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Show Horizontal shell boilers, though in more common use, are difficult to adapt to fbc since the headroom available in the conventional cylindrical fire tube is limited to, at most, 1.5 m. Nevertheless, four UK manufacturers, NEI Cochran, Danks of Netherton, Energy Equipment and Thorn EMI Energy Developments (formerly GWB Parkinson Cowan), have designed fbc systems to fit within the fire tube. All four have successfully demonstrated the operation of prototypes and commercial versions have been supplied to clients, including NCB mines, by NEI Cochran and Energy Equipment. An alternative approach is to use a modified horizontal shell boiler design in order to provide increased height for the combustion chamber. The traditional method of doing this is to use locomotive-type construction (Figure 3). The suitability of this design concept for fbc was demonstrated by an NCB prototype, a 10 MW boiler at Newcastle under Lyme, commissioned in 1978. Locomotive-type construction is used by the NCB's licensee in the USA, the Johnson Boiler Co. Ferrysburg, Michigan, which has supplied 15 fbc boilers with outputs in the range 1-15 MW. In the UK, Energy Equipment are offering a locomotive-type design for outputs up to 18 MW. Novel designs for fbc horizontal shells have been devised by Allied Boilers and Wallsend Slipway. Allied Boilers have supplied a 4.5 MW unit to a factory in Huddersfield, which is operating to meet site requirements, and have subsequently received an order for a 7.5 MW version. Following the successful operation of a 5 MW prototype of the Wallsend design at the NCB Coal Research Establishment, commercial orders have been received for one 1.5 MW and two 8 MW boilers. Water tube construction is used for outputs above 20 MW (25 t/h) and also for smaller boilers producing high pressure steam. An existing 13.5 MW water tube boiler was successfully converted to fbc in 1975 by Babcock Power Ltd using the NCB's crushed coal/deep bed technology under licence. To demonstrate a purpose-designed fbc water tube boiler, the NCB sponsored the design and manufacture of a 30 MW unit for superheated steam, which was commissioned at British Steel Corporation's River Don Works, Sheffield, in 1981. The NCB has also collaborated with Gibson Wells Ltd, a subsidiary of Foster Wheeler, to design a fbc version of their modular packaged water- 20-13 |