Abstract: The present invention relates to combustion devices such as incineration furnaces and the like, and in particular, relates to combustion devices which include a combustion gas cooling device by means of which slag, combustion by-products and the like are rapidly cooled and thereby converted to nonadhering fly ash. By converting slag to nonadhering fly ash, the accumulation of slag in downstream exhaust processing equipment is diminished, and hence, the necessity of halting the operation of the combustion apparatus in order to remove the accumulated slag is eliminated, thereby improving the efficiency of operations.