Device and process method for recovering synthetic ammonia tail gas to produce lng

Abstract

The invention discloses a device and a technological method for producing LNG (liquefied natural gas) by recycling ammonia tail gas. The device comprises a circulation nitrogen compressor, a first cooler, a second cooler, a third cooler, a pre-cooling heat exchanging device, a booster expansion turbine, a gas-liquid separator, a dehydrogenation and distillation tower and a methane distillation tower, wherein the pre-cooling heat exchanging device, the booster expansion turbine, the gas-liquid separator, the dehydrogenation and distillation tower and the methane distillation tower are arranged in a cold box; and the pre-cooling heat exchanging device comprises a carbon dioxide pre-cooler and a main heat exchanger. The device and the technological method for producing the LNG by recycling the ammonia tail gas has the advantages that by an ammonia tail gas cryogenic separation technology, methane is extracted sufficiently while useful hydrogen produced by using ammonia is recycled, the methane is liquefied into LNG with high added value, the cost of ammonia is reduced, ammonia tail gas resources are sufficiently recycled, and the environment is protected.

Description

technical field [0001] The invention belongs to the technical field related to the recovery and utilization of exhaust gas (tail gas) in the ammonia synthesis industry, and particularly relates to a device and a process method for producing LNG from ammonia synthesis tail gas by cryogenically separating and extracting methane from synthesis ammonia tail gas into liquefied natural gas (LNG) . Background technique [0002] In the field of chemical fertilizer industry, the process of producing ammonia will produce a purge gas containing about 25% methane, and in the production process of synthetic ammonia, it will also produce a synthesis gas containing about 35% methane. The above gases constitute the tail gas of synthetic ammonia. In order to ensure the normal progress of the ammonia synthesis reaction, it is necessary to discharge the tail gas of synthetic ammonia to control the concentration of methane. [0003] The most common way to deal with the tail gas of synthetic am...

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Problems solved by technology

[0003] The most common way to deal with the tail gas of synthetic ammonia today is to discharge it directly into the atmosphere. However, the methane in the tail gas is a greenhouse gas, and its power to cause global warming is 25 times that of carbon dioxide, which causes environmental pollution and waste of resources. The other is to burn after collection and convert it into secondary energy such as heat energy and electric energy. However, the economic benefits of this method are low, and components such as methane and hydrogen with high economic added value in the tail gas cannot be recycled; Filtration and purification technology extracts methane and other valuable components in tail gas, but existing technologies and production processes have disadvantages such as high energy consumption, high cost, and low extraction rate

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