a+ short primer

8/14/2019 A+ Short Primer

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A Short Primer for Using Aspen PlusProcessSimulation Software

Courtesy of College of Engineering and Technology, Brigham Young University

There are many subprograms within the Aspen Tech family of software tools. This short

primer focuses on Aspen Plus

, a process simulation tool. Many of the other toolsintegrate into Aspen Plus

while others are stand-alone systems. This first primer outlines

a simple flowsheet involving a distillation column. Hopefully it provides some useful

introduction to Aspen without involving unessential details.

I provide considerable editorial information in this primer that I hope is useful but that

makes it longer than necessary. The essential steps to completing this problem can beexecuted by focusing on the numbered items only and ignoring the introductory

explanations and figures in each section. The entire process should take less than 15minutes in this mode.

Getting Started

1. Navigate to the Aspen Plus User Interface program which will generally be foundunder the following sequence of program menus Aspen Tech -> Aspen

Engineering Suite -> Aspen Plus 2004.1 -> Aspen Plus User Interface.The first dialog box you encounter asks you to select either a new simulation or choose among

existing simulations saved to a disk, the latter choice including a listbox of past simulations. Here we

assume you are starting a new simulation. You may choose either a blank simulation or a template.

Here we assume you want to choose a template. Select Template and OK.2. Figure 1 illustrates this dialog box with some of the important selections

discussed above highlighted with red ovals.


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Figure 1 Opening dialog box in Aspen Plus

The next dialog box has two tabs one for simulations and one for refineries. Choose the simulation

tab for this primer. Also, the lower right corner has a drop-down list box labeled Run Type. Choose

Flowsheet for this primer (see Appendix for other options). Finally, choose a process type and units

in which you want to work from the list of options in dialog box. Here we suggest a Generic

Simulation with English Units. All of these choices can be modified later in the program if desired.

The essential difference among the process types is that Aspen preselects the thermodynamic models

most appropriate for the given process. However, you are able to override these pre-selected choices

if you choose to do so.

3. Figure 2 illustrates this dialog box with some of the important selectionsdiscussed above highlighted with red ovals.


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Figure 2 Second dialog box in Aspen Plus with selection of process type and run type.

You should now have a blank process simulation window open. Also, there should be series of unit

operations choices called the Model Library along the bottom of the dialog box. If the Model Library

does not appear, select Model Library under the View menu at the top of the page. This page is

illustrated in

4. Figure 3.5. You are now ready to construct a simulation.

From this point on, you can step through the minimally required input fields by selecting the Next

button at the top of the page (an uppercase, blue N with a right-pointing arrow highlighted with a

red oval near the top of

6. Figure 3). The Next function can alternatively be accessed by pressing F4 or byselecting it from the Tools menu. This will lead you through the various stages ofsetting up a simulation.

7. Help files are available at any point from the help menu or, for context-sensitivehelp, by pointing at the item with which you want help and pressing F1. However,Aspen includes several separate help files. They are each accessible from the

same menu, but searches and lists of help topics in the help interface are limited tothe help file that is open. For example, the default help file for the flowsheet is theAspen Plus Help file. It contains few details beyond the name and typical

application for the thermodynamic models used within Aspen. For detailed

thermodynamic information (form of equations, temperature and pressure

dependence, etc.), you must select the Aspen Physical Property System Help file.This (or any of several other help files) can be found by navigating to the Topics

tab in any help file and selecting the topmost choice (a document, not a folder)


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labeled Accessing Other Help in the tree-structured illustration of the help file

found in the left panel. The right panel will then include links to all help filesloaded in your software.

Figure 3 An example of a blank flowsheet, the starting point for process simulation, with several of

the items discussed above highlighted with red ovals.

Building the Flowsheet

The flowsheet is a graphical representation of your process. Aspen works somewhat more

elegantly if you first place equipment from the Model Library on the flow sheet and thenconnect these major components with streams rather than, for example, placing feedstreams on the flowsheet and connecting streams and equipment in the order they are

encountered in the process. However, either approach as well as many other approaches

will eventually work. Note that Aspen seems generally unaware of gravity (an important

consideration in liquid-liquid extraction processes) and of flow direction, but mypreference is to represent flow from left to right where possible (recycle streams being an

exception) and to try to place all initial (feed) and terminal (product) flow stream points


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such that they do not need to cross other flow lines to reach the flowsheet border that is,

to not leave them embedded in the diagram surrounded by flowlines and equipment.Note that the tabbed titles of the unit operations in the Model Library can be slightly

misleading. For example, the tab Separators includes only simple separators such as flash

drums or columns with specified output concentrations but not with model capabilities to

predict such concentrations. Distillation columns and liquid-liquid separators are includedin the Columns tab. Also pumps, compressors, turbines, etc. are under the tab Pressure

Changers. If your pointer hovers over any portion of the model library (or another hotspot

in the open window), the status bar (bottom-most portion of the window) displays a shortdescription of the unit operation that is quite useful in making selections.

Depressurization equipment such as turbines are modeled with the same tools as

compressors and pumps although the labels do not make this obvious but the status bardescription does. Also note that alternative icons for many of the unit operations are

available by clicking on the down arrow to the right of each existing icon. So far as I

know, these are cosmetic only. They do not change functionality, although they

sometimes appear to do so (distillation column with or without condenser specifically

drawn still has the some choices for inlet and outlet streams, for example).

1. Choose equipment from the Model Library and place it on the flowsheet bydragging it to the blank (white) area of the screen. Here we choose RadFrac from

the columns tab, which is a rigorous, multicomponent, multiphase distillation

column model. Note that nearly all equipment (indeed all equipment so far as Iknow) receives a default label of B*, consistent with flowsheet labeling practices

generally not too informative. These labels can be changed by selecting (single

clicking) the equipment and choosing cntrl-M or by right-clicking on it andchoosing Rename Block.

2. Connect feed, intermediate, and product lines to the equipment. This is done byselecting the left-most icon from the Model Library which is labeled Material

Streams. Doing so causes each piece of equipment on the flowsheet to indicate

with red arrows the required inlet/outlet streams and to indicate with blue arrows

optional inlet and outlet streams. Connect the equipment by clicking on a red orblue arrow and moving the pointer to either another arrow on another piece of

equipment (in the case of intermediate streams) or to a convenient and

aesthetically acceptable location on the flowsheet (in the case of feed and productstreams). Note that specifying a stream sometimes changes the status of remaining

streams for a piece of equipment. In this example, specifying a condenser liquid

stream changes the condenser vapor stream from red (required) to blue (optional)since at least one liquid or vapor stream is required, but not necessarily both.

Stream labels default to numerically increasing numbers in the order in which you

place them on the sheet. These can be changed, as with equipment, by selecting(single clicking) the equipment and choosing cntrl-M or by right-clicking on it

and choosing Rename Stream. The flowsheet should now look like Figure 4,

except possibly with more meaningful labels for the equipment and streams if you

choose to rename them.


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B2

1

2

3

Figure 4 Flowsheet illustration for a simple distillation column process.

3. After connecting all streams select the Next button near the top of the screen (orchoose it by pressing F4 or by selecting it from the Tools menu). If all streams areproperly connected, a dialog box for the project title and default specifications

will open. Otherwise, an indication of a problem will appear.

Overall Specifications

At this point you should be in the Data Browser. This is probably the first time you have

encountered it, but it is central to the program. The insert prompt should be located in a

text box labeled Title and is asking for you to enter a name for the process you aresimulating. Any title (or no title) is fine here. This is possibly the only non-essential

portion of the series of entries the program will ask you to make using the Next button.

However, take a moment to get a feel for the Data Browser as it will be a major interface

to everything else that happens.

Along the left side of the Data Browser dialog box is a tree structure that organizes theinput and output data. The portions that have blue check boxes have all the information

they need but those with red half-full signs require additional input. The Next button willstep through these in a logical sequence, or you can go directly to them using the tree

view. The logical sequence is essentially the same as the order in which red (incomplete)

items appear in this tree view. That is, next you will be asked to specify the componentsin the system, then the thermodynamic models you want to use, then the components in

individual streams, then you will skip the defaults for the flowsheet itself as these should

already be specified, then you will specify the concentration and condition (pressure,temperature, phase, etc.) of components in feed streams, and the final required input will

be specifications for the equipment (blocks) in the process in this case a single

distillation column.There are a great number of additional options that involve optimization, design, costs,convergence, etc., but these are not discussed here. For now, the task at this stage is

simple

1. Enter a suitable name for this process2. Press the Next button


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Component Specification

You should now be in the Components Specification section of the Data Browser. In the

tree diagram at the left you can tell where you are by locating the highlighted portion of

the tree. Also, the title of the dialog box should indicate similar information.There are four specifications for each component (chemical species) that you wish to use

in the calculation. The first is the ID, which is an arbitrary label of up to eight characters

and numbers. An ID that closely resembles the species name is highly preferred as this ID

is used in the output to indicate concentrations, etc. The type will, for now, always beconventional (other types allow for solids, pseudo species, etc., but conventional is

suitable for any fluid liquid or gas material that is an actual chemical species likely to

be available in the extensive Aspen database). The component name is the name Aspendatabases use for this component. If the ID is the name, such as ACETONE or

ETHANOL, Aspen automatically fills in all remaining boxes for each component. If the

eight-character limit of the ID is too short for the actual name or if there are severalcommon names for the component, such as BUTANOL, you must help Aspen identify

what you mean. This can be done by typing in as much of the name as will fit in the ID

and choosing the correct species from the list Aspen automatically presents or by usingthe Find button at the bottom of this dialog box, in which case Aspen offers several

suggestions based on what you enter and you are to select one. Note that only the species

entered in this dialog box are considered in any calculations specifically processes that

involve chemical reactions or equilibrium reactions only select from the choices enteredhere.

In this case, we specify acetone, ethanol, n-butanol, and phenol as the components.

1. Enter IDs in the ID column2. Complete specifications for any species Aspen does not recognize according to

instructions above.3. Click the Next button

(Thermodynamic) Properties Specifications

You should now have the dialog box used to specify thermodynamic models open. This

dialog box is where most of the art of thermodynamics lies. The first box asks for thetype of process. The function of this box is to select the most appropriate subset of

possible thermodynamics models for selection in subsequent boxes. You can select from

the dropdown box by clicking on the arrow. As your curser passes entries, a few words ofexplanation appear in the bottom box. You may note that the prompts in the bottom panel

of this box generally suggest you use the Property Method Selection Assistant. This is

found on the tools menu. In this case, we will leave the process as ALL, indicating allthermodynamic options will be available to us.


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The next dropdown box requests the default thermodynamic model for the process.

Different models can be used within individual blocks of the process, but the base modelis specified here. Again, the Property Method Selection Assistant is useful in making

these selections. For our simple system, there are many appropriate choices. We will try

UNIQUAC with ideal gas and Henrys law for non-condensable components, which is

specified as UNIQUAC.

The remainder of the dialog box allows non-condensable gas components to be specified

and a variety of specialty modifications to be made for electrolytes, changes in binaryinteraction parameters, etc., but none of these is essential for our problem.

Clicking Next will bring you to the parameters dialog box. Generally, nothing needs to be

specified here. It simply reviews the parameters, mostly the binary interactionparameters, available for the components in this system. These are pre-selected by Aspen

for your problem but can be changed to better suit your purposes. This dialog box may

represent the single greatest distinguishing characteristic of Aspen. It appears to have

more sophisticated equilibrium models and much more extensive databases of interaction

parameters than many of its competitors. Within the information it presents, some of theimportant information includes the temperature range over which the BIPs are valid

(appears near the bottom of the table for each pair) and the values of the BIPs (all zerosindicate no information available but nearly all zeros is not an indication of bad

information the various parameters are often for temperature dependencies, etc. and not

all of them would be expected to be non-zero in general). The final importantconsideration is the database from which the data come. There are many databases within

Aspen and while it tries to select the most appropriate for your problem, you may find a

more suitable one within the choices. For example, butanol and acetone form immiscibleliquid solutions under some conditions and, if these are important to the process, the

liquid-liquid equilibrium (LLE) database which is presumably optimized to predict phaseimmiscibilities rather than the vapor-liquid equilibrium (VLE) database may be more

suited for the simulation. Both can potentially predict two phases, but the former would

presumably be more accurate. The database-provided entries appear in grayed-out text.

Highlighting any one of these parameters and selecting help (F1) pops up an informationbox that summarizes the temperature, pressure, and composition range on which the data

are based, the number of data points, and the goodness of fit measured several ways. If

you change a parameter, it becomes black rather than gray and Aspen assumes it is yourinformation, in which case this database information is not available from Help.

For this case, the entries are relatively simple

1. Specify ALL for the Process Type2. Specify UNIQUAC for the Base Method3. Press Next4. Review the temperature-dependent interaction parameter data but dont change

anything

5. Press Next

This should bring you to the stream specification section.I provide a short list of the thermodynamic models and a logic diagram I tried to develop

but with which I am not satisfied in the Appendix.


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Streams

This section allows you to specify stream conditions (composition, temperature, pressure,etc.). The stream for which data are being entered appears in the title of the dialog box

which, although prominent, is easily overlooked. It will have the same ID as it has on the

flowsheet. Generally, at least two of temperature, pressure, or fraction of vapor must bespecified, with the remaining parameter calculated from thermodynamics. The units for

the specifications are based on the default units selected at the beginning of the run but

can be changed locally if desired. The composition of the stream can be specified in avariety of ways (mole fraction, mass fraction, flow rates, etc.). If you select an intensive

specification, then the total flow must also be specified.In this case

1. Specify a saturated liquid (0 vapor fraction)2. Specify14.7 psi3. Specify an equimolar composition of 25 lb mols/hr flow rate for each of the four

components.4. Press Next

Since the remaining streams in this simple simulation are all products, there are no more

specifications in the stream section and you should now be at the Block Setup dialog box.

Block Setup

Every type of unit operation has different specifiable parameters. In this case, we have adistillation column. In this dialog box we indicate whether we want to use an

equilibrium-based model (by far the most common) or a rate-based model (in somecircles more respected and an increasingly important approach). We will use the

equilibrium approach here.

Next we specify the total number of stages. This should be distinguished from thenumber of trays as the number of stages potentially includes the condenser (rarely only

if it is a partial condenser) and the reboiler (generally unless it is a total reboiler). We

specify 9 in this case. The type of condenser is specified from among the several choices.We choose a simple total condenser. We accept the defaults for everything else in the

setup.

We next specify the operation. Generally two of the many potential specifications arerequired. We choose a total distillate rate of 50 lb mols/hr and a reflux ratio of 5.

Pressing next takes us to the next tab in this specification where we indicate the feed

stage location, which we take as above the 5th

stage.

Pressing next again takes us to the pressure specification where we specify the pressure atthe condenser. If no other pressure or pressure drop is specified, the entire column is

assumed to operate at this pressure.


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Aspen can be used for design (calculating, for example, the reflux ratio needed to achieve

a target separation), optimization, cost accounting, etc. but its default use is as a simulatorand that is what is illustrated here. I will try to write another primer for design, etc. uses.

In this case

1. Accept the default equilibrium specification for the column

2. Specify 9 total stages in the column3. Accept the defaults for the remaining flows setup parameters.4. Specify a total distillate flow of of the inlet flow (50 lb mols/hr) and a reflux

ratio of 5.5. Press Next6. Specify that the feed is located above the 5thstage.7. Press Next8. Specify the column pressure is 1 atm (14.7 psi) at the condenser and no changes

across the stages (no entries in remaining boxes).

9. Press Next

This completes all of the specifications. Pressing next should pop up a dialog box thattells you that Aspen knows enough to complete the simulation and ask you if you want to

further specify anything. If you select Run, Aspen predicts the resulting compositions,temperatures, and pressures of the product streams, the stage-by-stage compositions of

vapor and liquid in the column, and all other details of the process.

Reviewing the Results

During the simulation, Aspen displays convergence and other data in a new dialog box

called the Control Panel (perhaps a misnomer as there is essentially nothing that can be

controlled from this dialog box it is mainly informational). If the simulation converges,

it will complete with a statement Simulation calculations completed. For this simpleproblem, this should not take long although it does take some time for the computation to

set itself up.To view the results, close the Control Panel, in which case the Data Browser should be

displayed. At the bottom of the tree structure on the left of the Data browser is the Results

Summary section. Open this section of the structure and choose streams to obtain asummary of the stream compositions, flows, temperatures, and pressures. This should

display a table of stream properties. In this case, the column performs a sharp separation

of the two light components (acetone and ethanol) from the two heavy components

(butanol and phenol) at temperatures near those of steam and hot water, as might beexpected. A copy of this summary information can be included on the flowsheet by

pressing the Stream Table button. In my case, the results look like Figure 5.


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B2

1

2

3

Simple Dist illation Colum n

Stream ID 1 2 3T emperat ure F 188.2 143.8 272.3

Pressure psi 14.70 14.70 14.70

Vapor Frac 0.000 0.000 0.000

Mole Flow lbmol/hr 100.000 50.000 50.000

Mass Flow lb/hr 6809.623 2608.586 4201.037

Volume Flow cuft/hr 132.753 55.931 80.871

Enthalpy MMBt u/hr -10.335 -5.508 -4.678

Mole Flow lbmol/hr

ACET ONE 25.000 24.956 0.044

ET HANOL 25.000 24.852 0.148

BUT ANOL 25.000 0.192 24.808

PHENOL 25.000 trace 25.000

Figure 5 Summary of stream conditions and flow diagram for this simple Primer.

To examine more details of column performance, return to the block specifications and

click on the profiles button. Here the stage-by-stage compositions, temperatures, k-values, etc. are displayed. As indicated, there are significant compositional changes

between every stage. These can be conveniently plotted within Aspen by running the Plot

Wizard found under the Plot menu in the Data Browser. For example, the gas and liquid

phase composition for the problem appear in Figure 6.


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Block B2: Vapor Composition Profiles

Stage

Y

(molefrac)

1 2 3 4 5 6 7 8 9

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

ACETONE

ETHANOL

BUTANOL

PHENOL

Block B2: Liquid Composition Profiles

Stage

X

(molefrac)

1 2 3 4 5 6 7 8 9

0.2

0.4

0.6

0.8

1

ACETONE

ETHANOL

BUTANOL

PHENOL

Figure 6 Vapor (top) and liquid compositions on a stage-by-stage basis in the simple column used in

this primer. Stage 1 is at the top of the column and Stage 9 is the reboiler.


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Appendix

Run Types

The following descriptions of alternative run types indicate the range of choices withinAspen, including the Flowsheet (process simulator) choice.

Run Type Description Use to

Assay Data Analysis A standalone assay data

analysis/pseudocomponents

generation run

Analyze assay data when you do

not want to perform a flowsheet

simulation in the same run.Data Regression A standalone data

regression run. Can contain

property constant estimation

and property analysiscalculations.

Fit physical property model

parameters required by

Aspen Plus to measured pure

component, VLE, LLE and othermixture data. Aspen Plus cannot

perform data regression in a

Flowsheet run.Flowsheet A process simulation

option, including sensitivitystudies and optimization.

Simulate complete processes.

Flowsheet simulations includeProperty Estimation, Assay Data

Analysis, and Property Analysis

capabilities but Data Regressioncannot be done within the

Flowsheet option.

Properties Plus A Properties Plus setup run Prepare a property package for

use with Aspen Custom Modeleror Aspen Pinch, with third-party

commercial engineering

programs, or with your company'sin-house programs. You must be

licensed to use Properties Plus.

Property Analysis A standalone propertyanalysis run. Can contain

property constant estimation

and assay data analysiscalculations.

Perform property analysis bygenerating tables of physical

property values when you do not

want to perform a flowsheetsimulation in the same run

Property Estimation A standalone propertyconstant estimation run

Estimate property parameterswhen you do not want to perform

a flowsheet simulation in thesame run.


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Summary of Aspen Property Methods

Ideal Property Methods

Ideal Property Method K-Value Method

IDEAL Ideal Gas/Raoult's law/Henry's lawSYSOP0 Release 8 version of Ideal Gas/Raoult's law

Equations of StateAbbreviation Equation of State

Lee-based MethodsBWR-LS BWR Lee-Starling

LK-PLOCK Lee-Kesler-PlckerPeng-Robinson-based Methods

PENG-ROB Peng-Robinson

PR-BM Peng-Robinson with Boston-Mathias alpha functionPRWS Peng-Robinson with Wong-Sandler mixing rules

PRMHV2 Peng-Robinson with modified Huron-Vidal mixing rules

Redlich-Kwong-based MethodsPSRK Predictive Redlich-Kwong-Soave

RKSWS Redlich-Kwong-Soave with Wong-Sandler mixing rules

RKSMHV2 Redlich-Kwong-Soave with modified Huron-Vidal mixing rules

RK-ASPEN Redlich-Kwong-ASPENRK-SOAVE Redlich-Kwong-Soave

RKS-BM Redlich-Kwong-Soave with Boston-Mathias alpha function

Other MethodsSR-POLAR Schwartzentruber-Renon


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Activi ty Coeff icient MethodsAbbreviation Liquid Activity Coefficient Vapor Fugacity Coefficient

Pitzer-based MethodsPITZER Pitzer Redlich-Kwong-Soave

PITZ-HG Pitzer Redlich-Kwong-SoaveB-PITZER Bromley-Pitzer Redlich-Kwong-Soave

NRTL-based Methods

ELECNRTL Electrolyte NRTL Redlich-Kwong

ENRTL-HF Electrolyte NRTL HF Hexamerization modelENRTL-HG Electrolyte NRTL Redlich-Kwong

NRTL NRTL Ideal gas

NRTL-HOC NRTL Hayden-O'Connell

NRTL-NTH NRTL NothnagelNRTL-RK NRTL Redlich-Kwong

NRTL-2 NRTL (using dataset 2) Ideal gas

UNIFAC-based MethodsUNIFAC UNIFAC Redlich-Kwong

UNIF-DMD Dortmund-modified UNIFAC Redlich-Kwong-SoaveUNIF-HOC UNIFAC Hayden-O'Connell

UNIF-LBY Lyngby-modified UNIFAC Ideal gas

UNIF-LL UNIFAC for liquid-liquid systems Redlich-KwongUNIQUAC-based Methods

UNIQUAC UNIQUAC Ideal gas

UNIQ-HOC UNIQUAC Hayden-O'ConnellUNIQ-NTH UNIQUAC Nothnagel

UNIQ-RK UNIQUAC Redlich-Kwong

UNIQ-2 UNIQUAC (using dataset 2) Ideal gasVANLAAR-based Methods

VANLAAR Van Laar Ideal gas

VANL-HOC Van Laar Hayden-O'Connell

VANL-NTH Van Laar NothnagelVANL-RK Van Laar Redlich-Kwong

VANL-2 Van Laar (using dataset 2) Ideal gas

WILSON-based MethodsWILSON Wilson Ideal gas

WILS-HOC Wilson Hayden-O'Connell

WILS-NTH Wilson Nothnagel

WILS-RK Wilson Redlich-KwongWILS-2 Wilson (using dataset 2) Ideal gas

WILS-HF Wilson HF Hexamerization model

WILS-GLR Wilson (ideal gas and liquid enthalpyreference state)

Ideal gas

WILS-LR Wilson (liquid enthalpy reference

state)

Ideal gas

WILS-VOL Wilson with volume term Redlich-Kwong


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Specialty Methods Abbreviation K-value Method Application

AMINES Kent-Eisenberg amines model H2S, CO2, in MEA,DEA, DIPA, DGA

solutionAPISOUR API sour water model Sour water with NH3,

H2S, CO2

BK-10 Braun K-10 Petroleum

SOLIDS Ideal Gas/Raoult's law/Henry's law/solid activitycoefficients

Pyrometallurgical

CHAO-SEA Chao-Seader corresponding states model Petroleum

GRAYSON Grayson-Streed corresponding states model Petroleum

STEAM-TA ASME steam table correlations Water/steamSTEAMNBS NBS/NRC steam table equation of state Water/steam

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