Patent Publication Number: US-2015060031-A1

Title: Plate heat exchanger with heat exchanger blocks joined by metal form

Description:
The invention relates to a plate heat exchanger with at least two heat exchanger blocks, each heat exchanger block having several sheets that are arranged parallel to one another and that form a plurality of heat-exchange passages for fluids that are involved in the heat exchange. The heat exchanger blocks are joined to one another via joining means and have at least one common header for distribution of a heat-exchanging fluid to the two heat exchanger blocks or for draining a heat-exchanging fluid from the two heat exchanger blocks. 
     Brazed plate heat exchangers made of aluminum are used in numerous installations at a variety of pressures and temperatures. They are used, for example, in the separation of air, the liquefaction of natural gas, and in installations for producing ethylene. 
     Such a plate heat exchanger is shown and described in, for example, “The Standards of the Brazed Aluminum Plate-Fin Heat Exchanger Manufactures Association” ALPEMA, Third Edition, 2010 on page 5. A figure taken from it is depicted in  FIG. 1  as prior art and is described below. 
     The plate heat exchanger shown in  FIG. 1  comprises several partitions  4  that are arranged in parallel to one another and that form a plurality of heat-exchange passages  1  for the media that are to be brought into heat exchange with one another. The heat-exchange passages  1  are closed to the outside by sheet metal strips  8 , hereinafter also called sidebars  8 , which are attached flush to the edge of the partitions  4 . Within the heat-exchange passages  1 , there are corrugated sheets  3 , so-called fins  3 . The partitions  4 , fins  3 , and sidebars  8  are permanently joined to one another and thus form a compact heat exchanger block  10 . The entire heat exchanger block  10  is bordered on the outside by cover sheets  5 . 
     For supply and drainage of the heat-exchanging media, semicylindrical collectors  7  with pipe connections  6 , used to join feed and drainage pipelines, are attached via inlet and outlet openings  9  of the heat-exchange passages  1 . The collectors  7  are also called headers  7  below. The inlet and outlet openings  9  of the heat exchanger passages  1  are formed by so-called distributor plates or distributor fins  2  that provide for a uniform distribution of the media within the individual heat-exchange passages  1 . The media flow through the heat-exchange passages  1  in the channels formed by the fins  3  and the partitions  4 . 
     The fins  3  are brazed at their contact sites to the partitions  4 , as a result of which intensive heat-conductive contact between the fins  3  and the partitions  4  is established. In this way, the heat exchange between the different media that flow in alternation in adjacent heat-exchange passages  1  is improved. 
     These plate heat exchangers are preferably formed from aluminum, the components being joined to one another by brazing. The fins, partitions, distributor fins, cover sheets and sidebars, all provided with brazing, are stacked on one another and then brazed in a furnace to form a heat exchanger block. Then, the headers with pipe connections are welded onto the heat exchanger block. 
     In the production method just described the maximum size of the heat exchanger block is dictated by the size and geometry of the brazing furnace. Often, however, processes require a larger heat-exchange area and thus larger heat exchanger blocks than can be produced in this furnace. In order to satisfy these requirements, it is suggested on page 6 under 1.2.3 of the aforementioned publication that two or more heat exchanger blocks be joined to one another by welding in order to thus obtain an assembled heat exchanger block with increased stack height. 
     In order to produce a plate heat exchanger with several heat exchanger blocks, first two or more heat exchanger blocks are produced separately from one another from partitions, fins and distributor fins as described above in a brazing furnace. The latter still have no headers. Strips that end flush with the edges of the cover sheet are welded onto the cover sheet of a first heat exchanger block along the edges of the cover sheet. These strips that are often also called sidebars thus form more or less a frame on the cover sheet. A second heat exchanger block that is to be joined to the first heat exchanger block is placed with its cover sheet on the strips of the first heat exchanger block and is welded to them. The arrangement of two joined heat exchanger blocks has a greater stack height than the individual heat exchanger blocks that thus exceeds the size and geometry of the brazing furnace. Any number of heat exchanger blocks can be joined to one another in this way to form a heat exchanger block arrangement of any size. Then, the resulting heat exchanger block arrangement is provided with headers and pipe connections in order to obtain a large plate heat exchanger that comprises several heat exchanger blocks joined to one another. 
     Between the cover sheets of two adjacent heat exchanger blocks of such a plate heat exchanger, there is a cavity that is filled with air and that is surrounded by the sidebars. The media that are involved in the heat exchange do not flow through this cavity. The cavity is not pressurized. 
     In the various applications in these plate heat exchangers of made of several heat exchanger blocks, high stress concentrations occur in the transition region of the heat exchanger blocks. 
     An object of this invention is to make available a plate heat exchanger comprising several heat exchanger blocks and a method for its production, the plate heat exchanger having mechanical strength that is as great as possible and stresses in the transition region of the heat exchanger blocks are reduced. 
     Upon further study of the specification and appended claims, other objects, aspects and advantages of the invention will become apparent. 
     These objects are achieved by a plate heat exchanger in which a metal foam is present in the interspace between the opposing outside surfaces of adjacent heat exchanger blocks and the metal foam that joins these outside surfaces to one another. On the process side, these objects are achieved by a method wherein a liquid, hardenable metal foam is introduced into the interspace between the opposing outside surfaces of adjacent heat exchanger blocks, or a metal foam is formed in the interspace. Such a method can be applied in the manufacture of a plate heat exchanger having at least two heat exchanger blocks or can be applied in retrofitting an existing plate heat exchanger having at least two heat exchanger blocks. 
     Accordingly, a plate heat exchanger with at least two heat exchanger blocks is made available, each heat exchanger block having several sheets that are arranged parallel to one another and that form a plurality of heat-exchange passages for fluids involved in the heat exchange. The heat exchanger blocks are joined via joining means—such as, for example, the aforementioned edge-flush strips—and having at least one common header for distribution of a heat-exchanging fluid to the at least two heat exchanger blocks or for draining a heat-exchanging fluid from the at least two heat exchanger blocks. According to the invention, a metal foam joins the outside surfaces to one another in the interspace between opposing outside surfaces of adjacent heat exchanger blocks. This means that the previously air-filled cavity between the cover sheets of the heat exchanger blocks is preferably completely provided with metal foam. 
     The joining of the outside surfaces of the heat exchanger blocks according to the invention via a metal foam ensures a considerably larger joining area than is the case in the prior art. The outside surfaces of the heat exchanger blocks, which are generally formed by the cover sheets of the heat exchanger blocks, are joined by the metal foam in an integral and thus heat-conductive manner. The heat conduction enables an equalization of temperature differences between the adjacent heat exchanger blocks, as a result of which temperature-induced stresses between the heat exchanger blocks in the joining region or transition region of the heat exchanger blocks are reduced. A non-positive joining of the center region of the opposing outside surfaces is formed via the metal foam insert between the heat exchanger blocks. As a result, the mechanical strength of the heat exchanger block joining is improved. In this way, the operating reliability and fault tolerance or the service life of the plate heat exchanger is greatly increased. 
     Conversely, in a plate heat exchanger formed of several heat exchanger blocks, according to the prior art, the opposing outside surfaces of two adjacent heat exchanger blocks are joined to one another via the edge-flush strips only on the respective edges of the outside surfaces. Thus, a plate heat exchanger according to the prior art does not have any connections in the center region of the opposing outside surfaces. Accordingly, the thermal contact between two heat exchanger blocks due to the air-filled cavity is much poorer than the thermal contact between the heat-exchange passages within a heat exchanger block. In this way, temperature-induced clamping stresses arise on the outside edge weld at individual local sites. In the various applications, this can lead to high thermal stresses within the plate heat exchanger at the transition region of the heat exchanger blocks. This is prevented with the metal foam insert according to the invention. 
     Preferably, the metal foam is formed from aluminum or an aluminum alloy. 
     In one preferred embodiment, the metal foam roughly completely fills the interspace between the opposing outside surfaces of the heat exchanger blocks. Thus, over the entire outside surfaces of the heat exchanger blocks, there is heat-conductive contact, as a result of which temperature equalization between the heat exchanger blocks can take place optimally. It is also possible, however, to fill only partial regions of the interspace with foam. Preferably, however, the metal foam extends covers the center regions of the opposing outside surfaces of the heat exchanger blocks. 
     Preferably, the joining means, which joins the heat exchanger blocks to one another, is formed by strips that are each applied to opposing outside surfaces of the adjacent heat exchanger blocks, preferably by welding. The strips preferably end flush with the outside edges of the opposing outside surfaces of the heat exchanger blocks. Advantageously, the strips are welded to cover sheets of the heat exchanger modules via a continuous weld. The strips can form a peripheral frame on the outside surfaces of the heat exchanger blocks. During the production of the plate heat exchanger, first of all at least one opening to the interspace between the opposing outside surfaces should remain free for introducing the metal foam. 
     In the heat-exchange passages of the heat exchanger blocks, the plate heat exchanger according to the invention preferably has means for subdividing the heat-exchange passages into a plurality of channels. Preferably, they are corrugated sheets that can have different executions known to one skilled in the art. They are used to increase the heat conduction between the heat-exchange passages and to distribute the fluids uniformly over the heat-exchange passages. Moreover, they increase the mechanical strength of the heat exchanger block. 
     This invention also relates to a method for producing a plate heat exchanger with at least two heat exchanger blocks. Each of the heat exchanger block has several sheets that are arranged parallel to one another and that form a plurality of heat-exchange passages for fluids involved in the heat exchange. 
     The heat exchanger blocks are joined to one another via joining means—such as, for example, the aforementioned edge-flush strips. According to the invention, a liquid, hardenable metal foam is introduced into the interspace between opposing outside surfaces of adjacent heat exchanger blocks or is formed in the interspace. 
     Preferably, the metal foam is introduced into the interspace or formed in the interspace after the joining of the heat exchanger blocks via the joining means. Subsequent to the introduction or formation of the metal foam, the heat exchanger blocks are preferably provided with headers for distributing or draining the heat-exchanging fluids, preferably at least one common header at a time being applied to adjacent heat exchanger blocks. 
     Existing plate heat exchangers can also be retrofitted with this invention. Accordingly, a method for retrofitting a plate heat exchanger having at least two heat exchanger blocks is made available, in which each heat exchanger block has several sheets that are arranged parallel to one another and that form a plurality of heat-exchange passages for fluids involved in the heat exchange, the heat exchanger blocks being joined via joining means such as, for example, the above-described strips welded edge-flush and having at least one common header for distributing a heat-exchanging fluid to the two heat exchanger blocks or draining a heat-exchanging fluid from the two heat exchanger blocks. According to the invention, a liquid, hardenable metal foam is introduced into the interspace that is present between outside surfaces of adjacent heat exchanger blocks, and is heretofore generally filled with air, or the metal foam is formed within the interspace. 
     In the described method according to the invention, the introduction of the liquid metal foam can take place by one or more of the following processes: spraying-in, injecting, or suction. 
     One preferred embodiment of the method according to the invention calls for introducing the liquid metal foam using at least one spraying or injection device from at least one side of the heat exchanger blocks into the interspace and at the same time aspirating the metal foam on at least one other, preferably opposing, side of the heat exchanger blocks. Thus, it is possible to completely fill the interspace with metal foam, even in cases where there are only small access openings in the strip frame. 
     Between the outside surfaces of the heat exchanger blocks, which surfaces are to be joined, one or more parent substances can also be introduced that form a liquid, hardenable metal foam by mixing and/or by changing the ambient conditions, preferably the pressure and/or temperature. Preferably, the parent substances are in the form of a powder that forms a liquid, hardenable metal foam when exceeding or falling below a certain temperature and/or a certain pressure. 
     In a plate heat exchanger according to this invention, the mechanical and thermal joining between two adjacent heat exchanger blocks is clearly improved compared to the prior art. The entire plate heat exchanger block having several heat exchanger blocks is clearly a more rigid and mechanically more stable structure than a plate heat exchanger according to the prior art. In addition, a plate heat exchanger according to the invention has much better temperature equalization between two adjacent heat exchanger blocks. Within the scope of this invention, plate heat exchangers can be made available that comprise two or more than two, for example three or four, heat exchanger blocks. Since the mechanical strength of the joining between the individual heat exchanger blocks is increased compared to the prior art, plate heat exchangers can also be built that have of a larger number of blocks than was conventional and seemed feasible in the past. 
     The plate heat exchanger according to the invention can be used especially advantageously for methods that require an especially intensive heat contact between the outside surfaces of adjacent heat exchanger blocks. This is the case, for example, for steep temperature gradients, major changes in the temperature gradient, or for uneven distributions of the fluids participating in the heat exchange (improper distribution or maldistribution). These states can often occur in certain vaporization processes of two-phase mixtures or pure substances, for asymmetrical passage arrangement, unspecified operating states, and shutdown or start-up processes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is to be explained in more detail below using a prior art heat exchanger block and an embodiment of the invention shown in  FIGS. 1 to 4  wherein: 
         FIG. 1  shows a prior art heat exchanger block; 
         FIG. 2  shows a perspective view of two heat exchanger blocks that are interconnected according to this invention, 
         FIG. 3  shows a cross-section through the arrangement of heat exchanger blocks according to  FIG. 2  (line A-A) in the joining region of the two heat exchanger blocks; and 
         FIG. 4  shows a plate heat exchanger with the heat exchanger blocks shown in  FIGS. 2 and 3 . 
     
    
    
       FIG. 2  shows two heat exchanger blocks  10   a  and  10   b . The heat exchanger blocks, like the block  10  shown in  FIG. 1 , comprise a plurality of flat sheets  4 , hereinafter also called partitions  4 , which are arranged in a stack in parallel and at a distance to one another. On the partitions  4 , there are sheet metal strips  8  arranged flush on their outside edges, which strips fix the distance between the partitions  4  and hereinafter are also called sidebars  8 . This structure between the partitions  4  forms a plurality of heat-exchange passages  1  that are available for indirect heat exchange of two or more fluids. The sidebars  8  close the heat-exchange passages  1  to the outside. 
     Within the heat-exchange passages  1 , corrugated sheets  3 , so-called fins  3 , are arranged. The latter are not apparent in  FIG. 3  since fins  3  are located within the heat-exchange blocks  10   a  and  10   b , not in the joining region. Reference is therefore made to  FIG. 1  that shows fins  3  in an elevation of the heat-exchange block  10 . At inlet and outlet openings  9  of the heat exchanger passages  1 , there are so-called distributor plates or distributor fins  2  that provide for a uniform distribution of the fluids over the flow cross-sections of the individual heat-exchange passages  1 . In the illustrated view, the two heat exchanger blocks  10   a  and  10   b  are each bordered to the outside to the top and bottom by cover sheets  5 . The cover sheets  5  generally have a greater material thickness than the partitions  4  that are located within the heat exchanger blocks  10   a  and  10   b . As material for the indicated components of the heat exchanger blocks  10   a  and  10   b , an aluminum alloy, for example aluminum alloy 3003 or 5083, is used. The heat exchanger blocks  10   a  and  10   b  can, however, also be produced from high-grade steel. 
     To produce the heat exchanger blocks  10   a  and  10   b , the brazing metal-plated partitions  4 , the fins  3 , the distributor fins  2  and the sidebars  8  are first stacked in alternation on one another. Then, the arrangement is brazed in a brazing furnace. After brazing, all of the above-mentioned components are securely joined to one another and thus form compact cuboidal heat exchanger blocks  10   a  and  10   b . The two heat exchanger blocks  10   a  and  10   b  are brazed separately from one another. They have two dimensions that constitute maximum dimensions for a conventional brazing furnace interior. If, for certain installations and processes, heat-exchange areas are required that are larger than a heat exchanger block of maximum possible brazing furnace size can make available, two or more heat exchanger blocks are joined to one another according to this invention. 
     In addition to  FIG. 2 , reference is also made to  FIG. 3  below. 
     After separate fabrication of the heat exchanger blocks  10   a  and   10   b , metallic joining strips  11  that end flush with the edges of the cover sheet  5  are welded onto the cover sheet  5  of one of the heat exchanger blocks, for example, the a prior art heat exchanger block heat exchanger block  10   a , along the edges of the cover sheet  5 . The joining strips  11  generally have roughly the same material thickness as the sheet metal strips or sidebars  8  that are used within the heat exchanger blocks  10   a  and  10   b.    
     The heat exchanger block  10   b  that is to be joined to the heat exchanger block  10   a  is placed with its cover sheet  5  on the joining strips  11  of the heat exchanger block  10   a . In doing so, the heat exchanger block  10   b  is arranged exactly flush with the heat exchanger block  10   a . This is important for the following application of common headers to the two heat exchanger blocks   10   a  and  10   b.    
     Then, the joining strips  11  are welded to the heat exchanger block   10   b  along the edges of the cover sheet  5 . In this way, the two blocks  10   a  and   10   b  are securely joined to one another. The arrangement of two heat exchanger blocks  10   a  and  10   b  has a larger stack height than the individual heat exchanger blocks themselves, which thus exceeds the size and geometry of the brazing furnace. In this way, any number of heat exchanger blocks can be joined to one another into a heat exchanger block arrangement of any size with increased heat-exchange area. 
     Between the cover sheets  5  of the heat exchanger blocks  10   a  and   10   b  that have been welded to one another, an interspace  12  is formed that is then filled at this point with a metal foam  13 . The metal foam  13  is formed from aluminum or an aluminum alloy. 
     Various possibilities are listed below for the manner in which the metal foam can be introduced into the interspace  12 , which possibilities can be used individually or in a variety of combinations: 
     Injecting the liquid metal foam at one or more sites with an injection apparatus; 
     Spraying-in the liquid metal foam at one or more sites with a spraying apparatus; 
     Delivering one or more solid or liquid parent substances, for example in powder form into the interspace, that can form a metal foam when exceeding or falling below a certain pressure and/or a certain temperature; 
     Injecting or spraying-in the liquid metal foam at one or more sites and sucking out the liquid metal foam at one or more other, preferably opposing, sites. 
     In this embodiment, two spray apparatuses  16  are introduced into the interspace  12  from two opposing sides of the heat exchanger blocks  10   a  and  10   b  through openings  15  that remain open to the interspace  12  between the joining strips  11 . These apparatuses are gradually pulled out of the interspace in the direction of the arrow while the liquid metal foam is being sprayed-in. In this way, the liquid metal foam  13  is uniformly distributed in the interspace  12 . After the metal foam  13  hardens, the metal foam that has emerged from the interspace  12  via the openings  19  is removed from the heat exchanger block arrangement. 
     As can be seen from  FIG. 3 , the hardened or solidified metal foam  13  fills the entire interspace  12  between the opposing outside surfaces   14   a  and  14   b  of the two heat exchanger blocks  10   a  and  10   b . Thus, a flat joining is provided between the outside surfaces  14   a  and  14   b  of the opposing cover sheets  5 . The metal foam  13  forms a heat bridge, as a result of which thermally-conductive contact is formed between the opposing cover sheets  5  of the heat exchanger blocks  10   a  and  10   b . The thermally-conductive joining provides a thermally-conductive contact that extends over the entire cover sheet surface between the heat exchanger blocks  10   a  and  10   b . Temperature differences between the blocks  10   a  and  10   b  can thus be diminished, as a result of which temperature-induced stresses are reduced. 
     Moreover, the two heat exchanger blocks  10   a  and  10   b  are non-positively joined to one another in a blanket manner by the metal foam  13 , as a result of which the mechanical strength of the heat exchanger block joining is improved relative to a joining that in the past has existed only on the edge over the metal joining strips  11 . 
     In this embodiment, the two blocks  10   a  and  10   b  are welded to one another via four joining strips  11 . The number and arrangement of the joining strips  11  can differ from the embodiment that is shown in  FIGS. 2 and 3 . An almost peripherally-closed attachment of joining strips  11  is possible. To deliver the liquid metal foam or parent substances for its formation, it is, however, necessary that at least one opening  15  to the interspace  12  remains open. The joining strips  11  are generally required where common headers for the two blocks  10  a and  10  b are provided, as shown in  FIG. 4 , in order to ensure a fluid-tight seal of the headers to the interspace  12  in the joining region of the two blocks. 
     As shown in  FIG. 4 , after joining the two heat exchanger blocks   10   a  and  10   b , common headers  17 , separate headers  18   a  and  18   b , all with pipe connections  6 , are applied to the heat exchanger blocks  10  and  10   b  by welding. The latter are used to distribute or collect the fluids involved in the heat exchange. 
     Also, a plate heat exchanger, as shown in  FIG. 4 , which is finally already completed and which has possibly already been started up, can be retrofitted with a metal foam insert for joining the heat exchanger blocks  10   a  and  10   b . If there is no opening  15  to the interspace  12 , since, for example, the joining strips  11  form a peripherally closed frame (see  FIG. 3  shown in broken lines), it is possible to make one or more bores  19  (see  FIG. 3 ) in the joining strips  11 . Then, liquid metal foam or corresponding parent substances can be delivered into the interspace through these bores. The bores are then sealed fluid-tight again, if necessary, for example by welding. 
     Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. 
     The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 
     The entire disclosures of all applications, patents and publications, cited herein and of corresponding European patent application EP 13004272.4, filed Aug. 29, 2013, are incorporated by reference herein. 
     
       
         
           
               
             
               
                   
               
               
                 Reference Symbol List 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Heat-exchange passage 
                 1 
               
               
                   
                 Distributor fin 
                 2 
               
               
                   
                 lamella, fin 
                 3 
               
               
                   
                 Partition 
                 4 
               
               
                   
                 Cover sheet 
                 5 
               
               
                   
                 Pipe connection 
                 6 
               
               
                   
                 Collector, header 
                 7 
               
               
                   
                 Sidebar 
                 8 
               
               
                   
                 Inlet or outlet opening 
                 9 
               
               
                   
                 Heat exchanger block 
                 10, 10a, 10b 
               
               
                   
                 Joining strip 
                 11 
               
               
                   
                 Interspace 
                 12 
               
               
                   
                 Metal foam 
                 13 
               
               
                   
                 Outside surface 
                 14a, 14b 
               
               
                   
                 Opening to interspace 12 
                 15 
               
               
                   
                 Spray apparatus 
                 16 
               
               
                   
                 Common header 
                 17 
               
               
                   
                 Separate header 
                 18a, 18b 
               
               
                   
                 bore in joining strip 11 
                 19