Alkylation of Benzene by Propylene to Cumene 6

6.5 Energy Integration 191Figure 6.11 Composite curves (a) and grand composite curve (b)after the heat integration of the benzene recycle column.the simulated flowsheet the reflux is identical in both columns at 0.26. The simulationshows that about 2660 kW may be saved by using the condenser of (C - 2B) asthe reboiler for (C - 2A). Since the net distillate flow of C - 2A is larger, a supplementaryreboiler duty of about 560 kW is necessary. The net hot - utility consumptionof benzene distillation drops from 7870 to 3794 kW, representing a saving of51.8%. Furthermore, by slightly increasing the pressure in the column (C - 3) allowsthe generation of low - pressure steam. For both columns (C - 2) and (C - 3) the hotutility can be ensured by Dowtherm A or another similar thermal fluid.The impact of the above approach on the overall energy management can beexamined again by plotting the composite curves (Figure 6.11 ). The minimum