Patent Publication Number: US-11656028-B2

Title: Drain pump for a spray-cooled metallurgical furnace

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional patent application Ser. No. 62/752,057, filed Oct. 29, 2018, which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     Field of the Disclosure 
     Embodiments of the present disclosure relates generally to a spray-cooled roof for a metallurgical furnace, particularly an electric arc furnace that heats charged metal by means of an electric arc via a graphite electrode. 
     Description of the Related Art 
     Metallurgical furnaces (e.g., an electric arc furnace or a ladle metallurgical furnace) are used in the processing of molten metal materials. The electric arc furnace heats charged metal in the furnace by means of an electric arc from a graphite electrode. The electric current from the electrode passes through the charged metal material forming a molten bath of the metal materials. The furnaces house the molten materials during the processing of the molten materials forming molten steel and slag (a stony waste material). 
     A metallurgical furnace has a number of components, including a roof that is retractable, a hearth that is lined with refractory brick, and a sidewall that sits on top of the hearth. The metallurgical furnace typically rests on a tilting platform to enable the furnace to tilt about an axis. During the processing of molten materials, the furnace tilts in a first direction to remove slag through a first opening in the furnace referred to as the slag door. Tilting the furnace in the first direction is commonly referred to as “tilting to slag.” The furnace must also tilt in a second direction during the processing of molten materials to remove liquid steel via a tap spout. Tilting the furnace in the second direction is commonly referred to as “tilting to tap.” The second direction is generally in a direction substantially opposite the first direction. 
     Because of the extreme heat loads generated during the processing of molten materials within the metallurgical furnace, various types of cooling methods are used to regulate the temperature of furnace components, for example, the roof and sidewall of the furnace. One cooling method, referred to as non-pressurized spray-cooling, sprays a fluid-based coolant (e.g., water) against an external surface of plate. The plate may be a part of a roof of the furnace or a part of a sidewall of the furnace. For this cooling method, the fluid-based coolant is sprayed from a fluid distribution outlet at atmospheric pressure. As the fluid-based coolant contacts the external surface of the plate, the plate is relieved of heat transferred to the plate from the molten materials within the furnace, thus regulating the temperature of the plate. An evacuation system is used to continually remove spent coolant (i.e., coolant that has contacted the external surface of the plate) from the plate. 
     The evacuation system has pumps which removes the spent coolant from the furnace. Due to the extreme heat of the furnace and the coolant, the pumps are typically located remotely from the furnace and the evacuation system is plumbed from the furnace to the pumps. However, the pumps can be quite large and take up valuable floor space at the furnace facility. The drain system is pressurized between the furnaces and the pumps drawing coolant away from the furnace. With pressurized drain systems comes the potential for plumbing leaks which can be dangerous if the spent coolant contacts an extremely hot surface of the furnace. Additionally, the distance requires a large amount of energy to pump the spent coolant from the furnace to the remotely located pump. 
     Therefore, there is a need for an improved evacuation system for the spray-cooled furnace. 
     SUMMARY 
     An apparatus is disclosed for a spray-cooled roof of a tilting metallurgical furnace having a drain pump. The spray-cooled roof has a hollow metal roof section. The hollow metal roof section has an outer metal covering member, an inner metal base member spaced from and opposite the outer metal covering member, an enclosed space disposed between the outer metal covering member and the inner metal base member, and a spray-cooled system disposed in the enclosed space. An evacuation drain is fluidly coupled to the enclosed space and a pump is integrated into the spray-cooled roof and coupled to the evacuation drain. 
     In another embodiment, a method for removing spent coolant from within a spray-cooled roof of a metallurgical furnace is disclosed. The method begins by directing spent coolant from inside the spray-cooled roof to a peripheral drain. The spent coolant is then pumped from the peripheral drain with a pump integrated into the spray-cooled roof and sending the spent coolant to a collection system external to the metallurgical furnace. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the way the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIG.  1    illustrates an elevational side view of a metallurgical furnace having a spray-cooled roof. 
         FIG.  2    illustrates a top plan view of the spray-cooled roof of the metallurgical furnace in  FIG.  1   . 
         FIG.  3    illustrates an elevation view of the spray-cool system of the spray-cooled roof of  FIG.  2   . 
         FIG.  4    illustrates an elevation view of the roof shown in  FIG.  2   . 
         FIG.  5 A  illustrates one embodiment of a venturi pump suitable for use in the spray-cooled roof. 
         FIG.  5 B  illustrates a second embodiment of a venturi pump suitable for use in the spray-cooled roof. 
         FIG.  6 A  illustrates a first embodiment of a pump positioned in the spray-cooled roof. 
         FIG.  6 B  illustrates a second embodiment of a pump positioned on the spray-cooled roof. 
         FIG.  7    illustrates a method for removing spent coolant from within a spray-cooled roof of a metallurgical furnace. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to a metallurgical electric arc furnace having a spray-cooled roof comprising a hollow metal roof section having an integral drain pump therein or thereon. The term integral herein meaning the body of the drain pump is physically attached to the roof by techniques extending beyond mere plumbing and moves with the roof, for example, the drain pump tilts with the roof as the furnace is tilted. The spray-cooled roof is subject to temperatures suitable for melting metal materials. A spray-cooling system is employed within the hollow metal roof sections to prevent overheating and thermal stress of the spray-cooled roof&#39;s inner metal base member. A coolant supply header is a source of coolant by way of an outboard coolant supply for the spray-cooled system. Gravity fed fluid passage from an enclosed space of the hollow metal roof section drains spent cooling fluid, i.e., hot coolant, to a periphery drain of the spray-cooled roof. The drain pump is fluidly coupled to the periphery drain at the roof and discharges the spent cooling fluid from the roof of the metallurgical furnace to a location where the spent coolant can be recycled or disposed. 
       FIG.  1    illustrates an elevational side view of a metallurgical furnace  190  having a spray-cooled roof  100 . The metallurgical furnace  190  is suitable for melting scrap and other metals therein. The metallurgical furnace  190  may have temperatures exceeding 1,650° Celsius therein. The metallurgical furnace  190  utilizes a spray-cool system to protect itself from these elevated temperatures so as to avoid damage such as structural melting, compromise of seals or valves and/or exceeding the yield strength for structural components. 
     The metallurgical furnace  190  has a body  192 . The body  192  has a hearth  101  that is lined with refractory brick  105 , and a sidewall  107  that sits on top of the hearth  101 . The sidewall  107  has a top  159 . The spray-cooled roof  100  is moveably disposed on the top  159  of the sidewall  107 . The metallurgical furnace  190  has an interior volume  111 . The interior volume  111  of the metallurgical furnace  190  enclosed by the spray-cooled roof  100  and the body  192 . The interior volume  111  may be loaded or charged with material  103 , e.g., metal, scrap metal, or other meltable material, which is to be melted within the metallurgical furnace  190 . 
     The metallurgical furnace  190 , including the body  192  and the spray-cooled roof  100 , is rotatable along a tilt axis  180  about which the metallurgical furnace  190  can tilt. The metallurgical furnace  190  may be tilted in a first direction about the tilt axis  180  toward the slag door (not shown) multiple times during a single batch melting process, sometimes referred to as a “heat”, to remove slag. Similarly, the metallurgical furnace  190  may be tilted in a second direction about the tilt axis  180  towards a tap spout (not shown) multiple times during a single batch melting process including one final time to remove the molten material  103 . 
     Roof lift members  102  may be attached at a first end to the spray-cooled roof  100 . The roof lift members  102  may by chains, cables, ridged supports, or other suitable mechanisms for supporting the spray-cooled roof  100 . The roof lift members  102  may be attached at a second end to a gantry superstructure  141 . The gantry superstructure  141  has one or more mast arms  104  and a mast post  108 . The mast arms  104  extend horizontally and spread outward from a mast support  108 . The mast support  108  is supported by the mast post  110 . A coupling  109  attaches the mast post  110  to the mast support  108 . The gantry superstructure  141 , i.e., mast support  108 , the coupling  109  and the mast post  110 , rotates for lifting the spray-cooled roof away from the sidewall  107 . In one embodiment, the spray-cooled roof  100  is configured to swing or lift away from the sidewall  107 . The spray-cooled roof  100  is lifted away from the sidewall  107  to expose the interior volume  111  of the metallurgical furnace  190  through a top  159  of the sidewall  107  for loading material therein. 
     The spray-cooled roof  100  may be circular in shape when viewed from a top plan view, such as shown in  FIG.  2   . A central opening  124  may be formed through the spray-cooled roof  100 . Electrodes  120  extend through the central opening  124  from a position above the spray-cooled roof  100  into the interior volume  111 . During operation of the metallurgical furnace  190 , the electrodes  120  are lowered through the central opening  124  into the interior volume  111  of the metallurgical furnace  190  to provide electric arc-generated heat to melt the material  103 . The spray-cooled roof  100  may further include an exhaust port to permit removal of fumes generated within the interior volume  111  of the metallurgical furnace  190  during operation. 
       FIG.  2    illustrates a top plan view of the spray-cooled roof  100  of  FIG.  1   . The spray-cooled roof  100  additionally has an outer wall  219  and an inner wall  218 . The inner wall  218  bounds the central opening  124  which is located concentric to a center (e.g., the centerline)  299  of the spray-cooled roof  100 . The central opening  124  is configured for electrodes to enter into the furnace for melting material therein. The spray-cooled roof  100  may have an upwardly sloping shape, for example a frustoconical or torispherical shape, and is disposed over the metallurgical furnace  190  to enclose the interior volume  111 . Alternatively, the spray-cooled roof  100  may have other shapes. 
     The spray-cooled roof  100  has a hollow metal roof section  203 . The spray-cooled roof  100  has a spray-cooling system  350  inside an enclosed space  430  of the hollow metal roof section  203  that is detailed further below with reference to  FIG.  3    and  FIG.  4   . A coolant supply  130  provides coolant to the spray-cooling system  350  interfaced with the spray-cooled roof  100 . The coolant, such as water or other suitable fluid, is provided internally to the hollow metal roof section  203  to cool the spray-cooled roof  100 . The coolant supply  130  is fluidly coupled to the spray-cooling system  350  inside the enclosed space  430 . The coolant is sprayed within the hollow metal roof section  203  to maintain the surfaces of the spray-cooled roof  100  facing the interior of the furnace below a maximum operating temperature. 
     The spray-cooled roof  100  includes an evacuation drain  213  provided along the outer wall  219  of the hollow metal roof section  203 . The evacuation drain  213  is a continuous unitary circumferential drain having dedicated one or more drain outlets, such as a first drain outlet  150  and a second drain outlet  152 . The drain outlets  150 ,  152  evacuate the coolant from the enclosed space  430  of the hollow metal roof section  203  via the evacuation drain  213 . 
     Referring now briefly to  FIGS.  3  and  4   , the hollow metal roof section  203  is shown in further detail. The hollow metal roof section  203  comprises an upwardly sloping inner metal base member  306  shaped to form a predetermined portion of the spray-cooled roof  100 . The inner side of the metal base member  306  faces the interior of the furnace. An outer metal covering member  307  may additionally be shaped to form a predetermined portion of the spray-cooled roof  100 . The outer metal covering member  307  is spaced from the inner metal base member  306 , such that the inner surface of the metal base member  306  faces the outer metal covering member  307 . The space between the metal base member  306  and the metal covering member  307  is the enclosed space  430 . The enclosed space  430  is sized for the spray cooling system  350  therein and is configured to prevent coolant sprayed therein from leaking into or onto the furnace. 
     The spray-cooling system  350  includes a liquid coolant supply header  308  affixed to the hollow metal roof section  203  and extends around the inner metal base member  306 . The coolant supply  130  communicates with the liquid coolant supply header  308  of the spray-cooling system  350  such that the entire spray-cooled roof  100  may be supplied coolant from a single supply source. The coolant supply  130  supplies liquid directly to the hollow metal roof section  203  from a liquid coolant supply source located outboard of the spray-cooled roof  100 . 
     The spray-cooling system  350  includes a plurality of branch conduits  352  and a plurality of fluid distribution outlets  354  fluidly coupled to the liquid coolant supply header  308 . The plurality of branch conduits  352  are fluidly coupled to the liquid coolant supply header  308  and extend therefrom within the enclosed space  430  of the hollow metal roof section  203 . The fluid distribution outlets  354  are disposed on the distal ends of each branch conduits  352 . Coolant flows into the liquid coolant supply header  308 , through the branch conduits  352 , out the fluid distribution outlets  354 , into the enclosed space  430 , and onto the inner surface of the upwardly sloping inner metal base member  306 . The spray-cooling system  350  maintains a temperature profile for the hollow metal roof section  203  by spraying coolant for maintaining the temperature of the inner metal base member  306  of the spray-cooled roof  100  at a desirable level. 
     The spray-cooling system  350  includes an evacuation system. The evacuation system which collects and removes the sprayed (i.e., spent) coolant from the enclosed space  430  of the hollow metal roof section  203 . The evacuation system has one or more outer liquid drain openings  424  located at the lowermost portion of the enclosed space  430  and one or more pumps. The outer liquid drain openings  424  collect the coolant sprayed in the enclosed space  430  by the spray-cooling system  350  and empties into the evacuation drain  213  for removal. The one or more pumps  200 , such as one or more venturi pumps, are coupled to the evacuation drain  213  and are utilized to empty the external evacuation drain  213  to drain the spray-cooled roof  100  of cooling fluid regardless of the tilt inclination of the spray-cooled roof  100 . 
       FIG.  5 A  illustrates one embodiment of the pump  200  suitable for use in the spray-cooled roof  100 .  FIG.  5 B  illustrates a second embodiment of the pump  200  suitable for use in the spray-cooled roof  100 . The pump  200  is suitable to withstand high temperatures and air gaps created in the fluid stream due to intermittent siphoning on going during the titling of the metallurgical furnace  190  and the spray-cooled roof  100 . The pump  200  illustrated in  FIGS.  5 A and  5 B  are a venturi pump or an aspirator/jet pump. The embodiment of  FIG.  5 B  has the motive source and the suction inlet swapped from the embodiment of  FIG.  5 A . It should be appreciated that choosing the appropriate embodiment to for the removal of spent coolant may be determined based on space constraints among other considerations. However, the understanding of operation for the venturi pump  200  in  FIG.  5 A  is essentially the same for that shown in  FIG.  5 B . Therefore, for the sake of brevity and simplicity, further discussion of the venturi pump  200  will be with regard to only  FIG.  5 A . Although, it should be appreciated that other types of pumps may be equally suitable, further discussion of the pump  200  will be with regard to venturi pump ( 200 ). The venturi pump  200  is well suited for high temperature conditions as the venturi pump  200  does not have any lubricated moving parts subject to expansion, wear, or other modes of failure. 
     The venturi pump  200  operates on the principle of a first fluid entraining a second fluid. The venturi pump  200  has a first inlet  510 , a motive inlet  530 , a suction chamber  580  and a discharge outlet  520 . The first inlet  510  and motive inlet  530  are fluidly coupled to the suction chamber  580 . The venturi pump  200  additionally has a tube  540  disposed between the suction chamber  580  and the discharge outlet  520 . 
     The motive inlet  530  is coupled to a source of motive fluid  532 . The motive fluid  532  may be a liquid, gas, or steam. In one embodiment, the source for the motive fluid  532  is liquid coolant supply header  308  and the motive fluid is the coolant therein the liquid coolant supply header  308 . In other embodiments, the motive fluid  532  is provided by plumbing externally routed to the roof. The motive fluid  532  is under pressure and enters the motive inlet  530 , travels through a nozzle assembly  564  into the suction chamber  580 . The nozzle assembly  564  converts the pressure of the motive fluid  532  into a high velocity stream, i.e., where the pressure energy is converted into kinetic energy. The nozzle assembly  564  directs the motive fluid  532  into the suction chamber  580 . 
     The suction chamber  580  provides a pressure drop for drawing the secondary fluid, i.e., spent spray-cooled coolant  501  through the first inlet  510  and into the suction chamber  580 . The pumping action begins when spent spray-coolant in the suction chamber is entrained by the high velocity stream emerging from the nozzle assembly  564 , lowering the pressure in the suction chamber. The entrained spent spray-cooled fluid mixes with the motive fluid  532  and acquires part of the energy from the high velocity stream of the motive fluid  532 . The resulting action causes the spent spray-coolant in the suction chamber  580  to flow toward the discharge outlet  520  via the tube  540 . 
     The tube  540  narrows in a first section  541  to a second section  542  and then expand to a third section  543 . The first section  541  acts as a converging inlet nozzle  546 . The second section  542  is a throat  547 . In operation, the converging inlet nozzle  546  of the first section  541  accelerates the fluid causing a first pressure drop while the throat  547  of the second section  542  causes an additional second pressure drop due to friction. The third section  543  is a diffuser  548  fluidly coupled to the discharge outlet  520 . The diffuser  548  of the third section  543  results in pressure recovery from the first section  541  and second section  542  pressure loss. The angle of divergence in the third section  543  is small to prevent flow separation. The third section  543  increases the head sufficiently to allow the spent coolant fluid to be piped away from the metallurgical furnace  190  for recovery or recycling. In the tube  540 , the velocity of the mixture is converted to a pressure greater than the suction pressure, but lower than the operating pressure. That is, the high-velocity jet entrains the secondary fluid. The two streams mix in the mixing tube, leading to pressure recovery. Further static pressure is recovered in a narrow-angle diffuser  548  downstream of the mixing tube. 
     The flow of the motive fluid  532  in the tube  540  produces a vacuum, by means of the venturi effect, which entrains, i.e., draws along with or after oneself, the spent spray-cooled coolant  501  for removal out the discharge outlet  520 . The discharge outlet  520  has a flange  534 . The flange  534  couples to external plumbing for removing the spray-coolant from the metallurgical furnace  190  for recovery or recycling. 
     The venturi pump  200  utilize the pressure energy of a high-pressure fluid stream from the liquid coolant supply header  308  to boost the pressure and/or flow of a low-pressure spent spray-coolant in the evacuation drain  213 . The venturi pump  200  operates with no moving parts. Three key parameters for venturi pump  200  are the pressure ratio, defined by: 
             N   =         P   5     -     P   2           P   1     -     P   5               
where P 1  is the primary flow pressure (motive fluid  532 ), P 2  is the secondary flow pressure (spent spray-cooled coolant  501 ), and P 5  is the combined outlet pressure ( 501 + 532 ).
 
     The flow ratio M={dot over (V)} 2 /{dot over (V)} 1  and the ratio of mixing tube-to-nozzle assembly  564  diameter (R) are related through the equation: 
             N   =               2   ⁢   R     +       2   ⁢     CM   2     ⁢     R   2         1   -   R       -         R   2     (     1   +   CM     )     ⁢     (     1   +   M     )     ⁢     (     1   +     K   m     +     K   d       )       -                     CM   2     ⁢     R   2           (     1   -   R     )     2       ⁢     (     1   +     K   s       )                 (     1   +     K   p       )     -     2   ⁢   R     -       2   ⁢     CM   2     ⁢     R   2         1   -   R       +         R   2     (     1   +   CM     )     ⁢     (     1   +   M     )     ⁢     (     1   +     K   m     +     K   d       )                 
where C is the density ratio of the spent spray-cooled coolant  501  (secondary) to motive fluid  532  (primary). The loss coefficients K p , K s , K m  and K d  account for losses in the nozzle assembly  564  of the primary fluid (motive), secondary flow (first inlet  510 ), suction chamber  580  and diffuser  548 , respectively. The equation can be solved directly for N if C, M and R are known. Given the primary and secondary flows/pressures, an optimum value of R can be found by trial and error. Once the ratios have been determined, the primary nozzle can be sized from
 
     
       
         
           
             
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     The venturi pump  200  has a first length  574  from the first inlet  510  to the motive inlet  530  of between about 1.5 inches to about 12 inches. The venturi pump  200  has a second length  572  (overall length) from the motive inlet  530  to the discharge outlet  520  of between about 5 inches to about 111 inches. The motive inlet  530  may have an operating water pressure between about 15 psig to about 200 psig. The venturi pump thus can be sized to pump the most suction liquid (spent coolant) with the least operating liquid (motive fluid). Thus, the venturi pump  200  can be made sufficiently small to be incorporated into or with the spray-cooled roof  100  saving valuable floor space and plumbing. 
       FIG.  6 A  illustrates a first embodiment of the pump  200  located in the spray-cooled roof  100 . The venturi pump  200  is disposed within the enclosed space  430  of the spray-cooled roof  100 . The venturi pump  200  may be cooled by the spray-cooling system  350  within the enclosed space  430 . The motive inlet  530  of the venturi pump  200  is fluidly coupled to the liquid coolant supply header  308 . The venturi pump  200  has a discharge connection  620  protruding through the spray-cooled roof. The discharge outlet  520  of the venturi pump  200  is fluidly coupled to the discharge connection  620  to flow the spent spray-cooled coolant  501  and motive fluid  532  via external plumbing to an external coolant recovery system. The first inlet  510  of the venturi pump  200  is situated in the evacuation drain  213 . Alternately, plumbing  670  may fluidly couple the first inlet  510  to the evacuation drain  213 . For example, the first inlet  510  may have a suction pipe  670  extending therefrom and into the evacuation drain  213 . Advantageously, the venturi pump  200  may be kept cool and protected within the spray-cooled roof  100  to prevent damage, have reduced plumbing requirements for the drain system, and a reduced overall impact for the foot print for the cooling/draining system on the facility floor. 
       FIG.  6 B  illustrates a second embodiment of the pump  200  located on the spray-cooled roof  100 . The venturi pump  200  is disposed on or coupled to the outer metal covering member  307  of the spray-cooled roof  100 . The motive inlet  530  of the venturi pump  200  is fluidly coupled through the outer metal covering member  307  of the spray-cooled roof to the liquid coolant supply header  308  within the enclosed space  430 . The spent spray-cooled coolant  501  and motive fluid  532  flows through the discharge outlet  520  of the venturi pump  200  to an external coolant recovery system via external plumbing. The first inlet  510  of the venturi pump  200  is plumbed through the outer metal covering member  307  to fluidly couple the first inlet  510  to the evacuation drain  213 . Advantageously, the venturi pump  200  is easily accessible for maintenance, has reduced plumbing requirements for the drain system, and a reduced overall impact for the foot print for the cooling/draining system on the facility floor. 
       FIG.  7    illustrates a method  700  for removing spent coolant from within a spray-cooled roof of a metallurgical furnace. The method begins at block  710  by directing spent coolant from inside the spray-cooled roof to a peripheral drain. At block  720 , the spent coolant is pumped from the peripheral drain with a jet pump disposed on the spray-cooled roof to a collection system external to the metallurgical furnace. As discussed above, the motive source of the jet pump is coupled to directly to the spray-coolant header disposed inside the spray-cooled roof. In one embodiment, the jet pump is disposed on top of the spray-cooled roof. In another embodiment, the jet pump is disposed in an interior portion of the spray-cooled roof. The jet pump disposed inside the roof permits spray-cooling of the jet pump with the spray-coolant prior to the spray-coolant entering the peripheral drain. 
     Advantageously, the venturi pump  200  has no moving parts, nothing to break or wear. There are no packing glands. No lubrication is required. They are practically noiseless in operation. The initial cost is low. Installation cost is low because they are compact and no foundation or wiring is necessary. They provide reliable operation with low maintenance cost. Furthermore, the plumbing of the motive source internally to the spray-cooled system reduces the amount of additionally plumbing required. The small footprint for the venturi pump  200  is coincident with the furnace reducing valuable factory space and has the added benefit of reducing water consumption. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.