Abstract:
Glass melting furnace comprised by several sections which are built entirely with refractory concrete of diverse refractory materials according to operation conditions, chemical environment, temperature, and mechanical load to which its several sections are exposed, as well as to the material thickness required, to assure an structural integrity and durability similar to the ones of furnaces of conventional design as well as a lower investment cost.

Description:
Cross-reference to Related Applications: 
     This Application is a National Phase of PCT/MX2007/000121, filed 17 Oct. 2007. 
     BACKGROUND 
     A. Field of the Invention 
     This invention is related to glass melting furnaces and more specifically to glass melting furnaces for the manufacture of glass containers or flat glass, entirely built with refractory concrete. 
     B. Description of the Related Art 
     The conventional design of furnaces for the glass production includes the use of masonry, that is to say, the use of bricks and blocks assembled using mortar and/or cement to build each one of the sections that constitute the unit. These refractory materials are chosen in order to attain an useful life of at least 12 years before requiring a total reconstruction. 
     The repairing of conventional furnaces used to produce glass, has been traditionally developed, by replacing the damaged or worn-out sections, using new bricks or blocks, incorporating them to the furnace&#39;s sections using mortar and/or cement. 
     However, when refractory concretes appeared, the repairing of furnace&#39;s sections was simplified because now it is only needed to remove the refractory bricks or blocks from the affected areas and to fill in these areas directly with refractory cement, being not required to place refractory bricks. 
     Examples of refractory cements for glass melting furnaces, are described in the U.S. Pat. No. 7,176,153 of Anderson, for an alumina, zirconium and silica refractory system that, as it is set forth in the said patent, can be used to produce blocks or can be used directly in a worn-out portion of the furnace; U.S. Pat. No. 6,313,057 of Brown et al, for a melted silica refractory material made up of granulated quartz, that contains a calcium oxide binder; U.S. Pat. No. 6,158,248 of Beppu, for a melted cast refractory of alumina, zirconium and silica; U.S. Pat. No. 6,554,058 among others. 
     Nevertheless, all these refractory cements have been used only to manufacture blocks and for repairing worn-out areas of furnace&#39;s sections. 
     This invention considers the design of a furnace with sections entirely built with refractory concretes that are total and hermetically joined forming a monolithic furnace. The achieved benefits hereof are the following: higher airtightness that improves the thermal efficiency, thus saving fuel; more durability of critical areas due to a reduction in the chemical erosion and corrosion, as a result of the absence of joints among the structural components. It is possible to achieve an important reduction in construction time due to the design of large elements, because the sections are directly shaped at the construction site, likewise, an important reduction is achieved in the warm-up and the operation startup time. 
     OBJECTIVES OF THE INVENTION 
     Thus, one main objective of this invention is to provide a glass melting furnace, entirely built with refractory concrete. 
     It is an additional objective of this invention is to provide a glass melting furnace, of the above described characteristics, with better airtightness that improves its thermal efficiency resulting in a fuel saving. 
     It is a further main objective of this invention, to provide a glass melting furnace, with the above described characteristics that has a longer durability of its critical areas, due to the reduction of chemical erosion and corrosion, as a result of the lack of joints among the structural components. 
     It is jet an additional objective of this invention, to provide a glass melting furnace, with the above described characteristics, with which because of the design of large elements, it is possible to achieve an important reduction in its construction time, as well as in its warm-up time at the operation startup stage. 
     These and other objectives and advantages of the glass melting furnace, built with refractory concrete, of this invention, can be viewed by the experts in the area in the following detailed description of the preferred embodiments of the invention, which will be within the scope of the invention claimed. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1 , is a cross section view of a side elevation a glass melting furnace for the manufacturing of containers, schematized, showing its several sections made up of several materials according to its coding, according to this invention; 
         FIG. 2 , is an upper plant cross section view of the furnace in  FIG. 1 , showing several sections made up of several materials according to its coding; 
         FIG. 3 , is a conventional perspective view of the regeneration section, showing its regenerating chambers with its side, front and rear walls and vaults. 
         FIG. 4 , is a conventional perspective view of the throat connecting the regeneration section with the melting section. 
         FIG. 5 , is a conventional perspective view showing the melting section of the monolithic furnace of this invention; 
         FIG. 6 , is a detailed, enlarged cross section of a side elevation view, of the refining section of  FIG. 1 ; and, 
         FIG. 7 , is a diagram of the codes of the materials that form part of the furnace. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The glass melting furnace of this invention will be described below making reference to the specific embodiments of the same and to the drawings enclosed as figures, where the same signs refer to the same parts of the shown figures. 
     A typical glass melting furnace, known as Regenerative Furnace with “End Port” includes sections that have specific functions such as: one melting section SF, one refining section SR and one regeneration section SRG ( FIGS. 1 and 2 ), each of which, according to this invention, is built entirely with refractory concrete made of specific materials and features and they will be described in detail below in the sequence in which this type of furnace is built. 
     Regarding to the type of materials used to build the furnace to be described in the following, it is important to state that the calculated thickness according to the design is such that the useful life of the operative unit is the same as the one of a conventional furnace, that is, at least 12 years of useful life until its next repairing, during this period of useful life minor maintenance services in warm conditions are considered to preserve the unit, as it is a common practice in current glass furnaces. 
     Regeneration Section: 
     Regenerative Chambers. 
     The regenerative chambers CRG 1  and CRG 2  ( FIGS. 2 and 3 ) of the furnace H are subject to thermal changes due to the burn cycle from one side to another of the furnace H, also, they are subject to differential temperatures from the combustion gas exhaust  1  of the melting section SF of approximately 1550° C. to the base  2  of the regenerative chambers CRG 1  and CRG 2  from about 400 to 500° C., therefore materials that remain stable under this operation conditions were chosen. 
     Also, due to the changing condition of combustion air intake (21% O2) and gases exhaust (4-5% O2) they are exposed to oxidation-reduction changes of state, at the same time that they present the above mentioned thermal gradient. 
     The following alumina-silica refractory materials were chosen to build the regenerative chambers CRL 1  and CRL 2 , which, because of their amphoteric characteristic, are able to resist the acid environments which are present due to the combustion and basic gases of the materials of the side and central walls of the regenerators.
         The lower area, side walls  3   a  and  3   b , front wall  4   a , rear wall  5   a  and central wall  6   a  ( FIG. 3 ) which are exposed to temperatures from about 400 to 800° C., are built with alumino-silicate refractory concrete.   The middle area, side walls  3   c  and  3   d , front wall  4   b , rear wall  5   b  and central wall  6   b  ( FIG. 3 ), which are exposed to temperatures from about 800 to 1100° C., are built with high alumina and low calcium oxide refractory concrete.   The upper area, side walls  3   e  and  3   f , front wall  4   c , rear wall  5   c  and central wall  6   c  ( FIG. 3 ), which are exposed to operation temperatures from about 1100 to 1500° C., are built with high alumina and low calcium oxide refractory concrete.   Finally, the vault  7  and overvault  8  that seals the regenerative chambers CRG ( FIG. 3 ), are built with high silica and low calcium oxide silicon refractory concrete.       

     These refractory materials offer high resistance to pressure under burning conditions and high resistance to sudden temperature changes due to changes in burning cycles. Also, at work temperatures they have a high chemical resistance to condensable gases and steams, such as the sodium sulphate. 
     Ports: 
     In order to build ports  10   a  and  10   b  that connect regenerative chambers CRG 1  and CRL 2  ( FIGS. 2 and 4 ) to the melting section SF, a high alumina (&gt;99.0%) and low calcium oxide (&lt;0.2%) refractory was considered, the chemical stability of the alpha alumina used, prevents the reactivity with other materials, also, the presence of low calcium oxide content prevents the reactivity with other compounds such as heavy metals from fossil fuels, making a high chemical resistance monolithic refractory. In addition, the thermal stability provided by the low expansion coefficient, allows an excellent behavior as a joining piece between the melting section and the regenerative chambers CRG 1  and CRG 2  due to the change of thermal cycles during the furnace operation, therefore:
         each of the ports  10   a  and  10   b , their side walls  11   a  and  11   b,  vault  12  and floor  13  ( FIG. 4 ) are built in a monolithic form with high alumina refractory concrete.
 
Melting Section:
 
Refractory in Contact with Glass:
       

     The refractory materials in contact with glass are of the zirconium-alumina-silica type, which include zirconium oxide in their chemical composition because, due to the presence of the same, it provides to the the products a higher resistance to corrosion, abrasion and compression. For this reason, the materials that are in contact with glass in the furnace H ( FIGS. 1 ,  2  and  5 ) of this invention, include the use of refractory concrete to form monolithic pieces with zirconium-alumina-silica refractory material with 20-24% of zirconium oxide content, as it is set forth in U.S. Pat. No. 4,053,321, therefore: 
     Floor: 
     
         
         
           
             The lower layer  20  of floor P of the melting section SF ( FIG. 5 ) is built with alumino-silicate refractory concrete; 
             The middle layer  21  of floor P ( FIG. 5 ) is built with high alumina refractory concrete; and 
             The upper layer  22  of floor P ( FIG. 5 ) is built with zirconium-alumina-silica refractory concrete. This last layer is the one that is in contact with the glass.
 
Cup:
 
             The cup  23  of melting section SF ( FIG. 5 ), including both side chargers  24   a  and  24   b , are built with zirconium-alumina-silica refractory concrete.
 
Superstructure:
 
           
         
       
    
     The superstructure SS of the furnace H, that comprises the overcup  25 , front wall  26 , rear wall  27  and side walls  28   a  and  28   b  of furnace H ( FIG. 5 ), requires high temperature resistant materials, because they are exposed to flames, and that provide resistance to combustion gases and gas and volatile compounds environment which come from glass manufacturing, such as the raw material dragging “carry over”, sodium oxide, sodium hydroxide, etc. That is why when choosing the materials to form the superstructure SE, high alumina refractory materials were used, which provide a high fusion point and chemical resistance to the corrosion of the alkaline environment of the glass and to the acid environment of the combustion gases because of its neutral feature. Also, more specifically, due to its low calcium oxide concentration in its structure, the possibility of forming liquid phases is reduced, avoiding any dripping problem and generation of defects in the melted glass, therefore:
         The overcup  25 , front wall  26 , rear wall  27  and side walls  28   a  and  28   b  of the melting section SF ( FIG. 5 ), are built with high alumina and low calcium oxide refractory concrete.
 
Vault:
       

     The vault  29  is the structural element of the melting section SF ( FIG. 5 ) that closes the upper space of the glass melting furnace H and this design considers refractory concretes with high SiO2 (&gt;99%) and low calcium oxide (&lt;0.2%) concentrations different from the common refractory which uses from 2.5 to 3.5% CaO. The manufacture in only one piece of the vault  29  prevents all kind of union joints among blocks and permits a better airtightness with the furnace walls, significantly reducing the appearance of joints and cracks. This condition together with the high SiO2 content and low CaO concentration reduces the potential reactivity between the volatile phases of alkalis of furnace H and the silica, preventing the reactivity between these compounds. On the other hand, it reduces the potential generation of corrosion points among joints because of the lack of heat and steam leaks that prevent the formation of liquid phases which form the “rat holes”. 
     Also, the sealing of the vault  29 , called overvault  30  installed once the heating process of the Furnace H has finished ( FIG. 5 ), eliminates any crack or leak of heat left in the vault during the heating of the same, maintaining the airthickness of the system, therefore:
         The vault  29  and sealing overvault  30  ( FIG. 5 ) are built with silicon refractory concrete with high silica and low calcium oxide contents;
 
Throat:
   The Throat  31  ( FIGS. 1 and 2 ) is built with zirconium-alumina-silica refractory concrete.
 
Refining Section:
   The base  40  of the refiner cup floor RC is built with alumina-silicate refractory concrete; and   The upper body  41  of the refiner cup RC and the upper layer  42  in contact with the glass, are built with zirconium-alumina-silica refractory concrete.       

     The chosen group of refractory concretes permits the construction of a monolithic glass furnace reducing its construction time compared against common furnaces made up of preformed blocks, as well as a low manufacture cost due to the low cost of the materials used while the design and calculation of the thickness of the involved materials provides an equal or longer useful life than the one of conventional furnaces, that is at least 12 years, it can also be mentioned that an additional advantage is the considerable reduction of time spent repairing the unit after the useful life of the furnace, since there is a fixed base of the previous furnace, thus allowing important savings in materials and time reduction to restart the unit&#39;s operation. 
     This development considers the design of monolithic pieces (see table of parts) to form the glass furnace, and the calculation of the thickness of the materials of each part to keep the useful life of the glass furnace the same as a conventional furnace. 
     Preferred Sample of Embodiment with Materials and Thicknesses Used in a 220-Ton/Day Furnace Regeneration Section. 
     Regenerative Chambers: 
     
         
         
           
             In the lower area, the side walls  3   a  and  3   b , front wall  4   a  and rear wall  5   a  were built with alumina-silicate refractory concrete which contains 36-38% alumina with a thickness of 28.5″ in the lower part and 24″ in the upper part, and central wall  6   a  with a thickness of 33″ in the lower part and 24″ in the upper part respectively, that are exposed to a temperature of around 400 to 800° C. 
             In the middle area, the side walls  3   c  and  3   d , front wall  4   b , rear wall  5   b  and central wall  6   b , that are exposed to temperatures of around 800 to 1100° C., were built with high alumina refractory concrete with Al 2 O 3  content with a thickness of 24″. 
             In the upper area, the side walls  3   e  and  3   f , front wall  4   c , rear wall  5   c  and central wall  6   c , that are exposed to temperatures of around 1100 to 1500° C., were built with high alumina refractory concrete with a 85 to 91% content of Al 2 O 3 , with a thickness of 24″. 
             Vault  7  and Sealing Overvault  8 , were built with silicon refractory concrete with high silica and low calcium oxide content, with a thickness of 13.5″ in the vault  7  and a thickness of 2″ in the sealing overvault.
 
Ports:
 
             Each of the ports  10   a  and  10   b  were built in a monolithic form with high alumina refractory concrete with Al 2 O 3  contents of 85 to 91%, with side walls  11   a  and  11   b  with a thickness of 9″, with a vault  12  thickness of 12″, and a floor  13  with a variable thickness of 9″ next to chambers and 4.5″ in the nose of the floor of the port.
 
Melting Section.
 
Refractory in Contact with Glass:
 
Floor:
 
             The lower layer  20  of floor P was built with alumino-silicate refractory concrete with a 47-52.5% alumina content with a thickness of 18″; 
             The middle layer  21  of floor P was built with high alumina refractory concrete with a 85-91% Al 2 O 3  content with a thickness of 8″; and 
             The upper layer  22  of floor P was built with zirconium-alumina-silica refractory concrete with a 20-24% zirconium oxide content with a thickness of 6″.
 
Cup:
 
             The cup  23  was built with zirconium-alumina-silica refractory concrete with a 20-24% zirconium oxide content with a thickness of 18″ including both chargers.
 
Superstructure:
 
             The overcup  25 , its front wall  26 , rear wall  27  and side walls  28   a  and  28   b  were built with high alumina refractory concrete with a 85-91% Al 2 O 3  content and low calcium content, with an overcup thickness of 8″ and side walls  28   a  and  28   b , front wall  26  and rear wall  27  with a thickness of  12 ″.
 
Vault:
 
             The vault  29  and sealing overvault  30  were built with silicon refractory concrete with high silica content and low calcium oxide content. with a thickness of 13.5″ in the vault in the vault  29 , and a thickness of 2″ in the sealing overvault.
 
Throat:
 
             The throat  31  was built with zirconium-alumina-silica refractory concrete with a 20-24% zirconium oxide content.
 
Refining Section.
 
             The Base  40  of the cup floor was built with alumino-silicate refractory concrete with a 47-52.5% alumina content and with a thickness of 7.5″. 
             The upper body  41  of the cup and the upper layer  42  in contact with glass, were built with zirconium-alumina-silica refractory concrete with a 20-24% zirconium oxide content with a thickness of 10″ in the upper body  41  and with a thickness of 6″ in the upper layer  42  in contact with glass. 
           
         
       
    
     All of the above is in the understanding that the aforesaid description of the invention, is only provided in order to show the specific embodiments of the same and the better way to develop it as of the time when this application for patent is filed and the invention will not be limited to these, but its scope must be considered regarding the enclosed claims.