Circulating fluidized bed furnace/reactor with an integral secondary air plenum

A circulating fluidized bed processor has a processor enclosure at least partially defined by a front wall and a rear wall spaced away from the front wall. A bottom wall is connected between the front and rear walls and a mechanism is provided for supplying primary air through the bottom wall for fluidizing a circulating bed in the enclosure. Another mechanism is provided for recirculating the bed from a top of the enclosure back to the enclosure. One or more secondary air plenum(s) are provided in the enclosure between the front and rear walls for supplying secondary air into the fluidized bed, above the bottom wall, so that secondary air reaches deep into the enclosure. The plenum(s) are formed of a waterwall which has a plurality of openings therein to allow communication of gases and solids therethrough from one side of the waterwall to the other.