A method of improving the recovery rate of liquefied natural gas

Abstract

The invention relates to the field of liquefied natural gases, and in particular to a method for recycling methane from an uncondensed gas of a liquefied natural gas purifying column by using a pressure swing adsorption method so as to increase the recycling rate of methane in the liquefied natural gas. According to the method, a raw material gas conveying pipe, the liquefied natural gas purifying column, the uncondensed gas discharged from the liquefied natural gas purifying column, and an adsorption tower are included. The method is characterized by comprising the following steps: adsorbing, vacuuming and increasing the pressure of the uncondensed gas, thereby obtaining a methane-rich gas, feeding back the methane-rich gas to the raw material gas conveying pipe or the liquefied natural gas purifying column to be recycled, adjusting the adsorption time so as to control the content of methane in a waste gas adsorbed by a pressure swing adsorption device, and achieving the purpose of increasing the recycling rate of methane of the liquefied natural gas purifying column. The method is simple to operate, the cost is reduced, the energy consumption is reduced, and the recycling rate of the liquefied natural gas is greater than 99.8%.

Description

technical field [0001] The invention relates to the field of liquefied natural gas recovery, in particular to a method for recovering methane from noncondensable gas in a liquefied natural gas purification tower by using a pressure swing adsorption method to improve the recovery rate of methane in liquefied natural gas. Background technique [0002] In the process of producing liquefied natural gas (LNG for short) from methane-rich mixed gas, especially in coke oven gas and other gas sources containing more hydrogen and nitrogen and other non-condensable gases, in order to reduce the non-condensable gas at the top of the liquefied natural gas purification tower To improve the recovery rate of liquefied natural gas, the method usually adopted is to reduce the temperature of the top of the liquefied natural gas purification tower, or even increase the cooler with liquid nitrogen as the refrigerant. A small amount of methane will be entrained, which is an important factor affec...

AI Technical Summary

Problems solved by technology

And as the efficiency of the heat exchanger at the top of the liquefied natural gas tower decreases, the methane in the vented air at the top of the tower will increase, reducing the methane recovery rate of the liquefied natural gas plant, resulting in an increase in energy consumption per unit of liquefied natural gas production

[0003] Chinese Patent Application Publication No. CN102079999A discloses a method for producing liquefied natural gas and synthesis gas by using coke oven gas as raw material. The inlet of the methane collection unit is mixed with the purified gas by pressure swing adsorption to separate H2, N2, CO and methane in the purified gas to obtain synthesis gas and methane-rich gas, because the content of non-condensable gas and methane in the liquefied natural gas cold box is several times Coal gas mixed with non-condensable gas is used as the raw material of the pressure swing adsorption methane enrichment unit, so that a part of methane will still be entrained in the synthesis gas obtained by the pressure swing adsorption device, which fails to improve the methane recovery rate of LNG and reduce the energy consumption of LNG. The role of consumption

[0004] Chinese Patent Application Publication No. CN102942972A discloses a method for producing liquefied natural gas using coke oven gas, which discloses the use of PSA molecular sieves to remove N2 from non-condensable gases, vacuum desorbs methane adsorbed by PSA molecular sieves, and returns more than 90% of the methane content in the desorption to coke oven gas In the method of recycling, since the content of methane in the desorption gas is as high as 90%, part of the methane will be released from the adsorption waste gas, thereby reducing the recovery rate of methane

Also fails to address increased LNG recovery

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