The Heat Integration Characteristics of Reactors

The heat integration characteristics of reactors depend both on the decisions made for the removal or addition of heat and the reactor mixing characteristics. In the first instance, adiabatic operation is considered, since this gives the simplest design. 

Adiabatic operation. If adiabatic operation leads to an acceptable temperature rise for exothermic reactors or an acceptable fall for endothermic reactors, then this is the option normally chosen. If this is the case, then the feed stream to the reactor requires heating and the efiluent stream requires cooling. The heat integration characteristics are thus a cold stream (the reactor feed) and a hot stream (the reactor efiluent). The heat of reaction appears as elevated temperature of the efiluent stream in the case of exothermic reaction or reduced temperature in the case of endothermic reaction. 

Heat carriers. If adiabatic operation produces an unacceptable rise or fall in temperature, then the option discussed in Chap. 2 is to introduce a heat carrier. The operation is still adiabatic, but an inert material is introduced with the reactor feed as a heat carrier. The heat integration characteristics are as before. The reactor feed is a cold stream and the reactor efiluent a hot stream. The heat carrier serves to increase the heat capacity fiow rate of both streams. 

Cold shot or hot shot. Injection of cold fresh feed for exothermic reactions or preheated feed for endothermic reactions to inter- 

Indirect heat transfer with the reactor. Although indirect heat transfer with the reactor tends to bring about the most complex reactor design options, it is often preferable to the use of a heat carrier. A heat carrier creates complications elsewhere in the flowsheet. A number of options for indirect heat transfer were discussed earlier in Chap. 2. 

Cold shot. Injection of cold fresh feed for exothermic reactions or preheated feed for endothermic reactions to intermediate points in the reactor can be used to control the temperature in the reactor. Again, the heat integration characteristics are similar to adiabatic operation. The feed is a cold stream if it needs to be increased in temperature or vaporized and the product a hot stream if it needs to be decreased in temperature or condensed. If heat is provided to the cold shot or hot shot streams, these are additional cold streams. 

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