Study On Flow Characteristic Of Gas-solid Fluidized Bed For Particles With Wide PSD

The traditional blast furnace has many problems such as long production process,huge investment, high energy consumption and reliance on coke heavily. The contradiction between the development demand of iron and steel industry and the supply of coke has become increasingly prominent with the increasing scarcity of coking coal resources. This has become the fundamental driving force for the research and development of non-blast furnace ironmaking. In the process of non-blast furnace,which is represented by fluidized reduction, it is concerned that it is not needed to use coke and can use the iron ore powder directly. The fluidized reduction of iron ore powder is a typical gas-solid two-phase mutual function process, if we fully understand the gas-solid two-phase flow characteristics and rules in fluidized bed, will be able to provide theoretical guidance for the optimization of process parameters in practical industrial applications, and can provide a theoretical basis for fluidized bed reactor design and amplification. In the application of industry production, the reaction material in the fluidized bed reactor is wide particle size distribution of particles. Therefore, the research on the flow characteristics of the particles with wide particle size distribution in the fluidized bed will help to fully understand the complex flow patterns inside the fluidized bed, so as to guide the practical production process.In the two-dimensional fluidized bed, this paper first conducted experiments with three type of wide particle size distribution of particles, including binary mixture,normal distribution and uniform distribution. Based on this, we studied the initial fluidization velocity of particles with different particle size distribution, and compared the experimental results with the calculation results of the critical fluidization velocity.And analyzed the differences and influencing factors. With the help of high-speed camera, the pictures of two-dimensional bed have been obtained. By using digital image analysis technology to deal with photographs, get what we pay close attention to the information on the bubble inside the two-dimensional bed. Simultaneously, we studied the two-dimensional bubble properties of wide size distribution of particles. On the basis of experiments, the relations of average bubble diameter and the bubble rise velocity are summarized. In addition, by taking photos to record the change of bed height, studied the bed expansion ratio and influencing factors of wide particle size distribution of particles. Through the experimental research, it is found that wideparticle size distribution of particles may occur segregation in the process of fluidization.Compared with normal distribution of particles, the binary mixture of particles and uniform distribution of particles are more likely to appear segregation.In the three-dimensional fluidized bed, the results of initial fluidization velocity calculated by the formula summarized in the two-dimensional fluidized bed are larger than the experimental results in the three-dimensional fluidized bed. This is because the two-dimensional fluidized bed exist wall effect, and particles need to overcome the greater resistance in the process of fluidization. This paper conducted experiments with normal distribution and uniform distribution of particles. We measured the instantaneous value of pressure along the axial direction of fluidized bed. The experimental results indicate that the pressure drop in the same bed height increases with the increase of superficial gas velocity. And in the same conditions of superficial gas velocity, the axial pressure drop of particles with wide particle size distribution is positive proportional to the static bed height. The pressure drop of particles with normal distribution continues to rise at about the same rate. But the particles with uniform distribution will appear segregation in the process of fluidization, the large particles sink on the bottom of bed and small particles float on the top of bed. Therefore the rising rate of pressure drop at the bottom of bed is large than the top of bed. The pressure fluctuation variance of particles with normal distribution increases firstly, and then decreases along the axial height of bed. And the pressure fluctuation variance of particles with uniform distribution always increases along the axial height of bed. In addition, by comparing with the axial pressure of the two dimensional bed and three dimensional bed, it is proved that the boundary effect of the three dimensional bed is weaker than that of the two-dimensional bed.