Some operations regarding PSA for hydrogen production

Our PSA hydrogen production system is relatively small, with a capacity of 5,000, but the principle should be the same. You say that for hydrogen production of 25,000 cubic meters per day, four towers are used; so how is the pressure difference for the gradual increase or decrease in pressure designed? I think that with four towers in use, the pressure difference for gradual changes must be quite high, and such a high pressure difference should result in greater fluctuations in the pressure of the desorbed gas.

Reply to 2# MysteriousBeyondMystery: You’re right. It was originally designed with 8 towers; however, since the stem of one manual valve broke, the last four towers had to be disconnected. Operation with 8 towers, 7 towers, or 6 towers works well, but operation with 4 towers is unstable. The adsorption time has been increased to 120 seconds, and the H2 content in the exhaust gas is around 67%! How can we ensure stable exhaust emissions?

Reply to 3# Shanghai JACK: I don’t understand what you mean by separating out the last four towers; the 8 towers in PSA should be relatively independent. Would a faulty manual valve cause 4 towers to be disconnected at once?

Reply to 4# Mysterious Beyond Mystery: Yes, since this manual valve is located right at the junction between the first 4 towers and the last 4 towers, it was necessary to isolate the last 4 towers! Do you have the operation data for the 4 towers? Have you encountered such accidents? Thank you! !

Reply to 5# Shanghai JACK: I’m truly sorry; I’ve never encountered this situation either. Switching from 8 towers to 4 towers is something we haven’t even considered in terms of operations. If one tower fails, production can still continue with minimal impact. If two towers fail, production can be maintained by reducing output appropriately. In the event of a failure in 3 towers, an emergency plan must be activated and production stopped. The fewer towers there are, the more difficult the operations become, which puts a great test on the skill level of the operators. I’m not sure how it’s designed at PSA. Since there’s a high possibility of cutting out 4 towers in one go, I wonder if they have provided any programming or data related to operating those 4 towers. They do have technical documentation for PSA; do you have it? You could check that. Another option is to contact PSA’s manufacturer and ask their technicians for guidance. If that’s not possible, then there really is nothing else that can be done. What is your PSA operating pressure? Our unit is still relatively new, and the pressure is set at 2.45 MPaG. You might consider reducing the pressure a bit; it could be beneficial for your exhaust gas treatment process.

Reply to 6# Mysterious Beyond: The operating pressure is 2.4 MPa. I’ll give it a try! I’ve thought about it too, but it might have a significant impact on the compressor! ! ! Thank you! ! !

A hydrogen production plant with a capacity of 25,000 Nm3/h should use a PSA system with six or more towers; four towers represent the minimum number required. Fluctuations in the pressure in the purge gas tank lead to variations in the amount of combustion exhaust fed into the converter, which in turn causes fluctuations in the temperature of the converter. If cascade control is properly applied to regulate natural gas, combustion exhaust, and combustion air, these temperature fluctuations will be relatively small. However, if all controls are handled manually using automatic valves, large temperature changes are likely to occur, which might result in excessively high temperatures and even cause the plant to shut down.