Syngas purification
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The factory plans to install a small-scale ammonia synthesis unit, using the exhaust gas from PSA-CO as the raw material. The existing PSA system operates in two adsorption stages, and the exhaust gas contains approximately 8% CO + CO2. It is said that the new system will include an additional PSA stage for carbon removal, built on top of the existing PSA system. Could anyone suggest whether such a process is feasible and whether it can achieve the desired level of purification?
In principle, two stages of PSA are sufficient to achieve H2 purification: the first stage is used for decarburization, while the second stage is used for hydrogen extraction; the exhaust gas from the second stage can be returned to the first stage of the compressor. This can improve the recovery rate of H2. As for adding another stage of PSA decarburization as you mentioned, I’m not sure what purpose that would serve If the previous processing volume was not sufficient, it is still possible to consider adding another set; however, in that case, the overall ratio of fillers in the mixture will likely need to be adjusted. The plan should be chosen based on the actual conditions of the factory.
As for the purification of syngas mentioned by the original poster, to what extent should it be precise? Reaching trace levels of CO and CO2 is, in my opinion, impossible.
Isn’t there something now called variable-temperature and variable-pressure adsorption that can remove impurities to trace levels?
The common processes for syngas purification include copper washing, liquid nitrogen washing, methanation, and alkoxylation; pressure swing adsorption is not yet used for syngas purification. There is indeed a process for purifying syngas using molecular sieves, but it serves only to further purify the refined gas so that it can be fed directly into the synthesis tower. This method achieves a high level of purity, yet the amount of adsorption capacity is low; toxins at constant concentrations cannot be purified using molecular sieves. Pressure swing adsorption is showing a trend toward greater purification precision; I’ve seen a report on this, and further improvements are still needed.