Abstract: Industrial furnace for the combustion of solid, liquid, pasty or gaseous fuels, including at least two fluidized beds through which hot gas passes from the bottom, and which are offset in height in the transport direction of the fuel into the combustion chamber according to a reciprocal delimitation one behind the other and in step, after adjusting a mean combustion temperature between preferably 500.degree. and 800.degree. C. It is further possible to recover from household refuse, and/or industrial refuse similar to household refuse, a fraction of fuel rich in energy and low in noxious products by preparation via drum screens, hammer mills, and sliding plate and rod screens of a particulate size between 120 and 500 mm.