Method for recovering hydrogen and ammonia in synthetic ammonia exhausted gas

Abstract

The method discloses a method for recovering hydrogen and ammonia in synthetic ammonia exhausted gas. The method comprises a pretreatment process, a membrane separation process and an ammonia recovering process; and an ammonia resistant membrane which can tolerate an ammonia gas phase with concentration lower than 6% (v / v) for a long time is adopted to treat the synthetic ammonia exhausted gas, hydrogen and most ammonia in the synthetic ammonia exhausted gas are recovered, and then ammonia contained in retention gas after membrane separation is recovered with methods of water washing and ammonia distillation and changed into a liquid ammonia product. According to the method for recovering hydrogen and ammonia in the synthetic ammonia exhausted gas, safe and stable operation of the membrane separation process is guaranteed essentially, and more than 85% of hydrogen and more than 75% of ammonia can be recovered; equipment investment and occupied land involved in the ammonia recovering process are reduced by 60%; and meanwhile, energy consumption of an ammonia absorption tower and an ammonia still is reduced by 70%-80%, and the operation cost is reduced by 70%-80%.

Description

technical field

[0001] The invention belongs to the technical field of recovery of synthetic ammonia purge gas, and in particular relates to a method for recovering hydrogen and ammonia from synthetic ammonia purge gas. Background technique

[0002] In the production process of synthetic ammonia, hydrogen and nitrogen are the raw materials of synthetic ammonia. Nitrogen is generally separated from air, and hydrogen is generally obtained through natural gas conversion or coal gasification. Hydrogen and nitrogen react under high pressure and temperature and under the action of a catalyst to produce ammonia. Restricted by the chemical balance, the reactants cannot be completely converted, and the unreacted nitrogen and hydrogen are mixed with the supplementary fresh gas through the circulating compressor and then enter the synthesis tower for the ammonia synthesis reaction. Since nitrogen and hydrogen, raw materials for ammonia synthesis, contain a certain amount of inert comp...

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