Experiment And Simulation Studies On The Thermal Behavior And Molecular Mechanism Of Loose Medium Component Of Coal

Loose Medium Component(LMC),which is a characteristic family of components obtained through coal extraction and anti-extraction methods,is a source material for generating expansible substances during coal pyrolysis and plays an essential role in the formation of coke from coking coal.The study of its pyrolysis behavior and reaction mechanism holds great theoretical significance for the reasonable processing and utilization of coal,particularly coking coal,and contributes to a deeper understanding of coal structure.Reactive molecular dynamics(Reax FF MD)is a method for simulating molecular reaction processes that continuously describes the breaking and formation of chemical bonds.This method has the advantages of high calculation accuracy and low computational complexity,making it a valuable tool for investigating LMC’s thermal behavior and reaction mechanisms.This thesis is based on a previous study that constructed a skeletal molecular structure model of Tongting coal LMC.Using this model as a foundation,the author built a skeletal aggregation model of LMC(LMC-25-GJ)and investigated the appropriate amount of small molecules present within it.The results were then compared with experimental data,and a complete model of LMC(LMC-25-PK)that includes stable structures with small molecules was obtained.The author conducted reactive kinetic simulations of the pyrolysis behavior on LMC-25-GJ and LMC-25-PK separately.During the pyrolysis process,the thermal weight loss behavior,product distribution,atomic bonding,and elemental migration patterns were analyzed.Additionally,the thesis analyzed the internal factors behind LMC’s thermal expansion behavior.Results are as follows:The stable LMC-25-GJ aggregate,formed from 25 LMC skeleton monomers,contained 165 extractable small molecules,comprising 11 types of alkanes(55molecules),10 types of alcohols(50 molecules),8 types of aromatics(40 molecules),and 4 types of ketones(20 molecules).The full model of the LMC aggregate,LMC-25-PK,was the most stable structure,with a density of 1.19 g/cm~3,which was close to the experimental value of 1.48 g/cm~3.Additionally,the content of small molecules was23.51%,almost identical to the experimental extraction rate of 22.69%.In simulating the thermal degradation of LMC,there is a certain correspondence between the experimental thermogravimetric curve and the drying and dehydrogenation stage,fast pyrolysis stage,and condensation and carbonization stage.During the drying and dehydrogenation stage,a small amount of initial activated gas is generated by LMC,mainly containing C-C(0.5)and C-O(1.5)bonds.The turning point at which there is a significant change in the number of bond formation and bond breaking occurs at a simulated temperature of around 2500 K,with a certain amount of C-C(1)and C-C(1.5)bonds breaking before this temperature to generate C-C(2.5)and C-C(3)bonds,and after this temperature,C-C(0.5),C-C(1),and C-C(1.5)bonds mainly break on a large scale to generate C-C(2),C-C(2.5),and C-C(3)bonds.During the initial stage of rapid pyrolysis of LMC,the absolute content of N element in the volatile products increased slightly within the simulated temperature range of 1700K to 2200K,and then decreased sharply to its minimum value at the end of this stage.However,in the aggregation stage,its absolute content began to increase significantly.On the other hand,O element in LMC was most likely to combine with other elements to generate small molecule gases during the pyrolysis process,and was least likely to form light tar.The main factor causing the differences in properties between LMC and the other family component,DMC(dense medium component),lies in the relative proportion of small molecule gases produced during the pyrolysis process and the liquid material,as well as the quantity and ratio between light and heavy tars.When the contents of heavy tars,light tars,and small molecule gases are roughly in a 2:2:1 ratio,it is more favorable for system fluidity.On the other hand,when the content of light tars decreases and the amount of small molecule gases increases,it is more favorable for system expansion.This thesis contains 51 figures,12 tables and 85 references.