Minimum fluidizing velocity of solid granular in fluidized bed with filter unit inserted-in

Successful development of advanced coal-fired power conversion systems, such as IGCC and PFBC etc., often require reliable and efficient cleanup devices which can remove particulate and gaseous pollutant from high-temperature high-pressure gas streams. A novel fluidized-bed granular filter (FBGF) is under developing in State Key Laboratory of Coal Combustion (SKLCC) which can be applied in advanced coal-fired power conversion systems. The filtration system consists of fine metal screen filter immersed in a fluidized bed of granular material. As the gas passes through the fluidized bed, a layer of the bed granular material is entrained and deposited at the screen surface. This material provides a nature granular filter to separate fine particles from the gas stream. Since the filtering media is the granular material supplied by the fluidized bed. the filter is not subject to blinding like candle filters. Because only the in-flowing gas, not fine particle cohesive forces maintains the granular layer at the screen surface, once the thickness and permeability of the granular layer is stabilized, it remains unchanged as long as the in-flowing gas flow rate remains constant. The weight of the particles and the turbulent nature of the fluidized bed limit the thickness of the granular layer on the filter, leading to self-cleaning attribute of the filter. Minimum fluidizing velocity, u(mf), is a key factor to design FBGF and determine its acceptable operating range. The fluidizing property of FBGF is investigated in the present paper when river sand of 0345mm in mean diameter is served as bed material. The more the filter unit number, n, in bed, and the deeper the unit immerses into the bed material, H-0-Hu-p, the larger the minimum fluidizing velocity is found through experiments. Finally, a dimensionless number. c(u), is defined as the ratio of the effective surface area of the unit immersed in the bed material to the fluidized bed cross-section area, to represent the influence of the inserted filter units on fluidizing feature, and a empirical formula about u(mf) is correlated with c(u) in consideration, which lays a solid foundation to further explore the properties of FBGF.