Study On The Ultra-fine Grinding Process Of Coal Particles On The Basis Of Fractal Theory

The fractal size and surface dimensions of coal particles are studied, and the hypothesis of micro-constraints energy is proposed, in order to define the difference between macromechanics and micromechanics behavior of ultra-fine grinding, which is produced by the particle agglomeration and characteristic changing. A new model for the ultra-fine grinding process of coal particles is developed, and the expression for energy consumption law is put forward on the basis of the bi-fractal law. The experiment on ultra-fine grinding of Qingshuiying coal particles is carried out, which are applied to analyze the fractal size dimensions of coal samples at various points during the ultra-fine grinding process. It is proved that the fractal size dimensions of coal samples should be characterized by the bi-fractal law, and the optimum processing time is7h in this experiment. It is also shown that the peak value of the fractal size dimension of smaller particles by the bi-fractal law can be used as a technological parameter for ultra-fine grinding. The fast macro-breakage prosess and the grinding priority are also interpreted. Moreover, pyrolysis and infrared spectrum analyses of the samples indicate that the temperature of coal pyrolysis is decreased by ultra-fine grinding. The breaking of partial chemical bonds with lower energy has been demonstrated in the process. Finally, the hypothesis of micro-constraints energy is proved. This investigation is focus on the micromechanics behavior of ultra-fine grinding process by fractal theory, aiming at providing a reference for the combined process of both coal ultra-fine pulverization and liquefaction as well.