Effect of Pulverized Coal Preheating on NOx Reduction during Combustion

Although various NOx removal technologies have been commercialized, NOx emissions are still so high that they cannot meet the newest standard and endanger the eco-environment and human health. Meanwhile, some NOx reduction technologies suffer from high costs. Recently, a cheap and pending technology called gas-fired coal preheating has surfaced again. This method introduces hot flue gas to heat a coal stream to high temperatures before the coal stream is injected into a utility boiler for combustion, thus resulting in a reduction in NOx. Considering the complex mechanisms during preheating, the effect of the preheating parameters, including temperature, residence time, excess air ratio, and coal type, are studied in a laboratory-scale drop-tube furnace in detail. Meanwhile, by means of Chemkin coupled with the mature NOx reduction mechanisms of GRI-mesh3.0 and Dagaut, as well as a CPD model, a detailed kinetics analysis on NO removal, including the migration and transformation of hydrocarbons and nitrogenous compounds during PC preheating, is performed. The research provides intuitive guidance, in practice, and a new scientific interpretation, in theory, for NOx reduction during PC combustion with preheating.