Determination of boiler efficiency for fluidized bed steam generators

Fluidized bed combustion steam generators are inherently different from conventional combustion systems. This paper presents suggested methods to account for these differences when determining boiler efficiency by the heat loss method. Operating data from an operating fluidized bed boiler plant are presented. The combustion process takes place in a bed of inert ash particles that are fluidized by combustion air. The fluidizing blower increases the combustion air temperature due to the adiabatic heat of compression and frictional heat. Methods of accounting for the fan horsepower and the heat of compression in the boiler efficiency are discussed. The ash streams generated in fluidized bed combustion are usually greater than in conventional combustion because sorbent material is usually employed to capture sulfur dioxide and because fuels containing high ash levels are very often burned in the fluidized bed. Methods of determining ash specific heat and total sensible heat of these ash streams are presented.