Patent Publication Number: US-8124004-B2

Title: Slag door assembly for an electric arc furnance

Description:
BACKGROUND 
     The present invention relates to metallurgical furnaces. In particular, the invention relates to metallurgical furnaces of the type having a slag door, such as electric arc furnaces used for steelmaking. 
     Metallurgical furnaces of the type having a slag door are well known. The slag door is typically positioned on the side of the furnace shell with a tunnel area leading from the furnace interior, and an apron extending below the opening on the exterior of the furnace. The slag door is used for periodic tapping of slag by tipping the furnace, but it is also used for many other operations, including charging of additives, sample collecting, temperature measurement, insertion of burners and oxygen lances, and visual inspection of the furnace interior. 
     In steelmaking operations, unmolten scrap metal tends to accumulate in the tunnel that extends through the furnace wall from the furnace interior to the slag door opening. Slag can also freeze in large quantities in the area of the tunnel and the threshold of the slag door opening. Commonly, operators must regularly try to clean out these areas by means of tractors equipped with long projecting rams, a technique that has limited efficacy and is also potentially dangerous for the operating personnel. 
     Known closures for slag doors consist essentially of a sliding panel that can be raised or lowered by a mechanical system of pulleys, sprockets, links and roller chains that is powered by hydraulic or air cylinders. Such closure mechanisms are vulnerable to jamming and blockages, and after being in service for some time, they typically provide only partial coverage of the slag door opening. 
     As a result, ambient air is sucked into the furnace through the slag door which is believed to lead to a number of drawbacks, including:
         heat losses due to excessive volumes of exhaust gas;   excessive pollution in the exhaust gases;   higher energy consumption; and   uncontrolled decanting of slag through the slag door.       

     It is therefore an object of the present invention to address the disadvantages of known metallurgical furnaces having slag doors, or at least to provide a useful alternative. 
     SUMMARY OF THE INVENTION 
     In accordance with the first aspect of the present invention, there is provided a sealing apparatus for a slag door of a metallurgical furnace comprising a mounting assembly for mounting the apparatus to the furnace, and at least one closure element having a rear, hot face panel, the closure element being held by the mounting assembly so that it is moveable from an open position that is exterior of the slag door opening, to a closed position that effectively seals against the slag door and in which the closure element extends into the slag door opening with its hot face being proximally aligned with the interior wall of the furnace. 
     Advantageously, the apparatus also comprises at least one wiping component moveable so as to sweep across the lower surface of the slag door from an open position, remote from the slag door opening, through intermediate positions, to a closed position, within the slag door opening, such that the wiping component can remove obstructions from the lower surface of the slag door. 
     More advantageously, the wiping component is provided by a pair of opposed, generally horizontally gyrating arms, and the closure element includes a gate mounted so as to be able to move downwardly and inwardly into the slag door opening above the arms. The arms are advantageously independently moveable and water cooled. They may in certain embodiments be controlled by at least one linear or rotary hydraulic actuator. 
     In certain embodiments, the closure element includes a gate supported by at least one parallelogram linkage mechanism such as the type having a motoring lever connected to a drive shaft, and a follower lever connected between the motoring lever and the closure element. The hot face panel of the gate is advantageously water cooled, and the gate may also include a water cooled bottom panel. In certain embodiments the water cooled bottom panel of the gate is pivotally mounted and can be activated to aid in breaking up and removing obstructions from the slag door. 
     In certain embodiments, the apparatus also includes a frame positioned exteriorly of the furnace, surrounding the slag door opening, and the closure element rests against the frame in its closed position. The frame is advantageously water cooled. 
     In other embodiments of the invention, the closure element includes a pair of opposed generally horizontally gyrating doors. The wiping component may be provided by the gyrating doors. The wiping component may also be provided by a panel mounted so as to be able to move downwardly and inwardly into the slag door opening below the doors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which illustrate embodiments of the present invention, and in which: 
         FIG. 1  is a front elevation view of a sealing apparatus for a slag door of a metallurgical furnace according to a first embodiment of the present invention, the apparatus being shown in a fully closed position; 
         FIG. 2  is a front elevation view of the same sealing apparatus being shown in a fully open position; 
         FIG. 3  is a sectional side elevation view of the sealing apparatus of  FIG. 1  taken along the line III-III; 
         FIG. 3   a  is a close up view of the encircled portion of the sealing apparatus of  FIG. 3 ; 
         FIG. 4  is a sectional side elevation view of the sealing apparatus of  FIG. 2  taken along the line IV-IV; 
         FIG. 4   a  is a close up view of the encircled portion of the sealing apparatus of  FIG. 4 ; 
         FIG. 5  is a sectional plan view of the sealing apparatus of  FIG. 1  taken along the line V-V; 
         FIG. 6  is a sectional plan view of the sealing apparatus of  FIG. 2  taken along the line VI-VI; 
         FIG. 7  is an isometric view of the same sealing apparatus shown in a fully closed position; 
         FIG. 8  is an isometric view of a sealing apparatus for a slag door of a metallurgical furnace in accordance with a second embodiment of the present invention, the sealing being shown in conjunction with a portion of the wall of the furnace viewed from the exterior; 
         FIG. 9  is an isometric view of the sealing apparatus of  FIG. 8  viewed from the interior of the furnace; 
         FIG. 10  is an isometric view of the same sealing apparatus shown in a fully open position; 
         FIG. 11  is a sectional side elevation view of a sealing apparatus for a slag door of a metallurgical furnace in accordance with a third embodiment of the present invention; 
         FIG. 12  is a plan view of a sealing apparatus for a slag door of a metallurgical furnace in accordance with a fourth embodiment of the present invention; 
         FIG. 13  is a front elevation view of the sealing apparatus of  FIG. 12 ; 
         FIG. 14  is a sectional side elevation view of a sealing apparatus for a slag door of a metallurgical furnace in accordance with a fifth embodiment of the present invention; and 
         FIG. 15  is a sectional side elevation view of a sealing apparatus for a slag door of a metallurgical furnace in accordance with a sixth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Referring to  FIGS. 1-7 , particularly  FIG. 1 , the sealing apparatus has two major component subassemblies, a rotating and retractable centrally located gate  2  controlled by two sets of rotating parallelogram levers ( 4 ,  8 ), and a pair of generally horizontally gyrating flipper arms  28 , located below the gate  2 . 
     One end of each of the motoring levers  4  is firmly attached to a driving shaft  14  via double-keyed hubs  7 . The other end of each of the motoring levers  4  is equipped with hub  5  and it is dressed with lubricated friction bushing  6 . The stabilized end of each follower levers  8  is equipped with hub  11 , dressed with lubricated friction bushing  12 , rotating around pin  19 . The rotating ends of the follower levers  8  are equipped with hubs  9 , dressed with lubricated friction bushings  10 , rotating around hollow pins  34 . The motoring levers  4  are connected to the double-bracket  3  of the gate  2  via pins  33  held firmly in the double-brackets  3 . The follower levers  8  are connected to the double-brackets  3  via hollow pins  34 , held firmly in the double-brackets  3 . The double-brackets  3  are permanently connected to the gate  2 . 
     The water cooled system driving shaft  14  is held and located in position via two pillow blocks  15 , equipped with lubricated friction bushings  16 . The shaft cooling media—water—is supplied and discharged from the shaft via swiveling joints  17  and  18 . The pillow blocks  15  are located on and bolted to the top of brackets  31 . The brackets  31  are welded to the furnace shell frame structure  1  and they serve also as base for follower levers  8 . The lever  52 , equipped with double-keyed hub  53  is attached to one end of the driving shaft  14 . An extended end of the lever  52  is connected via clevis  22  and pin  23  to the linear hydraulic cylinder  13 , attached to the furnace shell frame structure  1  via welded eye bracket  20  and pin  21 . 
     Each of the two water cooled generally horizontally gyrating flipper arms  28  is carried and rotated by a special hydraulic rotating actuator  29 . Rotation of each flipper arm  28  can be independently and/or simultaneously for a desirable angle and is achieved by remote controlled switching of the pressurized and non-pressurized hydraulic fluid via ports  30  and  32  of the hydraulic rotating actuator. A consumable threshold refractory  35  is advantageously extended by long lasting square shaped graphite slabs  36 . 
     An inverted “U” shaped water cooled frame  37  with a sealing flange  39  (shown more clearly in  FIG. 3  and  FIG. 4 ) is tightly fitted around the slag door opening and held securely in position by lugs  50  attached to the furnace structure  1 , and slotted pins  25  with wedges  38 , the pins being permanently attached to the furnace structure  1 . 
     Turning to  FIG. 2 , the sealing apparatus is fully open, with the gate  2  controlled by the two sets of rotating parallelogram  4 ,  8  and the gyrating flipper arms subassemblies  28  controlled by actuators  29 , located below the gate  2 . Heat radiation shielding plates  41  provide protection when the gate  2  is in transit between the first, closed position, and the second, open position. 
     Turning to  FIG. 3 , the gate  2  has water cooled panels  26  and  27 , and is held in position by the lever parallelogram mechanism consisting of the two motoring levers  4  and the two follower levers  8 ; 
     The water cooled frame  37  allows the rotating and retractable gate  2  to follow composite motion curve with minimum gap between the stationary and moving parts, so that even in intermediary positions there is reduced ingress of cold air into the furnace interior. Also supporting favourable interrelation between stationary and moving components of the gate  2  in closed position is the shape of the water cooled side component  43  of the inverted “U” shape water cooled frame  37 . It conforms to the outline and position of the water cooled panel  27 ; thus when closed it enlarges the flow resistance to the eventually ingressing cold air, and reduces its intake. Moreover, the water cooled hot face panel  27  aligns substantially with the interior wall of the furnace. 
     The inverted “U” shape water cooled frame  37  with sealing flange  39  (shown more clearly in  FIG. 3  and  FIG. 4 ) is tightly fitted into the slag door opening of the furnace shell  1  and held securely in position by square openings  24  in the flange  39  and lugs  50 , slotted pins  25  with wedges  38 , and elongated holes the pins being permanently attached to the furnace shell  1 . When gate  2  is in its fully closed position an inverted “U” shaped peripheral plate  40  is held tightly against the inverted “U” shaped water cooled plate  39  by the fully retracted hydraulic cylinder  13 . 
     The inverted “U” shaped water cooled plate  39  is an intrinsic part of the inverted “U” shape water cooled frame  37 . The tightness between items  40  and  39  is assuring that the main purpose of the embodiment of the invention is complied with, that being almost total elimination of the cold air ingress into the furnace inner hot operating chamber. 
     Remotely controlled extending of the linear hydraulic cylinder  13  invokes rotating motion of the driving shaft  14  and simultaneously parallel rotating motion of the motoring levers  4  and follower levers  8 . Since the centrally located gate  2  is connected to the motoring levers  4  and follower levers  8  via double-brackets  3  and pins  33  and  34 , the centrally located gate structural subassembly  2  repositions itself in predetermined curved motion from the fully closed position shown in  FIGS. 1 and 3  to fully open position shown in  FIGS. 2 and 4 . 
     As seen in  FIG. 4 , when the gate  2  is fully open, it allows greatly improved access for inspection and eventual repair of the inner of the metallurgical furnace compared to known prior art slag doors. 
     Turning to  FIGS. 5-7 , the refractory lining off the furnace bottom  35  is positioned interiorly of the opening. Although the main function of the water cooled generally horizontally gyrating flipper arms  28  is to expediently recondition the threshold refractory  35  by gyrating movement, they also contribute significantly to the sealing effect of the sealing apparatus effectively protecting the furnace interior from excessive ingress of ambient air. The shape of the column  47  of the furnace shell frame, matches the shape of the horizontally gyrating flipper arms  28 , leaving only a very small gap  48  between. The rotary hydraulic actuator  29  is water cooled, and is fixed to the furnace shell frame by bolts  46 . 
     Rectangular graphite slabs  36  serve as a non-sticking slag guiding apron. When gyrating flipper arms  28  are held in the closed position, they prevent materials such as liquid steel, liquid and solidified slag and floating refractory to leave freely by overflow of nominal threshold level from the furnace inner operating chamber. Hence, the closed position of the gyrating flipper arms  28  helps retention of more slag in the furnace, significantly contributing to reduction of FeO in the slag leaving the furnace. By gyrating the flipper arms  28  from the closed position through intermediate positions toward the open position, the outflow of slag and other materials can be continuously controlled. 
     As seen in  FIG. 6 , when desired, the fully open position of the horizontally gyrating flipper arms  28  allows an unobstructed flow of liquid slag over the nominal level of the threshold refractory. 
     As seen in  FIGS. 1 and 7 , a linear hydraulic cylinder  13  is used for control of the parallelogram levers  4 ,  8 , and rotating actuators  29  are used for controlling the gyrating flipper arms  28 . 
     In the embodiment of the sealing apparatus shown in  FIG. 8 , a water cooled rotating actuator  48   a  is used for control of the parallelogram levers  4 ,  8 , and linear hydraulic cylinders  49  are used for controlling the gyrating flipper arms  28 . 
     As seen in  FIGS. 9 and 10 , the sealing apparatus effectively eliminates the void in the furnace walls&#39; water cooled lining in the area of the slag door opening above the slag line, and also effectively eliminates the tunnel leading to the slag door opening. In particular, when the gate  2  is in closed position, the water cooled panel  27  generally aligns with the water cooled panels of the interior furnace wall. The two horizontally gyrating flipper arms  28 , whose bottom edges are generally at the level of the sill line of the top ledge of the slag door, effectively fill the opening below the gate  2  with minimal gap. 
     In the embodiment of the sealing apparatus shown in  FIG. 11  a water cooled panel  50   a  is mounted to the gate  2  rotatable around pivot pins  51 . A lever  52   a  is attached to the panel  50  and connected to a hydraulic cylinder  53   a  which is supported by a bracket  54  that is mounted on the gate  2  through a pivot connection  55 . The water cooled cleaning panel  50  can provide additional means for breaking up solidified slag in front of the flipper arms  28 . 
     In the embodiment of the sealing apparatus shown in  FIGS. 12 and 13  the closure element is provided a pair of opposed generally horizontally gyrating doors  56  each being controlled by a connected hydraulic cylinder  63 . A lever  57  is attached to each door  56  and connects to the hydraulic cylinder  63  via a pin  58 . The hydraulic cylinder, in turn, is supported by a bracket  59  through a pivot  60 . The bracket  59  is mounted on the furnace shell  61 . The furnace structure is protected in the opening area by a water cooled panel  62 . 
     In the embodiment shown in  FIG. 14  there is a also a pair of opposed generally horizontally gyrating doors  56 . However, additionally there is a water cooled centrally located panel  69  controlled by a set of rotating parallelogram levers  70 ,  71 . One end of each of the motoring levels  71  is attached to a driving shaft  72  via keyed hubs  73 . The other end of each of the motoring levers  71  is equipped with a hub  74  and dressed with a lubricated friction bushing  75 . 
     The stabilized end of each of the follower levers  70  is equipped with a hub  76 , dressed with a lubricated friction bushing  77 , rotating around a pin  78 . The rotating ends of the follower levers  70  are equipped with hubs  85 , dressed with a lubricating friction bushing  79 , rotating around a pin  82 . 
     The motoring levers  71  are connected to a double bracket  81  of the panel  69  via pins  80  held in the double brackets  81 . The follower levers  70  are connected to the double brackets  81  via the pins  82 , held in the double brackets  81 . The double brackets  81  are connected to the panel  69 . The driving shaft  72 , which is water cooled, is held and located in position via two pillow blocks  83 , equipped with lubricated friction bushings  84 . With brackets located on the furnace shell structure  1 . The driving shaft  72  is driven either by a hydraulic cylinder or a hydraulic actuator. 
     In the embodiment of the sealing apparatus shown in  FIG. 15 , the closure is provided by a water cooled centrally located panel  69 , controlled by a set of rotating parallelogram levers  70 ,  71 . The structure and operation of the panel  69  is similar to that of the embodiment shown in  FIG. 14 . However, this embodiment does not include a pair of opposed generally horizontally gyrating doors. 
     While the above description and accompanying various figures have been made in connection with embodiments of the present invention as presently contemplated by the inventor, it is to be understood that modifications and additions may be made to the described embodiments within the scope of the present invention. Therefore, the present invention should not be considered as being limited to the specific described embodiments, but construed in accordance with the appended claims.