Shallow fluidized beds

Figure 29. Motion of luminescent particles in shallow fluidized bed. (Qin, and Liu, 1982.)... 

In a shallow fluidized bed, temperature will be substantially uniform and will correspond to the effluent conversion. The absence of a composition gradient in a fluidized bed is less certain. Accordingly, three cases will be solved for comparison,... 

Modeling and Simulation of Dynamic and Steady-State Characteristics of Shallow Fluidized Bed Combustors... 

The dynamic and steady-state characteristics of a shallow fluidized bed combustor have been simulated by using a dynamic model in which the lateral solids and gas dispersion are taken into account. The model is based on the two phase theory of fluidization and takes into consideration the effects of the coal particle size distribution, resistance due to diffusion, and reaction. The results of the simulation indicate that concentration gradients exist in the bed on the other hand, the temperature in the bed is quite uniform at any instant in all the cases studied. The results of the simulation also indicate that there exist a critical bubble size and carbon feed rate above which "concentration runaway" occurs, and the bed can never reach the steady state. 

Let us consider a shallow fluidized bed combustor with multiple coal feeders which are used to reduce the lateral concentration gradient of coal (11). For simplicity, let us assume that the bed can be divided into N similar cylinders of radius R, each with a single feed point in the center. The assumption allows us to use the symmetrical properties of a cylindrical coordinate system and thus greatly reduce the difficulty of computation. The model proposed is based on the two phase theory of fluidization. Both diffusion and reaction resistances in combustion are considered, and the particle size distribution of coal is taken into account also. The assumptions of the model are (a) The bed consists of two phases, namely, the bubble and emulsion phases. The voidage of emulsion phase remains constant and is equal to that at incipient fluidization, and the flow of gas through the bed in excess of minimum fluidization passes through the bed in the form of bubbles (12). (b) The emulsion phase is well mixed in the axial... 

Andeen BR, Glicksman LR. Heat transfer to horizontal tube in shallow fluidized beds. National Heat Transfer Conference, St Louis, MO, paper no. 76-HT-67, 1976. 

Thodos G, Yoon P. Mass transfer in the flow of gases through shallow fluidized beds. Chem Eng Sci 27 1549-1554, 1972. 

Merry JMD, Davidson JF (1973) Gulf stream circulation in shallow fluidized beds. Trans Instn Chem Engrs 51 361-368... 

---