Semi-lean solution absorption low-temperature methanol washing system and method

Abstract

The invention provides a semi-lean solution absorption low-temperature methanol washing system and method. The method is characterized in that ionic liquid is used for absorbing methanol in tail gas in a high-selectivity way; the standard reaching discharging of the tail gas is realized; the ionic liquid absorbing methanol is regenerated through analysis and is then cyclically used; the system wastewater discharging quantity is greatly reduced; the recovered methanol returns to system for reutilization; nitrogen gas is used for performing gas stripping on a sulfur-free methanol semi-lean solution; the low-temperature and low-CO2 semi-lean solution can be further obtained; most semi-lean solution is conveyed to a main washing tower for auxiliary washing decarburization; the other part of the semi-lean solution is used for washing raw material gas for dehydration and drying; the system moisture content is reduced; methanol is sprayed on the raw material gas; water-containing methanol liquid generated after washing the semi-lean solution is subjected to pressure reduction and is then subjected to flash evaporation; flash evaporation gas is conveyed into a medium-pressure flash evaporation tower; flash evaporation condensed liquid is reheated and is then conveyed into a methanol water separation tower; the cold quantity of the water-containing methanol liquid is fully utilized; partial flash evaporation gas is recovered; the concentration of H2S in acid gas is improved.

Description

technical field [0001] The invention relates to a semi-poor liquid absorption low-temperature methanol washing system and method, belonging to the technical field of gas purification. Background technique [0002] In my country, due to the needs of economic development and energy security, as well as the characteristics of resource endowments rich in coal, short of oil, and low in gas, the development of coal chemical industry is an inevitable trend. In the face of the increasingly severe environmental pollution problems in China, realizing energy conservation and emission reduction, and meeting environmental protection standards and emissions are the top priorities for the future development of the coal chemical industry. In recent years, the national environmental protection department has specified a series of stricter environmental protection policies and standards. For example, the petrochemical industry pollutant discharge standard (GB31571-2015) requires that the meth...

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Problems solved by technology

[0006] (2) Large cooling loss

The temperature of the tail gas directly discharged to the atmosphere from the top outlet of the tail gas washing tower is usually low, generally around 16°C. The low-temperature cooling capacity in the tail gas is not utilized, which wastes part of the cooling capacity of the system; the lower temperature spray methanol condensate and methanol water The heat exchange of the reflux liquid of the separation tower not only fails to recover the cooling capacity of the condensate, but increases the heat load of the methanol-water separation tower

[0007] (3) The water content in the system circulating methanol is relatively high

In the above process, the water content in the system circulation methanol is generally controlled at 0.5%-0.6wt%. When the operation is unstable, when the water content in the system is high, it will not only reduce the desulfurization effect of methanol, but also easily cause carbon steel equipment damage. corrosion

[0008] (4) The loss of methanol in the system is relatively large

In the above process, the concentration of methanol in the tail gas and acid gas brought out of the system tends to be high, which not only increases the amount of methanol replenishment, but also causes some pollution to the environment

[0009] (5) Methanol in the tail gas is easy to exceed the standard

At present, most of the literatures report the absorption characteristics of imidazole ionic liquids to methanol, but there is no report on the process of removing methanol from low-temperature methanol scrubbing tail gas by ionic liquids.

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