Abstract:
A metallurgical furnace, which includes a furnace shell, an exhaust system, and a gas cleaning system, further includes a plurality of improved pipes and fume ducts throughout to increase operational life and productivity. The pipes and fumes ducts are comprised of an aluminum-bronze alloy which provides enhanced properties over prior art materials including thermal conductivity, modulous of elasticity and hardness. The use of the alloy also minimizes maintenance requirements of the pipes and fume ducts, thereby extending their operational life. In operation, gases formed from smelting or refining are evacuated from the furnace shell through the exhaust system into the gas cleaning system. The gases, as well as the system, are water cooled by way of the plurality of pipes displaced throughout.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/323,265, filed Sep. 19, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to a method and apparatus for metallurgical processing, particularly steel making. More particularly, the invention relates to a metallurgical furnace comprising, in part, an aluminum-bronze type alloy wherein the alloy is formed into piping which is mounted to the walls, roof, duct work and the off-gas system of the furnace for cooling the same, thereby extending the operational life of the furnace.  
         BACKGROUND OF THE INVENTION  
         [0003]    Today, steel is made by melting and refining iron and steel scrap in a metallurgical furnace. Typically, the furnace is an electric arc furnace (EAF) or basic oxygen furnace (BOF). With respect to the EAF furnaces, the furnace is considered by those skilled in the art of steel production to be the single most critical apparatus in a steel mill or foundry. Consequently, it is of vital importance that each EAF remain operational for as long as possible.  
           [0004]    Structural damage caused during the charging process affects the operation of an EAF. Since scrap has a lower effective density than molten steel, the EAF must have sufficient volume to accommodate the scrap and still produce the desired amount of steel. As the scrap melts it forms a hot metal bath in the hearth or smelting area in the lower portion of the furnace. As the volume of steel in the furnace is reduced, however, the free volume in the EAF increases. The portion of the furnace above the hearth or smelting area must be protected against the high internal temperatures of the furnace. The vessel wall, cover or roof, duct work and off-gas chamber are particularly at risk from massive thermal, chemical, and mechanical stresses caused by charging and melting the scrap and refining the resulting steel. Such stresses greatly limit the operational life of the furnace.  
           [0005]    Historically, the EAF was generally designed and fabricated as a welded steel structure which was protected against the high temperatures of the furnace by a refractory lining. In the late 1970&#39;s and early 1980&#39;s, the steel industry began to combat operational stresses by replacing expensive refractory brick with water-cooled roof panels and water-cooled sidewall panels located in portions of the furnace vessel above the smelting area. Water-cooled components have also been used to line furnace duct work in the off-gas systems. Existing water-cooled components are made with various grades and types of plates and pipes. An example of a cooling system is disclosed in U.S. Pat. No. 4,207,060 which uses a series of cooling coils. Generally, the coils are formed from adjacent pipe sections with a curved end cap which forms a path for a liquid coolant flowing through the coils. This coolant is forced through the pipes under pressure to maximize heat transfer. Current art uses carbon steel and stainless steel to form the plates and pipes.  
           [0006]    In addition, today&#39;s modern EAF furnaces require pollution control to capture the off-gases that are created during the process of making steel. Fumes from the furnace are generally captured in two ways. Both of these processes are employed during the operation of the furnace. One form of capturing the off-gases is through a furnace canopy. The canopy is similar to an oven hood. It is part of the building and catches gases during charging and tapping. The canopy also catches fugitive emissions that may occur during the melting process. Typically, the canopy is connected to a bag house through a non-water cooled duct. The bag house is comprised of filter bags and several fans that push or pull air and off-gases through the filter bags to cleanse the air and gas of any pollutants.  
           [0007]    The second manner of capturing the off-gas emissions is through the primary furnace line. During the melting cycle of the furnace, a damper closes the duct to the canopy and opens a duct in the primary line. This is a direct connection to the furnace and is the main method of capturing the emissions of the furnace. The primary line is also used to control the pressure of the furnace. This line is made up of water cooled duct work as temperatures can reach 4000° F. and then drop to ambient in a few seconds. The gas streams generally include various chemical elements including hydrochloric and sulfuric acids. There are also many solids and sand type particles. The velocity of the gas stream can be upwards of 150 ft./sec. These gases will be directed to the main bag house for cleansing as hereinabove described.  
           [0008]    The above-described environments place a high level of strain on the water cooled components of the primary ducts of the EAF furnace. The variable temperature ranges cause expansion and contraction issues in the components which lead to material failure. Moreover, the dust particles continuously erode the surface of the pipe in a manner similar to sand blasting. Acids flowing through the system also increase the attack on the material, additionally decreasing the overall lifespan.  
           [0009]    Concerning BOF systems, improvements in BOF refractories and steelmaking methods have extended operational life. However, the operational life is limited by, and related to, the durability of the off-gas system components, particularly the duct work of the off-gas system. With respect to this system, when failure occurs, the system must be shut down for repair to prevent the release of gas and fumes into the atmosphere. Current failure rates cause an average furnace shut down of 14 days. As with EAF type furnaces, components have historically been comprised of water-cooled carbon steel or stainless steel type panels.  
           [0010]    Using water-cooled components in either EAF or BOF type furnaces has reduced refractory costs and has also enabled steelmakers to operate each furnace for a greater number of heats then was possible without such components. Furthermore, water-cooled equipment has enabled the furnaces to operate at increased levels of power. Consequently, production has increased and furnace availability has become increasingly important. Notwithstanding the benefits of water-cooled components, these components have consistent problems with wear, corrosion, erosion and other damage. Another problem associated with furnaces is that as available scrap to the furnace has been reduced in quality, more acidic gases are created. This is generally the result of a higher concentration of plastics in the scrap. These acidic gases must be evacuated from the furnace to a gas cleaning system so that they may be released into the atmosphere. These gases are directed to the off-gas chamber, or gas cleaning system, by a plurality of fume ducts containing water cooled pipes. However, over time, the water cooled components and the fume ducts give way to acid attack, metal fatigue or erosion. Certain materials (i.e., carbon steel and stainless steel) have been utilized in an attempt to resolve the issue of the acid attack. More water and higher water temperatures have been used with carbon steel in an attempt to reduce water concentration in the scrap and reduce the risk of acidic dust sticking to the side walls of a furnace. The use of such carbon steel in this manner has proven to be ineffective.  
           [0011]    Stainless steel has also been tried in various grades. While stainless steel is less prone to acidic attack, it does not possess the heat transfer characteristics of carbon steel. The result obtained was an elevated off-gas temperature and built up mechanical stresses that caused certain parts to fracture and break apart.  
           [0012]    Critical breakdowns of one or more of the components commonly occurs in existing systems due to the problems set forth above. When such a breakdown occurs, the furnace must be taken out of production for unscheduled maintenance to repair the damaged water-cooled components. Since molten steel is not being produced by the steel mill during downtime, opportunity losses of as much as five thousand dollars per minute for the production of certain types of steel can occur. In addition to decreased production, unscheduled interruptions significantly increase operating and maintenance expenses.  
           [0013]    In addition to the water cooled components, corrosion and erosion is becoming a serious problem with the fume ducts and off gas systems of both EAF and BOF systems. Damage to these areas of the furnace results in loss of productivity and additional maintenance costs for mill operators. Further, water leaks increase the humidity in the off-gases and reduce the efficiency of the bag house as the bags become wet and clogged. The accelerated erosion of these areas used to discharge furnace off-gases is due to elevated temperatures and gas velocities caused by increased energy in the furnace. The higher gas velocities are due to greater efforts to evacuate all of the fumes for compliance with air emissions regulations. The corrosion of the fume ducts is due to acid formulation/attack on the inside of the duct caused by the meetings of various materials in the furnaces. The prior art currently teaches of the use of fume duct equipment and other components made of carbon steel or stainless steel. For the same reasons as stated above, these materials have proven to provide unsatisfactory and inefficient results.  
           [0014]    A need, therefore, exists for an improved water-cooled furnace panel system and method for making steel. Specifically, a need exists for an improved method and system wherein water cooled components and fume ducts remain operable longer than existing comparable components.  
         SUMMARY OF THE INVENTION  
         [0015]    The present method and system utilizes a heavy-walled type pipe comprised of an Aluminum-Bronze alloy used in a cooling panel, the panels being used in both EAF and BOF type furnaces. In an EAF, an array of pipes are aligned along the inside wall above the hearth thereby forming a cooling surface between the interior and the wall of the furnace. Generally, the EAF has a furnace shell, a plurality of electrodes, an exhaust system and off gas chamber that utilizes the aluminum-bronze alloy (“alloy”), which is custom melted and processed into a seamless pipe. The EAF system also utilizes fume ducts composed of the same material. In an alternative BOF system, a similar piping array forms an assemblage of panels used to line the furnace hood and off gas chamber. The aluminum-bronze alloy has superior thermal conductivity, hardness and modulus of elasticity over the prior art materials used. Thus, the operational life of the furnace is extended and corrosion and erosion of the water cooled components and the fume ducts is reduced.  
         OBJECTS OF THE INVENTION  
         [0016]    The principal object of the present invention is to provide an improved method and system for steel-making with a furnace wherein water cooled components remain operable longer than existing comparable components. Thus, the present invention is directed to a heavy-walled, aluminum bronze alloy pipe for use in a cooling panel in a metallurgical furnace.  
           [0017]    According to another object of the present invention, a method is provided for cooling the interior walls of a metallurgical furnace. The method includes providing a plurality of cooling panels having a plurality of extruded pipes or cast comprised of an aluminum-bronze alloy. The pipes have a generally tubular section and a base section. The method further includes the steps of attaching the cooling panels to the interior of the furnace and running water through the pipes thereby cooling the furnace.  
           [0018]    Another object of the invention is to provide an improved furnace with extruded seamless piping and duct work which better resists corrosion, erosion, pressure, and thermal stress.  
           [0019]    A further object of this invention is to provide an improved method and system for steel making with a furnace wherein maintenance costs are reduced and production is increased. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The foregoing and other objects will become more readily apparent by referring to the following detailed description and the appended drawing in which:  
         [0021]    [0021]FIG. 1 is a sectional view of a typical EAF used in the steel making industry wherein the cooling panels comprising an array of pipes is provided, said pipes being made of an aluminum-bronze alloy.  
         [0022]    [0022]FIG. 2 shows a front view of an array of pipes according to the present invention connected to a cooling panel.  
         [0023]    [0023]FIG. 3 is a cross-sectional view of an array of pipes according to the present invention connected to a cooling panel.  
     
    
     DETAILED DESCRIPTION  
       [0024]    As required, detailed embodiments of the present invention are disclosed herein, however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting.  
         [0025]    Referring to FIG. 1, the present invention is shown in an EAF type furnace. It is to be understood that the EAF disclosed is for explanation only and that the invention can be readily applied in BOF type furnaces and the like. In FIG. 1, an EAF  10  includes a furnace shell  12 , a plurality of electrodes  14 , an exhaust system  16 , a working platform  18 , a rocker tilting mechanism  20 , a tilt cylinder  22  and an off gas chamber  48 . The furnace shell  12  is movably disposed upon the rocker tilt  20  or other tilting mechanism. Further, the rocker tilt  20  is powered by tilt cylinder  22 . The rocker tilt  20  is further secured upon the working platform  18 .  
         [0026]    The furnace shell  12  is comprised of a dished hearth  24 , a generally cylindrical side wall  26 , a spout  28 , a spout door  30  and a general cylindrical circular roof  32 . The spout  28  and spout door  30  are located on one side of the cylindrical side wall  26 . In the open position, the spout  28  allows intruding air  34  to enter the hearth  24  and partially burn gases  36  produced from smelting. The hearth  24  is formed of suitable refractory material which is known in the art. At one end of the hearth  24  is a pouring box having a tap means  38  at its lower end. During a melting operation, the tap means  38  is closed by a refractory plug or a slidable gate. Thereafter, the furnace shell  12  is tilted, the tap means  38  is unplugged or open and molten metal is poured into a teeming ladle, tundish, or other device, as desired.  
         [0027]    The side wall  26  of the furnace shell  12  consists of water-cooled side wall panels  40  which produce a more efficient operation and prolong the operation life of EAF  10 . In a preferred embodiment, the panels  40  are comprised of an array of pipes  50  and are understood to include an inner metallic wall cooled by spray nozzles  52 . However, those skilled in the art will appreciate that the panels  40  may take any conventional form, since the details thereof form no part of the present invention other than the pipes comprising the same. In any event, the upper ends of the panels  40  define a circular rim at the upper margin of the side wall  26  portion.  
         [0028]    The roof  32  is water cooled by additional piping  50  and includes a cylindrical skirt portion located at the upper end of the upper side wall  26  section and forming an extension thereof. In particular, the lower margin of the skirt portion is complementary to and abuts the circular rim of the wall section. Also forming a part of the roof  32  is an annular section whose outer periphery is complementary to the upper end of the skirt portion. Disposed within the annular section is a central section having a circular outer periphery which is complementary to and abuts the edge of the opening defined by the annular section. Also forming part of the roof  32  is a plurality of perforations  42  centrally located thereon for inserting of one or more electrodes therethrough.  
         [0029]    Those skilled in the art will appreciate that the number of electrodes  14  in any particular furnace is determined by the metallurgical process to be performed and the nature of the energy source. However, in a preferred embodiment of this invention, the number of electrodes  14  is three. The electrodes  14  are vertically disposed through the perforations  42  of the roof  32  and extend downward into the hearth  24 . The general direction of the movement of the electrodes  14  is normally downwardly as their lower ends are consumed or broken away.  
         [0030]    The exhaust system  16  generally comprises a plurality of fume ducts  44  and panels  40  made of the piping  50  and which lead from a vent  46  in the furnace shell  12  to off gas chamber  48 . Those skilled in the art will appreciate that any exhaust system  16  utilizing water cooled components can be employed as the system&#39;s details form no part of the present invention. However, in a preferred embodiment of the invention, a “fourth hole” direct furnace shell evacuation system (“DES”) is used. The term fourth hole refers to an additional hole, the vent  46 , other than the perforations  42  for the electrodes  14 , which vent is provided for off gas extraction.  
         [0031]    In operation, hot waste gases  36 , dust and fumes are removed from the hearth  24  through vent  46  in the furnace shell  12  to a gas cleaning system (i.e., the off gas chamber  48 ) for filtering before discharge into the atmosphere. The vent  46  communicates with the exhaust system  16  comprised of the fume ducts  44  and piping  50 , which is connected to the off-gas chamber  48 .  
         [0032]    As shown in FIG. 2, a panel  40  has an inner surface or face that is exposed to a furnace interior. In one embodiment, nozzles  52  are positioned on the panel  40  for introducing and/or removing fluid from the piping  50 . A flange  54  is attached to an upper region  56  of the panel  40  for connecting the panel  40  to a furnace shell.  
         [0033]    The panel  40  is a pipe embodiment having multiple axially arranged pipes  50 . U-shaped elbows  58  connect adjacent pipes  50  together to form a continuous pipe system. Spacers  60  may optionally be provided between adjacent pipes  50  to provide structural integrity of the panel  40 .  
         [0034]    [0034]FIG. 3 is a cross-sectional view of the panel embodiment of FIG. 2. An array of pipes  50  having a tubular cross-section and a base section. The pipe  50  is attached to a panel back  64  thereby forming the panel  40  and positioned between and interior and a wall of a furnace. The pipes  50  are used to cool the wall of the furnace above the hearth in an EAF or the hood and fume ducts of a BOF.  
         [0035]    As further shown in FIG. 3 embodiment, the pipe  50  includes a tubular section and base section  62 . The tubular section is hollow for conveying water or other cooling fluids. The base section  62  has a planer bottom for connection to the panel  40 . The base section  62  is provided with protruding ends which preferably extend the distance of the outer diameter of the pipe  50  to contact the base section  62  of an adjacent pipe  50 . Alternatively, the protruding ends can extend more than, or less than, the outer diameter of the pipe  50 . The base section  62  additionally acts as a seal bar to ease the manufacturing process.  
         [0036]    As further shown by FIG. 3, the plurality of pipes  50  are connected to the panel  40 . The pipes  50  are parallel to each other and preferably arranged so that the base section  62  of each pipe  50  abuts the base section  62  of an adjacent pipe  50 . The pipes  50  are connected in serpentine fashion (shown in FIG. 2), that is, the elbow connects each pipe  50  to the succeeding pipe  50 . It is to be understood that the panel  40  of pipes  50  can be arranged in a horizontal fashion or in a vertical fashion. Further, the pipes  50  can be linear, or, the pipes  50  can curve to follow the interior contour of the furnace wall.  
         [0037]    The ducts  44  and piping  50  of the water cooled components are comprised of an aluminum-bronze alloy custom melted and processed into a seamless pipe  50 . Thereafter, the ducts  44  are formed and incorporated into the exhaust system  16 . Moreover, the piping  50  is formed into the cooling panels  40  and placed throughout the roof  32  and ducts  44 . The aluminum-bronze alloy preferably has a nominal composition of: 6.5% Al, 2.5% Fe, 0.25% Sn, 0.5% max Other, and Cu equaling the balance. However, it will be appreciated that the composition may vary so that the Al content is at least 5% and no more than 11% with the respective remainder comprising the bronze compound.  
         [0038]    The use of the Aluminum-bronze alloy provides enhanced mechanical and physical properties over prior art devices (i.e., carbon or stainless steel cooling systems) in that the alloy provides superior thermal conductivity, hardness, and modulous of elasticity for the purposes of steel making in a furnace. By employing these enhancements, the operational life of the furnace is directly increased. The properties of the alloy of the preferred embodiment of the invention is shown in Table 1 in conjunction with various thicknesses.  
                                                                             12.7-   25.4-   50.8-       Mechanical and       ≦12.7   25.4   50.8   76.2       physical properties   Units   mm ø   mm ø   mm ø   mm ø                   1) Tensile strength Rm   MPa   586 (552)   565 (517)   552 (496)   517 (485)       2) Yield strength Rp 0, 2   MPa   386 (352)   358 (317)   323 (288)   283 (248)       3) Elongation A5   %   35 (30)   35 (30)   35 (30)   35 (30)       4) Brinell hardness   HB 30   187   183   174   163       5) Rockwell hardness   HRB    91    90    88    85       6) Reduction of area ψ   %    55    55    60    63       7) Compressive strength Rmc   MPa   931   896   862   827       8) Compressive strength, 0.1%   MPa   —   324   —   —       perm. set       9) Proportional limit in   MPa   179   165   152   138       compression R oc         10) Shear strength R cm     MPa   331   310   276   276       11) Modulus of elasticity E   GPa   124   124   124   124       12a) Charpy ak     J    41    47    54    54       12b) Izod ak     J    61    68    75    75            13) Density ρ   g/cm 3     7.95       14) Coefficient of expansion α   10 −6 /K   16.3       15) Thermal conductivity λ   W/m · K   54       16a) Electrical conductivity γ   m/Ω · mm 2     7       16b) Electrical conductivity I.A.C.S   %   12       17) Specific heat C. °   J/g · K   0.42                  
 
         [0039]    In addition to the superior heat transfer characteristics, the elongation capabilities of the alloy is greater than that of steel or stainless steel thereby allowing the piping and duct work  44  to expand and contract without cracking. Still further, the surface hardness is superior over the prior art in that it reduces the effects of erosion from the blasting effect of off-gas debris.  
         [0040]    The process of forming the piping and fume ducts  44  is preferably extrusion, however, one skilled in the art will appreciate that other forming techniques may be employed which yield the same result, i.e., a seamless component. During extrusion, the aluminum-bronze alloy is hot worked thereby resulting in a compact grain structure which possesses improved physical properties. Further, a preferred embodiment of this invention utilizes piping and fume ducts  44  wherein the mass on each side of the center line of the tubular section is equivalent so that stress risers are not created during manufacture. Since relatively uniform temperature in stress characteristics are maintained within the piping or ducts  44 , the component is less subject to damage caused by dramatic temperature changes encountered during the cycling of the furnace.  
         [0041]    The composition of the piping and ducts  44  differs from the prior art in that piping and ducts  44  in the prior art were composed of carbon-steel or stainless steel. The composition of the alloy is not as prone to acid attack. In addition, a higher heat transfer rate exists over both carbon-steel or stainless steel. One of the properties which makes the alloy better than the stainless steel is that the alloy possesses the capability to expand and contract without cracking. Finally, the surface hardness of the alloy is greater than that of either steel thereby reducing the effects of eroding the surface from the blasting effects of the off-gas debris.  
         [0042]    In operation, extruded pipes  50  are attached to the panel  40 . The panel  40  is hung within a furnace or off-gas system. Circulating fluid provided to the pipes  50  feeds through each pipe  50  in serpentine fashion, thereby cooling the system. Upon failure of a pipe  50 , the panel  40  of pipes  50  can be removed for repair and replaced by a new panel  40  of pipes  50 .  
         [0043]    Although particular embodiments of the invention have been described in detail, it will be understood that the invention is not limited correspondingly in scope, but includes all changes and modifications coming within the spirit and terms of the claims appended hereto.  
       Summary of the Achievement of the Objects of the Invention  
       [0044]    From the foregoing, it is readily apparent that we have invented an improved method and system for steel making wherein the operational life of a metallurgical furnace is extended.  
         [0045]    It is further apparent that we have invented an improved method and system for steel making with a furnace by using extruded seamless piping and duct work which better resists corrosion and erosion.  
         [0046]    It is further apparent that we have invented an improved method and system for steel making with a furnace wherein water cooled components remain operable longer than existing comparable components.  
         [0047]    It is further apparent that we have invented an improved method and system for steel making with a furnace wherein maintenance costs are reduced and production is increased.  
         [0048]    It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departing from the spirit and scope of this invention.