Numerical Simulation Study On Ignition Characteristics Of Pulverized Coal And Pyrolysis Semi-coke Particles In Entrained Flow

As the main energy consumption in China,coal can be used for power generation,coking,gasification,and low-temperature carbonization;while gasification and low-temperature carbonization will produce by-products,semi-coke and residual carbon,and their carbon content is still very high.Direct abandonment will result in waste of energy.However,due to its low volatile content,it is still difficult to ignite,stabilize and burn down;therefore,in order to achieve efficient and clean utilization of pyrolyzed char,we need to explore its ignitionn characteristics.In this paper,the transient ignition model of pulverized coal is first established,and then based on it,the transient ignition model suitable for pyrolyzed char is established,and the ignition characteristics of Shenhua bituminous coal and pyrolyzed char under the conditions of entrained flow with different oxygen concentrations and different ambient temperature are studied.The ignition models of pulverized coal and pyrolyzed char particles include devolatilization models and volatiles and coal char combustion models;for the combustion models of volatiles and coal chars,this paper uses the general package reaction to describe the homogeneous and heterogeneous phases reaction to simplify the numerical calculation;for the devolatilization model,the Chemical Percolation Devolatilization model(CPD model)is used for coal powder calculation,and the single equation pyrolysis model of volatiles is used for pyrolyzed char calculation;then for the particle and gas phase transport control equations,the implicit control volume method is used to discretize the partial differential equations,and MATLAB is used to write the calculation program to solve the particle temperature,the concentration distribution of the gas components in the particle,the gas boundary layer temperature,and the concentration distribution of the gas components in gas boundary layer.Since the accuracy of the devolatilization model affects the accuracy of the simulation calculation of the ignition process,this paper first verifies it.For pulverized coal particles,compared with the Fu-Zhang general model and the double equation competition model,the CPD model can not only describe the total output of volatile matter of pulverized coal,but also predict the output of each component.For pyrolyzed char particles,compared with the CPD model,the single equation model with modified kinetic parameters can better describe its devolatilization process.Using the established coal powder and pyrolyzed char particle ignition model,the Shenhua bituminous coal and pyrolysis semi-coke were calculated under the entrained flow conditions of 1600K-1800 K and 5%-30% oxygen concentration.The results show that: under all calculation conditions,the ignition of Shenhua bituminous coal and pyrolysis semi-coke starts with homogeneous ignition first,and the heterogenous ignition time of Shenhua bituminous coal is later than pyrolysis semi-coke;as the oxygen concentration and ambient temperature increase,the ignition delay time of Shenhua bituminous coal and semi-coke is shortened,and the ignition delay time of pyrolysis semi-coke is later than the ignition delay time of Shenhua bituminous coal;as the oxygen concentration increases,the homogeneous and heterogeneous ignition temperatures of Shenhua bituminous coal and pyrolyzed semi-coke decrease;as the ambient temperature increases,the homogeneous ignition temperature decreases,but the heterogeneous ignition temperature has nothing to do with the ambient temperature.