Simulation of Gas Production Mechanisms in Shear Deformation of Medium-Rank Coal.

The discovery of mechanochemical action provides a theoretical basis for revealing gas production from coal under stress degradation. The research on gas production in such a manner is conducive to revealing mechanisms of coal and gas outburst and excess coalbed methane (CBM). By selecting a model of a macromolecular structure of Given medium-rank coal, its structure was optimized based on molecular mechanics, molecular dynamics, and quantum chemistry, and the six optimized models were constructed into a coal polymer cell. The coal polymer cell was loaded to shear deformation through large-scale atomic/molecular massively parallel simulator (LAMMPS) software. The Given model was optimized by quantum chemistry software Gaussian and the frequency was calculated to obtain the bond strength and average local ionization energy (ALIE). The following understanding was reached: under shear, bridge bonds of a ring structure, and large π-bonds are subjected to shear and tensile action, and atoms (atomic clusters) in the outermost region of coal macromolecules tend to be sheared by surrounding molecules. The shear action shortens a molecular chain of medium-rank coal with a cross-linked structure and promotes the evolution of the coal macromolecular structure. The shear action can lead to the formation of free radicals, such as H