Optimizing CO and NOx Emissions from Hog Fuel Boilers, 2007 Engineering, Pulping & Environmental Conference

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Most pulp and paper mills have boilers that burn hogged fuels to generate steam for mill use. The use of these fuels is important for off-setting the costs of purchasing fossil fuels and for disposing of wastes. Emissions from hog fuel boilers that are commonly regulated include carbon monoxide (in the range of 300 ppm to 800 ppm) and nitrogen oxides (ranging from less than 0.1 lb/million Btu to over 0.40 lb/million Btu). Nitrogen oxide (NO_x) emissions can be reduced by decreasing excess air but after a certain point this will lead to an increase in carbon monoxide (CO). In an example shown in this paper, NO_x was reduced from 0.32 lb/million Btu at 6% O₂ to 0.18 lb/million Btu at 3% O₂. But, at 3% O₂, CO increased to over 2,000 ppm. Many boilers have poorly designed combustion air systems resulting in poor mixing of air and combustibles. As a result, the boilers are fired with too much excess air, particularly undergrate air. This increases the amount of particle carryover as well as NO_x emissions.