US2169163A - Open hearth furnace - Google Patents

Description

Aug. 8, 1939. G. w. PUTNAM OPEN HEARTH-FURNACE Filed May 21, 1958 2 Sheets-Sheet l.n

Aug. 8, 1939.

G. w. PUTNAM OPEN HEARTH FURNACE 2 sheets-sheet 2 Filed May 21, 1938 ef of 6,45 Po/P INVENTOR. GOEGE W PUTA/AM ATTORNEYS Patented Aug. 8, 1939 UNITED STATES PATENT OFFICE OPEN HEARTH FURNACE Application May 21, 1938, Serial No. 209,299

12 Claims.

This invention relates to open hearth furnaces and is particularly concerned with such furnaces of the regenerative type which embody new and improved features of construction and operate with high efficiency as measured by tons of metal produced per hour and the fuel consumed in such production.

The high eiciency of furnaces embodying the present invention is believed to be the result of extremely rapid and thorough mixing of the fuel and air, and control of the length, shape, direction and temperature of the flame. These results are largely accomplished by a new and improved combination, location and arrangement of the parts of the port ends of the furnace including the floor, apron, roof and side walls thereof.

According to this invention a stream of fuel is discharged into a mixing chamber from av point high above the surface of the charge in the melting chamber and more or less horizontally and approximately kalong the longitudinal plan center line of the furnace. The stream of fuel is so discharged into the mixing chamber that after it enters the chamber it does not contact with the walls defining that chamber, and particularly the apron. Large volumes of air are directed downwardly onto the top, and around and later ally into the sides, of the fuel stream, and other large volumes of air are directed from each side underneath the fuel stream from the time it enters the mixing chamber. A'Ihus the air completely encircles the stream of fuel from the time itenters the mixing chamber until combustion is largely, if not entirely, completed and results in an extremely rapid mixing of air with the fuel, especially on the under side of the fuel stream. The resulting flame is short and is much hotter on the bottom than flames from prior ports with Which I am familiar.

The length of the flame may be Varied within certain limits by varying the amounts and pressures of gas and fuel and by varying the size,

shape and relative location of walls and floorsl Good results in the port ends of the furnace. have been obtained by regulating the length of the flame so that its tip is between the second and third doors of the melting chamber, i. e., with the flame extending for less than about onehalf of the length of the melting chamber. With such a flame the combustion -is completed long before the outgoing gases reach the exhaust port end of the furnace, with the result that combustion does not continue in the exhaust port end of the furnace and the brickwork therein is not subjected to excessively high heat.

The admission of fuel and air into the mixing chamber at elevation high above the surface of the charge in lthe melting chamber, together 5 with the shape, arrangement and location of the Walls defining the mixing chamber, result in directing the flame downwardly into the melting chamber to impinge on the surface of the charge therein near the adjacent end of the charge, and 10 to lie close to the charge from the point of rst impingement to points near the tip of the flame.

In this manner heat is transmitted to the charge by convection and radiation and a large amount is conducted directly from the iiamel to the l5 charge. In prior furnaces wherein the flame did not impn'ge on the charge the transfer of heat from the flame to the charge was mainly by convection and radiation.

The shape, arrangement and location of the mixing chamber walls are such that the areas of the mixing chamber expand from the points of entry of the gas and fuel passages thereinto to the mixing chamber port, i. e., the place where the mixing chamber opens into the melting chamber, and the mixing chamber walls are so arranged that the originally cylindrical shape of the flame is not distorted or flattened out to an objectionable extent when it i's deflected downwardly into the melting chamber, and the direction of the flame is held fairly close` to lines parallel to the center line of the furnace.

Briefly stated, important results of the rapid and thorough mixing of fuel and air, and particularly on the under side of the fuel stream, and the control of the length, shape, direction and temperature of the flame are much faster melting of the'charge, much less consumption of fuel, a material decrease in the amount of heat carried out of the furnace by waste gases 40 and less damage to the brickwork of the furnace. Another result of major importance is that the port ends of the furnacemay be relativelyshort as compared with prior port ends and the melting chamber may be considerably lengthened all without any increase in overall length of the furnace, and greater tonnages of steel can be produced in furnaces of this invention than in furnaces of the same overall length but equipped with prior port end constructions.

In the drawings accompanying and forming a part of this specification and in which one embodiment of the present invention is shown,

Figure 1 is a vertical, central, longitudinal, sectional view taken thru about one-half of an open hearth furnace embodying the present invention: Fig. 2 is a horizontal sectional view taken on line 2-2 of Fig. 1.

Figs. 3 and. 4 are fragmentary views corresponding to portions of Figs. 1 and 2 respec- Y tively;

- as "wing walls.

Figs. 5 and 6 are diagrams showing areas of the air and fuel passages entering the mixing chamber, and the mixing chamber port respectively.

Fig. 'l is a diagrammatic view showing the manner of development of the planes of Fig. 5.

Figs. 1 and 2 show about one-half of a regenerative type, producer gas, open hearth furnace embodying the present invention, it being understood that the remainder of the furnace is substantially the same as the part illustrated in these figures, and that the dot and dash lines indicating doors on Fig. l are not actually doors in the back wall but merely indicate where the doors in the front wall are located.

The furnace herein illustrated is supported on the ordinary supporting structure, and beneath the furnace are located the usual regenerator chambers and passages leading to and from the same, the supporting structure and regenerators not being shown. The furnace consists of two major parts, viz: the melting chamber I and port ends 2 at either end thereof.

The melting chamber I has a front Wall 3 provided with the usual charging door openings 4, the lower edges of which are located on what is known as the sill or fore plate line, indicated at 5 on Fig. 1. The back wall 6 of the melting chamber slopes upwardly and outwardly to about the elevation of the top of the front wall 3 and the arched roof l rests on the tops of walls 3 and 5. The ends 8 of the back wall incline toward the front wall 3 at the port ends of the furnace.

Each port end 2 includes an end wall, side walls, roof and bottom.- The endwall Il! is composed of upright bulkhead parts Illa and Illb. The side walls II and I2 unite with the end wall Il, extend forwardly, toward the melting chamber and merge into walls I3 and I4 respectively which, in turn, unite with end walls I5 and I5 of the melting chamber. 'I'he walls I3 and I4 have inner surfaces which extend convergingly at acute angles to the vertical plane on the center line of vthe furnace. The lwall portions I3, I4, I5 and I6 resemble, in certain respects, walls which have heretofore been known, collectively,

The roof includes a substantially horizontal, arc shaped part I1 which ex- -tends forwardly from the end wall III and a forward part Il sloping downwardly, at a steep angle to the horizontal, to the knuckle Isa, i. e., the' junction with the roof 1, the knuckle preferably being located at or near the walls I5 and II. The bottom of the port end 2 includes an apron I 0 which slopes upward, uninterruptedly and at a steep angle to the horizontal, from hearth l to its junction with the floors 20 and 2| respectively of the air and fuel passages presently to be described. The melting chamber end walls I5 and Il, the roof Il and the apron I8 define an opening, substantially as shown in Fig. 6, between the melting chamber and the port end 2. 'I'he melting chamber end of that opening is hereinafter referred to as the mixing chamber port. It will be noted that the knuckle Ila is high and in fact is not much lower than the roof 1. It is possible to keep the knuckle high because most of the mixing of fuel and air takes place before the gases reach the knuckle, and

the high heels of the fuel and air passages and steep roof and apron give the desired direction to the name without requiring a low knuckle.

An arch 22, shown as an inverted substantially U-shaped wall, is disposed within each port end 2 and rests on upright walls 23 and is united with the end wall I0 and the bottom of the port end. This arch, together with floor 20, defines a fuel passage 24 which is approximately horizontal, that is, it may incline downwardly at an angle in the neighborhood of about 10 degrees to the horizontal. The mixing chamber end of passage 24 is the fuel passage port into the mixing chamber. The passage .24 connects the mixing chamber with a vertical passage 25 which in turn communicates with a regenerator (not shown) thru passage 28.

It will be understood that the wall dening the sides and top of passage 24 need not be U-shaped as shown by arch 22 for this Wall may be variously shaped to constitute the sides and top of a tunnel-like structure for a fuel passage. The term arch-like structure is intended to include all such tunnel forming walls.

Upright air passages 2l and 28, connected thru passage 29 to a regenerator (not shown), open at their upper ends, into an inverted, generally U-shaped air chamber on both sides, and over the top, of arch 22. An air passage defined by the arch 22, floors 2l, side walls I3 and I4, roof I8 and parts of apron I9 connects that air chamber with the mixing chamber. The mixing chamber end of the air passage is the air passage port into the mixing chamber.

It will be noted, particularly by reference to Fig. 2, that the apron I9 intersects with floors 20 and 2l of the fuel and air passages in a substantially straight horizontal line extending transversely of the furnace and located at the lower side of the inner end of the fuel passage port, that is at the mixing chamber end of floor 2U of fuel passage 24, and that the floors 2l are somewhat steeper and shorter than floor 20, but extend up to substantially the same elevation. It will also be noted that the heels of the air and fuel passages leading to the mixing chamber are on substantially the same elevation and are far above the surface of the charge in the melting chamber, that is, the sill or fore plate line. The heel of the fuel passage is the intersection of the floor 2U and the upright frontwall surface defining vertical passage 25. The heel of the air passage is the intersection of the floors 2l and the upright front Walls of passages 21 and 2l.

The floors 2l of the air passages may intersect with apron I9 at a level below that at which the fuel passage floor 20 intersects with apron I9 if desired, for such a construction permits air to flow underneath the gas stream quite readily, but

the intersection of floors 2I,and I9 should not bematerially above the intersection of gas passage oor 20 91nd apron I9, for such an arrangement would`tend to reduce the amount of air which could flow under the fuel stream in the mixing chamber and might also tend to retard the speed at which such air could flow under the fuel stream.

From the preceding description it will be underplanes extending from the sides of arch 20 to the inner surfaces of walls I3 and I4 at substantially right angles to the latter., the upper parts of which planes are tipped forwardly so as to intersect the roof I8 at substantially right angles thereto, and the parts of roof I8 and apron I9 included by said planes, walls and ports.

The location and arrangement of the roof I8, apron I9, and the inner surfaces of walls I3 and Il, are quite important. The roof I8 may slope downwardly at an angle of between about degrees and about degrees to the horizontal. The angularity of the apron I9 to the horizontal may vary from about 30 degrees to 50 degrees or more.

The terms steep and steeply as used herein with reference to apron I9 and also to roof I8 are intended to include angles to the horizontal within the ranges just specified. The angularity of the inner surfaces of walls I3 and I4 to a vertical plane on the center line of the furnace may Vary from about 40 degrees to about 50 degrees. The intersection of the inner surfaces of walls I3 and I4 with the parallel opposed surfaces of walls I5 and I6 may be located in different places with respect both tc the knuckle and the melting chamber end of arch 22. If such intersections are too close to the arch 22, and too far away from the knuckle the size of the air passages will be reduced and the length of the mixing chamber may be shortened and the mixing of air and fuel in the mixing chamber may not be as rapid and thorough as desired and the flame may spread laterally to an undesired extent.

If those intersections are too far away from the arch 22 and too close to the knuckles, too much air or too little air may enter the mixing chamber, depending on the air velocity, or the air may be directed laterally toward the fuel stream at too small an angle so that the air may not be utilized to the best advantage in rapidly making a thorough and complete mixture of air and fuel.

It is important that the end 30 of arch 22 should be spaced far enough away from the under side of roof I8 to prevent premature injury to the roof and to itself by outgoing heated gases, and not so far away as to permit too much air to enter the top of the mixing chamber.

Very good results have been obtained commercially with 150 ton capacity furnaces in which the apron I8 made an angle of about 38 degrees with the horizontal, the fuel passage 24 made an angle of about 10 degrees with the horizontal, the roof I8 made an angle of about 35 degrees with the horizontal, the inner surfaces Vof walls I3 and I4 made angles to about 50 degrees with a Vertical plane on the center line ,of the furnace, the intersections of the inner surfaces of walls I3 and H with the opposed parallel faces of walls I5 and I6 were located about two feet from the melting chamber end of arch 22 and about one foot from the knuckle in the furnace roof, the front end 30 of arch 22 was about two feet from roof I8, the heels of the fuel and air passages were about four and one-half feet above the sill or fore plate line, and the apron intersected the floors of the fuel and air passages in a horizontal line drawn across the lower edge of the fuel passage port.

In the foregoing furnaces the combined area of the air and gas passages entering the mixing chambers was between one and two sq. ft. less than the 43-sq. ft. shown by Fig. 5 because the lower corners and floor of the fuel passagewere filled ln to make the opening more near-ly round.

The area of the mixing chamber port was about 48.3 sq. ft. (Fig. 6). Thus the mixing chamber expanded about six or seven sq. ft. or from about 14% to about 17% from the air and fuel passage ports to its port.

The arch 22 is slightly offset with respect to the furnace center line, as shown in Fig. 4. This offsetting results in passage 21 being slightly larger in area than passage 28. The inner surface of wall I3 makes a slightly greater angle with wall II than wall I4 makes with its wall I2.

Figure 3 and 4 show the herein described angles of the apron, roof, side walls and of the fuel and air land together with Figs. 5 and 6 will make clear how and where the areas of fuel and air passages and the area of the mixing chamber port are taken. The area of the latter port is taken on a plane indicated by lines 6-6 of Fig. 3.

Fig. 5 shows the cross-sectional areas of air and gas passages entering the mixing chamber and Fig. 6 shows the cross-sectional area of the mixing chamber port. As will be noted from these figures, the area of the mixing chamber port is somewhat greater than the combined areas of the air and gas passages entering into the mixing chamber. Moreover, the cross-sectional area of the mixing chamber increases more or less uniformly from the entering Vair and gas passages to its port, due in part to the divergence of the roof and apron.

The area of the air passage entering the mix.- ing chamber may be more readily determined by theoretically dividing the air passage into three parts and adding together their individual areas. As is shown by Fig. 5, two of these parts, :c and y, are on opposite sides of arch 22, and the third part .e lies over the arch 22 and joints the tops of parts n: and y. The area of each of these parts m, y and z, is determined by measuring the areas of the smallest plane disposed substantially at right angles to the direction of air flow thru each of these parts. Since the plane on which the areas of each of these parts are taken is curved or dished and it is difficult to show such a plane in the drawings, that plane has been shown flattened out into a, single plane, as shown in Fig. 5, wherein the parts x, y and e thereof are illustrated.

The operation of the above described furnace, particularly as regards the travel and action of the air and fuel, is substantially as followsz-A charge having been placed in melting chamber I, heated air and fuel are passed thru one port end 2, the mixture is burned in melting chamber I and the waste gases arewithdrawn thru the opposite port end 2. The heated fuel is directed thru fuel passages 24 across the mixing chamber toward the' central part of the mixing chamber port and along lines which are approximately horizontal. Simultaneously the heated air from passages 21 and 28 is directed into the mixing chamber. The roof I8 directs air down onto the top and along the sides of the fuel stream. The inner surfaces of walls I3 and I4 direct air laterally into opposite sides of the fuel stream. These surfaces and the roof direct air under the fuel stream in the space between that stream and apron I9. 'I'he air, which is traveling at a high velocity due partly to the high ports, thus begins to mix with the fuel on all sides of the fuel stream at the instant the stream enters the mixing chamber and almost instantly makes a goed combustible mixture particularly on the entire lower side of the stream of fuel.

and sidesof the stream of fuel and directs it,

At the same time "the air mixes thoroughly and rapidly with the top and the flame, downwardly thru the lower part of the mixing chamber port into the melting chamber where the very hot, largely undistorted flame impinges directly against the adjacent end of the top surface of the charge.

The part of the flame between its top and the place of such impingement lies close to the charge. The waste gases have to rise steeply to enter the exhaust port and hence are not able to carry with them as much slag and other solids as is the case with low port furnaces and thus the deposition of such materials in the ports and checkers is retarded and reduced.

Altho the hereinabove specifically described furnace is a producer gas furnace, the principles of the present invention may be employed advantageously in furnaces operating on natural gas, coke oven gas, mixed gases, oil, combination and other fuels, with such variations in the construction of the end ports as the nature of the fuel used may necessitate.

Producer gas furnaces embodying the present invention and having an overall length of about 70 feet have been operated commercially in two different plants and have consistently produced over 121/2 tons of steel per hour with a fuel consumption of about 3,600,000 B. t. usu per ton. The best that could be done with other furnaces ln the same plants and under comparable conditions, except that the furnaces were equipped with the prior ports, was about 111/2 tons per hour and a fuel consumption of over 4,400,000 B. t. u's.

It will be understood that this invention may be used to good advantage on furnaces having either long or short hearths and that on Short furnaces its advantages are even more pronounced than on longer furnaces.

Having thus described the present invention so that those skilled in the art may be able to understand and practice the same I state that what I desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

l. An open hearth furnace including a melting chamber and mixing chambers at each end of said melting chamber, each mixing chamber having fuel and air passages opening thereinto thru ports and having a port opening therefrom into the melting chamber, each mixing chamber having .a steep apron sloping down uninterruptedly from the lower side of said fuel passage port, the included angle between said apron and a projection of said fuel passage into the mixing chamber being greater than about 20.

2. An open hearth furnace including a melting chamber and mixing chambers at each end thereof, each mixing chamber having fuel and air passages opening thereinto thru ports and having a port opening therefrom into the melting chamber each mixing chamber having a steep apron sloping down uninterruptedly from the lower side of said air passage port, and making with the horizontal an included angle of between about and about 50.

3. An open hearth, regenerative type furnace including a melting chamber, mixing chambers at each end thereof, each mixing chamber having a fuel passage defined in part by a floor and opening thereinto thru an arch-like structure, an air passage opening into the mixing chamber on the sides and top of said arch-like structure, a`

port opening from each mixing chamber into the melting chamber, a roof for each mixing chamber spaced a considerable distance above said arch-like structure, and sloping down toward said said mixing chamber having a roof sloping down toward said melting chamber and an apron sloping down uninterruptedly and steeply from its junction with the floors of the fuel passage to the melting chamber and making an included angle with the horizontal approximating that made by said roof and greater than that made by said fuel passage floor, and opposite side walls extending convergingly toward the mixing chamber at acute angles to the center vertical plane of the furnace to direct air laterally into the mixing chamber against the sides of and underneath a stream of fuel issuing from said fuel passage.

5. An open hearth regenerative type furnace including a melting chamberY mixing chambers at each end of and communicating with said melting chamber, each mixing chamber having fuel and air passages opening thereinto thru ports, each mixing chamber having a downwardly sloping steep roof, an apron sloping down uninterruptedly and steeply from the lower side of said fuel passage port at an included angle to the horizontal of between about 30 and about 50, and side walls extending convergingly toward the mixing chamber at different acute angles to the center vertical plane of the furnace,

6. An open hearth, regenerative type furnace including a melting chamber, mixing chambers at each end of and communicating tiierewith, air and fuel passages at each end of the furnace having heels disposed relatively high above the top of a charge in the melting chamber and having floors sloping downwardly from said heels toward said mixing chamber said passages opening into the mixing chamber, said fuel passage being defined in part by an arch-like structure, a roof for each mixing chamber sloping downwardly toward the melting chamber at an included angle to the horizontal of between about 30 and about 40, an apron sloping down uninterruptedly from the mixing chamber ends of said passages to the melting chamber at a steep included angle to the horizontal of between about 30 and about 50 and greater than the included angle of said roof to said horizontal, said roof and arch-like structure being spaced apart sufliciently to prevent injury thereto by heated outgoing gases, and side walls partially defining the air passage and extending convergingly toward the mixing chamber at acute angles to the center line of the furnace.

7. An open hearth, regenerative type furnace including a melting chamber, a mixing chamber, an arch-like structure defining in part a' fuel passage positioned to direct an approximately horizontal stream of fuel into the mixing chamber and out of contact with the walls thereof, an apron in said mixing chamber sloping down uninterruptedly from the bottom of the mixing chamber end of said fuel passage at an included angle to the fuel stream of between about 20 and about 40, a downwardly sloping roof for said mixing chamber making an included angle with said fuel stream of between about 20 and about 30 and spaced far enough from said arch-like structure to prevent premature injury to itself by outgoing gases, and inwardly projecting opposed walls extending upwardly from the apron at the belting chamber end of said mixing chamber.

8. An open hearth furnace including a melting chamber and port ends opening thereinto at the ends thereof, each port end including an archlike structure and floor defining a fuel passage extending downwardly at a small included angle to the horizontal toward the melting chamber, en'd and side walls and a horizontal arched roof defining an air chamber on the sides of and above said arch-like structure, a steep roof sloping down at a large obtuse angle from said horizontal roof,

a relatively high knuckle, a steep apron sloping down at an included angle between about and about to the horizontal from the bottom of ie melting chamber end of the fuel passage to the hearth of the melting chamber, and opposed side walls having inner surfaces inclined at an acute angle to the vertical center plane of the furnace and terminating between the vertical plane of the knuckle and the melting chamber end of said arch-like structure and nearer to the former than to the latter.

9. An open hearth furnace comprising a melting chamber having a substantially horizontal roof, knuckles close to the elevation of said roof, and port ends, each port endincluding walls defining air and fuelpassages having relatively high heels, and other walls, including lateral converging walls and a steep apron sloping uninterruptedly upward from the hearth of the melting chamber to the lower side of the fuel passage and at an angle of above about 20 to a projection of said fuel passage into said mixing chamber, arranged to direct air underneath a stream of fuel from said fuel passage and .to deflect said stream of fuel downwardly into contact with the adjacent end of a. charge in said melting chamber.

10. An open hearth furnace including a melting chamber provided with a roof with knuckles at each end thereof disposed close to the lengthwise horizontal plane of said roof, port ends at each end of the melting chamber, air and fuel passages in each port end having relatively high heels, a mixing chamber connecting said passages in each port end with said melting chamber, wing Walls in each port end adjacent to a vertical plane thru the adjacent knuckle, a steep roof for each mixing chamber, and a step apron approximately parallel tosaid roof and sloping up from the melting chamber between the Wing walls to said air and fuel passages, said roof making an included angle of more than about 20 with the line of ow of fuel in the mixing chamber from said fuel passage.

11. An open hearth furnace including oppositely disposed port ends and a melting chamber therebetween, each port end includinga mixing chamber opening at one end into the melting chamber and air and fuel passages having relatively high heels disposed in substantially the same horizontal plane and opening into the other end of said mixing chamber, the top surface of said gas and air passages making an included angle of between about 20 and 4about 30, said mixing chamber having an apron sloping downwardly from the fuel passage at an angle of between about 30 and about 50 to the horizontal, the area of said mixing chamber increasing progressively from said passages to said melting chamber.

12. In an open hearth furnace, the combination in a port end thereof of air and gas passages having relatively high heels, the projections of said passages making an included angle of between about 20 and about 30, and a mixing chamber communicating with said passages at one end and increasing in area therefrom to its opposite end, said mixing chamber having an apron sloping downwardly from the fuel passage at an angle of between about 30 and about 50 to the horizontal.

GEORGE W. PUTNAM.

Images