Abstract:
A sealed plate heat exchanger includes a frame body with two frame plates and a plate stack between the frame plates. The plate stack is formed of a plurality of heat-exchange plates. Fluid channels allow feeding and leading away of heat exchange fluids that flow through the intermediate space between the heat-exchange plates. Devices for applying force to the frame plates, apply pressure to the plate stack. Seals are provided for sealing between the heat-exchange plates of the plate stack. A center of area of the area of the force application to the frame plate lies within an area that results from a linear projection of the area of the plate stack onto the frame plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation, under 35 U.S.C. §120, of copending international application No. PCT/EP2013/074819, filed Nov. 27, 2013, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application No. DE 10 2012 222 019.4, filed Nov. 30, 2012; the prior applications are herewith incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The present invention relates to a sealed plate heat exchanger comprising a frame body consisting of two frame plates, between which a plate stack of a plurality of heat exchange plates is arranged, means for feeding and discharging the heat exchange fluids that flow through the space between the heat exchange plates, and means for applying force to the frame plates, by way of which a pressure can be exerted on the plate stack. 
         [0003]    Plate heat exchangers contain a stack of heat exchange plates, between which heat transfer takes place. These plates are generally provided with a profile or with flow ducts and through-openings for the media. 
         [0004]    With plate heat exchangers, a basic distinction can be made between gasket-free and gasketed (sealed) designs. In the gasket-free configuration, the spaces between the plates are gasketed by the plates being rigidly connected, for example by welding, soldering or fusion technology. 
         [0005]    In the gasketed designs, gaskets, generally elastomer-based gaskets, are used to seal and separate the media chambers between the different plates. 
         [0006]    Depending on the media between which the heat exchange takes place, metals or metal alloys such as steel can be used as the material for the plates, or if the media are particularly corrosive, ceramic materials such as graphite or silicon carbide or fiber-reinforced ceramic materials can also be used. 
         [0007]    Owing to their high brittleness, graphite-containing or ceramic plate materials such as graphite or silicon carbide place particularly high demands on the seal between the individual plates. 
         [0008]    Such plate heat exchangers are generally produced in gasketed configurations owing to the brittleness of the graphite-containing or ceramic materials and to the fact that it is difficult to join these materials. 
         [0009]    Moreover, gasketed plate heat exchangers are advantageous in that it is easier than in gasket-free configurations to separate the plates for removal or cleaning or for replacing individual plates. 
         [0010]    In these plate heat exchangers in particular, a fluoropolymer, preferably based on polytetrafluoroethylene (PTFE), or graphite-based materials are generally used as the material for the gasket material. PTFE is highly ductile and only forms a low gasket thickness owing to its flow properties. As a result of this very low thickness of the gasket material, it is critical to ensure sufficient surface pressure on the gasket in order to achieve reliable sealing and to prevent leakages during operation. 
         [0011]    The surface pressure is generally brought about by arranging the plate stack of the heat exchanger between two frame plates, between which the plates are clamped with an adequate force. 
         [0012]    To apply the force for this clamping, tie rods are often used in combination with helical springs, which are arranged at a certain distance from the edge of the heat exchange plates. 
         [0013]    European patent application EP 0 203 213 A1 (commonly assigned) describes plate heat exchangers constructed from at least three parallel plate elements which are spaced apart from one another and made of a corrosion-resistant material, and from means for feeding and discharging the heat exchange fluids which flow through the space between the plates, the plate elements being produced from a graphite body bound to a fluoropolymer. 
         [0014]    German published patent application DE 10 2006 009 791 A1 describes a composite heat exchanger intended for use in the manufacture of chemical equipment and consisting of a metal frame body and a plate stack made of fiber-reinforced or monolithic ceramic, the stacked plates forming at least two duct systems which are arranged one above the other in any given number of layers in a manner separated by at least one plate and are delimited at opposite ends of the plate stack by cover plates which receive supply and outflow devices. In the regions surrounding the flow region and the through-openings for the media, the heat exchange plates comprise rectangular grooves in which sealing systems are arranged. 
         [0015]    The structural configuration of the pressure-bearing components in commercially available gasketed plate heat exchangers, in particular those comprising plates based on graphite-containing or ceramic materials such as graphite, silicon carbide or fiber-reinforced ceramic materials, is only suitable for larger models to a limited extent, because when the size of the structure is increased, specifically when the plate width and/or plate length is increased, the bending of the frame plates is increased in the regions that are critical for sealing the heat exchanger, and leakages can thus occur in the heat exchanger. 
       SUMMARY OF THE INVENTION 
       [0016]    It is accordingly an object of the invention to provide a plate heat exchanger in sealed configuration which overcomes the above-mentioned and other disadvantages of the heretofore-known devices and methods of this general type and which provides for a gasketed plate heat exchanger in which the above-mentioned problems are avoided or at least reduced. 
         [0017]    With the foregoing and other objects in view there is provided, in accordance with the invention, a gasketed plate heat exchanger, comprising: 
         [0018]    a frame body having two frame plates; 
         [0019]    a plate stack of a plurality of graphite-containing or ceramic heat exchange plates disposed between the two frame plates; 
         [0020]    means for feeding and discharging heat exchange fluids that flow through spaces formed between the heat exchange plates; 
         [0021]    seals disposed for sealing between the heat exchange plates of the plate stack; and 
         [0022]    force application devices configured to apply force to the frame plates of the frame body and for exerting pressure on the plate stack, wherein a centroid of a surface of at least one of the force application devices for applying force to the frame plate lies within an area produced from a linear projection of a surface area of the plate stack onto a corresponding the frame plate. 
         [0023]    In other words, the gasketed plate heat exchangers according to the invention comprise a frame body consisting of two frame plates, between which a plate stack of a plurality of heat exchange plates is arranged, and means for feeding and discharging the heat exchange fluids that flow through the space between the heat exchange plates, means for applying force to the frame plates, by means of which a pressure can be exerted on the plate stack, and means for sealing between the heat exchange plates of the plate stack. 
         [0024]    In contrast with the known heat exchangers of a similar construction, in the plate heat exchangers according to the invention at least one force application device is arranged such that the centroid of the surface for applying force to a frame plate is within the area produced from the linear projection of the surface area of the plate stack onto the corresponding frame plate. The term “centroid” is to be understood as the center of mass of the respective surface. 
         [0025]    In the known plate heat exchangers having a gasketed configuration, the force is applied to the frame plates in such a way that force is applied to the frame plates via connecting elements which interconnect the two frame plates outside the surface area of the heat exchange plates, and thus a pressure is also exerted on the plate stack of the heat exchange plates. Here, the centroid of the force application surface is outside the area produced from the linear projection of the surface area of the plate stack onto the corresponding frame plate. Depending on the design, this construction results in bending of the frame plates as a result of the applied force, which is most pronounced in the central part of the frame plates. The frame plates bend more the wider and/or longer the frame plates are, i.e. the problem is more severe in larger heat exchangers than in smaller devices. 
         [0026]    This bending leads to a sealing force or to a pressure on the gasket surface that is insufficient in the central region of the plate stack of the heat exchange plates to achieve perfect sealing in this region. Since the thickness of the gasket materials used is only very low, as mentioned above, this can result in mixing of the media between which heat is intended to be exchanged, and this leads to malfunction of the entire system and of all downstream units. 
         [0027]    Hitherto, the aforementioned problems have limited the maximum size of plate heat exchangers of this design having heat exchange plates which are based on graphite, silicon carbide or other ceramic materials and produced in a gasketed construction. 
         [0028]    The plate heat exchangers according to the present invention are distinguished in that at least one of the force application devices is arranged such that the centroid of the surface for applying force to a frame plate is within the area produced from the linear projection of the surface area of the plate stack onto the corresponding frame plate. 
         [0029]    In the context of the present invention, the centroid of the force application surface is to be understood as being the geometric center of gravity of the corresponding surface that corresponds mathematically to the average of all the points in the area. The geometric center of gravity corresponds to the center of mass of a physical body which consists of a homogenous material. In symmetrical figures, this center of gravity can be obtained by appropriate geometric considerations; in the case of asymmetrical surfaces, it can be obtained by integration. 
         [0030]    The center of gravity of a non-equilateral polygon can be calculated from the Cartesian coordinates of the corners; the center of gravity in regular polygons corresponds to the center of the circumcircle thereof. 
         [0031]    In rectangles, parallelograms or squares, the center of gravity is obtained, for example, from the point of intersection of the diagonals. In triangles, the geometric center of gravity is the common point of intersection of the three medians. In circular surfaces, the geometric center of gravity is the center of the circle. 
         [0032]    Therefore, when the shape of the force application surface is known, a person skilled in the art can determine the geometric center of gravity of the surface and design at least one force application device such that the geometric center of gravity of its force-applying surface is within the area produced from the linear projection of the surface area of the plate stack onto the corresponding frame plate. 
         [0033]    In the context of the present invention, the surface area of the plate stack is to be understood as the area defined by the main dimensions of the plate stack or of the individual heat exchange plates. This surface area includes any notches, drilled holes, etc. present in the plate stack or in the individual heat exchange plates, and differs in this respect from the surface area of the plate stack which is defined by the outer contour of the plate stack or of the heat exchange plates and thus does not include any notches or recesses that may be present. Plate heat exchangers according to the invention comprise at least one force application device designed as described above, although it is also possible and covered by the present invention to design a plurality of force application devices in this manner. 
         [0034]    Preferably, said force application device or said possible plurality of force application devices is/are arranged such that the force application surface is in the edge region of the surface area of the plate stack of the heat exchange plates, more preferably in the upper or lower region of the heat exchange plates, in which region the means for feeding and discharging the heat exchange fluids which flow through the space between the heat exchange plates are preferably also arranged. Good sealing is particularly essential in this region between the through-openings since this is where the heat exchange fluid flows are introduced into the plates, it being imperative to prevent said fluids from mixing or coming into contact with one another. 
         [0035]    In principle, it would also be possible to arrange force application devices at different points such that the center of gravity of the force application surface is arranged according to the invention. Generally, however, the result of this would be that the ducts provided in the plates, in which ducts the fluid media flow, would accordingly have to be designed such that they are not disrupted by the force application devices. In addition, arranging the force application devices in this way would require providing the heat exchange plates with holes or openings in the region of the ducts, which is generally not preferable. 
         [0036]    In general, therefore, it is more preferable to provide the force application devices such that none of the fluid-carrying ducts touch in the heat exchange plates of the plate stack. 
         [0037]    Suitable force application devices in the plate heat exchangers according to the present invention are known per se to a person skilled in the art and are described in the patent literature, and there is therefore no need to go into further detail here. A person skilled in the art will use a suitable force application devices according to the respective application 
         [0038]    According to one embodiment, the heat exchange plates can be provided with recesses or grooves, in which a sub-element, arranged between the frame plates, of a force application device is arranged. Said sub-element is guided through a hole or recess in the frame plates and end elements are connected to the sub-element such that a force can be exerted on the frame plate. Since the sub-element is arranged between the frame plates within the surface area of the heat exchange plates of the plate stack either completely or in part, the centroid of the force application surface of the corresponding means is within the area produced from the linear projection of the surface area of the plate stack or of the heat exchange plate onto the frame plate. 
         [0039]    In an embodiment of this type, tie bolts are preferred force application devices. Tie bolts are understood in this case to be a means which can absorb tensile stresses. Preferably, tie bolts consisting of round metal rods are used, said tie bolts extending between the frame plates and comprising, at the end, devices which can be used to clamp the two frame plates with a defined force by means of the tie bolt. The precise structural design is selected depending on the respective application on the basis of specialist knowledge. 
         [0040]    In the force application device, the centroid of the force application of which is within the area produced from the linear projection of the surface area of the plate stack or of the heat exchange plates onto the frame plate, the tie bolt arranged between the two frame plates is preferably positioned in a groove in the upper or lower side of the heat exchange plates, such that, in spite of the arrangement according to the invention of the force application devices, individual heat exchange plates can still be replaced without having to completely disassemble the plate heat exchanger. In principle, it is also possible for a blind hole to be provided in the upper region of the heat exchange plates, through which hole the tie bolt in guided. However, this then necessitates complete disassembly of the plate heat exchanger when replacing individual plates. 
         [0041]    The tie bolt can be guided through the frame plates in a groove in a similar manner as in the heat exchange plates, or a corresponding hole can also be provided in the frame plate. 
         [0042]    According to another embodiment of a plate heat exchanger according to the invention, the elements, arranged between the frame plates, of at least one force application device arranged according to the invention are designed such that they are located completely outside the surface area of the plate stack, or possibly even outside the surface area spanned by the frame plate. By means of an appropriate structural design, the force application onto the frame plate is designed according to the invention such that the requirement according to the invention is met. This can be achieved, for example, by the elements engaging around the frame plate in the manner of a clip and being attached to the frame plate such that the requirement according to the invention in terms of the centroid of the force application surface is met. Appropriate structural designs are known to a person skilled in the art, who will design a suitable means depending on the specific situation. 
         [0043]    According to a further embodiment, at least two force application devices are interconnected on the frame plate by means of a clip or the like. This clip can then additionally be connected to the frame plate, for example in the center thereof, so as to apply force, whereby the center of gravity of the force application surface also comes to rest as required according to the invention. 
         [0044]    According to a further, particularly preferable embodiment of the present invention, at least one of the frame plates comprises webs and/or ribs mounted thereon or rigidly connected thereto. Said webs or ribs further increase the stability and thus allow for use at even higher pressures. They can be produced from any material. Preferably, however, the webs and/or ribs are produced, in a similar manner as with the frame plates, from metals or metal alloys such as steel, or from plastics materials reinforced with fibers, in particularly carbon fibers, glass fibers or aramid fibers. 
         [0045]    A person skilled in the art can design variants of the above-mentioned embodiments on the basis of his expertise. It is essential that the centroid of the force application surface of at least one force application device is within the area produced from the linear projection of the surface area of the plate stack or of the heat exchange plates onto the frame plate. 
         [0046]    In structural terms, the connection dimensions of the means for feeding and discharging the fluid media and the type and shape of the force application devices create a minimum distance between the force application devices and the means for feeding and discharging fluid flows. 
         [0047]    The shape of the force application surface is not subject to any particular restriction, but is preferably substantially rectangular, elliptical, circular, or in the shape of a regular polygon. Here too, a person skilled in the art will select and use a suitable means, in line with structural specifications, according to the desired application. 
         [0048]    According to a preferred embodiment, the distance of the center of the force application device, the centroid of which is within the area produced from the linear projection of the surface area of the plate stack or of the heat exchange plates onto the frame plate, to the closest edge of the surface area of the stack of heat exchange plates is at least half the longest diagonal that can be formed in the force application surface. 
         [0049]    According to a further preferred embodiment, the force application surface of the means does not intersect with the surface area of the closest means for feeding and discharging the fluid media. 
         [0050]    Through-openings which are not restricted in any particular way in terms of cross section and which can be substantially circular, elliptical, rectangular, or in the shape of a polygon are preferably used as feeding and discharging means. The shape of the feeding and discharging means is not critical for the desired effect of improved sealing. 
         [0051]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0052]    Although the invention is illustrated and described herein as embodied in a plate heat exchanger having sealed construction, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0053]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0054]      FIG. 1  is a side view of a plate heat exchanger according to the invention; 
           [0055]      FIG. 2  is a view of the region of a heat exchanger plate, in which it is possible to see the means for feeding and discharging the fluid media and the course of the sealing means provided between the plates; 
           [0056]      FIG. 3  is a front view of the end face of a frame plate of a plate heat exchanger in which three force application devices are arranged according to the prior art; and 
           [0057]      FIG. 4  is a corresponding view of a preferred variant of a plate heat exchanger according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0058]    Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown a plate heat exchanger  1  according to the invention comprising a frame body  2  consisting of two frame plates  3 . A plate stack of heat exchange plates  4  is arranged between the frame plates  3 . A force application device  7  is also shown. 
         [0059]      FIG. 2  shows the contours of a heat exchange plate  5  of a plate stack  4  (not shown) comprising means  6  for feeding and discharging fluid media and a sealing means  8 . It can be seen that the sealing means  8  separates the feeding means and discharging means  6  from one another in a sealed manner. 
         [0060]      FIG. 3  shows the contours of a frame plate  3  and a heat exchange plate  5  and two means  6  for feeding and discharging fluid media, and three force application means or force application devices  7  denoted by way of black circles. It can be seen how the center of gravity of the force application surface in all the force application devices is outside the area produced by a linear projection of the surface area of the heat exchange plate  5  onto the frame plate  3 . 
         [0061]      FIG. 4  shows the contours of a frame plate  3  and of a heat exchange plate  5 , means  6  for feeding and discharging fluid media, and a plurality of force application devices  7 . It can be seen how one force application device  7  (the one in the center of the upper row) is arranged such that the centroid of the force application surface thereof is completely within the area produced from the linear projection of the surface area of the heat exchange plate  5  or of the plate stack  4  (not shown) onto the frame plate  3 .  FIG. 4  also shows a plate width B and a plate length L. 
         [0062]    The material of the heat exchange plates  5  in the plate heat exchangers according to the invention can be selected by a person skilled in the art from the materials which are known for this purpose and described in the prior art. The advantages of the design according to the invention are particularly effective when the plates are made from a graphite body impregnated with a polymer, a graphite body bound to a polymer, or from silicon carbide or a composite fiber ceramic. 
         [0063]    Preferred graphite-based materials preferably contain at least 50, more preferably at least 55 wt. % graphite. 
         [0064]    Suitable materials as a graphite base in the form of polymer-bound graphite bodies can be obtained under the brand name Diabon® F, and graphite bodies impregnated with polymers, in particular with phenol resins, are commercially available under the brand name Diabon® NS, both from the company SGL Carbon of Wiesbaden, Germany. 
         [0065]    Owing to the brittleness and material properties of all these materials, it is advantageous or necessary to design a plate heat exchanger which is to be built based on said materials in a gasketed construction, and the advantages of the present invention come into effect. 
         [0066]    The advantages of the above materials are based on their extraordinarily high corrosion resistance and temperature resistance, for which reason plate heat exchangers made of such materials can be advantageously used in particular when corrosive media or high temperatures are used. 
         [0067]    The frame plates  3  of the plate heat exchangers  1  according to the invention have to absorb significant forces owing to the clamping from the force application devices  7 , and therefore have to be structured to have corresponding levels of stability. Here too, a person skilled in the art will base their selection of the suitable material on the specific application of the plate heat exchanger  1 . On a merely representative basis, suitable materials for frame plates of the frame body  2  in this case are metals or metal alloys such as steel, or plastics materials reinforced with fibers, in particular carbon fibers, glass fibers or aramid fibers. It is primarily important in any case that the frame plates  3  can absorb the active forces such that the bending does not exceed certain limit values. 
         [0068]    In any case, it is extremely important that the maximum bending generally reached in the center of the frame plate  3  is kept lower than the thickness of the sealing material used, otherwise leakages occur. 
         [0069]    Since the materials used for sealing generally have a thickness of no more than 0.3 mm, preferably no more than 0.15 mm, the maximum bending of the frame plates  3  should also be below 0.3 mm, more preferably below 0.15 mm, to reliably ensure the leak-tightness of the plate heat exchanger  1 . 
         [0070]    Any sealing material that has the appropriate corrosion-resistance for the desired use and guarantees durable sealing under operating conditions can be used as seals  8 . Preferred materials for the seals  8  are in particular fluorine-based polymers or graphite-based materials. Preferred fluoropolymers are polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF). Appropriate materials are known to a person skilled in the art and are commercially available from many vendors. 
         [0071]    According to a preferred embodiment, the gaskets used to achieve reliable sealing between each two heat exchange plates  5  can be designed as flat gaskets and inserted into peripheral grooves having a rectangular cross section. In this case, the thickness of the flat gaskets is selected such that said gaskets protrude out of the grooves and the leak-tightness is thus produced when the heat exchange plate stack  5  is clamped. 
         [0072]    In principle, however, it is also possible to design the sealing means  8  as a sealing cord which can be placed in a simple manner between the heat exchange plates and guided through the force application to form a reliable seal. 
         [0073]    The plate heat exchangers  1  according to the invention can be produced having larger plate widths B and/or plate lengths L than was possible hitherto in such products. Since the bending when force is applied via the corresponding clamps  7  increases as the plate width B and/or plate length L increases, until now plate heat exchangers having a gasketed construction and heat exchange plates based on graphite, silicon carbide or other ceramic or fiber-reinforced materials could only be produced having a limited size, which was determined on the basis that the maximum bending of the frame plates  3  was not permitted to exceed the above-mentioned values. By increasing the thickness of the frame plates  3  or increasing the rigidity of the materials, it is possible to obtain some improvement in this respect. Nevertheless, with the plate heat exchangers  1  according to the present invention, larger plate widths B and/or plate lengths L can be achieved in any case while using the same material, since the maximum bending can be considerably reduced owing to the arrangement, according to the invention, of at least one force application device  7 . 
         [0074]    Tests have shown that the plate width B and/or plate length L can be increased by at least 20-30% without having to anticipate a higher degree of bending than in the plate heat exchangers of the same design according to the prior art. Therefore, under constant process conditions (pressure, temperature), a corresponding increase in the heat exchanger capacity can be achieved. 
         [0075]    A further advantage of the plate heat exchangers  1  according to the invention is that the larger plate width B and/or plate length L allows the required footprint of the plate heat exchangers  1  to be considerably reduced for a desired heat exchange capacity, which is particularly advantageous in existing systems, of which the capacity is intended to be increased. These configurations often do not offer the possibility of providing a correspondingly larger footprint for increasing the heat exchanger capacity. 
         [0076]    Overall, the plate heat exchangers  1  according to the present invention can therefore achieve heat exchanger capacities which, in relation to the required footprint for installing the corresponding heat exchanger, cannot be achieved by the heat exchangers of the same design according to the prior art. 
         [0077]    The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 
         [0078]      1  plate heat exchanger 
         [0079]      2  frame body comprising two frame plates 
         [0080]      3  frame plate 
         [0081]      4  plate stack consisting of heat exchange plates 
         [0082]      5  heat exchange plate 
         [0083]      6  means for feeding and discharging fluid media 
         [0084]      6   a  through-openings 
         [0085]      7  force application device, force application means 
         [0086]      8  seal, sealing means 
         [0087]      9  recess or groove for receiving a sub-element 
         [0088]      10   a  webs 
         [0089]      10   b  ribs 
         [0090]    B plate width 
         [0091]    L plate length