Patent ID: 6071377
Filing Date: 2000-06-06
Classification: D21C,F23G,F23J,Y02E

Abstract:
A method for combusting black liquor in a recovery boiler and producing flue gases having a low content of nitrogen oxides (NO.sub.x), comprising:providing a recovery boiler and having a region extending from a liquor injection device to a quaternary air supply unit;supplying primary, secondary and tertiary combustion air to the recovery boiler;determining a stoichiometric requirement for a complete reduction of the nitrogen oxides present in the flue gases;supplying a quantity of gaseous ammonia to the a quaternary combustion air at an upper portion of the recovery boiler, the quantity corresponding to between about 100% and about 400% of the stoichiometric requirement for complete reduction of the nitrogen oxides present in the flue gas;mixing the gaseous ammonia with the quaternary combustion air to form a combustion air mixture;supplying the combustion air mixture to the upper portion of the recovery boiler;maintaining a reducing atmosphere in the regions for a dwell time of at least 2.5 seconds.