Fluidized bed having modified surfaces in the heat extractor

A fluidized combustion bed having immersion heat exchanger tubular means, said tubular means having an inner surface and an outer surface;

• said tubular means comprising a plurality of tubes spaced away from one another;
• said bed having inlet means and outlet means for the flow of fluid therebetween;
• said tubes being disposed substantially transverse to the flow in said bed;
• said inner surface of said tubular means defining means for conducting a heat transferring medium through said tubular means;
• said outer surface of said tubular means having protrusions extending therefrom;
• said protrusions being disposed to deflect, at least partially, a flow of products of combustion in said fluidized bed from said outer surface;
• and
• said protrusions being pins disposed on and protruding from said outer surface and distributed thereover, whereby erosion of said outer surface of said tubular means is minimized, said pins being disposed on said outer surface of said tubular means in encircling, circumferential rows of spaced pins, adjacent circumferential rows being angularly displaced from one another about the longitudinal axis of said tubular means.