RadFrac

The calculations were made with the RATEFRAC program and comparisons were made with the compamon RADFRAC program, which utilizes the inside-out method for an eqiiilibniim-based model. 

The simulation is performed with the Radfrac module in ASPEN Plus and the NRTL liquid-activity model [20]. Tracing the RCM (Figure 3.15) shows that acetone and chloroform are unstable nodes, toluene is a stable node and the maximum-boiling azeotrope acetone-chloroform is a saddle. The distillation boundary shows a strong curvature. 

Rmin and the corresponding number of trays calculated ( 2N J. The shortcut models were replaced by rigorous RADFRAC units, where the reflux and distillate feed ratio were adjusted by means of design specifications, in order to meet the desired separation. The trays were sized using Aspen s facilities. Finally, the dimensions of the reflux drum and column sump were found based on a residence time of 5 min and aspect ratio H D = 2 1. Table 9.7 presents the results of distillation column sizing. 

Plus RADFRAC block using the Peng-Robinson equation of state. 

BLOCK RADFRAC RADFRAC PARAM NSTAGE = 28 COL-CONFIG CONDENSER = TOTAL FEEDS FEED 14... 

Hydraulic analysis of the Aspen Plus simulator produces thermodynamic ideal minimum flow and actual flow curves for rigorous distillation column simulations. These types of calculations are performed for RADFRAC columns. Using the input summary given in problem 4.48 construct the stage-flow curves. Assess the thermodynamic performance of the column. 

Using the following input summary for RADFRAC columns, construct the temperature-enthalpy, stage-enthalpy curves, and the stage-exergy loss profiles for each columns and assess the thermodynamic performance of the columns ... 

Rigorous distillation RadFrac, MultiFrac Distillation, 3-Phase Distillation... 

Absorption and stripping RadFrac Absorber, Refluxed Absorber, Reboiled Absorber... 

TABLE 6.3. Stream Table for Multicomponent Distillation with RadFrac, Reflux Ratio = 3.44... 

The next simulation is for the same column, but using the RadFrac block in Aspen Plus. The feed is the same, the pressure is 138 psia, and the Refinery/Chao-Seader property method is used. This example uses 26 stages, and you run Aspen Plus to see what the split is. (Notice that you cannot easily set the split and find the number of stages or reflux ratio needed to achieve it.) Set the reflux ratio to 3.44 and enter the feed on the thirteenth stage. 

X 10 Btu/h. Above the feed, the flow rate varies between 283 and 344 lb mol/h, and below it, the flow rate varies between 2998 and 3097 lb mol/h. While DSTWU assumes the same number of moles on each plate or tray, RadFrac calculates what actually occurs. To see the flow rates on each stage, choose the block, then Profiles. 

Figure 6.5. Multicomponent distillation with RadFrac, reflux ratio = 3.44. (a) Condenser (b) reboiler.

TABLE 6.4. Multicomponent Distillation with Radfrac, Reflux Ratio = 10... 

This chapter introduced you to the many thermodynamic models available in Aspen Plus. The equations for short-cut distillation were summarized, and the Aspen Plus was used to solve a variety of distillation problems, with either short-cut methods (DSTWU) or plate-to-plate methods (RadFrac). You also learned how to solve gas absorption problems using Aspen Plus. 

Model column B2 in Figure 6.8 using a detailed model, RadFrac. (Hint Use the results from Problem 6.1 to choose key operating parameters.) Prepare a report comparing the output when using DSTWU and RadFrac to model the distillation column. What information was needed for each How do the results compare ... 

Model example 1 on pp. 13-36 in Perry s Chemical Engineering Handbook (Seader et al., 1997) using (1) DSTWU (2) RadFrac. 

Use RadFrac with the reflux rate set by the output from the DSTWU model. 

RadFrac - rigorous two phase and three phase, absorber, stripper, distillation columns using stages... 

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