To always maintain a high reduction ratio of a chemical regardless of operation conditions by setting a temperature in a furnace independently of an air ratio in a black liquor combustion furnace such as a black liquor gasifying furnace, a black liquor boiler, etc.
In this black liquor combustion furnace for soda recovery by burning a black liquor discharged from a pulp digesting process and recovering a chemical, in order to raise the reduction ratio of the recovered chemical, the black liquor combustion furnace such as the black liquor gasifying furnace 12 is equipped with an auxiliary burner 20 for supplying an auxiliary fuel to the furnace and raising a temperature in the furnace and/or the black liquor gasifying furnace 12 is connected to an oxygen supplying means 18 for supplying an oxygen-enriched air or oxygen and raising the temperature in the furnace to keep the necessary temperature in the furnace.
TAKATANI YOSHIAKI
SUGAWA SEIICHI
YAMASHITA SEIJI
MASUDA TAKEJI
