Circulating fluidized beds system configuration

Figure 10.1. Various configurations of circulating fluidized bed systems (a) Mechanical valve with reservoir (b) Nonmechanical valve with reservoir (c) Nonmechanical valve without reservoir (d) Mechanical feeder without reservoir.

New applications and novel reactor configurations or operational modes for three-phase systems are continually being reported. These include the operation of a three-phase fluidized bed in a circulatory mode (Liang et al., 1995), similar to the commonly applied gas-solid circulating fluidized bed the application of a three-phase fluidized bed electrode that can be used as a fuel cell (Tanaka et al., 1990) magnetically stabilized three-phase fluidized beds centrifugal three-phase reactors and airlift reactors. 

A concurrent downward flow circulating fluidized bed, or a downer, is a new alternative flow arrangement for a high-velocity system. A downer reactor system has similar system configurations to a riser reactor system except that both the gas and the solid particles flow downward. Concurrent downward flow of particles and gas reduces the residence time of solid particles because the downward flow is in the same direction as gravity. More uniform radial gas and solids flow than those in a riser can be achieved. The downer leads to more uniform contact time between the gas and solids. With these advantages, downer reactors have been proposed for processes such as fluid catalytic cracking, which requires short contact time and uniform gas and solids residence time distributions. 

LaFanechere L, Basu B, Jestin L. Use of an expert system to study the effect of steam parameters on the size and configuration of circulating fluidized bed boilers. Journal of Engineering for Gas Turbines and Power—Transactions of the ASME 120(4) 813-819, 1998. 

A circulating fluidized bed ean also be constructed in a concentric configuration as an internally circulating fluidized bed. The riser is usually located in the interior with the downcomer as an outer armulus (e.g., Fusey el al., 1986). Such geometries simplify construction, facilitate direct heat exchange between the riser and the downcomer, and simplify the design of high-pressure systems. 

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