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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
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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
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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)
© 2010 Aspen Technology, Inc. All rights reserved | 4
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
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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
© 2010 Aspen Technology, Inc. All rights reserved | 6
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
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Basic Input
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Useful Options
GUI– Window->Workbook
mode
Automatic Naming of Streams and Blocks– Tools->Options-
>Flowsheet
Result in Flowsheet– Tools->Options->Results
View
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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.
© 2010 Aspen Technology, Inc. All rights reserved | 10
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
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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
© 2010 Aspen Technology, Inc. All rights reserved | 12
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
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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
© 2010 Aspen Technology, Inc. All rights reserved | 14
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
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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
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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
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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
© 2010 Aspen Technology, Inc. All rights reserved | 18
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
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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
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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
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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
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Reviewing Results
Control Panel Messages – Contains any generated errors or warnings – Block Results– Convergence
Steam Results
Custom Stream Results
Block Summary Grid
Block Results
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Stream Results
Contains stream conditions and compositions
Fraction basis in stream result– Data browser->Setup->Report options->Stream
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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
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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
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Benzene Flowsheet Conditions Workshop (2)
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
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Benzene Flowsheet Conditions Workshop (3)
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
© 2010 Aspen Technology, Inc. All rights reserved | 28
Benzene Flowsheet Conditions Workshop (4)
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RadFrac
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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
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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)
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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
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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
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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
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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
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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.
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RadFrac Setup Pressure Sheet
Specify one of:– Top/Bottom pressure– Pressure profile– Section pressure drop
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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
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Plot Wizard Demonstration
Use the Plot Wizard to create plots of temperature, flows, and compositions throughout the column
© 2010 Aspen Technology, Inc. All rights reserved | 40
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
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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? ___________________________________
© 2010 Aspen Technology, Inc. All rights reserved | 42
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
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Thermosiphon Configuration in RadFrac
RadFrac model supports various reboiler configurations
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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
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Specifying Efficiencies in RadFrac
RadFrac Efficiencies Options sheet
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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
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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
© 2010 Aspen Technology, Inc. All rights reserved | 48
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
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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
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RadFrac Workshop (2)
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
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RadFrac Workshop (3)
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:
_________
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RadFrac Workshop (4)
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: _________
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Reactor Models
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Reactor Overview
Reactors
Balance BasedRYieldRStoic
Equilibrium BasedREquilRGibbs
Kinetics BasedRCSTRRPlug
RBatch
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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
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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
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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
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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
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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
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Kinetic Reactors (2)
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
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Kinetic Reactors (3)
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
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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
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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
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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
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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)
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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
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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
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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
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Example of a Power Law Reaction ID (6) -Kinetic sheet
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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
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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
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Reactor Workshop (2)
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
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Reactor Workshop (3)
Results
RStoic RGibbs RPlug RCSTRAmount of Ethyl Acetate produced (kmol/hr)Mass fraction Ethyl Acetate in product streamHeat duty (kcal/hr)
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Physical Properties
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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
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How to Establish Physical Properties
Choose a Property Method
Check Parameters/Obtain Additional Parameters
Confirm Results
Create the Flowsheet
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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
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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
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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
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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
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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
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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?
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Property Method Selection Assistant
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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
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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)
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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
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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.)
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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
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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
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Cyclohexane WorkshopWon-Seok LeeAspenTech Korea, Business Consultant
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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
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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
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Sensitivity Analysis
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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
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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
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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
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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
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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
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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
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Design SpecificationsAspen Plus®: Process Modeling
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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
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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)
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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
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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
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Heat Exchangers
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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
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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
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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
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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
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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+)
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HeatX Key Options
Options– Valid phases
Block Options– Property method– Water Solubility
Setup->LMTD– Interval
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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
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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.
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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
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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
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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
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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
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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
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Cyclohexane HeatX Workshop (2)
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
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Cyclohexane HeatX Workshop (2)
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
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