Process for preparing natural gas by closed circulation and comprehensive use of synthetic ammonia after-tower gas

Abstract

The invention relates to a process for preparing natural gas by closed circulation and comprehensive use of synthetic ammonia after-tower gas. Low-pressure methane synthesis system after-tower gas isgenerated by a low-pressure methane synthesis system and sent into a low-pressure cold box, and nitrogen gas is injected into the low-pressure cold box at the same time, so that methane is removed under a low pressure and at -85 DEG C to -57 DEG C; the remaining gas is compressed by a six-stage high-pressure machine and sent to a synthetic ammonia system for reaction to produce synthetic ammonia,and along with the production of the synthetic ammonia, purge gas and recycle gas are combined to form synthetic ammonia after-tower gas containing 3% of ammonia and 24% of methane; the synthetic ammonia after-tower gas is sent to a first high-pressure cold box, so that ammonia is removed under a high pressure and at -109 DEG C to -73 DEG C; the remaining synthetic ammonia after-tower gas is sentto a second high-pressure cold box, and nitrogen gas is injected into the second high-pressure cold box at the same time, so that methane is removed under a high pressure and at -193 DEG C to -129 DEGC; and the methane is sent to a natural gas storage tank for storage, and the remaining gas is sent to the synthetic ammonia system through a circulation machine to produce synthetic ammonia. The design is reasonable, the concept is ingenious, and the design purpose of one tower and two products is realized.

Description

technical field [0001] The invention relates to the technical field of ammonia synthesis, in particular to a process for preparing natural gas through closed cycle comprehensive utilization of gas after an ammonia synthesis tower. Background technique [0002] China's synthetic ammonia industry started from Nanjing Yongli Ning Factory, and has gone through nearly a hundred years of history; the synthetic ammonia industry is one of the basic inorganic chemicals, and ammonia is the main raw material for the fertilizer industry and basic organic chemicals. Ammonia can be processed into nitric acid. , Nitric acid production is often attributed to the category of synthetic ammonia industry. The synthetic ammonia industry was formed in the early 20th century. It began to use ammonia as a raw material for rocket fuel and explosives industry to serve the war; after the end of the First World War, it turned to serve agriculture and industry. With the development of science and techn...

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Problems solved by technology

[0003] China's existing coal-based synthetic ammonia, medium-pressure combined alcohol, and combined urea (national standard) production lines, in which the post-column gas of the low-pressure one-step synthetic natural gas system is sent to the synthetic ammonia system to prepare synthetic ammonia, because there is methane in the post-column gas, which cannot be removed , the synthetic ammonia system synthesizes ammonia and produces methane-containing tower gas at the same time. The existence of methane affects the synthesis rate of NH3, which can only reach 11.5%. There is only one product in one tower, that is, synthetic ammonia

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