TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Method: The raw gas containing hydrogen and carbon monoxide is obtained by gasifying a raw material consisting of a composite solid fuel, which is obtained by carrying out compression molding of mixture of coal fuel having coal as main component or coal dust powder, and plant-type organic material powder. Coal is chosen from wood coal, sub-bituminous coal or bituminous coal. Raw gas containing methane is obtained by carrying out anaerobic fermentation of organic waste by microorganisms. An oxidizing gas containing air and/or ozone is reacted with slaked like aqueous solution or slaked lime dispersion liquid, to produce a deposit containing calcium sulfate and ammonium sulfate as main component. Carbon dioxide contained in raw gas is removed using a polymer film (43b), before mixing of raw gas with slaked lime aqueous solution or slaked lime dispersion liquid. Water contained in fuel gas is removed during purification of raw gas.Preferred Arrangement: The refiner further has a decarboxylation unit (43) provided at raw gas route (27) connected to raw gas inlet of reaction container, and a dehumidification unit (33) provided at fuel gas route (28) connected to fuel gas exit of reaction container. The refiner further has a processing container (36) having oxidizing gas inlet (36b), blowing-in unit (12) for blowing oxidizing gas containing air and/or ozone through inlet (36b), and stirring unit (22) for carrying out reaction of blown oxidizing gas and slaked lime aqueous solution or slaked lime dispersion liquid. A deposit containing calcium sulfate and ammonium sulfate is produced at the bottom portion of container (36) as byproduct. The by product ejected from reaction container (13) along with slaked lime dispersion liquid or slaked lime aqueous solution, are stored in container (36). Blowing-in units (11,12) and stirring units (21,22) are respectively inserted in reaction containers (13,36) from upper direction, and nozzles (31,32) are respectively positioned in upper portion of units (11,12). A rotational flow is generated during blowing of raw gas or oxidizing gas into slaked lime aqueous solution or slaked lime dispersion liquid, and air bubbles are generated.