The CFB Summerside project Canadian state-of-the-art in AFBC boilers

The paper describes two approaches to the design of a heating plant which will demonstrate the combustion of coal in atmospheric fluidized-bed boilers. The designs were prepared in response to competitive tenders sought for the supply and installation of a heating plant to operate in conjunction with an existing steam plant at Canadian Forces Base Summerside, Prince Edward Island. One design was based on British technology and the other on North American technology. The new plant will consist of two boilers, each with a generating capacity of 18 Mg/h of steam at 965 kPa. The design fuel is high-volatile bituminous coal containing approximately 20% ash and 5% sulphur. The performance of the boilers on inferior coals, and with wood chips as a supplementary fuel providing up to 30% of the heat input, will also be demonstrated. The design requirements call for overbed feeding of coal sized 50 mm x 0, special provisions to deal with wet and/or frozen coal, a 4.5 to 1 turn-down range, and limits on emissions of SO2 and particulates. The two boilers differ considerably. The British design incorporates a single combustion bed with three fluidizing zones, all situated in a refractory chamber beneath the radiant furnace of a normal watertube boiler. Immersed tubes with forced circulation of boiler water remove heat from the bed to stabilize the bed temperature. The coal and limestone are simultaneously fed directly over the three fluidizing zones, by watercooled screw conveyors. With the American concept there are two separate beds. Both have peripheral waterwall cooling with a common water wall between them, and one also has immersed tubes within the bed. This design uses natural circulation throughout. Coal is fed to each bed by a spreader stoker while the limestone is fed by a drop pipe into each bed at the end opposite from the coal spreader. Detailed designs and firm price proposals were received in January 1981. After thorough assessment by the sponsoring government departments the decision was made to purchase North American design. Construction is now in progress with completion scheduled for December 1982. Because of the design competition procedure adopted, two Canadian manufacturers have been brought to the point of being able to offer fluidized-bed boilers for burning low-grade coal.