Fluidized Bed Gas-solid Flow Characteristics And Numerical Simulation And Enhancement Of Coal Gasification Process

"Rich coal,poor oil and little gas"is the current situation of resource distribution in China.The conversion and utilization of coal is a current research highlights.Coal gasification technology,which is the source technology of coal-to-natural gas,is also the top priority of research work.Because fluidized bed coal gasifier has higher efficiency of heat and mass transfer and gas-solid contact,it is an ideal coal gasification reactor.In this paper,a laboratory fluidized bed reactor is used as a physical model,and the gas-solid two-phase flow process in the fluidized bed reactor is numerically simulated based on the CPFD method.The accuracy of cold simulation was verified through experiments.It was studied that the velocity field and pressure field distribution in the fluidized bed during the particle fluidization process and gas-solid flow pattern changes during the particle fluidization process.It was explored that influence of the initial bed material height,gas velocity and gas pressure on axial and radial particle volume fraction distribution.Based on the cold simulation,the thermal simulation of the fluidized bed coal gasification process is carried out with the Xinjiang Zhundong coal as the object.The thermal simulation method was established,and the accuracy of the simulation method was verified through literature data.They were studied including field distribution of temperature and each component gas concentration in the fluidized bed,and the main reaction rate change law of the coal gasification reaction during the coal gasification process.The effects are discussed that influence oxygen-to-coal ratio,steam-to-coal ratio,and coal particle size on coal gas calorific value,production rate,gasification efficiency and carbon conversion rate.Optimizing conditions of fluidized bed coal gasification process by response surface analysis.It was optimized that structure of the fluidized bed air inlet device.They were used to evaluate the particles uniformity and bed stability that minimum fluctuation variance of the cross-sectional average particle concentration,fluid velocity,and particle velocity.it were determined that appropriate nozzles number,inclination angle of air distribution board,spouting fluidization gas velocity ratio and particle size.The results show that:(1)When the initial bed material height H=1.2 m,the bed space utilization is the largest;when the fluidization gas speed U=1 m/s,the particle axial and radial concentration distribution is more uniform;when the fluidization gas pressure P>0.4 MPa,the phenomenon of particle clusters is serious,which is not conducive to particle fluidization.(2)Both CO and H₂,the effective components of gas,show the characteristics of‘Thick on top and thin on bottom'.(3)As the oxygen-to-coal ratio(0.2?O₂/Coal?0.8)increases,the gasification efficiency first increases to then decreases,?_max=0.723,the carbon conversion rate first increases and then stabilizes,with a stable value of 78%;The steam-to-coal ratio(0.2?H₂O/Coal?0.7)increases,the gasification efficiency decreases,and the carbon conversion rate first increases and then stabilizes,with a stable value of 70%;with the coal particle size of coal(1 mm?d_c?6 mm)increases,gasification efficiency and carbon conversion rate both first increase and then decrease.When d_c=3 mm,?_max=0.72,?_c,max=0.65.(4)The weight of the influence of each factor on the gasification efficiency is:oxygen-to-coal ratio>coal particle size>steam-to-coal ratio;the optimal combination of response surface process conditions is:O₂/Coal=0.476 kg/kg,H₂O/Coal=0.607 kg/kg,d_c=3.185 mm,at this time the maximum gasification efficiency?_max=0.751.(5)When the number of nozzles is 3,the inclination angle of the air distribution plate S_a=45°,the spouting fluidization gas velocity ratio R=2,and the particle size d=1.8 mm,the particle concentration distribution in the bed layer is more uniform,and it is better that the particle bed layer stability.