Method for producing synthetic natural gas

The invention discloses a method for producing synthetic natural gas, which belongs to the technical field of coal chemistry and new energy. The method for producing the synthetic natural gas comprises: dividing raw material gases from a general gas source into low-carbon synthetic gases with a hydrogen to carbon ratio, namely a (H2-CO2) to (H2+CO2) ratio, being 4.5 to 15.0 and high-carbon synthetic gases with a hydrogen to carbon ratio being 0 to 2.0; according to a reaction temperature requirement, mixing the low-carbon synthetic gases with steam at certain flow, allowing the mixed gases to enter a primary thermal-insulation reactor to undergo a methanation reaction, subjecting the gases from the primary thermal-insulation reactor to heat exchange, mixing the gases with the high-carbon synthetic gases at a certain flow, and allowing the newly mixed gases into a secondary thermal-insulation reactor to undergo a methanation reaction; repeating the previous process for several times; and finally, obtaining the synthetic natural gas by processes of heat exchange, cooling, drying, compression and the like. The method has the characteristics that: (1) circulating equipment is not used; (2) all reactions are performed in thermal-insulation reactors, multiple stages of reactors are connected in series, and the reaction space velocity is high; and (3) the hydrogen to carbon ratio of the whole reaction system can be regulated easily, and the methane content in the product gas may reach over 95 percent.