Influence Of Entrained Gas On Discharge Process Characteristics Of Geldart D Particles In Moving Bed

The discharge problem of Geldart D particles,e.g.,catalyst,granular coal,widely exists in industrial and agricultural production processes,e.g.,catalytic reforming,coal combustion,ethylene polymerization,gasoline desulfurization.With the gas introducing,the flow behavior of particles is improved,which including the promotion of the solid flow rate and inhibition of the arch formation,Besides,the solid flow rate can be adjusted flexibly,which enhances the bed efficiency.At present,there are few studies on the influence of different positive and negative pressure difference conditions in the study of regulating Geldart D particle discharge rate by introducing gas,and there is no study on the change rule of particle discharge rate in intermittent discharge process,especially after introducing gas.In this paper,a set of cold model test device is built up.Before and after the gas introduction,the pressure distribution is measured as well as the,solid flow state and flow rate of Geldart D particles in both intermittent and continuous beds.The influence of the gas introduction on the gas-solid two-phase characteristics of the bed is revealed.The calculation models of pressure drop and particle flow rate are then established,which provides a reference for the adjusting Geldart D flow rate by gas introduction.The results show that,in both intermittent and continuous discharge processes,the gas-solid two-phase flow characteristics differences from each other during different periods of time.Thus,the flow stages are firstly divided according to the variation of particle flow state and pressure value.The gas and particle flow characteristics of each stages are then investigated.The calculation formula of solid flow rate is also established.The intermittent discharge process can be divided into three stages:initial pressure-storage PS stage,stable discharge SD stage and partly-filled pipe-flow PP stage.Considering that the bed height remains almost unchanged with time,the continuous discharge process is divided into two stages:initial pressure-storage PS stage,stable discharge SD stage.The partly-filled pipe-flow PP stage doesn’t exist in the continuous discharge process.According to the characteristics of gas flow,the computation formulas suitable for both intermittent and continuous bed,e.g.,bed pressure dropΔp_b,particle resistanceΔp_o1 and local resistanceΔp_o2 at the discharge orifice.The formulas are determined by the fitting method based on the experimental data.However,due to the gas and solid flow characteristics differs in discharge modes and each stage,the pressure drop is got by the selectively summation of above formulas.According to the characteristics of solid flow,includes the average width of solid flow area,the size of solid dead flow area and the range of surface particle slope area,In both the intermittent and continuous discharge processes,the solid flow distribution is more uniform under positive pressure-difference condition;the uniformity increases with the growing of the gas velocity.It is vice versa under negative pressure-difference condition.At the same time,the solid flow has more uniform distribution in continuous bed than the intermittent one.In both intermittent and continuous discharge processes,it is found that the particle resistance at the discharge orifice is the key parameter affecting the particle flow rate in SD stage,which has long time and stable flow field.By modifying the formula of pressure drop at discharge orifice proposed by De Jong and the Beverloo correlation,the prediction models of particle resistance at the discharge orifice and the particle flow rate of Geldart D particles are established successively,which are in good agreement with the experimental values.