Method for preparing LNG (Liquefied Natural Gas) by recycling methanol tail gas

Abstract

The invention relates to a method for preparing LNG (Liquefied Natural Gas) by recycling methanol tail gas. Devices adopted in the method comprise a carbon removal tower, a molecular sieve, a high-low-temperature expansion machine, a heat exchanger and a rectifying tower, wherein the carbon removal tower is connected with the molecular sieve. The method comprises the following steps of removing carbon dioxide in the methanol tail gas by virtue of the carbon removal tower so that the content of carbon dioxide in the tail gas reaches below 30ppm, feeding the carbon-dioxide-removal methanol tail gas into the molecular sieve to remove heavy hydrocarbons and the moisture so that the dew point of the tail gas is less than -70 DEG C, exchanging heat with the purified and qualified methanol tail gas to -174 DEG C by virtue of the heat exchanger and feeding the methanol tail gas subjected to heat exchange to the low-temperature rectifying tower for rectifying and carrying out cryogenic liquefaction, separation and extraction to prepare LNG and obtain a LNG product of which the purity is 99.8%, wherein the tail gas discharged from the top of the rectifying tower is adopted as a cool source of a subcooler for cryogenic liquefaction of LNG, a small part of the tail gas is used as a regeneration gas of the molecular sieve and the other part of the tail gas is used as a fuel gas. By the method, the problem of environmental pollution caused by the burning of exhaust gas is reduced and meanwhile, the high value-added LNG is produced.

Description

Technical field [0001] The invention relates to a method for preparing LNG by recycling methanol tail gas. Background technique [0002] my country is a big energy consuming country, and the energy structure is still short of oil, gas, and coal. Energy shortage is still the main bottleneck of my country's economic development. On the one hand, my country still relies mainly on coal resources. On the other hand, the consequences of environmental degradation are very serious. Global warming, abnormal climate, continuous smog, and a series of pollution problems have raised the green environmental protection and circular economy to the agenda that needs to be solved and implemented urgently. The high efficiency and full utilization of coal has become the key direction of the new coal chemical industry. Coal-to-gas, coke oven gas, synthetic ammonia purge gas, methanol tail gas and other unconventional gas purification and natural gas production projects are energy-saving, high-effic...

AI Technical Summary

Problems solved by technology

The existing technology enriches the methanol tail gas with methane, carbon monoxide, hydrogen and other components, and usually sends it to the torch for treatment or uses it as fuel gas for coal preparation hot blast stove; it pollutes the environment and wastes resources

Images