Formation and control of NO emissions from coal-fired spreader-stoker boilers

Stoker coal-fired furnaces are significant in terms of coal consumption and environmental impact; however, they have received little research attention. This paper describes the results of a study on the formation and control of nitrogen oxides in coal-fired spreader-stoker systems. Three scales of experimental equipment were used to define the evolution and oxidation of fuel nitrogen in the fuel suspension phase, the conversion of fuel nitrogen during fixed-bed combustion, and the coupling between the two combustion phases. The results indicate that NO emissions from spreader-stoker-fired coal furnaces are the result of relatively high conversions of fuel nitrogen evolved from particles less than 0.1 inches in the suspension phase and low conversion of fuel nitrogen during the bed combustion. In the suspension phase, nitrogen is evolved at approximately the same rate as carbon is oxidized. Local oxygen availability is the primary control parameter for both phases of the combustion. Minimum overall fuel nitrogen conversions of 6 percent were achieved in the pilot scale facility by controlling the stoichiometry in both combustion zones.