Mapping, fast fluidization

As noted earlier, increasing gas velocity for any given fluidized bed beyond the terminal velocity of bed particles leads to upward entrainment of particles out of the bed. To maintain solid concentration in the fluidized bed, an equal flux of solid particles must be injected at the bottom of the bed as makeup. Operation in this regime, with balanced injection of particles into the bed and entrainment of particles out of the bed, may be termed fast fluidization, FFB. Figure 10 presents an approximate map of this fast fluidization regime, in terms of a dimensionless gas velocity and dimensionless particle diameter. 

Yang, W. Incipient Fast Fluidization Boundary and Operational Maps for Circulating Fluidized Bed Systems, in Circulating Fluidized Bed Technology IV (Amos A. Avidan, ed.), pp. 61-71. Somerset, Pennsylvania (1993). 

This locus is within the fast regime, near its upper boundary, on the map of Fig. 1. Therefore the proposed operation will be a fast fluidized bed. 

This locus is within the fast regime, near its center, on the map of Fig. 1. Therefore the proposed operation will be a fast fluidized bed. In actual operation, the bed average density, at elevation of the heat transfer surface, is found to be pb = 45kg/m. The values for volume fractions of solid and gas phases are then... 

Fig. 10.2 Flow regime map of gas-soUd contacting, a Characteristics of turbulent flow regime, b Characteristics of spouted beds, bubbling fluidized beds, fast fluidized beds and pneumatic transport regimes. In the figure notation the ordinate u = U p / n(pp — pg)g) is a dimensionless gas velocity, the abscissa d = dp[pg pp — Pg)glp ] a dimensionless particle size, the terminal velocity of a particle falling through the gas (m/s), and Umf the gas velocity at minimum fluidization (m/s). Letters A, B, C and D refer to the Geldart classification of solid particles. Reprinted from [49] with permission from Elsevier...

---