Coal is blown up by the strong wind from the air-blower and the “fluidized state”; coal and air are sufficiently touch and burnt. A large amount of coal particles carried by the smoke enter into the separator. Heavier particles collected by the separator are sent into the main combustion chamber via the recycle device to “recycle” and burn again. Light smoke enters into end heating surface of boiler and continues to provide heat for the drum. Advanced combustion technology enables the thermal efficiency of this kind of boiler can reach over 86%.
CFB is called “clean combustion technology” due to their outstanding performances in efficiency, energy-conservation, and low-pollution and low emission of carbon. It is pointed out in “The Outline for the 11th Five-year Plan for National Economic and Social Development” that “alterate or replace current medium and small coal-fired boiler (furnace) by adopting technologies such as CFB and coal powder combustion”
Advantage Feature of CFB Boilers
- Broad Fuel Adaptability: CFB makes the newly sent coal particles and the already burt coal particles mixed up sufficiently, so the newly sent coal particles are rapidly heated to ignition temperature and burn. As a result, all kinds of coal can be burnt steadily and efficiently.
- High Combustion Efficiency: the basic difference between CFB boilers and other types of boilers lies in the burning system. As stated previously, the thermal efficiency of CFB can be over 86%
- Wide range and Rapid Load Adjustment: the load of a boiler often charges when the boiler is working. When the load drops below 70%, the combustion efficiency and thermal efficiency of other types of boilers will drop noticeably and the burning will be unstable, sometimes even the burning cannot be maintained normally; while by simply adjust coal air feeding and recycled material, the load of CFB can be adjusted in a range of 30-110%; the rate of load-adjusting is also rapid (generally 4% per minute) due to high section wind speed and easy control of heat absorption.
- Clean Combustion Technology: simple desulphurization can conducted in the furnace when lime stones are added into furnace; desulphurization efficiency can be higher than 80% when mole ration of calcium and sulfur is 2; generation of NOx is extremely low because of the adoption of class-divided wind delivery and low temperature combustion, resulting in reduction of SOx and NOx emission and improvement of quality of environment.
- Easy to realize the integrated utilization of ashes: coal can be combusted completely; consequently carbon content in ash is very low. As a result, ash residue can be utilized directly into cement and construction material marking.
- Heating surface of immersed pipes is not in the fluidized bed furnace: heating surface of immersed pipe is not needed in the fluid bed, so there is no trouble of wearing of the surface.
Working Video of Circulating Fluidized Bed (CFB) Coal Fired Steam Boilers
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