RadFracProcess Modeling using Aspen PlusFaculty of Chemical and Natural Resources EngineeringUniversiti Malaysia Pahang2008

Aspen Workshop 2008

ObjectivesEnter the minimum input required for the RadFrac fractionation modelImplement design specifications

Aspen Workshop 2008

RadFrac Flowsheet Connectivity

Aspen Workshop 2008

Some RadFrac optionsTo 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 demonstrationRadFrac SpecificationsPartial condenserKettle reboiler15 stagesR = 1.5Distillate to feed ratio = 0.6Column pressure = 315 psiaFeed stage = 8Flow= 1000 lbmol/hrT= 190 FP= 315 psiaMole fractionC1: 0.26C2: 0.09C3: 0.25nC4: 0.17nC5: 0.11nC6: 0.12Use the RKS-BM Property method

Aspen Workshop 2008

RadFrac Configuration SheetSpecify

Number of stageCondenser and reboiler configurationTwo column operating specificationsDefault: distillate rate and reflux ratioValid phasesConvergence

Aspen Workshop 2008

RadFrac Setup Streams SheetSpecify

Feed stream locationFeed stream conventionAbove-stageOn-stageBottom and overhead product streamsSide products

Aspen Workshop 2008

RadFrac Setup Pressure SheetSpecify one of:

Top/bottom pressurePressure profileSection pressure drop

Aspen Workshop 2008

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 analysisPhysical property analysisData regression analysisProfiles for all separation models including RadFrac, MultiFrac, and PetroFracClick the object of interest in the data browser to generate plots for that particular object

Aspen Workshop 2008

Plot Wizard (2)The Plot Wizard guides you in the basic operations for generating a plotIn Step 2, click the plot type you wish to generate, then click Next> to continueClick the Finish button to generate a plot with default settings

Aspen Workshop 2008

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

Aspen Workshop 2008

Design Specs and VaryDesign specifications can be specified inside the RadFrac block using DesignSpecs and Vary formsOne or more RadFrac inputs can be manipulated to achieve specifications on one or more RadFrac performance parametersThe number of specs should, in general, be equal to the number of variesThe 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.

Aspen Workshop 2008

Workshop (1)Methanol Tower

Aspen Workshop 2008

Objective: Set up a methanol tower63.2 wt% water36.8 wt% methanolFlow= 120000 lb/hrPressure= 18 psiaSaturated liquid38 trtays (40 stages)Feed tray= 23 (stage 24)Total condenserTop stage pressure= 16.1 psiaPressure drop per stage= 0.1 psiaDistillate flow rate= 1245 lbmol/hrMolar reflux ratio= 1.3Use the NRTL-RK property method

Aspen Workshop 2008

Part ARecord 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

Aspen Workshop 2008

Part BSet up DesignSpecs within the column so that there is:99.95 wt% methanol in the distillate99.90 wt% water in the bottomVary the distillate rate (800-1700 lbmol/hr) and reflux ratio (0.8-2)Record the final values for:Distillate rate:Reflux rate:Condenser duty:Reboiler duty:

Aspen Workshop 2008

Part CPerform 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:

Aspen Workshop 2008

Part DPerform a tray sizing calculation for the entire column, given that Bubble Cap trays are usedRecord the predicted column diameter

Aspen Workshop 2008