Mixing and Segregation Behavior in a Spout-Fluid Bed: Effect of the Particle Density

The effect of the particle size on the mixing and segregation in a spout-fluid bed has been investigated (Zhang, Y.; Zhong, W. Q; Jin, B. S.; Xiao, R. Mixing and segregation behavior in a spout-fluid bed: effect of particle size. Ind. Eng. Chem. Res, 2012, Si, 14247-14257). This paper presents the effect of the particle density on the mixing and segregation behavior in a spout fluid. Four kinds of solid particles having the same size of 2.8 mm and different densities of 900, 1230, 1640, and 2540 kg/m(3) were used. Three kinds of binary mixtures were obtained, indicated as PB-SP, PB-MB, and PB-GB. For each mixture, three different mass ratios were prepared so that the mixing and segregation processes were examined. Thus, nine binary mixtures were made by mixing the bed material and tracer in different mass ratios. The initial bed stayed in the state of well-mixed and complete segregation, respectively. A wide range of flow regimes were covered by changing the ratio of spouting-to-fluidizing gas flow. The mixing and segregation were analyzed in terms of the concentration profile, mixing index, and flow regimes. The results show that, in the flow regime of IJ, local segregation occurs in the initial well-mixed case, whereas bed inversion takes place in the initially complete segregation bed. In the case of JFB, the entire bed is divided into three sections due to segregation: a pure layer of light particle, one jet region occupied nearly by a heavy particle, and one annulus remaining at the initial distribution at rest. In the flow regime of F, the segregation pattern is dependent on the mass ratio and density difference between the light and heavy particles. On the mixing/segregation pattern map, even though the bed is operated at the same flow regime, the mixing degree varies with the gas velocity. Also, a monotonic increase in the spouting or fluidizing gas velocity is not necessary to promote mixing. There lies one major difference on the mixing/segregation pattern map; that is, the location of the transition region for a binary mixture with different densities (DD mixture) is different from one for a binary mixture with different sizes (DS mixture).