Time during shutdown when the cyclohydrogen compressor is stopped
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During the normal shutdown of a hydrocracking unit, at what temperatures and pressures should the cycle hydrogen compressor be stopped? Why?
The circulation hydrogen compressor in the hydrogenation unit is stopped primarily based on the reactor temperature; in our company, it is stopped when the temperature drops below 100 degrees. Of course, the pressure also needs to be reduced appropriately, with 30–40 kilograms being sufficient in such cases
If the catalyst is not removed, it can be shut down according to one’s own requirements, provided that the temperature and pressure conditions required to avoid temper brittleness in CrMo steel are met. If it is catalyst desulfurization and regeneration, the temperature can be lowered slightly; generally, the temperature should be kept below 40°C during desulfurization. The pressure can be higher until the temperature reaches the desired level (provided that the temperature and pressure requirements for the tempering of CrMo steel are met).
The temperature must be below 50 degrees Celsius to prevent spontaneous combustion of ferrous sulfide and burns; the pressure should be at the lowest inlet pressure that the compressor can handle. «At this point, the hot hydrogen has been mixed with oil, and the reactor has stopped releasing hydrogen.»
Generally, it is required to lower the reactor temperature below 60 degrees before stopping the circulation pump, and then continue with nitrogen purging. Stopping too early makes it difficult to remove the catalyst, while stopping too late is pointless, as it becomes very hard to continue lowering the temperature once it drops to around 60 degrees.