Fluidized bed process heater

A fluidized bed process heater comprising a vessel of toroidal configuration having an outer wall and a generally concentric inner wall, a horizontal annular constriction plate extending between said outer and inner walls and separating a heater chamber in the upper portion of said vessel from a windbox occupying the lower portion of said vessel, said constriction plate being capable of supporting a fluidized bed of particulate solids thereon, a plurality of heat exchanger coil units within said vessel, said coil units each having a planar serpentine tube element composed of horizontal runs of tubing serially joined by return bends, the horizontal runs of tubing of each coil unit extending inwardly through the fluidized bed region of said heater chamber along a radius of said vessel with the plane of said coil unit in vertical orientation, means removably supporting said coil units at said outer wall, recess means mounted on said inner wall in said heater chamber in supporting contact with those return bends of said coil units proximate said inner wall, said recess means shielding the supported return bends from the erosive conditions prevailing in said heater chamber.