The working principle of
(a) Fluidized Bed Combustion
(b)Atmospheric bubbling bed combustor
(c) Circulating bed combustor
And write the advantages of fluidized bed combustion:
Principles of Fluidized Bed Combustion Operation:
A fluidized bed is composed of fuel (coal, coke, biomass, etc.,) and bed material (ash, sand, and/or sorbent) contained within an atmospheric or pressurized vessel. The bed becomes
fluidized when air or other gas flows upward at a velocity sufficient to expand the bed. The process is illustrated in figure. At low fluidizing velocities (0.9 to 3 m/s). relatively high solids densities are maintained in the bed and only a small fraction of the solids are entrained from the bed. A fluidized bed that is operated in this velocity range is refered to as a bubbling fluidized bed (BFB). A schematic of a typical BFB combustor is illustrated in figure.
Figure: Basic fluid bed Systems
ller particles are entrained in the gas stream and ell-defined for a BFB combustor becomes more . A fluidized bed that is operated at velocities in fluidized bed, or CFB. A schematic of a typical
Figure: Circulating bed combustor.
Advantages of fluidized bed combustion
The advantages of FBC in comparison to conventional pulverized coal-fueled units can be summarized as follows:
1. SO2 can be removed in the combustion process by adding limestone to the fluidized bed, eliminating the need for an external desulfurization process.
2. Fluidized bed boilers are inherently fuel flexible and, with proper design provision, can burn a variety of fuels.
3. Combustion FBC units takes place at temperatures below the ash fusion temperature of most fuels. Consequently, tendencies for slagging and fouling are reduced with FBC.
4. Because of the reduced combustion temperature, NOx emissions are inherently low.
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