Method for removing light hydrocarbons in crude synthesis gas and shift gas by eluting with low-temperature methanol

Abstract

The invention discloses a method for removing light hydrocarbons in crude synthetic gas and shift gas via low-temperature methanol washing. The method comprises the following steps: pre-washing: conveying precooled feed gas into the bottom of a pre-washing tower, washing light hydrocarbons included in the feed gas with a sulfur-free methanol-rich solution introduced from the top of the pre-washing tower so as to obtain a pre-washed solution which is discharged from the bottom of the pre-washing tower, and discharging pre-washed gas without light hydrocarbons from the top of the pre-washing tower; desulphurization and decarburization: conveying the pre-washed gas into a CO2 absorbing tower for counter-current contact with the sulfur-free methanol-rich solution so as to obtain qualified purified gas and conveying the qualified purified gas to a downstream procedure after re-heating; extraction: subjecting the obtained pre-washed solution to pressure-reduced flash evaporation so as to separate light components, then carrying out pressurization and re-heating, then carrying out liquid-liquid extraction in an extraction tower with process water, discharging light hydrocarbons from the top of the extraction tower and discharging an aqueous methanol solution from the bottom of the extraction tower; and methanol-water separation: separating the obtained aqueous methanol solution, discharging gas-phase methanol from tower top and recycling process water. The method provided by the invention can effectively remove light hydrocarbons in crude synthetic gas, shift gas and the like, can be applied together with a traditional low-temperature methanol washing system, thoroughly overcomes the problems of recovery of light hydrocarbons and pollution caused by accumulation of lean methanol and allows discharged tail gas to reach the standard.

Description

technical field [0001] The invention relates to the technical field of producing chemical products and oil products mainly using coal as raw material, and is applicable to the purification field of crude gas containing light hydrocarbons produced by certain gasification processes (such as Lugi, KBR, HYGAS, etc.) in coal chemical industry , and in the field of purification of industrial crude synthesis gas obtained in other ways such as coke oven gas, FT synthesis cycle tail gas, etc., the removal of light hydrocarbons in the process of purifying feed gas (desulfurization and decarbonization) by using low-temperature methanol washing process method. Background technique [0002] The existing purification technology for producing synthesis gas from industrial crude gas rich in light hydrocarbons is: generally in CO 2 The lower section of the absorption tower (i.e. the lower end of the desulfurization section or the decarburization section) is provided with a pre-washing secti...

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Problems solved by technology

[0004] (1) The existing prewashing strength is not enough and the effect is not good, so that excessive light hydrocarbons are brought into the desulfurization section and decarbonization section of the absorption tower, resulting in the pollution of the methanol solution system, so that the product gas (including purified gas, CO 2 gas, etc.) the content of light hydrocarbons is too high, especially the non-methane hydrocarbons in the released tail gas seriously exceed the standard;

[0005] (2) The extraction in the prior art is carried out at low pressure and medium temperature. During the extraction process, there are dissolved gas analysis and gasification of some lighter hydrocarbon components. In the so-called liquid-liquid extraction process, there are serious gasification phenomena. , actually turns the liquid-liquid extraction process into a three-phase separation of gas / liquid / liquid, which destroys the basic environment of liquid-liquid extraction

Therefore, on the one hand, the light hydrocarbon (or oil) phase has excess methanol / water, and the methanol / water phase has light hydrocarbons; on the other hand, due to the low operating pressure, the obtained gas phase is difficult to handle;

[0006] (3) The setup of the methanol recovery system in the prior art is complex and difficult to control, and it is also difficult to achieve effective separation and recovery of hydrocarbons in practical applications

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