Experimental Studies on Hydrodynamics of a Cyclone Separator Employed in a Circulating Fluidized Bed

Abstract

Hydrodynamics of a cyclone separator as element of a re-circulating fluidised bed circuit has been studied experimentally. The main efforts have been addressed the solids suspension density distribution along the cyclone axis at various solids circulation rates. In general, the suspension density decreases in the downward direction and becomes least in the cyclone conical section. At the cyclone exit it starts increasing and this trend persists in the dipleg of downcomer. The suspension density decreases as the bed inventory in inlet section of cyclone is increased and the solids circulation rate in the cyclone-downcomer branch of the fluidized bed circuit. It is to be noted that use of fluidized bed keeps the environment more clean. by direct measurements are in good agreement with those calculated from the measured solids concentration and velocity. The shapes of the radial solids flux profiles in three risers were found to be either flat with decreasing annulus or parabolic, depending on the operating conditions. The shape of the radial solids flux profile could be predicted using the effective saturation capacity, above which a parabolic profile prevails due to the increased solids down flow near the wall. The radial profile of solids flux is less uniform in a larger riser than in a smaller riser. The amount of down flowing solids is highest in the lower sections of the riser, but then begins to decrease as the measuring point is moved away from the distributor. Increases in Ug (superficial gas velocity) cause the amount of down flowing solids at the wall to decrease, resulting in a more flat radial profile of the solids flux in the columns. Increasing Gs (overall solids circulating rate) increases the amount of down flowing solids, resulting in a more parabolic shape. The flow development is affected in the same manner in different diameter columns: increases in Ug or decreases in Gs reduce the length of development. Flow development is slower with the increase of riser diameter by Yan et al. (2). The experimental work was carried out in a 12 MWth CFB boiler and in a cold CFR Three different distributions of the bubble flow in time and space, termed fluidization regimes, were identified in the cold CFB: the multiple bubble regime with many small bubbles evenly distributed in the bed; the single bubble regime, characterized by the presence of only one bubble at a time in the bed; and the exploding bubble regime with large, single, irregular voids stretching from the air distributor to the bed surface. These bubbling conditions were observed during variations in the gas velocity and the distributor pressure drop. A comparison with the 2-m2 cross-section CFB boiler showed that the boiler always operates in the single or in the exploding bubble regime, which indicates a bubble flow that is not continuous and not well distributed over the cross-section of the bed. Afsin Gungor worked on (3) a dynamic two dimensional model is developed considering the hydrodynamic behavior of CFB. In the modeling, the CFB riser is analyzed in two regions: The bottom zone in turbulent fluidization regime is modeled in detail as two-phase flow which is subdivided into a solid- free bubble phase and a solid-laden emulsion phase. In the upper zone core-annulus solids flow structure is established. Simulation model takes into account the axial and radial distribution of voidage, velocity and pressure drop for gas and solid phase, and solids volume fraction and particle size distribution for solid phase. The model results are compared