At the end of this module, you will be able to:
- Describe the advantages and disadvantages of fluidized bed boilers
- Differentiate between bubbling and circulating fluidized bed boilers
- Describe the operation of both fluidized bed boiler types
- Identify and describe the function of the key components of both fluidized bed boiler types
- Define conduction, convection, and radiation and describe how heat is transferred in boilers
- Describe how fluidized bed boilers can reduce emissions
- Describe safety guidelines for working around boilers
The following key questions are answered in this module:
What is a fluidized bed boiler?
Fluidized bed boilers use a hot bed in the bottom of the bed as a combustion source. This bed is fluidized by blowing hot air up through the bed at a high velocity. Fluidization provides good mixing and allows for effective combustion when fuel is added.
What is the difference between a bubbling bed and a circulating bed boiler?
A bubbling bed forces air up through the bed material to the point that it resembles a vigorously boiling liquid. In a circulating bed boiler the air velocity is high enough to entrain the particles in the air and disperse them throughout the boiler.
Are fluidized bed boilers better than conventional grate boilers?
Unless the fuel has a high alkali content, which can cause bed agglomeration, a fluidized bed boiler is superior to conventional boilers. Fluidized bed boilers have high efficiencies and produce lower emissions.
What materials are used for fuel in fluidized bed boilers?
Fluidized bed boilers can burn a variety of solid fuels, including, coal, bark, sludge, wood chips, and tire derived fuel (TDF). Oil or gas can also be used as supplemental fuel or during startup and upset conditions.
What are the important fuel particle parameters?
Particle size, shape, and density are important fuel and bed material parameters. The ideal bed would be a mixture of perfect spheres of the same diameter and density. Although this is not possible, the particle size distribution and density must be stable to maintain a stable fluidized bed.
Below is a transcript of the video sample provided for this module:
Fluidized bed combustion is an efficient process for burning solid fuels. A variety of fuel types and qualities can be effectively burned with low emission. Both types, bubbling and circulating, rely on a large fluidized mass of inert bed material to support combustion and heat transfer. The solids enable low combustion temperatures and greatly improve heat transfer. Bubbling bed boilers maintain a dense fluidized bed with a fixed level in the bottom of the boiler, and circulating bed boilers distribute solids throughout. The solids greatly improve heat transfer and enable low combustion temperatures.
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