Experimental Study On The Flow Characteristics Of Heterogeneous Structures In Bubbling Fluidized Beds

With the increasing depletion of coke resources and the increasingly strict requirements of environmental protection,blast furnace ironmaking process is facing unprecedented challenges due to its high pollution,high energy consumption,high material consumption and other problems.The fluidization reduction ironmaking process can directly use iron ore fines,which can save the most seriously polluted sintering and coking process in the blast furnace ironmaking process,get rid of the dependence on coke resources,and become an important direction for the development of non-blast furnace green metallurgy technology.Gas-solid two-phase fluidization is a complex non-linear,non-equilibrium,multi-scale problem with typical heterogeneous structure operating characteristics,so it is of great significance to study the heterogeneous structure and its evolution characteristics in the process of gas-solid two-phase fluidization for the development and application of fluidization reduction ironmaking process.This paper first analyzes the basic characteristics of gas-solid two-phase fluidization,then studies the heterogeneous structure and its evolution characteristics in the bubbling fluidized bed,and discusses the fluctuation of bed pressure drop,critical fluidization velocity,bubble behavior,macro-segregation,particle pulverization,bed expansion rate and other basic character description problems,and further study of the formation mechanism and evolution law of heterogeneous structure in bubbling fluidized bed.The research contents and results are summarized as follows:(1)Due to the "side-wall effect",the two-dimensional bubbling fluidized bed has a significant "hysteresis effect" during the ascending fluidization process,which makes the minimum fluidization velocity and the full fluidization velocity greater than the threedimensional bubbling fluidized bed.The modified parameters of the two-dimensional and three-dimensional bed minimum fluidization velocity and full fluidization velocity are obtained by experiments,and it is clear that the method based on Ergun formula and WenYu formula minimum fluidization velocity is suitable for two-dimensional bubbling fluidized bed,the method based on single particle force analysis minimum fluidization velocity is suitable for three-dimensional bubbling fluidized bed;the full fluidization velocity correction formula and method are suitable for two-dimensional bubbling fluidized bed and three-dimensional bubbling fluidized bed.(2)In a two-dimensional bubbling fluidized bed,the Bubble equivalent diameter increases linearly with the increase of superficial gas velocity,and the Bubble equivalent diameter increases linearly with the increase of axial height.At the same time,the rising velocity of bubbles increases with the increase of superficial gas velocity,and the rising velocity of bubbles increases linearly with the increase of axial height.For solid particles with wide particle size distribution,segregation will occur in the fluidization process,resulting in the stratification of particles.(3)When Australian iron ore powder particles begin to expand in the bubbling fluidized bed,the bed expansion height increases linearly with the increase of the superficial gas velocity;the correlation of bed expansion rate of three-dimensional bubbling fluidized bed established according to the experimental data has a good applicability in predicting the bed expansion rate of Australian iron ore powder particles in the three-dimensional bubbling fluidized bed with an average error of less than 3%;In the bubbling fluidized bed,fine suspended particles will appear in the upper part of the bed and the particle size is obviously less than 800?m after fluidizing for a period of time,which indicates that the particles of Australian iron ore powder have been pulverized in the fluidizing process.Through the two-dimensional bubbling fluidized bed and the three-dimensional bubbling fluidized bed cold state experimental study,it provides a theoretical basis for the dynamics of the development of fluidized metallurgy technology.