Study On The Molecular Structure And Pyrolysis/Chemical Looping Gasification Reaction Characteristics For Macerals Of High-rank Bituminous Coal In Western China

The high-order bituminous coal in Western China were taken as the research objects.Through experimental means and molecular simulation method,we hope to explore the internal relationship between chemical bond information and thermochemical transformation behavior in coal chemical structure from the micro perspective.Firstly,vitrinite and inertinite were separated by IDGC and characterized by elemental analysis,13C NMR,FTIR,XPS and XRD.Furthermore,the complex particle models with different particle sizes were determined based on the statistical average molecular structure approximation combined with molecular simulation method.Moreover,with the help of chemical index analysis method,the differences between the molecular structures of different macerals were explored.Then,a series of isothermal simulations were carried out using ReaxFF MD,focusing on the distribution of pyrolysis products and pyrolysis reaction characteristics of three complex particle models.And the pyrolysis experiments of the bituminous coal and its different macerals were carried out by thermogravimetry,the TG/DTG curves were analyzed combined with the simulation results,so as to deeply understand the differences of pyrolysis reactivity of different coal samples.Finally,the steam gasification experiments of the bituminous coal and its different macerals were carried out by thermogravimetry,and ten common gas-solid reaction kinetic models were selected for gasification kinetic analysis.The main results and conclusions were as follows:(1)Aromatics were the main components of the molecular structures of the two macerals.The structure of aliphatic hydrocarbon is methyl,methylene,methylene,methoxy and so on.The structure of oxygen-containing functional group is C-O,C=O and-COOH.The content of C-O in the two macerals is the highest.The main forms of nitrogen and sulfur atoms are pyrrole,pyridine and thiophene.Chemical structure index analysis showed that XBP,?,W and B values of vitrinite molecular structure were 0.17,9.27,1.80 and 28.29%,respectively.The XBP,?,W and B values of inertinite molecular structure are 0.20,9.41,1.78 and 27.34%,respectively.The results show that the number of aromatics in vitrinite is small,the structure of aliphatic hydrocarbon is rich,the unsaturation is small,and the reduction degree and cohesiveness are the largest.The inertinite has the largest number of aromatics,less aliphatic hydrocarbons,the largest unsaturation and the highest degree of coalification.The results of energy composition and RDF analysis of all the complex particle models show that the models are a complex aggregate formed by multiple single molecular models through weak interaction,and the energy is in balance with each other.There is no chemical reaction between molecules.(2)The molecular models of composite macerals with molecular formula C3214H2335O157N47S12,C3228H2352O156N48S12 and C3060H2148O168N36S12 were simulated.The results show that the content of C40+component decreases,the content of gas component and C5-C15 component increases,and the content of C16-C40 component first increases and then decreases.The reaction rate increases with the increase of pyrolysis temperature.In the initial stage of pyrolysis,weak interaction,weak bridge bond and side chain structure were broken.As a result,the aggregation state formed by the entanglement between molecules began to depolymerize and decompose.After that the free radicals and small molecular fragments produced in the initial stage of pyrolysis lead to the cleavage of bridge bonds and the shedding of side chains.At 2500 K and 3000 K,decomposition and polycondensation are the main reactions in the model.In the whole pyrolysis process,the relationship of pyrolysis reactivity is V12>V11I1>I12,which indicates that the difference of pyrolysis reactivity between different models is due to the different molecular structure.The smaller the heating rate,the longer the residence time of the sample at the pyrolysis temperature,and the more sufficient the pyrolysis reaction.However,the higher the heating rate is,the opposite result is shown.Therefore,the higher the heating rate is,the more unfavorable the pyrolysis reaction is.The thermogravimetry results show that the vitrinite has higher reactivity under the same pyrolysis condition because the coal degree of the molecular structure of the vitrinite is less than that of the inertinite group.(3)The results show that the carbon conversion of the bituminous coal and its different macerals increases with the increase of gasification reaction time at different gasification temperatures.The R2 fitting of ten gas-solid reaction kinetic models shows that the spherical symmetric shrinking core model can better simulate the gasification reaction process of the bituminous coal and its macerals,so the model is the best mechanism function.The results show that the activation energies of QH-C,QH-V and QH-1 are 165.44,169.78 and 176.46 kJ/mol respectively.The activation energy of inertinite is the highest,which indicates that the gasification reactivity of inertinite is the worst.