Fluid bed furnaces

A fluid bed-furnace comprising at least one combustion chamber housing a bed of incombustible particulate material within which fuel is to be burned when the bed material is fluidised, means for fluidising that bed material by distributing pressurised combustion-promoting gas at least to an upper part of the bed material, and means also for returning some of the furnace exhaust gases under pressure to the bed material, the return means including a gas distribution system to said bed material which is separate from that for the combustion-promoting gas, wherein each gas distribution system comprises at least one plurality of gas outlets from at least one duct traversing the bed, wherein the outlets for exhaust gas are at higher levels than at least adjacent ones of the outlets for combustion-promoting gas.

A fluidized bed furnace comprising at least one combustion chamber housing a bed of incombustible particulate material within which fuel is to be burned when the bed material is fluidised, means for fluidising that bed material by distributing pressurised combustion-promoting gas at least to an upper part of the bed material, and means also for returning some of the furnace exhaust gases under pressure to the bed material, the return means including a gas distribution system to said bed material which is separate from that for the combustion-promoting gas, wherein each gas distribution system comprises at least one plurality of gas outlets from at least one duct traversing the bed, wherein the or each plurality of gas outlets are take-off pipes extending upwardly from their supply duct by an extent that ensures that the supply ducts are below the fluidised part of the bed material.

A fluidized bed furnace comprising at least one combustion chamber housing a bed of incombustible particulate material within which fuel is to be burned when the bed material is fluidised, means for fluidising that bed material by distributing pressurised combustion-promoting gas at least to an upper part of the bed material, and means also for returning some of the furnace exhaust gases under pressure to the bed material, the return means including a gas distribution system to said bed material which is separate from that for the combustion-promoting gas, wherein the means for fluidising using combustion-promoting gas includes a plenum chamber to feed in-bed distribution means, and wherein said plenum chamber also houses the auxiliary burner for heating such gas and thus the bed material to ignition temperature of the fuel material.