97/02102 Influence of fuel type and steam cycle on CFB boiler configuration

Abstract

The configuration of a circulating fluidized bed boiler is influenced by the fuel type that is to be burned and the specified steam cycle conditions. High quality fuels such as bituminous coal and petroleum coke have a high adiabatic flame temperature and require a significant amount of heat removal from the furnace solids circulation loop. Low quality, waste fuels such as anthracite culm and bituminous gob are just the opposite and require more heat removal from the heat recovery area (HRA). In one case additional heat transfer surface such as full height furnace walls, wing walls, and/or an external heat exchanger are required to maintain the desired furnace operating temperature. In the other case, steam generating heat transfer surface or a steaming economizer may be required in the HRA to generate the required amount of steam. Also, economizer coils may be required in the bottom ash coolers to adequately cool large quantities of ash. Steam cycle conditions such as unit capacity, final steam temperature and pressure, feedwater temperature, and whether reheat is required also dictate how a unit will be configured. Small capacity units have a small furnace cross sectional area. enclosure heat transfer surface is therefore large compared tomore » the volume of gas and solids within the furnace. Large capacity units are just the opposite and may require internal heat transfer surface or an external heat exchanger to maintain the desired furnace operating temperature. High temperature reheat steam cycles require some reheat or superheat duty to be accomplished in the furnace solids circulation loop. Low temperature and pressure, non-reheat units may require little or no superheat, in which case a water-cooled may be preferred over a steam-cooled cyclone. Described in this paper is how these and other issues are addressed when designing a CFB boiler.« less