FLUIDISED BED COMBUSTION

Fluidised Bed Combustion (FBC) is a very flexible method of electricity production – most combustible material can be burnt including coal, biomass and general waste. FBC systems improve the environmental impact of coal-based electricity, reducing SOx and NOx emissions by 90%. In fluidised bed combustion, coal is burned in a reactor comprised of a bed through which gas is fed to keep the fuel in a turbulent state. This improves combustion, heat transfer and recovery of waste products. The higher heat exchanger efficiencies and better mixing of FBC systems allows them to operate at lower temperatures than conventional pulverised coal combustion (PCC) systems. By elevating pressures within a bed, a high-pressure gas stream can be used to drive a gas turbine, generating electricity. FBC systems fit into two groups, non-pressurised systems (FBC) and pressurised systems (PFBC), and two subgroups, circulating or bubbling fluidised bed. · Non-pressurised FBC systems operate at atmospheric pressure and are the most widely applied type of FBC. They have efficiencies similar to PCC – 30-40%. · Pressurised FBC systems operate at elevated pressures and produce a high-pressure gas stream that can drive a gas turbine, creating a more efficient combined cycle system – over 40%. · Bubbling uses a low fluidising velocity – so that the particles are held mainly in a bed – and is generally used with small plants offering a non-pressurised efficiency of around 30% · Circulating uses a higher fluidising velocity – so the particles are constantly held in the flue gases – and are used for much larger plant offering efficiency of over 40% The flexibility of FBC systems allows them to utilise abandoned coal waste that previously would not be used due to its poor quality.