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

A 293 kWt (1 million Btu/hr) pilot scale facility is used to develop a low NOx pulverized coal fired tangential system. A burner concept is developed which achieves low NOx by directing the fuel and a fraction of the secondary combustion air into the center of the furnace, with the remaining secondary combustion air directed horizontally and parallel to the furnance walls. Such separation of secondary combustion air creates a fuel rich zone in the center of the furnace where NOx production is minimized. This combustion modification technique lowers NOx 64%, relative to conventional tangential firing, by injecting 85% of the secondary air along the furnace walls. Under these conditions, NO emissions are 180 ppm corrected to 0% 02. Also at these conditions, CO, UHC, and unburned carbon emissions are less than 40 ppm, 3 ppm, and 2.4%, respectively, comparable to conventional tangentially fired pilot scale results.