NOVELTY - A fluidized bed methanation reactor comprises raw material inlet (1), catalyst inlet (7), catalyst outlet (2), gas-solid separator (5), gas product outlet (6), lateral feed gas inlet (8), at least one gas distribution plate (3) arranged inside the reactor, and cooling water spray device (4) adapted to control the temperature in the reactor. The gas distribution plate divides the reactor into fluidized bed layers forming the catalyst dense-phase regions (I, II). The cooling water spray device is disposed above each catalyst dense-phase region.    USE - Fluidized bed methanation reactor used for producing methane from gas mixture containing H2 and CO (claimed).    ADVANTAGE - The fluidized bed methanation reactor enables the circulating cooling water to be directly contacted with the high-temperature methanation gas product, thus improving the heat transfer, enabling the reaction temperature to be controlled easily, reducing the heat loss during the heat transfer process, and improving the utilization of the heat of reaction. It has high production throughput, high operational flexibility, high CO conversion rate, high methane production selectivity, small catalyst usage, high heat utilization rate, and great industrial application prospect.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for production of methane from a gas mixture containing hydrogen gas (H2) and carbon monoxide (CO) using the fluidized bed methanation reactor, comprising (a) adding catalyst into the reactor via the catalyst inlet (7), introducing an inert gas into the reactor via the raw material inlet (1), forming a first catalyst dense-phase region (I) above the gas distribution plate (3), switching the feeding in the raw material inlet from the inert gas into the raw material feed gas (A), contacting the raw material feed gas with the catalyst to carry out methanation reaction so as to produce methane and release heat, spraying with water via the cooling water spray device (4) to absorb the released heat; (b) introducing the obtained methane gas and unreacted raw material from step (a) into the upper fluidized bed layer, heat exchanging with the raw material that is fed into the reactor via the lateral feed gas inlet (8), forming a second catalyst dense-phase region (II), carrying out further methanation reaction, and introducing the reaction product into the gas-solid separator (5) to obtain the methane gas product.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic sectional view illustrating the fluidized bed methanation reactor.    Raw material inlet (1)    Catalyst outlet (2)    Gas distribution plate (3)    Cooling water spray device (4)    Gas-solid separator (5)    Gas product outlet (6)    Catalyst inlet (7)    Lateral feed gas inlet (8)    Catalyst dense-phase regions (I, II)