Patent ID: 7037356

Claim:
A method for operating a reducing rotary hearth furnace, comprising the steps of: (a) conforming a combustion gas which has been generated inside a rotary hearth reducing furnace to a temperature of at least 800° C. to be at least provided at one of: i. an internal portion of an exhaust gas outlet duct of the reducing furnace, and ii. a vicinity of the exhaust gas outlet duct; (b) making a concentration of carbon monoxide in the combustion gas to be not more than 200 ppm by volume ratio by controlling a concentration of oxygen in the combustion gas at the portion of the exhaust gas outlet duct connected with the waste heat boiler to be not less than 0.5% by volume ratio; (c) making the combustion gas to be in a well-developed turbulent state by controlling a gas flow rate considering a width of the hearth of the furnace or a diameter of the outlet duct; and (d) rapidly cooling the combustion gas after step (c).