Abstract: Semi-char is the product of low-rank coal pyrolysis at low temperature,which requires higher temperature for its ignition and stable combustion than raw coal.In order to expand semi-char's application in power plants and other fields,it is necessary to introduce some combustible and high-volatile coals as co-combustion fuel.On the other hand,domestic and foreign research on blended coal combustion is mostly based on small-scale test benches and numerical simulations,rather than pilot scale test systems.Therefore,the thermal experimental study was conducted to investigate the influence of different volatile content(lignite,bituminous coal,sub-bituminous coal) on the mixed combustion with Shenmu pyrolysis semi-char in a 350 k W pulverized coal-fired pilot-scale furnace.The furnace temperature at different axial and radial positions,and concentrations of gaseous species(O_2,CO,CO_2and NO_x) at furnace axis were measured in the primary combustion zone to study the effects of blended coal quality change on ignition,NO_xemission and burnout characteristics for co-combustion(the quality blend ratio of semi-char is 50%).The research results show that the ignition and combustion of the fuel-rich jet is better than that of the fuel-poor jet,and the O_2consumption and flue gas generation are also mainly concentrated on the fuel-rich jet.With the increase of dry ash-free volatile(V_(daf)) content in blended coal,the stand-off distance of blended coal decreases,the ignition temperature reduces,and the distance between the burner outlet and the stable combustion zone is shortened.At the exit section of the primary combustion zone,the NO_xemission concentration of the mixed jet for lignite+semi-coke,bituminous coal+semi-coke,and sub-bituminous coal+semi-coke are respectively 473,462 and 532 mg/m~3(under 6%O_2,the same below),while the difference of NO_xconcentration of lignite/semi-char and bituminous/semi-char jet is only 11 mg/m~3.Considering the ignition distance,combustion intensity and NO_xemission from the primary combustion zone comprehensively,the V_(daf)content which is not less than 16%is suitable for co-combustion(the quality blend ratio of semi-char is 50%).