Patent Publication Number: US-9429316-B2

Title: Burner arrangement and burner assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a national stage application filed under 35 USC 371 based on International Application No. PCT/FI2011/050502 filed May 31, 2011. 
     The invention relates to a burner arrangement comprising a fluid cooled copper block. Further, the invention relates to a burner assembly, a duct element, a gas circulating duct, and a metallurgical furnace comprising the burner arrangement according to the invention. 
     A burner is a device to generate a flame to heat up material by combustion of gaseous, liquid or pulverous fuel. 
     In metallurgical processes burners are used in several different applications, e.g. in gas circulating ducts to provide additional heat to circulating process gas (e.g. US 2009/017409), and in electric arc furnaces as auxiliary heaters to heat and melt metal (e.g. U.S. Pat. No. 6,614,831). 
     A typical burner arrangement comprises a burner for providing a flame, and an elongated burner channel in close proximity to the burner. The burner channel is configured to form a combustion space and to guide the flame. 
     US2009/017409 relates to equipment wherein the burner unit is attached directly to the wall of a gas channel and an opening in the refractory wall of the gas channel forms the burner channel. 
     A problem with this burner arrangement is that the attachment of the burner unit may loosen because the refractory material forming the burner channel tends to deteriorate by cracking due to thermal stresses and/or erosion. Further, erosion of the burner channel weakens its ability to guide the flame into a predetermined direction and to protect the burner unit. It has been tried to solve this problem by providing a cooling coil inside the refractory material defining/forming the burner channel. This arrangement has improved the durability of the burner channel. However, in some installations this is not sufficient. The deterioration of the refractory material of the burner channel may result in damaging the cooling coil which in turn may cause leaking of cooling fluid. Water is usually used as cooling fluid, and leaking of water may cause water-gas explosion inside the furnace. The erosion of the burner channel also weakens its ability to guide the flame into a predetermined direction and to protect the burner unit. 
     US2009/017409 further relates to a burner unit including a supporting structure that can be fitted as part of the wall of the gas channel. The maintenance of the deteriorated supporting structure requires that the sintering process is interrupted to be able to replace the damaged supporting structure which is a relatively large and heavy part of the gas channel. This causes a relatively long downtime. 
     U.S. Pat. No. 6,614,831 relates to a burner arrangement for the use in melting furnaces. The burner unit is installed in a fluid-cooled mounting block. The arrangement does not include a burner channel in close proximity to the burner unit and, therefore, the burner unit might get damaged due to blow-back of the flame. Blow-back of the flame to the burner unit may occur if the burner unit is fired at high rates against large pieces of metal scrap that is to be melted in the furnace. 
     It is an object of the invention to overcome the disadvantages of the prior art as outlined above. 
     A first aspect of the invention relates to a burner arrangement comprising a burner unit for providing a flame, and an elongated burner channel in close proximity to the burner unit, the burner channel forming a combustion space being configured to protect the flame and the burner unit. According to the invention the burner arrangement comprises a fluid cooled copper block, preferably a water cooled copper block, including a cooling conduit for circulation of the cooling fluid, preferably water, a first end to which the burner unit is releasably attached, and a second end, and the burner channel extends inside the fluid cooled copper block from the first end to the second end. 
     A second aspect of the invention relates to a burner assembly comprising the burner arrangement according to the invention and a refractory structure which is made of castable refractory material and to which the burner arrangement is connected, preferably releasably connected. 
     In one embodiment, the burner assembly comprises
         a burner arrangement according to the invention including a burner unit for providing a flame, and an elongated burner channel in close proximity to the burner unit, said burner channel forming a combustion space being configured to protect the flame and the burner unit, and   a refractory structure which is made of castable refractory material and to which the burner arrangement is connected,
 
characterised in that the burner arrangement comprises a fluid cooled copper block including a cooling conduit for circulation of the cooling fluid, a first end to which the burner is releasably attached, and a second end, and that the burner channel extends inside the fluid cooled copper block from the first end to the second end.
       

     In one embodiment of the burner arrangement and burner assembly, the diameter of the burner channel increases in the direction to the second end. For example, if the burner arrangement is installed in a gas duct of a strand sintering furnace or steel belt sintering furnace, as the diameter of the burner channel increases in the direction to the gas circulating duct the diameter of the burner channel decreases in the direction to the burner unit. This provides protection of the burner flame from the gas flowing in the duct. 
     In one embodiment of the burner arrangement and burner assembly, the cross section of the burner channel is circular. 
     In one embodiment of the burner arrangement and burner assembly, the cooling conduit has an inlet for introducing the cooling fluid to the cooling conduit, and an outlet for exiting of the cooling fluid from the cooling conduit, said inlet and outlet are located at the outer periphery of the copper block adjacent to the first end, and a coil section extending between the inlet and the outlet, said coil section being arranged to surround the burner channel. 
     In one embodiment of the burner arrangement and burner assembly, the burner unit comprises a connecting flange to attach the burner unit to the first end of the fluid cooled copper block through a bolted joint. 
     In one embodiment of the burner arrangement and burner assembly, the burner arrangement comprises a tubular mounting sleeve, which is preferably made of metal such as steel or mild steel, wherein the tubular mounting sleeve comprises anchor elements on the outer surface of the tubular mounting sleeve for anchoring the tubular mounting sleeve in a castable refractory material, and that the tubular mounting sleeve is adapted to receive the fluid cooled copper block inside the tubular mounting sleeve. 
     In one embodiment of the burner arrangement and burner assembly, the outer surface of the fluid cooled copper block is slightly conical because the outer surface of the copper block converges in the direction to the second end, i.e. its outer diameter decreases in the direction to the second end. In one embodiment of the burner arrangement and burner assembly, the inner surface of the tubular mounting sleeve has a conical shape corresponding to the shape of the outer surface of the copper block. 
     In one embodiment of the burner arrangement and burner assembly, the burner arrangement further comprises a ring-like connecting element for attaching the fluid cooled copper block to the tubular mounting sleeve. 
     In one embodiment of the burner arrangement and burner assembly, the ring-like connecting element comprises a first flange to attach the ring-like connecting element to the first end of the copper block through a bolted joint and a second flange to attach the ring-like connecting element to the mounting sleeve through a bolted joint. 
     In one embodiment of the burner assembly, the burner assembly comprises a tubular mounting sleeve which is preferably made of metal such as steel or mild steel provided with anchor elements on the outer surface of the tubular mounting sleeve for anchoring the mounting sleeve to the castable refractory structure, and the tubular mounting sleeve is adapted to receive the fluid cooled copper block inside the tubular mounting sleeve. 
     In one embodiment of the burner assembly, the burner arrangement further comprises a ring-like connecting element for attaching the fluid cooled copper block to the tubular mounting sleeve. 
     In one embodiment of the burner assembly, the refractory structure is a part of a channel wall of a gas duct, such as a wall of a gas circulating duct of a strand sintering furnace or steel belt sintering furnace. 
     In one embodiment of the burner assembly, the refractory structure is a refractory wall, or part of a refractory wall, of a metallurgical furnace, such as an electric arc furnace. 
     A third aspect of the invention relates to a duct element. The duct element according to the invention comprises a burner assembly according to the invention, wherein the refractory structure is a refractory block having a wall made of refractory material, preferably castable refractory material, said wall including a mounting sleeve for the burner arrangement, and complementary sector element which is releasably attached to the refractory block to form a tubular or ring-like structure together with the refractory block. 
     In one embodiment of the duct element, the refractory block comprises first connecting means for connecting the refractory block to the complementary sector element and second connecting means for connecting the refractory block to adjacent elements of a duct. 
     In one embodiment of the duct element, the complementary sector element comprises third connecting means for connecting the complementary sector element to the first connecting means of the refractory block, and fourth connecting means for connecting the complementary sector element to adjacent elements of the gas circulating duct. 
     In one embodiment of the duct element, the first connecting means, the second connecting means, third connecting means and/or the fourth connecting means comprise flanges provided with bolt holes to attach the refractory block and the complementary sector element to each other and to the adjacent elements of the duct through bolted joints. 
     A fourth aspect of the invention relates to a gas circulating duct, preferably a gas circulating duct of a strand sintering furnace, preferably a steel belt sintering furnace, comprising a burner arrangement according to the invention, a burner assembly according to the invention, or a duct element according to the invention. 
     A fifth aspect of the invention relates to a metallurgical furnace comprising a burner arrangement according to the invention, a burner assembly according to the invention, a duct element according to the invention, or a gas circulating duct according to the invention. In case that the metallurgical furnace is a strand sintering furnace or a steel belt sintering furnace, it may contain a burner arrangement, a burner assembly, a duct element or a gas circulating duct. In case that the metallurgical furnace is a melting furnace, such as an electric arc furnace, it may contain a burner arrangement or a burner assembly, but it preferably does not contain a duct element or a gas circulating duct. 
     Another embodiment of the invention relates to a metallurgical furnace comprising the burner arrangement in the burner assembly according to the invention. 
     A sixth aspect of the invention relates to a method for maintenance of the burner arrangement. The method comprises a step of detaching the burner unit from the fluid cooled copper block. 
     Another embodiment of the invention relates to a method for maintenance of a burner arrangement in a burner assembly according to the invention. The method comprises steps of removing the burner arrangement by pulling the fluid cooled copper block out from the mounting sleeve, and installing a new burner arrangement by inserting the fluid cooled copper block into the mounting sleeve. 
     Another embodiment of the invention relates to a method for maintenance of a gas circulating duct according to the invention to replace the burner unit. The method comprises the steps
         a) detaching the refractory block from the complementary sector element and from the gas circulating duct, wherein the burner arrangement is attached to said refractory block, and   b) detaching the burner unit to be replaced from the fluid cooled copper block which is still attached to the refractory block, and attaching a new burner unit to the cooled copper block, or   c) detaching the burner arrangement in which the burner unit and the fluid cooled copper block are connected to each other from the fluid cooled copper block, and detaching the burner unit from the fluid cooled copper block, and attaching a new burner unit to the cooled copper block, and   d) attaching the refractory block having the burner arrangement attached therein to the complementary sector element and to the gas circulating duct.       

     Another embodiment of the invention relates to a method for maintenance of a gas circulating duct according to the invention to replace the refractory block. The method comprises the steps
         e) detaching the refractory block to be replaced from the complementary sector element and from the gas circulating duct, wherein the burner arrangement is attached to said refractory block,   f) detaching the burner arrangement from the refractory block to be replaced, and attaching the burner arrangement to a new refractory block, and   g) attaching the refractory block to the complementary sector element and to the gas circulating duct, wherein the burner arrangement is attached to the refractory block.       

     Another embodiment of the invention relates to a method for maintenance of a gas circulating duct according to the invention to replace the complementary sector element. The method comprises steps
         h) detaching the refractory block having the burner arrangement attached therein from the complementary sector element and from the gas circulating duct,   i) detaching the complementary sector element to be replaced from the gas circulating duct,   j) attaching a new complementary sector element to the gas circulating duct, and   k) attaching the refractory block having the burner arrangement attached therein to the complementary sector element and to the gas circulating duct.       

     The invention provides many advantages. If the refractory around the burner opening is deteriorating, e.g. due to erosion or thermal stress, the fluid cooled copper block would not be damaged and optimal flow of the flame would be ensured. Thereby, the performance of the burner unit is ensured. The fluid cooled copper block is removable and, thus, there is no need to remove parts or a large block of the surrounding refractory material for maintenance. This will reduce maintenance downtime. A more uniform temperature profile is achieved in the refractory material as compared to having steel coils inside the refractory material because the fluid cooled copper block is surrounded by a tubular mounting sleeve. Further, damage to the cooling conduit is less likely to occur because the cooling conduit is located inside the fluid cooled copper block and the copper is surrounded by a metal sleeve, preferably a steel sleeve or mild-steel sleeve, hence, protecting the cooling conduit. The burner unit is located at the first end of the fluid cooled copper block, so that the burner flame is not interfered with by gas travelling in the gas duct. In case the burner arrangement is installed in the side wall of a melting furnace, the fluid cooled copper block with the burner channel protects the burner unit from flame blow-back. Further, replacement of the burner unit and/or the fluid cooled copper block is facilitated. 
     For the purpose of this description, the terms “refractory material” and “castable refractory material” stand preferably for refractory cement or refractory cement castable such as alumina low cement castable, more preferably alumina low cement castable comprising steel fibres or low cement alumina silica castable comprising steel fibres. 
    
    
     
       The accompanying drawings, which are included to provide a better understanding of the invention constitute part of the description, illustrate preferred embodiments of the invention and help to explain the principles of the invention. 
         FIG. 1  shows one embodiment of a gas burner arrangement according to one embodiment of the invention, with the fluid cooled copper block shown in cross section, 
         FIG. 2  is an axonometric exploded view of the burner arrangement of  FIG. 1  containing the ring-like connecting element, 
         FIG. 3  is an axonometric transparent view of the copper block of  FIG. 2 , showing the spatial arrangement of the cooling conduit with respect to the burner channel, 
         FIG. 4  is an exploded view of the burner assembly according to one embodiment of the invention, wherein the refractory structure and the tubular mounting sleeve are shown in cross section, 
         FIG. 5  shows the burner assembly of  FIG. 4  wherein the burner arrangement is installed into the tubular mounting sleeve, 
         FIG. 6  is a schematic illustration of a strand sintering furnace, preferably a steel belt sintering furnace, which comprises gas circulating ducts, 
         FIG. 7  shows one gas circulating duct including the burner assembly according to one embodiment of the invention, 
         FIG. 8  is an exploded view of a corner section of the gas circulating duct of  FIG. 7 , the corner section including a refractory block for installation of the burner arrangement, 
         FIG. 9  shows a cross section of the corner section of  FIG. 8 , and 
         FIG. 10  is a schematic illustration of an electric arc furnace including a burner assembly according to the invention. 
     
    
    
     Referring to  FIGS. 1 to 3 , the burner arrangement comprises a burner unit  1  to mix fuel and oxidiser, such as air, to a mixture which is ignited to provide a flame. The burner arrangement comprises an elongated burner channel  2  which is in close proximity to the burner unit  1 . The burner channel  2  forms a combustion space and is configured to protect the flame and the burner unit  1 . The burner arrangement comprises a fluid cooled copper block  3 . The burner unit  1  is releasably attached to the first end  5  of the fluid cooled copper block  3  to facilitate installation and replacement. The fluid cooled copper block  3  contains a cooling conduit  4  through which a continuous circulation of the cooling fluid, preferably water, can be conveyed to cool the fluid cooled copper block  3 . The cooling conduit  4  is inside the casted copper of the copper block  3 . The burner channel  2  which is a through-hole extends inside the fluid cooled copper block  3  from the first end  5  to the second end  6 . The first end  5  and the second end  6  are parallel. The burner channel  2  forms a combustion space which guides the flame and protects the burner unit  1 . 
     As shown in  FIG. 1 , diameter d of the burner channel  2  increases from the first end  5  in the direction to the second end  6 . The inner surface of the burner channel  2  comprises a short surface part  34  adjacent to the first end  5 , the diameter of the short surface part  34  increasing in the direction of the first end  5 . The short conical surface part  34  continues towards the second end  6  as a round dome surface part  35 . The round dome surface part  35  continues to the second end  6  as a conical surface part  36 . The cross section of the burner channel  2  is circular. Hence, the cross sections of the cylindrical surface part  34 , the round dome surface part  35  and the conical surface part  36  are circular. 
     Referring to  FIG. 3 , the cooling conduit  4  has an inlet  7  for introducing the cooling fluid to the cooling conduit  4 . The cooling conduit  4  has an outlet  8  for exiting of the cooling fluid from the cooling conduit  4 . The inlet  7  and outlet  8  both protrude from the outer periphery of the fluid cooled copper block  3  and are located adjacent to the first end  5 . A coil section  9  extends between the inlet  7  and the outlet  8 . The coil section  9  is spatially arranged to surround the burner channel  2 . 
     Referring to  FIGS. 1 and 2 , the burner unit  1  comprises a connecting flange  10  to attach the burner unit  1  to the first end  5  of the fluid cooled copper block  3  through a bolted joint. 
     With reference to  FIGS. 3 and 5  the burner arrangement comprises a tubular mounting sleeve  11  which is preferably made of metal such as steel or mild steel. The tubular mounting sleeve  11  comprises anchor elements  12  on the outer surface of the mounting sleeve  11  for anchoring the mounting sleeve to a castable refractory material. The tubular mounting sleeve  11  is dimensioned to receive the fluid cooled copper block  3  inside its inner space. The outer surface of the fluid cooled copper block  3  is slightly conical so that its outer surface converges in the direction to the second end  6 ; i.e. its diameter decreases in the direction to the second end  6 . The inner surface of the tubular mounting sleeve  11  has a conical shape which is complementary to the outer shape of the fluid cooled copper block  3  so that the fluid cooled copper block  3  fits sufficiently tightly inside the tubular mounting sleeve  11  and can easily be removed. 
     Referring to  FIGS. 2 to 5 , the burner arrangement further comprises a ring-like connecting element  13  for attaching the fluid cooled copper block  3  to the tubular mounting sleeve  11 . The ring-like connecting element  13  comprises a first flange  14  to attach the ring-like connecting element to the first end  5  of the copper block  3  through a bolted joint, and a second flange  15  to attach the ring-like connecting element to the mounting sleeve  11  through a bolted joint. 
     Referring to  FIG. 4 , for maintenance of the burner arrangement B, after the bolted joint between the tubular mounting sleeve  11  and the ring-like connection element  13  has been released, the burner arrangement B can be removed by simply pulling the fluid cooled copper block  3  out from the mounting sleeve  11 . A new burner arrangement B can then be installed by inserting the fluid cooled copper block  3  into the tubular mounting sleeve  11  and attaching the ring-like connection element  13  to the mounting sleeve  11  through a bolted joint. 
     Referring to  FIGS. 6 to 9 , there is shown one embodiment of the burner assembly according to the invention in a gas circulating duct  18   a ,  18   b  of the strand sintering furnace  19 , preferably a steel belt sintering furnace  19 , of  FIG. 6 . The strand sintering furnace or steel belt sintering furnace  19  comprises a strand  22  or steel belt  22 , which turns around cylinders  23 ,  24  (e.g. elevating wheels) that are at its ends, to form an endless conveyor belt. The sintering furnace  19  comprises gas circulating ducts  18   a ,  18   b ,  18   c , where the gas circulates within the different zones of the sintering furnace. Closed gas cycles are applied in continuous sintering, and the circulating gas is exploited in the various zones of the process. The material to be sintered is supplied to the strand  22  or steel belt  22  to form a bed on its upper surface. In the furnace, the material to be sintered first travels through a drying zone  25  and a pre-heating zone  26 , moving then to a sintering zone  27  that has one or several sections. After the sintering zone  27 , the equipment usually comprises a stabilising zone  28 , after which there is a cooling zone containing several stages  29 ,  30  and  31 . Gas is introduced to the sintering equipment, first, to the various stages  29 ,  30 ,  31  of the cooling zone. The arrows shown in  FIG. 6  indicate the direction of the gas flow in the gas circulating ducts  18   a ,  18   b  and  18   c . After the gas has travelled through the strand  22  or steel belt  22  and the bed of material to be sintered, which is on the upper surface of the same, the gas is sucked from each of the stages  29 ,  30  and  31  into the respective gas circulating duct  18   a ,  18   b ,  18   c . The gas that is to be removed from the outermost gas channel  18   c  (as viewed in the flow direction of the material to be sintered) is directed to the drying zone  25 , and this gas circulating duct  18   c  is generally not provided with burner units. Instead, the gas from the cooling stages  29  and  30  located nearer to the middle part of the strand sintering furnace  19  or steel belt sintering furnace  19  is directed to the gas circulating ducts  18   a  and  18   b , which are provided with burner units  1 . The inner part of the gas circulating ducts  18   a ,  18   b  is made of castable refractory material. The sintered material is removed from the strand  22  or steel belt  22  for further processing. The gases are removed from the sintering zone  27 , pre-heating zone  26  and drying zone  25  to gas cleaning and possibly recycled back to the sintering process. 
       FIG. 7  shows a gas circulating duct  18   a  of  FIG. 6  equipped with two burner arrangements B of  FIGS. 1 to 3  which are installed in a refractory block  16  according to the principles as already depicted with reference to  FIGS. 4 and 5 . 
     The refractory block  16  forms a part of the duct wall  17  of the gas circulating duct  18   a . The arrows show the direction of the gas flow. The burner arrangements B are arranged so that the burner channels  2  of the fluid cooled copper block  3  direct the flame F substantially to the direction of the gas flow in the gas circulating duct  18   a . Due to the angled arrangement of the burner arrangements B the burner unit  1  and burner channel  2  are well protected from the influences of the gas flow.  FIGS. 8 and 9  show a duct element  32  of  FIG. 7 . The duct element  32  comprises a refractory block  16  having a wall made of refractory material  37 . The refractory wall  37  of the refractory block  16  includes a tubular mounting sleeve  11  for attaching the burner arrangement B to the refractory block  16 . The tubular mounting sleeve  11  comprises anchor elements  12  on the outer surface of the mounting sleeve  11  for anchoring the mounting sleeve to a castable refractory material of the refractory block  16 . The duct element  32  further comprises a complementary sector element  33  having a wall made of refractory material  38 . The complementary sector element  33  when attached to the refractory block  16  forms a tubular or ring-like structure together with the refractory block  16 . 
     The refractory block  16  comprises first connecting means  39  for connecting the refractory block  16  to the complementary sector element  33  and second connecting means  40  for connecting the refractory block  16  to adjacent elements of the gas circulating duct  18   a ,  18   b . The complementary sector element  33  comprises third connecting means  41  for connecting the complementary sector element  33  to the first connecting means  39  of the refractory block  16 , and fourth connecting means  42  for connecting the complementary sector element  33  to adjacent elements of the gas circulating duct  18   a ,  18   b . The first connecting means  39  comprise flanges with bolt holes  43  to attach the refractory block  16  to the complementary sector element  33 , preferably through bolted joints. The third connecting means  41  comprise flanges with bolt holes  43  to attach the complementary sector element  33  to the refractory block  16 , preferably through bolted joints. The second connecting means  40  comprise flanges with bolt holes  43  to attach the refractory block  16  to the adjacent elements of the gas circulating duct  18   a ,  18   b , preferably through bolted joints. The fourth connecting means  42  comprise flanges with bolt holes  43  to attach the complementary sector element  33  to the adjacent elements of the gas circulating duct  18   a ,  18   b , preferably through bolted joints. 
     For maintenance of a gas circulating duct  18   a , to replace the burner unit  1 , the refractory block  16  having the burner arrangement B attached therein is detached from the complementary sector element  33  and from the gas circulating duct  18   a ,  18   b . Thereafter, the burner unit  1  to be replaced is detached from the fluid cooled copper block  3  which remains attached to the refractory block  16 . A new burner unit  1  can then be attached to the cooled copper block  3 . Alternatively, the burner arrangement B in which the burner unit  1  and the fluid cooled copper block  3  are connected to each other as an assembly can be detached from the refractory block  16  and thereafter the burner unit  1  is detached from the fluid cooled copper block  3 , and a new burner unit  1  is attached to the cooled copper block  3 . Finally, the refractory block  16  having the burner arrangement B attached therein can be attached to the complementary sector element  33  and to the gas circulating duct  18   a ,  18   b.    
     For maintenance of a gas circulating duct  18   a , to replace the refractory block  16 , the refractory block  16  to be replaced having the burner arrangement B attached therein is detached from the complementary sector element  33  and from the gas circulating duct  18   a ,  18   b . Thereafter, the burner arrangement B is detached from the refractory block  16 . The burner arrangement B is attached to a new refractory block  16 . Finally, g the refractory block  16  having the burner arrangement B attached therein is attached to the complementary sector element  33  and to the gas circulating duct  18   a ,  18   b.    
     For maintenance of a gas circulating duct  18   a , to replace the refractory block  16 , to replace the complementary sector element  33 , the refractory block  16  having the burner arrangement B attached therein is detached from the complementary sector element  33  and from the gas circulating duct  18   a ,  18   b . The complementary sector element  33  to be replaced is detached from the gas circulating duct  18   a ,  18   b . A new complementary sector element  33  is attached to the gas circulating duct  18   a ,  18   b . Finally, the refractory block  16  having the burner arrangement B attached therein is attached to the complementary sector element  33 ) and to the gas circulating duct  18   a ,  18   b.    
       FIG. 10  shows a metallurgical furnace  22  equipped with a burner arrangement B of  FIGS. 1 to 3  which is installed in the refractory wall  20  of an electric arc furnace  21  according to the principles as already depicted with reference to  FIGS. 4 and 5 . 
     It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.