Circulating fluidized bed combustion technology

　　Circulating fluidized bed combustion technology(CFBC) uses a fluidized bed, an apparatus that mixes solid fuel(coal, biomass, RDF fuel) and air with a sorbent such as limestone during the combustion process, to facilitate more effective chemical reactions and heat transfer. In a fluidized-bed combustor, combustion occurs when the mixture of fuel, a sorbent and fuel ash particles is suspended by using a continuous stream of primary combustion air to create turbulence in the bed. The gas cushion between the solids allows the particles to move freely, giving the bed a liquid-like (fluidized) characteristic.

　　The features of circulating fluidized-bed boilers:

　　1. Compatibility with wide range of fuels

　　Conventional boilers for power generation can use only fossil fuels, such as high-grade coal, oil, and gas. The CFBC is also capable of using low-grade coal, biomass, sludge, waste plastics, and waste tires as fuel.

　　2. Low polluting

　　NOx and SOx emissions are significantly decreased without special environmental modifications. In the case of fluidized-bed boilers, desulfurization is carried out in the furnace, using mainly limestone as the fluidizing material. For denitration, PC boilers operate at combustion temperatures from 1,400 °C to 1,500 °C, whereas circulating fluidized-bed boilers operate at lower temperatures, ranging from 850 °C to 900 °C, thereby suppressing thermal NOx emissions as the generation of NOx is dependent upon the combustion temperature. In addition, the operation of circulating fluidized-bed boilers involves a two-stage combustion process: the reducing combustion at the fluidized-bed section, and the oxidizing combustion at the freeboard section. Next, the unburned carbon is collected by a high-temperature cyclone located at the boiler exit to recycle to the boiler, thus increasing the denitration efficiency.

　　3. High combustion efficiency

　　Improved combustion efficiency is attained through the use of a circulating fluidization-mode combustion mechanism.

　　4. Space-saving, ease of maintenance

　　Space saving is attained because there is no need for separate desulfurization, denitration, and fine-fuel crushing units. Accordingly, trouble-spots are minimized, and maintenance is simplified.