PURPOSE: To conduct the hydrogenation reaction, desulfurization reaction, decomposition of raw material, methane synthesis reaction and steam reforming reaction in one reaction tower, to suppress loss of heat, to reduce production cost and to allow the desired catalytic reaction to proceed efficiently and surely.
CONSTITUTION: An inner tube 22 and an outer tube 21 are coaxially arranged to constitute a double reaction tube 12. A sulfide conversion chamber 37, desulfurization chamber 38 and methanation chamber 39 are separately formed toward the upper part in the axial direction of the inner tube 22 to efficiently heat a gaseous mixture 1d with a burner. A chamber 40 for the steam reforming reaction needing a large amt. of reaction heat is formed between the outer tube 21 to be heated by the burner and the inner tube tube 22. The sulfide conversion chamber 37, desulfurization chamber 38, methanation chamber 39 and reforming chamber 40 are successively formed along the passage to gasify the gaseous mixture 1d from an inlet 31 toward an outlet 23.