US3169159A - Open-hearth furnace - Google Patents

Description

Feb. 9, 1965 A; JACKSON OPEN-HEARTH FURNACE 7 Sheets-Sheet 2 Filed Feb. 18, 1959 Inventor 4/6 14 jack Soil y 4), 6 I trneys Feb. 9, 1965 A. JACKSON 3,169,159

OPEN-HEARTH FURNACE Filed Feb. 18, 1959 '7 Sheets-Sheet 3 y MP %ey Feb. 9, 1965 A. JACKSON 3,169,159

OPEN-HEARTH FURNACE Filed Feb. 18, 1959 7 Sheets-Sheet 4 In venlor J/Aar'f Jae ks a y W *%ys Feb. 9, 1965 A. JACKSON OPEN-HEARTH FURNACE 7 Sheets-Sheet 5 Filed Feb. 18, 1959 Inventor xf/bgrl Iac Kson y B M14 g I Attorn ys Feb. 9, 1965 A. JACKSON OPEN-HEARTH FURNACE 7 Sheets-Sheet 6 Filed Feb. 18, 1959 Inventor fl/berfi IQCkSOA B a J uaflw Attorn ys Feb. 9, 1965 A. JACKSON OPEN-HEARTH FURNACE 7 Sheets-Sheet 7 Filed Feb. 18, 1959 Inventor MfiMSQ Patented Feb. a, was

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3,169,159 WEN-EARTH FURNACE Albert Jackson, Scunthorpe, England, assignor to The United Steel Companies Limited Filed Feb. 18, 1959, Ser. No. 794,117

Claims priority, application Great Britaimheb. 21, 1958,

, s,7s/ss, 5,751/58, 5,752/58 4 Claims. (Cl. 266-34) In the normal operation of an open-hearth furnace for the manufacture of steel, coke oven gas or other fuel.

is blown into the furnace alternately through the two ends, in each of which there is a central gas port,'the mouth of which merges into that of a central air port. Impurities in the charge are removed by reaction with added oxides and fluxes'aided by the burning fuel, which also mairitainthe temperature for the process.

It has becn'proposed to remove the impurities from the charge in'a tilting open-hearth furnace by substantiallypure gaseous oxygen introduced through a lance above In this invention the object is to render the oxygen process practicable. Essentially this is doneby substan- ,with oxygen introduced through a lance.

content effected whilst burning fuel.

and thus the erection of the furnace; and it gives the smallest heat-radiating area per unit volume.

In making steel in the novel furnace fuel is burnt only.

at the beginning and towards the end of the process, and the greater part ofthe steel-making process is carried on Thus fuel is burnt during fettling and the charging of solid material, but the fuel supply is cut off and oxygen blowing begun when some molten metal has been charged. At the stage in the oxygen blowing at which the carbon content of the molten metalis only a little above that required in the steel and the impurities other than carbon have been reduced to substantially the amounts to be present in the steel when cast, the oxygen supply is cut off or substantially reduced and the final reduction in the carbon It is desirable to introduce air through the waste-gas port which is not in use as an otftake in order to burn to carbon dioxide the carbon monoxide evolved from the bath, but the volume ing the oxygen enters the furnace unaccompanied by much tially eliminating the infiltration of air into the furnace.

Complete elimination is impossible, but by employing a numberof novel constructional features the infiltration can be reduced to negligible amounts. i a

A normalre versible open-hearth furnace with a tilting hearth includes at each end a brickwork structure .into' steel members on their faces but these have neither been main load-bearingstructural members .nor continuous;

rather they have been added to. a brickwork" structure to, assist in holdingthe bricksin position or to face some of the walls. Inthe present invent-ion the various parts of the furnace; and in particular each otftake, downtake, slagpocket and regenerator, are steel casings providing a continuous gas passage, and they are lined with brick or refractory material because. in the absence of any flnfiltrationof a' into theifurnace is thus largely eliminated:- i '1 An advantage of the novel. construction isthat the air liningthe hot gases wofuld destroyor burn the steel.

introduced through the regenerator's can be enriched in oxygen without the risk that thisfoxygen may be lost b leakage through small cracks in the brickwork.

Numerous small cracks develop in all this-brick larger volumes of nitrogen, and second the amount of air entering by infiltration and joining the waste gases is small. In' consequence very considerable reduction can be made in the-size of the various parts of the gas system of the furnace, and this in turn renders possible the use of variousadvantageous features, which are useful both in newly built furnaces and in furnaces partly reconstructed towork with oxygen blowing.

The use of oxygen in an open-hearth furnace leads to a considerably greater reaction than in a conventionallyfixed furnace, and'accordingly to slag-foaming. There fore for the same weight of charge a deeper. bath is advantageous. Ina conventional furnace the weight of the cha'rgeis limited both by the position of the lower edge ofth'e mouth common to the gas and air ports at each end and by the height, of the slag notches. In the furnace according tothe'presentinvention there is preferably no central gas port at all, but ratherthe gas burnt initiallyandtowa'rds the endof each charge is introduced through four' burnersgon'e at each corner of the hearth. This feature, together with'the reduction in size of the port required to take the waste gases, makes it possible to provide at each end a single central port the lower edge of 'which'is higher than that of the central ports in a conventional furnace of the same capacity, so the chargecan be of the same weight without foaming slag overflowing into the gas otftake. During the period of considerable reaction when the slag foams the hearth may be'tilted to raise the slag notches, and thus to allow advantage to be taken of the raising 'of the lower edge of the port.

The single port'is preferably circular, both to lead to the.cylindrical:downtake and to enable another feature of importancefto be employed in a furnace with a tilting hearth. 1 This is that the oiftake is formed in a structure :The steel casings must, of cou rsebe of adequate strength to support the brick or refractory linings; As

far as possibleithey are circular in cross-section, because this construction requires theminimurn amount of structural steel; it also 'facilitatesprefabrication. of the-casings madeas an independent rnovable'unit with a single circular port substantially coaxial With the tilting axis of the hearth ahdhaving an end face of metalwhich mates with a similarfac'e on the tilting hearth; and means are provided for urging the: end face of each unit into contact The otftake unit just described may advantageously be.

usedfor the introduction of the lance or lances, so that the hearth can be tilted without effect on the position or movement of the lances.

, the furnace;

Another novel feature of the invention is the provision i when, according also to this invention, two regenerators are provided at each end, each connected to one of the slag pockets. Because of the reduction in the volume of the waste gases, each regenerator can be much smaller than usual and both can be accommodated in the space occupied by one conventional regenerator.

The preferred tilting-hearth furnace according to the invention is shown in the accompanying somewhat diagrammatic drawings, in which:

FIGURE 1 is a section through the left-hand oiftake unit and hearth end looking from the front of the furnace, and shows a lance in elevation;

FIGURE 2 is a vertical section at the same end; FIGURE 3 is a part-elevation of the right-hand end of FIGURE 4 is a horizontal section taken on the tilting axis through part of the furnace end shown in FIGURE 3;

FIGURE 5 is a cross-section through a burner; FIGURE 6 is a face view of the right-hand hearth end; FIGURE 7 is a plan of the right-hand olftake unit, various pipes being omitted for the sake of clarity;

FIGURE 8 is a section on the line A-A in FIG URE 3;

FIGURE 9 is a plan of a lance and oiftake unit; FIGURE lO shows the lance, partly in section, on a larger scale;

FIGURE 1'1 is a cross-section through the lance on a still larger scale;

FIGURE 12 is a plan of two slag pockets andregenerators;

FIGURE 13 'is an elevation, partly in section, of a regenerator and reversing valves; and

FIGURE 14 is a diagram of a waste-gas disposalplant.

The furnace shown is a 300 ton basic open-hearth fur-l nace with a tilting hearth 1 which includes a roof 2 and a hearth lining 3.

The tilting hearth 1 includes a conventional roof structure and frame 4 carrying curved rockers 5 supported by rollers 6 and can be tilted about an axis 7 by conventional mechanism not shown. The hearth has five charging doors 119, two with slag notches, and a tap hole 8 leading to a launder 9.

As is common practice, the two ends of the furnace are identical in construction, but contrary to the usual practice there is only a single central port 9 at each end and this is circular with its axis coincident with the tilting axis 7 of the hearth. This port is made ina movable oiftake unit It), in which a passage 11 is made to receive,

a lance 12 which can be introduced into and withdrawn fromthe furnace by a sliding movement and through which oxygen is supplied. i 7

Although the usual 'central'fuel-gas'port is omitted, there are four gas burners13, one at each corner of the furnace. at thefront and forming a water jacket, a cylindrical baffle 15 separating the supply and return flows of water. The tube14 houses a gas pipe 16 and two oxygen pipes 17. The cooling wateris supplied from a header pipe 18 through pipes 19 and discharged through pipes 20 into a box 21. The gasis supplied. th'rough'a pipe 22 and oxygen through a header pipe 23 and pipes 24, and air can alsobe supplied to the pipes 24 through pipes 25.

All these pipes arerigid and move with the tilting'hearth,

Each burner comprises a steel tube 14 closed of two slag pockets at each end, together with means by and if necessary replaced by another.

and they are in turn connected to flexible supply pip of the molten metal that forms the remainder of the charge. Then the flow of fuel is reduced or completely stopped and oxygen is supplied through the lance 12 above or below the slag-metal interface. The supply of oxygen or air or oxygen-enriched air through the port '9 may, however, be continued in order to burn carbon monoxide generated in the charge to carbon dioxide above the charge. The supply of oxygen through the lance is dis continued when the carbon percentage of the molten metal is greater by from say,-0.1 to 0.3 than the required final percentage. Each lance is withdrawn from the furnace when oxygen is not being supplied through it.

In the furnace shown in the drawings the port 9 merges into the upper part 26 of adowntake in the 'offtake unit Iii. This unit is formed from a steel casing 27 with a refractory lining 28, and a water-cooled cleaning hole} are welded to the casing to form feet for the unit 10, and

these feet are welded to a square frame 30, which thus forms part of the unit It). On its underside this frame carries runners 31, which engage with and run on rollers 32 mounted in bearings 33 carried by fixed girders 34.

An important feature of the furnace is that the mating; faces of the tilting hearth I and the unit 10 around the port 9 are of metal and are maintained in close contact with one another throughout thesteel-making process, On the tilting hearth the metal face is presented by an annular casting 35 which is cooled by water passed through passages 36 that each half-encircle the casting 35, the water being supplied through pipes 37 from the header I8 and discharged through pipes 38 that deliver into the box 21. The face of each casting 35 is machined to mate with the face of a similar casting 39 at the end of the unit It The casting 39 has similar water cooling passages 40.;

To ensure that the mating faces of the castings 35 and 39 are maintained in close contact, irrespectivev o'f 'contrao' tions and expansions'caused by changes in temperature, the

'unit 10 is continuously urged towards the tilting hearth 1 by two double-acting rams 41, one at eachside. Each ram is pivotally mounted in a bracket 45 on a girder 34 and engages a cross-pin 42 that spans plates 43 depending from and welded to the frame 30.

In each side of the unit 10 there is a small opening 46 for the introduction of a jet of steam. These steam jets are turned on at the end at which air enters through the port 9, and they direct the air stream along the bath surface and materially increase the roof life.

By removing the cross-pins 142 the unit It is rendered free to be lifted away by a crane. This is advantageous in that a unit in need of repair can be quickly removed,

In the unit 10 the passage 11 is made box 47 and has a cover made with an opening that fits the lance closely to make a good gas seal around the lance.

The lance is held ina carriage 48 havingfour wheels 49 running between the-flangesof two inclined rails 5th These rails, vertical girders 51' and 52 and a horizontal girder 53 make up a rigid framework. Brackets54 are fixed to this framework, above and below a kingpostSS which is fixed in a supporting'structure 56, and bearings 57 are'interposed toallow the whole framework, the

counterweightl18, runningalong the opposite faces of the rails, by a rope 58passingfover apulley59 at the top of therails. The counterweight 113' is connectedto a in a water-cooled winch 60 by a rope 61 passing over pulleys 62, and the winch is driven by a reversible electric motor 63. When the winch 60 winds in the rope 61 the counterweight 118 rises and allows the lance to move downwards under gravity. A remote-controlled brake 64 is interposed between the winch and the motor to hold the lance in its lowermost position, and on release of the brake the counterweight raises the lance. When the lance is fully raised it lies clear of the box '47 and can-be turned about the king post 55 into the position shown in dotted lines in FIGURE 9 for inspection and maintenance. When the lance is in use it is locked in the correct angular position by the engagement of a rocking lever'65, carried by the girder 53, between two lugs 66 on the unit 10.

The lance 12 comprises threeconcentric pipes. The innermost pipe 67 is of copper, and is connected through an inlet coupling 68 and a flexible pipe 69 to an oxygen supply. The middle pipe 70 is of mild steel and the outer pipe 71 of copper near the tip and of mild steel for the rest of its length. The pipes 67 and 71 are connected at the tip by a copper nozzle 72 which does not touch the pipe 70, the latter being separated from the other two pipes by spacers 73. A flexible pipe 74- leads water to an inlet coupling 75 communicating with the space between the pipes 67 and 70. The water then travels down the lance, back up the lance again between the pipes 70 and 71, and out through coupling 76 into a flexible pipe 77.

The oiftake unit lies above a downtake unit 78 having a downtake that registers with the downtake 26 in the unit 10. The unit 78 comprises a steel casing 79 lined with refractory 80. It is of dog-leg shape, circular in cross-section, and its upper end is surrounded by an annular water seal 81. A gas-tight seal between the units 10 and 78 is maintained by a shallow cylindrical skirt 82' clined to the vertical, for mating with a complementary mouth 39 of the lower end of the unit 78.

The downtake in the unit 78 consists of an upper cylindrical part 94 having a vertical axis and a lower cylindrical part 90 having an inclined axis and terminating in the mouth 89, which is perpendicular to that axis. The two parts 7 and 90 merge into one another in a plane inclined to the horizontal at an angle that is half that which the plane containing the mouth 89 of the lower part makes with the horizontal.

Each downtake unit 78 has round its lower edge a small flange 93 around each mouth 89. The unit 78 is readily movable to be disconnected from one of the two slag pocketsand connected with the other. It can in effect he swivelled about the vertical axis of its upper part 94 in moving from one slag pocket 84 to the other. In practice, it is most conveniently moved by a crane.

If in an existing furnace converted to embody the present invention there is not enough space to arrange the two slag pockets and a swivelling downtake unit 78, two downtake units may be provided, one for use with each slag pocket.

It is an advantage of the use of two slag pockets thatone can be allowed to cool and-can then be cleaned while the other is in use, and that the only time at which the downtake unit at one end is not connected to either of the corresponding slag pockets is during the changeover 'regenerator to a waste-gas reversing ,valve 100 and an air-reversing valve 101. The waste-gases flow from the valve through a flue 102 to a waste-heat boiler 103, and air flows tothe regenerator, when the valve 101 is open, from a main 104. Theflue 99 is a steel casing 105 lined, with refractory 106, and thus there is a continuous steel-encased gaspassage from the hearth to the reversing valve 100. There is one set of reversing valves for each regenerator. m I

From the boiler 103, the waste-gases flow to a heat economiser 115 and a fan 116 The fan 116 is connected to a recirculating 'flue 117 which, dependent on the setting of a butterfly damper 107 controlled by a thermostat 108, allows hot waste gas to pass twice through the boiler and economiser. Gas not recirculated by the fan 116 passes through cyclones 109 to a bag filter plant 110 from which it is drawn by a fan 111 to a chimney 112 and so escapes to the atmosphere. The dust collected by the filter plant is discharged onto a worm conveyor 113 from which it is delivered into a storage hopper 114.

By constructing the furnace as described and blowing the charge with oxygen, it is possible to reduce the volume of waste gases to about 50% or even as low as about 20% of that in a normal tilting open-hearth furnace.

The dust-collection plant may therefore be of reasonable proportions, and the slag pockets and regenerators may be reduced in size in comparison with the normal practice. For example, a regenerator in a furnace according to the invention may be a brick-lined steel cylinder of 80 square feet in cross-sectional area, whereas for the same size hearth a normal furnace would require a rectangular brickwork regenerator of 410 square feet in cross-sectional area.

It will be seen that the furnace of the invention also has the advantageous feature that the ports, downtakes, slag pockets, regenerator chambers and flues are circular in cross-section. This allows the casing of each of these parts to be of maximum strength for its weight. Moreover, with oxygen blowing the temperatures throughout are higher than usual, and to resist these temperatures high-quality and therefore costly refractory materials are required. The normal structure, which is rectangular, has many corners and places where refractory bricks are used for little more than filling. In a furnace according to the invention, however, almost all parts from the offtake unit to the flues can be lined with the desired thickness of refractory materials without involving'waste in corners and so on.

I claim:

'1. ;An open-hearth steel-making furnace comprising a tilting hearth with a hearth wall, and at each end an offtake comprising a steel casing and a refractory lining therefor defining a single circular port substantially coaxial with the tilting axis of the hearth, said casing and lining being formed with a passage leading to the port, an oxygen lance mounted to slide through the passage and-port into the hearth, and burner means opening into the hearth-through the hearth wall.

2. In apparatus as claimed in claim 1, means mounting the lance for sliding movement through the passage between positions inside and, outside the hearth, said mounting means being turnable about a vertical axis to clear said offtake.

3. In a furnace as claimed in claim 1, said burner means including four burners, one in each corner of the hearth. I

4. A reversible open-hearth steel-making furnace comprising a hearth with an outlet port, passage forming means for the discharge of'gases from the hearth'connected to the hearth outlet port, said passage-forming means comprising two fixed slag pockets, and including means for alternately and selectively connecting one only of said slag pockets at any one time to-the outlet port to receive the waste gases.

(References on following page) V Befgrencesfiited by the Examiner UNITED. STATES PATENTS Knox 263-45 Loftus 263-45 Kernohan et a1. 263-15 Loftus 75-02 Frank et a1 263-15 Brassert 2 66-36 Warlimont 266-33 Sprenger 26 6-33 Dow et a1. 266-24 Schwartz 75-43 Larsen 75-52 Graef 75-60 Krogh 266-24 FOREIGN PATENTS Great Britain. Great Britain. Australia. Great Britain. Great Britain.

France. Great Britain. Canada. France.

L. CAMPBELL, Examiners.

Claims (1)

1. AN OPEN-HEARTH STEEL-MAKING FURNACE COMPRISING A TILTING HEARTH WITH A HEARTH WALL, AND AT EACH END AN OFFTAKE COMPRISING A STEEL CASING AND A REFRACTORY LINING THEREFOR DEFINING A SINGLE CIRCULAR PORT SUBSTANTIALLY COAXIAL WITH THE TILTINT AXIS OF THE HEARTH, SAID CASING AND LINING BEING FORMED WITH A PASSAGE LEADING TO THE PORT, AN OXYGEN LANCE MOUNTED TO SLIDE THROUGH THE PASSAGE AND PORT INTO THE HEARTH, AND BURNER MEANS OPENING INTO THE HEARTH THROUGH THE HEARTH WALL.

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