HEAT REGENERATORS

Abstract: Exhaust gases (HFG) are constrained to pass through a chamber (404, 406) with walls (W) of heat retaining material. Air to be preheated is passed through pipes (400-403) within the chamber the pipes transferring heat from the exhaust gases to the air or from the walls to the air when the walls have been preheated to a high temperature.

Description: The present invention relates to heat regenerators for extracting heat from very hot exhaust gases from, for example, scrap reclamation furnaces. The exhaust gases given off by scrap reclamation furnaces are extremely hot and contain large quantities of contaminants and it is an object of the present invention to provide a heat regenerator which efficiently extracts heat from the exhaust gases for transfer to cold air for preheating the air, especially with heat storage capacity for evening out the temperature variation of the waste flue gases in the heat transfer process. British Patent No. 1527111 discloses a regenerative heat exchanger containing refractory brickwork comprising a plurality of masses of refractory bricks through which a hot gas is passed to heat up the brickwork and in which a cold gas is subsequently passed through the brickwork, the brickwork comprising passages formed therein for flow therethrough of the hot and cold gases alternately. U.S. Patent No. 1790172 discloses a furnace which can be provided with blast air at a selectable one of two opposite ends and has regenerators for each end which are individually controllable by valve means. The present invention provides a heat regenerator for extracting heat from hot exhaust gases and transferring the heat to air or other fluid which is required to be heated characterised as in Claim 1. In a first embodiment the pipes are wholly in separate chambers but in a second embodiment the paths cross over, each sharing a portion of a first and a second chamber. Preferably the heat retaining material may be fire brick or heat resistant steel castings or any other heat resistant material and preferably the walls of the chamber are corrugated to accommodate the pipe system. Preferably the pipe system is constructed from a series of pipe sections which are joined to form a continuous pipe. Each section preferably comprises an inner pipe member open at one end into an outer pipe member which outer pipe member at least within the chamber is constructed from heat resistant and heat conductive material. Preferably in a regenerator a plurality of different grades of heat resistant and heat conductive material are used the highest grade for heat resistance being at the hot exhaust gas inlet end of the regenerator. Embodiments of the present invention will now be described, with reference to the accompanying drawings, in which: Figure 1 shows, diagrammatically a portion of a first design of heat regenerator according to the present invention; and Figure 2 shows, diagrammatically a portion of a second design of heat regenerator according to the present invention. With reference to Figure 1 a portion of a first desing of heat regenerator is shown. The portion comprises two sections separated by walls W which are preferably constructed of fire brick or like material. In the embodiment of Figure 1 each heat exchange unit is split into two halves indicated by arrows 300 and 302. Each half is substantially identical and is mounted in a respective passage 304, 306 in the heat exchanger. Air is blown by a blower B either through 300 or 302 according to the position of valves 308, 310. As shown at present valve 308 is closed and valve 310 is open. The passage of hot flue gases HFG is indicated by the arrows. The heat exchanger operates by alternately opening valves 308 and 310 to blow combustion air either through 300 or 302. As shown combustion air is blown by blower B through side 302 and thus the temperature of walls W at the inlet end 312 is high (1100°C in this example) and at the other end 314 the temperature of the exhaust gas is low (200°C in this example) having been cooled by the combustion air flowing through pipes 302. In the other half 300 the respective air temperatures are high at 316 (1100°C) and lower at 318 (600°C) but this lower temperature is considerably higher than at 314. Thus if valves 310 and 308 are now switched over the combustion air will be heated more strongly because it will commence at 600°C and finish at 1100°C rather than commencing at 200°C. Thus by alternating at intervals the outlet combustion air can be maintained at a fairly high temperature. The "twin" system may be used to advantage in the event that the hot flue gases HFG suddenly cool down as for example when a furnace is loaded with new scrap. It is at this time that the burner requires the most heat and with suitable controls the combustion air can be diverted from for example path 302 to path 300. Even though the temperature of the flue gas at 316 will be reduced at least initially the walls W will be at 1100°C and at 318 at 600°C thereby providing hotter combustion air than would have been possible via path 302. With reference now to Figure 2 a further modification is shown in which each pipe 400, 402 is effectively in two joined sections 400 and 401 and 402, 403 which as shown run through the respective passages 404, 406. The cross over links may be external to the heat exchanger chambers. As with the arrangement of Figure 1 under suitable control the combustion air may flow through either pipes 400, 401 or 402, 403 by use of valves 408, 410. As presently shown valve 408 is closed and 410 is open therefore blower B blows combustion air for a burner through pipe section 403 and into section 402 before being fed via pipe 412 to a burner. The temperatures (which are exemplary) are shown and it can be seen that at the "bottom" end 414, 416 the temperatures are roughly equal (200°C and 180°C) and at the "top" end 418, 420 they are equal to the hot flue gas HFG temperature of 1100°C. In the centre however there is a large difference between the temperature at 422 (600°C) and that at 424 (200°C) because of the cooling effect of the combustion air. Again as in Figure 1 if the temperature of the hot flue gases HFG cools then it is possible to provide further heat for the combustion air by switching over valves 408 and 410. The advantage of the arrangement of Figure 2 is that the exhaust gases at 414, 416 are substantially at the same lower temperature and thereby more heat is extracted by this embodiment when compared to that in Figure 1 because in Figure 1 some flue gases are output from the regenerator at 600°C.

Claims: 1. A heat regenerator for extracting heat from hot exhaust gases and transferring the heat to air or other fluid which is required to be heated comprising a main chamber through which the exhaust gases are constrained to pass, a pipe system within the chamber through which air or other fluid to be heated is passed, in which the main chamber comprises at least one wall which is made from heat retaining material characterised in that a single regenerator comprises at least two paths (304, 306) for the combustion air or other fluid the paths being selected alternatively by valve means (308, 310) and in which each path (304, 306) comprises a pipe system which passes through separate passages in the regenerator. 2. A heat regenerator as claimed in Claim 1 characterised in that the pipes are wholly in separate passage (404, 406). 3. A heat regenerator as claimed in Claim 1 characterised in that the paths cross over, each sharing a portion of a first and second passage (404, 406). 4. A heat regenerator as claimed in any one of Claims 1 to 3 characterised in that the heat retaining material is fire brick, heat resistant steel castings or any other heat resistant material. 5. A heat regenerator as claimed in any one of Claims 1 to 4 characterised in that the walls (W(12, 14, 16)) each passage (304, 306, 404, 406) are corrugated to accomodate the pipe system. 6. A heat regenerator as claimed in any one of Claims 1 to 5 characterised in that the pipe system is constructed from a series of pipe sections (125, 126, 127) which are joined to form a continuous pipe. 7. A heat regenerator as claimed in Claim 6 characterised in that each section comprises an inner pipe member (226) open at one end into an outer pipe member (228) which outer pipe member at least within the passage (304, 306) is constructed from heat resistant and heat conductive material. 8. A heat regenerator as claimed in Claim 7 characterised in that a plurality of different grades of heat resistant and heat conductive material are used the highest grade for heat resistance being at the hot exhaust gas inlet end (HFG) of the regenerator.

Inventors: HENGELMOLEN, ADRIANUS JACOBUS
Applicants: COPERMILL LIMITED
Application year: 1988
Main classification: F28D17
IPC codes: F28F27, F28D7, F28D21, F28D20, F28D17, F27D17