How to protect hydrogenation catalysts when feed supply is stopped?
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If the feed to the hydrogenation catalyst is stopped, how should the catalyst be protected? There are several situations: 1. An emergency occurs, resulting in a stop to feed supply. How should the catalyst be protected in the presence of circulating hydrogen and in its absence? 2. Normal shutdown. During normal shutdown and oil removal, how can the catalyst be protected throughout this process? 3. Process changes. When one of the two reactors connected in parallel or series needs to be shut down for production reasons, how should the catalyst in the stopped reactor be protected? Please consider the parallel and series cases separately. In summary, I believe there are several aspects to keep in mind: one is coking, another is the presence of CO which leads to the formation of carbonyl compounds (such as nickel carbonyl), and yet another is whether a pure hydrogen environment will reduce the catalyst. I would like to ask how to prevent these three situations from occurring. Are there any other things to keep in mind?
Your description is not specific – hydrogenation units come in many types. The principles for dealing with accidents in hydrocracking and hydrorefining processes are different. But let me tell you one thing: follow the operating procedures.
Well, then you can discuss them separately. Even for the same set of equipment, under different circumstances – such as the emergency situations I mentioned earlier or normal shutdowns – the approaches to handling them are different. You can share as much as you know; just talk about what you are aware of. I am interested in hydrocracking and hydrorefining, and even reforming – in short, anything that involves hydrogen; I want to acquire knowledge and experience in these areas*
During normal shutdown, after cutting off the feed, hot hydrogen should be used to carry the oil; then the temperature should be reduced, pressure released, the vessel filled with nitrogen, and a slight positive pressure maintained inside the reactor. In an emergency, first shut down the furnace and stop feeding material. If the circulation of hydrogen cannot be restored, the reaction system must be depressurized immediately to maintain gas flow and prevent coking.
1. In case of an emergency, stop the feed supply. How should the catalyst be protected in the presence of circulating hydrogen and in its absence? With circulating hydrogen, first shut down the heating furnace and then cut off the feed ； Without circulating hydrogen, the reaction system is immediately depressurized to prevent catalyst coking. 2. Normal shutdown. During normal shutdown and oil removal, how can the catalyst be protected throughout this process? Normal shutdown: cut off the feed — hot hydrogen with oil — cool down — depressurize — purge with nitrogen — remove the reactor and maintain a slight positive pressure inside it. 3. Process changes. When one of the two reactors connected in parallel or series needs to be shut down for production reasons, how should the catalyst in the stopped reactor be protected? Please consider the parallel and series cases separately. I don’t understand your process; please describe it in detail.
During normal shutdown, hot hydrogen with oil should be used after cutting off the feed. In emergency situations, reduce the temperature and maintain circulating hydrogen with oil
1. In case of an emergency, stop the feed supply. How should the catalyst be protected in the presence of circulating hydrogen and in its absence? With circulating hydrogen, lower the reaction temperature appropriately and maintain the flow of circulating hydrogen. In the absence of circulating hydrogen, follow the plant accident protocol to gradually relieve pressure, maintain hydrogen flow, and shut down the furnace. 2. Normal shutdown. During normal shutdown and oil removal, how can the catalyst be protected throughout this process? Just follow the shutdown plan. 3. Process changes. When one of the two reactors connected in parallel or series needs to be shut down for production reasons, how should the catalyst in the stopped reactor be protected? Please consider the parallel and series cases separately. Just isolate the reactor, relieve pressure, and drain the oil. In hydrogen-related systems, the CO level is under control; generally, there is no CO present. If the CO level in the newly supplied hydrogen exceeds the allowed limits, it must be reported to the dispatch team and unit management, who will then take action to shut down the system urgently. In a pure hydrogen environment, the catalyst is not reduced; the hydrogen purity in the circulating hydrogen is usually above 95%, and it can reach 99% during operation, so there’s no problem – your concerns are unfounded.
Cyclic hydrogen contains H2S, so it will not reduce the catalyst; however, the bed temperature is generally lowered to 230 degrees before operating at a constant temperature with oil present.
In the event of an accident, vent the system to reduce the hydrogen partial pressure as much as possible. If it is for abnormal maintenance purposes, temperature is a key factor; as long as the temperature is below that required for pure hydrogen reduction, it doesn’t matter whether hydrogen sulfide is present or not. Nitrogen is still the better choice for protecting the catalyst
1. In case of an emergency, if there is circulating hydrogen, cool down while keeping the oil present; if there is no circulating hydrogen, relieve pressure while still keeping the oil present. When the pressure is low, use N2 to displace the oil. 2. During normal shutdowns, try to avoid large fluctuations in temperature and pressure. 3. Is there a difference between shutting down a reactor in parallel or in series? Make sure to completely displace the oil from the catalyst bed and maintain a slight positive pressure of N2 in the reactor. When circulating hot hydrogen, take into account the issue of desulfurization mentioned earlier; when cooling down, consider the CO content
I have few points; a +2 per time, so I won’t give it to each of you individually. Thank you all for your replies!
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