US2627398A - Combustion apparatus using preheated air - Google Patents

Description

`vented from the furnace.

Patented Feb. 3, 1953 UNITED STATES ;PATENT OFFICE COMBUSTION APPARATUS USING PREHEATED AIR 6 Claims. (Cl.263-) This invention relates to combustion apparatus `for high temperature heating furnaces such as soaking pits and the like. In high temperature furnace operation, it is common practice to preheat the air for support of combustion by means of a recuperator heated by astream of fiue gas A refractory tile recuperator is well adapted to withstand the high temperatures of the fiue gas Vented from the furnace but is not well adapted to withstand substantial difierental pressure between the air and the fiue gas streams -fiowing through the Vrecuperator and, therefore, it has been proposed to employ a hot fan for drawing the air rather than forcing it through the air passages ?of the recuperator and for forcing the'heated air to the urnace burner. However, because of hearing problems and temperature limitation's of the materials of which the fan is constructedthe safe Operating temperature ofthe'fan is usually substantiallybelowthe attainable preheat temperature of'the air, hence in such cases th preheat temperatures must be limitedto the safe operating temperature of the fan. The general object of the present invention is to make it practical to employ a jet pump instead of afan ior drawing the air` through` the recuperator andfor forcing it to the furnace burner where'by to permit ulluse of-the attainable preheat temperature of the air` and to avoid the numerou Operating difficulties inherent in the use of a hot fan. For a consideration of what I consider to be novel and my invention, attention is directed to the following specification and the concluding clains thereof.

In the accompanying drawings forming part of this specification, the single figure is a more or less diagrammatic view of a sua-king pit' with the present invention applied thereto.

The soaking pit comprises 'combined conbustion and heating chamberlo which is normally closed by a cover H, the chambernormally'being of a size to contain a plurality of steel ingots l2 indicated in-outline'by discontinuous lines. Heating ame enters the .chamber lfl from a firing port [3 whose inlet is coincident with the outlet oft` aburnerl l'to which fuel is `delivered by a supply pipe 15 having a control `Valve 13: and to which air for combustion is delivered` by a duct ll having a control valve !8. Flue gas (products of combustion) is vented-'from the chamberl'l) through an exhaust port IS. -The heating unit thus far described represents nothing new' and is usually one of 'several units having a common fiue gas-exhaust manifo-ld 2! and a'common burner air distributi-ngmanif-old z.

*The fiue gas exhaust manifoldZl connects with astack z't through a-connectng-fiue and there is positioned in said fiue next adjacent said exhaust manifold a refractory tile recuperator a which-maybe considered as being of the type disclosed in patent to Stein 1,404fl2l. A refractory tile recuperator is preferred over a metal recuperator because a tile recuperator is better adapted than a metal `recuperator to withstand the relatively high temperature of the flue gas coming irom said exhaust maniiold. The cold air inlet 'for said recuperator is indicated at 33 and the hot air outlet at 34.

A :hot air duet generally indicated at 35 *connects the recuperator hot air outlet 34 with ,the hot air distributing maniiold 22 for the burners !4 and the means for causing the `heated air to flow from said outlet 34 to said manifold 2 2 comprises a jet pump in said duct, the pump comprising an entraining tube 36 and a nozzle 31 for dischargingmotive fluid into the mouth-of said tube across -an intervening air space whereby to draw heated air from said outlet and thenceforce it to said airdistributing manifold 22. The resulting partial vacuum at said outlet 34 is-sufiicient to cause air at atmospheric pressure to enter and flow through the air passages of the recuperator from the air inlet 33 of the same.

The motive fluid for the jet pump is air under pressure that has been preheated by being passed through the air passages of a metal recuperator 413 positioned in the flue 30 at a point between the stack 21 and the tile recuperator 3! whereby the fiue gas which heats the metal recuperator is flue gas which has already passed through the tile recuperator and which therefore is cool enough to make it practical to employ a metal recuperator at that point. The metal recuperator may be considered as being of the type disclosed in patent to Mantle 2,332A50. The motive air is delivered underpressure to the air intake side of the metal recuperator 40 by a motor driven blower 41, the delivery conduit from the blower being indicated at 42. The delivery conduit from the metal recuperator to the jet pump nozzle 31 comprises the conduit sections 43, 44, 45 and 46.

The stack 21 may be of the ejector type comprising a nozzle 51 for the discharge of motive fluid for drawing fiue gasfrom the flue 30. The motive fluid may be heated air coming from the metal recuperator 40, the delivery conduit in such case comprising the conduit sections 43 and 44. branch line 60, valve Gi and line 62.

The air from the blower 4l can be byl-passed around the metal recuperator 40 during needed repairs to the latter by opening an outletvalve 14 between the blower discharge conduit 42 and the branch pipe 60, the recuperator being isolated by the closing of valves 15 and 16 at the air inlet and outlet sides of the recuperator.

Withoutintending to limit the application of theinvention, it may be stated that depending on Operating conditions the pressure of the air delivered by the blower 4I to the metal recuperator 40 may be about two pounds gauge pressure; that the exit temperature of the air from the metal recuperator will ordinarily be about 500- 600 deg. F., and that the air heating capacity of the tile recuperator 3! will ordinarily be such that the mean temperature of the air at the burner air distributing manifold 22 will be about 900-950 deg. F.

It will be understood that th recuperator 40 is made of metal primarily in order that air under pressure may be heated therein without leakage. However, a metal recuperator also has rapid heat transfer characteristics and is therefore particularly well adapted for use downstream from the tle recuperator 3! which of course has heat storage characteristcs. Although the preferred location of the metal recuperator 40 is downstream in the fiue 30 with respect to the tile recuperator 3! there may be cases where it may be otherwise located and therefore no limitations on its locations are intended except a expressed in the concluding claims hereof.

Certain features herein disclosed but not claimed are claimed in application Serial No. 130294 filed concurrently herewith by C. Cone et al. and owned by the same assignee as the present application.

VJhat I claim as new is:

1. In combustion apparatus for a furnace having a heating chamber, th combination which comprises a burner arranged to fire into the chamber, an air heating recuperator, means for venting fiue gas from the chamber through the recuperator, means forming an air passage connecting the hot air outlet of the recuperator with the burner, a jet pump in the passage for drawing air through the recuperator and for forcing heated air therefrom to the burner, a source of motive fluid under pressure for the pump, a second recuperator, conduit means for delivering said motive fluid through said second recuperator, for heating therein, and thence to the jet pump, and means for venting fiue gas from the chamber through the second recuperator.

2. In combustion apparatus comprising means forming a combustion chamber, the combination which comprises a burner arranged to fire into the combustion chamber, first and second air heating recuperators, means for Venting fiue gas from the chamber through said recuperators, means forming an air passage connecting the hot air outlet of the first recuperator with the burner, a jet pump in the passage for drawing air through the air passages of the first recuperator and for forcing heated air therefrom to the burner, means for producing air under pressure to serve as motive fluid for Operating the jet pump, and conduit means for routing said fluid through the air heating passage of the second recuperator and delivering said motive fluid to the jet punp whereby motive fluid is preheated before it is delivered to said pump.

3. In combustion apparatus for a furnace having a work heating chamber, the combination which comprises a burner arranged to fire into the chamber, a first air heating recuperator, means for Venting fiue gas from said chamber through the recuperator, means forming an air pressure connecting the hot air outlet of the first recuperator with the burner, a jet pump in said passage for drawing air through the air passages of the first recuperator and for forcing heated air therefrom to the burner, the jet pump comprising an entraining tube and a nozzle for discharging motive fluid thereinto, a blower constituting a source of air under pressure to serve as motive fluid for Operating the jet pump, a second air heating recuperator arranged to be heated by fiue gas which has already heated the first recuperator, and conduit means for routing said motive fiuid'from the blower through the air passages in the second recuperator and to the nozzle.

4. Air supply apparatus for supplying air to a burner for combustion in a furnace comprising, in combination, fiue means forming a fiue gas passage from the furnace, first and second recuperators disposed in said passage and each having an air conduit therethrough, first duct means connecting the first recuperator air conduit to the burner, a jet pump in the first duct means for drawing air from the first recuperator and delivering at least a portion of said air to the burner, second duct means connecting the second recuperator air conduit to the j et pump to supply air under pressure thereto for Operating the jet pump and means comprising a blower for supplying air to the second recuperator and air conduit.

5. Air supply apparatus for supplying combuston air to a furnace comprising, in combination, fiue means forming a fiue gas passage from the Iurnace, first and second recuperators disposed in said passage and each having an air conduit therethrough, first duct means connecting the first recuperator air conduit to the furnace, a jet pump in the first duet means for drawing air from the first recuperator and delivering at least a portion of said air to the furnace, second duct means connecting the second recuperator air conduit to the jet pump to supply air under pressure thereto for Operating the jet pump and means comprising a blower for supplying air to th second recuperator air conduit.

6. Air supply apparatus for supplying air to burners for combustion in a plurality of urnaces comprising, in combination, fiue means forming at least two fiue gas passages from the furnaces, first and second recuperators disposed in said passages and each having an air conduit therethrough, an air supply conduit for supplying air to said burners, first duct means connecting the first recuperator air conduit to the air supply conduit, a jet pump in the first duct means for drawing air from the first recuperator and delivering at least a portion of said air to the air supply conduit, second duct means connecting the second recuperator air conduit to the jet pump to supply heated air under pressure thereto for Operating the jet pump and means comprising a biower for supplying air to the second recuperator air conduit.

WILLIAM M. HEPBURN.

REFEREN CES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,635,939 Isley July 12, 1927 1,717,115 McCann June 11, 1929 1,786,293 Do-wns et al Dec. 23, 1930 1,792,021 Loftus Feb. 10, 1931 1,896,910 Merkt Feb. 7, 1933 2,171,353 Brassert Aug. 29, 1939 2,44,888 Morton et al a Jan. 28, 1947

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