Experimental Study On Gas-solid Two-phase Fluidization Characteristics In Bubbling Fluidized Bed

The fluidized bed reactor is the main equipment of FINEX technology that is new metallurgical process,because it not only can fully mix reducing gas and iron ore fines but also can significantly strengthen gas-solid two-phase heat transfer,mass transfer and reaction process.However,it is difficult to understand what the law of gas-solid flow is in the fluidized bed duo to the complexity and nonlinearity.In addition,it is hard to design,amplify and optimize the operating conditions of fluidized bed.According to the theory of multi-phase flow,an experimental system was designed and built to control particle pass in and out of the bubble fluidized bed in this thesis,and the fluidization characteristics about gas-solid two-phase was explored in three-dimensional bubbling fluidized bed based on different particle properties and inlet-outlet regulation.The glass beads of Geldart group B with 500~600?m was chose as material during the experiment.The fluidization characteristics of gas-solid was studied in threedimensional beds,and the validity of the experimental system was tested.Glass beads minimum fluidization velocity was measured,the value was 0.227m/s,and comparing with Wen-yu formula,the error of the calculated value was-0.8%.There are the same regulation between measured value of rising bubble velocity in the bed and calculated value via the Davison formula,the feasibility of the experimental system was verified for this thesis.Comparing with experimental data of three-dimensional bed and twodimensional bed under the same initial bed height conditions,we found that the error of minimum fluidization velocity was-1.3%,and the error of bubble velocity in rising was 2 to 4 times.Thus,the study also demonstrated that there is a weak wall effect in the three-dimensional bed.The wall effect made the gas velocity of the particle fluidization smaller,and less impediment to rising movement of bubble.To study the fluidization characteristics of Australian ore fines with a narrow particle size distributional,and compare them with the experimental results of two-dimensional beds.The experimental study on the fluidization characteristics of Australian ore fines with a particle size distribution of 500~600?m shown that there were progressive fluidization phenomena which caused by the degradation problem of ore fines in both three-dimensional bed and two-dimensional bed.Moreover,according to the bed porosity and sphericity of ore fines,a formula was updated based on Wen-Yu and Gupta,and the critical fluidization velocity of Australian ore fines was calculated via this formula.The result of verification experiments for 100~500?m(change by 100?m)Australian ore fines shown that the average error between measured value and calculated value of the minimum fluidization velocity was 6.2%,and for complete fluidization velocity was 5.8%.The formula was suitable for calculating the critical fluidization velocity of Geldart group B with narrow size distribution of Australian ore finesThe Australian ore fines of Geldart group B with a size of 500~600?m was mixed various volume ratios with 200~300?m,400~500?m and Australian ore fines of Geldart group D with 600~800?m,800~1000?m to explore the fluidization characteristics,respectively.The experimental results shown that progressive fluidization was observed when mixed Australian ore powder between Geldart group B and B was fluidized.Nevertheless,obvious localized fluidization was appeared when the Geldart group B and D ore fines were mixed and fluidized,and the smaller ore fines would escape from the bed so that pressure drop in bed was reduced.It was further explained that the smaller ore fines would change the size distribution of the Australian ore fines,which in turn to affect the fluidization characteristics of the Australian fines.Finally,the critical fluidization velocity measurement of Australian fines with mixed particle size distribution was compared with calculated value of the corrected formula,and the applicability of the modified formula was verified.We carried out the experimental study of the feeding and discharging control in bubbling fluidized bed system,and found the glass beads of Geldart group B with a size of 400~500?m went through four stages when particles from rest to fluidization: system startup,material pressure storage,bed and material leg coordination,bed and material leg particles circulation movement.The velocity of the particles at the leg was related to the superficial velocity,initial static bed height and the average particle size.The superficial velocity increased,the initial static bed height increases,and the average particle size smaller,the particles velocity of the material leg would increase;this relationship was only valid within the self-regulating range of the system.In summarize,from the aspect of different particle properties,it was found that Australian ore fines of Geldart group B and D not only have similar fluidization characteristics as conventional Geldart group B and D particles but also have unique fluidization characteristics such as degradation and progressive fluidization.Additionally,from respects feeding and discharging control,we explored and obtained the influencing factors for the process of particles feeding and discharging in bubbling bed.This thesis may provide basic data and reference for the further development of FINEX pre-reduction technology in non-blast furnace ironmaking.