US1504656A - Structure and method of operation of heating furnaces - Google Patents

Description

Aug. 12 1924. 1,504,656

W. TRINKS STRUCTURE AND METHOD OF OPERATION OF HEATING FURNACES Filed July 1'7. 1923 4 Sheets-Sheet 1 HWEA/TOR WITNES$ES .M Li

Aug. 12 1924.

W. TRINKS STRUCTURE AND METHOD OF OPERATION OF HEATING 'YFURNACES 4 Sheets-Sheet 2 Filed July 17. 1923 1 Hdi 0 INVENi'OR Aug. 12. 1924.

W. TRINKS STRUCTURE AND METHOD OF OPERATION OF HEATING FURNACES Filed July 17, 1923 4 Sheets-Sheet 4 "H m-h INVE/V 7'01? WITNESSES Patented l2 UNITED STATES.

wnmam) TRINKS, or ,PITTSBURGH, PENNSYLVANIA.

STRUCTURE AND IMIIBTHOD OF OPERATION OF HEATING-FURNACES.

Application filed "July 17,

To all whom it may concern:

. Be it known that I, WILLIBALD TRINKS, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania, a citizen of the United States, have invented or dis-" covered certain new and useful Improvements in Structures and Methods of Operation of Heating Furnaces, of which improvements the following is a specification. My invention relates to improvements in the structure of and in the method of operation of heating furnaces. It includes improvements uponthe disclosuresof an application of Kernohanand Lochhead, for United States Letters Patent, filed October 29th, 1920, Serial No. 420,377, and of an application filed by me June-22nd, 1923, Serial No. 647,008. In my [prior application last alluded to I speak of a highvelocity jet as a .fl0w-impelling agent, and claim a specific furnace and its method of o eration, in which such a jet may be emp oyed. In this application I shall mo re minutely describe that jet and claim-1t 1tself, as the a cut for the purpose indicated.

My invention," as inthe sequel will appear, is applicable generally to heatm furnaces' and their operation, but. I shal first describe it in the particular application in which I have developed it, the. applicatlon,

namely, to an open-hearth steel furnace.

In the accompanying drawings, Figure I is a view in approximately horizontal section, on the plane indicated by the broken line I-I, Figure II, of an open-hearth steel furnace, 'in which, and in the operation of which, my invention is present and may be carried out. Figure II is a view 1n vertical section of the same furnace, on the plane indicated by the broken line IIII, Figure I. Figures III, IV and V are views in vertical section, III and V through ingot-heating furnaces, IV through a billet-heating furnace, and in these figures the applicability of my invention to these furnaces, various in kind, is illustrated. Figure VI is a view in lon itudinal section and to much larger scafis of a certain-nozzle, which I preferably em loy, as hereinafter explained.

ferring first to Figures I and II, the furnace includes the usual hearth 1, upon which the charge is borne and where the essential refining operation takes place. Producer gas, preheated in the regenerator (not shown) flows through passageway 3; thence 1923. Serial N0. 652,061.

it rises throu h vertical passageway 6, and enters from t e rear the medially arranged downwardly inclined tunnel port 4. Through this port thev stream of gas is carried into the furnace chamber. Atmospheric air, preheated'in the air regenerator (not shown),

flows through passageway. 2; thence it rises in divided flow through two vertical passageways 7 and 8, symmetrically arranged one on either side of the mid-line of the'furnace, and enters from the rear the downwardly inclined port 5, over-arching port 4. Through "this port air is carried into the furnace chamber. Ducts 9-and 10 lead from air .passagewa s .7 and 8 and open into port 4, Of these ucts it is to be observed that they are symmetrically arranged, and that the flow through them will be symmetrical with respectto the mid-line of the furnace; they extend obliquely forward, and the streams flowing through them will converge with the stream flowing directly through the tunnel port '4; they open into the tunnel port 4 at an intermediate point inthe length thereof, and the'conver ing streams will min le before the mout of the, port is reac ed. Nozzles 19 and 20 are provided, through which com iressed air from a supply P1 e 21 may be lown in jets forwardly throng ducts 9 and 10. In supply pipe 21 is a valve 23 for regulating the flow, and

conveniently a secon valve 22, for cutting off the flow entire] "The showing aflXirded in Figs. I and II will be understood to be diagrammatic, and particularly in these respects: The ducts 9 and 10 are shown as rectangular in cross section and uniform in dimensions throughout their extent. Manifestly' they may be articularly shaped accordin to the te'ac ing of neumatics, to afford in highest degree the efi'ect described; the nozzles'l9 and 20 shown diagrammatically as mere tapered terminations of the feed pipes protruding into the ducts, may be elaborated and refined inform; they may be made of the multi le-jet type; they may in position be. so re lated to the form of the ducts as best to achieve their effect again, the openings through the walls of passageways 7 and 8, through which the nozzles 19 and 20 are shown to be movable are, in order that the structure may be clearly understood, shown diagrammatically as greater in dimensions than in actual building they would be.

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- the arrangement here described is a preferred, but not a limiting feature.

I have just said of the nozzles. 19 and 20 that they may be elaborated and refined in form. And here I pause and anticipate a description of mode of operation to remark that 'ets of compressed air are projected longitu inally in ducts 9 and 10 at the intake end of the furnace to induce flow of streams of air from uptake passageways 7 and 8 through these ducts 9 and 10 and into port 4. My furtherand more specific invention in respect to these ducts is illustrated in Fig. VI, where I show a nozzle of a convergentdivergent shape, sometimes called a De Laval nozzle. Inspection of Fig. VI will in view of the foregoing statement make plain the feature here dwelt upon.

The convergent-divergent nozzle has this capacity,that if gas under pressure exceeding a critical minimum (for air discharging into the atmosphere this critical minimum is a pressure of approximately two atmospheres) be jetted through it, a very high jet velocity may be attained. From an ordinary convergent nozzle jet velocity is limited to the velocity .of sound in the medium employed. This velocity is for air about 1,100 feet a second. Froma convergent-divergent nozzle jet Velocities of 1500 feet a second in air and even higher may be got.

The advantage of this high-velocity nozzle to my invention is this: If the compressed air jetted through nozzles 19 and 20 be unheated it will on mixing with the air drawn from passageways 7 and 8 effect some cooling of the streams, and there is apoint beyond which such cooling may not advantageously be carried. On the other hand, it is an economic advantage if the air jetted from-the nozzles may. be used in unheated condition. Increased velocity of jet means that the same flow of heated air from passageways 7 .and 8 through ducts 9 and 10 may be got with jets of diminished weight.

Accordingly, the employment of convergentdivergent nozzles means that I can use'unheated air under conditions which otherwise would require preheating,-preheat ing, that is, of the compressed air etted from the nozzles. I

I have shown the compressed air supply pipes 21 at opposite ends of the furnace, together with the connections which terminate in nozzles 19 and 20, to be suspended, as by chains 24, and it will be understood that by such means the nozzles 19 and 20, positioned as shown at'the intake (left hand) end of the furnace, may at the outtake (right hand) end be swung aside, away from the deleterious influences of the outflowing products of combustion. As an alternative ex edient, these pipes may be stationaryan the nozzles water-jacketed--an expedient so well known in the general field of furnace structure as to require no illustration.

As shown in the drawings, the furnacereversing instrumentalities will be understood to be arranged for the inflow .of gas and air at the left-hand end and for the outflow of products of combustion at the righthand end. At the left-hand end of the furnace the valve 22 in the supply pipe 21 will be understood to be open, and at the righthand end the corresponding valve will be understood to be closed, and at that end the pipe itself is shown to be retracted and the nozzles 19 and 20 withdrawn beyond the walls of vertical passageways'7 and 8. Gas and air are entering through the ports at the left-hand end and are burning in a flame which sweeps from left to right, and the products of combustion are escaping throu h the ports and passageways at the rightand end. At proper intervals of time the furnace is reversed and, incidentally to reversal, the pipe 21 and nozzles 19 and 20 at the right-hand end which had of the furnace requires no illustration, and

I have not sought to afford illustration of it.) The degreeof opening of valve 23 may, if desired, be diminished as operation upon'a given furnace charge progresses, to the end that at the beginning the flame may be relatively short and sharp and toward the end relatively long and lazy.

In the operation of open-hearth furnaces ascommonly conducted hitherto, the draft through the furnace has. been relatively feeble, and combustion has been imperfectly controlled. This has been particularly true of furnaces fired with producer gas. In the operation of these furnaces the air ordinarily has been drawn through the air rcgenerators and into the furnace merel by the stack effect of the regenerators an the uptakes. The gas flowing from the producer and through the gas regenerator and thence to the furnace has been commonly subjected only to such pressure as is incident to its delivery from the producer. In some cases a blowing fan has been placed in the stream of the air supply to the furnace, but there is a practical limitation upon the building up of the pressurethere. \Vhen the pressure exceeds a small amount, leakage through the masonry of the furnace structure becomes too great. It is difficult. be-

cause of expansions and contractions inciin order to produce a sharp flame, require that the ports be relatively narrow, and narrow ports do not afford at the discharge end of the furnace unhindered exit for the products of combustion. (It is of course to be understood,and the condition has already been alluded to,that in ordinary openhearth operation the flow of the flame is periodicallyreversed, and duplicate sets of ports at opposite ends of the furnace serve alternately to lead in'the gas and air and to lead out the vastly greater volumes of hot products of combustion.) Because of these difliculties chiefly, and in spite of various relief projects, open-hearth operationas a matter of practice has been limited to low rates of flow of, air'and of gas and to the generation of a consequent long and lazy flame. This flame is still burning when it reaches the ports at the outgoing end of the furnace and combustion continues through the ports and even down into the regeneratorsa state ofthings both wasteful and destructive. A roposal to use dampers for,

reducing the e ective size of the passageways at the intake end of the furnace, with the end in view of increasing there the velocity of flow, involves complication of structure, and the dampers, when present,

absorb a great deal of heat. v

In the furnace of F ig's, I and II,'while operation is in-progres s, compressed air is blown through nozzles 19 and 20 into ducts 9 and 10. This compressed air may, as has been explained, be preheated or not, as

found desirable 'or convenient, and if preheated, the preheating may be carried to any desired degree. But, as;.I have explained, the necessity for preheatin may within wide limits, be "avoided. The ets of air issuing from the nozzles have high velocity-from GOO-to 1509 feet per second or more,--a matter conditioned upon the actual pressure of the "supply and upon the shapeof the nozzle and the s'ize and shape of the orifice. This highvelocity jet entrains hot air from the uptake passages7 and 8,-and induces a'flow ofair through ducts 9 and 10 into the stream of gas ad vancing through port 4. Thus the entering stream of air isdivided;-one portion. is directed into port 4, where it mingles with the gas before entering the furnace chamber;

the other portion flows unmingled through port 5 into the furnace chamber. The relative value of these two portions 7 of the stream of entering air is variable and responsive to the degree of opening of regulatin valve 23; if that valve be closed complete y, all of the air will, under suchcon ditions as usually obtain, enter the furnace chamber through port 5and*,indeed, because of the fact that usually the gas advances to the furnace under pressure greater than that of the air, there will be some back opened Wider.

tieth to one sixth by weight of the air flow-' iug in ducts 9 and 10 is that which flows from the nozzles; the rest is drawn in from the streams of air rising through uptakepassag 7 and 8. By roperly proportioning in size ports 4 and 5, passageways 7 and 8, and ducts 9 and 10, it is possible by the means described to divert through ducts 9 and 10 into port 4 any "desired fraction of the streams of air rising through uptake passageways 7 and 8 Indeed, it is possible so to divert substantially the whole of these streams; ordinarily it is not desirable in operation to go so far as that, but it is-preferable toallow some air to enter the furnace through port 5. I

'When valve 23 is nearly closed the flame is long and lazysuch a flame in fact as is usual in open-hearth operation as commonly conducted hitherto; if the valve 23 is opened wide, the flame is short and sharp.

Any desired sharpness of flame may be ob tained by movement of the regulatingvalve 23. A shorter sharper flame than that usual in the open-hearth operation is desirable; combustion; is then completed within the furnace chamber, where alone combusmay be relatively short-and sharp, and toward the end relatively lon and lazy. -As has been intimate I 0. not intend ordinarilyto resort to .special means for building 'up pressure on air or gas on'the intake end of the furnace nor to special vmeans for drawing the products of combustion out from the outgoing end. Nevertheless, the practice of my invention does not forbid the use of such ancillary apparatus, if for any reason it be found desirable.

The streams of air entering port '4 through ducts 9 and 10 produce combustion in port 4, to the extent that the air and gas mix. Mixture, however, is not complete until the gases have just left port 4 on their way to the furnace; Inconsequence, com-v bustion in and just beyond the opening from port 4 is so rapid that an-extremely high.

greater. than issue from the jets) from the air passageways 7 and 8 through ducts 9 and 10 into port 4. Furthermore, by the I use of the jets of compressed air, this proing air or 45 jecting of streams of air through ports 9- and 10 .is attained without subjecting the furnace structure to augmented'pressure 1n the regenerators or in the air uptake passageways' 7 and 8, and without resort to dampers.

I have consistently spoken of the substance projected through nozzles 19and 20 as compressed air, andcrdinar ly'compi'essed air will be best; air is requisite to combustion in ordinary practice, and is one component of the combustiblemixture within the furnace chamber. But manifestly the jetmight be constituted of some other fluidof steam, for example, or of oxygen, or of a substance which, while not entering into the act of combustion, still serves mecham ically, to divert the substance of one of the two streams through the ducts 9 and 10.1nto

the other stream.

The arrangementof ports and passage -ways might be reversed, and gas rising through passageways7 and 8 diverted and projected into the air advancing from passageway 6 through port 4. a

The use of a high velocity jet for entrainnaces is not limited to the use of auxiliary ports 9 and 10, as shown in Figures I and II. A jet traveling at high velocity entrains and induces the surrounding fluids by VlS cous drag and forces them to travel in the direction of the jet. The velocity of the et slows down as more and more'of the surrounding fluid is 'entrained.- no matter whether that fluid be air, gasor vapor such as vaporized oil or tar; The jet has a double action, firstit entrains, accelerates, and GIYQS direction, and, second, it mixes the fluids which are entrained.

By experimenhl'have found that a'high velocity jet spreads from thenozzle entraining the surrounding fluid, making a total cone angle of about 26 degrees if flowing in a reasonably open space. Within the jet the total momentum remains approximately constant at any cross section along Y the flow.

fuel in heating or'melting fur-l No inatter whether the jet entrains fluid in a duct or whether it does so in a reasonably open space, such as the main chamber of a furnace, the outstanding fact remains that the jet issuing at very high velocity from a high pressure convergent-divergent nozzle has much more directing and entraining power than a jet which is discharged from a convergent nozzle and that, by this very fact,

the use of a high velocity jet becomes possible when the ordinary jet would be a failure because of too much mass of the entraining The furnace illustrated in Figures I and II is an open-hearth furnace, designed for the use of gas as fuel and, specifically, producer gas. Figure-III shows diagrammatically a heating furnace for ingots, the fa- ;miliar pit furnace provided at .a blooming mill. In it ingots I are shown restin on the hearth 301 of the furnace chamber. urnaces for this purpose are ordinarily regenerative furnaces and admit of a considerable latitude in structure and considerable modification in mode of operation. The furnace shown will however serve as a typical fur mice of this general sort. In this particular instance it w ll be observed that it is the air only which is regenerated in regenerators 30, while thefue (which in this instance will-be understood to be gas relatively richin quality.-coke-oven gas,for instance) is introduced through pipe 31 into the stream of regenerated air as it advances to the furnace port. Astructure is built upon the wall of the passageway fromregenerator to furnace port which in mill parlance is called a .doghouse. Within this doghouse, as clear ly a pears, is formed a b -pass 32, through whic a fraction of thee vancing stream of air is shunted. Into this b pass open fuelsupply pipes 327 '(the'num er and arran ement may be such as desired, ordinaril t e arrangement will be symmetrical wit respect to the line of flow) The fuel introduced will ordinaril be gas; itmay, however, be powdered car naceous material borne on a gaseous stream. Pipe 319 carries compressed air (or equivalent fluid). It extends into the byass 32, and from it a ct is projected in the ine of flow through t is bypass and in the "direction of the furnace chamber and such jet serves, as in the othercases already descr bed, to impel flow throu 11 the bypass and throu h the port, into tIi'e furnace. The structure. iflers from the structure of Figures 1 and II, in that the jet-impelled branch of the stream reunites with the other branch ,and the united stream enters thrpugh the single port into the. furnace. This is a variant which may be noted in passing. I have said that a gas of relative richness will in ordinary contem lation be introduced through the fuel-supp y ipe.31 atthe inlet end of the furnace. Tiis gas may be natural gas, for example, or cokeoven gas, or even producer gas, or 1t may be a gaseous stream carrying a burden of powdered carbonaceous material. From what has gone fore the operation will be fully understood.

Figure V serves merely to indicate how the same essential invention may be appliedmiliar construction. Uponthe furnace wall is built a doghouse, into which doghouse there opens an uptake passageway 407 for air, which it Iwiltbe understood may lead The chamber 404 within the doghouse, so supplied with air, opens to the furnace chamber. Into chamber 404 fuel is intro- 'duced,.as is indicated at 427, and nothing more need be said about fuel than to remark that fuel of any preferred character within the range already noted may be introduced I in the manner and by the means already de:

scribed. A compressed-air pipe 419 dis-'- ch'arges a jet in the line of flow of airthrough the chamber 404, and into the furnace chamber.

Mention of a recuperator gives occasion to note a further advantage of my invention. A recuperator is .a heat exchanger in which streams of entering air glor gas) and of outflowingflaming gases or ot products of-combustion flow 1n contiguous passage: Ways, separated by a heat-penetrable partition wall. This'wall ordinarily is .a thin wall of brickwork. Draft through the furnace is ordinarily maintained by a stack; and in the recuperator, while the stream of air flowing on one side of the partition is under a pressure slightly in excess of that "of the atmosphere, the stream of hot gas flowing on the other side of the partition is, in consequence of the draft condition established by the stack, under a pressure appreciably less than atmospheric. A thin wall of brickwork'is liable to deterioration and leakage, and with inequality of pressure on its opposite sides, leakage means disturbance suck the preheated air out of the recuperator except by its own buoyancy which, in some cases, has been augmented by the'action of a fan at the cold air inlet of the recuperator.

" In any such case there is a pressure greater than atmospheric either throughout the whole! length of the air passageways in the recuperator or at least in that portion nearest to the hot-air outlet. The application rom a recuperator or from a regenerator.

of my invention 'now described toa furnace whose air supply is preliminarily heated in a recuperator achieves a proper firing of the furnace without the attendant necessityof an unbalancing of pressures in the recuperator; the suction effect of the jet in the air passageway leading to the furnace is to reduce the pressure of the entering air in the recuperator to substantially that of the products of combustion flowing out through the recuperator to the stack. Consequently, wear and tear does not bring about that loss in efficiency just pointed out.

In describing the structure ofthese Figures III, IV and V I have said, generally, that the jetis ordinarily of compressed air,

and it ordinarily'will be, but it is to be understood that I am not limited tothe use of compressed air, in view of what I have already said, m invention is embodied in the provision of a jet of fluid. With this brief definition of parts, it is believed that the structure and operation ofthe furnace of gigure III also will be clearly understoo All that was said with reference to the furnace of Figs. I and II concerning variations'in and refinements of structure; concerning the nature of the fluid projected from nozzles 19 and 20, and concerning its pressure and temperature, and the effects of variation in these matters; all that was said concerning draft conditions maintained and means of maintainin them, will be understood to be applicab e to the furnaces of Figures III-V and their operation. What has been said concerning pressure and temperature of fuel will be understood to be applicable generally in the operation of the furnaces described.

Reviewin the structures of all of the figures, it wil? be seen that there is throughout a chamber which, varying in detail, possesses constant characteristics. I allude to the chamber 4 of Figures I and II, 304 of Figures III and V, and 404 of Figure IV. In the ensuing claims I use in some cases the term port, in some cases the term mixing chamber. It will be understoodthat the varying phrase merely lays emphasis upon certain characteristics of this same structural element, and neither term is used in an specifically limiting sense.

I have i ustrated a considerable latitude in modification of structure, and in method of operation.- In so doin I have not intended to limit the range 0 permissiblelatitude, but to indicate rather that the field is wide within which my invention may be herein described which consists in maintainingya passageway for such preheated .air

leading to the furnace chamber and in projecting into such passageway a flow-inducmg jet of compressed gas at a velocity ex ceeding that of sound; and causing fuel to mingle in the stream.

2. In the operation of a furnace -usin preheated air for combustion the metho herein described of impelling the flow of air to the furnace chamber which consists in that of sound, and means foradmitting file substantially as described.

to the induced stream, substantially as described. W

4. In a heating-furnace structure the combination with a furnace chamber of an air passageway leading thereto, a conduit for compressed gas provided witha convergent-- divergent nozzle arranged within said pas sageway and meansfor admitting fuel to a stream of air flowin in. said v 5. In he structure of a heating furnace using preheated air for combustion the com- ;in sai passageway,

bination with a passageway forpreheated air leading to the furnace chamber, a conduitfor compressed gas provided with a conver ent-divergent nozzle arranged withpassageway, substantially as described.

6. In a heating-furnace structure the combination with a furnace chamber provided with an intake passageway for air and an outgoing passagewa for products of combustion, means for rawing the products of combustion through the outgoin passageway and means for projecting a ow-inducing jet of fluid at a velocity exceeding that of sound within the intake passageway, substantially as described.

7. The method herein described of firing a furnace which consists in establishing conditions of low-velocity flow through the furnace as a whole and at the intake end increasing locally the flow to a flow of high welocity by projecting into the flow a jet of fluid at a velocity exceeding, that of sound.

In testimony whereof I have hereunto set my hand.

WILLIBALD TRINKS. Witnesses:

FREDERICK L. JENKINS, JOHN C. CARR.

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