System and technology for synthesis of methanol and co-production of methane by using synthesis gas

The invention belongs to the technical field of chemical industry, relates to the technical field of comprehensive utilization of methanol synthesis and methanation by using synthesis gas prepared from coal, coke oven gas, calcium carbide furnace exhaust, coal bed gas and shale gas, and particularly relates to a system and a technology for synthesis of methanol and co-production of methane by using synthesis gas. In the system, a methanol synthesis reactor is connected with a methane synthesis reactor in a series or parallel manner; the methanol synthesis reactor is put at any position except for the terminal position; the reactor at the tail end is the methane synthesis reactor; the quantity of the methanol synthesis reactors is greater than or equal to 1; the quantity of the methane synthesis reactors is greater than or equal to 1; the synthesis gas is not recycled. The synthesis of methanol and co-production of methane are achieved by using the synthesis gas; meanwhile, production of coal-produced methanol