Method for preparing liquefied natural gas from semi-coke tail gas

Abstract

The invention relates to a method for preparing liquefied natural gas from semi-coke tail gas. The method includes: firstly, after decoking and benzene and naphthalene removal of semi-coke tail gas, and sending to a rectisol unit for purification and desulfurization; then, mixing the desulfurized semi-coke tail gas with high-methane gas, jointly sending into a methanation unit for methanation to obtain a crude methane gas product, sending into the rectisol unit for purification and decarbonization; finally, performing cryogenic separation to remove nitrogen to obtain liquefied natural gas. Compared with the prior art, the method has advantages that by semi-coke tail gas treatment through the rectisol unit and the methanation unit, circulation absorbing agent consumption is sharply reduced,and energy consumption and system CH4 loss in a decarbonization process are reduced; in addition, by adoption of recovered CH4-rich gas and injection of water and / or system self-produced water vaporinto the methanation unit, methanation reaction temperature rise can be controlled so as to guarantee a methanation process against temperature runaway; moreover, heat balance of a whole system can beeffectively realized in the whole process, and economy in preparation of LNG (liquefied natural gas) from the semi-coke tail gas is improved.

Description

technical field [0001] The invention relates to the fields of gas purification and natural gas preparation, in particular to a method for producing liquefied natural gas from semi-coke tail gas. Background technique [0002] Semi-coke is usually obtained from high-quality coal in Shenfu Coalfield by low-temperature dry distillation process, and low-temperature coal tar and semi-coke coke oven gas (also known as semi-coke tail gas) are produced as by-products. At present, semi-coke is mostly produced by internal heating vertical furnaces , about 700Nm by-product per ton of semi-coke produced 3 semi-coke exhaust. The semi-coke tail gas produced by the internal heating vertical furnace has the following characteristics: (1) H 2 The content is low, usually 20-28%, and the CO content is about 10%; (2) the nitrogen content is too high, usually 37-43%, and the CO content is about 10%. 2 The content is generally greater than 10%, and the calorific value is low. At present, there...

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Problems solved by technology

The reaction temperature in this patented technology is too low, which is not conducive to the by-production of high-quality steam, and will increase the number of reaction stages and reactors; in addition, it is necessary to install a circulating gas compressor, which will increase equipment investment and energy consumption

[0005] Patent CN 105647607A discloses a "method and device for producing natural gas from low hydrogen carbon ratio blue-coke tail gas". methane gas, but the patented technology still needs to install a circulating gas compressor to control the reaction temperature rise, which will increase equipment investment and operating costs, and also bring certain hidden dangers to production safety

[0006] The above patents are all about the technology of producing synthetic natural gas from purified semi-coke tail gas through methanation reaction. At present, there is no patent technology for semi-coke tail gas to produce liquefied natural gas with integrated planning of semi-coke tail gas purification, methanation, and liquefaction.

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