Study On The Relationship Between Aggregate Structure And Pyrolytic Behavior Of Coals With Different Metamorphic Degree

This paper analyzes the aggregate structure and pyrolysis behavior of gas coal(PS9),coking coal(TL2),and meager coal(CZ3),and explore the relationship between pyrolysis behavior and aggregate structure.XRD was used to characterize the microcrystalline structure parameters such as the distance between the aromatic layers d₀₀₂,the stacking height L_c,the ductility L_aand the stacking layer number N_avein the coal sample from the aggregate scale,Raman was used to analyze the order of coal samples,HRTEM was used to systematically observe the aggregated structure of coal samples,and qualitatively and quantitatively characterize the length,curvature and orientation characteristics of the lattice fringe.Based on the analysis of coal aggregate structure,a thermogravimetric mass spectrometry(TG/MS)experiment was performed on coal to study the characteristics of coal pyrolysis and the generation characteristics of main gaseous products.The main conclusions are as follows:(1)By comparing the XRD microcrystalline structure parameters of the three coal samples,it is found that when the vitrinite reflectance increases,d₀₀₂decreases,L_a,L_cand N_aveincrease,indicating that the higher the degree of deterioration,the larger the aromatic system,and the more aromatic stacking layers.(2)Raman analysis shows that when the vitrinite reflectance increases,the parameters that characterize the degree of order:the peak position difference(P_(G-D))between the D peak and the G peak,the intensity ratio(I_G/I_GL)of the G peak and the G_Lpeak,and the half-width ratio(F_D/F_G)of D peak and G peak gradually increases,indicating that the degree of metamorphism increases,the defect structure in the coal decreases,the microcrystalline structure increases,and the degree of order becomes better.(3)Through HRTEM research,it is found that the length and curvature of lattice fringes in different regions of the coal sample do not change much.The distribution of aromatic rings is mainly 1×1,2×2 and 3×3,and the curvature is between 1.0-1.2.As the coal rank increases,the lattice fringes in the coal sample become longer and more curved.The orientation of the lattice fringes in different regions of PS9V-T and TL2V-T is messy and the degree of order is poor,while the orientation of lattice fringes in different regions of CZ3V-T is good and tends to be consistent.Combining the results of XRD,Raman and HRTEM,it is found that as the degree of metamorphism increases,the hetero-functional groups in the coal sample decrease,the defect structure decreases,the groups connected to the aromatic system fall off,and the aromatic system gradually transforms to graphite crystallites,and the degree of order changes better.(4)The pyrolysis characteristics show that as the coal rank increases,the thermal weight loss decreases and the peak temperature of pyrolysis increases.Correlating pyrolysis characteristic parameters with structural parameters,it is found that as d₀₀₂decreases,L_c,I_G/I_GL,P_(G-D)increase and the length and curvature of lattice fringes increase,and the thermal weight loss and the maximum thermal weight loss rate decrease decreases,the peak temperature of pyrolysis increases,indicating that the larger the crystallite structure in the coal,the better the order of the aromatic structure and the more stable the structure.(5)Research on the main gaseous products of pyrolysis methane,low-carbon aliphatic hydrocarbons,hydrogen,small molecular aromatic hydrocarbons,water,carbon dioxide and carbon monoxide,found that the yield of C₂-C₄aliphatic hydrocarbons and oxygen-containing in PS9V-T is greater,indicating that it contains a lot of fatty side chains and oxygen-containing functional groups,the yield of methane in TL2V-T is the largest,indicating that it contains more small molecular structures and long-chain aliphatic hydrocarbons,the yield of hydrogen in CZ3V-T is the largest,indicating that its condensation polymerization is strong.