Abstract:
A system for supporting and cooling a furnace roof comprised of refractory bricks comprises a plurality of roof support members extending across the furnace and being supported from above the furnace roof. The support members are provided with internal channels for circulation of a cooling fluid, and are provided with side surfaces adapted to support rows or refractory bricks between adjacent roof support members. The system eliminates the need to suspend individual bricks from above the roof, and provides simultaneous support and cooling of the roof structure.

Description:
FIELD OF THE INVENTION 
     The invention relates to systems for suspending and cooling refractory furnace roofs. 
     BACKGROUND OF THE INVENTION 
     High temperature furnaces have roof structures comprised of refractory bricks. The bricks are supported from hanger beams by metal hangers. A number of systems are known whereby the bricks interlock with one another so that the number of hangers may be reduced. Nevertheless, a large number of these hangers typically protrude from a furnace roof, making it difficult to keep the roof free of dust and debris, thereby hindering heat removal from the roof refractory and hence reducing its service life. 
     Generally, furnace roof suspension systems do not include means for cooling the refractory bricks comprising the roof. One exception is the system disclosed in U.S. Pat. No. 1,404,845 (Gates), issued on Jan. 31, 1922. This patent discloses a furnace “arch” having a grid of interconnected tubular members through which coolant is circulated. Inlets for the coolant are provided in the longitudinal tubular members and outlets for the coolant are provided in the transverse tubular members. The refractory bricks comprising the arch are notched for support from the longitudinal tubular members, while the ends of the transverse tubular members rest on the furnace walls, thereby supporting the roof. 
     The Gates patent shows two different arrangements for constructing an arch. In one arrangement, shown in FIG. 1 of Gates, the tubular members  15  are inserted into channels between the bricks from above, therefore requiring the use of wedges or fillers to hold the bricks in suspension. In a second arrangement, shown in FIG. 4 of Gates, a cooling tube is required between each pair of bricks. 
     Although the Gates system provides some advantages over conventional hanger systems, the grid of transverse and longitudinal tubular members may interfere with the ability to remove dust and debris from the furnace roof. This cleaning is essential for maximum roof life, as the dust is insulating and, if not removed, will cause the bricks to run hotter, thus reducing their life. Furthermore, it appears that the refractory bricks of the Gates furnace arch cannot be replaced from above, but rather must be replaced from inside the furnace, requiring a furnace cold shutdown and consequent loss of production. 
     In addition, supporting the roof on the walls as disclosed by Gates is undesirable in that the roof must be removed or otherwise supported to replace the wall bricks, which must typically be done much more frequently than roof repairs. 
     In order to address these deficiencies in the prior art, it is desirable to provide an improved system for suspending and cooling a refractory furnace roof. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of the prior art by providing a system for supporting the roof of a furnace, the system comprising a plurality of elongate roof support members extending across the furnace, with the bricks of the furnace roof being supported by support surfaces on the sides of the roof support members in such a manner that the bricks are removable from above the roof. The roof support members are preferably provided with at least one interior coolant passage which circulates a cooling fluid between a coolant inlet and a coolant outlet. In the preferred embodiment, the roof support members thus simultaneously serve the dual purpose of both supporting and cooling the bricks. 
     In the system according to the invention, the need to attach hangers to individual bricks is eliminated, and the bricks can be removed and replaced from above without shutting down the furnace to a cold state, thereby greatly simplifying and shortening the time duration and expense of repair procedures. Furthermore, in the preferred system of the invention, the coolant inlets and outlets are provided in the roof support members, thereby eliminating the need for coolant-carrying cross members as in the Gates patent. 
     In one aspect, the present invention provides a roof for substantially covering an interior space of a furnace, the furnace roof comprising: a plurality of elongate roof support members extending across a top of the furnace, with spaces being provided between adjacent roof support members; a plurality of refractory bricks provided in the spaces between adjacent roof support members, the roof support members and refractory bricks substantially completely covering the interior space, wherein the bricks are arranged in rows extending along the roof support members, with at least one row of bricks being provided between adjacent roof support members, each of the bricks having a bottom surface facing the interior of the furnace, a top surface facing away from the interior of the furnace, and a pair of opposed side surfaces extending between the top and bottom surfaces; and each of the roof support members having opposed sides extending along substantially its entire length, at least one of the sides being provided with a support surface which is in direct contact with the side surfaces of a plurality of the refractory bricks of one said row of bricks, and upon which said plurality of refractory bricks is at least partially supported, wherein the side surfaces of the bricks and the sides of the roof support members are shaped such that the bricks which are in direct contact with the support surface of the roof support member can be removed from the space between adjacent roof support members by raising the bricks from above the roof. 
     In another aspect, the present invention provides a support member for supporting a plurality of refractory bricks in a furnace roof, the support member being elongate and having a first end, a second end and a pair of opposed sides extending along substantially its entire length, each of the sides being provided with a support surface for supporting said refractory bricks, wherein said support surfaces each comprise a shoulder forming a transition between upper and lower portions of one of one of the sides, such that a width of the roof support member between the upper portions of the sides is less than a width of the roof support member between the lower portions of the sides. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a schematic transverse cross-section through a furnace roof incorporating a preferred system according to the present invention; 
     FIG. 2 is a longitudinal cross-section through a portion of the furnace roof of FIG. 1; 
     FIG. 3 is an enlarged cross section through one of the roof support members shown in FIG. 2; and 
     FIG. 4 is an enlarged view of a refractory brick shown in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 schematically illustrates a portion of a furnace  10  being rectangular in shape and having four vertically extending walls surrounding an interior space  11 , the walls preferably formed from a refractory material. Portions of side walls  12 ,  14  and end wall  16  are illustrated in FIG.  1 . Although the preferred embodiment of the invention is described in connection with a rectangular furnace, it will be appreciated that the principles embodied in the present invention can be applied to furnaces of various shapes, for example circular furnaces having generally cylindrical side walls. 
     Supporting the side walls  12  and  14  of furnace  10  are vertical beams  18  commonly referred to as “buckstays”. These buckstays are paired along opposite sides of the furnace  10 . Although only one pair of buckstays  18  is illustrated in FIG. 1, it will be appreciated that there are preferably a plurality of such pairs spaced along the lengths of side walls  12  and  14 . Extending horizontally between each pair of buckstays is a horizontal girder  20 . The buckstays  18  and girder  20  are illustrated in the drawings as comprising I-beams. However, beams having other cross sections may also be suitable. 
     Substantially completely covering the open top of furnace  10  is a roof  22  which, in the preferred embodiment shown in the drawings, is arch-shaped and comprises a plurality of refractory bricks  24  and a plurality of elongate support members  26 . It will, however, be appreciated that the roof is not necessarily arch-shaped, and may instead be flat. In fact, the benefits of using the support system according to the invention may be greater in a flat roof than in an arched roof, since an arched roof is at least partially self-supporting and would generally have fewer brick hangers than a flat roof. It will also be appreciated that the roof  22  may be formed with openings (not shown) for charging of materials or to receive electrodes. 
     The elongate roof support members  26  extend across the top of the furnace  10 , with spaces being provided between adjacent roof support members  26 . In the preferred system shown in the drawings, in which the furnace  10  is rectangular, the roof support members  26  are arranged in spaced, parallel relation to one another along the opposed side walls  12 ,  14  of furnace  10 , as illustrated in FIG. 2, or may be parallel to the end walls  16 . 
     In the preferred embodiment of the invention, the roof support members  26  are each comprised of a pair of roof support beams  27  arranged in end-to-end, parallel relation to one another to form a roof support member  26 . Each of the roof support beams  27  has a first end  28 , a second end  30 , an upper surface  32 , a lower surface  34  and a pair of opposed side surfaces  36 . The upper surface  32 , lower surface  34  and side surfaces  36  are also referred to herein as the upper, lower and side surfaces of the roof support members  26 . Although the roof support members  26  shown in the drawings comprise two roof support beams  27  arranged end-to-end, it will be appreciated that the roof support beams  26  may instead be comprised of a single beam  27  extending completely across the furnace  10 , or that the roof support members  26  may each be comprised of more than two roof support beams  27  arranged end-to-end. 
     The first end  28  of each roof support beam  27  is located proximate an outer edge  38  of the furnace roof  22  and may be at least partially supported on a side wall  12  or  14  of the furnace  10 . However, it will be appreciated that the roof support beams  27  are not necessarily supported on the side walls  12  or  14  of the furnace. Rather, the beams  27  may be entirely supported by other means, such as by suspension from support members located above the furnace roof  22 . 
     Each of the roof support members  26  is preferably provided with at least one interior coolant passage  40  through which a liquid coolant, such as water, is circulated in order to maintain the temperature of the support members  26  and the refractory bricks of the roof  22  within a desired range. The interior coolant passage  40  extends continuously between a coolant inlet  42  and a coolant outlet  44 . In preferred embodiments of the invention in which the roof support members  26  are comprised of a plurality of roof support beams  27 , each beam  27  is preferably provided with an internal coolant passage  40 , an inlet  42  and an outlet  44 . 
     The locations of the coolant inlets  42  and  44  in the roof support beams  27  are variable. For example, as shown in FIG. 1, the inlet  42  may be located proximate the first end  28  of the roof support beam  27 , at the edge  38  of roof  22 , and the outlet  44  is provided at the second end  30  of the roof support beam  27 . However, it may be preferred to locate both the coolant inlet  42  and the coolant outlet  44  proximate the first end  28  of the roof support member  26 , with the coolant passage  40  being U-shaped and extending from the inlet  42  to a point proximate the second end  30  of the roof support member  26 , and back to the outlet  44 . Location of the inlet  42  and outlet  44  at the edge of the furnace may be preferred as it brings the piping connections away from the top of the furnace roof. 
     As shown in FIG. 2, the spaces between adjacent roof support members  26  are filled with refractory bricks, which are generally identified herein by reference numeral  24 . The drawings, however, show three different shapes of bricks which are identified in FIG. 2 by references  24   a ,  24   b  and  24   c . The bricks  24  are arranged in rows  47  (FIG. 1) extending along the roof support members  26 , with at least one row of bricks  24  being provided between each adjacent pair of roof support members  26 . In the preferred embodiment shown in the drawings, two or three rows of refractory bricks  24  are supported between adjacent pairs of roof support members  26  (FIG.  2 ). 
     At least one of the side surfaces  36  of roof support members  26  are each provided with a support surface  50  with which a plurality of refractory bricks  24  are in direct contact and on which they are at least partially supported. Preferably, both side surfaces  36  are provided with support surfaces  50  extending along substantially the entire length of the roof support member  26 . 
     In the preferred embodiment shown in the drawings, each support surface  50  comprises a shoulder forming a transition between upper and lower portions  49  and  51  of the side surfaces  36 . In the preferred embodiment shown in the drawings, the upper and lower portions  49 ,  51  are parallel to one another and substantially flat, with the shoulder  50  extending outwardly between the upper and lower portions  49 ,  51 . Therefore, the width of the roof support member  26 , measured between the upper portions  49  of side surfaces  36 , is less than the width of the roof support member  26  measured between the lower portions  51  of the side surfaces. 
     As shown in FIG. 2, the bricks  24   a  or  24   b  which are in direct contact with the roof support members  26  each have a side surface  53  which is shaped to mate with a side surface  36  of a roof support member  26 . In the preferred embodiment shown in the drawings, the side surfaces  53  of bricks  24   a  and  24   b  each have a mating shoulder  52  which is directly supported on the shoulder  50  of a support member  26 , such that the upper portions of bricks  24   a  and  24   b  have a wider transverse cross section than the lower portions of bricks  24   a  and  24   b . As used herein with reference to bricks  24 , the term “directly supported” is intended to mean that these bricks are at least partially supported by direct contact with the supporting surfaces of the roof support members  26 . 
     Therefore, the side surfaces  53  of the bricks  24   a  and  24   b  and the side surfaces  36  of roof support members  26  are shaped such that the bricks  24   a  and  24   b which are in direct contact with the side surface  36  of the support member  26  can be removed from the space between adjacent support members  26  by raising them from above. In some preferred embodiments, each of the bricks  24  may be individually removable from above, while in others a group of bricks  24  must be simultaneously removed. However, it will be appreciated that the bricks can be removed from above without repositioning or removing the support members. In order to assist in removing the bricks  24  from above, each of the bricks  24  is preferably provided with at least one hole  70  (FIG. 4) in its upper surface through which the brick may be hooked for removal from above. The holes  70  may preferably intersect with a horizontal bore  72  (FIG. 4) so as to allow the bricks  24  to be lifted by a tool with a hooked end (not shown). 
     As mentioned above, there is at least one row of bricks  24  between adjacent roof support members  26 . In typical installations, there will be up to two rows of refractory bricks  24  between adjacent roof support members  26 . Where there is only one row of bricks  24  between adjacent roof support members, the bricks  24  will be T-shaped (not shown), having a pair of opposed side surfaces  53  provided with shoulders  52  which are supported on the shoulders  50  of the adjacent support members  26 . Where there are two rows of bricks  24   a  between adjacent roof support members, as in the right hand portion of FIG. 2, each of the rows will be in direct contact with one of the roof support members  26 . 
     In some portions of the furnace roof  22 , the cooling requirements will be less, and therefore the spacing between adjacent roof support members  26  can be increased. This is schematically illustrated in the left hand side of FIG.  2 . In regions where the spacing between adjacent roof support members  26  is relatively large, there will be at least one row of bricks  24   c  which are not in direct contact with any of the roof support members  26 . These bricks  24   c  are wedge-shaped and are provided between rows of bricks  24   b  which have side surfaces  53  provided with shoulders  52  and are directly supported by the roof support members  26 . The wedge-shaped bricks  24   c  are indirectly supported by roof support members  26 , and preferably have downwardly and inwardly converging faces  56  and will mate with downwardly and outwardly diverging rear faces  58  of bricks  24   b . As used herein with reference to bricks  24   c , the term “indirectly supported” is intended to mean that these bricks are supported by roof support members  26 , but are not in direct contact with the supporting surfaces of the roof support members  26 . It will be appreciated that all the bricks  24  shown in the drawings are removable from above the furnace roof  22 . 
     In the preferred embodiment shown in the drawings, the bricks  24  and the roof support members  26  are configured such that the upper surfaces  32  of roof support members  26  are substantially flush with the upper surface of the furnace roof  22 . This assists in maintaining the top of roof  22  clean and free from dust and debris. In another preferred embodiment, the roof support members  26  each have a height, measured between their upper and lower surfaces  32  and  34 , which is less than the thickness of the furnace roof  22  such that the lower surface  34  of each roof support member  26  is inset relative to the lower surface of the furnace roof. This forms a channel in the lower surface of the furnace roof which extends along the length of the support member  26 . This channel  60  is preferably filled by a refractory material, for example in the form of a plug of castable material, thereby protecting the lower surface  34  of roof support member  26  from direct exposure to the intense heat flux inside the furnace. It will be appreciated that the refractory material will be eroded during operation of the furnace and will be replaced by a frozen slag and/or dust accretion. 
     In order to better retain the refractory material  62  inside channel  60 , the refractory material  62  may be keyed into a dovetail-shaped slot (not shown) formed in the lower surface  34  of each roof support member  26 . 
     The furnace roof  22  in the preferred embodiment is arched across the furnace between side walls  12  and  14 . Accordingly, each of the roof support members is arcuate. In the preferred embodiment shown in the drawings, each of the roof support members  26  extends partway across the furnace  10 , and preferably extends approximately halfway across the furnace  10 . As shown in FIG. 1, the roof support members  26  are paired end-to-end with one another, such that the second ends  30  of a pair of roof support members are in close proximity to one another, and are preferably joined together, such that the paired support members  26  together extend across the entire width of the furnace  10 . 
     The roof support members are supported from above the furnace by a plurality of elevated support members which, in the preferred embodiment shown in the drawings, comprise horizontal girders  20 . As mentioned above, the girders  20  extend across the width of furnace  10  and above the roof  22  and the roof support members  26 . Preferably, each of the roof support members  26  is supported at one or more points along its length from one of the girders  20 . More preferably, the roof support members  26  and the girders  20  are parallel to one another, and each of the roof support members  26  is supported at two or more points along its length from a girder  20 . As shown in the drawings, the roof support members are supported from the girders  20  by hangers  68 , which preferably are comprised of metal rods. 
     Although the roof support members  26  are shown in the preferred embodiment as being hung from girders  20 , it will be appreciated that a number of alternate arrangements for supporting the roof support members exist, and that such alternate arrangements may be preferred in some embodiments of the invention. For example, other types of elevated support members could be used, such as support members which extend perpendicular to the roof support members  26 . 
     Although the invention has been described in connection with certain preferred embodiments, it is not limited thereto. Rather, the invention includes all embodiments which may fall within the scope of the following claims.