The volume hypothesis,a theory about the energy scale of comminution,was adopted to analyze the degradation behavior of lump coal under different heating time.The breakage energy of chars was determined by a compression test,and the results show that the ultimate strength of chars decreased at the early stage during the heating process,resulting in a decrease of the char breakage energy.At the late stage during the heating process,the char breakage energy increased with the increase of heating time.The power consumption coefficients CKof different chars were determined by a drum experiment,and then the char degradation behavior under different power consumptions was predicted.In addition,agasification experiment was conducted to determine the gasification activation energy(with CO_2)of lump coal heated for different time.The results show that the gasification activation energy increased greatly at the early stage during the heating process,which showed opposite change to the breakage energy of chars.Furthermore,the internal temperature and heat changes of the bonded coal briquette were calculated by using an unsteady heat conduction equation.The large difference between the surface and the center temperatures of coal and the large amount of heat absorption at the early stage during the heating process may have a negative effect on the breakage energy of chars.
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