What are the advantages of using a gas-controlled external heat exchanger in catalytic cracking?
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What are the advantages of using a gas-controlled external heat exchanger in catalytic cracking? The pneumatically controlled external heat exchanger is quite sensitive in terms of heat absorption, but its operation is more complex and cumbersome than that of the downflow type; the catalyst can easily stop functioning and is difficult to restore to normal operation, while the bottom of the vertical pipe is prone to clogging, resulting in poor fluidization. Why is such an external retrieval mechanism still implemented? Isn’t a downstream type more appealing? {:1_90:}
No advantages of air-controlled operation have been observed for now; in practical use, it is difficult to control the heat output by adjusting the air flow, as there is little capacity for adjustment. In some areas, the catalyst flow tends to get clogged, resulting in a decrease in steam generation, and it is hard to restore normal conditions.
Due to spatial constraints, it is difficult to install a downstream-type external heat extraction system for coaxial single-end counterflow regeneration; gas-controlled external heat extraction systems are more commonly used, and it is indeed challenging to achieve the designed performance in actual operation.
To reduce the impact of the lifting air on the fluidized bed layer, it is also possible to make full use of this air for burning; since both the volume of the fluidizing air and the lifting air is low, their effect on the fluidization in the regenerator is minimal. Moreover, the operation is quite sensitive. The issue you mentioned regarding catalyst disruption might be due to too low steam production – trying to increase the steam output could help
The amount of steam produced is determined by the properties of the raw materials, specifically by the bed temperature; if the bed temperature is not high, it is not possible to increase the amount of steam generated