Solid-liquid separator
Fig. 16. Flowsheet of the original SCD process for producing cumene. 1 - SCD column; 2 - benzene column; 3 - cumene column; 4 - fixed-bed reactor.
Under steady-state conditions all of the time derivatives in the MESHR equations are equal to zero. The modified relaxation method where the MESHR equations are written in unsteady-state form and are integrated numerically until the steady-state solution has been found, is used to solve the above equations.
It is known that transalkylation reaction is reversible, and in this work it is supposed to reach chemical equilibrium at each stage. The chemical equilibrium constant K is written below [83]:
It can be seen from Figs. 16 and 17 that the distinguishable difference between a single alkylation reaction and simultaneous alkylation and transalkylation reactions in a column is that a DIPB stream is fed into the catalytic distillation column in the improved process. It is evident that the flowrate of DIPB fed into the column 1, Fl, is an important parameter influencing the column design and operation. In the simulation of the column it is found that Fl can not be arbitrarily given and should be equal to the flowrate of DIPB leaving from the column, F2. Therefore, Fl should be determined in advance in a continuous production. In the simulation Fl is constantly adjusted until it is equal to F2, and thus Fl is determined.
It is assumed that the SCD column is divided into 41 theoretical stages, and the condenser is the stage 41 and the reboiler the stage 1. The operating pressure is 700 kPa and reflux rate 960 kmol h"1, while the feed of benzene and propylene arc 100 kmol h'1 and 50 kmoi BT, respectively. The relation of F1 and F2 in the SCD column is shown in Fig. 18, and the point where F1 - F2 can be found, which means that the process has reached steady-state, and the number of steady-states is only one. The computation has been performed on a PC (Pentium 4 1,5G). Each case needs about ten minutes for simulation, fn the case that F1 = F2. temperature and composition of the bottom stream in the SCD column are listed in Table 5.
Table 5
Temperature and molar composition of the bottom stream in the SCD column
Table 5
Temperature and molar composition of the bottom stream in the SCD column
Tí K |
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