Pilot-scale development of a low-NOx coal-fired tangential system

Abstract

A 293 kW pilot-scale facility was used to develop a low-NO x pulverized coal-fired tangential system. Low NO x is achieved by directing the fuel and 20 percent of the secondary combustion air into the center of the furnace with the remaining 80 percent of the secondary combustion air directed parallel to the furnace walls. The separation of secondary combustion air in this manner creates a fuel rich zone in the center of the furnace where NO x production is minimized. This combustion modification technique has lowered NO x 60 percent relative to conventional tangential firing. In addition, CO, UHC and unburned carbon emissions are substantially unaffected by the modification. Also, the modification places a blanket of air on the furnace walls which is beneficial from a wall corrosion and slagging point of view. Finally, the modification shows a decrease in NO x emissions as firebox gas temperature is increased. This characteristic might be beneficially applied in a large-scale system to reduce furnace volume, and thereby capital cost, for a given combustion heat release. Tests are now underway to further optimize and characterize this low-NO x combustion modification technique.