Recovery method and device for helium in flash steam of liquefied natural gas

Abstract

The invention provides a recovery method and device for helium in flash steam of liquefied natural gas. The recovery method comprises the following steps: sending the flash steam of the liquefied natural gas into a compression unit for compression to make the pressure reach 2.0-6.0 MPaG; feeding the compressed gas into a purification unit for dehydrogenation reaction, wherein the purification unitcontains an oxidant; feeding the dehydrogenated gas into a membrane separation unit, and feeding the gas subjected to membrane separation into a variable-pressure adsorption unit to obtain the product, namely helium. The invention further provides the recovery device using the method. The recovery method and the recovery device aim at the recovery of helium in the liquefied natural gas in small and medium-sized factories, the cost is low and the efficiency is high.

Description

technical field [0001] The invention relates to a method and a device for recovering helium in BOG in liquefied natural gas in small and medium-sized factories, and belongs to the technical field of waste gas recovery. Background technique [0002] Helium is a non-condensable gas in the liquefied natural gas (LNG) process. The removal of helium is very beneficial to the liquefied natural gas process. The reduction of non-condensable gas will significantly reduce the circulating gas volume and reduce the BOG tail gas at the top of the large LNG storage tank. The non-condensable gas content in LNG can greatly reduce the liquid tumbling and vaporization phenomenon caused by the density difference of LNG in large LNG storage tanks, and can avoid a large amount of discharge of BOG tail gas and safety accidents of large LNG storage tanks [0003] At present, the conventional helium extraction methods mainly include: condensation method, air separation method, hydrogen liquefaction...

AI Technical Summary

Problems solved by technology

The above-mentioned condensation method, air separation method, hydrogen liquefaction method, and high-purity helium method all adopt the process of cryogenic separation or the process of cryogenic separation plus pressure swing adsorption. Since the normal pressure boiling points of hydrogen and helium are -252.6°C and -268.9°C, the method of cryogenic separation needs to cool the process medium to an extremely low temperature, and maintaining the cooling capacity balance of the cold box requires a circulating refrigeration system, and the cost of energy consumption is very huge

[0005] Especially helium in liquefied natural gas in small and medium-sized factories. Helium is a non-condensable gas. When part of BOG is recycled to the natural gas raw material inlet of the LNG plant, it will increase the accumulation of non-condensable gas, affect the heat transfer efficiency, and reduce the liquefaction of natural gas. , the production capacity of the LNG plant will be partially affected, the LNG recovery rate will be reduced, the BOG gas volume will increase, and the operation fluctuation of the BOG compressor will increase.

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