In-situ characteristics and evolutionary law of plastic layer during pyrolysis of coking coal

BAI Xiaoyan

doi:10.3969/j.issn.1007-7677.2025.04.001

Abstract：To investigate the characteristics thoroughly of the plastic mass developed during coking process of coking coal,and the changes of the microstructure of coal coke during the pyrolysis process,in-situ pyrolysis experiments were carried out on Gu jiao coking coal(JM),Lin fen rich coal(FM)and Huai Nan 1/3 coking coal(1/3JM)samples by in-situ pyrolysis equipment,and the colloid in situ semi-coke was prepared.Combined with the thermos gravimetric(TG)and Gieseler fluidity characteristics of coal samples,Raman spectroscopy(Raman),X-ray dif-fraction(XRD),scanning electron microscopy(SEM)and coke micro-strength index(MSI)were used to charac-terize in-situ semi-coke at different temperatures,and the softening-melt-curing process of the colloids was analyzed.The results showed that the maximum thermogravimetric rates(Kmax)of JM,FM and 1/3JM coal samples were 0.3%/min,0.58%/min and 0.84%/min,respectively.And the corresponding temperature points(Tmax)were 482.2,462.3 and 431.2℃,which overlapped with the melting stage of the plastic layer.As the pyrolysis tempera-ture T increased from the initial softening temperature(Ts)to the curing temperature(Tr),the semi-coke half-peak width(FWHM)increased,the relative absorption strength(AG/Aall)increased,AD3/AG decreased,AD1/AG decreased,and AD4/AG decreased first and then increased.These showed that the order degree of semi-coke was in-creased,the defects were reduced,and the microcrystalline structure units were gradually improved.Among the T from Tsto Tr,the AG/Aall values of JM,FM and 1/3JM increased from 16.38%to 17.21%,15.29%to 17.76%and 14.75%to 17.01%,respectively.Also,for FWHM values,JM＜FM＜1/3JM.As T increased from Tsto Tr,the crystallite structure parameters such as aromaticity(fa),carbon crystallite stacking thickness(Lc)and carbon plane size(La)increased of semi-coke.From Tsto Tr,the La of JM,FM and 1/3JM increased from 2.87 to 3.47 nm,2.34 to 3.38 nm and 2.40 to 3.36 nm,respectively.In addition,Lc increased from 2.13 to 2.27 nm,2.04 to 2.24 nm and 2.02 to 2.18 nm,respectively.With T increased from Tsto Tr,the diameter of aperture and pore size of the semi-coke surface increased gradually.1/3JM coal samples were pyrolyzed at different pyrolysis tempera-tures from 401℃to 950℃.When T was less than Tr,the MSI value of coke samples was close to zero.When T in-creased from 474℃(Tr)to 950℃,MSI value of coke sample increased from 10.20%to 56.95%.