Study On The Spatial Characteristics And Bubble Behavior In Gas-Solid Separation Fluidized Bed

Coal has always played an important role in primary energy consumption in China.Based on the strategic demand for efficient recovery and high-quality utilization of coal resources,it is urgent to develop the theory and technology of efficient gas-solid fluidization separation in western water-deficient areas.Gas-solid fluidization separation is an effective dry separation technology,the related research mainly focuses on particle properties,operating conditions,and applied energy,and there are fewer studies based on the overall and local inhomogeneity of the gas-solid fluidized bed and the regulation of the fluidization effect by air distributors.Therefore,in this work,the spatial characteristics of gas-solid separation fluidized bed and the basic theoretical research work is carried out to form a stably fluidized bed by the regulation of bubble behavior.The pressure drop fluctuations of the gas-solid fluidized bed under different gas velocities and air distributors were investigated,and the density distribution was used to characterize the basic spatial characteristics of the gas-solid fluidized bed.The results illustrate that the drastic fluctuations of bed pressure drop are mainly caused by the uneven distribution of the gas phase and the generation and movement of bubbles.As the bed height increases,the fluctuation range of the pressure drop signal increases and the density distribution of the bed is small at the center and large at the edges.Geo Detector is a new statistical method to reveal spatial differentiation and the driving factors behind it.This method is introduced to quantify the dominant factors of axial spatial position,radial spatial position,gas distributor,and gas velocity on the spatial characteristics of the bed.The interaction between the factors was quantified by the characteristic indexes of bed uniformity,q-value,and solid mass flow rate,corresponding to q _Axial=0.9423>q _Gas=0.0199>q _Radial=0.00078>q _Distributor=0.00021.The interactive relationship between variables on the spatial characteristics of gas-solid separation fluidization shows a nonlinear enhancement,which proves that there is a certain overall and local dependence of the fluidization spatial differentiation phenomenon,and increasing the gas velocity can improve the particle spatial distribution uniformity in a certain range.The solid particle flow has an obvious non-uniform characteristic in the axial space,and the theoretical solid mass flow rate model is modified by introducing the bed expansion rate.The error of the result is controlled within 20%,and the error of the machine learning result is within 15%,which achieved a better prediction result.A semantic segmentation method based on deep learning for bubble identification in a gas-solid separation fluidized bed was developed.The automatic segmentation recognition of dense medium and bubbles was achieved by using the deep learning model DeepLab V3+.The powerful feature representation learning ability of convolutional neural network shows high accuracy for bubble recognition,with pixel accuracy of 0.9776 for the image taken at near fluidized bed and 0.9795 for the whole bed image,and MIoU of 0.7969,0.8091,respectively.The model has strong portability and improves the efficiency of experimental analysis.The formation of bubbles under the single-hole distributor,double-hole distributor,and the uniform perforated plate was investigated,and the characteristic parameters such as bubble equivalent circle diameter,bubble shape factor,bubble void fraction,and bubble velocity were used to characterize the properties of bubbles under different air distributors.According to the motion of single bubbles,it is concluded that the coalescence of gas-solid fluidized bed bubbles is mainly dominated by the leading trailing.The penetration height of single jet bubbles is mainly related to the diameter of the air distributor,and the larger diameter is,the more unstable the penetration height of bubbles is,corresponding to the heavier the mass disturbance is in the jet area.The smaller the aperture,the greater the number of bubbles in the distribution plate area,the farther the distance from the air distribution,the greater the standard deviation of the percentage of bubble area,and the greater the perturbation of the bed by the aggregation and rupture of bubbles.The hole pitch is the main reason for inducing the dead zone in the bed,and the dead zone area decreases in a certain range when the gas velocity increases.The bubble aggregation under the uniform perforated plate is the main reason for the increase in its bubble size.Besides,bubble velocity and bubble size are proportional.Different air distributors were designed to study bubble behaviors.It is demonstrated that the non-uniform air distributor intensifies the lateral motion of bubbles,increases the bubble splitting probability,induces the splitting of large bubbles into small bubbles,and prolongs the bubble motion time.The initial size of the bubbles is the main reason affecting the bubble aggregation behavior and the average size change,which is directly related to the air distribution plate.The coalescence of bubbles in the uniform perforated plate can be divided into fours stages:slow coalescence stage（K_b=-0.01351）,accelerated coalescence stage（K_b=-0.06324）,stable coalescence stage（K_b=-0.0135）,and splitting dominant stage.The bubble coalescence in the sintered plate can be divided into two stages,accelerated coalescence stage（K_b=-0.03332）and decelerated coalescence stage（K_b=-0.02753）.The bubble size distribution model is obtained for the bubble collision and coalescence in random space,and the bubble size distribution model is obtained.The spatial distribution characteristics of the bubbles were studied by using the time-frequency domain analysis method.The region close to the air distributor showed a wide range of high-frequency and low-magnitude activities,and the region far from the air distributor displayed low-frequency and high-magnitude activities with a smaller number of bubbles.The improvement of fluidization quality in the gas-solid fluidized bed was enhanced by using microplates,and the E was 0.094g/cm³ at the fluidization number of 1.6.In summary,the separation performance in a gas-solid separation fluidized bed was significantly improved under the micro-plate distributor.There are 108 figures,12 Tables and 223 references in this dissertation.