Abstract: In the research on the adaptability of large-proportion semi coke co-combustion in a 660 MW supercritical bituminous coal boiler，the problems faced by the boiler was pointed out through semi coke characteristic analysis. And numerical simulation results located the blending position for semi coke.Semi coke adaptability adjustment test was made on the coal pulverizers.In the test，the pulverized coal fineness R90 was controlled below 10% and co-combustion was taken by the pulverizer group in the middle.The test results verify that semi coke combustion can alleviate the coking in power plant boilers，and reduce the mass concentration of SO2 by 40.65%，while slightly increase the NOx mass concentration by 18.42%.The boiler co-combusting coals with high sulfur content and high calorific value shows advantage over its substitutes，since its pulverized coal combustion efficiency reaches 99.09% while its boiler efficiency shows a 0.82% decline.Studying the adaptability of semi coke in bituminous coal boilers with medium-speed mill direct-firing pulverizing systems，the key points of semi coke co-combustion，an appropriate co-combustion method， and principles of boilers' adjustment can be obtained.It is considered that the 660 MW supercritical bituminous coal boiler blending with 50% semi coke during its co-combustion runs safely and economically.

Key words: coal-fired boiler, semi coke, co-combustion, coal adaptability, boiler efficiency, boiler combustion efficiency