Dry coal separation has been the most significant process in the field of coal beneficiation to date, because of its special advantage of operation with no water consumption. Mineral dry separation research has received wide attention, particularly in countries and regions experiencing drought and water shortages.During the process of dense coal gas–solid fluidized bed beneficiation, the material is stratified according to its density; the high density material layer remains at the bed bottom, and thus the high density coarse particle bed becomes an important influencing factor in fluidized bed stability. In the steady fluidization stage, a small number of large radius bubbles are the direct cause of unsteady fluidization in the traditional fluidized bed. The dispersion effect of the secondary air distribution bed for air flow is mainly apparent in the gas region; when the particle size exceeds 13 mm, the secondary air distribution bed has a synergistic effect on the density stability of the upper fluidized layer. When the particle size is small, especially when less than 6 mm, particles will constantly move, accounting for instability of the secondary air distribution bed and distorting the stability of the upper fluidized bed. Under optimum operation conditions, the probable deviation E of gas–solid separation fluidized with a high density coarse particle layer can be as low as 0.085 g/cm3.
Bed stability, and especially the bed density distribution, is affected by the behavior of bubbles in a gas solid fluidized bed. Bubble rise velocity in a pulsed gas-solid fluidized bed was studied using photographic and computational fluid dynamics methods. The variation in bubble rise velocity was investigated as a function of the periodic pulsed air flow. A predictive model of bubble rise velocity was derived: ub=ψ(Ut+Up-Umf)+kp(gdb)(1/2). The software of Origin was used to fit the empirical coefficients to give ψ = 0.4807 and kp = 0.1305. Experimental verification of the simulations shows that the regular change in bubble rise velocity is accurately described by the model. The correlation coefficient was 0.9905 for the simulations and 0.9706 for the experiments.
Dong LiangZhao YueminLuo ZhenfuDuan ChenlongWang YingweiYang XuliangZhang Bo
In order to study the settling mechanism of particles in an air-solid magnetically stabilized fluidized bed(MSFB) for separation,we carried out free settling and quasi-zero settling tests on the tracing particles.The results show that the main resistance forces as the tracing particles settled in an air-solid MSFB were motion resistance force and yield force.The motion resistance and yield forces greatly hindered the free settling of the particles by greatly decreasing the acceleration for settling process of the particles.The acceleration decreased from 3022.62 cm/s 2 to zero in 0.1 s,and in the end,the particles stopped in the air-solid MSFB.The yield force on particles increased with increasing the magnetic field intensity,resulting in decrease of the quasi-zero settling displacement.However,the yield force on particles decreased with increasing the fluidized air velocity,leading to increase of the quasi-zero settling displacement.When the structure and operating parameters of the air-solid MSFB were set up,the yield stress on particles stopped in an air-solid MSFB was a function of diameter and density of particles.The settling displacements of equal diameter particles increased with increasing their densities,and the settling displacements of equal density particles increased with increasing their diameters.
Song Shulei a,,Zhao Yuemin a,Luo Zhenfu a,Tang Ligang b a School of Chemical Engineering and Technology,China University of Mining & Technology,Xuzhou 221116,China b Coal Mining and Designing Department,Tiandi Science & Technology Company Co.Ltd.,Beijing 100013,China
