Optimizing post-combustion nitrogen oxide and sulfur dioxide reductions and improving combustion efficiency in coal fired boilers

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, NOx, concentrations, while reducing carbon dioxide, CO2, and sulfur dioxide, SO2, 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 NOx to at least 0.3 lb/MMBtu;
• if required to augment the aqueous urea or ammonia solution to achieve the reduction of the NOx, 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-NOx reaction to function at temperatures for effective post combustion NOx reducing reactions.