Daily Question: October 12, 2015 – Passivation of Hydrogenation Reactors
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When each unit is passivated, to what temperature does the temperature of the hydrogenation reactor drop before passivation begins? What was the maximum temperature of the bed during the passivation process? How long is the passivation time?
100 degrees – 400 degrees – 48 hours –
①After sulfurization is complete and the temperature is reduced to 150°C, about 20% of the normal feeding rate of low-nitrogen oil is introduced into the system. Only after the heat wave associated with adsorption has passed through the catalyst bed and a liquid level has been established in the high-pressure separator can the feeding rate be gradually increased to around 60% of the normal level, thereby establishing a large-scale cycle for reaction and distillation. ②Once the temperature of the catalyst bed in the reactor stabilized, the ammonia injection pump was started to feed ammonia into the reaction system at a rate of 220 kg/h, while raising the inlet temperatures of the refining and cracking reactors to 228°C and 203°C respectively. ③Water injection began 2 hours after ammonia injection, and the ammonia content in the high-pressure wash water was analyzed every half hour. Before high-yield ammonia formation, maintain the inlet temperatures of the refining and cracking reactors below 230°C and 205°C respectively. ④During ammonia passivation, a sulfiding agent should be injected as needed to maintain the hydrogen sulfide content in the circulating hydrogen at not less than 0.1 v%. ⑤When the ammonia content in the high-pressure water reaches 1.5% (wt), it is considered that ammonia has penetrated extensively; the ammonia injection rate is then reduced to 75 kg/h (one-third of the initial rate), and the ammonia concentration is maintained at 1.5% until the feed rate reaches 60%. ⑥After ammonia penetrated the catalyst, the inlet temperatures of the purification and cracking reactors were increased at a rate of 15°C/h to 325°C and 315°C respectively. Through automatic control, quench hydrogen was used to maintain a temperature gradient of 3°C decrease per bed inlet. If the temperature rise in any bed exceeded 10°C, the inlet temperature remained unchanged until the rise fell below 6°C. ⑦While increasing the inlet temperature of the cracking reactor, the temperature of the recycle oil should also be raised, but it must not exceed the inlet temperature of the cracking reactor. ⑧When the inlet temperature of the refining reactor reaches 320°C and that of the cracking reactor reaches 315°C, with a bed temperature difference of less than 6°C, it indicates that the passivation is complete. However, the ammonia and sulfur injection facilities must remain in operation until the second hour after 75% of the designed feed rate has been reached, at which point the ammonia and sulfur injection can be stopped.
This is the sulfur unit, not the hydrogenation reactor for hydrocracking. :);P
Our plan sets the temperature at 120 degrees; in practice, it starts around 140 degrees. The maximum temperature is not allowed to exceed 300 degrees, as higher temperatures might make it difficult to maintain control. Generally, after 48 hours of passivation, the oxygen content remains unchanged; it has already reached a high level, and there is little increase in temperature. But every time it opens, spontaneous combustion occurs
①After sulfurization is complete and the temperature is reduced to 150°C, about 20% of the normal feeding rate of low-nitrogen oil is introduced into the system. Only after the heat wave associated with adsorption has passed through the catalyst bed and a liquid level has been established in the high-pressure separator can the feeding rate be gradually increased to around 60% of the normal level, thereby establishing a large-scale cycle for reaction and distillation. ②Once the temperature of the catalyst bed in the reactor stabilized, the ammonia injection pump was started to feed ammonia into the reaction system at a rate of 220 kg/h, while raising the inlet temperatures of the refining and cracking reactors to 228°C and 203°C respectively. ③Water injection began 2 hours after ammonia injection, and the ammonia content in the high-pressure wash water was analyzed every half hour. Before high-yield ammonia formation, maintain the inlet temperatures of the refining and cracking reactors below 230°C and 205°C respectively. ④During ammonia passivation, a sulfiding agent should be injected as needed to maintain the hydrogen sulfide content in the circulating hydrogen at not less than 0.1 v%. ⑤When the ammonia content in the high-pressure water reaches 1.5% (wt), it is considered that ammonia has penetrated extensively; the ammonia injection rate is then reduced to 75 kg/h (one-third of the initial rate), and the ammonia concentration is maintained at 1.5% until the feed rate reaches 60%. ⑥After ammonia penetrated the catalyst, the inlet temperatures of the purification and cracking reactors were increased at a rate of 15°C/h to 325°C and 315°C respectively. Through automatic control, quench hydrogen was used to maintain a temperature gradient of 3°C decrease per bed inlet. If the temperature rise in any bed exceeded 10°C, the inlet temperature remained unchanged until the rise fell below 6°C. ⑦While increasing the inlet temperature of the cracking reactor, the temperature of the recycle oil should also be raised, but it must not exceed the inlet temperature of the cracking reactor. ⑧When the inlet temperature of the refining reactor reaches 320°C and that of the cracking reactor reaches 315°C, with a bed temperature difference of less than 6°C, it indicates that the passivation is complete. However, the ammonia and sulfur injection facilities must remain in operation until the second hour after 75% of the designed feed rate has been reached, at which point the ammonia and sulfur injection can be stopped.
Wasn’t it said that the passivation process must be controlled below 100°C? At 300°C, wouldn’t it become catalyst oxidation regeneration?
That’s right; 300-degree control involves oxidation regeneration, or high-temperature passivation, which converts the sulfide state into the oxide state. I remember that the previous procedure stated that it was necessary to reduce the temperature to 60 degrees, but it took too long; when dealing with ferrous sulfide, 60, 100, 140 – I don’t think there’s any difference. 60 degrees simply means a larger operating space. 300 degrees represents an upper limit, a ceiling value; it’s not advisable to reach such a temperature. Under normal operating conditions, control should be exercised when the temperature reaches around 200 degrees.
The design temperature for the bed of the hydrogenation reactor is 400°C; generally, a temperature not exceeding 400°C is sufficient, and it’s okay to exceed this value slightly for short periods in actual operation. Before passivation, the bed temperature is generally reduced to 200°C; going any lower may cause the sulfur accumulated in the bed to mix with other solid impurities and solidify, leading to flow deviation or bed blockage during passivation. With current strict environmental regulations, it is not allowed for sulfur dioxide emissions to exceed limits during the shutdown of the plant; trying to stop sulfur production first and then the hydrogenation of exhaust gases has yielded decent results.
Even if sulfur production is stopped first, isn’t there a high risk of introducing sulfur-containing flue gas into the hydrogenation process?
First stop sulfur production, then stop the hydrogenation reactor – what are the specific procedures? Flue gas containing sulfur into the hydrogenation reactor?