Principle of Operation of Fluidized Bed Combustion System
- Figure A shows the simple fluidized bed which has a finely divided particles of fuel half filled in the column.
- At its bottom a distributor plate is fitted through which the air is passed in upward direction with some low velocity.
- The pressure drop across the combustion chamber can be measured with the help of a manometer.
Figure A
- The velocity of air is increased gradually and the logarithmic plot of pressure drop Ap and velocity C is shown in Figure B.
Figure B
- Upto the point A the bed is stable. Between the points A to B the bed is unstable and the particles tend to adjust their position to present as little resistance to flow as possible.
- At point B the particles are just in contact with each other and beyond this point on further increase in velocity, the particles start moving freely in the bed with frequent collision with each other.
- Point B is called the point of fluidization and the corresponding velocity is called the minimum fluidization velocity.
- Beyond point B on further increase in velocity the resistance to flow decreases as the particles get separated and become freely suspended in gas stream.
- In this state, the bed continues to expand and it becomes turbulent, also, there is rapid mixing of particles.
- Under these conditions the mixture of bed and gas behaves like a fluid and the burning of the fuel in such a state is called fluidized bed combustion.