RadFrac - A. Hisyam
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Transcript RadFrac - A. Hisyam
RadFrac
Process Modeling
using Aspen Plus
Faculty of Chemical and Natural Resources Engineering
Universiti Malaysia Pahang
2008
Objectives
Enter the minimum input required for the
RadFrac fractionation model
Implement design specifications
Aspen Workshop 2008
RadFrac Flowsheet Connectivity
Aspen Workshop 2008
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 efficiency on either a stage or
component basis can be specified on the RadFrac Efficiency
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 phase
Reboiler and condenser heat curves can be generated
Aspen Workshop 2008
RadFrac demonstration
Mole fraction
RadFrac Specifications
Partial condenser
Kettle reboiler
15 stages
R = 1.5
Distillate to feed ratio = 0.6
Column pressure = 315
psia
Feed stage = 8
OVHD
C1: 0.26
C2: 0.09
C3: 0.25
nC4: 0.17
nC5: 0.11
nC6: 0.12
FEED
B1
Flow= 1000 lbmol/hr
T= 190 F
BOTM
P= 315 psia
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Use the RKS-BM Property
method
RadFrac Configuration Sheet
Specify
Number of stage
Condenser and reboiler
configuration
Two column operating
specifications
Default: distillate rate and
reflux ratio
Valid phases
Convergence
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RadFrac Setup Streams Sheet
Specify
Feed stream location
Feed stream convention
Above-stage
On-stage
Bottom and overhead
product streams
Side products
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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 (1)
Use the plot wizard (on th eplot menu) to quickly
generate plot results of a simulation. You can
use the Plot wizard for displaying results for the
following operations:
Assay data analysis
Physical property analysis
Data regression analysis
Profiles for all separation models including RadFrac,
MultiFrac, and PetroFrac
Click the object of interest in the data browser to
generate plots for that particular object
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Plot Wizard (2)
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
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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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Workshop (1)
Methanol Tower
Objective: Set up a methanol tower
B1
DIST
FEED
63.2 wt% water
36.8 wt% methanol
BOTM
Flow= 120000 lb/hr
Pressure= 18 psia
Saturated liquid
Use the NRTL-RK
property method
38 trtays (40 stages)
Feed tray= 23 (stage 24)
Total condenser
Top stage pressure= 16.1 psia
Pressure drop per stage= 0.1
psia
Distillate flow rate= 1245
lbmol/hr
Molar reflux ratio= 1.3
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Part A
Record the column duties:
Condenser duty:
Reboiler duty:
Record composition:
Mass fraction of methanol in the distillate:
Mass fraction of water in the bottom:
Make plots of temperature, flows, and
composition
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Part B
Set up DesignSpecs within the column so
that there is:
99.95 wt% methanol in the distillate
99.90 wt% water in the bottom
Vary the distillate rate (800-1700 lbmol/hr)
and reflux ratio (0.8-2)
Record the final values for:
Distillate rate:
Condenser duty:
Reflux rate:
Reboiler duty:
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Part C
Perform the same calculations after
specifying a 65% Murphree efficiency for
each tray. Assume the condenser and
reboiler have stage efficiencies of 90%.
Determine how these efficiencies affect
the column duties:
Condenser duty:
Reboiler duty:
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Part D
Perform a tray sizing calculation for the
entire column, given that Bubble Cap trays
are used
Record the predicted column diameter
Aspen Workshop 2008