Decarbonisation of large ammonia plants using the dual high pressure adsorption process can be seen as using PSA decarbonisation as a pre-treatment unit for PSA purification of hydrogen and nitrogen. The process is to first remove the conversion gas to obtain 98% (v) decarbonised gas for urea and other processes and then to enter the PSA purification small air separation unit to obtain C02 0.02% (v) hydrogen and nitrogen as the feed gas for ammonia synthesis.
The choice of pretreatment technology in small air separation unit will vary depending on the components of the raw gas. If the dust content is high, a water washing process can be considered; if the boiling point difference in the components is large, freezing separation can also be considered, pre-treatment of sulphur containing gases, high sulphur content and large gas flow can be considered when choosing a mature wet desulphurisation process, in practice it will usually be a combination of several technical solutions. Some purification processes, such as low-temperature methanol washing and liquid nitrogen washing, are more expensive and can only be considered in combination with the entire plant process and economic and environmental protection.
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