GB787010A - Improvements in or relating to furnace recuperators or like recuperative heat exchangers - Google Patents

Abstract

787,010. Heating air for comubustion; tubular heat exchange elements. WELLMAN SMITH OWEN ENGINEERING CORPORATION, Ltd., and MC LAY, G. S. Aug. 31, 1956, No. 26710/56. Classes 64(1) and 64(3) An element for a furnace recuperator or like recuperative heat exchanger comprises three vertical, annularly spaced concentric tubes 21, 22, 23, the medial and inner tubes 22, 23 respectively being metallic and the outer tube 21 being of refractory material, the inner tube 23 being open at both ends, the medial tube 22 being open at its upper end and closed at its lower end e.g. by a plate 26, the open bottom end of the inner tube 23 being axially spaced from the closed bottom end of the tube 22, and the element being mounted so that all three tubes may expand or contract independently of each other and so that the metallic tubes are not directly exposed to the heating medium. In the recuperator element shown, a core member 39 is disposed within the inner tube 23 and forms therewith an annular air passage 40 communicating with a further annular air passage 25 formed between the medial and inner tubes 22, 23. The refractory tube 21 is made in a plurality of sections retained in axial alignment with one another and concentrically with the metallic tubes by metal rings 28 which also serve to hold the parts of the tube together in the event of cracking under extreme conditions. The space 24 between the refractory tube 21 and medial tube 22 may be charged with an inert gas. The tube 21 and core 39 are supported by the plate 26 which is welded to the medial tube 22 and may be protected by refractory material. A helical baffle the pitch of which may increase in the direction of air flow, may be provided in the passage 25 (Fig. 2, not shown). The cross-sectional area of the annular passages 25, 40 may decrease in the direction of air flow therethrough to retain or increase the the air velocity. This may be effected by changing the diameter of the tube 23 and/ or the core 39 either gradually or in stages. Hot gases, e.g. from a furnace, flowing through the recuperator chamber 11 impinge on the outer surface of the refractory tube 21 and heat is radiated from this tube across the space 24 to the metallic tubes therby heating the air flowing from an inlet conduit 17 through annular air heating passages 25, 40 to the outlet conduit 19 leading e.g. to a furnace burner. The tubes 22, 23 may be made of heat resisting steel and have oxidized inner and outer surfaces. The tube 22 may have its outer surface knurled.