User Guide for
Multiflash for Windows
Infochem/KBC Advanced Technologies plc
Version 4.4
February 2014
Infochem/KBC Advanced Technologies plc
Unit 4, The Flag Store
23 Queen Elizabeth Street
London SE1 2LP
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/KBC Advanced Technologies plc
Unit 4, The Flag Store 23 Queen Elizabeth Street London SE1 2LP, 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
The Multiflash GUI ... 1
Multiflash Software System... 1
Document Organisation ... 2
New Features and Changes in Version 4.4 and 4.3 ... 2
New Features and Changes in Version 4.2 ... 2
Running Multiflash... 2
HELP ... 3
Case studies ... 3
Appendix - Multiflash Commands ... 3
Installation ... 3
New Features and Changes in Version 4.4 and 4.3
5
Introduction ... 5Models ... 5
Huron-Vidal-Pedersen mixing rule... 5
Sutton Model for surface tension... 5
LBC ... 5
Salt component ... 5
High accuracy reference eos for water-ammonia binary system ... 6
New high accuracy reference eos ... 6
Activity Coefficient models... 6
Performance enhancements ... 6
Phase key components... 6
Windows GUI... 6
PVTSim import tool ... 6
Models tab ... 6
Inhibitor calculator ... 6
Surface tension ... 7
Petroleum Fraction Input Table ... 7
Tables... 7 OLGA tables... 7 Interfaces ... 7 Excel Interface... 7 CAPE-OPEN ... 7 Databanks ... 7 Infodata... 7 DIPPR... 7
New Features and Changes in Version 4.2
9
Introduction ... 9Models ... 9
CSMA model... 9
Mercury ... 9
Poynting correction ... 9
Activity coefficient model for gas phase ... 9
Binary Interaction Parameters ... 10
Multiflash phase equilibrium algorithm... 10
Flash calculations... 10
Databanks ... 10
Infodata... 10
Windows GUI... 11
PVTSim import tool ... 11
Reid vapour pressure ... 11
Liquid dropout and Wax precipitation curve... 11
New icon for Asphaltene precipitation curve ... 11
Phase envelopes for solids... 11
Hydrate models... 11
Inhibitor calculator ... 11
PVT Analysis ... 11
Retrograde Dew Point ... 11
Calculation options ... 11
Usability ... 12
Tables... 12
OLGA tables... 12
Multiflash Excel Interface ... 12
Joule-Thompson coefficient ... 12
Getting Started
13
Starting Multiflash ... 13Multiflash Main Window... 13
Input section ... 14 Conditions ... 14 Fluid identification ... 14 Compositions... 14 Results window ... 14 Menu options ... 14 The Toolbar ... 18
Defining a problem in Multiflash ... 18
Loading an existing problem file ... 18
Loading a problem setup file ... 18
Calculations ... 19
The results ... 19
Additional calculations ... 20
Setting up a new problem ... 21
Clearing previous problems... 21
Defining the components... 21
Defining the models ... 22
Set Input Conditions ... 23
Carrying out the flash calculation... 23
Other calculations... 24
Phase envelope ... 24
Saving the problem setup... 25
Backup file ... 26
Loading a existing MFL file ... 26
Warning option for matching and PVT form... 26
Printing the output ... 26
Saving the output ... 27
How to exit the program ... 27
Technical support... 28
Models
29
Introduction ... 29What is a model? ... 29
Equation of state models... 30
When to use equation of state methods ... 30
Equations of state provided in Multiflash ... 30
Ideal gas equation of state ... 30
Peng-Robinson equation of state ... 30
Peng-Robinson 1978 (PR78) equation of state... 31
Redlich-Kwong (RK) and Redlich-Kwong-Soave (RKS) equations... 31
Advanced Equation of state options ... 31
When to use cubic equations of state... 32
Cubic plus association (CPA) model ... 32
PSRK equation of state... 32
ZJ (Zudkevitch-Joffe) model ... 33
PC-SAFT equation of state... 33
Lee-Kesler (LK) and Lee-Kesler-Plöcker (LKP) equations of state... 34
Benedict-Webb-Rubin-Starling (BWRS) equation of state ... 34
Multi-reference fluid corresponding states (CSMA) model ... 35
IAPWS-95 ... 35
Water-Ammonia ... 35
Carbon Dioxide high-accuracy model ... 36
GERG-2008... 36
GERG-2008 (Infochem extension)... 36
Activity coefficient methods... 37
Activity coefficient equations in Multiflash ... 37
Gas phase models for activity coefficient methods ... 38
When to use activity coefficient models... 38
Models for solid phases ... 39
Solid freeze-out model ... 39
Scaling and general freeze-out model... 39
Modelling hydrate formation and inhibition... 39
Modelling wax precipitation... 42
Modelling asphaltene flocculation... 43
Other thermodynamic models ... 43
Transport property models... 44
Viscosity... 44
Thermal conductivity... 45
Surface Tension ... 46
Diffusion coefficient... 46
How to specify models in Multiflash... 47
Using the menu... 47
Loading a model from a .mfl file... 48
Setting up preferred models in Multiflash ... 48
How to change a model ... 48
Models for solid phases ... 48
Hydrates ... 48
Pure solid phase... 49
Waxes ... 50
Asphaltenes ... 51
Combined Solids Model ... 52
Troubleshooting - models ... 52
Model is not available ... 52
Groups not available for UNIFAC model ... 52
Binary interaction parameters ... 53
BIPs and models ... 53
Temperature dependence of BIPs... 54
BIPs available in Multiflash ... 54
Viewing BIP values ... 55
Units for BIPs... 57
Supplementing or overwriting BIPs ... 58
BIPs for CSMA and GERG mixing rule ... 59
Units ... 60
BIP databank ... 60
Differences between the PR Model in Multiflash and Aspen Hysys ... 60
Components
63
Introduction ... 63Normal components... 63
Petroleum fractions... 65
Defining a mixture ... 65
Specifying the data source... 66
Selecting components ... 66
Adding, inserting, replacing and deleting components... 69
Viewing and editing pure component data ... 70
User-defined components ... 72
Adding a user-defined component... 72
Specifying data for a user-defined component ... 73
Models and input requirements ... 74
Stream types ... 76
Hydrate inhibitors ... 79
Inhibitor calculator: alcohols/glycols ... 79
Salt calculator ... 81
Troubleshooting - components ... 84
Databank not found ... 84
Databank not licensed... 85
Component cannot be found... 86
Too many components in the mixture ... 87
Petroleum fluids
89
Introduction ... 89PVT Lab Analysis input ... 89
Component list ... 91
Petroleum fluid composition ... 94
Molecular weight and specific gravity ... 95
Total amount of fluid... 96
Water cut ... 97
Total Wax Content ... 97
SARA Analysis ... 97
Pseudocomponents ... 98
Characterisation... 99
User Defined Cuts ... 100
Saving a PVT Analysis... 101
Black Oil Analysis ... 101
Input data... 102
Distillation curves ... 102
TBP distillation... 102
ASTM D86 distillation ... 104
PVT Lab Analysis input with n-paraffin analysis... 105
n-Paraffin distribution ... 105
Characterisation... 107
Estimated n-paraffin distribution... 108
Troubleshooting – PVT Analysis... 109
Sensitivity to characterisation... 109
Presence of water... 109
Defining petroleum fractions ... 109
Basic characterisation properties ... 109
Other properties ... 110
Entering petroleum fractions ... 110
Editing petroleum fraction data ... 112
Problems defining a petroleum fraction ... 113
Delumping tool ... 113
How to use the delumping utility ... 114
Matching using petroleum fraction properties ... 116
Matching dew and bubble points... 116
Matching Density/Volume ... 122
Matching wax data/WAT ... 123
Matching liquid viscosity ... 125
Matching vapour viscosity ... 126
Problems when matching ... 127
Petroleum Fluid Blending ... 127
Blending method ... 128
Fluid file name... 128
Fluid amounts ... 129
Model definition ... 129
Blending procedure ... 129
Example for blending ... 130
Example with waxy crudes... 132
Example with asphaltenic crudes ... 133
Input conditions
137
Introduction ... 137Specifying compositions... 137
Specifying temperature, pressure and volume ... 138
Specifying enthalpy, entropy and internal energy... 139
Troubleshooting - input conditions ... 139
Calculations
141
Introduction ... 141The basis of a flash calculation... 141
Flashes available in Multiflash ... 142
Isothermal (P,T) flash ... 142
Isenthalpic flashes ... 143
Isentropic flashes ... 143
Isochoric flashes ... 143
Bubble and dew point flashes ... 143
Fixed phase fraction flashes ... 144
Phase Envelopes ... 148
Phase Envelopes for solids ... 157
Liquid dropout curve calculation... 158
Hydrate calculations ... 159
Wax calculations ... 159
Tolerance calculations ... 161
Reid Vapour Pressure ... 162
Property output in Multiflash... 164
Troubleshooting - flash calculations ... 165
Plot the phase envelope ... 166
Use the P,T flash ... 166
Limit the number of phases ... 167
Consider all types of solution ... 167
Provide a starting estimate... 167
Provide a key component ... 168
Units
169
Introduction ... 169Default units ... 169
Changing units ... 170
Output
173
Introduction ... 173
The results window... 173
Font... 174
Writing the results to a file ... 174
Printing the output ... 175
Calculation output... 175
Manipulating the Output... 177
Phase Labelling... 178
Aqueous phase labelling... 178
Enthalpy definition ... 178
Activity Models ... 179
Entropy definition ... 180
Activity Models ... 180
Errors and warning messages ... 181
Displaying status for current settings... 181
Troubleshooting - output ... 181
The output does not include everything expected ... 181
Phase labelling... 182
Fonts ... 182
Interfaces with other programs
183
Introduction ... 183Pipesim PVT files ... 183
OLGA ... 184
OLGA hydrate file... 186
OLGA wax file ... 186
Prosper PVT files... 187
To generate the file ... 187
CAPE-OPEN Interface ... 188
PVTSim CHC file import tool ... 189
Help
191
Introduction ... 191On-line help ... 191
Help Topics ... 191
Multiflash Error Codes ... 193
Check for Updates ... 193
About Multiflash ... 194
Technical support... 194
Case studies - Pure component data
197
Introduction ... 197Physical properties of a pure component ... 197
Defining the problem in Multiflash ... 197
Obtaining properties from the Pure Component Data option ... 200
Excel interface ... 202
Case studies - Phase equilibria
205
Introduction ... 205Oil and gas systems ... 205
Calculating the bubble point curve ... 206
Calculating the dew point curve ... 207
Phase envelope ... 208
Adding water to the system ... 209
Other flash calculations ... 212
PVT Analysis... 214
User defined carbon number cuts ... 219
TBP curves ... 221
Black Oil Analysis ... 223
Delumping tool – Case study... 225
Refrigerant mixtures ... 229
Polar systems ... 230
Modelling a polar mixture ... 230
Liquid-liquid equilibria ... 234 Vapour-liquid-liquid equilibria... 235 Azeotropes... 235 Eutectics ... 236 Polymers ... 237 Data input ... 237 Co-Polymers ... 239
Case studies - Hydrate dissociation, formation and inhibition
243
Introduction ... 243Defining the hydrate models... 243
Fluid phase model ... 244
Hydrate model ... 244
Nucleation model ... 245
Ice model ... 245
Scale model ... 245
Phases ... 245
Hydrate calculations with Multiflash... 246
Will hydrates form at given P and T ?... 246
Hydrate formation and dissociation temperature at given pressure ... 247
Hydrate formation and dissociation pressure at given temperature ... 250
Hydrate phase boundary ... 251
Other flash calculations with hydrates... 251
Maximum water content allowable before hydrate dissociation ... 251
Calculations with inhibitors ... 252
Can hydrates form at given P and T ?... 252
Hydrate dissociation temperature at a given pressure ... 254
Hydrate dissociation pressure at a given temperature ... 254
Hydrate phase boundary ... 254
Amount of inhibitor required to suppress hydrates ... 255
Salt inhibition ... 256
Scale precipitation ... 258
Case studies – Wax precipitation
260
Introduction ... 260Defining the wax model... 260
Calculating wax appearance temperature (WAT)... 261
Calculating wax precipitation ... 264
Case studies – Asphaltene flocculation
267
Introduction ... 267Input data ... 267
Defining the asphaltene model ... 268
Asphaltene matching ... 270
Saturation P at reservoir T ... 272
Calculating asphaltene precipitation conditions ... 272
Sensitivity of calculations to variation in input data ... 276
Choice of Analysis method ... 276
No reservoir or precipitation conditions ... 280
Gas injection ... 282
Titration ... 283
Case studies – Combined solids
287
Introduction ... 287Asphaltene precipitation ... 287
Wax and Asphaltene precipitation ... 288
Hydrates, Waxes and Asphaltenes ... 289
Case studies – Excel spreadsheets
293
Introduction ... 293UNFACFIT.xls ... 293
Notes... 294
UNIFAC ... 294
Activity model worksheets ... 294
VLEFIT.xls... 295
Solids.xls... 296
PVT Analysis ... 296
Match bubble point... 297
Wax ... 298
Asphaltenes ... 299
Asphaltene with gas injection... 300
Hydrates ... 301
Case study – Mercury partitioning
303
Introduction ... 303Defining the mercury model ... 303
Calculating mercury partitioning and dropout ... 304
Other calculations ... 308
Distribution of mercury species ... 308
Appendix - Multiflash Commands
311
Introduction ... 311Commands ... 311
When you may need to use commands ... 311
Defining models... 312
What the model definition means ... 312
Supplying an external file of BIPs ... 313
Defining phase descriptors and key components ... 314
Overview
Introduction
Multiflash is a powerful and versatile system for modelling physical properties and phase equilibria. It can be used as a stand-alone program or in conjunction with other software. This manual describes the features of the Multiflash Windows Graphical User Interface (GUI) and explains how it can be used to solve engineering problems.
The Multiflash GUI
The Multiflash Windows GUI gives you access to the full capabilities of the program, including:
All the thermodynamic and transport properties needed for engineering studies.
Comprehensive fluid characterisation and model tuning for petroleum fluids.
Flash calculations to determine the phases present at specified conditions and their type, composition and amounts.
Modelling solids formation, including pure solids, halide scales, hydrates, waxes and asphaltenes.
It is easy to set up all aspects of a study: components, models, units, type of calculation etc. via menu options or tool bar buttons. This configuration can then be saved for future use with the GUI or other applications.
Virtually any flash calculation can be carried out irrespective of the number and type of phases present. Complete phase envelopes can be plotted showing phase boundaries and critical points.
Multiflash Software System
In addition to the Windows GUI, it is possible to use the Multiflash calculation engine in a variety of ways. There is a Multiflash add-in for Microsoft Excel and an interface for use with Matlab. A CAPE-OPEN physical property package interface allows Multiflash to be used by any application that is CAPE-OPEN enabled. Multiflash may also be used with any software that can call a Windows DLL. We provide support for applications written in various programming languages including C++, Visual Basic and Fortran. Linux applications can also be supported.
Separate documentation is available for each of these interfaces.
Document Organisation
The rest of this document is divided into the following sections.
New Features and Changes in Version 4.4 and
4.3
New developments and additions are listed, although more details of how to use new features will be covered in the appropriate section. Information is also given on changes to models or data which may give rise to different results from those obtained with earlier versions of Multiflash. Version 4.3 was an interim internal release of Multiflash.
New Features and Changes in Version 4.2
The developments done in the previous version are listed for reference.
Running Multiflash
Each section provides details on different aspects of the software.
Getting Started
Describes the different parts of the Multiflash main window and shows how to use the program by running a simple example with step-by-step instructions.
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 types 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.
Petroleum Fluids
Covers a number of topics related to modelling petroleum fluids: how to use the information measured by a PVT laboratory to produce a compositional fluid model; how to define the properties of petroleum fractions (pseudocomponents); how to use experimental data to tune the petroleum fluid model.
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 which 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
The Multiflash command language is used to store information about the problem setup (databanks, components, models etc.) in Multiflash .mfl files. Although users should not need to understand the command language it is fully described in the Multiflash Command Reference manual.
In some circumstances it may be necessary to use Multiflash commands to configure the software. The Tools menu has a Command option which allows commands to be entered. Those commands that users of the Multiflash GUI may find useful are discussed in the appropriate sections of the User Guide or in the Appendix.
Installation
Information on how to install Multiflash software is provided in the separate
New Features and Changes in
Version 4.4 and 4.3
Introduction
As usual the new version includes the results of general maintenance and improvements in numerical methods over the past year, as well as performance enhancements. Specific features are described below.
Models
Descriptions and references detailing the models are provided in the User Guide
for Models and Physical Properties.
Huron-Vidal-Pedersen mixing rule
This mixing rule has been implemented for both the Peng-Robinson and the Redlich-Kwong-Soave equations of state. Binary interaction parameters are included for defined components.
Sutton Model for surface tension.
This model has been implemented to allow for a computationally inexpensive way to calculating the surface tension of systems containing water.
LBC
It is now possible to specify a critical volume specifically for the LBC model for each component, and to specify the LBC model parameters A1-A5.
Salt component
The salt pseudo-component can now be used with the following models: PR, PRA, PRA-Infochem, PR78, PR78A, PR78A-Infochem, RKSA, and RKSA-Infochem.
High accuracy reference eos for water-ammonia
binary system
The Tiller-Roth high accuracy corresponding equation of state model for water-ammonia binary system is now available.
New high accuracy reference eos
High accuracy reference eos for dodecane, DME, R161, R236EA and R236FA are implemented in Multiflash 4.4. For the details, refer to “Multi-reference fluid corresponding states (CSMA) model” on page 35.
Activity Coefficient models
For very light components, like N2, O2, etc, the Poynting is disabled. This allows a more correct description of mixtures of these components with heavier ones such as water.
Performance enhancements
The cubic equations of state and the CPA equations have been optimized in such a way that from Multiflash 4.3 onwards it is possible to perform flash
calculations about 1.5 to 2 times faster than the previous versions of Multiflash.
Phase key components
It is now possible to specify multiple key components for phases. It is useful for defining aqueous phases where the amount of water may be small.
Windows GUI
PVTSim import tool
It is now possible to import characterised fluids from PVTSim if they were exported to a CHC file. This tool accepts systems with aqueous components, and allows the user to define the desired number of phases. It is possible to select an option to define models where the density of the gas phase is calculated using the GERG-2008 model while the rest of the thermodynamic properties are calculated using cubic models.
Models tab
The "Select Model Set" tab for Cubic Eos now also has an option where the GERG 2008 model can be used to estimate the density of the vapour phase. The Huron-Vidal-Pedersen mixing rule can be selected for PRA and RKSA. A second liquid hydrocarbon was added to the Mercury model tab.
Inhibitor calculator
Surface tension
The user can select the MacLeod-Sugden 2 phase variant for the calculation of surface tension. This model can be selected under the MCSA (MCS-Advanced) tab.
Petroleum Fraction Input Table
The user can now specify the critical volume to use in the LBC model in the pseudo component generation table. The property has the name VCLBC and is only used in the LBC model.
The maximum dimension of the petroleum fraction input table is now extended from 25 to 100.
Tables
OLGA tables
The OLGA table generator was made more robust and more compliant with the file format accepted by OLGA.
The maximum dimension of the temperature and pressure grid is now extended from 50 to 100 for the current version of Multiflash.
Interfaces
Excel Interface
The Excel-AddIn can now be used in 64 bit versions of Microsoft Office 2010 and later.
CAPE-OPEN
Better support for multithreaded applications. Native support for 64bit applications.
Databanks
Infodata
Saturated liquid surface tension of MEG, TEG corrected.
DIPPR
New Features and Changes in
Version 4.2
Introduction
As usual the new version includes the results of general maintenance and improvements in numerical methods over the past year. Specific features are described below.
Models
Descriptions and references detailing the models are provided in the User Guide
for Models and Physical Properties.
CSMA model
New high accuracy corresponding state models are implemented for the refrigerants: R1234YF and R1234ZE(E) in Multiflash 4.2.
Mercury
The mercury model has been extended, so that it can now be used in connection with PR78A and CPA, as well as with RKSA.
Poynting correction
The Poynting correction has been modified to give zero correction to the enthalpy and entropy at saturation pressure. The enthalpy, entropy and heat capacity calculated with activity coefficient models with Multiflash 4.2 are therefore different from the results with previous version, but the new pure component values are closer to correlations for saturated liquid Cp.
Activity coefficient model for gas phase
A new model, ACG (activity coefficient model for gas phase), has been included in Multiflash to allow the user to calculate thermal properties for the gas phase based on correlations for saturated liquid heat capacity and heat of vaporisation.
LBC viscosity model
The LBC viscosity model has been fixed to work properly with petroleum fraction with carbon number lower than C7.
Binary Interaction Parameters
Several BIPs were added or corrected in Multiflash version 4.2.
CPA model CPA
water/Hg, MEG/Hg, correct BIP for ethane/MEG, THF/water, O2+H2O, O2+n-octane
RKSA-Info, CPA and PR
H2 + (methane, ethane, propane, butane, pentane, hexane, heptane, octane, decane, dodecane, hexadecane, eicosane, octacosane, n-hexatriacontane, carbon dioxide and water)
RKSA
O2+H2O
PRA
O2+n-octane
Multiflash phase equilibrium algorithm
Make the Pressure-Enthalpy and Pressure-Entropy flashes more robust in particular in the single phase region.
Flash calculations
In Multiflash 4.2, the Reid vapour pressure calculation is implemented. The Reid vapour pressure (RVP) is usually employed by refineries to quantify and modify the vaporization of gasolines and other volatile petroleum products. For the details, see the section on “Reid Vapour Pressure” on page 162.
When the flash calculation involves solid phases, the errors about not being able to calculate viscosity of a phase were removed. It is not possible to calculate viscosity of solid phases.
The Joule-Thompson coefficient has been added as an output property of the flash calculations.
Databanks
Infodata
New components, R365mfc, R1234YF and R-1234ZE(E) are added into the INFODATA databank.
The ideal gas heat capacities of Na+, Cl-, Ca++ and Br- in the databank have been revised.
The ions Mg++, Ba++, Sr++, H+, CO3--, HCO3-, OH- and SO4—have been added to the INFODATA databank.
Windows GUI
PVTSim import tool
It is now possible to import characterised fluids from PVTSim if they were exported to a CHC file.
Reid vapour pressure
It is now possible to calculate the Reid Vapour pressure via the calculation
Liquid dropout and Wax precipitation curve
The liquid dropout and wax precipitation curve tools have been improved to allow more control of the plotting.
New icon for Asphaltene precipitation curve
A new tool was added to determine graphically the precipitation of asphaltenes at constant pressure.
Phase envelopes for solids
The automatic calculation of the V/L phase envelope as well as solid phase boundaries has been made more robust.
It is now possible to right click in area of this plot and to a PT flash.
Hydrate models
The RKSA-Infochem model has been removed from the hydrate model selection form, so that it is now only possible to select CPA-Infochem, with or without the electrolyte model. It is possible to load an .mfl file with the RKSA-Infochem hydrate model defined and use it in Multiflash 4.2.
Inhibitor calculator
The salt component tab has been removed from the inhibitor calculator.
PVT Analysis
The PVT analysis tool has been updated to allow the user to specify density in API degrees.
Retrograde Dew Point
A new button was added to the main window to calculate automatically the retrograde dew point at a fixed temperature with having to resort to the Fixed Phase Fraction tool.
Calculation options
The calculations options have been simplified. Now only “Normal”, “Upper Retrograde” and “Unspecified” are show for the type of solution where that is necessary.
Usability
In the forms where is necessary to input data, such as the Matching forms or the PVT Analysis input, the user is warned that those values are lost if the dialog box is closed without performing any operation with the data.
Tables
OLGA tables
The OLGA table generatas made more robust and more compliant with the file format accepted by OLGA.
Multiflash Excel Interface
Joule-Thompson coefficient
The Joule Thompson coefficient was added to the list of properties that is possible to get in a flash calculation.
Getting Started
Starting Multiflash
Start Multiflash by clicking on the Multiflash 4.4 shortcut on the desktop.
Alternatively, from the Windows Start menu choose All Programs and then Multiflash 4. The Multiflash Main Window will be displayed.
Input section
The Input section of the Multiflash main window is located below the Toolbar. It comprises the Conditions and Fluid identification widgets.
Conditions
The input conditions, such as temperature and pressure, used in Multiflash calculations are shown below the Toolbar. The current units are shown next to each value.
Fluid identification
A text box labelled Fluid identification is located to the right of the Conditions section of the main window.
Use of the box is optional but it does allow you to add any comments or notes and, subsequently, to save these as part of the .mfl file. This can be useful for future reference, perhaps for identifying the study and the source of the fluid data, etc. When the file is loaded again any notes will be shown in the Fluid identification box.
Compositions
The Compositions button is located below the Fluid identification box. It allows the fluid composition to be entered once components have been selected.
Results window
All the phase equilibrium flash calculations, error/warning messages, echoes and results from Multiflash operations are displayed in the main window of
Multiflash.
Menu options
The menus allow you to control all aspects of running Multiflash. Options are 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 as well as the saving and printing of results.
In menu items ending with triple dots you will need to define further items, such as the directory and file to be loaded. A dialogue box will be displayed to allow you to do this.
The last nine recently-used setup files are listed in the File menu. To load a file from the list, double-click on the file name.
Edit
This controls the normal windows editing functions of Cut, Copy and Paste, which can be used on text in the results window.
Select
The Select menu option allows you to select the fluid-phase components, components that may appear as pure solids (Freeze-out Components), petroleum fluid characterisation (PVT Lab. Input) physical property models, level of property output, stream types, units of measurement and the use of starting values for calculations. All the menu options except Use Starting Values activate dialogue boxes which are described in later sections of this guide. Items marked with the right pointing triangle contain submenus.
Tools
The Tools menu groups together options for displaying information about the current problem, utilities for handling data and settings that control the calculations or other aspects of the way Multiflash works.
The Command option can be used to enter Multiflash commands (see the Appendix on page 311). This is not normally necessary but may sometimes be useful for setting options that are not, otherwise, accessible in the Multiflash GUI.
Pure Component Data and BIPs options allow you to view and edit the properties of any component in the mixture and any binary interaction parameters being used.
The Inhibitor calculator allows you to add water and hydrate inhibitors (alcohols, glycols, salts) in volume, mass or molar units. A salt analysis may be entered in a wider variety of units.
The Matching function tunes the properties of petroleum fractions in the mixture to reproduce user-supplied measurements. The quantities for which data may be supplied are: dew points, bubble points/GOR, liquid viscosity and liquid density. The wax model may be tuned to match a wax appearance temperature or precipitation data and the asphaltene model parameters may be tuned to match flocculation or titration data.
The Blend Fluids option allows the user to blend (mix) a number of fluids by mass, volume or molar amounts.
The Preferences option allows the user to set the default behaviour when Multiflash is started. You can set the preferred units and the calculated
properties, the locations of files used by Multiflash, the appearance of the results in the results window and the default models to be used for calculations. All
these preferences are stored in the Windows Registry. Any changed items will be used the next time that Multiflash is started. Settings such as models and units may be changed at any time during a Multiflash session using the Select menu but this has no effect on the Preferences.
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 provides a choice of flash calculations. Different types of calculations are grouped together as: Standard Flashes; Bubble and Dew Point Flashes; Fixed Phase Fraction Flashes; (see “Fixed phase fraction flashes” on page 144), the tolerance calculation, (see “Tolerance calculations” on page 161), the phase envelope calculation , (see “Phase Envelopes” on page 148) , phase envelope for solids, special-purpose Hydrate and Wax calculations, liquid dropout, waxes, asphaltene precipitation curve calculations, and Reid vapour pressure calculation.
Table
The Table menu is for creating input files for use with other applications, currently PIPESIM, OLGA and Prosper.
See “Interfaces with other programs” on page 183.
Help
The HELP menu enables you to get help on a variety of topics, see “Help” on page 191.
The Toolbar
The Toolbar provides a quick way of accessing some of the most common operations. Holding the cursor over a toolbar button displays a tool-tip that describes its function. For example, the PT button for the flash at fixed P and T calculation.
Defining a problem in Multiflash
This means selecting the components in the mixture and setting their
compositions, choosing the models you wish to use to calculate properties and setting the input conditions (e.g. temperature and pressure). The steps are described in detail in the appropriate sections below. In this tutorial we will first use an existing problem file and then go through the steps required to set up a problem from scratch.
Loading an existing problem file
Infochem supplies a series of sample problem setup files covering a variety of typical problem types. These can be used as examples when testing the program or can be used as a basis for defining your own setup files. By convention problem setup files for Multiflash have the extension .mfl.
The file used for the simple tutorial is C4C5.mfl. 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.
Loading a problem setup file
The problem setup file for our tutorial is C4C5.mfl. To load the file: 1. From the File menu choose “Load Problem Setup”
Or
Click on the Load Problem Setup button on the toolbar. This will display the file selection dialogue
which will show a list of available setup files (*.mfl) contained in the problem files directory. By default this is the directory where Multiflash was installed. This directory might be different if earlier versions of Multiflash were used on your computer. After the Multiflash is launched, the Multiflash working directory can be changed from the menu option, Tools/Preferences/General/Folders.
2. Select C4C5.mfl and click on Open or double-click on the file name. The file will be read by Multiflash and the contents are echoed in the Results
window. The file contains the complete definition of the problem including:
Data sources
Models
Phases
Components
Compositions
Temperature and pressure
The input conditions section of the main window will look like this
Calculations
You can now carry out a flash calculation at the specified temperature and pressure by clicking on the PT flash toolbar button .
The results
The results of any calculations are displayed in the Results section of the main Multiflash window.
You may need to scroll the window to see all the results. Size of window can also be changed by clicking and dragging its borders and corners.
Additional calculations
Any of the input conditions may be changed by entering new values to overwrite or supplement those shown in the Conditions 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 toolbar button or select the calculation from the Calculate menu.
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 69.
Some simple changes are shown below:
Change the pressure
1. Click in the Pressure box of the Conditions panel in the main window and change the pressure to 14e5 Pa.
2. Click on P,T flash toolbar button
or
use the Calculate menu and choose Standard Flashes and then P.,T Flash.
3. The calculation shows that the system is a one-phase liquid under these conditions.
Change the composition
1. Click on the Compositions… button in the Fluid identification 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 “mole” column of the drop-down table so that there are 9 moles of butane and 1 mole of pentane.
2. Recalculate the P,T flash as above. The mixture is now two-phase.
Carry out an isenthalpic flash
1. Enter a value of 1000 in the Enthalpy box.
2. Click on the P,H flash toolbar button or use the Calculate
menu.
Setting up a new problem
To set up a new problem you must enter the following information:
Data sources
Models
Components
Compositions
Input conditions
Clearing previous problems
You can restore all settings in Multiflash to the state when the program was started by selecting the “Clear Problem Setup” option from the File menu.
Defining the components
Choose the components for any problem by clicking on Components in the Select menu. Alternatively you can click on the Select Components toolbar button, . Either will display the Select Components Dialogue box.
The default data source is the Infochem fluids databank which is called Infodata. If you have licensed the DIPPR databank this may be selected from the drop-down list.
Components may be selected in a variety of ways e.g. by name, by scrolling through a list or by searching for a formula or substring. The various methods are fully described in “Selecting components” on page 66.
Choose the components needed for the problem, in this case butane and pentane as follows:
1. Make sure the Name option button is selected. 2. Click in the box next to “Enter name” and type
butane
and then press the <Enter> key or click on the Add button. BUTANE is transferred to the Components selected list. Do the same for pentane.
3. Click on the Close button, this will return you to the Main Window.
Defining the models
To define the models and phases to be used for the calculations choose Model set from the Select menu.
Each tab of this window groups together similar types of model, e.g. cubic equations of state, activity coefficient models and so on.
For general advice on which models to choose for a particular application and more information about each model, see “What types of model are available?” on page 29 or consult the “Models and Physical Properties” manual.
We will use the Peng-Robinson equation of state: click on PR. You can also change the transport property models and the phases to consider but the default set will usually be appropriate.
Click on the Define Model button. The following message should confirm that the models have been successfully defined.
Click on OK and then Close the Select Model set dialogue to return to the main window.
Set 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 Condition section of the main window.
Compositions
To enter the composition click on the Composition button. The drop-down table shows the components in the left-hand column. The amount of each component in the mixture is typed in the right-hand column. The default unit for amounts is moles. Note that the amounts do not have to sum to 1 or 100 or any other value. Click on the Compositions button and enter 0.4 for butane and 0.6 for pentane.
The composition table can be hidden by clicking on the up-arrow button
Pressure and temperature
Other input conditions will depend on the type of flash calculation to be carried out, e.g. for an isothermal flash you must enter a pressure and a temperature in the appropriate text boxes and in the units shown next to them. The units may be changed as described in the section “Units” on page 169.
Type 9e5 in the Pressure box and 375 in the temperature box.
Carrying out the flash calculation
To carry out a flash calculation you either click on the appropriate flash button on the toolbar or select the required flash from the Calculate menu.
The most commonly encountered flash options have been allocated toolbar buttons; these are the isothermal flash, dew and bubble points, isenthalpic and isentropic flashes at fixed pressure and fixed phase fraction flashes.
Other flashes, such as isochoric flashes or isentropic and isenthalpic flashes at fixed temperature, are specified using the Calculate menu. To calculate the bubble point at the pressure of 9 bar click on
To carry out an isothermal flash at 9 bar and 375K click on
A short description of the function of each toolbar button is displayed when the cursor is placed over the button.
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 the main window.
Compositions for a mixture may be altered as described above.
Ensure that all necessary input conditions are defined for the flash calculation you wish to carry out and then click on the appropriate toolbar button or select the required flash from the Calculate menu.
To replace a component or to add new components see “Adding, inserting, replacing and deleting components” on page 69.
Phase envelope
You can plot the complete phase envelope by clicking on the phase envelope button or selecting Phase Envelope from the Calculate menu.
Click on the VLE AutopPlot button; the vapour-liquid phase boundary will be displayed in a separate window. Click No in response to the message "Maximum number of points reached …" if the phase envelope is completed. If more points along the phase envelope are required, click Yes to complete the envelope.
The legend can be changed by clicking Options button on the Phase Diagram form.
The phase diagram may be edited or printed as described in, ”Customising the phase envelope plot” on page 155. Alternatively it can be exported to Excel (Excel 97 or later).
Saving the problem setup
Once you have defined the components and models you can create a problem setup file containing this information for future use. If compositions and other input conditions are set these values will also be saved in the file.
To save the setup either click on Save problem setup button, , or
select “Save Problem Setup” or” Save problem Setup As” from the File menu. The dialogue box allows you to specify the name of the .mfl file and the directory where you want it stored.
If the problem file to be saved is based on an existing file, the default file name given will be the same as the existing one and a warning message will pop up.
Otherwise Multiflash will provide a default file name which can be overwritten. Keep in mind that in order to write files into the default mfl directory you should have a right to do this. If your system administrator deprived you of such a right, it might be useful to copy the entire directory to somewhere in your working space and continue to work with Multiflash in there.
Backup file
For any existing MFL files loaded to Multiflash, a backup file with a file extension .MFB will be created if the existing MFL file is overwritten with the changes.
Loading a existing MFL file
A warning message is given when loading a saved MFL file to Multiflash to overwrite the current project.
Warning option for matching and PVT form
A warning message is given when leaving the form without matching the data from all the matching forms and PVT forms.
Printing the output
You can print the output from your calculations by selecting “Print Results” from the File menu or clicking on the Print Results button,
This Print dialogue (see below) allows you to select the printer and its settings 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 elsewhere, see “Output” on page 173. All the output from any Multiflash session is automatically stored in a file called MFLASH.LOG in the Multiflash working directory. This file will be re-named the next time the program is started. The names are allocated
sequentially as MFLASH_1.LOG, MFLASH_2.LOG, etc., up to MFLASH_9.LOG.
If you wish to save the output to another file, select Save Results from the File menu.
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 300kb of text. If there is too much output only the last 300kb is displayed on the screen or in the log file.
How to exit the program
To exit Multiflash select Exit from the File menu. If the current fluid definition has changed the user is asked if saving is necessary.
Technical support
Models
Introduction
This section defines what a model is in terms of the Multiflash nomenclature, which models are available and when you might wish to use them, as well as how to specify and use them in Multiflash. For information on specifying models, see “How to specify models in Multiflash” on page 47. Detailed model descriptions may be found in our separate User Guide for Models and Physical
Properties.
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 depends on pressure, temperature and composition.
What types of model are available?
The key calculation carried out in 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
if
v 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 in terms of
temperature, pressure (and composition) 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 (EOS) method all thermodynamic 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 a combination of models which include a representation of the excess properties.
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 generally derived from semi-empirical models which will be discussed later.
Equation of state models
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 between 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, CO2and N2, is the norm. Equation of state methods do not
necessarily well-represent highly non-ideal chemical systems such as alcohol-water. 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 parameters 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 53.
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
Peng-Robinson 1978 (PR78) equation of state
The 1978 revised version of the Peng-Robinson equation has a different treatment for the parameter
. This model removes a defect in the original equation where heavy components with higher acentric factors become more volatile than components with somewhat lower acentric factors. For any mixture containing components with acentric factors greater than 0.49 the PR78 equation will give different results and must therefore be treated as a different model.Redlich-Kwong (RK) and Redlich-Kwong-Soave
(RKS) equations
Like Peng-Robinson, the Redlich-Kwong and Redlich-Kwong-Soave equations and their 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, PR78A 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 User Guide for Models and Physical Properties, and the user may enter all three coefficients as pure component properties.
Fitting the vapour pressure curve
For each component the equation of state a parameter is fitted by linear regression to the vapour pressure over a range of reduced temperatures corresponding to the stored data. Up to 5 coefficients may be used but fewer coefficients will be fitted if there are insufficient data or if the extrapolation to low temperatures is unrealistic. If there is no vapour pressure equation for a component, the standard expression for each equation of state is used.
Mixing Rules
The standard mixing rule for the cubic equations of state is the, so-called, van der Walls 1-fluid mixing rule. This is a simple recipe for obtaining the properties of a mixture by combining the pure-component properties. It is a widely used and highly effective method for many non-polar mixtures encountered in the oil and gas industries.
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 User Guide for Models and
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, PR78A) model sets which use the Peneloux correction, fit the EOS parameters to match the vapour pressure and use the Van der Waals 1-fluid mixing rules. RKSA with the Infochem mixing rules can be 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. The RK EOS 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.
Finally, the GUI provides a checkbox that allows the user to use the GERG 2008 model to calculate the density of the vapour phase while estimating the rest of the thermodynamic properties (e.g., fugacity coefficients, vapour pressures, etc.) with the selected cubic Eos.
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.
The CPA model is the recommended model for hydrate calculations, or other cases including water, methanol, ethanol, MEG, DEG, TEG and salts. For other (non-polar) components CPA reduces to the RKSA EOS.
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.
ZJ (Zudkevitch-Joffe) model
The ZJ equation of state model is a variant of the original RK cubic eos. Unlike the original RK, the “a” and “b” parameters are expressed explicitly in terms of the critical temperature and pressure, the “a” and “b” parameters in ZJ eos are defined by simultaneously solving the equations of fugacity coefficients along the saturation line and the equation of pressure for both vapour and liquid phase.
When to use ZJ model
The model provides a tool for giving better predictions on enthalpy departures of saturated and compressed liquids, both pure and liquid mixtures with suitable interaction parameters (BIPs). However the BIPs are required in order to use the model as the default BIPs in our databank are not regressed against any
experimental data.
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 are 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 this guide. Further information and references are provided in the User Guide for
Models and Physical Properties.
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. We also include the dipolar and quadrupolar terms when the dipole moment and quadrupole moments are available.
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 1000000.019=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 Modelling
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 Modelling 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 (LK) and Lee-Kesler-Plöcker (LKP)
equations of state
The LK and LKP methods are 3 parameter corresponding states methods based on interpolating the reduced properties of a mixture between those of two reference substances.
When to use LK or LKP
The methods predict fugacity coefficients, thermal properties and volumetric properties of a mixture. However, they are rather slow and complex compared to the cubic equations of state and are not particularly recommended for phase equilibrium calculations, although they can yield accurate predictions for density and enthalpy. They 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 method is an 11 parameter non-cubic equation of state. For methane, ethane, ethylene, propane, propylene, iso-butane, n-butane, iso-pentane, 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 is included for the convenience of users that wish to reproduce calculations based on this method. It is not generally recommended. The BWRS equation can give 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 we do not provide many BIPs in our databank. Owing to its complexity, it requires more computing time than the cubic equations of state.