Abstract: A rotary kiln or combustor having a plurality of water cooled pipes secured together to define a cylinder in which material is burned. The cylinder slowly rotates about its axis, and the pipes are secured together so as to define a plurality of intermediate openings making the cylinder gas porous and through which combustion air is introduced. The improvement comprises providing a plurality of pins, secured directly to the pipes on the inside of the cylinder, that create a pattern of projections to support burning material slightly spaced from the inner cylinder wall.