Dense-phase fluidized beds turbulent fluidization

The basic MS-FBC concept incorporates an entrained fluidized bed superimposed on an inert, dense-phase fluidized bed as shown in Figures 1 and 2 for the MSW/DSS application. As currently operated in the MSW/DSS experiments, the dense phase is African iron ore. This dense bed remains in the comb 3tor and its height essentially defines the combustion zone (760-870 C) its high density permits dense-phase turbulent fluidization to be achieved at gas velocities exceeding 9.0 m/sec. 

Dense phase fluidization Gas fluidized beds are considered dense phase fluidized beds as long as there is a clearly defined upper limit or surface to the dense bed. The dense-phase fluidization regimes include the smooth fluidization, bubbling fluidization, slugging fluidization, and turbulent fluidization regimes. In a dense-phase fluidized bed the particle entrainment rate is low but increases with increasing gas velocity. 

Yerushalmi and Cankurt considered the transport velocity as the boundary between the turbulent and the fast fluidization [4], The transition takes place gradually through a turbulent state where both voids and clusters coexist. During fast fluidization a dense phase exists at the bottom of the bed while a lean phase exists at the top. 

Fluidization occurs in stationary (segregation of bed and free board), turbulent (circulating fluid bed), and forced dense-phase (transport reactor) mode. All systems require hot gas cyclones either to recycle entrained particles back into the fluid bed or just to separate them from the product gas. 

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