Why can’t the hydrocracking unit use supplemental hydrogen to cool the bed temperature?
Thread Content
The operating procedures for the hydrocracking unit state clearly that in the event of an accident in the reaction process or an excessive rise in temperature, the recycle hydrogen compressor should be stopped immediately and an emergency pressure relief system should be activated; cooling the bed layer cannot be achieved by using additional hydrogen. Personally, I think it would be more effective to both supply hydrogen and allow gas to escape at the same time. The procedures explain that adding additional hydrogen would cause intense reactions in the bed layer, but I doubt this – isn’t it already a hydrogen-rich environment? Would the hydrogen inside not still react and release heat if no additional hydrogen is added?
For example: A house is on fire, the fire brigade is spraying water, and you are blowing air into the burning house
The temperature of the supplementary hydrogen cooling bed is limited; in the event of overheating, the priority is to reduce the system pressure as quickly as possible, which creates a conflict with the need to inject supplementary hydrogen.
In the event of an accident, it is not possible to use supplementary hydrogen to cool the bed layer, as this could lead to a secondary temperature spike; liquid nitrogen is the best option in such cases
Generally, a pressure drop of 2.1 bar to zero should be sufficient to lower the temperature. If there is still a rise in temperature (as nitrogen is not always in abundant supply in refineries), it seems that using fresh hydrogen would work as well
Generally, if there is still a temperature rise, nitrogen is used, but there isn’t that much nitrogen available
Is there a possibility of catalyst reduction due to bed temperature spikes or the continuous addition of fresh hydrogen after the recycle hydrogen compressor stops?
Why isn’t it possible to use supplementary hydrogen? I think the original poster is absolutely right! The fear of a reaction is absolutely nonsense! It’s somewhat plausible to say it’s done in order to lower blood pressure as quickly as possible; certainly, supplementing with hydrogen is one of the methods, and there’s nothing wrong with that. It makes no sense to prohibit it
The system is so large that when adding new hydrogen, it’s necessary to pay attention to changes in the hydrogen sulfide content in the circulating hydrogen. Moreover, when the hydrogen circulation pump stops and the furnace goes out, the temperature drops rapidly; once it falls below 230°C, the probability of excessive reduction of the catalyst becomes very low!
I agree with the original poster’s view; when the emergency pressure relief valve opens, the flow rate of circulating hydrogen increases significantly, which results in an excellent temperature reduction effect. Adding new hydrogen increases the amount of circulating hydrogen, thereby causing the temperature to drop even faster! Although the addition of new hydrogen causes the reaction to release heat, an increase in the amount of new hydrogen enables continuous discharge of recycled hydrogen, thereby continuously removing heat! The pressure drops more slowly, and the temperature is maintained for a longer period of time
Previously, when working on diesel hydrogenation for viscosity reduction, I modified the forced interlock of the outlet valve of the new hydrogen generator; it could be set to the bypass route to prevent interlocking (of course, the shutdown of the new hydrogen generator was also routed through the bypass). In this way, the supply of new hydrogen wasn’t affected when the cycle hydrogen compressor stopped operating, thereby buying time to start the steam turbine