Research On Hydrodynamic Characteristics Of Three-Phase Inverse Internal Circulating Fluidized Bed

In the project,light particles are introduced into a three-phase internal circulating fluidized bed system,and a new type of three-phase inverse internal circulating fluidized bed is custom-designed and constructed.The influences of different operating parameters on its basic hydrodynamic characteristics were comprehensively investigated,which could provide theoretical guidance for the development and industrial applications of such new fluidized bed reactors.Firstly,the operating conditions of a fixed initial height of three-phase separation zone are determined by observing the influence of the initial height of the three-phase separation zone on the flow state of the three-phase inverse internal circulating fluidized bed.Minimum fluidization gas velocity and minimum circulating gas velocity in the three-phase inverse internal circulating fluidization system were defined respectively based on flow state in the bed.And,an initial height of three-phase separation zone was decided via tests and kept on the same height for all the experiments.The effects of operating parameters as initial particle loading,particle diameter,and particle density on minimum fluidization gas velocity and minimum circulating gas velocity were fully investigated.The results show that the minimum fluidization gas velocity increases with particle loading and particle diameter,while decreases with particle density.The minimum circulating gas velocity also decreases with particle density while increases with particle diameter.However,when the particle loading gradually increases involving PE2,PE3 and PP particles,the minimum circulating gas velocity shows a trend of decreasing first and then increasing.For PE1 particles,the minimum circulating gas velocity increases with the particle loading.Secondly,the measuring instrument for particle concentration,named PC6 M,was applied to measure the local solids holdup at different axial positions and radial positions.With the increase of the superficial gas velocity,when the PE1 particles expand to the entire bed,the distribution of particles in the axial direction of the bed shows a trend of ups and downs.In the radial direction,the distribution of solids holdup at the bottom of the bed is relatively uniform,but in the upper part of the bed,the distribution of solids holdup fluctuates greatly in the radial direction due to the influence of the bubble flow at the top of the draft tube.Finally,the effects of the diameter of the gas distributor and the diameter of the draft tube on the hydrodynamic characteristics of particles in the three-phase inverse internal circulating fluidized bed were also studied.When the particle loading of PP particles is 5%,as the diameter of the gas distributor increases,the minimum fluidization gas velocity is stable.When the particle loading of PP particles are 7.5%,10% and 15%,as the diameter of the gas distributor increases,the minimum fluidization gas velocity tends to decrease slightly.For four different particles with the same particle loading,the minimum fluidization gas velocity decreases slightly with the increase of the gas distributor’s diameter.Under different particle loadings,the minimum circulating gas velocity of PP particles increases with the diameter of gas distributor.At the same particle loading,the minimum circulating gas velocity in the cases of PP particles,PE3 particles and PE2 particles increases with the diameter of gas distributor,while the minimum circulating gas velocity for PE1 particles decreases slightly with the diameter of gas distributor.With the increase of the inner diameter of the draft tube,the gas volume flow rate of PE2 particles under different particle loadings showed a gradual decrease during the minimum circulating,while the gas volume flow rate showed a gradual increase during the minimum fluidization.