Methanation system for coal natural gas

The utility model relates to a methanation system for coal natural gas. The methanation system comprises four methane reactors which are connected in series and in sequence and then are connected with a 2# boiler feed water pre-heater and a 2# separator; the methanation system further comprises an injector, a purifier heat exchanger and a 1# separator, wherein the injector, the purifier heat exchanger and the 1# separator are sequentially connected with the four serially-connected methane reactors by pipelines; in the four serially-connected methane reactors, a synthesized gas outlet of the 1# methane reactor is connected with a synthesized gas inlet of the 2# methane reactor by a 1# waste boiler; the synthesized gas outlet of the 2# methane reactor is connected with the synthesized gas inlet of the 3# methane reactor by a 2# waste boiler and a steam superheater; the synthesized gas outlet of the 3# methane reactor is connected with the synthesized gas inlet of the 4# methane reactor by a purifier pre-heater