Abstract:
An existing steel making installation having a basic oxygen furnace facility is converted to an electric arc furnace facility for refining steel by modifying the furnace support pedestals to form spaced apart horizontal rail support pads and spaced apart rails are mounted on the pads and a superstructure extending horizontally at one side of the space formally occupied by the basic oxygen furnace. An electric arc furnace is mounted on a furnace transfer car for movement along newly installed horizontal rails between a furnace operating position and a furnace exchange position. The electric furnace having a tapping orifice for discharging treated steel and a slag discharge trough. Ladle transfer cars previously used for handling slag and steel from the basic oxygen furnace are reused for the same purpose during operation of the electric arc furnace. A fume opening in the electric furnace roof is connected by a vertical fume section and an elbow to the existing fume system. Bins used for supplying materials to the basic oxygen furnace are used to supply in some instances different materials to the electric arc furnace.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to patent application Ser. No. (docket number 20110-36) filed Dec. 12, 2000 entitled Electric furnace for steel making. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to converting from the use of a basic oxygen furnace in an existing steel making facility to the use of an electric furnace and more particularly to effecting such a conversion by minimizing disruption to existing operation of the facility and using existing material and flow paths.  
           [0004]    2. Description of the Prior Art  
           [0005]    Steel making facilities used blast furnaces extensively in the past to provide a supply of liquid iron for conversion to steel. Open hearth furnaces used for the conversion process were replaced by oxygen steel making process used extensively for the conversion process. Oxygen is introduced through, onto or over a bath containing blast furnace iron, steel scrap and fluxes. The facility required for the oxygen steel making process include not only a large open top refractory liquid vessel but also slag and steel transfer ladles as well as storage bunker and conveying equipment for the fluxes and scrap. Blast furnaces represent an extensive capital investment and maintenance costs. Direct reduction is sometimes a less expensive alternative supply of iron and an abundant supply of scrap are large reducing the demand for iron. As blast furnaces are taken out of service and not replaced, the investment in the facility for the oxygen steel making process is a loss because of the loss of the source of liquid iron.  
           [0006]    It is an object of the present invention to provide an economical way to convert basic oxygen furnace equipment by making extensive continued reuse of ancillary equipment with a newly installed electric furnace.  
           [0007]    It is another object of the present invention to provide for the modification of the foundation for a basic oxygen furnace vessel to support an electric furnace and allow continued use of ladle transfer cars for slag and tapped steel.  
           [0008]    It is a further object of the present invention to provide a method for relatively rapid replacement of a basic oxygen furnace with an electric furnace to minimize loss of production.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    According to the present invention there is provided in a steel making installation having a basic oxygen furnace facility essentially including basic oxygen furnace vessel, pedestal bearings, furnace support pedestals, furnace tilting drive, oxygen lance, fume duct cleaning, flux additive system, ladle alloy addition system, and scrap handling systems, a method for revamping the steel making installation to convert the basic oxygen furnace facility to an electric furnace facility, the method including the steps of discarding each of the basic oxygen furnace vessel, pedestal bearings, furnace tilting drive and oxygen lance, modifying the furnace support pedestals to form spaced apart horizontal rail support pads extending generally horizontally between a furnace operating position and a furnace exchange position, installing car rails on the spaced apart horizontal rail support pads, installing an electric furnace on a transfer car for movement along the car rails between the operating position and the furnace exchange position, the electric furnace having a tapping orifice for discharging treated steel and a fume opening for discharging an exhaust fume while residing at the furnace operating position, and modifying each of the fume duct, flux additive system, ladle alloy addition system, and scrap handling systems to establish operative communication with the electric furnace at the furnace operating position.  
           [0010]    According to another aspect of the present invention, there is provided an apparatus for revamping a steel making furnace installation to convert a basic oxygen furnace facility to an electric furnace facility, the basic oxygen furnace facility essentially including bearing pedestals to pivotally support a basic oxygen furnace vessel, a fume duct and transfer cars for ladles containing tapped steel and slag, the apparatus including the combination of spaced apart horizontal rails supported by the bearing pedestals, an electric furnace supported on a transfer car for movement along the rails between an operating position formerly occupied by basic oxygen furnace when supported by the bearing pedestals and a furnace exchange position, the electric arc furnace having a tapping orifice for discharging a burden treated in the furnace and a fume discharge opening, the furnace being position by the rails for tapping steel and slag to ladles on the transfer cars, and fume duct sections for delivering a fume received from the furne discharge opening to the fume duct. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0011]    The present invention will be more fully understood when the following description is read in light of the accompanying drawings in which:  
         [0012]    [0012]FIG. 1 is a side elevational view of a basic oxygen furnace facility;  
         [0013]    [0013]FIG. 2 is a front elevation view taken along lines II-II of FIG. 1;  
         [0014]    [0014]FIG. 3 is a side elevational view illustrating an electric furnace installation using existing and modifications to the facilities shown in FIGS. 1 and 2;  
         [0015]    [0015]FIG. 4 is a plan view of the electric furnace shown in FIG. 3;  
         [0016]    [0016]FIG. 5 is a front elevational view taken along lines V-V of FIG. 3;  
         [0017]    [0017]FIG. 6 is a schematic illustration of the material storage and handling systems for the electric furnace of FIGS.  3 - 5 ;  
         [0018]    [0018]FIG. 7 is a schematic illustration of a volume metric feeder for delivering material from a hopper to a new conveyor system according to the present invention;  
         [0019]    [0019]FIG. 8 is a schematic illustration of a conveyance system for supplying alloys to a ladle containing tapped steel at an alloying station; and  
         [0020]    [0020]FIG. 9 is an enlarged fragmentary illustration of a modification to the electric arc furnace shown in FIG. 3- 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    In FIGS. 1 and 2 there is illustrated an example of a basic oxygen furnace facility suitable for modification according to the present invention to provide for the installation and operation of an electric furnace. A basic oxygen furnace  10  has trunnions extending from diametrically opposite sides of the furnace and mounted in bearing assemblies  12  and  14  that are in turn supported by upstanding bearing pedestals  16  and  18  carried by massive reinforced foundation pedestals  20  and  22 . Rails  24  and  26  extend in the space between the foundation pedestals for the movement of a plurality of transfer cars  28  used to transport ladles containing tapped steel and slag incident to the operation of the basic oxygen furnace. A trunnion pin for the furnace projects beyond the bearing assembly  12  for connection by a coupling to a furnace tilting drive  30  that is operated to tilt the furnace in a direction to drain slag over the furnace mouth opening lip into a slag pot on one of the transfer cars  28 . The furnace is tilted in the opposite direction by drive  30  to supply liquid steel through an opening in the furnace wall to a teeming ladle on another of the transfer cars  28 . A large opening in the top of the furnace discharges fume into an overlying fume collection and cooling hood  32  which supplies the fume to an evaporation chamber and filter equipment, not shown, to recover pollutants. The hood extends upwardly in an acute angle to the vertical and is provided with an opening in the upwardly directed wall of the hood to introduce an oxygen lance  34  through the opening in the overlying furne cooling hood  32  and into the basic oxygen furnace  10  for introducing oxygen to the surface or into the metal in the furnace. It is, however, within the scope of the present invention to modify a basic oxygen furnace installation where the furnace is provided with a tuyerse in the bottom for the introduction of oxygen commonly known as Q-BOP. Another opening in the lower end of the overlying fume cooling hood receives a duct  36  connected to a hopper  38  which is supplied with fluxing and additive materials by conveyors  40  extending to a plurality of side-by-side storage bins  42 . Building columns are used to form supports for floors at various elevations throughout the facility and provide access to the ancillary equipment such as the storage bins  42 . There is illustrated a floor  44  supported by pillars  46  above ground level to carry rails  48  for a scrap charging car  50 . The car  50  supports a scrap box  52  that can pivot about a shaft  54  by operation of a piston and cylinder assembly  56 . Shown in FIG. 2 is a ladle alloying station  58  located at a laterally spaced site at the furnace and used to deliver alloying materials from a hopper  60  located above a ladle on a transfer car  28 . Sometimes there is no car and the scrap boxes are charged by means of an overhead crane.  
         [0022]    The present invention seeks to maintain the material and process flow paths of the basic oxygen furnace installation by using the output from an electric furnace to provide supplies of liquid steel for use as consumed previously by the basic oxygen furnace. The conversion process is devised to minimize disruptions to the existing operations of the existing installation and minimize costs to the extent possible by the reuse of existing equipment and buildings. The design of the electric furnace used in the conversion according to the present invention permits operation of the furnace without requiring an overhead crane to charge the furnace and lift furnace components from their operating location. It is necessary however to abandon the basic oxygen furnace vessel  10 , the bearing assemblies  12  and  14  and furnace tilt drive  30  as well as the bearing pedestals  16  and  18 . Part of the furme cooling hood  32  and some but not all of the flux additive systems formed by the plurality of side-by-side bins  42  and the fluxing and additive conveyor system will be abandon.  
         [0023]    As shown in FIGS.  3 - 5 , ladle transfer cars  28  remain unchanged for movement along the same rails  24  and  26 . The foundation pedestals  20  and  22  are modified by the removal of the bearing pedestals  16  and  18  and foundation pedestal  20  altered by forming a shelf  62  at the same elevation as the upper face surface  64  of foundation pedestal  22 . Shelf  62  and surface  64  serves as support pads for rails  66  used to support a furnace transfer car  68 . The rails extend beyond the existing foundation pedestals  20  and  22  to an adjacent bay in the steel making facility where the rails are supported by a superstructure  70  and form a furnace exchange site  72 . The furnace transfer car is provided with wheels for movement by a winch  74  from a furnace operating position  76  where the transfer car is secured against movement against a stop by a ratchet, not shown. The winch  74  includes a cable  75  secured to opposite ends of the furnace transfer car. The furnace transfer car includes a furnace support frame  80  on which there is mounted an electric arc furnace  82  formed by a lower furnace shell  84 , an upper furnace shell  86  and a furnace roof  88 . The furnace roof  88  includes roof panels formed by an array of side-by-side coolant pipes with the coolant passageways communicating with annular upper and lower water supply headers  92  and  94 , respectively, interconnected by radial distributing pipes to form a water circulating system communicating with service lines  96  containing water supply and return lines. The service lines  96  include a flexible section to avoid the need to disconnect the service lines when it is desired to lift the furnace roof alone or combined with the upper furnace shell a short distance, e.g., 24 inches, for servicing the lower furnace shell. The upper water supply header  92  encircles a triangular array of three apertures in a roof insert  94 . The apertures are dimensional and arranged to receive the phase A, B and C electrodes  98 ,  99  and  100  supported by electrode support arms  102 ,  104  and  106 , respectively. Each of the electrode support arms is independently positioned vertically by support posts  108  restrained by horizontally spaced guides  110  in a newly formed superstructure  112  for vertical displacement by actuator  114  typical in the form of piston and cylinder assembly. The electrode support arms  102 ,  104  and  106  support water cooled cables for transmission of electrical current from transformers in a transformer vault  115  to the respective phase A, B and C electrodes.  
         [0024]    A fume duct  116  extends vertically from an annular opening in the furnace roof between the upper and lower water supply headers  92  and  94  for exhausting fumes from the interior of the furnace to an enlarged and vertically spaced duct section  118 . The vertical duct section  118  forms a replacement to a discarded section of the overlying fume hood  32 . The vertical duct section  118  is joined to the remnant of the overlying fume hood  32  by the elbow  120 . The duct  118  and elbow  120  are formed by side-by-side coolant pipes to provide thermal protection, the same construction as the overlying fume hood  32 .  
         [0025]    The furnace upper shell includes superimposed convolutions of coolant pipe supplied with coolant from spaced apart supply headers that are interconnected by vertical distribution pipes to form a water circulating system communicating with service lines  128  containing water supply and return lines. Metal panels may be supported by the coolant pipes of the furnace roof and the coolant pipe of the furnace upper shell for confinement of the fume to the interiors of these furnace components. The service lines  128  include a flexible section to avoid the need to disconnect the service lines when it is desired to lift the furnace roof combined with the upper furnace shell a short distance, e.g., 24 inches, for servicing the lower furnace shell. The convolutions of coolant pipe forming the upper furnace shell  86  are interrupted by a scrap charge opening  132  in one quadrant and a slag discharge opening  134  in an adjacent quadrant of the annular configuration shell. The scrap charge opening  134  is used to introduce quantities of scrap at closely spaced apart intervals throughout the major portion of the furnace operating cycle and the scrap residing in a retractable chute of a scrap charger  136  serves as a media to prevent unwanted escape of the fume from the furnace in the scrap charger. A bunker  138  embodies a fabricated construction to supply scrap to the scrap charger  136 . The scrap charger car  50  is relocated to move along installed rails  139 . A slag door  140  is lifted to allow the flow of slag beyond a threshold formed by a carbon rod insert  142  which is supported by suitable brackets on the lower furnace shell  84  to a slag pot on a transfer car  28 .  
         [0026]    The furnace charging material for the most common steel making operation will be scrap which is preferable continuously introduced at closely spaced time increments. In addition to the charging of the furnace with scrap, direct reduction pellets, DRI, may be introduced to an opening  162 , shown in FIG. 4, in the roof insert by a chute  164  extending from a DRI storage hopper. The chute  164  is arranged at an angular relation to the vertical so that the DRI impacts with the metal bath at a site proximate to the triangular array of electrodes to take advantage of the highly heated area in the metal bath for rapidly melting the pellets of DRI material. There are additional openings  166  and  168  in the furnace roof. Openings  166  are used to insert carbon/oxygen lances, shown in FIG. 6, for producing foamy slag. Openings  168  communicate with chutes  170  for introducing fluxing and carbon materials to the melt in the furnace. Liquid metal may also form a furnace charge or a part thereof. Typically, the liquid metal will comprise blast furnace iron when available and can be introduced to the furnace by use of a pouring tundish with wheels arranged for supporting the tundish on the rails  74  and  76 . The tundish will include a launder arranged to allow the introduction of liquid metal through openings formed by the slag discharge trough. A ladle will be carried by crane to tundish for introducing liquid metal to the tundish.  
         [0027]    The refractory lining in the lower furnace shell is preferably constructed to allow a larger tonnage output at a shorter furnace operating cycle by maintaining a liquid metal heel provided by the configuration of the liquid metal cavity in the refractory after tapping is at least 70% preferably 100% of the heat before tapping. Such a liquid metal heel provides a substantial thermal benefit after tapping to maintain flat bath operation throughout the charging of scrap and/or other forms for charging material. Melting a newly introduced scrap charge combined with the introduction of heat by operation of electrodes can continue throughout the charging of the furnace. FIG. 3 illustrates the use of a control  172  typically located in an operator pulpit and having a summation circuit receiving input signals from the load cells  174  on the furnace support frame  80  in load bearing contact with struts  176  affixed to the outer surface of the lower furnace shell  84 . Electrical signals supplied by the load cells  174  corresponding to the weight of the furnace including the liquid metal heat which is modified by a signal to provide an output signal representing only the weight of the liquid metal heat. The weight of the liquid metal heat may be displayed in any convenient way such as a numerical read out  178 . The read out will be used to control the furnace operation including start and stop of charging and tapping.  
         [0028]    Mechanical shock due to tilting of the furnace in opposite directions for tapping and slag off is eliminated throughout the furnace operation cycle. The feature of operating the furnace while completely static, serves also to shorten the operating cycle time by allowing power on the electrodes throughout tapping, slagging and charging. Also, tapping of a heat is simplified as compared with tapping a basic oxygen furnace because the ladles receiving slag and the stream of liquid steel remain stationary because the furnace is stationary throughout its operation.  
         [0029]    [0029]FIG. 6 schematically illustrates the continued use of bins  42  for direct reduction iron pellets which pass through gravimetric feeders  180 , as shown in FIG. 7, that are added to each of the bins for delivery of the pellets to suitably arranged conveyors  182  and  183  for introduction into the furnace using chute  164 . Another suitably arranged conveyors  184  and  185 supplies dolomite, lime, and carbon from respective supplies in individual ones of the bin&#39;s  42  to the furnace using chutes  170 . The opening  166  in the furnace roof receives carbon/oxygen lances  186  connected by and using volume metric or gravimetric control supply lines to a batching hopper  188  communicating with a foaming slag carbon silo  190 . The alloy station is relocated and expanded by the addition of a synthetic slag feed system that includes the addition of a jib crane  192  for introducing synthetic slag to a hopper  194  which in turn discharges desired quantities of synthetic slag through a chute to a ladle on a transfer car  28 . Another chute, conducts a desired quantity of alloy material from a hopper  60  receiving supplies of alloy material from the relocated alloying supply vessel  198 .  
         [0030]    FIGS.  3 - 5  illustrate the preferred form of an electric furnace to carry out the conversion of a basic oxygen furnace installation. FIG. 9 illustrates a modification to the electric arc furnace which essentially provides for the pivotal support of the lower furnace shell on the furnace car. For this purpose the furnace support frame  80  is provided with spaced apart rollers  200  rotatably supported by bearing assemblies. The bottom of the lower furnace shell is provided with spaced apart arcuate bars  202  in load bearing contact with the rollers  200 . The entire furnace is supported on the furnace car by the rollers and can be tilted in opposite directions by operation of a piston cylinder assembly  204  mounted on the furnace car and its rod end clevis mounted to the lower furnace shell. The construction of the furnace in all other respects will be the same as shown in FIGS.  3 - 5  and described hereinbefore. However, the present invention is equally applicable to other well known forms of steel making furnaces. For example, arc heating furnaces used to heat a metal charge by heat radiation from arcs passed between electrodes above the metal charge. Other furnace designs include an electrically conductive furnace bottom which forms part of an electrical circuit powered by direct current. Induction furnaces can also be installed which operate to heat a metal charge by either using inductors according to a transformer principle where the secondary winding is formed by a loop of liquid metal in a refractory channel or a coreless principle where induction coils surround the furnace wall and generates a magnetic field to impart energy to the metal charge in the furnace.  
         [0031]    While the present invention has been described in connection with the preferred embodiments of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.