Patent Publication Number: US-2021190430-A1

Title: Water cooled box for a metal making furnace

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/922,608, filed Mar. 15, 2018, which is a continuation-in-part of U.S. patent application Ser. No. 29/628,938, filed Dec. 8, 2017. 
    
    
     FIELD OF THE INVENTION 
     This technology relates to water cooled boxes that are installed in a side wall of a metal making furnace for the general purpose of housing and protecting various implements used to affect the contents (i.e., a molten metal bath) of the furnace. 
     BACKGROUND OF THE INVENTION 
     Metal making furnaces operate under severe conditions. For example, high mechanical stresses are exerted, particularly in furnace vessels, when large amounts of metal scrap weighing many tons are dumped from above into the vessel. The mechanical stress is further compounded by tilting of the vessel to pour the molten metal. Even more significantly, metal making furnaces are exposed to extremely stressful thermal conditions. The temperature around electrodes in an electric arc furnace (“EAF”) can reach 6000 degrees Celsius (“° C.”), or approximately 11,000 degree Fahrenheit (“° F.”). Moreover, the furnace must withstand frequent and vast temperature fluctuations as an EAF furnace can be cycled (i.e., filled with scrap, drained of the melt, and filled, and prepare for filling with scrap again) more than once per hour. 
     Until the early-1970&#39;s, manufacturers of industrial furnaces for metal making attempted to protect the outer steel shell of the furnace from the extreme conditions by completely lining the shell wall with refractory brick. Refractory brick by itself was subject to considerable wear which resulted in periodic furnace outages that decreased production and caused considerable expense. During the mid-1970&#39;s, water cooled box type panels, and other panels of various designs, were introduced to replace refractory brick in portions of the furnace vessel outside of the melt zone where molten metal is contained in the furnace vessel. The present invention relates to improvements of these water cooled boxes for metal making furnaces. 
     Numerous types of water cooled boxes are known. They typically comprise a metal enclosure generally including, but not limited to, the shape of a truncated pyramid mostly of rectangular cross section. The interior of the enclosure is typically arranged to have an inlet and an outlet for cooling water that is circulated through the enclosure for the purpose of cooling the box. In view of their general “box” shape and circulating cooling water, these devices are commonly referred to as “cooling boxes.” 
     Metal making furnaces of the prior art have openings in the vessel wall of the furnace to accommodate these cooling boxes. The cooling boxes are mounted in the openings, whereby the boxes generally extend inwardly toward the inner diameter of the vessel wall. The boxes typically further comprise a nose that, when the box is mounted in the wall, is typically provided in an orientation that faces and is proximal to the molten metal in the vessel. Moreover, the nose of the box is generally located in such a way as to house a device, such as a burner, a lance, or a material (i.e., carbon or lime) injection device, closer to the metal bath to increase the efficiency of the melting or injection process, as the case may be. The closer the injection is to the bath, the deeper the heat, oxygen, or material penetrates into the bath. This construction is advantageous because, for example, a closer location of the injection device relative to the molten metal bath reduces the amount of injected material otherwise lost to a draft out of a top exhaust hole of the furnace. 
     Some of the known cooling boxes are made from steel, such that they are easy to manufacture and may be welded without substantial difficulty. Additionally, cooling boxes comprised of steel are relatively inexpensive. However, the lifespan of steel boxes is short because the low thermal conductivity of the steel, which allows it to overheat and ultimately deteriorate by way of thermal cracking. A consequence of thermal cracking is the possibility that cooling water will be permitted to leak into the melt, which can result in an explosion. 
     Other prior art cooling boxes are made from copper or copper alloy, which benefit from the high thermal conductivity of the metal. The principal disadvantage of the all-copper box is the very high price due to the cost of the material. Many of these boxes are plug-welded fabrications or cast monolithic blocks with frequent joints between the exposed sides (i.e., facing the melt) and non-exposed sides. The copper faces of the box that are exposed to the high heat of the furnace will expand significantly, as compared to the copper faces that are otherwise not exposed to the furnace heat. This thermal growth causes significant mechanical stress at joint locations in the box. A consequence of the thermal stress is thermal cracking, which can permit leakage of the cooling water in the molten metal batch of the furnace and result in an explosion. 
     Therefore, there exists a heretofore unmet need in the art for a novel and inventive water cooled box that alleviates the aforementioned disadvantages of prior art cooling boxes. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a water cooled box for installation in a metal making furnace, wherein the box can accommodate the thermal stresses inherent in the metal making process without cracking, while also having a cost of manufacture that is significantly less than that of a primarily copper box. 
     A preferred embodiment of the present invention comprises a water cooled box for a metal making furnace, the water cooled box comprising: (i) a preferably U-shaped copper outer shell; (ii) a preferably U-shaped steel inner shell liner; (iii) the shell and the liner being welded together to form a chamber through which cooling water passes; (iv) at least one inlet and one outlet water connection to the chamber; (v) one or more conduit passages between the copper shell and the steel shell for mounting devices used to access the metal bath; (vi) a flexible joint where the conduit passage is attached to one of the shells; (vii) the copper shell further comprising slag bars for slag retention on the copper shell; (viii) the steel shell further comprising a flange for mounting the water cooled box into a wall of the furnace; and (ix) the chamber between the copper shell and the steel shell comprising water baffles to direct the water flow in the chamber in a serpentine path for consistent cooling of the outer copper shell of the water cooled box that is exposed to the furnace heat. 
     The flexible joint may be comprised of a diaphragm flexible joint, which is preferably one or more thin, high-strength metallic diaphragms that reduce restraint in both the radial and axial direction of the conduit passageways. 
     The flexible joint may be comprised of one or more thin, high-strength cans that allow deformation in the high-strength can that reduces restraint on the conduit passageways. 
     The flexible joint may be comprised of a bellows with one or more bellows convolutions that reduce restraint in both the radial and axial directions between the copper shell and the steel shell. 
     The flexible joint may be comprised of a thinned flange on either the bath facing side of the outer shell or the inner shell facing side of the outer shell, the flexible joint reducing radial restraint between the shells. 
     One of the benefits of the present invention is the ability to separate and replace either of the outer or inner shell if one of the shells should become worn or damaged. The preservation and reuse of the non-damaged shell provides a significant economic benefit over traditional water cooled boxes. 
     Another preferred embodiment of the present invention comprises: 
     a water cooled box for use in a metal making furnace, the water cooled box comprising: 
     an outer shell having a substantially U-shaped cross-section, an inner surface, and at least one conduit passageway; 
     an inner shell having a substantially U-shaped cross-section, an inner surface, a plurality of water baffles, at least one conduit passageway, and at least one mounting flange; 
     wherein the outer shell is primarily comprised of a metal having a higher thermal conductivity than that of a metal primarily comprising the inner shell; 
     wherein the outer shell and the inner shell are joined at the at least one mounting flange, thereby defining a chamber through which water flows along a path defined by the water baffles, the inner surface of outer shell, and inner surface of the inner shell; and wherein the at least one conduit passageway of the inner shell or the outer shell comprises a flexible joint. 
     Yet another preferred embodiment of the present invention comprises: 
     a water cooled box for use in a metal making furnace, the water cooled box comprising: 
     an outer shell having a substantially arcuate cross-section, an inner surface, and at least one conduit passageway; 
     an inner shell having a substantially arcuate cross-section, an inner surface, a plurality of water baffles, at least one conduit passageway, and at least one mounting flange; 
     wherein the outer shell and the inner shell are joined at the at least one mounting flange, thereby defining a chamber through which water flows along a path defined by the water baffles, the inner surface of outer shell, and inner surface of the inner shell; 
     wherein the at least one conduit passageway of the outer shell comprises a flange flexible joint formed of material that is thinner than the metal material comprising the outer shell; and 
     wherein the at least one conduit passageway of the inner shell comprises a flexible joint. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is an elevated perspective view of a water cooled box provided in accordance with a preferred embodiment of the present invention, the water cooled box being installed in a vessel wall of a metal making furnace. 
         FIG. 2  is an elevated perspective view of an outer surface of an outer shell of a water cooled box provided in accordance with a preferred embodiment of the present invention. 
         FIG. 3  is a front perspective view (the surfaces facing toward the bath when mounted in a furnace) of a water cooled box provided in accordance with a preferred embodiment of the present invention. 
         FIG. 4  is an elevated perspective view of an inner surface of an inner steel shell of a water cooled box provided in accordance with a preferred embodiment of the present invention. 
         FIG. 5  is a back perspective view (the surfaces facing away from the bath when mounted in a furnace) of a water cooled box provided in accordance with a preferred embodiment of the present invention. 
         FIG. 6  is a cross-sectional view of a water cooled box provided in accordance with a preferred embodiment of the present invention, the box comprising flexible joints. 
         FIG. 7  is a cross-sectional view of a water cooled box provided in accordance with a preferred embodiment of the present invention, the box comprising alternative flexible joints. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a water cooled box  1  provided in accordance with a preferred embodiment of the present invention, the water cooled box  1  being installed in a metal making furnace  2 . As shown, the furnace  2  further comprises a vessel  3 , a vessel wall  4 , and, during normal operation of the furnace  2 , a molten metal bath  5  contained by the vessel  3 . 
     As shown in  FIG. 1 , the box  1  is preferably mounted on the vessel wall  4  of the metal making furnace  2  using fasteners as will be appreciated by one of ordinary skill in the art. As shown, the furnace  2  has an inner diameter defined by the vessel wall  4 , wherein when the box  1  is mounted at a wall  4 , the box  1  extends within the inner diameter toward the bath  5 . This allows the implements that are deployed through the conduit passageways  14 ,  24  (see  FIGS. 3, 5-7 ) to affect the bath  5  at a closer distance than that afforded by traditional boxes. 
       FIGS. 2-7  illustrate the water cooled box  1  comprising an outer shell  10  and an inner shell  20 . The outer shell  10  comprises an inner surface  11 , an outer surface  12 , one or more conduit passageways  14 , and one or more slag retention bars  15 . In some alternative embodiments, the outer shell  10  may comprise slag retention grooves  16  instead of bars  15  on the outer surface  12 . In other alternative embodiments, the outer shell  10  may comprise a combination of grooves  16  and bars  15 . The outer surface  12  further comprises a plurality of faces, including bottom face  17   a , side faces  17   b ,  17   c , curved face  17   d , conduit face  17   e , and top face  17   f.    
     The outer shell  10  is preferably comprised primarily of copper and is formed to have a substantially U-shaped or substantially arcuate profile in cross-section, wherein the curved face  17   d  is directed toward the bath  5 . More specifically, as best shown in  FIG. 2 , the U-shaped profile of the outer shell  10  is substantially defined by the shape of the top face  17   f , which is typically oriented perpendicularly to the vessel wall  4  when the box  1  is mounted thereon. As shown, the legs of the U-shaped top face  17   f  are substantially linear and abut the respective top edges of side faces  17   b ,  17   c , whereas the curved portion of the top face  17   f  abuts a top edge of the curved face  17   d . Thereby, the substantially U-shaped profile of the outer shell  10  is formed, and it persists away from the top face  17   f  to a certain depth of the outer shell  10  until the U-shaped profile is truncated at the curved face  17   d  by the conduit face  17   e  toward the bottom face  17   a.    
     The inner shell  20  comprises an inner surface  21 , an outer surface  22 , water baffles  23 , one or more conduit passageways  24 , a water inlet  25 , a water outlet  26 , first and second mounting flanges  13   a ,  13   b , and a top flange  28 . The inner shell  20  also provides strength to hold the shape and position of the outer shell  10 , and the use of steel rather than copper in the inner shell  20  reduces the cost of the box  1 . The one or more conduit passageways  14 ,  24  of the outer shell  10  and the inner shell  20 , respectively, are complementary in shape as well. Various implements, such as a burner, a lance, or a material (i.e., carbon or lime) injection device may be protected and deployed through the body of the box  1  via the passageways  14 ,  24  and into the furnace  2 . 
     The inner shell  20  is preferably formed of steel, and has a substantially U-shaped or substantially arcuate profile in cross-section that is complementary to the shape of the outer shell  10 . The inner shell  20  may be formed of stainless steel. The inner shell  20  further comprises a plurality of faces, including bottom face  27   a , side faces  27   b ,  27   c , curved face  27   d , and conduit face  27   e . More specifically, as best shown in  FIG. 4 , U-shaped profile of the inner shell  20  is substantially defined by the respective top edges of side faces  27   b ,  27   c  and curved face  27   d . Thereby, the substantially U-shaped profile of the inner shell  20  is formed, and it persists to a certain depth of the inner shell  20  until the U-shaped profile is truncated at the curved face  27   d  by the conduit face  27   e  toward the bottom face  27   a.    
     Returning to  FIGS. 2 and 3 , as shown, the slag retention bars  15  and/or grooves  16  of the outer shell  10  catch slag of the furnace  2  and cause slag buildup on the outer surface  12  of the outer shell  10 . The slag buildup acts as both a thermal and electrical insulator for the water cooled box  1 . This is because the thermal conductivity of the slag buildup is fairly low, thereby reducing the amount of heat that is transferred from the molten metal bath  5  to the outer surface  12  of the outer shell  10 . The thermal conductivity of the copper preferably comprising the outer shell  10 , by contrast, is very high, which allows heat that is transferred to the outer shell  10  to efficiently and quickly pass through the outer shell  10  into water that is circulating through a water chamber  30  (described further below), which carries the heat away from the box  1 . 
     As best shown in  FIGS. 6 and 7 , the water cooled box  1  is formed by fitting the inner shell  20  into the outer shell  10 . More specifically, the inner surface  11  of the outer shell  10  is married to the inner surface  21  of the inner shell  20  such that the shells  10 ,  20  are united to define the water chamber  30  between the inner surfaces  11 ,  21 . The outer shell  10  is cooled by water that enters the box  1  via the inlet  25 , is directed through the water chamber  30  by the baffles  23 , and exits the box  1  via the outlet  26 . The inlet  25  and the outlet  26  are preferably welded to the mounting flanges  13   a ,  13   b , and inlet  25  and outlet  26  defining respective apertures that extend through the flanges  13   a ,  13   b  into the chamber  30 . 
     The shells  10 ,  20  are joined at lateral back edges  18  of the outer shell  10  to the mounting flanges  13   a ,  13   b , preferably by welding, at the inner surface  11  portion of the top face  17   f  to the top flange  28 , preferably by welding, and also at the complementary conduit passageways  14 ,  24 . The conduit passageways  14 ,  24  preferably have a flexible connection at a joint to one of the shells  10 ,  20 , or the conduit passageways  14 ,  24  have a flexible member comprising the conduit passageways  14 ,  24  themselves. 
     For example, in a preferred embodiment as shown in  FIG. 6 , the box  1  comprises conduit passageways  14 ,  24  wherein the conduit passageway  14  of the outer shell  10  is preferably formed of metal having a substantial thickness and comprising a flange flexible joint  40  that is joined to the outer shell  10 , preferably by welding. The conduit passageway  24  of the inner shell  20 , meanwhile, is preferably comprised of a diaphragm flexible joint  50   a  and a can flexible joint  52   a , wherein the joints  50   a ,  52   a  connect the conduit passageway  14  of the outer shell  10  to the inner shell  20 . The diaphragm flexible joint  50   a  and a can flexible joint  52   a  are preferably ring-shaped devices that surround the conduit passageway  14 . 
     In an alternative embodiment as shown in  FIG. 7 , the box  1  comprises conduit passageways  14 ,  24  wherein the conduit passageway  14  of the outer shell  10  is preferably formed of a bellows flexible joint  42 . The bellows flexible joint  42  is substantially cylindrical. The conduit passageway  24  of the inner shell  20 , meanwhile, is preferably comprised of a diaphragm flexible joint  50   b  and a can (or cup) flexible joint  52   b . As shown in  FIG. 7 , the bellows flexible joint  42  is connected at a first end to the outer shell  10  and at a second to the diaphragm flexible joint  50   b . The can flexible joint  52   b  is connected at a first end to the diaphragm flexible joint  50   b  and at a second end to the inner shell  20 . 
     As shown in  FIGS. 6 and 7 , the water in the chamber  30  will flow between the flexible joint mechanisms  40 ,  42  of the outer shell  10  and the flexible joint mechanisms  50   a,b ,  52   a,b  of the inner shell  20 . 
     When the temperature of most objects is increased, the volume (length, width, and height) of the object increases. As long as the object is not restrained, the stress state of the object remains unchanged. When the temperature of an object is increased and the object is restrained in one or more planes, the volume of the object cannot increase in the direction of the restraint. This subjects the object to mechanical stress. 
     During operation of the furnace  2 , the temperature of the inner shell  20  formed of steel is almost the same as the temperature of the cooling water circulating through the water chamber  30 . The cooling water temperature is much cooler than the temperature of the outer shell  10  formed of copper, and therefore the temperature of the inner shell  20  is much lower than that of the outer shell  10 . Further, the coefficient of thermal growth of steel is much lower than that of copper. Between the temperature differential and dissimilar coefficients of thermal growth between the copper and steel preferably comprising the outer shell  10  and the inner shell  20 , respectively, the outer shell  10  grows thermally much more than the inner shell  20 . Accordingly, points of restraint between the two shells  10 ,  20  may create a thermal mechanical stress on the box  1 . 
     To offset this potential mechanical stress, the curved U-shape of the box  1  allows the outer shell  10  to move out of plane, thereby reducing the in-plane restraint experienced by the outer shell  10 , as compared to the in-plane restraint experienced by traditional flat plate surfaces fixed between two side walls. This is one of the mechanical stress reduction mechanisms of the present invention. 
     It is noted that the metal making processes in which furnaces such as furnace  2  are employed are, by nature, a very violent processes that cause vibration in essentially everything with a certain proximity to the process being performed. When an object is vibrated at its natural frequency, the vibrational energy is amplified and the energy from this amplification can create cracking in traditional furnace components. This cracking can cause cooling water to leak into the furnace, which can result in an explosion. The U-shaped surface of the outer shell  10  has a higher natural frequency than a flat plate surface of traditional water cooled boxes. Higher frequency vibration has less energy that low frequency vibration, which reduces energy available to create cracks and thereby enhances the durability and integrity of the outer shell  10 . 
     Additionally, the outer shell  10  and the inner shell  20  of the box  1  are joined at the mounting flanges  13   a ,  13   b  and at the conduit passageways  14 ,  24  between shells  10 ,  20 . The flanges  13   a ,  13   b  are the coldest parts of the box  1  and the thermal growth difference between the outer shell  10  and the inner shell  20  at the mounting flanges  13 ,  13   b  is minimal. Consequently, the thermal mechanical stress at the connection of the shells  10 ,  20  at the mounting flanges  13 ,  13   b  is low enough that it will not cause cracking. 
     By contrast, the conduit passageways  14 ,  24  between shells  10 ,  20  are located at the highest differential temperature between the shells  10 ,  20  and will experience the high thermal mechanical stress sufficient to cause cracking in traditional water cooled boxes. The conduit passageways  14 ,  24  of the present invention, however, have one or more flexible joint mechanisms  40 ,  42 ,  50   a,b ,  52   a,b  either at the joint of the passageway  14 ,  24  to its corresponding shell  10 ,  20  or a flexible member designed into the conduit passageway  14 ,  24  itself. The flexible joint mechanisms  40 ,  42 ,  50   a,b ,  52   a,b  are preferably formed of a copper alloy, such as a copper-nickel alloy. 
     This flexible joint mechanism reduces the restraint between shells  10 ,  20  due to thermal growth and thereby reduces the thermal mechanical stress experienced by the box  1 . Some flexible joint mechanisms for this invention, such as diaphragm flexible joints  50   a ,  50   b , include the use of a plurality of thin high-strength metallic diaphragms that reduce restraint in both the radial and axial direction of the conduit passageways  14 ,  24 . Alternative flexible joint mechanisms, such as can flexible joints  52   a ,  52   b , include the use of thin metallic high strength cans that allow deformation in the can that reduces restraint of the conduit passageways  14 ,  24 . Other alternative flexible joint mechanisms, such as flexible bellows joint  42 , are designed into the conduit passageway, particularly conduit passageway  14 . The flexible bellows joint  42  is formed like a bellows with a plurality of bellows convolutions to reduce both axial and radial restraint between the outer shell  10  and inner shell  20 . As the box  1  heats up and experiences thermal growth, the bellows joint  42  will tend to straighten out, thereby absorbing mechanical stress of the box  1 . Yet another alternative flexible joint mechanism, such as flange flexible joint  40 , comprises a separate article that is preferably thinner than the surrounding metal of the outer shell  10 , and welded onto the outer shell  10  at either the inner surface  11  or the outer surface  12 . One or more flange flexible joints  40  may be used. For example, if two flange flexible joints  40  are used, one may be connected to the inner surface  11  and another may be connected to the outer surface  12 . The flange flexible joint  40  reduces radial restraint between the shells  10 ,  20 . The flexible joint mechanisms  40 ,  42 ,  50   a ,  50   b ,  52   a ,  52   b  may be used independently (i.e., without other flexible joint mechanisms in the box  1 ) or in combination with one or more flexible joint mechanisms  40 ,  42 ,  50   a ,  50   b ,  52   a ,  52   b.