideal systems e It has shown to match vapour pressure curves of pure components and mixtures especially at low vapour pressures e Ithas been successfully extended to handle non ideal systems giving results as good as those obtained by activity models A limited amount of non hydrocarbon interaction parameters are available Activity Models Although equation of state models have proven to be very reliable in predicting properties of most hydrocarbon based fluids over a large range of operating conditions their application has been limited to primarily non polar or slightly polar components Polar or non ideal chemical systems have traditionally been handled using dual model approaches Activity Models are much more empirical in nature when compared to 6 Thermodynamics and HYSYS Thermodynamics and HYSYS Activity Models produce the best results when they are applied in the operating region for which the interaction parameters were regressed the property predictions in the hydrocarbon industry For example they cannot be used as reliably as the equations of state for generalized application or extrapolating into untested operating conditions Their tuning parameters should be fitted against a representative sample of experimental data and their application should be limited to moderate pressure
24. ty coefficient curves HYSYS has an extended multicomponent Margules equation with up to four adjustable parameters per binary The four adjustable parameters for the Margules equation in HYSYS are the ajj and aj temperature independent and the b j and bj terms temperature dependent e The equation will use parameter values stored in HYSYS or any user supplied value for further fitting the equation to a given set of data e In HYSYS the equation is empirically extended and therefore caution should be exercised when handling multicomponent mixtures van Laar The van Laar equation was the first Gibbs excess energy representation with physical significance This equation fits many systems quite well particularly for LLE component distributions It can be used for systems that exhibit positive or negative deviations from Raoult s Law Some of the advantages and disadvantage for this model are e Generally requires less CPU time than other activity models e lItcan represent limited miscibility as well as three phase equilibrium e It cannot predict maxima or minima in the activity coefficient and therefore generally performs poorly for systems with halogenated hydrocarbons and alcohols e It also has a tendency to predict two liquid phases when they do not exist Thermodynamics and HYSYS 9 and HYSYS 9 The Wilson equation CANNOT be used for problems involving liquid liquid equilibrium The additional parameter in t
25. ue of one of these both cells of the pair automatically update with the same value In many cases the library interaction parameters for PRSV do have K K j but HYSYS does not force this if you modify one parameter in a binary pair 13 14 Thermodynamics and HYSYS If you are using PR or SRK or one of the Sour options two radio buttons are displayed at the bottom of the page in the Treatment of Interaction Coefficients Unavailable from the Library group e Estimate HC HC Set Non HC HC to 0 0 this radio button is the default selection HYSYS provides the estimates for the interaction parameters in the matrix setting all non hydrocarbon pairs to 0 e Set All to 0 0 when this is selected HYSYS sets all interaction parameter values in the matrix to 0 0 Activity Model Interaction Parameters Activity Models are much more empirical in nature when compared to the property predictions in the hydrocarbon industry Their tuning parameters should be fitted against a representative sample of experimental data and their application should be limited to moderate pressures The Activity Model Interaction Parameters group appears as follows on the Binary Coeffs tab when an Activity Model is the selected property package Fluid Package Stripper of x Activity Model Interaction Parameter r Coeff Estimation Coeff Matrix To View o UNIFAC VLE Chloroform Toluene Ethanol H20 Nin C UNIFAC LLE
26. z in 1975 uses statistical mechanics and the quasi chemical theory of Guggenheim to represent the liquid structure The equation is capable of representing LLE VLE and VLLE with accuracy comparable to the NRTL equation but without the need for a non randomness factor it is a two parameter model The UNIQUAC equation is significantly more detailed and sophisticated than any of the other activity models e Its main advantage is that a good representation of both VLE and LLE can be obtained for a large range of non electrolyte mixtures using only two adjustable parameters per binary e The fitted parameters usually exhibit a smaller temperature dependence which makes them more valid for extrapolation purposes e The UNIQUAC equation utilizes the concept of local composition as proposed by Wilson Since the primary concentration variable is a surface fraction as opposed to a mole fraction it is applicable to systems containing molecules of very different sizes and shape such as polymer solutions e The UNIQUAC equation can be applied to a wide range of mixtures containing H2O alcohols nitriles amines esters ketones aldehydes halogenated hydrocarbons and hydrocarbons In its simplest form it is a two parameter model with the same remarks as Wilson and NRTL UNIQUAC needs van der Waals area and volume parameters and those can sometimes be difficult to find especially for non condensable gases although DIPPR has a fair number avail
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