Investigating Pyrolysis Reaction Of Shenfu Coal Based On Molecular Dynamics

Coal has always played an important part in China's energy consumption structure.Nonetheless,the environmental pollution problem was not ignored by using the coal for a long time.Therefore,it is needed to improve the clean and efficient coal utilization.In fact,the coal pyrolysis is the basis for clean and efficient use of coal.However,the coal pyrolysis mechanism is difficultly studied by using the experimental method.Fortunately,a molecular simulation based on the reactive force field provides an effective tool to assess the reaction mechanism.Therefore,coal pyrolysis mechanism was researched by using experimental and simulative method in my work.According to experimental results and reported coal molecular structures,the three-dimensional periodic structure model of Shenfu coal and classic Wiser coal was constructed by using MS(Materials Studio)7.0 software,respectively.Then,molecular mechanics and molecular dynamics optimization were conducted to optimize those structures.After that,pyrolysis reaction mechanism of Shenfu coal and Wiser coal was simulated based on ReaxFF(Reactive Force Field)by using ADF(Amsterdam Density Function)software,respectively.Finally,coupled pyrolysis mechanism whose reactants were syngas combined with Shenfu coal and Wiser coal were explored,respectively.Thus,coal pyrolysis reaction was illuminated based on simulation results,and expressed as follows.(1)Proximate analysis,ultimate analysis,thermogravimetric analysis and infrared spectroscopy analysis of Shenfu coal were performed in my work.Industry analysis and elemental analysis provide basic datum for the construction of coal molecular model structure in the next section,thermogravimetric analysis shows that temperature is the primary influencing factor of pyrolysis reaction.And,the infrared spectroscopy analysis showed that the number of aliphatic structure was increased with the rising temperature due to carbon chain fracture,which is in agreement with the simulated results.(2)Periodic structure models of Shenfu coal and classic Wiser coal were constructed by MS 7.0 software,and optimized based on molecular mechanics and molecular dynamics method,respectively.Optimized density results of Shenfu coal and classic Wiser coal were 1.367 g/cm~3 and 1.519 g/cm~3,respectively.Depending upon relevant energy analysis,it was showed that van der Waals energy and torsion can play a stabilizing role in the optimization process of coal molecular structure model.(3)Based on optimized structures of Shenfu and Wiser coal model by using ADF software,two kinds coal pyrolysis processes were simulated in the temperature range of 1600-2800 K.The calculated results showed that amount of representative pyrolysis products of Shenfu coal is similar to Wiser.Further,the sequence of pyrolysis product quality was H2>H2O>CH4>CO.By analyzing the pyrolysis product source,it is found that the initial fracture position of Shenfu coal firstly occurs at the C-S bond and the C-O bond.Further,it was also identified that and the number of fracture location was increased,and the fracture time was shortened,with rising temperature.(4)The coupled pyrolysis reaction process was proposed,whose reactants were real syngas(H2:CO=2:1)combined with Shenfu coal.Where after,the co-pyrolysis reaction processes were simulated by using ADF software with different hydrogen-carbon ratio in syngas.The simulation results show that the total number of molecules in the Shenfu coal pyrolysis system and the amount of light hydrocarbon products was increased with the presence of syngas.In addition,the amount of light hydrocarbon products was obviously most when hydrogen-carbon ratio in syngas was equal to 3:2.In this thesis,pyrolysis reaction processes of proposed and classical coal model were conducted by using molecular simulation method.Further,the coupled coal pyrolysis reaction process combined with syngas was simulated.Based on pyrolysis results analysis,the coal pyrolysis mechanism was clarified,and was in deep understood,which provides an elementary support for the clean and efficient coal utilization in the future.