Waste-Heat Utilization and Cooling

The trend followed in newer plants is to increase conversion per pass with the result of higher ammonia outlet concentrations and lower outlet temperatures from the last bed. However, as optimum energy efficiency of the whole ammonia plant requires maximum high-pressure steam generation, part of the heat must be recovered before the reaction is completed in the reactor system. This can be accomplished [900], [901], [930], [931] by using three catalyst beds in separate pressure vessels with boilers after the second and the third vessel and an inlet - outlet heat exchanger for the first catalyst bed. 

Appropriate design of waste-heat boilers is described in Section 4.6. 

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