Why must the hydrogenation unit be shut down first when shutting down the sulfur unit?

Who decided that one must listen to hydrogenation first?

During shutdown, sulfur dioxide purging is generally required; if hydrogenation is not stopped first, the large amount of sulfur dioxide will be too much for the hydrogenation unit to handle.

The Claus unit and exhaust gas treatment in sulfur recovery plants are two separate units, and their shutdown procedures also differ. Therefore, when the plant is shut down, the two units are usually operated separately. Compared to steps such as thermal soaking in the Claus unit and sulfur injection into the reactor, the shutdown procedures for the flue gas hydrogenation unit are relatively simpler. It is not necessary to stop the hydrogenation unit first; both can be shut down simultaneously. However, since the shutdown time of the exhaust unit is relatively short, it is usually shut down first. Sometimes, in order to concentrate on shutting down the Claus unit, operators tend to stop the relatively simpler hydrogenation unit first. On the other hand, as mentioned above, when the Klaus unit is shut down, its air distribution is different from that during normal operation, and SO2 levels tend to be excessive. In such cases, it is absolutely not allowed for exhaust gases to enter the hydrogenation reactor; therefore, it makes sense to stop the hydrogenation unit first.

Why is sulfur dioxide used for purging during shutdown?

During the sulfur dioxide purging phase, the hydrogenation system must be shut down. This purging process is carried out in order to use the high-temperature flue gas to melt the sulfur accumulated in the bed, thereby converting all of the sulfur into sulfur dioxide gas. Those who wish to learn more about this should contact me at liujw395@sina.com

This isn’t a rule; it stems from practical experience. If you don’t manage the exhaust gas, the bed temperature cannot be controlled, and accidents can occur. Take a look at your operating procedures

This post was last edited by Drunk Talk on 2012-3-10 at 11:03. My understanding is to maintain the sulfided state of the hydrogenation catalyst, preventing it from being reduced to elemental metal by hydrogen and thus avoiding a decline in the catalyst’s activity. I’m not sure if it’s correct; please have experts give their opinion!