While the burning of fossil fuels such as coal is deterred, there is an abundance of this fuel source leading to “Clean Coal” development. Early designed incorporated bed combustion moving through pulverising of the fuel to a fine powder. Feed water heating and steam extraction has also raised cycle efficiencies to the ~36% area. With new materials the cycle has again been modified by removing the latent heat required to false water to steam resulting in supercritical operation. Today’s ultra-critical pressure boilers are achieving >42% efficiency through the Rankin cycle.
With the plush to “Clean Coal”, One of the emerging developments is the Sub and Super Critical Circulating Fluidised Bed boiler (CFB). This coal boiler has the following advantages over its PC counterparts:
(a) A wide range of fuels can be used down to low grade municipal waste and biomass.
(b) Lower pollution is achieved as the combustion temperatures in the boiler are below 900 °C which reduces the generation of NOx gases. SOx gases are removed intra furnace by limestone injection.
(c) High combustion efficiency is attained by excellent combustion mechanism of circulating fluidization mode.
(d) Space Saving and highly maintainable due to the removal of separate desulphurisation and fuel milling plant. Accordingly, high maintenance items of equipment reducing the overall O&M cost.