PhysProps of Aspen

Introduction to Aspen Plus Physical Properties

Aspen Technology, Inc.8 – 1© 2003 AspenTech. All Rights Reserved.

©2003 AspenTech. All Rights Reserved.

Physical Properties

Introduction to Aspen Plus


Lesson Objectives

• Introduce property methods and physical property parameters

• Identify issues involved in the choice of a property method

• Cover the use of Property Analysis for reporting physical properties

Aspen Plus References:User Guide, Chapter 7, Physical Property MethodsUser Guide, Chapter 8, Physical Property Parameters and DataUser Guide, Chapter 29, Analyzing Properties




• Correct choice of physical property models and accurate physicalproperty parameters are essential for obtaining accurate simulation results.

Specification: 99.5 mole %

acetone recovery

Case Study – Acetone Recovery

COLUMNFEED

OVHD

BTMS

Approximate cost ($)

Predicted number of stages required

520,000

11

Ideal Approach

390,000

7

Equation of State Approach

880,000

42

Activity Coefficient Model


How to Establish Physical Properties

Choose a Property Method

Check Parameters/Obtain Additional Parameters

Confirm Results

Create the Flowsheet




Definition of Terms

• Property Method – Set of property models and methods used to calculate the properties required for a simulation.

• Property – Calculated physical property value, such as mixture enthalpy.

• Property Model – Equation or equations used to calculate a physical property.

• Property Parameter – Constant used in a property model.

• Property Set (Prop-Set) – A method of accessing properties so that they can be used or tabulated elsewhere.


Property Methods

• A Property Method is a collection of models and methods used to calculate physical properties.

• Property Methods containing commonly used thermodynamic models are provided in Aspen Plus.

• Users can modify existing Property Methods or create new ones.




• Approaches to representing physical properties of components

• Choice of model types depends on degree of non-ideal behavior and operating conditions.

Physical Property Models

Ideal Equation of State(EOS)Models

ActivityCoefficient

Models

SpecialModels

Physical Property Models


• What do we mean by ideal behavior?– Ideal Gas law and Raoult’s law

• Which systems behave as ideal?– Non-polar components of similar size and shape

• What controls degree of non-ideality?– Molecular interactions,

e.g., Polarity, size and shape of the molecules

• How can we study the degree ofnon-ideality of a system?– Property plots (e.g., TXY & XY)

x

y

Ideal vs. Non-Ideal Behavior




Comparison of EOS and Activity Models

Examples: – NRTL – UNIFAC – UNIQUAC – WILSON

Examples: – PENG-ROB – RK-SOAVE

Inconsistent in critical regionConsistent in critical region

Binary parameters are highly temperature dependent

Parameters extrapolated reasonably with temperature

Many binary parameters requiredFewer binary parameters required

Can represent highly non-ideal liquids

Limited in ability to represent non-ideal liquids

Good for liquid phase modeling onlyGood for vapor phase modeling and liquids of low polarity

Activity Coefficient ModelsEquation of State Models


Henry's Law

• Henry's Law is only used with ideal and activity coefficient models.

• It is used to determine the amount of a supercritical component or light gas in the liquid phase.

• Any supercritical components or light gases (CO2, N2, etc.) should be declared as Henry's components (Components Henry Comps Selection sheet).

• The Henry's components list ID should be entered on Properties Specifications Global sheet in the Henry Components field.




Do you have any polar components in your system?

Are the operating conditions near the critical region of the

mixture?

Use activitycoefficient model with Henry’s Law

Use activity coefficient

model

Use EOS Model

N

N

NY

Y

Y

References:Aspen Plus User Guide, Chapter 7, Physical Property

Methods, gives similar, more detailed guidelines for choosing a property Method.

Choosing a Property Method – Review

Do you have light gases orsupercritical components

in your system?


Choosing a Property Method – Example

• Choose an appropriate Property Method for the following systems of components at ambient conditions:

Activity CoefficientActivity Coefficient

Equation of State

Model Type

NRTL-RK, WILSONAcetone, WaterNRTL-RK, UNIQUACBenzene, Water

RK-SOAVE, PENG-ROBPropane, Ethane, Butane

Property MethodSystem

Ethane, PropanolWater, Cyclohexane

Acetone, Water, Carbon DioxideBenzene, TolueneEthanol, Water

Property MethodSystem







Confirm Results



Pure Component Parameters

• Represent attributes of a single component

• Input in the Properties Parameters Pure Component folder.

• Stored in databanks such as PURE10, ASPENPCD, SOLIDS, etc. (The selected databanks are listed on the Components Specifications Databanks sheet.)

• Parameters retrieved into the Graphical User Interface by selecting Retrieve Parameter Results from the Tools menu.

• Examples– Scalar: MW for molecular weight– Temperature-Dependent: PLXANT for parameters in the extended

Antoine vapor pressure model




Binary Parameters

• Used to describe interactions between two components

• Input in the Properties Parameters Binary Interaction folder

• Stored in binary databanks such as VLE-IG, LLE-ASPEN

• Parameter values from the databanks can be viewed on the input forms in the Graphical User Interface.

• Parameter forms that include data from the databanks must be viewed before the flowsheet is complete.

• Examples– Scalar: RKTKIJ for the Rackett model – Temperature-Dependent: NRTL for parameters in the NRTL model


Displaying Property Parameters

• Aspen Plus does not display all databank parameters on the parameter input forms.

• Select Retrieve Parameter Results from the Tools menu to retrieve all parameters for the components and property methods defined in the simulation.

• All results that are currently loaded will be lost. They can be regenerated by running the simulation again.

• The parameters are viewed on the Properties Parameters Results forms.




PHYSICAL PROPERTIES SECTION PROPERTY PARAMETERS -------------------PARAMETERS ACTUALLY USED IN THE SIMULATIONPURE COMPONENT PARAMETERS-------------------------COMPONENT ID: BENZENE FORMULA: C6H6 NAME: C6H6 SCALAR PARAMETERS-----------------

PARAM SET DESCRIPTIONS VALUE UNITS SOURCENAME NO. API 1 STANDARD API GRAVITY 28.500 PURE10

CHARGE 1 IONIC CHARGE 0.00000E+00 AQUEOUS CHI 1 STIEL POLAR FACTOR 0.00000E+00 DEFAULT DCPLS 1 DIFFERENCE BETWEEN LIQUID AND 0.31942 CAL/MOL-K PURE10

SOLID CP AT TRIPLE POINT

DGFORM 1 IDEAL GAS GIBBS ENERGY 30.954 KCAL/MOL PURE10 OF FORMATION

Reporting Parameters

• To get a Report of the retrieved parameters in a text file: 1. Select Retrieve Parameter Results from the Tools menu.2. Select Report from the View menu. Choose to display report for

Simulation and click OK.


Reporting Physical Property Parameters

• To obtain a report file containing values of ALL pure component and binary parameters for ALL components used in a simulation:

1. On the Setup Report Options Property sheet, select All physical property parameters used (in SI units) or select Property parameters’ descriptions, equations, and sources of data.

2. After running the simulation, export a report (*.rep) file by selecting Export from the File menu.

3. Edit the .rep file using any text editor. (From the Graphical User Interface, you can choose Report from the View menu.) The parameters are listed under the heading PARAMETER VALUES in the physical properties section of the report file.




Additional Property Data from DETHERM

• DETHERM databank, maintained by DECHEMA, contains the world’s most comprehensive single source of thermophysical properties.

– Phase equilibria data– Azeotropic data– Excess properties– PVT data

• Data is received into Aspen Plus– Scalar data is entered on Property Parameters forms.– Temperature dependent and Binary data sets are entered on the

Properties Data forms.

• Data can be regressed using Aspen Plus Data Regression


Interface to DETHERM Example (1)

• The interface is launched from within Aspen Plus to access data via the Internet.

1. Enter your components, then click the DETHERM Interface button on the toolbar.

2. Choose Selected Components.

3. Choose the desired property from Available Properties list.

4. Click OK to connect to the internet.

5. Check the box of the data set youdesire, and click Next>.

6. Click on ‘proceed to login and download the data cart.’




7. Enter your user ID information and password. Users are charged for each set of data that is downloaded. The data are then transferred into Aspen Plus.

Interface to DETHERM Example (2)





Confirm Results





Property Analysis

• Used to generate simple property diagrams to validate physical property models and data

• Diagram Types– Pure component, i.e., vapor pressure vs. temperature– Binary, i.e., TXY, PXY

– Ternary residue maps

• Select Analysis from the Tools menu to begin Analysis.

• Property analysis input and results can be saved as a form for later reference and use.


• Predicting non-ideal behavior:

• When using a binary analysis to check for liquid-liquid phase separation, remember to choose Vapor-Liquid-Liquid as Valid phases.

Property Analysis Plots

XY Plot showing two Liquid phases:Ideal XY Plot:

XY Plot showing an Azeotrope :

y-x diagram for METHANOL / PROPANOL

LIQUID MOLEFRAC METHANOL0 0.2 0.4 0.6 0.8 1

0.2

0.4

0.6

0.8

1V

AP

OR

MO

LEFR

AC

ME

THA

NO

L

(PRES = 14.7 PSI)

y-x diagram for ETHANOL / TOLUENE

LIQUID MOLEFRAC ETHANOL0 0.2 0.4 0.6 0.8 1

0.2

0.4

0.6

0.8

1V

AP

OR

MO

LEFR

AC

ETH

AN

OL

(PRES = 14.7 PSI)

y-x diagram for TOLUENE / WATER

LIQUID MOLEFRAC TOLUENE0 0.2 0.4 0.6 0.8 1

0.2

0.4

0.6

0.8

1V

AP

OR

MO

LEFR

AC

TO

LUE

NE

(PRES = 14.7 PSI)







Confirm Results



Establishing Physical Properties – Review

1. Choose Property Method – Select a Property Method based on:– Components present in simulation– Operating conditions in simulation– Available data or parameters for the components

2. Check Parameters – Determine parameters available in Aspen Plus databanks

3. Obtain Additional Parameters – Possible data sources include:– Literature searches (DETHERM, etc.)– Regression of experimental data (Data Regression)– Property Constant Estimation (Property Estimation)

4. Confirm Results – Verify choice of Property Method and physical property data using Physical Property Analysis




Property Sets

• A property set (Prop-Set) is a way of accessing a collection, or set, of properties as an object with a user-given name. Only the name of the property set is referenced when using the propertiesin an application.

• Use property sets to report thermodynamic, transport, and other property values.

• Current property set applications include:– Design specifications, Fortran blocks, sensitivity– Stream reports– Physical property tables (Property Analysis)– Tray properties (RadFrac, MultiFrac, etc.)– Heating/cooling curves (Flash2, MHeatX, etc.)


Properties Included in Prop-Sets

• Properties commonly included in property sets include:– VFRAC Molar vapor fraction of a stream– BETA Fraction of L1 to total liquid for a mixture– CPMX Constant pressure heat capacity for a

mixture– MUMX Viscosity for a mixture

• Available properties include:– Thermodynamic properties of components in a mixture– Pure component thermodynamic properties– Transport properties– Electrolyte properties– Petroleum-related properties

Reference: Aspen Plus Physical Property Data Reference Manual, Chapter 4, Property Sets, has a complete list of properties that can be included in a property set.




Predefined Property Sets

• Some simulation templates contain predefined property sets.

• The predefined property sets and the types of properties they contain for the General template are:

Vapor-liquid-liquid equilibriumVLLE

Vapor-liquid equilibrium (PHIMX, GAMMA, PL)VLETransport propertiesTXPORTMixture thermal (HMX, CPMX, KMX)THERMAL

Heat exchanger designHXDESIGN

Types of PropertiesProperty Set


Specifying Property Sets

• Use the Properties Prop-Sets form to specify properties in a property set.

– The Search button can be used to search for a property.– All specified qualifiers apply to each selected property, where

applicable.




Stream Results Options

• On the Setup Report Options Stream sheet: – Check the Flow Basis

and Fraction Basis boxes to specify how stream composition is reported.

– Click Property Sets button to specify names of property sets containing additional properties to be reported for each stream.


Aspen Properties

• Aspen Properties is now a stand-alone product.

• In addition to the standard property features available in AspenPlus, Aspen Properties includes:– Excel Interface – Web Interface

• Excel Interface is an Excel Add-In that has Excel functions to do property calculations such as:– Flash at a given set of conditions– Calculate a property such as density or viscosity

• Web Interface is currently only available for pure components.




Physical Properties Workshop (1)

• Objective: Simulate a two-liquid phase settling tank and investigate the physical properties of the system.

• A refinery has a settling tank that they use to decant off the water from a mixture of water and a heavy oil. The inlet stream to thetank also contains some carbon-dioxide and nitrogen. The tank and feed are at ambient temperature and pressure (70°F, 1 atm), and have the following flow rates of the various components:

Water 515 lb/hrOil 4322 lb/hrCO2 751 lb/hrN2 43 lb/hr

• Use n-decane to represent the oil. It is known that water and oil form two liquid phases under the conditions in the tank.



1. Choose an appropriate Property Method to represent this system.Check to see that the required binary physical property parameters are available.

2. Retrieve the physical property parameters used in the simulation and determine the critical temperature for carbon dioxide and water.

TC(carbon dioxide) = _______; TC(water) = _______

3. Using the property analysis feature, verify that the chosen physical property model and the available parameters predict the formation of 2 liquid phases.

4. Set up a simulation to model the settling tank. Use a Flash3 block to represent the tank.

5. Modify the stream report to include the constant pressure heat capacity (CPMX) for each phase (Vapor, 1st Liquid and 2nd Liquid), and the fraction of L1 to total liquid for a mixture (BETA), for all streams.





This Portion is Optional

• Objective: Generate a table of compositions for each liquid phase (1st Liquid and 2nd Liquid) at different temperatures for a mixture of water and oil.

• Tabulate the vapor pressure of the components in the same table.

• In addition to the interactive Analysis commands under the Tools menu, you also can create a Property Analysis manually, using forms. – Manually generating a Generic Property Analysis is similar to the

interactive Analysis commands, however it is more flexible regarding input and reporting.

– Detailed instructions are provided on the following slide.



Problem Specifications:1. Create a Generic property analysis from the Properties/Analysis Object

manager.

2. Generate points along a flash curve.3. Define component flows of 1 lbmol/hr for both water and oil.

4. Set Valid phases to Vapor-liquid-liquid.

5. Click on the Range/List button and vary temperature from 50 to 400°F.6. Use a vapor fraction of zero.

7. Tabulate a new property set that includes:a. Mole fraction of water and oil in the 1st and 2nd liquid phases (MOLEFRAC)

b. Mole flow of water and oil in the 1st and 2nd liquid phases (MOLEFLOW)c. Beta – the fraction of the 1st liquid to the total liquid (BETA)d. Pure component vapor pressures of water and oil (PL)

PhysProps of Aspen

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