Abstract: A stationary weakly expanded fluid bed for combustion of coal, refuse, sludge and the like has a free space above the fluid bed in which a so-called upper firing is effected with secondary air. The temperature of the secondary air is maintained above the temperature of the fluid bed to handle problems resulting from variations in fuel quality and varying loads and guarantees a stable upper firing.

Abstract: A parameter, especially the temperature of the bed in a fluidized-bed furnace, is maintained constant by a regulator (24) positioned in a line (20) that supplies fluidizing air to a trap (15), through which solids that have been precipitated out of the flue gas are recirculated into the fluidized bed (5). The servo mechanism (23) that drives the regulator is coupled to a temperature sensor (27) in the bed such that the volume of fluidizing air is increased when the measured bed temperature exceeds a prescribed level and decreased when it drops below that level.