Multi-stage heat exchange reactors

The reaction rate of the whole process in some reversible exothermic reactions, such as the carbon monoxide shift reaction, can be considerable. The heat needed to be extracted from unit volume of catalyst at the beginning and the ending stages of the reaction may vary by 10 times or more. These reactions require multi-stage heat exchange reactors. Other reactions, such as the ammonia synthesis... 

For endothermic reactions the problem can be solved by dividing the reactor into multiple stages, with intermediate heat exchangers, defining a multi-bed reactor. In exothermic processes, the intermediate cooling may be achieved by mean of heat exchangers or by injection of cold feed. A schematic illustration of a multi-bed reactor is shown in Fig 11.2. 

In view of these temperature rises, a fixed-bed reactor would be feasible only if the oxygen could be added in stages in a multi-bed reactor so that the temperature rise across each bed were limited. Interstage cooling could be accomplished by injection of recycle methane and indirect heat exchange. For example, if the performance in each reactor bea is as shown in Fig. 2a, the temperature rise across each bed will be 46°C. Laboratory experiments [ref.4] have shown that selectivity is not significantly affected by a temperature rise of this magnitude. 

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