Why is it strictly prohibited for gas to enter the reactor during an emergency stop?

Everyone has already stopped the machines urgently; what’s there to react to?

So why not allow air intake? What is the fear, or are there other reasons?

The original poster, please clarify: what gases are not allowed to enter the reactor?

Perform an emergency stop and activate the pressure relief system specified in 2.1; the purpose is to release hydrogen gas. Due to concerns over excessive temperature rise, no more hydrogen can be introduced into the reactor.

Vague question: Intake air? Which gas (hydrogen/nitrogen)? Pressure relief occurs first as a result of equipment failures or process accidents. The purpose of pressure relief is to bring the equipment back to a safe state as quickly as possible, thereby preventing the accident from spreading. By releasing pressure, it is possible to cut off the feed materials (feed oil and hydrogen), thus stopping or reducing the chemical reactions taking place in the reactor. Rapid pressure relief increases the space velocity and reduces the reaction rate, helping to get the main equipment back to a safe state swiftly. If more gas (hydrogen) is introduced, it is equivalent to adding feed gas, the reaction continues, and heat is released by the system, which hinders the safe handling of the system as quickly as possible. However, after pressure relief or when the pressure is reduced, injecting high-pressure nitrogen into the system can quickly displace the original medium within the system, **accelerating the accident response process

Emergency pressure relief involves rapidly reducing the system pressure to minimize the impact of an accident, while also using gas flow to carry away the heat from inside the reactor. Generally, in cases of emergency pressure relief caused by excessive temperature, it is not necessary to prevent hydrogen from entering the reactor, as hydrogen acts merely as a heat carrier; this is unless there is a concern that too low sulfur content in the hydrogen could lead to catalyst reduction. In high-pressure systems, such measures may be taken to avoid hydrogen embrittlement resulting from severe fluctuations in temperature and pressure. Of course, in the event of a leak and an emergency pressure release, it is definitely necessary to cut off the flammable medium

The emergency pressure relief in the hydrogenation unit can remove some of the heat generated during the reaction, with the aim of reducing temperature and thus slowing down the reaction as well as minimizing heat release, thereby protecting the catalysts and equipment. However, this process may result in hot spots within the reactor (the thermometers in the reactor can only measure the temperature at specific points; even if the readings indicate that the temperature is within limits, the possibility of hot spots still exists in emergency situations). In the case of high-pressure hydrogenation reactions, due to the high purity of hydrogen, introducing hydrogen hastily could lead to further reaction and heat release, which might damage the catalysts and equipment. Therefore, it is recommended not to introduce hydrogen under such conditions. A high-pressure nitrogen line is specifically provided for high-pressure hydrogenation units; introducing nitrogen eliminates the possibility of the reaction continuing, and it can further lower the catalyst temperature, so this approach is feasible. However, after introducing nitrogen, the purging time required to restart the system will inevitably increase, which will affect the restart time of the plant. So, try not to introduce nitrogen if possible