Info

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TAC [$1000/year]
Reboiler Duty [kW]

the number of trays in the rectifying section (NR) is one of the dominant variables for optimization. Changes in NRX result in a rather small variation in the TAC. Note that the top two graphs in Figure 7.7 are obtained by fixing the feeds at the top and bottom of the reactive section. The other important variable is the feed ratio as shown in Figure 7.7. The results indicate a slight excess of alcohol is favorable because it facilitates LL separation. For the IPAc process, the minimum number of reactive trays needed to achieve the desired purity (mole fraction of acetate = 0.99, acid impurity < 100 ppm) is 9 (i.e., NRX,min = 9). The operating window for the feed ratio ranges from 0.946 to 0.99 for the desired specification. Again, some feedback mechanism is needed to adjust the feed ratio.

Type III: BuAc and AmAc. The type III flowsheet has been studied by several researchers.7 In theory, we have the following optimization variables: NR, NS, NRX, NFheavy, and NFlight. For the BuAc system, the top graph of Figure 7.8 shows that variations in NR and NS result in rather small changes in the TAC. Note that the TACs are obtained by fixing the feeds at the top and bottom of the reactive section. The bottom graph in

NFBuOH

Figure 7.8 Effects of design variables on TAC for the BuAc system.

NFBuOH

Figure 7.8 Effects of design variables on TAC for the BuAc system.

TABLE 7.5 Steady-State Operating Condition and TAC for Reactive Distillation (RD) Designs of Five Esterification Systems

System

Column Configuration

Stripper

Stripper

Total no. of trays including reboiler 39 No. of trays

Stripping section (Ns) 3

Reactive section (Nrx) 34

Rectifying section (Nr) 1

Reactive trays 4-37

Acetic acid feed tray 36

Alcohol feed tray 13 Feed flowrate (kmol/h)

Acid 50.00

Alcohol 50.00 Product flowrate (kmol/h)

Top 50.35

Acid 0.00087

Alcohol 0.00556

Acetate 0.98000

Water 0.01357 XB (mf)

Acid 0.01237

Alcohol 0.00763

Acetate <10"8

Water 0.98000

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