Upper limit of hydrogen content in the synthesis system
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Recently, the low-temperature waste gas converter failed; syngas entered the carbon dioxide stream, and the temperature after dehydration exceeded the limit. The hydrogen content reaches 2.5%. I would like to ask my colleagues whether they are aware of the maximum allowable hydrogen concentration in the synthesis tower – that is, the range within which the explosion limit lies! Fortunately, maintenance was scheduled before reaching the warning line! Make sure there’s no loud boom!
Bro, what’s the deal here? We have to stop driving at 100 PPM, but you guys are still driving:funk:
Our target is below 50 ppm; if it exceeds 100 ppm, the operation stops. With such high hydrogen levels, you’re still operating – won’t the dehydrogenation unit overheat? Carry out maintenance right away. Amen.
If the urea plant is equipped with a dehydrogenation system, it is generally required that the plant should be shut down once the temperature after dehydrogenation exceeds 250°C. In fact, if the hydrogen content in CO2 is high, it indicates that the purity of CO2 is also low, and as a result the conversion rate in urea synthesis is low as well; in such cases, the system should be shut down.
Yes, I’m referring to the hydrogen in the carbon dioxide feed gas, not the one after dehydration. But now, data or evidence has to be provided to the boss before parking is allowed
A hydrogen content this high shouldn’t be used at all; it’s terrifying. A 316 tank area at Lanzhou Petrochemical exploded and caught fire yesterday; it is recommended that you stop operations immediately to deal with the situation. ! ! !
Each process operation method has strict requirements and contingency plans; the urea plant where I work does not have a dehydrogenation unit, and the contingency plan specifies that the system should be shut down if the concentration reaches 4%.
Discussion with the Haina Chuan forum moderator: Stopping the machine only when the hydrogen content in CO2 reaches 4% seems a bit high. At this point, the purity of CO2 is estimated to be below 95%. The urea conversion rate in the unit is low, which means that a large amount of exhaust gas is released from the medium and low pressure absorption systems; this increases the risk of overpressure accidents, thereby raising the safety risks associated with the operation of the unit. It is recommended to lower this value accordingly. As a reference for everyone, from a safety perspective, it is advisable that the hydrogen content in CO2 not exceed 1.5%.
If the hydrogen content in the carbon dioxide gas used as feedstock for the dehydrogenation unit is 2%, there is no problem
Original poster, I’m not sure what urea production process you use. If it’s the CO2 stripping method for urea production, the design manual specifies that the hydrogen content in the CO2 gas should be less than 1% (by volume), and the sulfur content should be less than 15 PPM – these are basic principles of such production processes. Producing urea beyond these limits is dangerous; although there may be no problems in the short term, the risk of accidents always exists, and once such an accident occurs, it cannot be reversed.
Thank you! Less than 4% in the feed gas – this is acceptable for now!