How to improve the PSA hydrogen recovery rate
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I would appreciate the advice of experts: Our company’s PSA unit has ten towers. The feed gas is methanol synthesis off-gas in an amount of 12,000 cubic meters; through the PSA process, hydrogen with a purity of over 99% is obtained, and this hydrogen is combined with nitrogen supplied by air separation to produce ammonia. Currently, the carbon dioxide content in the feed gas is 14%, which is much higher than the specified value of 5%. The hydrogen recovery rate is around 60%, and it is no longer possible to extend the adsorption time due to concerns that carbon dioxide might penetrate the adsorbent. The following plan has been devised to increase production: first, remove the ten-tower molecular sieve to increase the amount of activated carbon. II. Add a carbon dioxide adsorption unit before the PSA. III. Add a membrane device after gas separation to recover hydrogen. Which option is more valuable? What are the drawbacks of the other options, or are there any better suggestions? I am not very familiar with membrane processes, and I would like to ask: for a situation where the gas flow rate is 5,000 cubic meters, the hydrogen content is around 25%, and the remaining gases are mainly nitrogen, carbon dioxide, carbon monoxide, and methane, with a pressure of 10 KPa, how much investment would be required to set up a membrane hydrogen extraction system like this? What devices are there?
Personally, I think the second option is more reliable; for the third option, when adding a membrane, one needs to consider the pressure issues after membrane separation
Haha, just ask a manufacturer – they can definitely help you solve this issue. There are also separate methods for CO2 absorption; it depends on the approach adopted by each manufacturer.
The first option may reduce the processing capacity; it is necessary to consult the design manufacturer for assistance in making calculations. The second option is more feasible, as pressure swing adsorption for CO2 removal is relatively simple; it’s easy to reduce the CO2 concentration from 14% to below 5%. The third method has a problem: both H2 and CO2 are components that readily permeate through the membrane, which may result in poor separation efficiency. In addition, the pressure loss associated with membrane separation is high, leading to increased overall energy consumption.
It is recommended to add an MDEA CO2 removal system before the PSA unit; this will increase the dynamic H2 adsorption capacity of the PSA unit. The gas released from the PSA unit can be sent back to the MDEA CO2 removal system. Since the CO2 removed by MDEA contains almost no H2, the H2 recovery rate approaches 100%, and the total investment is reduced as well.