Abstract:
A cooled furnace wall comprises a furnace shell with an inner and an outer side and cooling plates lining the inner side of the furnace shell. Each of the cooling plates has a plate body and protruding connection pieces for supplying the cooling plate with a coolant. The furnace shell has connection openings therein for interconnecting the connection pieces of adjacent connection plates from the outer side of the furnace shell. At least one of the connection pieces is formed by a tube bend that protrudes from an edge face of the plate body and that has a connection end to extending through one of the connection openings in the furnace shell.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is entitled to the benefit of International Application No. PCT/EP2004/050518 filed on Apr. 14, 2004. European Patent Application No. 03 008 562.5 filed on Apr. 14, 2003 and Luxembourg Patent Application No. 91 025 filed on Jun. 5, 2003. 
   FIELD OF THE INVENTION 
   The present invention generally relates to a cooled furnace wall. It relates more particularly to a furnace wall comprising a furnace shell with an inner side and an outer side and cooling plates lining the inner side of the furnace shell. Each of these cooling plates has a plate body with protruding connection pieces for a coolant. The furnace shell has connection openings therein, which enable to interconnect the protruding connection pieces of adjacent cooling plates from the outer side of the furnace shell. 
   BACKGROUND OF THE INVENTION 
   It is well known to line the inner side of a furnace shell of a metallurgical furnace, in particular a blast furnace, with cooling plates. Such a cooling plate, also called “stave”, comprises a rectangular, solid plate body with cooling passages therein. Connection pieces, which protrude from the rear side of the cooling plate, debouch into the cooling passages of the cooling plate. These connection pieces are led in a sealed manner through connection openings in the furnace shell. At the outer side of the furnace shell, flexible metal tubes are used to interconnect the connection pieces of adjacent cooling plates and to connect the cooling plates to a cooling water distribution circuit. 
   The plate body of such a cooling plate is made either from cast iron (in particular modular cast iron) or from copper or a copper alloy, or more recently also from steel. In cooling plates made from cast iron, the cooling passages are generally formed by cast-in U-shaped steel tubes, wherein the ends of a cast-in tube protrude from the rear side of the plate body as connection pieces. In virtually all cooling plates made from copper or steel, however, the cooling passages are directly formed in the solid cooling plate body. 
   DE 2 907 511 discloses a cooling plate which is made from a forged or rolled block of copper. The cooling passages in the copper block are blind bores produced by mechanical deep-drilling. The openings of these blind bores are sealed off by soldering or welding plugs therein. Connecting bores are drilled from the rear side of the plate into the blind bores, and connection pieces for the coolant feed or coolant return are inserted into these connecting bores and soldered or welded in place. 
   WO 98/30345 describes a process for manufacturing a cooling plate in which a blank of the cooling plate is produced by continuous casting. Inserts in the continuous-casting mould produce passages running in the casting direction, which form the cooling passages in the finished cooling plate. A plate is separated from the continuously-cast blank by making two cuts transversely with respect to the casting direction, thus forming two end faces, wherein the distance between these two end-faces corresponds to the desired length of the cooling plate. In the next manufacturing step, connection bores are drilled into the plate body perpendicular to its rear surface, so as to open into the through-passages. Thereafter connection pieces are inserted into the connection bores and soldered or welded in place and the end-side openings of the passages are sealed off by soldering or welding plugs therein. 
   The processes described in DE A 2907511 and in WO 98/30345 both enable high-quality cooling plate bodies to be produced from copper or copper alloys. However, compared to cooling plates with cast-in cooling tubes or compared to mould-cast cooling plates, the finished cooling plates produced by both processes have the drawback of relatively high pressure losses in the transition regions between the connection pieces and the cooling passages. 
   WO 00/36154 proposes to reduce the pressure losses in copper cooling plates with cast or drilled cooling passages by inserting a shaped piece into a cut-out in the cooling plate body, so as to form a diverting passage with optimised flow conditions for the cooling medium. However, this solution is relatively labour-intensive and results therefore in higher production costs for the cooling plates. 
   DISCLOSURE OF INVENTION 
   Technical problem 
   It is an object of the present invention, to optimise the connections between the cooling plates in a furnace wall as defined in the preamble. 
   OBJECTS AND SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, this object is achieved through the fact that a connection piece of a cooling plate is formed by a tube bend that protrudes from an edge face (i.e. a narrow side face) of the plate body and that has a connection end extending through one of the connection openings in the furnace shell. A connection piece of this type may, for example, be formed by a 90° tube bend, a first end of which is inserted into an opening of a cooling passage in the edge face of the plate body. In other words, the connection piece no longer opens perpendicularly through the rear side of the cooling plate body into the cooling passage, but rather in axial extension of the cooling passage through an edge face of the cooling plate body. The cooling fluid is consequently diverted within the tube bend connection piece itself, which causes relatively low pressure losses. 
   It will also be appreciated that production of a cooling plate with cooling passages formed directly in a solid plate body is significantly simplified by the present invention. In fact, the openings of the cooling passages in the edge faces of the cooling plate body no longer have to be sealed by soldering or welding plugs therein, and there is also no need to drill separate connection passages for the connection pieces from the rear side of the cooling plate. In the process which is known from DE-A-2907511, the blind bores can be replaced by through-bores, which simplifies cleaning of the drilled cooling passages. Moreover, dead end sections (i.e. passage end sections through which there is no flow), in which sand, weld beads and rust particles normally accumulate and/or air pockets or vapour bubbles form, are avoided, which will result in an improved cooling capacity and service life of the cooling plates. Also the cooling of the bottom and top ends of the cooling plates is significantly improved, since the cooling medium now flows directly through these top and bottom ends. 
   Cooling plates with cooling passages directly formed in a solid plate body may, for example, comprise a continuously cast cooling plate body made from copper or a copper alloy with cast-in cooling passages, a forged or rolled cooling plate body made from copper or a copper alloy with drilled or milled cooling passages, or a cooling plate body made from steel with drilled or milled cooling passages. In the case of a cooling plate body made from copper or a copper alloy, tube bends made from copper or a copper alloy or from stainless steel will normally be used. In the case of a cooling plate body made from steel, steel tube bends are preferred. 
   Generally, vertical cooling plates, i.e. cooling plates with vertically running cooling passages, are used in the context of the present invention. It is however also possible to use horizontal cooling plates, meaning cooling plates with horizontally running cooling passages. In the case of vertical cooling plates, a cooling passage forms an opening in an upper or lower edge face of the cooling plate body. In the case of horizontal cooling plates, a cooling passage forms an opening in the left-hand or right-hand edge face of the cooling plate body. 
   In accordance with the present invention, the tube bend connection pieces of two adjacent cooling plates connected in series may lie relatively close together. This is of advantage with regard to the arrangement of the connection openings in the furnace shell and the interconnection of the connection pieces. 
   The tube bend connection pieces of two cooling plates are preferably connected by means of flexible connection means. In accordance with another aspect of the present invention, these flexible connection means are accommodated in a sealed connection box which is arranged on the outer side of the furnace shell and is preferably closed off by means of a removable blind flange. This eliminates the need for expensive, sealed tube passages through the furnace shell and results in significant time savings when mounting the cooling plates. Furthermore, it will be appreciated that a connection box of this type may also be dimensioned in such a manner that a cooling plate can be removed from the furnace and introduced into the furnace through the connection box. 
   The flexible connection means advantageously comprises a tube compensation bend which connects the tube bend ends of two cooling plates in the connection box and compensates for differential movements of the cooling plates. Compared to a conventional metal hose, a tube compensation bend of this type produces significantly lower pressure losses and moreover has a longer service life. 
   To reduce the distance between the edge faces of two adjacent cooling plates, the second ends of the tube bends of the first cooling plate and the second ends of the tube bends of the second cooling plate may be arranged in a row. In this case, the flexible connection means may, for example, comprise a bent tube segment which is arranged in the connection box and is substantially in the shape of racing cycle handlebars. A shape of this type ensures the required resilience to absorb differential movements of the cooling plates. 
   As an alternative solution to a connection box, the connection opening in the furnace shell may for example be covered by a socket piece. The latter has for each connection end a separate through-opening, and each of these connection ends is connected in a sealed manner to the socket piece by means of a compensator. 
   In order to protect the tube bends with respect to the interior of the furnace, a plate extension may be arranged in front of the tube bends at the edge face of the cooling plate. 
   If there are two rows of cooling plates arranged directly vertically above one another, the vertical joins between the cooling plates belonging to the upper row may be offset relative to the vertical joins between the cooling plates belonging to the lower row. In this arrangement, the tube bends of a cooling plate belonging to the lower row can be connected to the tube bends of two adjacent cooling plates belonging to the upper row. 
   The edge face of the plate body from which the connection pieces protrude is advantageously bevelled towards the inner side of the furnace shell. This allows two cooling plates which are to be connected by means of their connection pieces to be arranged significantly closer together. Furthermore, the bent connection pieces lie in the shadow of the bevelled cooling plate edge and are therefore at least partially protected from heat radiation from the furnace interior. If two cooling plates are to be connected, the opposite edge faces from which the connection pieces protrude are advantageously bevelled in a mirror image, so that they delimit a wedge-shaped space which narrows towards the interior of the furnace. 
   To enable two cooling plates which are to be connected by means of their connection pieces to be arranged even closer together, the connection piece has, at the outlet from the edge face of the plate body, a first curvature in the mid-plane of the plate body and thereafter a second curvature in a plane which is perpendicular to this mid-plane of the plate body. The connection piece may advantageously be composed of a 30° tube bend and a 90° tube bend, the centre lines of which lie in two planes which are perpendicular to one another. Two adjacent cooling plates can then be arranged above or next to one another in such a manner that the outlet of a connection piece in one edge face of the first cooling plate and the outlet of a connection piece in an opposite edge face of the second cooling plate lie axially opposite one another, wherein the first curvature of a bent connection piece of the first cooling plate is directed in a first direction and the first curvature of a bent connection piece of the second cooling plate is directed in the opposite direction. In this embodiment, the second curvatures of the bent connection pieces advantageously define parallel planes of curvature, the distance between which corresponds to 1.1 to 1.5 times the tube diameter of the bent connection pieces. 
   A plug made from an elastic material, in which there are through-openings for the connection ends, is advantageously inserted into a connection opening in the furnace shell. This plug advantageously has a lateral securing flange which is clamped between cooling plates and furnace shell. At least two connection ends are guided through the plug into a connection box on an outer side of the furnace shell, where they are connected to one another by means of flexible connection means. To improve the sealing of the connection box with respect to the interior of the furnace, a section of the connection box between the plug and the flexible connection means is advantageously sealed with a foamed sealing material. Moreover, the connection box may have a leak-test valve at its deepest point. 
   The present invention is also applicable to cooling plates which have at least one cooling passage which is formed by a cast-in tube. (This is for example the case with most cooling plates made from cast iron). For these cooling plates, at least one end of the tube protrudes from an edge face of the plate body and forms the tube bend connection piece. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Preferred embodiments of the invention will now be described with reference to the accompanying drawings in which: 
       FIG. 1 : is a longitudinal section through a first embodiment of a cooled furnace wall; 
       FIG. 2 : is a longitudinal section through a second embodiment of a cooled furnace wall; 
       FIG. 3 : is a plan view of a first arrangement of cooling plates in an embodiment of a cooled furnace wall; 
       FIG. 4 : is a plan view of a second arrangement of cooling plates in an embodiment of a cooled furnace wall; 
       FIG. 5 : is a plan view of a third arrangement of cooling plates in an embodiment of a cooled furnace wall; 
       FIG. 6 : is a longitudinal section through a third embodiment of a cooled furnace wall; 
       FIG. 7 : is a longitudinal section through a first variant of the embodiment shown in  FIG. 6 ; 
       FIG. 8  is a longitudinal section through a second variant of the embodiment shown in  FIG. 6 ; 
       FIG. 9 : is a longitudinal section through a third variant of the embodiment shown in  FIG. 6 ; 
       FIG. 10 : is a longitudinal section through a fourth embodiment of a cooled furnace wall; 
       FIG. 11 : is a longitudinal section through a first variant of the embodiment shown in  FIG. 10 ; 
       FIG. 12 : is a longitudinal section through a fifth embodiment of a cooled furnace wall; 
       FIG. 13 : is a longitudinal section as in  FIG. 6 , with further details; 
       FIG. 14 : is a plan view of a connection box in which connection pieces of two cooling plates are connected to one another; and 
       FIG. 15 : is a plan view of an arrangement of cooling plates with connection boxes in accordance with  FIG. 14 ; 
       FIG. 16 : is a three-dimensional view of a first embodiment of a turbulator to be inserted in a cooling passage of a cooling plate; 
       FIG. 17 : is a three-dimensional view of a second embodiment of a turbulator to be inserted in a cooling passage of a cooling plate. 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION WITH REFERENCE TO THE DRAWINGS 
   The furnace wall  10  shown in the drawings to illustrate the invention is a blast furnace wall cooled by means of cooling plates. In  FIGS. 1 and 2 , reference numeral  12  denotes a furnace shell. An upper end of a lower cooling plate  14  and a lower end of an upper cooling plate  14 ′ can be seen on the inner side of the furnace shell  12 . These cooling plates  14 ,  14 ′ are affixed to the furnace shell  12  by means of threaded bolts  16  and form a cooled lining of the inner side of the furnace shell  12 . “D” denotes the vertical distance between the upper edge face  18  of the lower cooling plate  14  and the lower edge face  18 ′ of the upper cooling plate  14 ′. In the embodiments shown in  FIG. 1  and  FIG. 2 , this distance “D” approximately corresponds to three times the thickness “E” of the cooling plates  14 ,  14 ′. 
   The cooling plates  14 ,  14 ′ shown in  FIG. 1  and  FIG. 2  have a solid cooling plate body  20 ,  20 ′ made from copper or a copper alloy. Vertical cooling passages  22 ,  22 ′ are arranged directly in this solid cooling plate body  20 ,  20 ′, i.e. they have, for example, been cast, drilled or milled into the base material of the cooling plate body  20 ,  20 ′. These cooling passages  22 ,  22 ′ are formed as vertical through-passages which extend parallel through the cooling plate body  20 ,  20 ′. It can be seen from  FIG. 1  and  FIG. 2  that the cooling passage  22  forms an opening  24  in the upper edge face  18  of the lower cooling plate  14 , and that the cooling passage  22 ′ forms an opening  24 ′ in the lower edge face  18 ′ of the upper cooling plate  14 ′. 
   Reference numerals  26  and  26 ′ denote thick-walled 90° tube bends made from copper which form connection pieces of the cooling plates  14 ,  14 ′. It can be seen that one end  28  of the lower tube bend  26  is welded or soldered into the openings  24  in such a manner that the second end  30  (also referred to as connection end  30 ) of the lower tube bend  26  faces a connection opening  32  in the furnace shell  12 , and that one end  28 ′ of the upper tube bend  26 ′ is welded or soldered into the opening  24 ′ in such a manner that the second end  30 ′ (also referred to as connection end  30 ′) of the upper tube bend  26 ′ faces the same connection opening  32  in the furnace shell  12 . In this arrangement, the two tube bends  26  and  26 ′ lie vertically above one another in the free space which is formed between the upper edge face  18  of the lower cooling plate  14  and the lower edge face  18 ′ of the upper cooling plate  14 ′. To shield the free space  34  in which the tube bends  26  and  26 ′ are located with respect to the interior of the furnace, a plate extension  36 ,  36 ′ is arranged both at the upper edge face  18  of the lower cooling plate  14  and at the lower edge face  18 ′ of the upper cooling plate  14 ′, in each case towards the interior of the furnace. 
   DETAILED DESCRIPTION OF THE INVENTION 
   In the embodiment shown in  FIG. 1 , the lower tube bend  26  is connected to the upper tube bend  26 ′ by means of a compensation tube bend  40 , the compensation tube bend  40  being welded to the free ends  30 ,  30 ′ of the tube bends  26 ,  26 ′. This compensation tube bend  40  passes the cooling medium (generally cooling water) out of the cooling passage  20  into the cooling passage  20 ′, wherein its resilience in the vertical direction compensates for temperature-related changes in the distance “D”. The compensation tube bend  40  projects into a connection box  42  which is arranged on the outer side of the furnace shell  12  over the connection opening  32  in the furnace shell  12 . This connection box  42  is connected in a gastight manner to the furnace shell  12  and is likewise closed off in a gastight manner by means of a removable blind flange  44 . After removal of the blind flange  44  one has direct access to the compensation tube bend  40  from the outer side of the furnace shell  12 . 
   In the embodiment shown in  FIG. 2 , extended connection ends  46 ,  46 ′ of the tube bends  26 ,  26 ′ are led in a sealed manner out of the furnace shell  12 . For this purpose, the connection opening  32  in the furnace shell  12  is covered by a socket piece  48  which forms a passage  49 ,  49 ′ for each connection end  46 ,  46 ′. Each connection end  46 ,  46 ′ is in this case connected in a sealed manner to the socket piece  48  by means of a compensator  50 ,  50 ′. The compensators  50 ,  50 ′ (bellows compensators are illustrated in  FIG. 2 ) must be designed so as to be able to absorb lateral and angular movements of the connection ends  46 ,  46 ′. A common protective housing  52  surrounds the two compensators  50 ,  50 ′. In the embodiment shown in  FIG. 2 , the connection ends  46 ,  46 ′ will be interconnected, for example, by means of a metal hose coupling as shown in  FIG. 13 . (The term “metal hose” shall also encompass a metallically reinforced synthetic hose). 
     FIG. 3  shows a first arrangement of cooling plates on the inner side of the furnace shell  12 . The cooling plates  14 ,  14 ′ are located vertically flush above one another, but the cooling plates of two adjacent columns are vertically offset by half the height of a cooling plate. As a result, the connection openings  32  in the furnace shell  12  are likewise vertically offset, so that the furnace shell  12  is weakened to a lesser extent. This is particularly important for the design variant indicated in the right-hand column. In this case, the connection opening  132  in the furnace shell  12  and the connection box  42  are dimensioned in such a manner that a cooling plate  14 , after removal of the blind flange  44  and disconnection of the tube connections, can be removed from the furnace or introduced into the furnace through the connection box  42 . 
     FIG. 4  shows a second arrangement of cooling plates  14 ,  14 ′ on the inner side of the furnace shell  12 . These cooling plates  14 ,  14 ′ are positioned in rows above one another, but the cooling plates of two adjacent rows are offset by half the width of a cooling plate. In this arrangement, the upper tube bends  26  belonging to a lower cooling plate  14  are in each case connected to tube bends  26 ′ of two adjacent upper cooling plates  14 ′. 
     FIG. 5  shows a third arrangement of cooling plates  14 ,  14 ′ on the inner side of the furnace shell  12 . These cooling plates  14  are likewise located in rows above one another, the cooling plates belonging to two adjacent rows being slightly offset. It will be observed that the ends  30  of the tube bends  26  belonging to the lower cooling plates  14  and the ends of the tube bends  26 ′ belonging to the upper cooling plates lie in a row. As a result, the vertical distance “D” between the upper edge face  18  of a lower cooling plate  14  and the lower edge face  18 ′ of an upper cooling plate  14 ′ is reduced (and now approximately corresponds to twice the thickness “E” of the cooling plates  14 ,  14 ′). In the cooling plates of the left hand side of  FIG. 5 , the tube bends  26 ,  26 ′ are connected by means of fixed tube segments  60  which, in order to absorb temperature-related movements between the cooling plates, are substantially in the shape of racing cycle handlebars. In the cooling plates on the right-hand side of  FIG. 5 , the tube bends  26 ,  26 ′ are connected by means of metal hoses  62 . 
     FIG. 6  shows a further embodiment of the cooled furnace wall. In this embodiment, the two edge faces  18 ,  18 ′ of the cooling plates  14 ,  14 ′ out of which bent connection pieces  26 ,  26 ′ are led out of the plate bodies  20 ,  20 ′ are bevelled in mirror-image fashion towards the inner side of the furnace shell  12 , in such a manner that they delimit a wedge-shaped space  69  which narrows towards the interior of the furnace. The angle a between the respective rear side of the cooling plate  14 ,  14 ′ and the corresponding edge face  18 ,  18 ′ is advantageously in the range from 105° to 150° and is preferably 120°. In the wedge-shaped space  69 , the bent connection pieces  26 ,  26 ′ are substantially shielded from the thermal radiation from the interior of the furnace. They are located, so to speak, in the shadow of the edges of the cooling plates  14 ,  14 ′. Moreover, the wedge-shaped space  69  may be filled with a refractory material, in which case, however, the expansion of the cooling plates  14 ,  14 ′ and their connection pieces must not be excessively impeded. Since the bent connection pieces  26 ,  26 ′ are now relatively well protected from thermal radiation, they may also be made, for example, from stainless steel. In this context, it should be noted that tube bends made from stainless steel have better mechanical properties and lower prices than thick-walled tube bends made from copper. 
     FIG. 7  shows a modification to the embodiment shown in  FIG. 6 . The two plate bodies  20 ,  20 ′ are arranged vertically above one another on the inner side of the furnace shell. The edge face  18  of the lower plate body  20  has a nose-like projection  70  facing the interior of the furnace, which is bevelled parallel to the opposite edge face  18 ′ of the upper plate body  20 ′, so that this nose-like projection  70  and the edge face  18 ′ of the upper plate body  20 ′ form a gap  72  which slopes from the interior of the furnace upwards towards the inner side of the furnace shell  12 . This gap  72  which rises upwards towards the inner side of the furnace shell  12  makes it more difficult, for example, for settling burden to penetrate into the wedge-shaped space  69 . 
     FIG. 8  shows a modification to the embodiment shown in  FIG. 7 . The edge face  18 ′ of the upper plate body  20 ′ has a nose-like projection  70 ′ facing the interior of the furnace, which is bevelled parallel to the edge face  18  of the lower plate body  20 , so that this nose-like projection  70 , and the edge face  18  of the lower plate body  20  form a gap  72  which slopes from the interior of the furnace downwards towards the inner side of the furnace shell  12 . This gap sloping downwards in the direction of the inner side of the furnace shell  12  makes it more difficult for hot gases to penetrate into the wedge-shaped space  69 . 
     FIG. 9  shows a further modification to the embodiment shown in  FIG. 7 . In this case, the two bevelled edge faces  18 ,  18 ′ each have a nose-like projection  70 ,  70 ′ facing towards the interior of the furnace, which nose-like projections overlap one another. In this case the two nose-like projections  70 ,  70 ′ are separated by a type of labyrinth gap  74 . The latter makes it more difficult for hot gases and settling burden to penetrate into the wedge-shaped space  69 . 
     FIG. 10  shows a further embodiment of the cooled furnace wall. The lower cooling plate  14  comprises a plate body  20  made from copper or steel. However, the upper cooling plate  14 ′ comprises a plate body  20 ′ made from cast iron in which the cooling passages are formed by cast-in tubes  76 ′. The end of a tube  76 ′ of this type is led out of the edge face  18 ′ of the plate body  20 ′, where it forms a bent connection piece  26 ′ with a connection end  30 ′ which is guided through the connection openings  32  in the furnace shell  12 . It will be noted that the edge face  18 ′ is bevelled at the front and at the rear, the bent connection piece  26 ′ emerging from the edge face bevelled at the rear. The bevelling towards the interior of the furnace results in an improved transition between the cooling plate  14 ′ made from cast iron and the thinner cooling plate  14  made from copper or steel. 
     FIG. 11  shows a modification to the embodiment shown in  FIG. 10 . In this embodiment, the upper plate body  20 ′ made from cast iron, like the lower cooling plate  14  made from copper or steel, has an edge face  18 ′ which is bevelled exclusively at the rear. Since the two front sides of the plate bodies  20  and  20 ′ are flush, the gap between the rear side of the plate body  20  made from copper or steel and the furnace shell  12  is wider than the gap between the rear side of the thicker plate body  20 ′ made from cast iron and the furnace shell  12 . However, the gap between the rear side of the plate body  20  made from copper or steel and the furnace shell  12  can be reduced, for example, by a constriction in the furnace shell (not shown). 
     FIG. 12  shows a further embodiment of the cooled furnace wall. Both the lower cooling plate  14  and the upper cooling plate  14 ′ comprise a plate body  20 ,  20 ′ made from cast iron in which the cooling passages are formed by cast-in tubes  76 ,  76 ′. The edge face  18 ,  18 ′ is in each case partially bevelled at the rear, the tube bend  26 ,  26 ′ emerging from the edge face which is bevelled towards the rear. 
     FIG. 13  shows a cooling plate arrangement as in  FIG. 6  with further design details. It can be seen that a plug  80  with through-openings for the connection ends  30 ,  30 ′ of the bent connection pieces  26 ,  26 ′ has been inserted into the connection opening  32  in the furnace shell  12 . The plug  80  consists of an elastic material, so that it does not significantly impede the free expansion of the connection pieces  26 ,  26 ′ and cooling plates  14 ,  14 ′. At its edge, it has an encircling securing flange  82  which is clamped between the cooling plates  14 ,  14 ′ and the furnace shell  12 . The connection ends  30 ,  30 ′ are guided through the through-openings in the plug  80  into the connection box  42 , where they are connected to one another by means of a flexible connection line  84  with quick-acting couplings  86 ,  86 ′. Immediately behind the plug  80 , a partial section of the connection box  42  is filled with a foamed elastic material  83  around the connection ends  30 ,  30 ′. The rear end of the connection box  42 , which is not filled with foam and in which the connecting line  84  is arranged, has a leak-test valve  88  at its lowest point. In the event of a leak in the connections between the connection pieces  26 ,  26 ′, cooling water collects in the rear end of the connection box  42 . The leak-test valve  88  can be used to check the connection box  42  for the presence of leakage water without the blind flange  44  of the connection box  42  having to be opened. 
     FIG. 14  shows a plan view of a connection box  42  in which a plurality of connection pieces  26 ,  26 ′ of two cooling plates  14 ,  14 ′ are connected to one another. It can be seen that each of the bent connection pieces  26 ,  26 ′, at the exit from the edge face  18 ,  18 ′ of the plate body  20 ,  20 ′, first of all has a first curvature  102 ,  102 ′ in the mid-plane of the plate body  20 ,  20 ′ (=plane parallel to the plane of the drawing) and then a second curvature  104 ,  104 ′ in a plane which is perpendicular to the mid-plane of the plate body  20 ,  20 ′. The connection pieces  26 ,  26 ′ shown are composed, for example, of a 30° tube bend and a 90° tube bend, the centre lines of which lie in two mutually perpendicular planes. 
   In  FIG. 14 , the cooling plates  14 ,  14  are positioned above one another, in such a manner that the outlet point of a bent connection piece  26  in an edge face  18  of the first cooling plate  14  and the outlet point of a bent connection piece  26 ′ in an opposite edge face  18 ′ of the second cooling plate  14 ′ lie axially opposite one another. The first curvature  102  of a bent connection piece  26  of the first cooling plate  14  is directed towards the right. By contrast, the first curvature  102 ′ of a bent connection piece  26 ′ of the second cooling plate  14 ′ is directed towards the left, i.e. in the opposite direction. The planes of curvature  106 ,  106 ′ of the second curvatures  104 ,  104 ′ are parallel to one another and have a spacing “d” between them which corresponds to 1.1 to 1.5 times the tube diameter of the bent connection pieces ( 26 ,  26 ′). It will be noted that the double curvature of the connection pieces  26 ,  26 ′ makes it possible for the two cooling plates  14 ,  14 ′ to be arranged very close together. 
     FIG. 15  shows an arrangement of cooling plates with connection boxes  42  as shown in  FIG. 14 . Each of the connection boxes  42  can be used to install and remove a cooling plate  14 ,  14 ′. It will be seen how the connection boxes  42  are offset in terms of height in order not to excessively weaken the furnace shell  12 . 
   It will be appreciated that the tube bend connection piece may advantageously be used to mount a turbulator into a cooling passage of the cooling plate.  FIG. 16  and  FIG. 17  show possible embodiments of such a turbulator  200 ,  200 ′. The latter comprises a turbulator body  202 ,  202 ′ and a ring-shaped fixing flange  204 ,  204 ′. The turbulator body  202 ,  202 ′ is axially inserted into the cooling channel. The ring-shape fixing flange  204 ,  204 ′ bears on a shoulder surface in the opening of the cooling channel in the edge face of the cooling plate. It is blocked on this shoulder surface by means of the connection piece, whose end is inserted into this opening and sealingly connected to the edge face by means of a welding or brazing joint. Such a turbulator will increase efficiency of thermal transfer by adding a transversal velocity component to the cooling fluid in the cooling channel.