Process for preparing substitute natural gas through sulphur-tolerant methanation of coal synthesis gas

Abstract

The invention provides a process for preparing substitute natural gas through sulphur-tolerant methanation of coal synthesis gas. The process is characterized in that the synthesis gas enters sulphur-tolerant methanation reactors I and II in sequence, and the mixed gas of the synthesis gas and water vapor enters a rectisol system so as to remove the impurities such as CO2, H2S and the like in the gas after undergoing sulphur-tolerant shift and sulphur-tolerant methanation reaction on a molybdenum-based bifunctional catalyst and then undergoes methanation reaction in methanation reactors I and II in sequence under the action of Ni-based methanation catalysts, thus obtaining the natural gas product. The process has the advantages of simple process flow, small equipment investment, low comprehensive energy consumption and excellent natural gas products.

Description

technical field [0001] The invention belongs to a coal-to-natural gas process, in particular to a process for preparing coal-to-synthetic gas through sulfur-resistant methanation to replace natural gas. Background technique [0002] my country is rich in coal, poor in oil and low in gas, and the proportion of natural gas consumption is far lower than the world average. In recent years, with the rapid increase of natural gas demand in my country, the gap between domestic natural gas supply and demand has gradually increased, which in turn has restricted the steady and rapid development of my country's national economy. Coal-to-natural gas is a technology that uses coal as raw material to produce natural gas. It can convert coal into a clean fuel CH that is convenient for long-distance transportation. 4 , is an important way to optimize the domestic energy structure, alleviate the contradiction between supply and demand of natural gas, and realize the efficient and clean conv...

AI Technical Summary

Problems solved by technology

Although coal-to-natural gas is the best choice for coal cleanliness and optimal utilization, there are still many problems in the above-mentioned industrial coal-to-natural gas technology due to the limitation of methanation nickel-based catalysts: (1) The low-temperature methanol washing makes the synthesis gas have to undergo "thermal (transformation) )-cold (methanol washing)-heat (methanation)-cold (cooling compression)", the temperature has been varied from 300 to 400°C to -40°C for many times, greatly increasing equipment investment, energy consumption and operating costs; ( 2) The separate sulfur-resistant conversion unit not only increases equipment investment and energy consumption, but also due to the low heat release of water vapor conversion, when the syngas temperature and water vapor content fluctuate, it often encounters the phenomenon that the conversion temperature is too low , so that the organic sulfur in the synthesis gas cannot be completely converted into inorganic sulfur, thereby affecting the subsequent sulfur recovery efficiency; (3) Methanation is a strong exothermic reaction. Dilution will greatly increase the cycle equipment investment and cycle energy consumption

The inventors of this patent have further researched and found that when shift and methanation are carried out simultaneously under the dual-function catalyst, three reactions of methanation, water vapor shift and reverse water gas shift inevitably occur, while the syngas prepared by the existing coal gasification technology contain a lot of CO 2 , especially in the synthesis gas of crushed coal pressurized gasification mostly used in coal-to-natural gas technology 2 The volume content is as high as 28%, and after conversion and methanation, CO 2 content will further increase, a large amount of CO 2 It will lead to the occurrence of reverse water shift reaction, which will greatly reduce the conversion rate of CO. After the acid gas is eluted with low-temperature methanol, there are still a large amount of unconverted CO and H in the product gas. 2 Gas, which affects the quality of natural gas and limits its industrial application

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