PURPOSE: To remove CO2 and moisture in the byproduct gas of an iron mill economically in a simple process, by a method wherein CO2 and moisture are adsorbed in an adsorbing tower filled with a CO2 selective adsorbent and said adsorbing tower is desorbed by air with a room temp. and atmospheric pressure after purged by an inert gas.

CONSTITUTION: A stock gas such as a converter gas is supplied to an adsorbing tower 1 filled with an adsorbent having CO2 selective absorbability such as activated carbon or zeolite and held under a room temp. and atmospheric pressure condition from a pipe 2 and the dried gas subjected to adsorption is taken out from a pipe 3. When the CO2 adsorbing capacity of the adsorbent is saturated, the supply of the stock gas is stopped and an inert gas such as N2 is supplied from the pipe 2 to purge the combustible gas in the adsorbing tower 1 for the sake of preventing explosion. After purging is completed, air with a room temp. and atmospheric pressure is sent into the adsorbing tower 1 in a direction reverse to the direction in the adsorbing process to exhaust the desorbing gas from the tower bottom. This operation is successively repeated.