CURRENT AND ADVANCED NOx -CONTROL TECHNOLOGY FOR COAL-FIRED INDUSTRIAL BOILERS

摘要

A NOx-control-technology assessment study of coalfired industrial boilers was conducted to examine the effectiveness of combustion-modification methods, including low excess air, staged combustion, and burner modifications. Boiler types considered included overfed and underfed stokers, spreader stokers, pulverized-coal and coal-fired cyclone units. Significant variations in NOx emissions occur with boiler type, firing method, and coal type;a relative comparison of emission-control performance, cost, and operational considerations is presented for each method.nBaseline (as-found) emissions from grate-fired stokers were shown to be in the range of 200 to 300 ppm. Similarly, as-found emissions from suspension-fired units were quite low (350 to 600 ppm) as compared to comparably designed utility-sized units. Low excess air was shown to be the most effective method on existing units, reducing emissions by approximately 10%. Evaluation of staged combustion and burner modification, however, were limited due to current boiler designs. Major hardware modification design and implementation are necessary before the potential of these techniques can be fully evaluated.