Study Of Heat Transfer And Kinetics In The Pyrolysis Of Large-particle Longkou Oil Shale

In this paper,the basic properties of Longkou Beizao oil shale and the pyrolysates are evaluated,including Fischer assay,proximate analysis,heat value,ultimate analysis,simulated distillation and composition of retorting gas.A 2D cylinder transient heat transfer model is established according to pyrolysis of single-particle oil shale in the fixed bed reactor.Variations of physical properties of oil shale with temperature and heat absorption during the pyrolysis are considered in this model.The ANSYS is used to simulate the pyrolysis process.The temperature distribution of the oil shale at different time and the temperature distribution in the different experimental conditions are obtained.The heat transfer experiment of cylindrical oil shale is carried out in a self-designed fixed-bed reactor.The change of surface and center temperature with time is measured,and the simulation results and experimental results are compared.The results show that many temperature gradients are formed from outside to inside of oil shale throughout the whole pyrolysis process.The center-surface temperature difference of oil shale particle increases firstly and then decreases.With the increase of sample particle size,the maximum center-surface temperature difference increases continuously and the center-surface temperature difference at the end of pyrolysis increases accordingly.With the increase of heating rate during the pyrolysis process,the center-surface temperature difference of oil shale expands significantly.Given the same particle size,the center temperature at the end of pyrolysis reaction is positively related with heating rate.The deviation between the calculated result and the experimental result is small.The model and calculation method can predict the temperature in pyrolysis of large-particle oil shale well,which is of great significance for industrial production.Overall first order reaction model with the effects of temperature gradient and Friedman model are established to simulate the pyrolysis process of large particle and powdered oil shale.The kinetic parameters of Longkou oil shale are determined.The calculation results of overall first order reaction model show that the pyrolysis apparent activation energy of large particle Longkou oil shale are about 131.28¹34.71kJ·mol^-1 and the frequency factor are about 3.99×10¹²⁵.51×10¹² s^-1.The model can describe the pyrolysis process of large particle oil shale well.The pyrolysis apparent activation energy calculated by Friedman model are 170.9²88.3 kJ·mol^-1.It is found that with the reaction proceeds,the apparent activation energy and the frequency factor basically showed the trend of increase.