Study on the Pore Structure Evolution and Fractal Feature in the Process of Spontaneous Combusiton of Coal

Abstract

This paper studies the variation of pore structure of coal and the fractal law of pores in two-dimensional and three-dimensional space in coal spontaneous combustion using scanning electron microscope and mercury injection experiment. The pore structure of coal changes slowly during 30 ° C-200° C and there is a great change during 200° C-300°C. The most probable pore size is about 5nm during 30° C-200° C and micropore and transitional pore are dominating. The most probable pore size reaches 310nm at 300° C and macropores and mesopores are dominating during 200° C-300° C. During coal spontaneous combustion, the total pore volume and porosity rise gradually, the specific surface area of pores first rises and then goes down, the permeability goes down first then rises sharply and then goes down, the diameter of the pore with fractal feature gradually goes up and the fractal feature is more and more obvious. Both in two-dimensional and three-dimensional spaces, the fractal dimension of the pore enlarges gradually, indicating that the surface of the coal is becoming more and more coarse and the pore structure is gradually uniform, and the growth rate of fine pore is faster than that of macro pore.