User Guide for
Multiflash for Windows
Infochem Computer Services Ltd
Version 3.6
11 May 2007
Infochem Computer Services Ltd
13 Swan Court
9 Tanner Street
London SE1 3LE
Tel: +44 [0]20 7357 0800
Fax: +44 [0]20 7407 3927
e-mail: [email protected]
This User Guide and the information contained within is the copyright of Infochem Computer Services Ltd.
Infochem Computer Services Ltd
13 Swan Court 9 Tanner Street London SE1 3LE, UK Tel:+44 [0]20 7357 0800 Fax:+44 [0]20 7407 3927 e-mail:[email protected]
Disclaimer
While every effort has been made to ensure that the information contained in this document is correct and that the software and data to which it relates are free from errors, no guarantee is given or implied as to their correctness or accuracy. Neither Infochem Computer Services Ltd nor any of its employees, contractors or agents shall be liable for direct, indirect or consequential losses, damages, costs, expenses, claims or fee of any kind resulting from any deficiency, defect or error in this document, the software or the data.
Contents
Overview
1
Introduction ...1
Multiflash phase equilibrium utility...1
Chemreact ...2
Multiflash Software System ...2
Documentation...2
Overview...2
New Features and Changes in Version 3.6 ...3
Running Multiflash ...3
HELP ...4
Case studies ...4
Appendix - Multiflash Commands ...4
Installation ...4
New Features and Changes in Version 3.6
5
Introduction ...5 Models ...5 Hydrates ...5 Asphaltenes...5 UNIFAC...6 BIPs...6 Fluid characterisation...6 Matching ...6 Wax calculations...6 Phase labelling ...7 Databanks...7 DIPPR...7 Infodata...7 Front-end...8 Icons...8 Graphics ...8 Inhibitor Calculator...8 Preferences...8Model Set Tabs ...8
Interfaces...8
Installation ...8
Simple Tutorial
9
Introduction ...9Starting Multiflash...9
Defining a problem in Multiflash ...10
Problem setup file ...10
Loading an existing problem file ...10
Loading a problem setup file ...10
The results...11
Additional calculations...12
Setting up a problem interactively ...13
Defining the model...14
Defining the components ...14
Define Input Conditions ...15
Carrying out the flash calculation...16
Additional calculations...16
Phase envelope...16
Saving a problem setup ...17
Printing the output...18
Saving the output...19
Starting a new problem...19
How to exit the program...19
Input
21
Introduction ...21 Input files ...21 Menu options...22 File ...22 Edit ...22 Select ...23 Tools ...23 Calculate...24 Table ...24 Help ...24 Toolbar buttons ...25Dialogue boxes, text boxes, tab controls, drop-down tables and menus...25
Commands ...25
Models
27
Introduction ...27What is a model? ...27
What types of model are available? ...27
Equation of state method...28
When to use equation of state methods ...28
Equations of state provided in Multiflash ...28
Activity coefficient methods ...33
Activity coefficient equations in Multiflash ...33
Gas phase models for activity coefficient methods ...35
When to use activity coefficient models ...35
Models for solid phases ...35
Other thermodynamic models ...41
Transport property models ...41
How to specify models in Multiflash ...43
How to load a model...43
What the model definition means...45
How to change a model ...46
Loading hydrate models ...46
The Freeze-out model ...48
How to define a wax model...48
How to define the asphaltene model ...49
Combined Solids Model...49
Troubleshooting - models ...50
Incorrect path...50
Model is not licensed ...51
Groups not available for UNIFAC model...51
Binary interaction parameters ...52
Number of BIPs related to any model...52
Units for BIPs...52
Temperature dependence of BIPs ...53
Viewing BIP values...54
Supplementing or overwriting BIPs ...56
Troubleshooting - BIPs...59
Units...59
Order of components...59
Number of BIPs for the model...59
Naming the components ...59
BIP databank ...60
BIPs not displayed...60
Components
61
Introduction ...61Normal components ...61
Condensed components ...63
Petroleum fractions ...63
Defining a mixture (stream) in Multiflash ...64
Specifying the data source ...64
Selecting components ...65
Adding, inserting, replacing and deleting components ...68
Viewing and editing pure component data...69
User-defined components...71
Models and input requirements ...73
Stream types ...76
Hydrate inhibitors ...79
Inhibitor calculator ...79
Salt calculator...80
Troubleshooting - components...82
Databank not found...83
Databank not licensed...83
Component cannot be found...84
Too many components in the mixture...84
Petroleum fractions
85
Introduction ...85Defining petroleum fractions...85
PVT Analysis ...86 Analysis method ...87 Component list...88 Fluid composition...90 Wax Content...96 Water cut...96
Total amount of fluid ...96
SARA Analysis ...96 Characterisation ...97 Saving a PVT Analysis ...99 Troubleshooting – PVT Analysis ...99 Sensitivity to characterisation ...99 Presence of water...100
Calculating petroleum fraction properties ...100
Editing petroleum fraction data...101
Matching using petroleum fraction properties...102
Matching dew and bubble points ...102
Matching Density/Volume ...108
Matching wax appearance temp erature ...110
Matching liquid viscosity...111
Problems defining a petroleum fraction ...112
Input conditions
115
Introduction ...115
Specifying compositions ...115
Specifying temperature, pressure and volume ...117
Specifying enthalpy, entropy and internal energy ...117
Troubleshooting - input conditions ...117
Calculations (flashes)
119
Introduction ...119The basis of a flash calculation. ...119
Flashes available in Multiflash...120
Isothermal (P,T) flash...121
Isenthalpic flashes ...121
Isentropic flashes ...121
Isochoric flashes ...122
Bubble and dew point flashes...122
Fixed phase fraction flashes...122
Hydrate calculations...126
Scale calculations ...126
Wax calculations...126
Tolerance calculations ...128
Provide a starting estimate ...129
Phase diagrams ...130
Property output in Multiflash ...137
Troubleshooting - flash calculations ...138
Plot the phase envelope ...139
Use the P,T flash...139
Limit the number of phases ...139
Consider all types of solution...140
Provide a starting estimate ...140
Provide a key component...140
Chemical reaction...140
Troubleshooting - chemical reaction...141
Units
143
Introduction ...143Working units...143
Default units ...143
Changing units ...144
Changing units interactively ...144
Changing units in a problem setup file ...145
Troubleshooting - units...146
Output
147
Introduction ...147The results window. ...147
Font ...148
Writing the results to a file ...148
Printing the output...149
Calculation output ...150
Manipulating the Output ...152
Phase envelope output ...152
Errors and warning messages ...152
Displaying status for current settings...153
Troubleshooting - output...154
The output does not include everything expected...154
Phase envelope...154
Fonts ...154
Interfaces with other programs
155
Introduction ...155 Pipesim PVT files...155 OLGA ...156 CAPE-OPEN Interface ...158Help
159
Introduction ...159 On-line help ...159 Website support ...162 Technical support ...162Case studies - Pure component data
163
Introduction ...163Physical properties of a pure component...163
Defining the problem interactively ...163
Producing a problem setup file...167
Obtaining properties from Pure component Data option...167
Excel interface...169
Case studies - Phase equilibria
171
Introduction ...171Oil and gas systems ...171
Calculating the bubble point curve...172
Calculating the dew point curve...173
Phase envelope...174
Adding water to the system ...175
Including a petroleum fraction ...176
Other flash calculations ...177
PVT Analysis ...179
Black Oil Analysis ...185
Refrigerant mixtures ...186
Polar systems ...188
Modelling a polar mixture. ...188
Liquid-liquid equilibria ...192 Vapour-liquid-liquid equilibria ...192 Azeotropes ...193 Eutectics ...193 Polymers...194 Data input...194 Co-Polymers ...197
Case studies - Hydrate dissociation, formation and inhibition
201
Introduction ...201Defining the hydrate models ...201
Fluid phase model ...202
Hydrate model...202
Nucleation model...202
Ice model...202
Scale model ...203
Phases ...203
Hydrate calculations with Multiflash ...203
Hydrate formation and dissociation temperature at given pressure ...205
Hydrate formation and dissociation pressure at given temperature ...207
Hydrate phase boundary ...208
Other flash calculations with hydrates ...208
Maximum water content allowable before hydrate dissociation...209
Calculations with inhibitors ...210
Can hydrates form at given P and T ? ...210
Hydrate dissociation temperature at a given pressure ...211
Hydrate dissociation pressure at a given temperature ...212
Hydrate phase boundary ...212
Amount of inhibitor required to suppress hydrates ...213
Salt inhibition...214
Scale precipitation ...215
RKSA(Infochem) mo del ...217
Case studies – Wax precipitation
219
Introduction ...219Defining the wax model ...219
Coutinho wax model...220
Calculating wax appearance temperature (WAT)...220
Calculating wax precipitation...223
Multisolid model...226
Case studies – Asphaltene flocculation
227
Introduction ...227Input data ...227
Defining the asphaltene model...228
Calculating asphaltene flocculation conditions...232
Sensitivity of calculations to variation in input data ...235
Choice of Analysis method...235
Data Availability...235
No reservoir or flocculation conditions ...238
Gas injection...239
Titration...240
Case studies – Combined solids
245
Introduction ...245Asphaltene flocculation...245
Wax and Asphaltene precipitation...246
Hydrates, Waxes and Asphaltenes...247
Case studies – Excel spreadsheets
251
Introduction ...251UNFACFIT.xls ...251
Notes...251
UNIFAC...252
Activity model worksheets ...252
VLEFIT.xls ...253
SolidsB.xls and SolidsA.xls ...253
PVT Analysis ...254
Match bubble point...255
Wax...255
Asphaltenes...256
Asphaltene with gas injection...257
Hydrates ...258
Introduction ...260
Defining the mercury model...260
Calculating mercury partitioning...261
Calculating mercury dropout...263
Other calculations...264
Case studies - chemical equilibria
265
Introduction ...265Xylene isomerisation ...265
Steam cracking of ethane ...266
Appendix - Multiflash Commands
269
Introduction ...269When you may need to use commands...269
Defining models ...269
Supplying an external file of BIPs...270
Defining phase descriptors and key components ...270
Overview
Introduction
Multiflash is an advanced software package for performing complex equilibrium calculations quickly and reliably. The main utility is a multiple phase
equilibrium algorithm that is interfaced to Infochem’s package of thermodynamic models and a number of physical property data banks. The program also contains Infochem’s Chemreact utility for performing simultaneous phase and chemical equilibrium calculations.
Multiflash phase equilibrium utility
Multiflash can perform multiphase equilibrium calculations between any numb er of phases of different types. Each property of each phase may be described by a different thermodynamic model if required. The phases that can be modelled include gases, liquids and solids, for example hydrates, waxes and asphaltenes, depending on which models are available under your licence.
Multiflash incorporates a phase stability analysis procedure whereby it can establish automatically which of the possible phases are present at equilibrium. Phase equilibria can be calculated for the following conditions:
• fixed pressure and temperature
• fixed fraction of any specified phase at fixed pressure (includes dew and bubble points)
• fixed fraction of any specified phase at fixed temperature (includes dew and bubble points)
• fixed pressure and enthalpy
• fixed temperature and enthalpy
• fixed pressure and entropy
• fixed temperature and entropy
• fixed pressure and internal energy
• fixed temperature and internal energy
• fixed pressure and volume
• fixed temp erature and volume
• fixed entropy and volume
• fixed enthalpy and entropy
• fixed pressure, temperature and fraction of any specified phase (variable composition)
A full range of thermodynamic and transport properties is availa ble for any fluid phase.
Chemreact
Chemreact is a utility for performing simultaneous phase and chemical equilibrium calculations. Currently Chemreact can handle equilibria involving combinations of one gas phase, one liquid phase and any number of pure solids. It is interfaced to the same package of thermodynamic models and physical property data banks as the phase equilibrium utility.
As in the phase equilibrium utility, Chemreact incorporates a phase stability analysis procedure to establish automatically which phases are present at equilibrium.
Chemreact can calculate equilibria for the following specifications:
• fixed pressure and temperature
• dew point at fixed pressure
• dew point at fixed temp erature
• bubble point at fixed pressure
• bubble point at fixed temperature
When using Chemreact the user does not need to specify any reaction mechanism but only list all the possible products and reactants.
Multiflash Software System
In addition to the Microsoft Windows program, Multiflash is also available as an add-in for use with the Microsoft Excel spreadsheet program, for use with Matlab, as a DLL and as a suite of sub-routines for interfacing to other application packages. A CAPE-OPEN physical property package interface is also available. The package can be accessed from programs written in Fortran, Visual Basic, VBA and C. All versions share the capability to use the problem setup files which can store all aspects of a user’s problem, see “Setting up a problem interactively” on page 13.
Separate documentation is available for these interfaces.
Documentation
The supporting documentation is grouped into sections.
Overview
This section describes what the Multiflash software is used for, what it contains and how it is made available.
New Features and Changes in Version 3.6
New developments and additions are listed, although the detailed review of how to use new features will be covered in the appropriate section. Information is also given on changes to code or data which may give rise to different results from those obtained with earlier versions of Multiflash.
Running Multiflash
Each section provides details on different aspects of the software.
Simple tutorial
This section is based on starting the program and running a simple example with step by step instructions.
Input
This section provides an overview of the various ways you can enter data and commands in Multiflash for Windows.
Models
This section describes the mixture models available in Multiflash and shows how to define a model. How and when to use models is reviewed, together with the availability and use of model interaction parameters. Detailed specification of the models can be found in a separate manual.
Components
The type of components that are available from Multiflash are defined, together with a description of the physical property databanks available. This section also shows how to search for and select components, including how to define and edit data for petroleum fractions.
Petroleum Fractions
How to carry out PVT characterisation and calculate petroleum fraction physical properties.
Input Conditions
The necessary conditions for carrying out different types of calculations are defined, together with how to enter and change these within the program.
Calculations
The final step in running Multiflash, the specification of the calculations wh ich can be carried out, and the circumstances where they might be most appropriate, are outlined.
Units
This section defines the standard working units of the software, the range of options available for input and output units and how to change them.
Output
This section reviews the different levels of output available, where output is reported and how it may be saved.
HELP
The various types of help available and how to access them are reviewed.
Case studies
Additional examples of how to tackle typical problems using Multiflash are provided.
Appendix - Multiflash Commands
Nearly all the facilities available in the command processor version of Multiflash have been incorporated as menu options in the current version of Multiflash for Windows, and can be now readily accessed from either menu options or tool bar. An example would be the ability to edit or change model binary interaction parameters (BIP) in the BIP values window by selecting the BIPs option from the Tools menu. However a Tools Command option is still available which allows the user to enter any command and apply this in the Windows version. Those commands which users of the Windows version of Multiflash may find useful are discussed in the appropriate section of the User Guide or in the Appendix.
Commands are used to create or edit problem setup files for use with Multiflash.
A Contents list and an Index are also supplied to h elp you find your way around the User Guide.
Installation
Information on how to install Multiflash software is provided in the separate "Installation Guide for Multiflash for Windows".
New Features and Changes in
Version 3.6
Introduction
There are several improvements and extensions in Multiflash 3.6. The major developments for this version are the inclusion of a model for chloride scales and a review and update of asphaltene mo del parameters. A new graphics plotting package replaces the package used for previous versions of Multiflash. The inclusion of chloride scales has required significant extension to the Multiflash flash algorithms. We have carried out a comprehensive QA procedure and in some cases you may find that calculated results vary from previous versions. Where we are aware of significant differences we will point these out. All our hardware dongles are valid for previous licensed versions of Multiflash so you can reproduce earlier calculations if required.
Models
Descriptions and references detailing the models are provided in our "Models and Physical Property Guide"
Hydrates
The extension to prediction of chloride scales is part of our hydrate module and can be activated as part of the Hydrate Model Set, see “Loading hydrate models ” on page 46. The scales considered in this version of Multiflash are NaCl, NaCl.2H2O, KCl, CaCl2.6H2O, CaCl2.4H2O and CaCl6.H2O. The effect on salt solubility of other hydrate inhibitors, such as methanol and MEG, are also considered.
Asphaltenes
Since the addition of an asphaltene model several versions ago, mo re data on asphaltene flocculation has been published and we have carried out further proprietary studies. As a result of this new information we have carried a out a review and upgrade of the asphaltene model parameters. The greatest changes in ADE predictions are likely to be for reservoir fluids with MW between 180-240, but at temperatures of operational interest these are not likely to be greater than experimental error. For lighter oils the improved temperature dependence of the resin-asphaltene parameter means that the ADE are more likely to close at lower
temperatures. However, we would also recommend, if possible, two measurements of asphaltene onset for light oils if possible.
In order for you to be able to use two ADE measurements, another improvement in MF3.6 is the extension of the Matching Asphaltene Phase form to process both points.
In the PVT Analysis the SARA values must be supplied for the STO rather than the total fluid and the asphaltene content that precipitated by heptane.
UNIFAC
In MF3.6 users can now add their own user-defined UNIFAC groups if no existing group is suitable. There are no specific menu options as yet. You would have to enter commands through the command box – and information on the commands can be found in the Command Reference Manual.
BIPs
There have been some minor modifications to the existing binary interaction parameters between ions and other components for the Electrolyte salt model and new parameters to support salt precipitation.
Fluid characterisation
The PVT Analysis form for fluid characterisation has been modified in MF3.6. There are now two forms, one for analyses including n -paraffins and one for those without. This allows us to introduce mo re flexibility for entering n-paraffin data as it is supplied by the laboratory, without making the PVT form for more routine analyses too complex. The n-paraffin data can now be supplied either as total amounts in the STO or as a fraction of the STO cuts , see “PVT Analysis ” on page 86.
The method for estimating STO composition has been improved to better reproduce supplied MW and specific gravity.
The n-paraffin distribution generated from wax content has been improved, which may effect WAT calculations.
Matching
Matching to measured WAT or to amounts of wax precipitated has now been allocated a specific menu option under Tools/Matching. Amounts of wax can be provided relative to either the oil plus wax phases or relative to the total material.
Wax calculations
There have been some modification to wax calculations. In MF3.6 the amount of wax specified for calculations is now relative to the liquid plus wax phases for the wax matching, the wax precipitation curve calculation and WAT calculated using the WAT button. For the fixed phase fraction flashes and the phase boundary plotting the specified amounts of wax are relative to the total fluid as in previous versions.
After careful consideration of the data we have decided to recommend that calculations of WAT should be considered relative to positive amounts of wax precipitated, rather than zero, as this appears to be the case in experimental
measurements. Different measurement techniques rely on different amounts of precipitated wax to determine the WAT. Accordingly the WAT button in MF3.6 now allows you to specify the mass or mole% of wax to be precipitated at the calculated WAT and recommends specific values for WAT measurements by CPM (Cross Polar Microscopy) and DSC (Differential Scanning Calorimetry). The values can still be set to zero percent wax if preferred. See “Wax
calculations” on page 126 for more information.
The Wax precipitation curve is now plotted in addition to the values being displayed in the Window.
Phase labelling
The criterion used to decide whether a supercritical phase is to b e labelled as gas or liquid has been changed. This change has the effect that more of the
supercritical region is considered to be gas. It does not affect any property values. Specific details of the change can be found in the Programmer’s Guide.
Databanks
DIPPR
The latest version of DIPPR linked to Multiflash is now DIPPR 2006. This has increased the number of components by 48. A list of the additional components is available on request.
Infodata
The number of components in Infodata has increased to 240. Those added for Multiflash 3.6 are: 1-hexene 1,3-cyclopentadiene, 1,4-pentadiene 1-heptene 1-octene 2-methyl,1-butene 2-methyl,2-butene 2-methyl,1-heptene 2-methyl,1-hexene 2-methyl,1-pentene cyclohexene cyclopentene n-propylcyclohexane n-propylbenzene n-butylbenzene 1,2,4-trimethylbenzene 1,3,5-trimethylbenzene
Front-end
Icons
There is now a new icon for PVT analysis including a n -paraffin analysis .
Graphics
We have introduced a new graphics package in MF3.6, TeeChart from Steema Software. We feel that this provides a better display and improved facilities for adding experimental or other data, editing legends and titles.
Inhibitor Calculator
MF3.6 will now save the original salt analysis data supplied during a problem calculation as part of the .mfl file and this can be displayed when the file is loaded.
Ethanol is now displayed on the Alcohols/Glycols tab is the Inhibitor tab in addition to methanol, MEG, DEG and TEG.
Preferences
There have been two extensions to Tools/Preferences. You can now set the preferred level of property output to appear when Multiflash is loaded. The display is the same as that used for Select/Property Output. If you wish to change the property level during any run you should still use the Select menu option.
The other extension is Folders, where you can specify the directory where the software can find the Databank and Help files, the Problem files and the CAPE-OPEN property packages. This means you can set a default working directory where you prefer to save your .mfl files.
Model Set Tabs
The arrangement of models in the Model Set form has b een modified slightly. There are now separate tabs for the cubic and non-cubic equations of state and an additional tab has been added for the mercury model.
Interfaces
The Matlab/Simulink interface is upgraded with each new Multiflash release. MF3.6 now supports CAPE-OPEN 1.1 as well as 1.0
Installation
The installation procedure will copy any Preferences set in Mf3.5 to MF3.6 as part of installation.
Simple Tutorial
Introduction
This section concentrates on how to run Multiflash using a simple problem as an example. The assumption is that the user is already familiar with Windows terms and techniques.
Starting Multiflash
You start Multiflash by clicking on the MFW3.6 shortcut.
The Multiflash Main Window should then appear.
If, in a previous run of Multiflash, an error has caused an abnormal termination, you may see a message box saying Multiflash DLL already loaded. In this case you may need to click the Start button and select “Restart the computer”.
Defining a problem in Multiflash
You need, first of all, to define the problem you want to solve using Multiflash. This means choosing the model you wish to use to describe your system, setting the source for the pure component data, the components in the system and their compositions, the input conditions (e.g. temperature and pressure) and the calculation you wish to carry out. This is described in detail in the appropriate sections. Initially a simple problem is defined and Multiflash is used to calculate the physical properties of the system.
The system is 0.4 moles of butane and 0.6 moles of pentane. The model used to describe the system is the Peng -Robinson equation of state with the pure component data taken from the INFODATA databank and interaction parameters from the default BIP databank called OILANDGAS. First we are going to calculate the bubble point (the point at which the gas phase first appears) at fixed pressure followed by an isenthalpic flash (a flash calculation at fixed enthalpy and, in this case, pressure).
There are two ways of setting up the problem. You can prepare a problem setup file using a text editor, either by typing in all the necessary commands or by copying and editing an existing file. However, it is more usual to set up the problem completely within Multiflash for Windows and save the problem file for future use. This is activated by “Save Problem setup” from the File menu “Save Problem setup” will save the current problem definition, excluding flash calculation options.
Problem setup file
Infochem supplies a series of sample problem setup files covering typical problem types. These can be used as examples when testing the program or can be copied and edited to define your own problems. By convention problem setup files for Multiflash have the extension .mfl.
Loading an existing problem file
Infochem has provided several problem set up files (extension .mfl) covering a variety of typical problems. Any of these may be used as an example when running Multiflash; the setup file used for the simple tutorial is C4C5.mfl. If the problem set up file has been edited to include a full definition of the problem, including input conditions and a specification of the flash calculation, then once the file is loaded the flash calculation will be carried out and the results shown. If it contains only a partial definition of the problem then the remaining specifications must be completed interactively.
Loading a problem setup file
1. Either selecting File from menu bar, then selecting “Load Problem Setup” from the sub-menu
or
Clicking on Load problem setup button .
This will activate the “Load Multiflash File” Dialogue box,
which will show a list of available setup files (*.mfl) contained in the current directory.
2. Scroll to C4C5.mfl, which will now be highlighted, and either double click on it or select it and click on OK. The Dialogue box will disappear and the file will be read in. This file contains the complete definition of the problem including:
• Data sources • Model • Phase descriptors • Compounds • Compositions • Input conditions • Calculation
The results
The results of any calculations are displa yed in the results section of the main Multiflash window and the last set of input conditions echoed in the input conditions section of the window. You can scroll up and down to look at earlier calculations.
displaying the set pressure and the enthalpy for the final calculation, which was an isenthalpic flash.
The results of the isenthalpic flash calculation will be the last item displayed the results window
You can scroll up to look at the earlier bubble point calculation at a pressure of 10e5Pa.
Additional calculations
You can pre -set all the calculations you wish to carry out for any one problem within the problem setup file. However, it is probable that once you have seen the results of one calculation you may wish to make other changes or perform other calculations.
Any of the input conditions may be changed by entering new values to overwrite or supplement those shown in the input section of t he main window. Simply type the value for the input condition in the appropriate text box, ensure that all necessary input conditions are defined for the flash calculation you wish to carry out and then click on the appropriate flash icon or select the required flash from the menu options.
Compositions for a mixture may be altered by clicking on the composition button and editing the right-hand column of the drop-down table where the amounts of each component are defined.
To replace a component or to add new components see Adding, inserting, replacing and deleting components .
Some simple changes are shown below:
Change the pressure
1. Place cursor in Pressure box of the Conditions panel in the main window and change the pressure to 20e5 Pa.
2. Click on P,H flash button
or
use the drop down menu by selecting Calculate in the menu bar, then selecting Standard flashes in sub-menu and finally
selecting P,H flash in sub-sub-menu.
Change the enthalpy
1. Change the enthalpy for the isenthalpic flash by typing -1000 in the enthalpy box of the Conditions section
2. Recalculate the isenthalpic flash by repeating step 2 as above.
Change the composition
1. Click on the Composition button in t he Conditions section of the main window. The component names are displayed in the first column and the number of moles of each component in the mixture is shown in the second column. Edit the “mol” column of the drop-down table so that there are 3 moles of butane and 7 moles of pentane.
2. Recalculate the isenthalpic flash as above
Carry out an isothermal flash
1. Enter a temperature in K in the temperature text box in the Conditions section, e.g. 300K
2. Click on the P,T fla sh button
or
select the P,T flash option starting from Calculate in the Menu bar.
Setting up a problem interactively
You can define all the necessary input for a problem calculation interactively. This input must include:
• Data sources • Model • Compounds • Compositions • Input conditions • Flash Calculation
Clearing previous problems
Each time you start Multiflash from the Windows icon you start with a “clean sheet”, i.e. there are no models or components pre -loaded. However, the INFODATA databank, see “Normal components ” on page 61, will be set as the default data source. If you have already carried out a series of calculations for a previous problem and want to start a new one then
Select “Clear Problem Setup” from the File menu.
This will remove the current specification and reset the unit definitions to those in place when you started the program. INFODATA will still remain as the default data source for the pure component data.
Defining the model
To define the model Select Select in the menu bar and from the drop-down menu select Model set. A tabbed dialogue box will offer a choice of different types of model, e.g. equation of state, activity coefficient method, hydrate, wax and asphaltene or a combination of solid models. Within each group a specific model along with a number of phases may be chosen by name and a combination of transport models chosen. For general advice on which models to choose for an application and a detailed definition of each model, see “What types of model are available?” on page 27 or consult the “Models and Physical Properties” manual.
Once you have selected a model a message will be displayed to tell you that the model has been successfully loaded, click on OK and close the Select Model dialogue box to return to the main window. The model set will include a data source for binary interaction parameters.
We will use the Peng-Robinson equation of state, see ”Peng-Robinson equation of state” on page 28, for this problem. Select Select in the menu bar and from the drop-down menu select Model set to open the Select Model Set tabbed dialogue box. In the Model Set window, select Equations of State, and from the following menu select PR. You can also select phases and transport property models in this window but the default set will already be selected. After the selection, click the Define Model button. You should see the following message.
Click on OK to return to the Select Models dialogue box. Click on Close to return to the main window.
Defining the components
Choose the components for any problem by Selecting Select then selecting Components from the sub-menu. Alternatively you can click on the Select Components button, . Either will result in the display of the Select Components Dialogue box.
Specify the data source and the individual components. Components may be selected in a variety of ways e.g. by name, by scrolling through a list or b y searching for a formula. The various methods are fully described in “ Selecting components ” on page 65.
Choose the components needed for the problem, in this case butane and pentane, by:
1. Selecting Select again, but this time selecting Components from the sub-menu. Alternatively you can click on the Select Components button, . Either will result in the display of the Select Components Dialogue box. At this stage we will ignore the search facilities and enter the components by the simplest route possible.
2. INFODATA will be the default data source. Make sure the Name option button is selected.
3. Type
butane
in the Enter Name box and either press Enter
or click on the Add button to tra nsfer butane to the Components selected list. Do the same for pentane.
4. Click on the Close button, this will return you to the Main Window.
5. To check the components are correctly loaded, click on the Composition button and check the drop-down table, which should look like this
Define Input Conditions
Before a flash calculation can be carried out you must define all necessary input conditions, including the composition of the mixture. All input conditions are specified in the input condition section of the main window.
The composition is entered by clicking on the Composition button. The drop-down table shows the chosen components in the left -hand column and the amount of each component in the mixture is typed in the right-hand column. The default unit for amounts is moles.
Other input conditions will depend on the type of flash calculation to be carried out, e.g. for an isothermal flash you must type in a pressure and a temperature in the appropriate text boxes and in t he units shown next to them. Enter the input conditions in the Conditions section of the main window
Compositions
1. Type the number of moles of each component, in this case 0.4 for butane and 0.6 for pentane.
2. Close by clicking on roll-up button if you wish. The table can remain down if you prefer.
Pressure
Type the pressure in Pa., in this case 10e5, in the Pressure text box.
Carrying out the flash calculation
To carry out a flash calculation you either click on the appropriate flash button or select the required flash from the menu.
Only the most commonly encountered flash options have been allocated buttons; these are the isothermal flash, dew and bubble points, isenthalpic and isentropic flashes at fixed pressure and fixed phase flashes. To carry out the latter you also have to fill in supplementary information in a dialogue box.
Other flashes, such as isochoric flashes or isentropic and isenthalpic flashes at fixed temperature, are specified using the options accessed under Calculate in the menu bar. To calculate the bubble point at fixed pressure, either
Click on the bubble point at fixed pressure button,
or
1. Select Calculate from the menu bar, then
2. Select Bubble or dew point flashes in sub-menu, then 3. Select P, Bubble point flash in the next menu.
To carry out the isenthalpic flash, type -11078 in the enthalpy text box and click on the P,H button. The results will be identical to those shown earlier.
Additional calculations
Any of the input conditions may be changed by entering new values to overwrite or supplement those shown in the input section of the main window. Simply type the value for the input condition in the appropriate text box, ensure that all necessary input conditions are defined for the flash calculation you wish to carry out and then click on the appropriate flash icon or select the required flash from the menu options.
Compositions for a mixture may be altered by clicking on the composition button and editing the right-hand column of the drop-down table where the amounts of each component are defined.
To replace a component or to add new components see “Adding, inserting, replacing and deleting components ” on page 68.
Phase envelope
1. Clicking on the phase envelope button or clicking on the Calculate menu followed by clicking on Phase Envelope
2. In the Phase Envelope tabbed dialogue box click on VLE Autoplot
The phase envelope will be displayed in a separate window.
The phase diagram may be edited or printed as described elsewhere, ”Customising the phase envelope plot” on page 135.. Alternatively it can be exported to Excel, provided you are running Excel 97 or later.
Saving a problem setup
Once you have defined the model, components, compositions and conditions interactively you can create a problem setup file containing this information for future use. It does not matter whether these were entered through dialogue boxes, from an existing problem setup file or the Tools/Command option. To save the setup either
Select File from the menu bar and then select “Save Problem Setup”
or
Click on Save problem setup button,
The dialogue box that is activated allows you to specify the name of the .mfl file and the directory where you want it stored.
Multiflash will provide a default file name which can be overwritten.
Printing the output
You can print the output from your calculations by Selecting File from the menu bar, then
selecting Print Results
or
Clicking on the Print results button,
This leads you to a print panel (see below), so that you can change the printer‘s setting and its properties, and print out all the output currently stored in the results window.
If you only wish to print part of the output you should select the relevant section by highlighting it with the cursor. This time the print range in the print panel shows you the option of printing out only the selected text.
Alternatively you can cut or copy the relevant sections and paste them to another application, such as Word.
Saving the output
The output from Multiflash is described in detail e lsewhere, see “Output” on page 147 All the output from any run is automatically stored in a file called MFLASH.LOG. This file will be overwritten when the program is started unless you rename it. If you wish to save the output to another file directly from Multiflash, then
Select File from the menu Select Save Results
As with printing the results you will see a message box whic h allows you to write the entire output window to file. If you have previously highlighted a section of the output then the message box offers the option of writing the selected text to file.
A dialogue box allows you to choose the file name and directory . The
convention is that the extension for output files is .out, but you may alter this if you wish.
Note that the amount of output produced by any calculation or problem setup file is limited to 32kb of text. Any output beyond this limit will not be dis played on the screen or in the log file.
Starting a new problem
To load a new problem
Select File from the menu, followed by Selecting Clear Problem Setup.
The message “Clear current problem setup” will appear in the results window. Select a new problem setup file or enter a new problem interactively.
How to exit the program
To exit Multiflash
Select File from the menu bar then Select Exit
Input
Introduction
This section concentrates on the methods of providing input information for Multiflash, rather than the specification of that input information, which will be discussed in the sections relating to the various types of information which must be supplied.
The information you need to supply will include
• Model specification
• Data sources for pure component data
• Compounds in the mixture.
• Input conditions including composition
• Calculation (flash) to be carried out You may also wish to alter
• Units
• Level of property output
You can supply all of the input specification interactively, all of the input specification in a problem setup file or use a mixture of both.
Input files
An input file may contain a full specification of the problem or define only part of it.
We have usually referred to the former as problem setup files (extension .mfl) and have supplied several to use as test examples or templates for producing your own setup files. As a minimum they should define the model, data sources for pure components and model interaction parameters (BIPs) and components for your mixture. Usually they will also contain a composition and possibly the flash calculation and the input conditions related to it.
We recommend that any setup file that contains the numerical values for any input variables also defines the units for these to prevent any mismatch on loading.
Typical of partial setup files are those which are supplied to define a model (extension .mfc). These contain a specification of the model and a list of phase descriptors, which give the possible phases that may be encountered in calculations. The .mfc files we supply normally define up to four phases: one
vapour phase, two liquid phases and a water phase. More phases are needed for some applications, for example the hydrate I/II model configuration file contains seven phase descriptors, the hydrate I/II/H model configuration file has eight phase descriptors.
Exceptions are the input files for PVT analysis. They do not need to define either a model or a source for the BIPs but must include a source for the pure component data.
Menu options
Multiflash for Windows includes a menu bar and several drop-down menus. These allow you to control all aspects of running Mult iflash for Windows, grouped under the main menu headings of File, Edit, Select, Tools, Calculate, Table and Help.
File
The File menu controls the loading, saving, clearing and printing of setup files and the saving and printing of results.
Where you need to define further items, such as the directory and file to be loaded, a dialogue box will be activated.
If the setup files you want have been used re cently, you may find them listed. To load a setup file from the list, move the pointer to the file and double click on it.
Edit
This controls the normal windows editing functions of Cut, Copy and Paste, which can be used on text in the result s window.
Select
The Select menu option allows you to select the components, freeze-out model and related components, PVT Lab. Input, models, level of property output, stream types, units and the use of starting values. All the menu o ptions except Use Starting Values activate dialogue boxes.
Tools
The Tools menu allows you to use commands to access all options that are supported by Multiflash. This is most useful for options which have not yet been allocated a button or specific menu item in Multiflash for Windows. The Tools menu also allows you to view and edit the properties of any component in the stream and any binary interaction parameters being used. The Inhibitor calculator allows you to add water and inhibitors without defining them in the pure component list. It also allows you to define the amount of the inhibitor in the water phase in mass, mole or volume units and the calculator then determines the amount of inhibitor to be added to the overall compositio n in the units currently in use. The Salt Calculator is part of the Inhibitor Calculator dialog box. The Matching function amends the properties of petroleum fractions in the stream to reproduce user supplied liquid viscosity, wax appearance temperature, density/volume and dew or bubble points/GOR. For the asphaltene phase the matching function modifies the asphaltene model parameters.
The Preferences option allows the user to configure the appearance of the results in the results window, e.g. Font size , and to set the default units and level of property output for Multiflash.
The Show option allows you to see the current problem status such as the whole problem description or the models, pure component data source or BIP bank in force.
Calculate
The Calculate menu option controls the choice of flash options, tolerance calculation, phase envelope and chemical equilibria. Sub-menus are activated for Standard Flashes, Bubble and Dew Point Flashes, Hydrate and Wax flashes and Chemical Equilibria. Dialogue boxes are activated for Fixed Phase Fraction Flashes, (see “Fixed phase fraction flashes ” on page 122), tolerance calculation, (see “Tolerance calculations” on page 128), and phase envelope, (see “Phase ” on page 130) .
Table
The Table menu is for the option of creating output files for use with other applications, currently PIPESIM and OLGA. See “Interfaces with other programs ” on page 155.
Help
The HELP menu enables you to get help on a variety of topics, see “Help” on page 159.
Toolbar buttons
Some of the most common menu options have been allocated individual Toolbar buttons (located in the Tool bar section of the main window or in individual dialogue boxes).
Dialogue boxes, text boxes, tab controls, drop-down
tables and menus
Where additional information is needed for any menu option then you may be asked to supply this through dialogue boxes, text boxes, tab controls, drop-down tables or menus. These are described individually in the sections relating to the input variable being specified.
Commands
There may be some Multiflash facilities that have not been allocated a menu option. These are still accessible by using the Tools Command menu option. Some of these commands will be discussed in other sections where they are used in examples or case studies. They can be specified in Multiflash either as part of a problem setup file or through the Tools/Command menu, options, e.g.
will provide more details of the chosen model, including the name of the associated BIP set.
Models
Introduction
This section defines what a model is in terms of the Multiflash nomenclature, what models are available and when you might wish to use them, as well as the practical means of specifying and using them in Multiflash. For information on specifying models, see “How to specify models in Multiflash” on page 43. Detailed model descriptions may be found in our separate "Models and Physical Properties Guide".
What is a model?
Within the context of Multiflash, a model is a mathematical description of how one or more thermodynamic or transport properties of a fluid or solid will depend on pressure, temperature or composition.
What types of model are available?
The key thermodynamic property calculation carried out within Multiflash is the determination of phase equilibrium. This is based on the fundamental
relationship that at equilibrium the fugacity of a component is equal in all phases. For a simple vapour-liquid system
f
ivf
i l
=
where
f
iv is the fugacity of componenti
in the vapour phase andf
il is the fugacity of componenti
in the liquid phase.The models used in Multiflash to represent the fugacities from the phase equilibrium relationship in terms of measurable state variables (temperature, pressure, enthalpy, entropy, volume and internal energy) fall into two groups, equation of state methods and activity coefficient methods. The basis of each of these methods is described below.
With an equation of state method all thermal properties for any fluid phase can be derived from the equation of state. With an activity coefficient method the vapour phase properties are derived from an equation of state, whereas the liquid properties are determined from the summation of the pure component properties to which a mixing term or an excess term has been added.
Multiflash may also be used to calculate the phase equilibrium of systems containing solid phases, either mixed or pure. These may occur either when a normal fluid component freezes or may be a particular solid phase such as a
hydrate, wax or asphaltene. Models used to represent these solids are discussed below.
The transport properties of a phase (viscosity, thermal conductivity and surface tension) are derived from semi-empirical models which will be discussed later.
Equation of state method
An equation of state describes the pressure, volume and temperature (PVT) behaviour of pure components and mixtures. Most equations of state have different terms to represent the attractive and repulsive forces b etween molecules. Any thermodynamic property, such as fugacity coefficients and enthalpies, can be calculated from an equation of state relative to the ideal gas properties of the same mixture at the same conditions.
When to use equation of state methods
Equations of state can be used over wide ranges of temperature and pressure, including the subcritical and supercritical regions. They are frequently used for ideal or slightly non-ideal systems such as those related to the oil and gas industry where modelling of hydrocarbon systems, perhaps containing light gases such as H2S, CO2 and N2, is the norm. Equation of state methods do not necessarily represent highly non-ideal chemical systems, such as alcohol-water, well. For this type of system, at low pressure, an activity coefficient approach is preferable but at higher pressure you may need to use an equation of state with excess Gibbs energy mixing rules, such as RKSA(Infochem).
All equations of state will describe any system more accurately when binary interaction parameters (BIPs) have been derived from the regression of
experimental phase equilibrium data. BIPs are adjustable factors that are used to alter the predictions from a model until these reproduce as closely as possible the experimental data. The use of interaction parameters in Multiflash is discussed separately, see “Binary interaction parameters” on page 52.
The thermal properties of any fluid phase can be derived from an equation of state. However, one property which is often poorly represented by the simpler equations of state is the liquid density. Multiflash offers enhanced versions of both the Redlich-Kwong-Soave (RKS) and Peng-Robinson (PR) cubic equations of state where the equation of state parameters can be fitted to reproduce both the pure component saturated vapour pressure using a databank correlation and the saturated liquid density at 298K or Tr=0.7 (Peneloux method). These are
referred to in Multiflash as the advanced version of the particular equation of state.
Equations of state provided in Multiflash
The following equations of state are available in Multiflash.Ideal gas equation of state
This model is normally used in conjunction with an activity coefficient method when the latter is used to model the liquid phase. It could also be used to describe the behaviour of gases at low pressure.
Peng-Robinson equation of state
Redlich-Kwong (RK) and Redlich-Kwong-Soave (RKS)
equations
Like Peng-Robinson, the Redlich-Kwong and Redlich-Kwong-Soave equation and its variants are examples of simple cubic equations of state.
Advanced Equation of state options
The advanced implementation of both the Peng-Robinson and the Redlich-Kwong-Soave equations of state (PRA and RKSA models) contain additional non-standard features. These include the ability to match stored values for the liquid density and the saturated vapour pressure and a choice of mixing rule.
The Peneloux density correction
This correlation is used to match the density calculated from the equation of state to that stored in the chosen physical property data system. For light gases, the density is matched at a reduced temperature of 0.7 and the volume correction is assumed constant. In Multiflash, for liquid components the volume shift is treated as a linear function of temperature; the density is matched at 290.7K and 315.7K so as to reproduce the density and thermal expansivity of liquids over a range of temperatures centred on ambient. However, a third term is available, see the “Models and Physical Properties Guide”, and the user may enter all three coefficients as pure component properties.
Fitting the vapour pressure curve
For each component the constants are fitted by linear regression to the vapour pressure over a range of reduced temperatures corresponding to the stored data. Fewer than 5 coefficients will be fitted if there are insufficient data or if the extrapolation to low temperatures is unrealistic. If the vapour pressure is undefined, the correlation reverts to the standard equation for that component.
Mixing Rules
For highly non-ideal systems it is often useful to be able to use a Gibbs energy excess model (e.g. UNIQUAC or NRTL) as part of the mixing rule for the equation of state. The possibilities are outlined in the separate "Models and Physical Properties Guide".
When to use cubic equations of state
The simple cubic equations of state, PR and RKS, are widely used in engineering calculations. They require limited pure component data and are robust and efficient. Both PR and RKS are used in gas -processing, refinery and petrochemical applications. They will usually give broadly similar results, although if one model has been fitted to experimental data and there are no interaction parameters for the other then the optimised model is always preferable. There is some evidence that RKS gives better fugacities and PR better volumes (densities) but both can be improved if the Peneloux correction is used.
For most applications we would recommend the use of the RKSA (or PRA) model sets which use the Peneloux correction, fit a to the vapour pressure and use the Van der Waals 1-fluid mixing rules.
RKSA with the Infochem mixing rules is used as part of the hydrate model and provides extra flexibility to represent the highly non-ideal aqueous system. It does, however, require suitable BIPs for such systems.
The API variant of RKS is applicable to petroleum systems and mixtures containing hydrogen, while RK may be used instead of the ideal gas model for the vapour phase of systems where the liquid phase is being modelled with an activity coefficient model.
Cubic plus association (CPA) model
The CPA model consists of the Redlich-Kwong-Soave equation plus an additional term based on Wertheim’s theory that represents the effect of chemical association.
The CPA model also uses the Peneloux density correction to match the liquid density calculated from the equation of state to that stored in the chosen physical property data system. The volume shift is a linear function of temperature which is set to match the saturated liquid density at two different temperatures. For light gases, a constant volume shift is used that is fitted to the gas’s liquid density at a reduced temperature of 0.7.
When to use CPA.
In MF3.6 the CPA model may be used for hydrate calculations with methanol, ethanol, MEG, DEG, TEG and salt inhibition, as these are the only cases for which parameters are currently provided. Parameters for additional substances may be added in future versions of Multiflash.
PSRK equation of state
This model consists of the RKSA equation of state with vapour pressure fitting, the Peneloux volume correction and the PSRK type mixing rules. The excess Gibbs energy is provided by the PSRK variant of the Unifac method. This is the same as the normal VLE Unifac model except that the group table has been extended to include a large number of common light gases.
When to use PSRK
The PSRK model is an extension of the Unifac method. It is intended to predict the phase behaviour of a wide range of polar mixtures using the solution of groups concept as embodied in Unifac. The main benefit of PSRK is that it is able to handle mixtures containing gases much better than Unifac and unlike a normal equation of state it can handle polar liquids. This is because (a) it uses an equation of state with an excess Gibbs energy mixing rule thereby avoiding problems of how to handle supercritical components in an activity coefficient equation; (b) the Unifac group parameter table has been extended in PSRK to include 32 common light gases.
LCVM equation of state
This model consists of the PRA equation of state with vapour pressure fitting, the Peneloux volume correction and the LCVM type mixing rules. The excess Gibbs energy is provided by the LCVM variant of the Unifac method. This is the same as the normal VLE Unifac model except that the group table has been extended to include a number of common light gases found in petroleum fluids.
When to use LCVM
The LCVM model is an extension of the Unifac method. It is intended to predict the phase behaviour of petroleum fluids mixed with polar compounds using the solution of groups concept as embodied in Unifac. The main benefit of LCVM is that it is better able to handle asymmetric mixtures. This is because it uses an equation of state with an excess Gibbs energy mixing rule that was specifically
designed to work with Unifac for mixtures of light gases and heavy hydrocarbons.
The models discussed are all examples of cubic equations of state. Multiflash also includes several other equations of state that are non-cubic.
PC-SAFT equation of state
The PC-SAFT equation is a development of the SAFT model that has been shown to give good results for a wide range of polar and non-polar substances including polymers. Polymers is one of the most important areas of application of PC-SAFT. The model appears to be one of the most accurate and realistic equations of state currently available for modelling polymer systems.
PC-SAFT stands for the Perturbed Chain Statistical Associating Fluid Theory and it incorporates current ideas of how to model accurately the detailed thermodynamics of fluids within the framework of an equation of state. The mathematical structure is very complex and cannot be conveniently described in a manual. However, references where this information may be found are given in our "Models and Physical Properties Guide".
The Multiflash version includes an implementation of the association term of PC-SAFT which follows the same general structure as the association term in the CPA model.
Polymers are not well defined chemical compounds but rather a distribution of chain molecules of varying molecular weight. In Multiflash, polymers must be represented by one or more pseudo components which must be set up as user-defined components.
Using PC-SAFT, every pseudo component for a given polymer must be assigned the same values of the pure -compound parameters SAFTSIGMA (in metres, not Ångstrom units) and SAFTEK. In addition, the SAFTM parameter must be specified. This is normally quoted as a ratio to the molecular weight, so it has to be calculated for each polymer pseudo component knowing the molecular weight. For polystyrene, for example, Gross and Sadowski give the ratio as 0.019, so for a polystyrene pseudo component of molecular weight 100000, the SAFTM parameter should be set to 100000×0.019=1900, etc.
Additionally, the user can define association parameters if the polymer forms hydrogen bonds. These parameters are SAFTBETA which defines the
volumetric or entropic parameter, and SAFTEPSILON, the energy or enthalpy parameter. Multiflash also provides an extension to the PC-SAFT definition: so that the user can also supply a heat capacity parameter SAFTGAMMA for the association term. For the association term to be non-zero, the user must also define the parameter SAFTFF which denotes the number of donor bonding sites per segment of polymer.
Values of PC-SAFT parameters for polymers can be found in Modeling Polymer
Systems Using the Perturbed-Chain Statistical Associating Fluid Theory Equation of State by Gross and Sadowski in Industrial and Engineering
Chemistry Research, 41, 1084, (2002) and in Modeling of polymer phase
equilibria using Perturbed-Chain SAFT by Tumakaka, Gross and Sadowski in
Fluid Phase Equilibria, 194-197, 541, (2002).
Multiflash allows the user to define up to four polymer segments which can be used to define any number of homopolymers or copolymers following the method of Tumakaka, Gross and Sadowski described in the reference above. If the polymer is formed from only one type of segment, it is a homopolymer of that segment; if it is formed of two or more types of segment, it is a copolymer. Multiflash also has a version of PC-SAFT with simplified mixing rules as proposed by researchers at the Danish Technical University. The same pure component parameters can be used for this model variant but the model interaction parameters will be different.
Lee-Kesler-Plöcker (LKP) equation of state
The LKP method is a 3 parameter corresponding states method based on interpolating the reduced properties of a mixture between those of two reference substances
When to use LKP
The method predicts fugacity coefficients, thermal properties and volumetric properties of a mixture. However, it is rather slow and complex compared to the cubic equations of state and is not recommended for phase equilibrium
calculations, although it can yield accurate predictions for density and enthalpy. It would normally be applied to non-polar or mildly polar mixtures such as hydrocarbons and light gases.
Benedict-Webb-Rubin-Starling (BWRS) equation of state
The BWRS equation method is an 11 parameter non-cubic equation of state. For methane, ethane, ethylene, propane, propylene, isobutane, n-butane, isopentane, n-pentane, hexane, heptane, octane, carbon dioxide, hydrogen sulphide and carbon dioxide, the pure component parameters are set to values recommended by Starling in his book ‘Fluid Thermodynamic Properties for Light Petroleum Systems’, Gulf Publishing Co., Houston, 1973. For other substances the pure component parameters are estimated using correlations developed by Starling and Han which are given in the same book.When to use the BWRS equation
The BWRS equation gives much more accurate volumetric and thermal property predictions for light gases and hydrocarbons. Given suitable interaction
parameters it should give reasonable vapour-liquid phase equilibrium predictions but owing to its complexity, it requires more computing time than the cubic equations of state.
Multi-reference fluid corresponding states (CSM) model
The CSM model is based on a collection of very accurate equations of state for a number of reference fluids. It will provide accurate values of thermodynamic properties for any of the reference fluids (see below for a list) and it uses a 1-fluid corresponding states approach to estimate mixture properties. It is formulated so that mixture properties will reduce to the (accurate) pure component values as the mixture composition approaches each of the pure component limits.Reference fluids
The current model implementation includes reference equations of state for the following substances: argon, iso-butane, n -butane, CO, CO2 , ethane, ethylene, fluorine, H2S, hydrogen, methane, nitrogen, octane, oxygen, n-pentane, propane, water (IAPSW 95), xenon, helium, hexane, heptane, octane, ammonia, neon, propylene, R123, R152a, R124, R125, R134a, R22, R32, R11, R113, R114, R115, R116, R12, R13, R14, R23, and RC318. Hydrocarbons between pentane and octane are modelled as combinations of these substances. The equations of state are taken from various sources and do not all have the same quality or range of applicability.
