Abstract: The influence of fuel particle diameter on co-combustion characteristics of pyrolyzed semi-coke and bituminous coal was studied in a 350 kW pilot-scale pulverized coal combustion system.The variation of flue gas temperature and the mass concentrations of O2，CO and NO in the flue gas were measured along the furnace central axis and the primary combustion zone radial direction.According to the testing results，with the increase of blended fuel particle diameter，the jet flame ignition distance decreased first and then increased，while the overall combustion intensity was of an opposite change trend.When R90 is 20%，the ignition distance bottomed out at 164 mm and the overall combustion intensity reached the highest value.At the initial stage of combustion，the mass concentration of NO dropped with the enlarging particle size until it hit the bottom at 438 mg/m3 when the R90 was 20%.In this test，considering the ignition distance，combustion intensity and NO emission from the primary combustion zone comprehensively，it is found that pyrolyzed semi-coke and bituminous coal particle of this size is more conductive to co-combustion.

Key words: semi-coke, co-combustion, particle size, ignition characteristics, NOx emission