PURPOSE: To obtain inexpensively raw gas for synthetic chemistry without requiring any desulfurizer and any reformer, by carryig out the desulfurization of C gas and the decomposition of methane by utilizing a blast furnace process in which pure oxygen is introduced.

CONSTITUTION: Coal is dry-distilled in a coke oven 1 to prepare coke. In the production of pig iron by introducing ores and said coke into a blast furnace 2 and introducing pure oxygen through the tuyere of the furnace thereinto, C gas formed in the coke oven 1 and pure oxygen are introduced through the tuyere into the furnace, whereby methane in the C gas is decomposed to form CO and H2 and sulfur in the C gas is fixed to slag to thereby effect desulfurization. CO2 and H2O are removed from gas leaving the top of the furnace 2 to obtain product gas (raw gas for synthetic chemistry; part thereof is used as gas for coke oven).