Reactor heat integration quench

Figure 4.11 present the complete flowsheet together with the control structure. The reaction takes place in an adiabatic tubular reactor. To avoid fouling, the temperature of the reactor-outlet stream is reduced by quenching. A feed-effluent heat exchanger (FEHE) recovers part of the reaction heat. For control purposes, a furnace is included in the loop. The heat-integrated reaction system is stabilized... 

In the first step we examine the possibility of heat integration of streams around the reactor. In a first approach we may disregard the quench. Table 17.5 presents the stream population for an operating point at a conversion of about 77 %. 

The overall balance gives an excess of 1500 kW, so the problem does not require hot utility. There is need only for cold utility (cooling water). Thus, feed preheating may be covered exclusively by the exothermic reaction and save a significant amount of energy. However, a furnace is necessary before reactor to ensure constant temperature. The reactor outlet is quenched at 620 °C. Assume that the furnace has to preheat the reaction mixture from 520 °C to a reaction temperature of 630 °C. By simulation we find a duty of 3800 kW. The new stream population for heat integration becomes ... 

The next synthesis step involves task integration, that is, the combination of operations into process units. In one task integration, shown in Figure 4.20, reactor effluent is quenched rapidly to 1,150 F, primarily to avoid the need for a costly high-temperature heat exchanger, and is sent to a feed/product heat exchanger. There, it is cooled as it heats the mixture of feed and recycle chemicals to 1,(X)0°F. The stream is cooled further to 100°F, the temperature of the flash separator. The liquid from the quench is the product of the reactor section, yet a portion of it is... 

Sample integrations similar to pharmaceutical approaches were already examined in 1997 [39]. Here, a chip-like microsystem was integrated into a laboratory automaton that was equipped with a miniaturized micro-titer plate. Microstructures were introduced later [40] for catalytic gas-phase reactions. The authors also demonstrated [41] the rapid screening of reaction conditions on a chip-like reactor for two immiscible liquids on a silicon wafer (Fig. 4.8). Process conditions, like residence time and temperature profile, were adjustable. A third reactant could be added to enable a two-step reaction as well as a heat transfer fluid which was used as a mean to quench the products. 

The program numerically integrates the differential component and heat balances for the combined feed and recycle gas through the individual beds of both reactors accounting for the addition of cold quench gas between reactor beds and the recycling of fractionator bottoms to the second reactor inlet. 

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