Evolution law of micro-meso pore-fracture structure of anthracite in pyrolysis

Through the high-precision micro CT technology,the evolution law of micro pore fracture structure of Jincheng Anthracite samples with diameter of 7 mm and length of 10 mm under different temperature conditions is studied. The 3D reconstruction of pore fracture is carried out through MATLAB and Avizo,and the 3D characteristic parameters of pore fracture are quantitatively analyzed. The study results on Jincheng Anthracite show that during a low temperature pyrolysis from room temperature to 600℃,① When the temperature is below 200℃,the pore fracture structure changes slowly under the action of thermal cracking; at over 200℃,the pyrolysis of anthracite occurs,the number of fractures with a diameter greater than 1 000 μm increases first and then decreases,and the maximum diameter and volume of fractures increase gradually. At 300℃,the number of fractures reaches the maximum number.When the temperature reaches 600℃,the fractures are overlapped and connected with each other,the number of fractures is the least,the diameter of a fracture is the largest and its volume is the largest,the connectivity is the best.②With the increase of temperature,the porosity of Jincheng Anthracite shows an upward trend,and the porosity in-creases rapidly at from 100℃ to 200℃ and from 400℃ to 600℃ separately; the fractal dimension shows three stages:the fractal dimension increases rapidly from room temperature to 300℃,and decreases slowly from 300℃ to 500℃,then increases again from 500℃ to 600℃. ③ The 300℃ is a key temperature in the process of low-temperature pyrolysis of anthracite. At this temperature,the large fractures are formed,the porosity is 36.7%,the fractal dimension of the surface area of the pores and fractures is up to 2.236,and the permeability has reached the index of complete permeability. Therefore,for anthracite,the 300℃can be the temperature of heat injection to increase permeability.