Aspen+ Essential

Aspen+ Essential Workshop 2010-03-08

AspenTech All Right Reserved 1

© 2010 Aspen Technology, Inc. All rights reserved© 2010 Aspen Technology, Inc. All rights reserved

WonSeok LeeAspenTech Korea, Business Consultant

Aspen+ Getting Started - Essential

© 2010 Aspen Technology, Inc. All rights reserved | 2

Flowsheet Simulation

What is flowsheet simulation?– Use of a computer program to quantitatively model the

characteristic equations of a chemical process

Uses underlying physical relationships– Mass and energy balance– Equilibrium relationships– Rate correlations (reaction and mass/heat transfer)

Predicts– Stream flowrates, compositions, and properties– Operating conditions




Advantages of Simulation

Reduces plant design time– Allows designer to quickly test various plant configurations

Helps improve current process– Answers “what if” questions– Determines optimal process conditions within given constraints– Assists in locating the constraining parts of a process

(debottlenecking)


General Simulation Problem

What is the composition of stream PRODUCT?

To solve this problem, we need:– Material balances– Energy balances

REACTOR

FEED

RECYCLE

REAC-OUT

COOL

COOL-OUT SEP

PRODUCT




Good Flowsheeting Practice

Build large flowsheets a few blocks at a time– This facilitates troubleshooting if errors occur

Not necessarily a one-to-one correspondence between pieces of equipment in the plant and Aspen Plus blocks

Ensure flowsheet inputs are reasonable

Check that results are consistent and realistic


The User Interface

Run ID

Tool Bars

Title Bar

Menu Bar

Select ModeButton Model

Library

ModelLibrary Tabs

Process Flow Diagram

Next Button

Status AreaHelp Line

Resize Window Buttons




Basic Input


Useful Options

GUI– Window->Workbook

mode

Automatic Naming of Streams and Blocks– Tools->Options-

>Flowsheet

Result in Flowsheet– Tools->Options->Results

View




Useful Options

Save options– Tools->Options->General– Recommend *.BKP

File Type Extension Format DescriptionDocument *.apw Binary File containing simulation input, results and

intermediate convergence informationBackup *.bkp ASCII Archive file containing simulation input and

results

Compound *.apwz Binary Compressed file which contains the model (the BKP or APW file) and external files referenced by the model. You can add additional files such as supporting documentation to the APWZ file.


When finished, save as BENZENE FLOWSHEET.BKP

Benzene Flowsheet Definition Workshop

Objective: Create a graphical flowsheet– Start with the General with English Units template– Choose the appropriate icons for the blocks

FL1COOLER

FEED COOL

VAP1

LIQ1FL2

VAP2

LIQ2




Data Browser

Menu Tree

Previous Sheet Next

Sheet

Status Area

Parent Button Units

Go BackGo

Forward

Comments

Next

Description Area

StatusView List

Resource Link Tool


Basic Input

The minimum required inputs to run a simulation are:– Setup– Components– Properties– Streams– Blocks

Enter data on the input forms in the above order by clicking the Next button

Or, these input folders can be located quickly using the Data menu or the Data Browser toolbar buttons




Setup

Most of the commonly used Setup information is entered on the Setup Specifications Global sheet– Flowsheet title to be used on reports– Run type – Input and output units– Valid phases: vapor-liquid (default) or vapor-liquid-liquid– Ambient pressure

Stream report options are located on the Setup | Report Options | Stream sheet


Components

Pure component databanks contain parameters such as molecular weight, critical properties, etc.; the databank search order is specified on the Databanks sheet

The Find button can be used to search for components

The Electrolyte Wizard can be used to set up an electrolyte simulation




NIST Databank

The NISTV71 database contains a single databank called NIST-TRC– Available from Aspen Plus 2006

only– Includes approximately 15,000

compounds (mostly organic) 13,000 new components 2,000 components already in

Aspen Properties databanks

– The database is available in the Enterprise Database architecture only; it is not available in the legacy DFMS format

NIST = US National Institute of Standards and Technology


Properties

Property methods are a collection of models and methods used to describe pure component and mixture behavior

Choosing the correct physical properties is critical for obtaining reliable simulation results




Streams

Use Stream | Input forms to specify feed stream conditions, including two of the following:– Temperature– Pressure– Vapor Fraction

Plus, for stream composition either:– Total stream flow and

component fractions– Individual component flows

Specifications for streams that are not feeds to the flowsheet are used as estimates


Streams

Stdvol– Standard liquid volume (1 atm and 60 F)

Vol– Ref. Temperature

Mole– Standard vapor volume (Ideal gas)– 14.696 psia & 60 F– 1 atm & 0 C




Blocks

Each Block | Input or Block | Setup form specifies operating conditions and equipment specificationsfor the unit operation model

Some unit operation models require additional specification forms

All unit operation models have optional information forms (e.g., Block Options form)

Block

Tin

Pin

Fin

Xin

Tout

Pout

Fout

Xout

e.g. Heater block needs both Tout and Pout operating specs


Starting the Run

Select Control Panel from the View menu or press the Next button to be prompted– Execute the simulation when all required forms are complete.

Run Start or continue calculationsStep Step through the flowsheet one block at a timeStop Pause simulation calculationsReinitialize Purge simulation resultsResults Check simulation results




Cumene Production Demo

Q = 0 Btu/hrPdrop = 0 psi

C6H6 + C3H6 C9H12

Benzene Propylene Cumene (Isopropylbenzene)

90% Conversion of Propylene

T = 130°FPdrop = 0.1 psi

P = 1 atmQ = 0 Btu/hr

Benzene: 40 lbmol/hrPropylene: 40 lbmol/hr

T = 220°FP = 36 psia

Use the RK-SOAVE Property Method Filename: CUMENE.BKP

REACTOR

FEED

RECYCLE

REAC-OUT

COOL

COOL-OUT SEP

PRODUCT


Reviewing Results

Control Panel Messages – Contains any generated errors or warnings – Block Results– Convergence

Steam Results

Custom Stream Results

Block Summary Grid

Block Results




Stream Results

Contains stream conditions and compositions

Fraction basis in stream result– Data browser->Setup->Report options->Stream


Custom Stream Results

This feature makes it much easier to customize the stream report format

With Custom Stream Summary Views you can:– Select a list of streams to display– Select the properties to be displayed– Select the units of measure and numerical formats– Specify calculation options for each property– Eliminate or change the labels used in the table

Custom stream summary views can be exported and imported as .APCSV files

You can use any number of custom views within the same simulation




When finished, save asfilename: BENZENE.BKP

Benzene Flowsheet Conditions Workshop (1)

Objective: Add the process and feed stream conditions to a flowsheet. Start with the Benzene Flowsheet (BENZENE FLOWSHEET.BKP).

Use the PENG-ROB Property Method

FeedT = 1000°FP = 550 psiaHydrogen: 405 lbmol/hrMethane: 95 lbmol/hrBenzene: 95 lbmol/hrToluene: 5 lbmol/hr

T = 200°FPdrop = 0

T = 100°FP = 500 psia

P = 1 atmQ = 0

FL1COOLER

FEED COOL

VAP1

LIQ1FL2

VAP2

LIQ2



Results– What is the heat duty of the COOLER block? _________– What is the temperature in the FL2 block? _________

Note: Answers for all of the workshops are located in the back of the course notes in Appendix C





Optional

Create a Custom Stream Summary with the following properties:– Temperature– Pressure– Total Mole Flow– Liquid and Vapor Component Mole Flows– Liquid and Vapor Mixture Mass Density in gm/cc– Liquid and Vapor Mixture Viscosity in cP






RadFrac


Rigorous Multistage Separation Using RadFrac

Vapor-Liquid or Vapor-Liquid-Liquid phase simulation of:– Ordinary distillation– Absorption, reboiled absorption– Stripping, reboiled stripping– Azeotropic distillation– Reactive distillation

Configuration options– Any number of feeds– Any number of side draws– Total liquid draw off and pumparounds– Any number of heaters– Any number of decanters




RadFrac Flowsheet Connectivity

Vapor Distillate

Top-Stage or Condenser Heat Duty

1

Liquid DistillateWater Distillate (optional)

Feeds Reflux

Side Products (optional)

Pumparound (optional)

DecanterProductReturnBoil-up

Bottom Stage or Reboiler Heat Duty

NstageHeat (optional)

Bottoms

Pseudo Streams (optional)

Heat (optional)

Heat (optional)

Heat (optional)

Heat (optional)

Feed (optional)


Some RadFrac Options

To set up an absorber with no condenser or reboiler, set condenser and reboiler to none on the RadFrac Setup Configuration sheet

Either Vaporization or Murphree efficiencies on either a stage or component basis can be specified on the RadFrac Efficiencies form

Tray and packed column design and rating is possible

A second liquid phase may be modeled if the user selects Vapor-liquid-liquid as Valid phases

Stage Wizard for adding/removing stages from column

Option to select different reboiler configurations

Reboiler and condenser heat curves can be generated




RadFrac Demonstration

Use the RKS-BM Property Method

Mole fractionsC1: 0.26C2: 0.09C3: 0.25nC4: 0.17nC5: 0.11nC6: 0.12

COLUMNFEED

OVHD

BTMS

Kettle Reboiler 15 StagesReflux Ratio = 1.5 (mole)Distillate to feed ratio = 0.6Column pressure = 315 psiaFeed stage = 8

RadFrac specificationsPartial Condenser

T = 190°FP = 315 psia

Flow = 1000 lbmol/hr

Filename: RADFRAC.BKP


RadFrac Setup Configuration Sheet

Specify:– Number of stages– Condenser and

reboiler configuration– Valid phases

– Convergence– Two column operating

specifications

Defaults: Distillate rate and reflux ratio




RadFrac Setup Streams Sheet

Specify:– Feed stage location– Feed stream

convention Above-Stage On-Stage On-Stage-Liquid On-Stage-Vapor Decanter (for three

phase calculations only)

– Bottom and overheadproduct streams

– Side products


Feed Convention

On-Stage

n

Above-Stage (default)

n-1

n

VaporFeed to stage n

n-1

LiquidFeed to stage n

• Above-Stage: RadFrac introduces the material stream between adjacent stages - the liquid portion flows to the specified stage and the vapor portion flows to the stage above

• On-Stage: RadFrac introduces both liquid and vapor portions of the feed flow to the stage specified• On-Stage-Liquid and On-Stage-Vapor are similar to On-Stage, but no flash is ever performed with

these specifications. Feed treated as being entirely in the phase specified.




RadFrac Setup Pressure Sheet

Specify one of:– Top/Bottom pressure– Pressure profile– Section pressure drop


Plot Wizard

The Plot Wizard guides you in the basic operations for generating a plot

In Step 2, click the plot type you wish to generate, then click Next> to continue

Click the Finish button to generate a plot with default settings




Plot Wizard Demonstration

Use the Plot Wizard to create plots of temperature, flows, and compositions throughout the column


Design Specs and Vary

Design specifications can be specified inside the RadFrac block using DesignSpecs and Vary forms

One or more RadFrac inputs can be manipulated to achieve specifications on one or more RadFrac performance parameters

The number of specs should, in general, be equal to the number of varies

The DesignSpecs and Varys in a RadFrac are solved in a “Middle loop”; if you get an error message saying that the middle loop was not converged, check the DesignSpecs and Varys you have entered




Design Specs and Vary Demonstration

Part A– Record the molar composition of C3 in OVHD stream.

_______– What reflux ratio is required so that this value is 0.41?

_______

Part B– Change the current Design Spec so that the sum of light key

(C1 + C2 + C3) molar compositions in the OVHD stream is set to 0.99. What happens to the predicted reflux ratio given this new specification? ___________________________________


RadFrac Stage Wizard

Use the Stage Wizard to change the number of stages in the column while also updating stage numbers throughout the specifications for the block– Enter the New total number of stages– Choose Above or Below and specify a Stage number - the

stages will be added or deleted according to the choices– Click OK to update the specifications




Thermosiphon Configuration in RadFrac

RadFrac model supports various reboiler configurations


Thermosiphons and columns

Traditional method– Reboiler appears as simple

heat input in column model– Column and reboiler

designed and simulated separately

– Feed composition to reboilerestimated

– Reboiler and column models interact through: input liquid level, estimated feed composition and calculated flowrate and heat load

Rigorous reboiler modeling– Integrate heat exchanger

model into column model A Reboiler Wizard (Reboiler

sheet) can be used to explicitly simulate the reboiler using a heat exchanger block (HeatX block - see Heat Exchangers section) or using a rigorous Aspen Shell & Tube Exchanger model to design, rate, or simulate the reboiler

– Correctly models column/reboiler interaction

– Allows modelling of tower bottom baffle arrangement




Specifying Efficiencies in RadFrac

RadFrac Efficiencies Options sheet


Sizing and Rating for Trays and Packing

Extensive capabilities to size, rate, and perform pressure drop calculations for trayed and packed columns

Calculations are based on vendor-recommended procedures when available. When vendor procedures are not available, well-established literature methods are used– Bubble Cap Trays– One pass tray– Tray Spacing = 2 ft– Diameter = 10 ft




RadFrac Convergence Problems (1)

If a RadFrac column fails to converge, doing one or more of the following could help:– Check that physical property issues (choice of Property Method,

parameter availability, etc.) are properly addressed– Ensure that column operating conditions are feasible– If the column err/tol is decreasing fairly consistently, increase

the maximum iterations on the RadFrac Convergence Basic sheet


RadFrac Convergence Problems (2)

Provide temperature estimates for some stages in the column using the RadFrac Estimates Temperature sheet (useful for absorbers)

Provide composition estimates for some stages in the column using the RadFrac Estimates Liquid Composition and Vapor Composition sheet (useful for highly non-ideal systems)

Experiment with different convergence methods on the RadFrac Setup Configuration sheet

Note: When a column does not converge, it is usually beneficial to Reinitialize after making changes




Filename: MEOH_COL.BKP

RadFrac Workshop (1)

Objective: Set up a Methanol tower

Use the NRTL-RK Property Method

38 trays (40 stages)Feed tray = 23 (stage 24)Total condenserTop stage pressure = 16.1 psiaPressure drop per stage = 0.1 psiDistillate flowrate = 1245 lbmol/hrMolar reflux ratio = 1.3

63.2 wt% Water 36.8 wt% Methanol Flow = 120000 lb/hrPressure 18 psiaSaturated liquid

COLUMNFEED

DIST

BTMS



Part A– Fix the simulation to eliminate any warning messages

– Record the column duties:

Condenser Duty: _________ Reboiler Duty: _________

– Record compositions:

Mass fraction of methanol in the distillate: __________ Mass fraction of water in the bottoms: __________

– Make plots of temperature, flows, and composition





Part B– Set up Design Specs within the column so that there is:

99.95 wt% methanol in the distillate 99.90 wt% water in the bottoms

– Vary the distillate rate (800-1700 lbmol/hr) and the reflux ratio (0.8-2)

– Record the final values for:

Distillate Rate: _________ Reflux Ratio: _________ Condenser Duty: _________ Reboiler Duty:

_________



Part C– Perform the same calculations after specifying a 65%

Murphree efficiency for each tray. Assume condenser and reboiler have stage efficiencies of 90%. Determine how these efficiencies affect the column duties:

Condenser Duty: _________ Reboiler Duty: _________

Part D– Perform a tray sizing calculation for the entire column, given

that Bubble Cap trays are used

Record the predicted column diameter: _________




Reactor Models


Reactor Overview

Reactors

Balance BasedRYieldRStoic

Equilibrium BasedREquilRGibbs

Kinetics BasedRCSTRRPlug

RBatch




Balanced Based Reactors (1)

RYield– Requires a mass balance only, not an atom balance– Is used to simulate reactors in which inlets to the reactor are

not completely known but outlets are known (e.g., to simulate a furnace)

70 lb/hr H2O20 lb/hr CO260 lb/hr CO250 lb/hr tar600 lb/hr char

1000 lb/hr Coal

IN

OUT

RYield


Balanced Based Reactors (2)

RStoic– Requires both an atom and a mass balance– Used in situations where both the equilibrium data and the

kinetics are either unknown or unimportant– Can specify or calculate heat of reaction at a reference

temperature and pressure

2 CO + O2 2 CO2C + O2 CO22 C + O2 2 CO

C, O2

IN

OUT

RStoic

C, O2, CO, CO2




Equilibrium Based Reactors (1)

These reactors:– Do not take reaction kinetics into account– Solve similar problems, but specifications are different– Allow individual reactions to be at a restricted equilibrium

REquil– Computes combined chemical and phase equilibrium by solving

reaction equilibrium equations– Cannot do a three-phase flash– Useful when there are many components, a few known

reactions, and when relatively few components take part in the reactions


Equilibrium Based Reactors (2)

RGibbs– Useful when reactions occurring are not known or are high in

number due to many components participating in the reactions– A Gibbs free energy minimization is done to determine the

product composition at which the Gibbs free energy of the products is at a minimum

– This is the only Aspen Plus block that will deal with vapor-liquid-solid phase equilibrium




Kinetic Reactors (1)

Kinetic reactors are RCSTR, RPlug and RBatch

Reaction kinetics are taken into account, and hence must be specified

Kinetics can be specified using one of the following built-in models, or with a user subroutine:– Power Law– Langmuir-Hinshelwood-Hougen-Watson (LHHW)

A catalyst for a reaction can have a reaction coefficient of zero

Reactions are specified using a Reaction ID



RCSTR– Use when reaction kinetics are known and when the reactor

contents have same properties as outlet stream– Allows for any number of feeds, which are mixed internally– Up to three product streams are allowed – vapor, liquid1,

liquid2 or vapor, liquid, free water– Will calculate duty given temperature or temperature given

duty– Can model equilibrium reactions simultaneously with rate-

based reactions





RPlug– Handles only rate-based reactions– A cooling stream is allowed– You must provide reactor length and diameter

RBatch– Handles rate-based kinetics reactions only– Any number of continuous or delayed feeds are allowed– Process duration can be specified using stop criteria, cycle time,

and result time– Holding tanks are used to interface with steady-state streams

of Aspen Plus


Using a Reaction ID (1)

Reaction IDs are setup as objects, separate from the reactor, and then referenced within the reactor(s)

A single Reaction ID can be referenced in any number of kinetic reactors (RCSTR, RPlug and RBatch)

Multiple reaction sets can be referenced in the reactor models

Each Reaction ID can have multiple and/or competing reactions




Using a Reaction ID (2)

To set up a Reaction ID, go to the Reactions, Reactions Object Manager– Click on New to create a new Reaction ID– Enter ID name and select the reaction

type from the drop-down box– Enter appropriate reaction data in the

forms


Example of a Power Law Reaction ID (1)

i

ReactionRate

Kinetic Factor

[Componenti]Exponenti

• The general Power Law kinetic reaction rate is:

− [Componenti] : concentration of component i− Exponenti : kinetic exponent of component i

• Within a Reaction ID you need to specify:− Stoichiometry sheet: stoichiometric coefficient and kinetic

exponent for each component i− Kinetic sheet: kinetic factor data




Example of a Power Law Reaction ID (2)

For a reversible kinetic reaction, both the forward and reverse reactions have to be specified separately

Example: DCBAk

k

2322

1

DCBA k 232 1

BADC k 322 2

− k1 : Kinetic factor for forward reaction− k2 : Kinetic factor for reverse reaction

Forward reaction

Reverse reaction

Assuming 2nd order in A

Assuming 1nd order in C and D (overall 2nd order)


Example of a Power Law Reaction ID (3) –Stoichiometry sheet

• Stoichiometry coefficients quantitatively relate the amount of reactants and products in a balanced chemical reaction− By convention - negative for reactants and positive for products

Forward reaction coefficients: A: B: C: D:

Reverse reaction coefficients: A: B: C: D:

Forward reaction exponents: A: B: C: D:

Reverse reaction exponents: A: B: C: D:

• Kinetic exponents show how the concentration of each component affects the rate of reaction− Typically obtained from experimental data




Example of a Power Law Reaction ID (4) –Stoichiometry sheet

Coefficients

Forward reaction: A: -2 B: -3 C: 1 D: 2

Reverse reaction: A: 2 B: 3 C: -1 D: -2

Exponents

Forward reaction: A: 2 B: 0 C: 0 D: 0

Reverse reaction: A: 0 B: 0 C: 1 D: 1

Forward reaction

Reverse reaction


Example of a Power Law Reaction ID (5) -Kinetic sheet

If reference temperature, T0, is specified, Kinetic Factor is expressed as:

Kinetic Factor

00

11REexp

TTTTk

n

− k : Pre-exponential factor− n : Temperature exponent− E : Activation energy− T0 : Reference temperature

Kinetic Factor

RTEexpnkT




Example of a Power Law Reaction ID (6) -Kinetic sheet


Heats of Reaction

Heats of reaction need not be provided for reactions

Heats of reaction are typically calculated as the difference between inlet and outlet enthalpies for the reactor (see Appendix A)

If you have a heat of reaction value that does not match the value calculated by Aspen Plus, you can adjust the heats of formation (DHFORM) of one or more components to make the heats of reaction match

Heats of reaction can also be calculated or specified at a reference temperature and pressure in an RStoic reactor




Reactor Workshop (1)

Objective: Compare the use of different reactor types to model a reaction

Use the NRTL-HOC property method

Temp = 70°CPres = 1 atm

Feed:

Water: 8.892 kmol/hrEthanol: 186.59 kmol/hrAcetic Acid: 192.6 kmol/hr

Length = 2 m

Diameter = 0.3 m

Volume = 0.14 m3

70% conversion of ethanol

RSTOICF-STOIC P-STOIC

RGIBBS

F-GIBBS P-GIBBS

RPLUGF-PLUG P-PLUG

DUPL

FEED

F-CSTR

RCSTR

P-CSTR



Reactor Conditions: Temperature = 70°C, Pressure = 1 atm

Stoichiometry: Ethanol + Acetic Acid Ethyl Acetate + Water

Kinetic Parameters:– Reactions are first order with respect to each of the reactants

in the reaction (second order overall)– Forward Reaction: k = 1.9 x 108, E = 5.95 x 107 J/kmol– Reverse Reaction: k = 5.0 x 107, E = 5.95 x 107 J/kmol– Reactions occur in the liquid phase– Composition basis is Molarity

Hint: Check that each reactor is considering both Vapor and Liquid as Valid phases

Filename: REACTORS.BKP





Results

RStoic RGibbs RPlug RCSTRAmount of Ethyl Acetate produced (kmol/hr)Mass fraction Ethyl Acetate in product streamHeat duty (kcal/hr)


Physical Properties




Case Study – Acetone Recovery

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

Specification: 99.5 mole %

acetone recovery

COLUMNFEED

OVHD

BTMS

Ideal Approach

Equation of State Approach

Activity Coefficient Model

Predicted number of stages required

11 7 42

Approximate cost ($) 650,000 490,000 1,110,000


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


Physical Property Models

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




Ideal vs. Non-Ideal Behavior

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


Comparison of EOS and Activity Models

Equation of State Models Activity Coefficient ModelsGood for vapor phase modeling and liquids of low polarity

Good for liquid phase modeling only

Limited in ability to represent non-ideal liquids

Can represent highly non-ideal liquids

Fewer binary parameters required Many binary parameters requiredParameters extrapolated reasonably with temperature

Binary parameters are highly temperature dependent

Consistent in critical region Inconsistent in critical regionExamples:

− PENG-ROB − RK-SOAVE

Examples: − NRTL − UNIFAC − UNIQUAC − WILSON




Henry's Law

Henry's Law is used to determine the amount of a supercritical component or light gas in the liquid phase– It is only used with Ideal and Activity Coefficient models

Declare any supercritical components or light gases (CO2, N2, etc.) as Henry's components on the Components Henry Comps Selection sheet

Then, select the Henry's components ID from the Henry Components dropdown list on the Properties Specifications Global sheet


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

Use activitycoefficient model with Henry’s Law

Use activity coefficient

model

Do you have any polar components in your system?

N Y

Are the operating conditions near the critical

region of the mixture?Use EOS Model

N

Y

NY

Do you have light gases or supercritical components

in your system?




Property Method Selection Assistant


Choosing a Property Method – Example

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

System Model Type Property MethodPropane, Ethane, Butane Equation of State RK-SOAVE, PENG-ROBBenzene, Water Activity Coefficient NRTL-RK, UNIQUACAcetone, Water Activity Coefficient NRTL-RK, WILSON

System Property MethodEthanol, WaterBenzene, TolueneAcetone, Water, Carbon DioxideWater, CyclohexaneEthane, Propanol




Property Analysis Plots

Predicting non-ideal behavior:

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

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

(PRES = 14.7 PSI)

y-x diagram for ETHANOL / TOLUENE

LIQUID MOLEFRAC ETHANOL0 0.2 0.4 0.6 0.8 1

(PRES = 14.7 PSI)

y-x diagram for TOLUENE / WATER

LIQUID MOLEFRAC TOLUENE0 0.2 0.4 0.6 0.8 1

(PRES = 14.7 PSI)


How to Establish Physical Properties –Review

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

2. Check Parameters– Determine availability of parameters in the Aspen Plus

databanks, and obtain additional parameters if necessary

3. Confirm Results– Verify choice of Property Method and physical property data

using the Property Analysis plotting tool




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 properties in an application

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

Current property set applications include:– Design specifications, Calculator blocks, Sensitivity analysis– Stream reports– Physical property tables (Property Analysis)– Tray properties (RadFrac, MultiFrac, etc.)– Heating/cooling curves (Flash2, HeatX, etc.)


Properties Included in Prop-Sets

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

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




Specifying Property Sets

Select properties for a property set using the Properties Prop-Sets form– The Search button can be used to search for a property– The Units fields are optional;

DataBrowser->Setup->Report Options->Stream– Click the Property Sets button and move the Prop-Set name from the

available to selected area


Cyclohexane WorkshopWon-Seok LeeAspenTech Korea, Business Consultant




Process Description

Part A: Create a flowsheet to model a cyclohexane production process– Cyclohexane can be produced by the hydrogenation of benzene

in the following reaction: C6H6 + 3H2 C6H12– The benzene and hydrogen feeds are combined with recycle

hydrogen and cyclohexane before entering a fixed bed catalytic reactor. Assume a benzene conversion of 99.8%

– The reactor effluent is cooled and the light gases separated from the product stream. Part of the light gas stream is fed back to the reactor as recycle hydrogen

– The liquid product stream from the separator is fed to a distillation column to further remove any dissolved light gases and to stabilize the end product. The remaining portion is recycled to the reactor to aid in temperature control


Use the RK-SOAVE property method

Filename: CYCLOHEXANE.BKP

Process Flowsheet

P = 25 barT = 50°C

Molefrac H2 = 0.975N2 = 0.005CH4 = 0.02

Total flow = 330 kmol/hr

T = 40°CP = 1 barBenzene flow = 100 kmol/hr

T = 150°CP = 23 bar T = 200°C

Pdrop = 1 barBenzene conv = 0.998

T = 50°CPdrop = 0.5 bar

92% flow to stream H2RCY

30% flow to stream CHRCY

Specify cyclohexane mole recovery in PRODUCT stream equal to 0.9999 by varying Bottoms rate from 97 to 101 kmol/hr

REACTFEED-MIXH2IN

BZIN

H2RCY

CHRCY

RXIN

RXOUT

HP-SEP

VAP

Bottoms rate = 99 kmol/hr

Theoretical Stages = 12Reflux ratio = 1.2

Partial Condenser with vapor distillate only

Column Pressure = 15 barFeed stage = 8

COLUMN

COLFD

LTENDS

PRODUCT

VFLOW

PURGE

LFLOW

LIQ




Sensitivity Analysis


Sensitivity Analysis Example

Determine the effect of cooler outlet temperature on the purity of the product stream– What is the manipulated (varied) variable?

– What is the measured (sampled) variable?

Filename: CUMENE-S.BKP

» COOL outlet temperature

» Purity (mole fraction) of cumene in PRODUCT stream

REACTOR

FEED

RECYCLE

REAC-OUT

COOL

COOL-OUT SEP

PRODUCT




Sensitivity Analysis

Allows user to study the effect of changes in input variables on process outputs

Located under Data Browser | Model Analysis Tools | Sensitivity

Results can be viewed by looking at the Results form in the folder for the Sensitivity block

Plot results to easily visualize relationships between different variables


Uses of Sensitivity Analysis

Studying the effect of changes in input variables on process (model) outputs

Graphically representing the effects of input variables

Verifying that a solution to a design specification is feasible

Rudimentary optimization

Studying time varying variables using a quasi-steady-state approach

Doing case studies




Steps for Using Sensitivity Analysis

Specify measured (sampled) variable(s)– These are quantities calculated during the simulation to be used in step

4 (Define sheet)

Specify manipulated (varied) variable(s)– These are the flowsheet variables to be varied (Vary sheet)

Specify range(s) for manipulated (varied) variable(s)– Variation for manipulated variable can be specified either as

equidistant points within an interval or as a list of values for the variable (Vary sheet)

– Tip: You can check the Disable variable box to temporarily not vary that variable

Specify quantities to calculate and tabulate– Tabulated quantities can be any valid Fortran expression containing

variables defined in step 1 (Tabulate sheet)– Tip: Click the Fill Variables button to automatically tabulate all of the

define variables


Plotting

Select the column containing the X-axis variable and then select X-Axis Variable from the Plot menu

Select the column containing the Y-axis variable and then select Y-Axis Variable from the Plot menu

(Optional) Select the column containing the parametric variable and then select Parametric Variable from the Plot menu

Select Display Plot from the Plot menu

Note: To select a column, click the heading of the column with the left mouse button




Workshop : Sensitivity Analysis

Part B: Add a sensitivity analysis to study the effect of the recycle flowrate on the reactor duty– Plot the variation of REACT duty as the recycle split fraction in

LFLOW is varied from 0.1 to 0.4– In addition to the split fraction, vary the conversion of benzene

in the reactor from 0.9 to 1.0. Tabulate the reactor duty and construct a parametric plot showing the dependence of the reactor duty on recycle split fraction and the conversion of benzene

– Note: Both of these studies should be set up within the same sensitivity analysis block


Design SpecificationsAspen Plus®: Process Modeling




Design Specification Example

Determine the cooler outlet temperature to achieve a cumene product purity of 98 mole percent:– What is the manipulated (varied) variable?

– What is the measured (sampled) variable?

– What is the specification (target) to be achieved?

Filename: CUMENE-D.BKP

» COOL outlet temperature

» Mole fraction of cumene in PRODUCT stream

» Mole fraction of cumene in PRODUCT stream = 0.98

REACTOR

FEED

RECYCLE

REAC-OUT

COOL

COOL-OUT SEP

PRODUCT


Steps for Using Design Specifications (1)

Identify measured (sampled) variables– These are flowsheet quantities, usually calculated, to be

included in the objective function (Define sheet)

Specify objective function (Spec) and goal (Target)– This is the equation that the specification attempts to satisfy

(Spec sheet)

Set tolerance for objective function– The specification is converged when the objective function

equation is satisfied to within this tolerance (Spec sheet)

Specify manipulated (varied) variable– This is the variable whose value changes in order to satisfy the

objective function equation (Vary sheet)




Steps for Using Design Specifications (2)

Specify range of manipulated (varied) variable– These are the lower and upper bounds of the interval within

which Aspen Plus will vary the manipulated variable (Vary sheet)

By default, the units of the variable(s) used in the objective function (step 2) and those for the manipulated variable (step 5) are the units for that variable type as specified by the Units Set declared for the design specification; you can change the units using the Object-level Units dropdown list in the Data Browser toolbar; however, if you do, it changes the units for all sheets in this form; for example, if you change the units to MetCBar in the Specs sheet, the units in the Vary form are also MetCBar


Workshop : Design Specification

Part C: Hide the sensitivity analysis and use a design specification to fix the heat load on the reactor by varying the recycle flowrate

The cooling system around the reactor can handle a maximum operating load of 4.7 MMkcal/hr. Determine the amount of cyclohexane recycle necessary to keep the cooling load on the reactor to this amount: ________ kmol/hr

Note: The heat convention used in Aspen Plus is that heat input to a block is positive, and heat removed from a block is negative




Heat Exchangers


Heater Model

The Heater block mixes multiple inlet streams to produce a single outlet stream at a specified thermodynamic state

A Heater can be used to represent:– Heaters– Coolers– Valves– Pumps (when work-related results are not needed)– Compressors (when work-related results are not needed)

Heater also can be used to set the thermodynamic conditions of a stream

Vapor fraction of 1 means dew point condition, 0 means bubble point




Heat Streams

One outlet heat stream can be specified for the net heat load from a Heater– The net heat load is the sum of the inlet heat streams minus

the actual (calculated) heat duty

Heat streams flow in the direction that information (not heat) flows

When a heat stream is an inlet to a block, you only need one thermodynamic specification (temperature or pressure), Heater uses the sum of the inlet heat streams as a duty specification


HeatX Model

HeatX can perform shortcut, detailed rating and simulation calculations, and rigorous design calculations

Shortcut rating calculations (simple heat and material balance calculations) can be performed if exchanger geometry is unknown or unimportant

For detailed and rigorous heat transfer and pressure drop calculations, the heat exchanger geometry must be specified




HeatX Model

You can access Aspen rigorous heat exchanger modeling software directly within the HeatX block– Aspen Shell & Tube Exchanger– Aspen Air Cooled Exchanger– Aspen Plate Exchanger– Hetran– Aerotran

Information related to the heat exchanger configuration and geometry is entered through the individual program on the EDR Browser form


HeatX Run Type

Shortcut Detail / Shell & Tube

Input Output Input Output

Design Duty or Tout UA Duty or Tout Geo*

Rating Duty or Tout and UA Over Design% Duty and Geo Over Design%

Simulation UA Tout and Duty Geo Tout and Duty

Max. fouling N/A N/A

Tout : Stream condition in one of outlet streams. e.g. vapor fraction or tempGeo : HX geometry* : Available in only Shell & Tube (TASC+)




HeatX Key Options

Options– Valid phases

Block Options– Property method– Water Solubility

Setup->LMTD– Interval


HeatX versus Heater

Use HeatX when both sides are important

Use Heater when one side (e.g., the utility) is not important

Use two Heaters (coupled by a heat stream, Calculator block, or Design Spec) to avoid flowsheet complexity created by HeatX




HeatX Workshop (1)

Objective: Compare the simulation of a heat exchanger that uses water to cool a hydrocarbon mixture using three methods: two Heaters connected with a Heat stream, a Heater using a Utility, and a detailed HeatX

Filename: HEATX.BKP

DHEATX

DHOT-IN

DCLD-IN DCLD-OUT

HEAT-C

HCLD-IN

Q-TRANS

HCLD-OUT

HEAT-H

HHOT-IN HHOT-OUT

DHOT-OUT

HEAT-U

UHOT-IN UHOT-OUT

Tip: In HeatX, make sure that you connect cold streams to cold ports and hot streams to hot ports.


HeatX Workshop (2)

Streams– Hydrocarbon stream: 200°C, 4 bar, 10000 kg/hr

50 wt% benzene, 20% styrene, 20% ethylbenzene, 10 wt% water

– Cooling water: 20°C, 10 bar, 60000 kg/hr water– Choose the appropriate Property Method for both the hot and

cold sides of this system

Unit Operations– For the Heater blocks:

Hydrocarbon stream exit has a vapor fraction of 0 No pressure drop in either stream




HeatX Workshop (3)

For the HeatX block:– First run as a Shortcut model with: Hydrocarbon stream exit has a vapor fraction of 0 No pressure drop in either stream

– For the Detailed HeatX block:1. Enter Geometry: Shell diameter 1 m, 1 tube pass 300 bare tubes, 3 m length, pitch 31 mm, 21 mm ID, 25 mm OD All nozzles 100 mm 5 baffles, 15% cut

2. Run in Rating mode where the hydrocarbons in the shell leave with a vapor fraction of 0

Required area ______ m2 Actual area ______ m2

Over/under-surfaced ______ % Hot outlet stream T ______ °C

3. Change the Calculation Type to Simulation and re-runHot outlet stream T ______ °C

4. Create heat curves containing all info required for thermal design


HeatX Workshop (4)

Utility– Cooling water

Inlet Conditions: 20°C, 10 bar Outlet Conditions: 35°C, 10 bar Price: 0.0001 $ / kg

– How much Cooling Water is needed?

Bonus– Add a design specifications to determine how much cooling

water is needed in stream HCLD-IN for HCLD-OUT to have a temperature of 35°C




Cyclohexane HeatX Flowsheet

Filename: HEATX-CYCLOHEXANE.BKP

H2IN

BZIN

H2RCY

CHRCY

RXINRXOUT

VAP

COLFD

LTENDS

PRODUCT

STG2

PURGE

COOLWAT

CNDSATEB

WARMWATFEED-MIX REACT

HP-SEP

COLUMN

VFLOW

LFLOW

COND

Optional Workshop


Cyclohexane HeatX Workshop (1)

Part A: Using a Utility in the Condenser

1. Create a new utility for cooling water; use the following state variables to specify the heat release of the water:

Inlet Outlet

Temperature (C) 5.0 20.0

Pressure (bar) 3.0 2.9

Purchase price 0.0005 $/kg

2. Associate the cooling water utility with the RADFRAC Block’s (“COLUMN”) condenser; Hint: This is done on the COLUMN | SETUP form’s Condenser sheet





Part B: Rigorous Rating of the Condenser

Add a new HEATX block called “COND” to the flowsheet

For the hot feed stream to the COND block, connect the source of the feed stream to the PSEUDO stream connection port on the right side of the COLUMN block; you will have to later navigate to the COLUMN | REPORT form’s PSEUDO sheet and define the stream as the vapor on stage 2

Add a new cold feed stream to the COND block and use the calculated cooling water flowrate and conditions from part A

Change the COND block’s calculation TYPE to “RATING” and change the exchanger specification field to “EXCHANGER DUTY”; for the value field, use the calculated condenser duty from the COLUMN block



Specify the hot fluid on the SHELL side

Use the TEMA data sheet on the next page to enter the following information:

Shell inside diameter (see the size item in row 6 and the shell OD in row 42 of the TEMA sheet), number of tubes, tube OD, tube thickness, tube pitch, tube pattern, baffle type, baffle cut, center-to-center (c/c) baffle spacing, and all 4 nozzle diameters

NOTE: Use 29 total baffles

Allow all other input fields to use default values

Documents

Aspen+ Essential