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Show tube boiler (Figure 4). Units of 15 MW and 7.5 MW are nearing completion at Ambergate, Derbyshire and Bradford, Yorkshire, respectively. In addition to these UK developments, there are a number of demonstration fbc water tube boilers in the USA and Germany and commercial orders are being received by the manufacturers. These units incorporate limestone addition for sulphur retention. For outputs up to 30 MW and steam pressures to 35 bar, Babcock Power Ltd have developed a composite boiler design, incorporating a water-tube combustion chamber and a shell and tube convection section, arranged in the geometry of a locomotive-type boiler. A fbc version has been designed in collaboration with the NCB and a 4.5 MW prototype has been successfully demonstrated at the Coal Research Establishment (Figure 5). A commercial order has been received for a 15 MW unit and further orders are expected. All of these various fbc boilers have automatic start-up and load following and those at commercial sites have proved fully able to meet the load demand placed on them. They have demonstrated that tube fouling is minimal, enabling boilers to be operated for up to a year without loss of efficiency. It is expected that fbc boilers will play a major role in regaining coal's share of the industrial boiler market. 2.2.3 Drying and heating applications Development of fluidised bed furnaces for the production of hot gas for industrial and agricultural drying started in 1974. In such furnaces all the heat released during combustion is removed from the shallow bed by hot combustion gases leaving the bed at up to 950 C. Initially development concentrated on applications where the hot combustion gases are used for direct contact drying and where contamination (8) of the product by small amounts of ash is tolerable (Figure 6) . The first application was in drying grass to produce high protein animal feed. Following the successful operation of NCB 2 MW and 6 MW prototypes, five 5 MW fbc hot gas furnaces, designed and manufactured by GP Worsley in collaboration with the NCB, were installed to convert existing grass dryers 20-15 |
