Requirements for loading and unloading hydrogenation catalysts in hydrogenation units
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After the hydrogenation catalyst in the hydrogenation unit has been used, it is necessary to remove and replace the catalyst inside the hydrogenation reactor. What precautions should be taken during catalyst removal, and how should the internal components of the hydrogenation reactor be handled?
Hydrogenation catalysts contain ferrous sulfide, so a nitrogen-rich environment is required when removing them; it is best to do this under negative pressure (self-flowing methods also carry significant risks). The catalysts released release heat, so it is advisable to place them in sealed bags with dry ice inside iron drums. If they are not to be regenerated or resold, water can be applied directly to them, but it is still recommended to store them in iron drums. When loading the catalyst, a nitrogen atmosphere is required for the sulfided state, while oxygen-containing environments can be used for the oxidized state. For large quantities of catalyst to be loaded, dense-phase loading is preferred. To protect the catalyst, it is advisable to carry out drying before loading, as well as again after loading; however, in most cases, the drying step before loading is omitted to keep the project on schedule. As for all the accessories for dust protection and preventing drops, they are more or less the same. As for the internal components, it is generally not necessary to dry them when they contain agents; however, in some reactors the cold hydrogen tanks must be removed in order to load or unload the agents, and in some cases welding is required for removal – so one has to assess the risks on their own.
The replacement of catalysts in hydrogenation units is generally necessary when the catalyst becomes inactive or its pores become blocked. This occurs because, over time, the surface of the catalyst is covered with ferrous sulfide formed as a result of the hydrogenation reaction, and ferrous sulfide undergoes natural reactions when it comes into contact with oxygen in the air. Therefore, the removal of the agent must be carried out in an anaerobic environment, usually under nitrogen protection. The unloaded catalyst must be promptly placed in iron drums lined with bags, and dry ice or nitrogen should be used to seal the drums in order to prevent the catalyst from coming into contact with air and undergoing spontaneous reactions. The reactor internals are disassembled and cleaned after the catalyst is removed; if they are not to be replaced, they can be inspected and cleaned inside the reactor. For those cases where catalyst loading cannot be carried out without removing the internal components, simply removing and cleaning the internal components is sufficient. For the loading of new catalysts, if they are in an oxidized state, they can be loaded directly in an aerobic environment; whereas catalysts in a sulfided state need to be loaded under anaerobic conditions. During loading, pay attention to keeping the catalyst dry; it is best to carry out the process on a dry day. After the new catalyst is loaded, catalyst drying, which is also known as system drying, is carried out.
Caking on the surface of the catalyst bed layer may occur, which can lead to sudden pressure release from the upper part when the top is opened, thereby posing a risk of injury
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