ReaxFF Simulation Of The Nitrogen Transformation During The Lignite Pyrolysis Process

The pyrolysis of lignite is very complex because of its heterogeneous and amorphous structure.Many elementary reactions and intermediates are all contained in the pyrolysis of lignite.Besides the intermediates are hard to detect through experiments.In this paper,Reax FF force field(abbreviated as Reax FF)is used to perform a serious of pyrolysis of lignite in different conditions.Nitrogen containing free radicals are detected and captured in this paper,too.Then the transformation mechanism of nitrogen in the pyrolysis are discussed by analyzing and classifying nitrogen containing elementary reactions.Wolfrum is chosen as structural unit of the three pyrolysis systems: oxygenpyrolysis system(gasification process),hydrogen-pyrolysis system(liquidation process)and lignite pyrolysis system(pyrolysis process).LAMMPS is used in Reax FF simulation and corresponding C++ programs have been written to count common nitrogencontaining products and search for nitrogen-containing elementary reactions in the pyrolysis.It shows that there's seldom nitric oxide in hydrogen-pyrolysis system and lignite pyrolysis system,and the main nitrogen-containing products in the two systems are HCN,NH3 and nitrile.There's a large number of nitric oxide in the oxygen-pyrolysis system,and the main nitric oxide is NO.The result is in agreement with experiments.There are a lot of intermediates in the pyrolysis,such as CH2 NH and NH free radicals.In the hydrogen-pyrolysis system,HCN and NH3 are generated by the interaction of these free radicals with H radicals or H2.In the oxygen-pyrolysis system,NO is generated by the interaction of these free radicals with O radicals or O2.This study provides reliable theoretical foundation for gasification and liquidation process.