Numerical Simulation Of Pulverized Coal Gasifier With High-Speed Air Jet

Coal gasification is one of the key technologies to utilize coal cleanly and efficiently.According to the process methods,it can be divided into three categories:fixed bed,fluidized bed,and entrained-bed gasification technology.Among them,the entrained-bed gasification technology has advantages of wide coal adaptability,large processing capacity,and high carbon conversion,but its high-temperature and high oxygen concentration requires high-cost materials.In this paper,based on the idea of MILD combustion,the gasification atmosphere of "high temperature and low oxygen"and the uniform mixing of pulverized coal are created through the high-speed air jet,and the gasification efficiency can be improved by the homogeneous and distributed gasification reaction in the furnace.In order to study the coal gasifier with high-speed air jet,this paper takes the pulverized coal gasifier as the research object,and the main tasks are as follows:(1)The gasifier geometry model was chosen as height of 4 m and an internal diameter of 0.8 m.According to the selected coal,the amount of air and coal was determined.Based on the operating characteristics of the pulverized coal gasification,the appropriate numerical model and chemical reaction mechanism were selected and validated.(2)Numerical method was employed to study the impact of relative positions of jet nozzles,jet velocity,particle size distribution on the flow field in the gasifier,the flue gas recirculation ratio,the average particle residence time,the concentration distribution of pulverized coal particles under on-reacting state.It was found that the distribution of the flow field in the gasifier was greatly affected by the position and velocity of the secondary air jet,and the reflux ratio firstly increased and then decreased with the increase of the secondary air jet nozzle spacing,and the maximum value was about 4.The average residence time of pulverized coal particles was greatly affected by the secondary air jet velocity.The faster the jet velocity,the shorter was the particle residence time.When the jet velocity was 120 m/s,the residence time was 4.8 s;the peak value of coal particle concentration appeared at 1 m distance from the entrance.And the greater the jet velocity,the greater was the degree of dispersion of pulverized coal.(3)The numerical method was employed to study the velocity distribution,temperature distribution,and species distribution characteristics of the gasifier under the reacting state.The experiment was performed on the existing gasifier to verify the reliability of the numerical model.The computational results showed that the jet velocity and turbulence intensity decayed rapidly within 0?1.5 m in the axial direction of the furnace,and there was a clear recirculation zone in the flow field.In this zone,the backflow of flue gas and the newly entered coal powder and oxidant were fiercely mixed.The furnace temperature distribution was relatively uniform,and the maximum temperature occurred at 1.5 m.The concentration of CO2 firstly increased and then decreased;the concentration of CO increased slowly,and reached its maximum value at the outlet.(4)The effects of process parameters and structural parameters on the gasification performance of the gasifier with the high-speed air jet were studied by numerical method.The impacts of oxygen-carbon atomic ratio,load,particle size,the heat loss,furnace height,and furnace diameter on the temperature and species distribution,the syngas quality,and the carbon conversion were investigated.