Excessive fluctuations in bed temperature rise in the pre-hydrogenation reactor of the hydrogen production unit using coking dry gas
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I have a hydrogen production plant with a capacity of 10,000 cubic meters of coked dry gas; it has been in operation for one year. Recently, the pre-hydrogenation reactor has experienced frequent fluctuations in bed temperature. Previously, the inlet temperature was 205 degrees, while the bed temperature was 380 degrees. The inlet temperature remains basically constant now. The bed temperature fluctuates between 210 degrees and 490 degrees. The time is two hours. I’m asking the teachers: what is the reason exactly? What are the hazards of high temperatures?
Please, the original poster, answer the following: 1. Has there been any change in the composition of the coking dry gas in your facility? 2. What is the amount of hydrogen produced by the 10,000 cubic meter coking dry gas hydrogen production unit before and after hydrogen production? 3. What is the temperature difference across the bed of the pre-hydrogenation reactor? Excessively high temperatures can affect the activity and lifespan of the catalyst.
What type of hydrogenation reactor do you use? Perhaps the olefin and sulfur content in the coker dry gas is too high; using an isothermal or variable-temperature reactor will eliminate that problem
Hydrogenation catalysts are used for the saturation of olefins in the feed gas as well as for hydrodesulfurization; under conditions where desulfurization is required, the operating temperature should be maintained between 340°C and 400°C. An increase in the bed temperature can lead to the cracking of hydrocarbons and carbon deposition. Therefore, it is better to keep it at or below the lower limit. Excessively high temperatures may be caused by a high content of olefins in the coking dry gas; as mentioned on floor 3, it is recommended to use a variable-temperature hydrogenation reactor. If such a reactor is not available, it is suggested to increase the hydrogen supply in order to lower the temperature.
Possible reasons: 1. Oxygen has mixed into the feed gas; this is unlikely in the case of pure coking dry gas. It is recommended to consult with the operators of the upstream facilities during periods of operational fluctuations. 2. As the olefin content increases, sampling for analysis is required. 3. Fluctuations in the circulation gas flow rate: check the circulation gas flow rate and temperature. 4. Methanation reaction occurs: CO and CO2 in coker dry gas may undergo methanation under specific conditions.
Oxygen enters the hydrogenation reactor? ? ? I’ve never seen what the consequences are! What are the consequences? :handshake
It’s absolutely impossible for oxygen to get in – the catalyst would have already sintered if oxygen were to enter! ! ! ! ! Could it be that there has been a change in the composition, or has the pressure during subsequent operations changed? ? ? ? Has there been any change in your hybrid hydrogen as well? ? ? ?
It is possible to first analyze the composition of the feed gas, to determine whether the difference between the inlet temperature and the bed temperature mentioned by the poster is due to a high content of olefins in the feed; if so, a variable-temperature reactor can be used. The hydrogenation inlet temperature in my unit is around 300, and the maximum bed temperature is around 380. If the temperature of the hydrogenation catalyst exceeds 400, carbon deposition may occur. If, as the original poster mentioned, the temperature reaches 490 degrees, then has the catalyst been damaged as well?
Increase the reactor inlet temperature appropriately to resolve it； The activity of the inlet catalyst decreases; when the composition of the raw materials changes, a reaction delay occurs (no reaction at the front end, and reaction starts upon reaching the high-temperature bed), resulting in fluctuations in the bed temperature between 210 and 490 degrees
We encountered this problem before; the considerations at that time were similar to those analyzed by the others above. In the end, it was because the coking dry gas contained liquefied gas, which caused an increase in the density of its components. It’s likely that you’re facing the same issue as well. Olefins alone would not cause such significant fluctuations, and their levels generally don’t get this high. Some people mentioned oxygen as a possible cause, but it would be better to consider the levels of carbon monoxide and carbon dioxide, which can contribute to liquid formation. However, this is also unlikely. You guys can check for any liquid at the outlet of the compressor to see if there is any present.
We also consider it from two aspects: H2 in PSA contains CO and CO2； The upper catalyst is deactivated.