Circulating fluidized bed reactor having extensions to its heat exchange area

A circulating fluidized bed reactor comprising a top zone surrounded by walls defining a top portion and provided with heat exchange tubes, and a bottom zone provided with a fluidizing grid, a primary air injector beneath the grid, a secondary air injector above the grid, and a fuel injector above the grid, the walls surrounding said bottom zone being provided with heat exchange tubes, wherein at least one wall of at least one of said zones is provided with vertical heat exchange panels comprising extensions, each of said extensions comprising a plurality of substantially vertical heat exchange extension tubes which are aligned proximate to one another so as to extend perpendicularly with respect to the wall, at least one of a top portion and a bottom portion of said extension tubes being embedded in a protective concrete layer, the horizontal width of the extensions lying in the range of 150 mm to 500 mm, and the extensions being spaced apart from one another by a distance lying in the range of 1.5 times to 4 times their width,

• wherein solid particles move upward above the grid and travel toward the top portion of the reactor, and at least a portion of said solid particles moves proximate to the walls of the top and bottom zones and then flows downward along the walls thereby forming a layer of solids which travels down along the walls and along the extensions, and further wherein the horizontal width of the extensions and the distance by which the extensions are spaced apart from one another are chosen based on a thickness of the layer of solids.