US2228722A - Furnace - Google Patents

Description

Patented Jan. 14, 1941 `UNITED STATES FURNACE v William Isaacs, .Struthers, and Elmer E. Motley, t

Steubenville, Ohio Application August 18, 1939, Serial No. 290,798

Claims.

Our invention relates more particularly to `gas fired open hearth regenerative furnaces such as 'are commonly employed in the steel industry although it is equally applicable to other forms of regenerative furnaces.

Open hearth regenerative furnaces' as usually constructed comprise the furnace proper including the hearth, a set of regenerators disposed near'each end of the furnace at `a lower level than Vis its hearth and passages respectively extending therefrom through which the incoming heated air and gas is conducted to the furnace from one set of regenerators and the waste gases discharged from the furnace into the other set of regenera tors alternately. In accordance with usual practice the chambers of each set -of regenerators are Aeither disposed side by side and thus separated by a single partition wall vor spaced apart for a Ashort distance and vthus separated by two walls with a space or opening therebetween. The air and gas passages leading from the chambers to 'the furnace are often separated by 'but a single wa-ll irrespective of the particular Larrangement -of -the regenerator chambers andthe -heated gas which isun'der Aconsiderable pressure, -tends to leak through any-cracks or openings in this wall and mix with the air int-he lair passage. t Asfboth 'the air and gas vare lin highly heated condition,

"ignition vfrequent-ly takes place in the 'air passage and the wall adjacent thev cracks-where the gas `has leaked vthrough is burned away gradually'in cone-shaped depressions. Additionally, premature Aignition and burning 'of the ai-r and gas in I'the air passage yrenders proper control of the `furnace very diicult -if not impossible with consequent enhancement of operating costs and 'gen- Verally unsatisfactory operative resul-ts and these disadvantages become greatly accentuated as the leakage of the -gas through the division wall -between the gas and air passages Aproceeds at a progressively lgreater amount `-for the burning.

away -of the Wall adjacent the leaks and consequent lformation of the vcone-shaped depressions lor holes therein facilitates the passage of the gas so 4that more and more of it -leaks through and is burnedastime-goes-on.

In ULS. Letters :Patent No. 1,831,354, granted to us vNovember 10, 1931,'we disclosed and claimed certain improvements in furnaces bythe utilizaltion fof which this :leakage of .gas through the'wall adjacent .the vair passage lmay be minimized and leakage of gas into the latter eliminated entirely and 'the present invention embodies further Sim- `provenlents whereby the -sameadvantages may be realized, but to a greater degree, `together with (ci. zes-.15)

additional ones promoting maximum efficiency ofthe furnace as a whole.

It is therefore a principal object of the invention to provide an'open hearth or like furnace embodying means for preventing a leakage of gas l5 from the gas passage to` the air passage combined with means for effecting more efficient combusf tion of the gas in the furnace and more accurate control of the latterthan has heretofore been attainable. 1 v

Another object is'the provision of mean-s in combination with such leakage-preventing means operable to -deliver into the ycombustion area in the furnace substantially at the pointof Aemission of thef heated gas from the gas passage there- 2:1!5

into, a continuous directionally controlled relaj tively high velocity stream or 'jet of air, preheated by residual heat which might otherwise be lost, which increases the capacity of the fuel when mixed with air to impart heat to the fur- :20 'nace charge. f l

Further objects ofthe invention are the provision of means for vthe purposes aforesaid which may be readily embodied in open hearth or like furnaces without material alteration of their usual structural arrangement, which do not materially increase the initial cost of furnace installation and which'are entirely satisfactory for the performance of their intended functions.

A still further object is to provide a method of operating open hearth or like furnaces to insure Acomplete combustion of the gaseous fuel adjacent -the surface of the charge, and to lprevent blanket? ing of the latter with a layer of unconsumed fuel, l by introducing into the lfurnace between the stream of fuel and the charge a stream of preheated air which enables the lower part of the c fuel stream to burn substantially in contaet'with the surface of the charge;

Other objects, advantages and novel features of f4() design, constructionA and arrangement comprehended by our invention are hereinafter more particularly pointed out or will be apparent from the following description of an open hearth furnace constructed in accordance with the invenf tion and a portion of which is illustrated in the accompanying drawing.

As our invention relates more particularly `to those parts of the furnace, considered as a whole, which concern the conduction of the air and gas 59 from the respective regenerative 'chambers to the inside of the furnace ladjacent the ends of its hearth, and as regenerative furnaces are usually similar at both ends, we have, in the accompanying drawing, shown only those parts adjacentlthe end of the furnace substantially on the plane `ter of the furnace than the of line 2-2 in Fig. 1 and Fig. 3 is a horizontal section through the gas and air passages and adjacent parts on the plane of line 3-3 in Fig. 1.

Like symbols of reference are used to designate the same parts in the several figures.

The furnace, as shown, save in particulars hereinafter mentioned, is of ordinary construction comprising a hearth I adjacent and above the end of which is disposed the outwardly and upwardly inclined gas port 2 from which the gas is discharged towards the hearth and which communicates at its outer end with a downwardly extending neck 3 in turn communicating by a horizontal passage 4 with a gas regenerative or checkerschamber (not shown) disposed laterally of the furnace, the gas'port 3` being desirably provided with cooling coils 5 in` its top and side walls. Abovethe gas port is disposed the usual air port 6 through which the air is discharged toward the hearth and which near its outer endl communicates with downwardly extending necks 1 on either side of the furnace in turn communicating at their lower ends with-the air passage 8 which extends laterally outward alongside but inwardly of the gas passage and is connected with the air regenerative or checker chamber (not shown) located alongside of but nearer the vcengas checker chamber. The hearth of the furnace is supported on pillars and beams and the walls by buckstays in the customary manner and as these parts are well understood and may be of any desired or preferred construction and arrangement, no extended reference to or detailed illustration of them is required. I

In accordance with the invention disclosed in our said prior patent, instead of utilizing a single solid division wall between the gas and air passages 4 and 8, we provide in this zone two longitudinally spaced, generally transversely extending walls I0 and Ii to respectively form the adjacent side walls of these passages and dispose between these walls means which in accordance with the present invention not only form a barrier to the escape of gas from the gas passage into the air passage and a support for the walls of the latter but also provide a tortuous course for a stream of air delivered by an air fan or blower I2 connected therewith as will hereinafter more fully appear.

The said means include sheet metal facings or sheathings I4, I5 applied to the adjacent vertical sides of the gas and air passages with a metal bottom channel I6 and end plates I1, I8 welded or otherwise secured to the facing sheets at their lower edges and ends respectively, the plate I8 at the opposite ends of the facing sheets from the regenerator chambers comprising near the bottom channel I6 an aperture I9 for interconnection of the discharge pipe 20 of the blower i2 with the interior of the casing formed by these several parts. The upper edges of the facing sheets as well as of the end plates are secured to upper channel section strips 2I, 22 which are spaced apart at the center ofthe casing and form a top therefor provided with 'an exit port for interconnectlon with an upwardly extending metal conduit 23 built into the furnace parallel to the vertical portion ofthe gas passage neck 3 between the air passage necks 1.

A pair of vertically spaced horizontal baille strips 24, 25 respectively extend from the ends of the casing inwardly for a distance somewhat less than its length and substantially divide it into `three interconnected elongated horizontal sections forming a continuous tortuous passage for air from the blower as indicated by the arrows in Fig. 2.

The facings I4, I5 and the horizontal baffles are reinforced at spaced intervals along the course of the air stream by short I-beam sections 26 extending vertically between the several horizontal elements of the casing and having elongated holes 21 in their webs for passage of the air. These various metal parts are hot when the furnace is in operation through their direct or indirect contact with or proximity to the walls of the gas and air passages and as the air from the blower passes over them as it traverses the tortuous passage formed from inlet I9 to conduit 23, it absorbs heat from them and thus not only prevents overheating of the said walls but is raised here connects with a substantially horizontal slot or jet 28, the upper surface or roof of which g slopes inwardly and downwardly toward the hearth and which is preferably of less eective area than the conduit, whereby the heated air forced through the conduit from the casing is ejected into the furnace beneath the stream of gas flowing thereinto through the gas port. The gas is thus induced to burn at its lower surface and inA intimate proximity to the furnace charge, thus enhancing the transmission of the heat of combustion to the latter.

In an open hearth furnace of usual construction the gas port lies below the air port adjacent theend of the hearth and such furnaces are normally operated insuch a way that the vtemperature of the entering gas is about 1100 to 1200 F. and that of the air from the regenerators about 2400" F. immediately after a rey maximum efliciency. Consequently the introduction of additional or supplementary heated air into the furnace in such a Wayas to prevent this blanketing of the charge materially promotes efficient combustion of the gas and economic operation of the furnace as a whole.

To prevent overheating of the upper vwall or Iroof of the jet 28, it is desirably provided with a hollow cooling plate 29 having interconnected with it cooling fluid tubes or pipes 30 which maintain a flow of cooling water through the plate.v

In accordance with our invention the introduction of supplementary air beneath the gas stream brings about earlier combustion of the gas than heretofore obtained as well as a higher heating of the mixture and consequent intensication of the heating of the charge and the preliminary heating of this air, in its traverse of the tortuous passage in which it absorbs residual heat from the gas and air passage walls, further intensifies the heat of the flame and thereby enables production to be accelerated and the time required for the refining of each charge to be reduced.

Moreover, by preventing leakage of gas from the gas passage into the air passage while the gas is owing from its checker chamber to the furnace We eliminate pre-ignition of gas in the air passage and resulting loss of operative control of the furnace, while any gas which may in some way leak through the gas passage wall into the casing and/or conduit is carried into the furnace and consumed in heating the charge.

It will, of course, be understood that the supplementary air is delivered by the blower I2 at either end of the furnace only while that end is being used as the inlet end and not while the products of combustion are being discharged therethrough, and it is usually most convenient, although not necessary, to have each blower interconnected with other furnace controls in such a way as to operate automatically at the proper times and to remain inoperative at others.

A further important feature of our invention resides in the fact that the initial cost of a furnace of given capacity is not materially enhanced by the inclusion of our improvements therein and thatexisting furnaces can readily be modied to incorporate them without extensive alteration, whereby the advantages of the invention including increase of operative life, reduction in cost of repairs and replacements and satisfactory and efficient operative control may be attained at a comparatively small expense in prospective as well asin present furnace installations.

While we have herein illustrated and described with considerable particularity one form of open hearth furnace constructed in accordance with our invention, we do not thereby desire or intend to limit or conne the use thereof solely to a furnace of that type as its principles and advantages may be readily embodied in furnaces of other types if desired without departing from the spirit and scope of the invention as defined in the appended claims.

Having thus described our invention, we claim and desire to protect by Letters Patent of the United States:

1. In a furnace comprising a hearth, means defining passages respectively terminating in gas and air ports adjacent the hearth, metal sheets disposed in heat exchange relation with adjacent walls of the said passages, means extending between said sheets forming therewith a substantially closed casing and a continuous tortuous passage therein, means for forcing air into said tortuous passage, a conduit for said air extending therefrom toward the gas port and means comprising a horizontally elongated, vertically constricted port subjacent the gas port forming an outlet for the conduit adapted to project said air at relatively high velocity into the furnace between the charge and the gas issuing from the gas port.

2. In a furnace comprising a hearth, means dening passages respectively terminating in gas and air ports adjacent the hearth, metal sheets disposed in heat exchange relation with adjacent walls of the said passages, means extending between said sheets forming therewith a substantially closed casing and a continuous tortuous passage therein, heat exchange elements in said tortuous passage, means for forcing air into said tortuous passage, a conduit for said air extending therefrom toward the gas port, and a port at the upper end of the conduit subjacent the gas port forming a relatively restricted outlet for the conduit and having a sloping roof directed downwardly toward the hearth adapted to project said air into the furnace between the charge and the gas issuing from the gas port.

y3. In a regenerative furnace having separate air and gas regenerators adjacent each of its ends, walls extending from each of said regenerators and defining separate air and gas passages between the regenerators and the furnace throat respectively adapted to conduct air and gas thereto, the walls most nearly adjacent each other being spaced apart, means interposed between said walls in heat exchange relation therewith dening a tortuous enclosed passage, means denning a substantially vertical passage leading from said tortuous passage and a port having a downwardly sloping roof, communicating with said vertical passage and disposed beneath the outlet of said gas passage and means for forcing air into said tortuous passage during operation of the furnace to thereby eject heated air from said port into a zone between the furnace charge and gas issuing from said outlet.

4. In a furnace having separate air and gas passages extending in close proximity adjacent its ends and terminating in ports within the furnace, a hollow metal casing disposed between the air and gas passage walls in heat exchange relation therewith, baflles in the casing presenting heat exchange surfaces and forming with the casing walls a substantially closed tortuous passage through the casing, means for supplying air to one end of said passage and a sloping partition spaced above the other end of the passage between it and the gas port providing a restricted discharge port for said air, after it is heated in the casing, adapted to dei-lect said air toward the interior of the furnace and impart to it a relatively high velocity and to direct it into the furnace in substantial parallelism with and the same direction as gas from the gas port and between said gas and the furnace hearth.

5. In a furnace having separate air and gas passages extending in close proximity adjacent its ends and terminating in ports within the furnace and a chamber interposed between said passages, means for forcing air into the chamber, a conduit leading therefrom and a discharge port interconnected with the conduit Within the furnace having a roof sloping inwardly and downwardly toward the furnace hearth subjacent the gas port.

WM. ISAACS. ELMER E. McVEY.

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