Hydrogen purification
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Our company uses PSA purification for the production of hydrogen from 5,000 cubic meters of natural gas, with requirements that the levels of carbon monoxide and methane be below 10 ppm. Currently, the hydrogen content in the off-gas is relatively high, at around 40%. Is there any way to reduce the hydrogen content in this off-gas?
Increase the adsorption time; each time it is increased, observe the test parameters. If these parameters are satisfactory, continue to increase the adsorption time!
Given the requirement of 99.998% purity for the product hydrogen as you mentioned, to further reduce the hydrogen content in the feed gas, it is necessary to increase the investment in equipment; this can be achieved by using two-stage PSA systems. However, such systems are rarely used in facilities with a capacity of less than 10,000 units, unless high-purity hydrogen is required. The decision ultimately depends on the return on investment – if the cost of installing two-stage PSA systems, along with the associated operating and maintenance costs, is offset by higher profits from the increased hydrogen production, then such systems may be considered. After all, no PSA system can achieve 100% hydrogen recovery rate. Another viable approach is that hydrogenation units generally have strict requirements regarding CO; therefore, the CO content can be used as a criterion for adjustment, or the amount of filler in the PSA unit can be adjusted. Adsorbents with better selectivity for CO and CH4 can be used specifically to increase the hydrogen recovery rate.
40% is indeed very high; extend the adsorption time to observe the changes in purity
Parse 40% of the hydrogen in the gas? Isn’t it a bit too high?
If a two-stage PSA is used, is a compressor needed?
Of course it is necessary; the desorption gas pressure is only 0.05 MPa, so the adsorption effect is poor. High pressure facilitates adsorption, while low pressure facilitates desorption
The owner wants to know whether the current hydrogen yield of your unit matches the design value, and what is the designed hydrogen content in the gas released from the unit? Has the adsorption time reached the designed value? If it has, and the hydrogen content in the desorbed gas is high, it may be due to deviations in the composition of the feed gas or in the way the adsorbent is packed. You can consult the manufacturer to see whether it’s possible to modify the procedure by increasing the number of pressure equalization steps. The simplest approach at the moment is to first extend the adsorption time to see the effects, or to increase the adsorption pressure slightly.
The product gas parameters have just met the requirements; it’s no longer possible to increase the adsorption time