The effects of coal types with a wide range of volatile matter content including lignite, bituminous coal, and lean coal, as well as the effects of reaction temperature, coal particle size, the primary-zone stoichiometry (SR1) and reburning-zone stoichiometry (SR2), etc. on NO reduction efficiency were carried out systematically in an entrained flow reactor. The heterogeneous NO reduction mechanism was analyzed. The results indicate that the NO reduction efficiencies increase with decreasing SR2 and coal particle size, and with increasing reaction temperature. The char contributions to the total NO reduction efficiency increase with increasing proximate volatile matter, coal particle size, and with decreasing reaction temperature. The char contribution can be reached more than 40% when SR2 is larger than 1.06 or less than 0.92 for XLT lignite. The char contribution at the conditions of SR1 = 1.0 and SR1 = 1.2 is significantly larger than that at SR1 = 1.1 for coals with high-volatile matter at a fixed reburning fraction. (c) 2008 Elsevier Ltd. All rights reserved.