Process Modeling using Aspen Plus 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 RadFrac Specifications Partial condenser Kettle reboiler 15 stages R = 1.5 Distillate to feed ratio = 0.6 Column pressure = 315 psia Feed stage = 8 Mole fraction C1: 0.26 C2: 0.09 C3: 0.25 nC4: 0.17 nC5: 0.11 nC6: 0.12 Flow= 1000 lbmol/hr T= 190 F P= 315 psia Use the RKS-BM Property method Aspen Workshop 2008

RadFrac Configuration Sheet Specify Number of stage Condenser and reboiler configuration Two column operating specifications Default: distillate rate and reflux ratio Valid phases Convergence Aspen Workshop 2008

RadFrac Setup Streams Sheet Specify Feed stream location Feed stream convention Above-stage On-stage Bottom and overhead product streams Side products Aspen Workshop 2008

RadFrac Setup Pressure Sheet Specify one of: Top/bottom pressure Pressure profile Section 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 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 Aspen Workshop 2008

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 Aspen Workshop 2008

Plot Wizard Demonstration Use the Plot Wizard to create plots of temperature, flows, and compositions throughout the column Aspen Workshop 2008

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. Aspen Workshop 2008

Workshop (1) Methanol Tower

Objective: Set up a methanol tower 63.2 wt% water 36.8 wt% methanol Flow= 120000 lb/hr Pressure= 18 psia Saturated liquid 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 Use the NRTL-RK property method Aspen Workshop 2008

Part A Record the column duties: Record composition: 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 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: Reflux rate: Condenser duty: Reboiler duty: Aspen Workshop 2008

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: Aspen Workshop 2008

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