Abstract: Description is of fluidized bed shell boiler arrangements in which the sides of the bed within the furnace tube are generally vertical, being provided by vertical walls within the furnace tube. The bed walls may include water tubes or be substantially vertical portions of arcuate panels mounted within the furnace tube. Fluidizing gas is fed to fluidizing gas ducts communicating with the bed from a plenum chamber including paddles movable into positions closing off at least some of the ducts during initial start up of the boiler to reduce the amount of combustible gas (or hot gases) fed to the ducts when heating the bed to its operating temperature. The ducts may be formed by mounting halfround or U-shaped member on the bottom of the furnace tube, the ducts tapering along their lengths such that the gas passing into the bed exits at substantially the same velocity across the width and length of the bed.

Abstract: The specification describes arrangements in which the attemperation or control of the temperature of a fluidized bed in a fluidized bed combustion unit effected by means of the mixture of a variable proportion of inert gas with fluidizing air fed to the bed may be supplemented with steam. Supplementation with steam being effected to a relatively minor extent during normal operation of the unit but being effected to a major extent when the temperature of the bed passes outside the range at which attemperation may be effected by use of recycled flue gas. The combustion unit is described in use within an arrangement including process plant in the form of a rotary drum dryer.