Abstract: Ultra-low volatile carbon-based fuels，such as semi-coke and gasified residual carbon，are produced in pyrolysis and gasification of low-rank coal.A preheating combustor and auxiliary systems were installed on a 35 t/h coal-fired boiler combusting pure ultra-low volatile carbon-based fuels，so as to stabilize and enhance the burning of ultra-low volatile carbon-based fuels and lower the emission of pollutants. In the experiments carried out on the boiler，using Shenmu bituminous coal，Shenmu semi-coke and gasified residual carbon，effects of fuel type，preheating temperature，secondary air equivalent ratio and boiler load on combustion characteristics and pollutant emission were studied. The results showed that the three fuels can burn stably，and so can the pure semi-coke powder with dry ash-free volatilization fraction of 4.30%，which indicated the good fuel adaptability of the boiler. Been preheated，all the combustion efficiencies of the three fuels exceeded 99%. With the rise of preheating temperature，the overall temperature of the furnace increased，and the NOx emission mass concentration decreased first and then increased，indicating that the increase of preheating temperature was conducive to the combustion and heat release of preheated fuel in the furnace.When the preheating temperature was 887 ℃，the minimum NOx emission mass concentration was 110.6 mg/m（3 standard state，φ（O2）=9%）.The preheated boiler has good combustion stability under low loads. As boiler load is lower，the NOx emission decreased and bottomed at 108.0 mg/m3（standard state，φ（O2）=9%），which reflects the advantages of preheating combustion technology in stabilizing combustion，burnout and low NOx emission.

Key words: ultra-low volatile, carbon-based fuel, semicoke, gasified residual carbon, preheating combustor, boiler, NOx emission, combustion efficiency