US3301664A - Apparatus for and method of production of steel - Google Patents

Description

Jan. 31, 1967 T. A. HALL 3,301,664

APPARATUS FOR AND METHOD OF PRODUCTION OF STEEL Filed March 27, 1964 FIG.

3 Sheets-Sheet 1 THOM AS A. H ALL T. A. HALL Jan., 31, 1967 APPARATUS FOR AND METHOD OF PRODUCTION OF STEEL Filed March 27, 1964 3 Sheets-Sheet 2 INVENTOR T HOM AS A.

ALL

Jn- 31, 1967 T. A. HALL 3,301,664

APPARATUS FOR AND METHOD OF PRODUCTION OF STEEL Filed March 27, 1964 3 Sheets-Sheet 5 OXYGEN IGNITION (I MIN.)

CHARGING (2 MIN.) HOT METAL CHARGING 2 MIN.) w

SAMPLING AND TAPPING (l5 MIN.)

AND REBLOW (6 MIN.)

FIG. 9.

United States Patent O 3,301,664 APPARATUS FOR AND METHOD F PRODUCTION 0F STEEL Thomas A. Hall, Canfield, Ohio, assignor to The Youngstown Sheet and Tube Company, Youngstown, Ohio, a

corporation of Ohio Filed Mar. 27, 1964, Ser. No. 355,159 4 Claims. (Cl. 75-60) 'Iihis invention relates to the production of steel and is more especially directed to a means and method enabling a higher than normal proportion of scrap, pig iron or the like to be utilized in the composition of the furnace charge and heat to be efficiently employed which otherwise would be wasted; it is concerned, however, solely with what is known as the basic oxygen furnace process in which vessels more or less approximating a Bessemer converter in shape are employed for containing the furnace charge while it is being refined and are so mounted on trunnions or other supports they can be tilted like such converters when the refined charge of molten steel (and slag) is to be poured. Thus the invent-ion is distinguished from inventions in the field of open vhearth furnace practice not only by, among other things, t-he shape, size and tiltability of the refining chamber, but also by the extreme violence of the reactions taking pla-ce during the refining of the charge due in part to the use of oxygen in greatly increased amount as compared Iwith the maximum permissible in open hearth furnace practice, such use often exceeding the maximum supplied therein by la factor of 60 to 180 or even more, i.e., the basic oxygen process in a single furnace normally consumes oxygen at 20,000 to 24,000 standard cubic feet per minute whereas open hearth furnaces utilizing oxygen normally cannot accept much more of it than these amounts per hour Without excessive roof, door sill and furnace bottom damage. Hence in terms of increased production of steel in tonnage refined of comparable charge capacity the customary basic oxygen far exceeds the open hearth practice, and the present invention constitutes a further improvement upon the former.

In the lbasic oxygen process for producing refined steel gaseous oxygen is introduced into la mass of molten metal in an appropriate vessel through an elongated tube or lance whereby the carbon content or a predetermined proportion of it is oxidized and the lmetal otherwise changed in character by reaction with other materials present; this operation generates a large volume of highly heated gases, including some combustible ones, which have usually been discharged as waste products, or at best uneconomically employed for purposes extraneous to the process.

In basic oxygen practice it has been customary to first charge into the furnace substantially unheated scrap or pig iron prior to addition of molten metal but certain governing factors including the tendency of the hot met-al to freeze coincident with its introduction and contact with the relatively cold scrap have limited to about 30% of the total metal charged the amount of scrap which can be utilized without jeopardizing the fluidity of the entire charge and thus nullifying in whole or in part the effect of the subsequently introduced oxygen. Hence, while scnap on a per ton basis is usually less costly than molten metal newly recovered from ore and hence from an economic standpoint more desirable as a raw material from which steel can be made, the practical limitations upon the proportion of relatively cold scrlap that can be used in conjunction with subsequently charged hot metal have made it difficult if notI impossible to use larger proportions of the less costly material.

It is therefore a principal object of this invention to permit in the charge of a basic oxygen steel producing furnace a relatively larger proportion than heretofore of scrap or other initially relatively cold metal and a correspondingly smaller proportion of hot molten metal preparatory to the oxygen treatment or blow through the provision of means for preliminarily heating the cold metal portion of the charge by conduction thereto of heat generated in the simultaneous refining of another charge in a furnace remote from but interconnected with the first one.

A further object is to conserve energy by utilizing heat generated in a furnace during a metallurigical refini-ng openation to raise the temperature of metal in another furnace adjacent thereto and suitably interconnected therewith through appropriate ducts or conduits preparatory to subjection of such metal to a like refining operation, whereby with the so-heated metal may be combined a complementary quantity of molten metal heated by other means to constitute a charge suitable for blowing with oxygen to effect its refining.

A Astill further object is to provide a method of steel production utilizing a battery of not less than two interconnected metallurgical furnaces operating concurrently in mutually out-of-phase operating cycles -with heat ygenerated during the refining phase in the cycle of one furnace transferred to another furnace in the battery to therein effect attainment of a preheating phase in the cycle of the second furnace.

An additional object is to provide novel apparatus adapted for performance of the method of the invention in realizing the foregoing among other objects thereof.

Additional objects, purposes and advantages of the invention will hereinafter more fully appear or be understood from the following description of certain apparatus embodying it and especially designed for carrying out the method comprehended thereby wherein reference will be had to the accompanying drawings in which:

FIG. l is a diagrammatic fragmentary top plan view of one form of said apparatus;

FIGS. 2, 3 and 4 are staggered vertical sections on lines 2 2, 3 3 and 4 4 respectively in FIG. 1 wherein certain parts are viewed as if rotated about vertical axes with relation to adjacent parts;

FIG. 5 is a view corresponding to FIG. 1 showing another form of the apparatus which is further illust-rated in FIGS. `6, 7 and 8 in the same manner as that in which FIGS. 2, 3 and 4 illustrate the apparatus of FIG. l, `the lines 6 6, 7 7 and 8 8 in FIG. 5 indicating `the planes of section on which the views of FIGS. 6, 7 and `8 respectively are taken and, as in the case of FIG. 1 in relation to FIGS. 2, 3 and 4, with certain parts viewed as if rotated 90 about vertical axes relative to adjacent parts and FIG. 9 is a flow diagram hereinafter more fully described.

Referring now more particularly to the drawings it -will be understood that certain conventional auxiliary apparatus normally employed in steel making plants is not illustrated therein, the structure, function and operation of such units being well known in the art; hence only those essential to an understanding of the invention by one of ordinary skill are shown and specifically described.

Thus in FIG. 1 there is indicated a battery of furnaces respectively designated 1, 2, 3 which may be substantially identical upright, generally cylindrical basic refractory lined open mouthed vessels supported from their respective trunnions 4, 5, 6 in such manner they may be tilted toward the horizontal or beyond to receive a charge or to discharge one after it has been processed.

The open upper end of each furnace is provided with a vertically movable cover 7 with each of which is associated certain ducts and other apparatus while an oxygen lance 8 vertically supported from a lsuitable overhead crane or the like (not shown) extends through a hole 9 in the cover for -directing a jet of oxygen downwardly against the surface of a molten bath, for example, bath B in furnace 1 (FIG. 2). Obviously when the furnace is being charged or discharged the lance 8 is not in use and will be raised concurrently with furnace cover 7 and at other times may be raised and lowered relatively to the cover (FIGS. 3 and 4).

With the covers 7 of each of furnaces 1 and 3 there are associated also substantially identical movable ducts including for each an exhaust duct 10, controlled by a damper 11 and a transfer duct 12 in which is interposed a fuel and oxygen supply pipe or burner 14 the yfunctions of which will hereafter appear.

The ducts, dampers and burners to which reference has just been made are, as noted, movable with fur-nace covers 7; when the latter are closed on their respective furnaces the exhaust ducts communicate wit-h spark traps and cooling chambers 15 the entrances to which, normally aligned with exhaust ports 16 of the ducts, are controlled respectively by dampers 17 while the corresponding ports 18 of transfer ducts 12 communicate with heat-insulated hot blast mains 20. These mains connect the transfer ducts of furnaces 1 and 3 together under control of dampers 21 and with transfer duct 22 of median furnace 2, controlled in turn by a damper 23. The exhaust duct 24 of the latter furnace controlled by damper 25 is connectible selectively through exhaust mains 26, 27, controlled by dampers 28, 29, with either of the spark traps and cooling chambers 15, or may be provided wit-h an independent sp-ark tra-p and cooling chamber (not shown) like the others. It Will be understood each spark trap and cooling chamber is arranged to discharge into a stack or the like (not shown) and coolant spray nozzles 30 may be disposed therein in accordance with usual practice.

Of course where a battery of furnaces comprises more than three similar connections among them can readily be made While it is permissible to omit the median furnace 2 and utilize but two in which case when one is shut down for repairs the principal objects and advantages of the invention are not realized if the other be kept in operation.

As the practice of the method of the invention with either form of apparatus illustrated in the drawings is substantially the same an-d the construction of that shown in FIGS. 5-8 identical with that of FIGS. 1-4 except for the interposition in hot blast mains of regenerators 35, 36 and dampers 37, 38 associated respectively with them, the parts in FIGS. 5-8 generally corresponding to those of FIGS. 1-4 are designated by like num-bers with a prime(') appended and the differences in operation when not obvious will be mentioned as they become pertinent in the following description of my improved steel refining process utilizing the apparatus of FIGS. 1-4.

As the process normally is carried out in a recurring cycle and start up operations lbeginning with cold furnaces after initial construction of total prolonged shutdown as for repairs will be evident from what follows, it Will be assumed that the battery is in operation and at the beginning of a phase in its cycle in which a molten bath B in furnace 1 at the left of FIG. 1 is being subjected to Oxy-gen treatment or blowing 'by impingement of an oxygen jet from lance 8 against its surface or, more specifically, against the slag (not shown) floating upon it. In consequence there is a continuous evolvement in fur-nace 1 of extremely high temperature gases including a significant proportion of car-bon monoxide (CO) and some carbon dioxide (CO2) and this stream of gases, due to dampers 11 and 17 associated with furnace 1 and 23 and 25 with furnace 2 being closed and dampers 21 open, passes through the hot blast mains to right hand furnace 3 which it is here assu-med has previously been charged with an appropriate quantity of cold metal S such as scrap, pig iron or the like. As the gaseous stream enters that furnace now containing the cold charge its sensible heat is supplemented by introduction through proximate burner 14 of an appropriate fuel plus sufficient oxygen not only to effect its combustion but also to oxidize the combustible constituents, pri-ncipally carbon monoxide, of the stream itself to thereby release their caloric value and pro-duce a llame for impingement upon the charge to increase its temperature toward that of the molten metal later to be added. During this part of the cycle dampers 11 and 17 controlling the exhaust passage from furnace 3 are kept open so that the gases after passing through the furnace traverse said passage and enter the adjacent spark trap and cooling chamber 15 on their way to the stack.

After the charge in left hand furnace 1 has been blown with oxygen for a suitable time the oxygen supply may be temporarily reduced and then increased for reblow if desired followed by a period during which the charge may be sampled and tested. Then in the case of the battery shown in FIGS. 1 4, the oxygen supply to furnace 1 is shut off and the furnace cover and associated auxiliary apparatus raised to allow the furnace to be tilted and tapped in the normal manner, its lining then repaired if required by appropriate fettling and a succeeding cold char-ge deposited in it. By the time these operations have been completed t-he cold charge furnace 3- should be and normally is at a temperature approaching that of molten steel and this furnace is therefore now ready to receive its charge of hot metal Without risk of inimical chilling o-f the latter. The fuel and loxygen to burner 14 associated with furnace 3 are therefore shut off, the furnace opened and the appropriate quantity of hot metal introduced after which it and its exhaust dampers 11 and 17 are closed, dampers 11 and 17 associated with now closed furnace 1 are opened, and as oxygen is directed through lowered lance 8 in furnace 3 the How of hot gases is reversed to heat the cold charge while the charge in furnace 3 is being refined, thus completing the full operating cycle for both furnaces.

Little mention has been made of the intermediate furnace 2 shown in FIGS. 1 and 3 as its principal function is to serve as a standby, usually containing a cold charge of scrap and/or pig iron, so that in the event of either of the other furnaces, but not both, being forced to shut down production may 'be continued by use of furnaces 1 and 2 or 2 and 3 as the case may be, the furnace kept in operation discharging hot gases to and receiving discharged hot gases from intermediate furnace 2 in substantially the same manner as hereinabove described in connection with furnaces 1 and 3.

The cyclic nature of the method of my invention is diagrammatically demonstrated in FIG. 9 in which concurrent operations of furnaces 1 and 3 have been plotted in concentric annular -ow paths circumferentially against time in out-of-phase relationship, the progress of one cycle for each furnace being represented as proceeding in a clockwise direction With the circumferential offsetting of the respective steps representing the phase separation of the cycles.

Thus the outer annulus in FIG. 9 corresponding for example to the cycle of furnace 1, shows that the preheating period of 57 minutes or 50% of the full 1l4minute cycle and which requires little or no attention from the furnace crew is concurrent with processing operations Vassociated with furnace 3 and represented by the inner annulus which, on the contrary, do require the crews attention; likewise while a cold charge is being preheated in furnace 3 the corresponding processing operations at furnace 1 are under Way. Thus but a single crew is required for both furnaces, its services being utilized in connection with one during a period in which the other needs none and vice versa.

Certain additional steps are normally incident to the use of the apparatus comprising regenerators 35, 36 (FIGS. 5-8) and some reference thereto may be appropriate although it will be recognized opinions may differ as to the precise points in the cycle of operations at which it may be desirable to bring the regenerators into play or to cause them to be bypassed. As will be readily understood the regenerators are in effect merely heat accumulators, containing reticulated firebrick checker work or any other suitable gas-permeable heat storing material capable of extracting heat from hot gases passing therethrough and of yielding heat to gases of lower temperature. So during the oxygen blowing phase of furnace it may be deemed advisable to close dampers 37, 38 and thereby direct the hot gases from that furnace through regenerators 35, 36 on their passage through hot blast mains 2G to furnace 3 so the checker work will be heated thereby to a desired temperature. This enables furnace 3 to continue to receive hot air after furnace 1 has been shut down as when it is opened for tapping, fettling and reception of a cold charge, dampers 21 being left open under such conditions. Obviously by reverse operation the blow-off gases generate-d in furnace 3 can be directed through the regenerators and thence to furnace 1 to be followed by air while 3 is open.

It is of course contemplated that the specific schedule of operations described may be varied in many respects, such as by the utilization of air with or without oxygen in place of the latter alone to support combustion of the evolved gases and the fuel; by prolonging or shortening any or all phases of the operations and, in general, in any way deemed likely to improve results. Furthermore both forms of apparatus illustrated will be understood as typical of that comprehended by the invention but that the latter is not to be deemed as specifically limited thereto as different types of dampers, burners, furnaces and other elements may be substituted for those shown.

As examples of the manner in which in accordance with the invention the heat supplied to a charge by the hot metal portion of it may be supplemented it should be noted that when 70% hot metal is added to a cold charge of scrap constituting but 30% of the total charge (disregarding fiuxing and small quantities of alloying materials and the like) there is a suiiicient excess of heat in the hot metal to obviate the necessity for supplemental heat to prevent freezing. When the hot metal is reduced to, say, 50% however, and the cold charge correspondingly increased, the cold charge must be preheated to at least 1,535 F. before the addition of hot metal to prevent freezing. To raise the cold charge to this temperature 1,464,829 B.t.u.s are required per ton of cold charge, of which approximately 734,322 Btufs (per ton of cold charge) are available from the combustion of the CO in the evolved gases. This leaves approximately 730,507 Btufs (per ton of cold charge) to be supplied to the cold charge by combustion of .supplementary fuel in accordance with the invention. It is of course theoretically possible to heat a charge of scrap sufficiently to render unnecessary any heat be imported by hot metal, about 3,011,429 Btufs per ton being required to bring a charge of unheated scrap or pig iron to proper temperature for oxygen treatment but in practice a charge consisting solely of scrap is seldom if ever used .so that the amount of heat required therefor is academic. It will be evident, however, that the invention may be utilized in a wide range of conditions and many variations in the apparatus as well as in the method of its operation in attaining its objectives will readily occur to those skilled in the art and may be adopted if desired without departing from the spirit and scope of the invention except as defined in the appended Claims.

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

1. Apparatus of the character described comprising a plurality of furnaces, a cover for each furnace movable relatively thereto, a conduit extending from adjacent the cover of one furnace to adjacent the cover of ya second furnace, means carried by one of said covers providing communication between said conduit and the interior of the second furnace when said cover is in one position relative to said furnace, means for introducing fuel and a combustion-supporting gas into said last mentioned means for projection into said second furnace, and means carried by each cover for exhausting gases from its furnace when the cover is in said position.

2. Apparatus as dened in claim 1 in which each furnace and said conduit have refractory linings and the conduit has at least one regenerator associated with it adapted to receive heated gases therefrom and to heat air for discharge thereinto.

3. The method of refining steel in a plurality of interconnected basic oxygen furnaces which comprises the steps of subjecting a molten charge in one furnace to an oxygen blast, conducting the gases thereby evolved to a second furnace and directing them upon a relatively cold charge of metal therein, supplementing the sensible heat of said gases by introduction of oxygen to the gaseous stream before reaching the second furnace to effect combustion of combustible components thereof before contact of the stream with the cold charge, arresting the passage of oxygen into the first furnace and tapping the refined charge therefrom, charging molten metal into the second furnace for combination with the now heated but previously relatively cold charge therein, charging a relatively cold charge into the first furnace, refining the charge in the second furnace by an oxygen blast, directing the gases thereby evolved into the first furnace, introducing oxygen into said gases before reaching the first furnace to effect combustion of the combustible components thereof and impinging the gaseous stream against the relatively cold charge in the rst furnace.

fi. The method of refining steel in a plurality of interconnected basic oxygen furnaces which comprises the steps of subjecting a molten charge in one furnace to an oxygen blast, conducting the gases thereby evolved to a second furnace and directing them upon a relativeiy cold charge of metal therein, supplementing the sensible heat of said gases by introduction of oxygen to the gaseous stream to effect combustion of the contained carbon monoxide before contact of the stream with the relatively cold charge, burning in said stream fuel delivered from an outside source to supplement the heat conveyed by the gases in the stream to the relatively cold charge, arresting the passage of oxygen into the first furnace and tapping the refined charge therefrom, charging molten metal into the second furnace for combination with the now heated but previously relatively cold charge therein, charging a relatively cold charge into the first furnace, refining the charge in the second furnace by an oxygen blast and directing the gases thereby evolved toward the rst furnace, introducing oxygen into said gases to effect combustion of the contained carbon monoxide before the gases reach the first furnace and then impinging the said gases against the cold charge in the first furnace.

References Cited by the Examiner UNTED STATES PATENTS 2,813,247 1,2/1957 Francis. 3,060,0l4 10/1962 Aihara 75--60 3,231,369 l/l966 Gorlich etal --60 BENAMlN HENKN, Primary Examiner.

Claims (2)

1. APPARATUS OF THE CHARACTER DESCRIBED COMPRISING A PLURALITY OF FURNACES, A COVER FOR EACH FURNACE MOVABLE RELATIVELY THERETO, A CONDUIT EXTENDING FROM ADJACENT THE COVER OF ONE FURNACE TO ADJACENT THE COVER OF A SECOND FURNACE, MEANS CARRIED BY ONE OF SAID COVERS PROVIDING COMMUNICATION BETWEEN SAID CONDUIT AND THE INTERIOR OF THE SECOND FURNACE WHEN SAID COVER IS IN ONE POSITION RELATIVE TO SAID FURNACE, MEANS FOR INTRODUCING FUEL AND A COMBUSTION-SUPPORTING GAS INTO SAID LAST MENTIONED MEANS FOR PROJECTION INTO SAID SECOND FURNACE, AND MEANS CARRIED BY EACH COVER FOR EXHAUSTING GASES FROM ITS FURNACE WHEN THE COVER IS IN SAID POSITION.

3. THE METHOD OF REFINING STEEL IN A PLURALITY OF INTERCONNECTED BASIC OXYGEN FURNACES WHICH COMPRISES THE STEPS OF SUBJECTING A MOLTEN CHARGE IN ONE FURNACE TO AN OXYGEN BLAST, CONDUCTING THE GASES THEREBY EVOLVED TO A SECOND FURNACE AND DIRECTING THEM UPON A RELATIVELY COLD CHARGE OF METAL THEREIN, SUPPLEMENTING THE SENSIBLE HEAT OF SAID GASES BY INTRODUCTION OF OXYGEN TO THE GSEOUS STREAM BEFORE REACHING THE SECOND FURNACE TO EFFECT COMBUSTION OF COMBUSTIBLE COMPONENTS THEREOF BEFORE CONTACT OF THE STREAM WITH THE COLD CHARGE, ARRESTING THE PASSAGE OF OXYGEN INTO THE FIRST FURNACE AND TAPPING THE REFINED CHARGE THEREFROM, CHARGING MOLTEN METAL INTO THE SECOND FURNACE FOR COMBINATION WITH THE NOW HEATED BUT PREVIOUSLY RELATIVELY COLD CHARGE THEREIN, CHARGING A RELATIVELY COLD CHARGE INTO THE FIRST FURNACE, REFINING THE CHARGE IN THE SECOND FURNACE BY AN OXYGEN BLAST, DIRECTING THE GASES THEREBY EVOLVED INTO THE FIRST FURNACE, INTRODUCING OXYGEN INTO SAID GASES BEFORE REACHING THE FIRST FURNACE TO EFFECT COMBUSTION OF THE COMBUSTIBLE COMPONENTS THEREOF AND IMPINGING THE GASEOUS STREAM AGAINST THE RELATIVELY COLD CHARGE IN THE FIRST FURNACE.

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