RadFrac block

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

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. 

To draw an absorber, use the RADFRAC icon. Draw a system with a vapor feed at the bottom, a liquid bottoms product, a second feed (liquid) at the top, and a vapor distillate. In the configuration window for the RADFRAC block set ... 

In the streams window for the RADFRAC block set Liquid feed above stage 1, and Vapor feed on the last stage. 

The RadFrac block can be used for the ordinary distillation column and also for the extractive distillation column as shown in the example in Section 3.1. It can also be used as strippers (with a reboiler but no condenser), rectifiers (with a condenser but no reboiler), absorbers (with neither), and more complex columns with side pmnp-around. In the following, several columns other than the ordinary distillation will be outlined. The RadFrac can also be used as a heterogeneous azeotropic distillation column with decanter replacing the reflux drum at top of this column. The vapor-liquid-liquid calculation can be performed inside the column if needed. 

Sidestream Column. The RadFrac block in Aspen Plus can be used for the ordinary distillation column with one feed stream and two outlet streams (distillate and bottoms). This block can also be used for multiple feed streams or more than two ordinary outlet streams. For example, the extractive distillation column in Section 3.1 demonstrated that two feed streams can be connected to the RadFrac block. In a similar way, more outlet streams can be drawn out of the RadFrac block as a sidestream column. The sidestream draw-off can be either a liquid stream or a vapor stream. AU these varieties of different columns can easily be configured by adding material streams to the flowsheet with the RadFrac block (see previous Fig. 3.5). 

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

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. 

Model column B3 in Figure 6.8 using a short-cut, DSTWU block. (2) Then model the same column using RadFrac. How do the results compare ... 

Process simulation units (that is, blocks, modules, or subroutines) are mapped into more descriptive models of process equipment (e.g., mapping a HEATX simulation unit into a floating-head, shell-and-tube heat exchanger mapping a RADFRAC simulation unit into a tray tower, complete with reboiler, condenser, reflux accumulator, etc.) and associated plant bulks, which include installation items, such as piping, instrumentation, insulation, paint, etc. 

In designing a conventional single column, the RadFrac model in Aspen Plus is used. To use a. MultiFrac model with a Peflyuk configuration, select the appropriate icon and drop it onto the process flow diagram as shown in Figure 12.2. Then feed, distillate, and bottoms material streams are added as shown in Figure 12.3. The model block is labeled DWC. 

BLOCK COLI RADFRAC PARAM NSTAGE=I5 COL-CONUG CONDENSER TOTAL... 

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