GB590382A - Improved recuperator means for combustion furnaces - Google Patents

Abstract

590,382. Regenerators. AUSTRALIAN IRON & STEEL, Ltd. Jan. 19, 1945, No. 1619. Convention date, April 4, 1944. [Class 64 (i)] A recuperator comprises a flue-gas conduit 6 which communicates at opposite ends with the flue-gas outlet 46 of a furnace 9 and with the atmosphere and has an unobstructed radiation zone 13 beginning at its entrance end, an air or gas heating passage formed by a shell 14 surrounding the flue-gas conduit 6, and air or gas inlet and outlet boxes 15, 16, surrounding the ends of the air or gas heating passage, air or gas being fed under pressure to the inlet box 15 and being conducted from the outlet box 16. The radiation zone 13 is the zone in which the flue gases give up at least as much heat by radiation as by conduction or convection. In the air heater shown, the radiation zone 13 is lined with refractory material 18 and the casing 17 may be of heat-resistant steel. The remainder of the conduit contains a baffle 22 and fins 21. Fins 23 and a heat-absorbing and radiating sleeve 26 with projecting tongues are provided in the air passage. A pump 31 supplies air to the annular inlet box 15, which has a flexible connection 30 with the shell 14. To prevent excessive heating of the air in the passage between the conduit 6 and the shell 14, the pump may also supply cooling air to a passage 42 around part of the shell 14, or to the outlet 46 of the furnace to mix with the flue gases, or to both. This supply of cooling air may be controlled by a damper 48 operated manually or automatically against the action of a spring 56 by thermal expansion of the casing 17, the outlet end of which carries a bracket 51 linked by a rod 52 and bell-crank lever 53 to the valve. A damper 50 may control the proportions of air supplied to the flue gases and to the passage 42. The shell 14 may have a heat-insulating band 39 and fins 40. In another form, the flue-gas conduit and surrounding passage are vertical, and are supported by a pair of vertical fins which project from opposite sides of the conduit through slots in the surrounding shell and rest on a pair of girders. A sand seal is provided at the bottom, and a vertically adjustable damper is provided above the outlet of the flue gas conduit. The air inlet and outlet boxes are at the top and bottom respectively. One or more baffles may be provided within the conduit above the radiation zone. In a third form, for use with a batch type heating furnace of the soaking pit type, the flue-gas conduit comprises a horizontal section and a vertical section each surrounded by an annular passage. The horizontal section through which the flue gases first flow is used to heat air supplied to a burner, and the vertical section, which has internal longitudinal fins in its upper part, is used to heat gas supplied to the burner. Cooling air, controlled by a valve operated by thermal expansion and contraction of the vertical section, may be mixed with the hot gases entering the vertical section. A fourth form, for use with an open hearth melting furnace, comprises a vertical downdraft section connected by an ash-pit to a parallel updraft section. Each section has two surrounding annular heating passages arranged one above the other and each provided at its ends with surrounding inlet and outlet boxes. Air to be heated passes first downwardly through the upper-passage in the downdraft section, then downwardly through the lower passage around the updraft section, and finally upwardly through the lower passage around the downdraft section. At intervals the first of these passages may be by-passed so that the temperature of that part of the conduit may be raised sufficiently to melt slag or clinker deposits. Combustion gas to be heated passes downwardly through the upper passage around the updraft section. The lower part of the downdraft section and both parts of the updraft section are externally lagged.