Fludised bed combusion

1. Fluidized combustion boiler
by
Rampal Singh
Assistant Professor
Rai University, Ahmedabad
B.E. (Mechanical), M.Tech (Production Engineering),
Thrice GATE Qualified

2. Mechanism of FBC
As air velocity is gradually increased, a stage is reached when the
individual particles are suspended in the air stream – the bed is called
“fluidised”.
With further increase in air velocity, there is bubble formation,
vigorous turbulence, rapid mixing and formation of dense defined
bed surface. The bed of solid particles exhibits the properties of a
boiling liquid and assumes the appearance of a fluid – “bubbling
fluidized bed”
At higher velocities, bubbles disappear, and particles are blown out
of the bed. Therefore, some amounts of particles have to be
recirculated to maintain a stable system - "circulating fluidised bed".

4. Fluidized bed combustion
• Fluidized bed combustion (FBC) is a combustion technology used to burn solid
fuels.
• In its most basic form, fuel particles are suspended in a hot, bubbling fluidity bed
of ash and other particulate materials (sand, limestone etc.) through which jets
of air are blown to provide the oxygen required for combustion or gasification.
• The resultant fast and intimate mixing of gas and solids promotes rapid heat
transfer and chemical reactions within the bed.
• FBC plants are capable of burning a variety of low-grade solid fuels, including
most types of coal and woody biomass, at high efficiency and without the
necessity for expensive fuel preparation (e.g., pulverizing).

7. Advantages
• High thermal efficiency.
• Short commissioning and erection period.
• Efficient operation at temperatures down to 150° C ( i.e. well below
the ash fusion temperature).
• Reduced coal crushing etc. (pulverised coal is not a necessity
here).
• The system can respond rapidly to changes in load demand, due to
quick establishment of thermal equilibrium between air and fuel
particles in the bed.
• The operation of fluidized bed furnace at lower temperature helps in
reducing air pollution.

8. Disadvantage
• There may be problem in distribution of coal and dolomite.
• The direct contact of flue gases and tubes may erosion.
• High pressure air is required