Abstract:
The heat exchanger according to the invention consists of two flat or slightly incurved parallel surfaces formed in two sheets of metal ( 2 ) and ( 3 ). The longitudinal edge pieces ( 8 ) and ( 9 ) and transverse edge pieces ( 12 ) and ( 13 ) have rounded edges. The entire exterior surface is coated with enamel. These exchangers may be used in groups of several parallel units arranged inside a tubular body, or they may be disposed in a radiating pattern inside a cylindrical tank in a chemical reactor, forming a complex exchanger. This invention is of interest to manufacturers of industrial heat exchangers, particularly exchangers designed for the chemcial, pharmaceutical or agricultural/food industries.

Description:
The invention concerns a flat, enameled, pouch-shaped heat exchanger that is useful for many purposes, especially processes involving strong chemicals such as those used in the chemical and pharmaceutical industries. 
     BACKGROUND OF THE INVENTION 
     Plate-type, enameled heat exchangers consist of a series of superimposed plates each defining a flat space, through which streams of two liquids of different temperatures flow alternately from one space to the next. 
     Heat exchangers such as this are described in Patent No. EP No. 0566208 filed by ABB LUMMUS HEAT TRANSFER BV and No. EP 0522360 filed by ROTHEMUHLE BRANDT KRITZLER. 
     The first invention consists of a block comprising a stack of enameled plates separated from one another by cross pieces, which may be formed in the elements that constitute a set of braces. The plates are enameled first and then joined at the edges or sealed along the perimeters. 
     The second invention consists of a stack of metal plates or sheets that are alternately flat and undulating. The wavy shape of the undulating metal pieces defines flat, adjacent channels between two successive pieces of metal providing passageways for fluids of different temperatures. 
     These exchangers are designed primarily for thermal exchange between two gaseous fluids. Their enamel coating provides increased corrosion resistance when potent condensing agents are used. 
     The condensing agents in these exchangers are neither massive in volume nor highly potent, and for this reason, the exchangers do not require the same degree of protection as those used in the chemical and pharmaceutical industries. 
     Heat exchangers currently used in the chemical and pharmaceutical industries and therefore subjected to strong chemicals typically consist of bundles of enameled tubes. Chemical exchangers of this type have been described in Patent Nos. FR 2392349 in the name of PFAUDLER and EP No. 0203288 in the name of TYCON Spa. The enameled tubes are either soldered or banded together onto terminal plates. They are also attached to these plates with a gasket seal. The tubes are either coated with enamel before attachment or coated together after attachment to the terminal plates. In the first instance, one seal is required for each tube, which increases the risk of leakage in proportion to the number of seals used. 
     In the second instance, coating the joined tubes afterwards is complicated by the large number of tubes that must be coated simultaneously. 
     Heat exchangers with flat elements to contain the fluid are particularly useful because they have a large heat exchange surface, but only one inlet and one outlet. 
     In addition, a thin, pouch-like shape provides very effective, rapid heat exchange. 
     Flat elements serving as heat exchangers are made primarily of metal, like a flat radiator. The metal pieces are bent to form a flat half-shell. Then two half-shells are joined at their peripheral edges, generally by electrical soldering, forming a thin longitudinal ridge. 
     A disadvantage shared by all these exchangers is that there are seams and assembly areas which also must be coated with enamel. For example, not only are there connections between the plate edges and the supporting structure, but there are also seals between the tube extremities and the flanges. 
     Coating these areas is problematic because of the raised portions and the mechanical properties of the surfaces. Moreover, flat exchangers have multiple connecting points on their lateral surfaces where two plates are joined. This uneven surface is not conducive to applying a regular coat of enamel. On the contrary, there is a considerable risk that a flawed, discontinuous surface will be produced, causing weak points in the enamel which will be quickly attacked in a corrosive environment, thus causing leaks. These difficulties require operators to take many precautions and to be constantly on the lookout for leaky areas. 
     In addition, larger dimension flat heat exchangers have multiple connection points on their lateral surfaces designed to ensure consistent spacing between the two pieces of metal and to make the entire unit mechanically rigid. 
     Enameling these areas requires considerable skill and care, and thus, if the exchangers are being mass produced, there is a high risk that the coating will be defective in this area. Only certain carefully selected workers possess the necessary skill and will take the care required, and thus, it is apparent that the enamel coating process increases product cost considerably. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to enamel-coat flat metal exchangers and render them resistant to chemical products, thereby opening up a vast field of industrial applications, especially in the fields of chemistry and pharmaceuticals. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and features of the invention will be apparent from the following description, given by way of example, and accompanied by the drawings, in which: 
     FIGS. 1,  2 ,  3 : perspectives of three variations of unitary enameled exchangers according to the invention, respectively: 
     a single compartment exchanger with an inlet/outlet connection at each of its extremities, 
     a double, parallel compartment exchanger with a common outlet at each of its extremities, and 
     a double, parallel compartment exchanger with distinct individual outlets on the same side; 
     FIG.  4 : a schematic perspective of a parallel grouping of several unitary exchangers incorporated in a tubular envelope forming a tubular exchanger with a broad exchange surface; 
     FIGS.  5  and  6 : schematic transverse cross-sections of two possible dispositions of a tubular exchanger occupied by flat unitary exchangers in parallel arrangement, of identical size or increasing in size from the extremities to the center, respectively; 
     FIG.  7 : a schematic transverse cross-section showing an example of a support for the body of elementary enameled exchangers; 
     FIG.  8 : a plan view showing a star-shaped arrangement inside a vertical cylindrical container, which could be used with a chemical reactor; 
     FIG.  9 : a schematic perspective of a tubular body exchanger containing flat exchangers according to the invention and showing the extremities of the hydraulic connectors; 
     FIG.  10 : a longitudinal cross-section of the extremity of the hydraulic connectors; 
     FIG.  11 : an enlarged cross-section of a passageway through the sealing plate of the extremity of the hydraulic connectors; 
     FIG.  12 : a schematic cross-section of a tubular body exchanger with baffle plates enclosing a plurality of flat exchangers, of flattened cross section, supported by said baffle plates; 
     FIGS.  13  and  14 : elevations of one example of a baffle plate without and with the exchangers, respectively; 
     FIG.  15 : a plan view of flat overlapping exchangers asymmetrically arranged, with the lateral extremities of each exchanger varying in section; 
     FIGS.  16  through  18 : schematic vertical cross-sections with enlargements of the lower supporting extremity in the first two drawings, showing the use of unitary exchangers in a vertical cylindrical container, for example, when used in a chemical reactor; and 
     FIGS.  19  through  24 : successive mixed cross-sections with an extended perspective of various forms of flat unitary exchangers that fall within the scope of the present invention. 
     FIG.  25 : a mixed cross-section with an extended perspective showing an example of flat unitary exchanger, similar to the embodiment of FIG. 19, whose edge piece is covered with a rounded reinforcing piece, which is, in this case, a slit tube member. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1,  2 , and  3  show unitary exchangers, slightly incurved, of the type which are the subject of the invention. 
     These are metal exchangers, and have all the technical characteristics necessary for successful application of an enamel coating which will provide a durable seal, resistant to even potent chemicals. 
     First, unitary exchangers will be described, before proceeding to a description of how groupings of exchangers are used in specific applications. 
     Each exchanger has a generally flat metal body  1 , with a slightly incurved or planar transverse section and with a lateral surface formed of two sheets of metal, a front sheet  2  and a rear sheet  3 , spaced apart by cross pieces or interior indentations  4  stamped into the metal and defining a completely open interior space  5  or interior compartments or channels  6  between one or more interior divisions (FIGS.  19  through  24 ). 
     According to a preferred embodiment, the walls defining interior space  5  are joined at connection points or weld zones  7 , for example, using an electrical or laser welding, or some other form of connection, as shown in FIGS. 19 through 24. 
     These embodiments endow the heat exchanger with excellent mechanical qualities. It is important to pay particular attention to the connecting points or areas  7  during preparation and enameling to ensure a continuous coating and reliable sealing. 
     Longitudinal edge pieces  8  and  9  protrude somewhat or may be capped with rounded reinforcing elements  9   a,  for example, tubular sections  10  which either engage the edge pieces by locking onto them, as shown in the drawings, or which may even replace the edge pieces. Also, some other means may be used to achieve rounded, raised edges. In a preferred embodiment, shown in FIG. 25, a tube  10   a  is slit longitudinally and the tube is threaded onto the open edge piece  11  through the slit  11   a  and then connected to it. 
     Naturally, it is also possible to use semi-circular shapes slightly flattened on the sides, or any other similar shape. 
     Transverse edge pieces  12  and  13  are covered in the same way with a curved tubular piece or a flat piece with a rounded section, resulting in a raised shape that is easy to enamel, as it is larger and more rounded than the longitudinal edge pieces. 
     It is preferable for the transition between the rounded areas and the adjacent flat surface to be as gradual as possible, eliminating any narrow grooves or channels that would be difficult to coat. 
     The transverse edge pieces have near their median portion in the extension of the surface of the exchanger one or more tubular protrusions or stump-like portions  14  serving as an inlet and/or outlet, and inlet and/or outlet tubes or conduits for the liquid flowing through the exchanger are either integral with or connected to said protrusions. There may be either two distinct elements  15  and  16  located at each end of the exchanger or at a distance from each other on the same transverse extremity (FIGS. 1 and 3, respectively), or a single coaxial element  17  accepting two concentric conduits, an intake conduit  18  and an out take conduit  19  (FIG.  2 ). In both examples shown in FIGS. 2 and 3, the interior space is divided into two longitudinal compartments  20  and  21  by a longitudinal median interior partition  22  and open at the extremity. In the variations with a closed extremity there is a longitudinal median immobilizing bracket  23 . 
     The shapes and surfaces created in this way have no thin, linear ridges extending beyond or below the surface. They have no protrusions or concave areas, nor any raised or small, slightly curved hollow areas with complicated shapes that would be difficult to coat. 
     This regular formation with rounded shapes and no pronounced raised areas provides the best surface for applying a uniform coating of enamel and ensures that the coating will remain durable over time. 
     Additional mechanical resistance or improved heat transmission can be obtained through the use of an enamel with a specialized composition. 
     The exchangers may be associated or assembled in different groups where they are arranged parallel to one another. They may also be grouped inside some type of container or tank. 
     One interesting application is shown in FIGS. 4 through 15, where the exchangers are arranged in parallel inside an enameled tubular container defined by a cylindrical tubular envelope  24  along which the exchange fluid flows, for example, a corrosive fluid which must be heated or cooled by circulating a heat-conveying fluid through the exchangers. 
     The unit formed by the parallel arrangement of exchangers  1  may be placed on transverse supports  25 , in a Teflon cradle either supporting or forming a rack  26  with receptor slits  27  forming parallel housings, as shown in FIGS. 7 and 12 through  14 . Preferably there are at least two racks, a lower rack  28  and an upper rack  29  designed to keep the unitary exchangers parallel to each other inside tubular container  24 . This unit of two rack supports  28  and  29  may repeated some distance away. 
     FIGS. 12 through 14 show an interesting variation. 
     There is an exchanger with a tubular body  24  surrounding baffle plates  30  formed of transverse support racks  28  and  29 , which may be approximately the same height as the radius of tubular body  24 . These transverse supports  28  and  29  are located in several places so as to constitute several baffle plates  30  running the entire length of the exchanger between the corrosive fluid inlet  31  and outlet  32  (FIG.  12 ). 
     It is advantageous for transverse supports  28  and  29  forming baffle elements  30  to fulfill a second function. As described above, they are equipped with parallel receptor slits  27  which support the exchangers inside tubular body  24  and maintain them in a parallel arrangement. 
     In this variation, the exchangers are intentionally flat, although it is possible for them to be slightly curved. 
     To improve the coefficient of volume of tubular body  24 , which is proportionate to the performance of the exchanger, flat asymmetrical exchangers  33  are used, such as those shown in FIG. 15, for example. These exchangers have an inlet/outlet element on the same extremity. The body of these exchangers differs from the other embodiments in that the transverse edge pieces on the two extremities are not identical. Rounded transverse edge piece  34  on the closed extremity, that is, the sealed extremity, has a smaller diameter than that of rounded edge piece  35  on the opposite extremity comprising the inlet and/or outlet portions. This configuration allows compact groups  36  to be formed by staggering the position of two adjacent exchangers and thus tightly compacting two successive exchangers with minimal space between them. This will result in improved performance by tubular exchanger  24 . 
     One example of a passage through an end wall  37  of the tubular exchanger  24  is shown in FIGS. 10 and 11. 
     This passage may take place by direct contact between the interior enamel layer  38  of tubular body  24  with an exterior layer  39  protecting the inlet and outlet elements. A sealing material  40  is forced into a conical housing  41  using a pressure element such as a screw  42  attached to threaded extremity  43 . 
     Another application concerns the use of at least one enameled exchanger inside the tank of a mixer or a reactor  44 , particularly in a tank or a reservoir where a controlled chemical reaction takes place. The exchanger can absorb and then evacuate excess calories or even contribute the calories required to begin the reaction process, and then evacuate the excess calories when the reaction is produced. 
     The preferred embodiment will consist of a plurality of incurved exchangers  45  arranged around a central agitator  46  whose central shaft  47  holds one or more rotors  48  equipped with blades  49 , as shown in FIGS. 16 through 18. This complex exchanger  50  consists of a unit of elementary incurved exchangers such as those described above, in vertical arrangement, and radially disposed inside a cylindrical container. This unit is preferably static and when viewed from above, it resembles a turbine rotor, with exchangers  45  arching slightly to form the blades. 
     Exchangers  45  are mounted inside the tank forming the reservoir or chemical reactor using different techniques, as shown in FIGS. 16 through 18. 
     First, there are exchangers with an inlet/outlet in the form of a coaxial tubular portion  17  extending upward into an extension  51  passing through the tank of reactor  44  at the upper portion through passageways  52  in tubes arranged around the central upper opening  53  (FIGS.  16  and  17 ). The exchangers are mechanically immobilized at their lower extension  23  so their body remains parallel to the longitudinal axis of the tank and especially to permit expansion and compensate for the force of agitation. They may be attached by an immobilizing extension piece  54  whose extremity lodges in a receptor  55  made of chemically resistant synthetic plastic material (FIG.  16 ). Receptor  55  may consist of stopper  56 , which may or may not be movable, and which receives the end of the immobilizing extension  54 , as shown in detail in the drawings. According to the variation shown in FIG. 17, these stopper elements  56  are made of chemically resistant synthetic material recessed within the openings of a crown  57  transversely positioned in relation to the tank defining a central opening  58 . Naturally, other embodiments are possible. 
     Yet another embodiment consists of providing on each exchanger a lower opening  59  through a transverse end conduit  60  which simultaneously forms the lower mechanically immobilizing support as shown in FIG.  18 . Note in this drawing that the inlet consists of a reinforcing element  61  on the lower edge piece of the exchanger and that the exchanger opens onto a lower lateral flange  62  which serves as an interface with the coolant fluid circulation network in each exchanger. 
     The transverse shapes of the exchangers may vary, as shown in FIGS. 19 through 24. These drawings show an interior space  5  defined by two pieces of metal  2  and  3  which are connected at points by local solder-connection zones  7 . Note also that transverse edge piece  12  and longitudinal edge piece  9  have a rounded, tubular shape that is easily coated with enamel.