Patent ID: 7435400

Claim:
A method for complete combustion of a carbonaceous fuel, low volatile matter, low sulfur coal, in a primary combustion zone of a boiler or furnace operating at about 3000° F. gas temperature and near to or at stoichiometric condition of unity in order to increase combustion efficiency and nitrogen oxide, NO x , concentrations, while reducing carbon dioxide, CO 2 , and sulfur dioxide, SO 2 , concentrations in the primary combustion zone below levels attainable with more fuel rich combustion and higher sulfur coal, comprising: identifying a post-primary combustion zone within the boiler or furnace having gas temperatures between about 1700° F. to 2500° F.; injecting an aqueous urea or ammonia solution as dispersed air atomized droplets of varying diameters across a planar spray pattern perpendicular to gas flow direction for reducing NO x to at least 0.3 lb/MMBtu; if required to augment the aqueous urea or ammonia solution to achieve the reduction of the NO x , injecting in the post-primary combustion zone, a solid or liquid carbonaceous fuel to convert by reburn gases to local fuel rich conditions, followed by injection of additional air into a post reburn combustion zone to return the gases to excess air conditions; and adjusting water concentration in the aqueous urea or ammonia solution to levels that are high enough to cool the gases to about 2100° F. to 2200° F. or below in order to enable urea or ammonia-NO x reaction to function at temperatures for effective post combustion NO x reducing reactions.