Fluid bed technologies
Metso has supplied over 100 fluid bed dryers and coolers under the Pyrotherm, Svedala and Allis Chalmers brand names.
The term "fluidized bed" usually refers to a bed of finely divided solids through which a gas is passing and which is in a state between that of a static bed and one where all the solids are suspended in the gas stream, as in pneumatic conveying.
The introduction of an appropriate gas flow into the material bed brings about the onset of fluidization. Bubbles of gas pass through the bed of material creating a condition of rapid mixing. The bed has the appearance of a vigorously boiling liquid, and in fact the bed of material takes on many of the properties of a fluid. It exerts a hydrostatic head, and the material will flow through a hole in the vessel or over and under a weir within the bed.
The boiling action in a fluidized bed brings particles into contact with each other, removing dust that is carried off in the gas stream. The same boiling action ensures very thorough mixing, giving uniform temperature conditions and enabling complete drying to take place without overheating the material.
Principles of fluidisation
The term "fluidised bed" usually refers to a bed of finely divided solids through which a gas is passing and which is in a state intermediate between that of a static bed and that where all the solids are suspended in the gas stream, as in pneumatic conveying.
The introduction of an appropriate air flow into the system brings about the onset of fiuidisation. The particles move only slowly, but the system is fluid. In fact the bed takes on many of the properties of a fluid, hence the name fluid bed. It exerts a hydrostatic head, and the material will flow steadily through a small hole in the side of the vessel or flow over and under a weir within the bed.
Advantages of Fluidized bed
- Extremely high surface area contact between fluid and solid per unit bed volume
- High rates of heat exchange
- Does not overheat individual particles
- High relative velocities between the fluid and the dispersed solid phase.
- High levels of intermixing of the particulate phase.
- Is suited for powders, granules, agglomerates, and pellets (50 – 5,000 microns)
Our fluidization is done by blowing air (heated/cooled - application dependant) vertically through a distributor plate. Typically, pressurized air enters the fluidized bed vessel through numerous holes via a plate known as a distributor plate, located at the bottom of the fluidized bed. The air flows upward through the bed, causing the solid particles to be suspended. If the inlet fluid is disabled the bed may settle or pack onto the plate.
Fluid beds for lime calcining