Search

Although the filtration efficiency can be increased because of the use of small-sized particles in granular beds, the bed pressure drop may be increased. This study presents a numerical solution of a moving bed that can facilitate instantaneous separation of binary particles into a top layer of larger particles and a bottom layer of smaller particles during the flow. The particle discrete element method is used to simulate the flow process of binary particles, which is verified by experiments. An index to measure the effect of stratification and the separation degree (SD) are proposed. Results show that SD increases as the particle size ratio and the mass fraction of coarse particles increases. The thickness of the coarse particle layer increases as the mass fraction increases. The surface thickness and segregation are within the optimum when the particle size ratio is 2.5 and the mass fraction of coarse particles is 65%.

A moving granular bed with a dual-layer particle structure was designed on the basis of the segregation performance of binary particle flow, and the stratification characteristics of the filter area was studied by using experiment and simulation methods. The results show that the segregation degree (SD) in the filter area is related to the inclined groove length (L) and the binary particle size ratio (γ); specifically, the SD increases with the increase in the L and the γ. When the SD reaches the maximum, a significant dual-layer particle structure appears. On this condition, the SD no longer rises with the increase in the γ or the L. When the SD reaches the maximum, the thickness percentage of the coarse particle layer in the filter area is approximately equal to the mass percentage of coarse particles in the mixed particles.

This study is based on high-temperature flue gas containing condensed dust and the dust removal of granular bed. The effects of adhesion temperature, filter plate material (99% and 85% corundum), and dust materials (tin, ferric oxide, and fly ash mixed with sodium chloride) on the desorption stress of dust on the filter surface are explored through desorption stress tests. Results show that the desorption force of tin peaks at 800 °C. Adhesion at 900 °C for fly ash blended with sodium chloride. The mixture adheres on the filter surface at >800 °C, and desorption force increases as adhesion temperature and sodium chloride proportion increase. Large desorption stress occurs on the extremely rough surface of the filter material.

In this work, we studied the flow characteristics of particulates in a novel moving granular bed by using experiments and numerical simulations. The new moving granular bed was equipped with one adjustable baffle and two slopes to adjust filter thickness and increase the gas-particle contacting surface. Doing so overcomes the poor adaptability and low collection rate of fine dust during the filtration, and improved the filtering performance of filter devices. In the experiment, the movement of particulates in a moving bed was recorded using a camera, and the effects of the device structure and the filter moving speed on the flow of filter particles were examined. Combined with Discrete Element Method (DEM) to simulate the velocity variation of particles in the granular bed, the mechanism of particulate flow was analyzed. The inclined surface was found to affect the flow of filter particles, and a small angle of inclination was not conducive to the particle flow. Therefore, a layer of dead particles was easily formed. The dead zone particle layers on the left slope could protect the insulation layer and the heat insulation layer outside the particle bed. Increasing the moving speed of the filter increased the velocity difference between the particles in the wall surface and the middle part. The fluidity of particles also increased to make the particle layer of dead area become thinner. The trajectory of a single particle was greatly affected by the overall moving speed, and the single particle tended to move toward the faster direction in the same plane with the increase of the filter moving speed.

The entrainment characteristics of fine silicon particles from solid mixtures (Geldart groups C and B) are investigated in a cylindrical fluidized bed with an inner diameter of 30 mm and a height of 450 mm and that is equipped with an agitator and an electromagnetic vibration table. Silicon particles (mean size of 2.7 μm) are used as entrained materials (group C), hollow alumina pellets (mean size of 1200 μm) are used as coarse particles (group B), and nitrogen gas is applied as carried gas. The effects of the superficial velocity of nitrogen gas at room temperature (U, 0.39 m/s to 0.98 m/s), the initial loading quantity of fine particles (M, 5 g to 20 g), the vibration intensity (Γ, 1.3 to 4.83), the stirring speed of agitator (V, 75 rpm to 195 rpm), the mass ratio of coarse to fine particles (N, 0 to 1.5), and the preheating temperature of nitrogen gas (T, 20 °C to 170 °C) on the entrainment characteristics (entrainment rate Wi and entrained powder–gas ratio R) are experimentally studied under atmospheric pressure. Significance analyses of U, M, Γ, and V are performed via the analysis of variance. M and U both significantly affect Wi, but only M significantly affects R. The experimental results show that an increase in U, M, N, and T constantly improves the entrainment characteristics, an increase in Γ deteriorates such characteristics, whereas there exists an optimal value for V to obtain the optimum entrainment characteristics. This study also determines that an optimal operating condition can result in optimal entrainment characteristics (Wi, 9.27 g/min and R, 0.19 g/g), which can be achieved with a U of 0.98 m/s, M of 20 g, Γ of 1.3, V of 155 rpm, N of 1.0, and T of 170 °C.