US1741024A - Open-heabth fttbnace - Google Patents

Description

Dec. 24, 1929. R. B. KERNOHAN ET AL OPEN HEARTH FURNACE 5 Sheets-Sheet Filed Oct. 29. 1920 aw z o s.

Dec. 24, 1929.

Filed Oct. 29, 1920 R. B. KERNOHAN ET AL OPEN HEART FURNACE 5 Sheets-Sheet 2 INVENTORS l Dec. 24, 1929. R. B. KERNOHAN ET Al. 1,741,024

OPEN HEARTH FURNACE Filed Oct. 29, 1920 5 Shets-$heet 4 nwz/vro/es MAM/W414,

l l L 1 l l I W/T/VESSESI I y mw Dec. 24, 1929.

R. B. KERNOHAN ET'AL OPEN HEA'RTH FURNACE Filed Oct. 29. 1920 5 Sheets-Sheet 5 WITAIIESSES lmkmwz M/VENTORS Patented Dec. 24, 1929 um'rsn STATES P T BOBIBL'I. B. KEBNOHAN AND JAMES B. IOCHHEAD, OI PITTSBURGH, PENNSYLVANIA OPEN-HEABTB roan-Lon Application fled October 29, 1820. Serial No. 420,877.

Our invention relates to improvements in the structure of, and in the method of operation of, metallurgical furnaces in which continuous streams of gas are burned. We havemadc particular application of the invention -to regenerative furnaces, and specifi cally to open-hearth furnaces. The objects in view are economy-economy in method, obtaining the most from the materials employed, and economy in structure, saving space and material and adhering to simplicity inform. In the accompanying drawings furnace structure is illustrated in which and in the u used which our invention is practiced. In these drawings Fig. I'is atview in horizontal section through the ports and above the hearth ofJan open-hearth furnace; Fig. II is a view in medial and vertical sectiornon the m planeindicated by the line 11-11 in Fig. I.

In Fig. IIa dotted line II indicates approximately the plane of section of Fig. I,

. although it will be found that, for simplicity of illustration, Fig. I affords representation of more than any single lane of section would afford. Figs. III and V are views in transverse and vertical section, on the planes indicated at III-III and IV-IV, respectiveiy, Fig. 1.- Fig. V is a view similar in part to andshowing' additionally in plan the stack connections, in connection with which a further feature of invention is found; Fig. VI is a view in vertical medial section, corresponding. to Fig. II, but drawn to larger scale, and showing in this aspect the-variants in structure alluded-t0 in characterizing Fig. V. The furnace includes the usual earth 1 and air and gas passageways 2 and 3. duplicated' at the opposite ends of the furnace. At one end of the furnace streams of air from i the atmosphere and of gas from a producer advance t rough regenerators into passageways 2 and 3 and flow thence through suitable ports to the furnace chamber; at the opposite end of the furnace the products of combustion emerge through corresponding ports and, entering passageways 2 and 3, flow through the regenerators and thence to the stack. At suitable intervals Oftime the ig. I, illustrating modifications in form,

direction of flow is reversed, so that what is first (so far as concerns these heat-affording gases) the intake end of the furnace becomes the delivery end, while the end at which the roducts of combustion had been escaping ecomes in turn the intake end.

It is in the ports through which the incoming ases flow from passageways 2 and 3 to the, urnace chamber (and through which at. the op osite end the products of combustion escape i where our invention centers.

It is already familiar in furnace structu to arrange the gas port on the medial line of the furnace, in the form ofan arched tunnel, and to arrange the air port above and around 66 this gas rt. As the drawings show, we adopt sue a medial, tunnel-shaped port. It is indicated at 4. The surrounding space bears the reference numeral 5.

In the typical open-hearth furnace the 70 heated streams of air and gas are delivered separatel into the furnace chamber, above the heart they meet for the first-time there, above the hearth, and there theybegin to unite, in the reaction called, combustion. We have departed from this, theusual ractice, and have directed our efforts to e ecting a mixture of air and gas immediately before delivery into the furnace chamber, and for this reason: Mixture of as and of air within an the furnace chamber, ing relatively uncontrolled and casual, is relatively incomplete; by s ial provision just before d'eliveryto the urnace chamber, the mixing of and air may be controlled and made muc more 86 thorough, intimate, and com lete. It is true that, immediately on the mingling of 1 these heated components, combustion be '11s; but, since the mixing which we efiect 1s accomplished within'a short reach of the advancing 90 streams, andimmediately before delivery into the furnace chamber, the gases are delivered while-the operation of combustion is at its very beginning. Stated in another way, in

the usual practice, when gas and air are de- 08 livered separately into the furnace chamber,

the flame springs from a int within the furnace chamber; when in t e practice ofour invention the air and gas are mingled just. before delivery into the furnace chamber, the-:10)

flame springs from a point slightly further back in the stream, a point within the port, just before the now burning gases emerg into the furnace chamber.

But we find there is no disadvantage'in this. To the contrary, because of the relatively more thorough mixing which we achieve of the gas L 11d the air together, combustion is much more nearly complete, the heat units available are in larger measure released within the furnace chamber, and, using gas of given composition and temperature and air of given temperature, flowing from the regenerators in given relative quantities, better heating effects can be got by following our invention than by the usual practice indicated above. The advantage of our invention may be stated in another way: by virtue of the more intimate mingling of gas and air which we effect, and the consequent more complete combustion and greater release of heat within the furnace'chamber, it becomes possible for one who follows our invention to accomplish more in a furnace of given dimensions, or it may be to operate with a leaner gas, than the usual practice indicated above admits of.

' regenerator, flows through passageway 3, as-

cends the vertical passageway 6, and, entering port 4 from the rear, sweeps through that port to the furnace hearth. The air advances in a stream from the air regenerator into passageway 2; from this passageway the now' divided stream ascends through the two vertical passageways-7 and 8, and thence discharges, through the injection ducts 9 and 10, directly into the medial port 4:.

A minor variation in this detail of structure is illustrated in Figs. V and VI, where the stream of gas flows from a header chamber 11 in the gas passageway through a single duct 12 into the port 4.

In both of these alternate arrangements, however, it will be noted, first, that, since port 4 is medially arranged, the instreaming flame is directed centrally into the furnace chamber; second, that the stream of air which is directed into the stream of gas to mingle with it (or the reverse), whether it approach in a single stream or in a plurality of branches, enters through leads which are symmetrically arranged, with respect to the medial vertical plane of the furnace: and, third, that the air lead (or gas lead, Figs. V and VI) approaches the. port obliquely, in the direction of flow, and that the two streams consequently meet at an acute angle,-and flow on wiflilminimum deviation of course. The port is of bifurcated shape; the'trunk portion opens directly to furnace hearth ;-the branches converge, not abruptly, but gradually, and

ceived that in one case the confluent streams are disposed horizontally and in the other vertically. In open-hearth steel furnaces the former arrangement is ordinarily preferred. The substance upon which heat is to be expended is after all the pool of metal on the furnace hearth, and, as the drawings show, the port 4 is downwardly inclined, in order to project the flame upon-the surface of the pool. A horizontal arrangement of the confluent streams of air and of gas gives us we find a flame which centers the heat on the pool of metal, rather than spreading it laterally to the detriment of the front and back walls of the furnacethe lateral walls relative to the line of flame projection. i

It will further be noted that, beyond the point where the air enters, port 4, as shown in these drawings, flares toward the furnace chamber. Thus allowance may be made for the enlarged and now burning volume of gas.

This detail is, however, a nicety of engineering, not essential to the practice of our invention in its broader aspect.

Such being the arrangement of ports and passageways, it remains to note certain features of operation which We preferably employ. These features enter into our inven- .ti.on, particularlywhen regarded as as improvement in method. At the same time, even while our invention is regarded as embodied in apparatus, these are features which preferably are employed in the use of the apparatus. a

' Ordinarily, in open-hearthpperation, while the gas is introduced under pressure, the stream of air through air regenerator and into furnace chamber is impelled in no other manner than by the draft conditions set up' by the open-hearth operation itself. No means are provided for driving the air in; it is drawn in by the furnace draft. In practicing our invention, we preferably introduce the stream of air also under pressure. For such worka blowing fan is suitable; the construction and manner of use of such fans are well known, and we have deemed it unnecessary to show a fan in the drawings. Ordi narily the-gas enters the furnace from the producer under a pressure of three quarters of an inch, more or less, water gauge. We have found that pressure adequate for the gas in the practice of our invention. In correlation with such a pressure uponthe gas, we preferably exert upon the air a driving pressure of an inch and a half, more or less, water gauge; that is to say, a pressure twice as great as that obtaining upon the gas. It

- ing not so hot a flame.

will be apparent to the engineer that, in "consequence of the obliquity at which the air is injected into the stream of gas and in consequence of the major pressure under which the air is injected, a larger flow of gas through the port is induced than otherwise would obtain.

Recurring now to consideration of port construction, it is manifest that port 4,

through which as we have said we introduce both air and gas is little larger (we preferably make it slightly'larger) than the port through which ordinarily gas alone is introduced. It is in consequence of the fact that we put the air under pressure as well as the gas, that we are able to introduce through port 4 alone both the components of the combustible mixture in adequate quantities. Furthermore, in consequence of so driving the is achieved before entrance into the furnace the consequence and effect is a shorter hotter flame. I v

Since the pressures under which the gas and the air are introduced are variable, this important matter of length and intensity of flame is brought within the control of the operator. 1 Up to this point in the description we have spoken only of the air and gas entering the furnace chamber through port 4. And indeed no other or additional quantities either of air or of gas are necessary to accomplish the invention. However, varying conditions make desirable the possibility of further 'adaptations. The drawings show the space 5 extending archlik above port 4. This'in ordinary structure and operation is the airport. As we have now explained, our air supply primarily enters the furnace chamber, already mingled with the gas, through port 4. Supplementary volumes of air may, however, be admitted through port 5 directly into the furnace chamber. To that end. the rising air assageways 7 and 8, through which air is .fe as already described into ducts 9 and 10, may communicate additionally with space 5. Furthermore. dampers 18 and 14 may be provided, controlling the effective opening from passageways 7 and 8 into port 5. By adjustment of these dampers supplementary volumes of air may or may not be the furnace.

admittedthrough port 5 to the furnace chamber, as may be desired; and, if admitted, the amounts admitted may be adjusted, relatively to the amounts of mingled air and gas advancing through port 4c. This feature gives supplementary control, to the ends already indicated.

In Fig. V a further structural feature is indicated diagrammatically. It consists in a fan. located at the point 15between the regenerators and the stack 16. Such a fan may be employed to draw the products of combustion from the furnace chamber. lVhen used, a new factor is introduced, entering into the problem of the engineer in designing If no such fan be contemplated, and the furnace be designed to operate in the usual manner, the area of the furnace ports will be determined. not by the volumes of entering air and gas, but by the volumes of outgoing products of combustion.

" These being much hotter than the entering gases are much more voluminous. As a mat ter of actual observation, the volume. of outgoing gases is'one and three quarters times that of the entering gases. It is because the port areas are made large enough to carry away the products of combustion. and under usual circumstances much larger than is needed for the supply of air and gas on the intake side of the furnace, that it becomes possible to use dampers such as 13 and 14, cutting down more or less the effective area of the ports when used for intake. But if a fan be employed, sucking the products of combustion from the furnace, the problem of designing of ports is relieved of one limitation; it will now be possible to make the ports smaller, reducing their area (if desired) even to the'minimum requisite to pass the needed volumes of entering gas and air. and. in theeduction of the products of combustion, to compensate for diminution in port area by the suction of the fan.

withdrawing the gases through ports of diminished area, to be sure. but at greater velocity.

The introduction of the fan, then, into the structure, makes possible the diminution of port area; if this diminution be carried to the limit, the possibility of employing the dampers 13 and 14 is eliminated. However.

given stable conditions, the ports may be properly proportioned, so that it will be quite possible to dispense these dampers; while, on the other hand, the economies achieved in the use of a fan will justify themselves. Fig. VI shows a construction in which port 5 of the earlier figures is eliminated, and allthe air enters necessarily th"ough port 4. It will be understood from what has gone before that ordinarily a furnace so modified will have associated with it",

in operation a suction fan, drawing the prodber. y

We have described the invention as focussed in a stream of gas impelled through a medially arranged port into the furnace chamber, with a stream or streams of air in]ected into thegaseous streams and mingling with the gas in a combustible mixture while the stream is still in the port, .though about to pass thence into the furnace chamber. This arrangement'is capable of inversion: the air may enter the medially arranged port and flow therethrough from rear to front, and

' operators control.

the gas may be projectedthrough the obliquely arranged duct or ductsinto the advancing stream of air. The means by which this vari- 13 and 14 be used, the effective area of the ports in which they are placed-is under the The open-hearth furnace is in some respects peculiar among regenerative furnaces. The operationwhich is performed within it is periodic or cyclic: acharge is introduced and refined and removed and then a new charge is'introduced. This condition of service presents problems very different from those found in the ope-ration of continuous furnaces, where substantially unchanged heat conditions are to be maintained throughout long intervals of time. When a charge is first introduced" into an open-hearth furnace and treatment begins, an intense and relativeshort flame is most effective; as operatlon progresses the flame should lengthen, and finally the flame should sweep through the whole length of the hearth and disseminate as nearly as ma be an even heating efiect' throughout. '1 roughout all the 0 ration, care must, betaken, so to control t e flame, that it shall not spread and burn the front .and back" walls of the furnace (the walls with respect to the line of flame, are

which, lateral). p i

' Such adaptability to conditions of use is found in pressure conditions for air andfor gas so established as to be under. control severally and jointly, as well as in the dampercontrolled air passageways.

In a word, our invention affords control of intensity and of length of flame to meetcond1t1ons of cyclic eperation.

In the foregomg description novelties both of structure and of procedure are indicated.

nets of combustion from the furnace cham It will be understood that themode of operation is essentially that of the ordinary openhearth furnace, modified only in respect to those matters which have been explained.

We have in the course of this specification indicated certain respects in which latitude is permissible in the'practice of our invention. We desire to say further in this con-' motion that the drawings and the description here presented are exemplary. In the ensuing claims we define what is of the essence of our invention; if this be present our invention will be practiced, regardless of details of structure and procedure. As was said at the outset, the invention is ap licable to regenerative furnaces, and indee generally to metallurgical furnaces into which burns a continuous stream of gaseous fuel.

We claim as our invention Y 1. In a regenerative furnace, a central port leading to the furnace, means forforcing regenerated air through said rt, 8. slag pocket communicating with sai port, a sec- 0nd slag pocket beyond said first mentioned slag pocket, a passage for fuel-connecting said second slag pocket and said port, an aux-- iliary flue connecting the first mentioned slag pocket with the furnace and acting as an out flue on the out-end of the furnace and means for closingsaid auxiliary flue on the in-end of the furnace.

2. In a regenerative furnace, a central port leading to the furnace, means for forcing regenerated air through said port, a slag pocket communicating with said port, a second slag pocket beyond said first mentioned slag ice pocket.'a passage for fuel connecting said second slag ocket and said port, an auxiliary flu on eac side of said central; port. connee-ting the first mentioned slag pocket with the furnace and acting as an out flue on the out-end of the furnace andameans for clos ing said auxiliary flues on the in-end of the furnace.

3. In a regenerative furnace, a central port leading to the furnace, means for forcing regenerated air through said port, a slag pocket communicating with said art through a plurality of openings, a secon slag pocket beyond said firstmentioned slag pocket a passage for fuel connecting said second slag pocket and said port, an auxiliary flue con-.'

meeting the first mentioned slag pocket with the furnace and acting as an out flue on the ou t-end of the furnace and means for closing said auxiliary flue on the in-end of the furnace. i In testimony whereof we have hereunto set our hands. s 1

ROBERT E. KERNOHAN. JAMES S. LOCHHEAD.

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