the particles in secondary fluidizing gas entering at 10 which then carries the calcined lime product through cyclone 8 for recovery the secondary fluidizing gas has a lower space velocity than the primary fluidizing gas 3 in the primary combustor and the fine recirculating particles which are denser than the lime product are able to move out the bottom of the secondary fluidized bed against the secondary fluidizing gas and back to the primary combustor the inventive method using the apparatus of fig1 may be explained as follows fluidizing gas 3 typically air is introduced through distributor plate 16 at a space velocity sufficient to fluidize the large particles into a stationary dense bed 14 and to entrain the fine particles into a recirculating fine bed 15 fuel enters the combustor at 2 and is burned therein giving up heat to the large particles in the dense bed and to the recirculating fine particles temperatures on the order of 1700 u00b0 2200 u00b0 f are employed the heated fine particles are entrained with the fluidizing gas out the top of the combustor and are separated from the gas by cyclone 4 the gas is removed for ash separation cleaning and scrubbing and heat removal the heated fine particles are directed to the secondary external fluidized bed wherein they contact particulate limestone introduced at 11 secondary fluidizing gas 10.