ES2896068T3 - Composite material plates forming a heat exchanger - Google Patents

Abstract

Plate heat exchanger (1) for fluid circulation, comprising: - plates (3) for fluid circulation, - a holding frame (2) for the plates (3) suitable for compressing the plates (3) , the frame (2) and the plates (3) being connected two by two in a sealed manner, characterized in that the plate heat exchanger (1) comprises at least one metal mesh plate (3) comprising: - at least a metal mesh sheet (31), and - a coating (32) of thermosetting or thermoplastic resin that covers at least one face of the metal mesh sheet (31).

Description

DESCRIPTION

Composite material plates forming a heat exchanger

The present invention relates to the field of heat exchangers and, more particularly, to plate heat exchangers.

A heat exchanger is a device that allows thermal energy to be transferred, through an exchange surface, from a first fluid at temperature T1 to a second fluid at temperature T2 (T2 being less than T1). In this way a heat flow is created without mixing the two fluids.

The plates are stacked and compressed in a frame made up of two ends. Each plate comprises corrugations (undulations) that will generate turbulence in the flow of fluids that will be heated or cooled. Fluids circulate in the free space between the plates. Gaskets are installed between the plates to ensure tightness between the circuit called “service circuit” (the service fluid is generally water, steam or oil) and the circuit called “procedure circuit” (sometimes the procedural fluid is a corrosive fluid). Energy is exchanged between the service side and the process side through the thickness of the plate. When the plates are made of metal, they can be welded together without requiring the positioning of sealing gaskets on their contact surface, which allows resorting to higher temperatures and pressures of use. However, at the same time it is no longer possible to separate the plates for usual operations such as cleaning operations.

Conventionally, these plates are made from different metallic, plastic or ceramic materials. When they are metallic, these plates are made by drawing. The great flexibility of these materials allows numerous configurations and small thicknesses. These plates are very efficient in terms of heat exchange. However, such plates are not suitable for applications requiring corrosion resistance.

For such applications, metal alloys, noble metals, resin-impregnated graphite, silicon carbide, or plastic materials can be used. However, a drawback of such plates is the very significant cost of the metals used to make them. Furthermore, for certain applications involving particular corrosion resistance, such as resistance to corrosion by chlorides or fluorides, some of the mentioned metals cannot be used as they are ineffective.

Impregnated graphites, which comprise a mixture of carbon and graphite carbon, and silicon carbide are metals that are relatively resistant to the high temperatures and corrosion mentioned. They also have good thermal conductivity (up to 105 W/m.K in a radial propagation direction). However, the machining operations, specifically aimed at making the corrugations, are difficult to carry out due to the brittleness of graphite and the very high hardness of silicon carbide. Consequently, the cost of machining is very important and the production rates are low. In addition, the configuration of the corrugations and the significant thickness of the plates for this type of particular application, which can reach up to 10 mm, do not allow heat exchange as high as that of metal plates. In conclusion, the thermal conductivity of these plate heat exchangers is not optimized with respect to heat exchangers provided with metallic plates. On the other hand, the cost of graphite is very high compared to classical metals. DE-A-102010015212 discloses a plate heat exchanger having coated metal heat exchanger plates.

The invention aims to remedy these drawbacks by providing a plate heat exchanger for the circulation of fluids comprising plates for the circulation of fluids and a frame for holding the plates suitable for compressing the plates, the frame and the plates being connected in such a way. two by two in a sealed manner, characterized in that the plate heat exchanger comprises at least one metal mesh plate, comprising at least one metal mesh sheet, and a coating of thermosetting or thermoplastic resin that covers at least one face of the metal mesh sheet.

According to the invention, "connected two by two" means the fact that two elements are connected to each other. Therefore, the fact that the frame and the plates are connected two by two means both that each end of the frame is connected to the neighboring plate and that two neighboring plates are connected to each other.

In this way, a plate exchanger is obtained with a mechanical resistance superior to that of an exchanger consisting solely of graphite, ceramic or plastic plates. The plate or plates comprising at least one sheet of metal mesh and a coating of thermosetting or thermoplastic resin of the exchanger are suitable for withstanding several thermal cycles without being damaged, they are watertight and resistant to erosion and numerous types of corrosion, including corrosion by chlorides or fluorides. Indeed, the use of a metal mesh favors the fixing of the coating on the metal. This good coupling of the resin coating on the metal gives the plate better resistance to erosion and a longer useful life compared to a conventional metal plate.

The plate heat exchanger according to the invention also has advantageous thermal conductivity properties.

The plate heat exchanger according to the invention may further comprise one or more of the following features, taken alone or in combination:

- the metal mesh plate is formed by drawing the metal mesh sheet, preferably by drawing several sheets of metal mesh welded together, for example by five sheets of metal mesh welded together;

- the metal mesh plate has a thickness of at least 0.8 mm, preferably the thickness is 1.5 mm; - the porosity of the plate can be equal to 10% by volume in the thickness of the plate, ideally 20%. The size of the pores can be a minimum of 25 microns and a maximum of 2 millimeters;

- the specific surface of the plate can be between 5 m2/m2 and 250 m2/m2 (internal surface in the thickness of the plate with respect to the surface of the plate), preferably 15 m2/m2 for plates associated with thermosetting resin, for example phenolic resin, and 80 m2/m2 for plates associated with thermoplastic resin, such as, for example, polyvinylidene fluoride (PVDF) resin;

- the metal mesh plate comprises mesh with a length of 0.05 mm to 5 mm. When the metal mesh plate comprises several sheets of metal mesh, the length of the meshes can vary from one sheet to another, for example the length of the meshes can decrease in the thickness of the plate;

- the tightness is preferably obtained with the aid of a joint and/or a weld between the plates or between the frame and at least one of the plates;

- the metal mesh sheet is made of carbon steel or any other material of a nature that resists corrosion, for example stainless steel, zirconium, titanium or nickel alloy;

- the thermosetting or thermoplastic resin coating is obtained by coating the metal mesh sheet with thermosetting or thermoplastic resin, or by impregnating the metal mesh sheet with thermosetting or thermoplastic resin;

- the thermosetting or thermoplastic resin coating completely covers the metal mesh sheet; - the frame has an internal face, located opposite the plates, and an external face that receives connections for the circulation of fluids; The frame includes an anti-corrosion coating that continuously covers the connections and the internal face of the frame. In this case, "continuously" means without leaving any passage for a fluid;

- the anti-corrosion coating of the frame is a thermosetting or thermoplastic resin coating;

- the frame comprises a metal mesh sheet that covers at least partially the internal face and the anti-corrosion coating covers the metal mesh sheet of the frame;

- the metal mesh sheet of the frame is made of carbon steel or any other material of a nature that resists corrosion, for example stainless steel, zirconium, titanium or nickel alloy; - the metal mesh sheet of the frame comprises meshes with a length of 0.05 mm to 5 mm. When the frame comprises several sheets of metal mesh, the length of the meshes can vary from one sheet to another; - the metal mesh sheet of the metal mesh plate and the metal mesh sheet of the frame are welded together along an area devoid of thermosetting or thermoplastic resin coating, said area is surrounded by thermosetting or thermoplastic resin coating in such a way that it is isolated from at least one of the fluids, in such a way that the tightness between the two fluids is guaranteed;

- the plates form corrugations arranged to generate turbulence during fluid flow;

- the corrugations are formed by a single face of the metal mesh plate. The plates may be arranged such that the face of a first plate that forms the corrugations is in sealing contact with the substantially flat face of a second plate. In this way, the contact between two plates extends over a larger area than that of a corrugation-corrugation contact in the case where the corrugations are present on both faces of the metal mesh plate. The increase in the contact area between the plates reduces the friction rate of the lining and, therefore, increases its useful life;

- the corrugations are formed by the two faces of the metal mesh plate, the plates being arranged in such a way that the contact between two adjacent plates is made outside of a vertex protruding from a corrugation. In other words, two adjacent plates are guaranteed to have a contact surface important enough to reduce frictional forces;

- the plates each comprise a gasket seat and at least one gasket is arranged on the gasket seats of two neighboring plates, in order to guarantee sealing when stacking the two neighboring plates;

- several gaskets are arranged, each one, on the gasket seats of two neighboring plates and the corrugations have a less important height on the periphery of the gaskets so as to allow a uniform compression of the gaskets;

- the thermosetting or thermoplastic resin of at least one of the thermosetting or thermoplastic resin coatings comprises powder filled with silicon carbide, graphite, quartz, carbon or a mixture of these fillers;

- the frame further comprises a second sheet of metal mesh arranged on a second internal face, located opposite the plates.

The invention also has as its object a process for manufacturing a plate heat exchanger comprising the following steps:

- covering at least partially the internal face, located opposite the plates, of a holding frame for the plates, for a metal mesh sheet,

- welding together the metal mesh sheet of the frame and metal mesh sheets of metal mesh plates located opposite each other, along an area devoid of thermosetting or thermoplastic resin coating, the area being surrounded by resin coating thermosetting or thermoplastic so that it is isolated from at least one of the fluids.

The process for manufacturing a plate heat exchanger according to the invention may also comprise steps in which:

- several sheets of metal mesh are superimposed and/or welded together before being drawn to form the corrugations of a metal mesh plate;

- at least one metal mesh plate is made by sintering metal powder;

- the thermosetting or thermoplastic resin coating includes, at the contact points between two plates, a load or a hard element that makes it possible to prevent wear due to friction of the plates during cycles of pressurization, decompression and thermal expansion movement.

Brief description of the figures

The invention will be better understood after reading the attached figures, which are provided by way of examples and do not present any limiting character, in which:

[figure 1] figure 1 is a perspective view of a plate heat exchanger according to an embodiment of the invention,

[figure 2] figure 2 is a longitudinal section view according to A-A, taken in figure 6, of the plate heat exchanger of figure 1,

[figure 3] figure 3 is a cross-sectional view according to B-B, taken in figure 6, of the plate heat exchanger of figure 1,

[figure 4] figure 4 is a sectional view, analogous to figure 3, of two adjacent plates that allow the passage of the corrosive fluid,

[figure 5] figure 5 is a sectional view, analogous to figure 3, of a configuration of the plates on the edge of an exchanger according to a particular embodiment of the invention,

[figure 6] figure 6 is a front view of a plate on the procedure side,

[figure 7] figure 7 is a front view of a plate on the service side,

[figure 8] figure 8 is a longitudinal sectional view of a plate heat exchanger according to an embodiment illustrating the passage of the corrosive fluid, and

[ Figure 9 ] Figure 9 is a sectional view of a plate heat exchanger according to an embodiment illustrating the passage of the service fluid.

Detailed description

In the following description, the expressions "heat exchanger" and "plate heat exchanger" are used interchangeably, which are synonymous when designating one of the objects of the invention.

The heat exchanger 1 comprises:

- 3 plates for fluid circulation,

- a holding frame 2 for the plates 3, suitable for compressing the plates 3. The frame 2 and the plates 3 are connected two by two in a sealed manner. The heat exchanger 1 comprises at least one metal mesh plate 3 comprising:

- at least one sheet of metal mesh 31, and

- a coating 32 of thermosetting or thermoplastic resin that covers at least one face of the metal mesh sheet 31.

The metal mesh sheet 31 can be made of carbon steel or any other material of a nature that resists corrosion, for example stainless steel, zirconium, titanium or nickel alloy. The coating 32 of thermosetting or thermoplastic resin may comprise powder filled with silicon carbide, graphite, quartz, carbon or a mixture of these fillers. This type of resin improves the resistance to erosion and corrosion of the plates and allows good thermal conductivity.

It is also possible to use plastic materials such as, for example, polypropylene (PP), perfluoroalkoxy (PFA), ethylene-chlorotrifluoroethylene (ECTFE), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene (ETFE), fluorinated ethylenepropylene (FEP ) or polyethylene (PE).

The support frame 2 of the heat exchanger 1, visible in figures 1 and 2, comprises a fixed platform 21 suitable for receiving connections (illustrated in figure 1 by means of the fixings P that delimit its contour) for the circulation of fluids and a mobile platform 22 for the compression of the plates 3. The fixed platform 21 and the mobile platform 22 are connected by means of an upper guide (not shown) that allows the alignment of the plates 3. Threaded rods 23, which connect the two plates 3 of end, they guarantee the compression of the stacked plates 3 by clamping.

The fixed platform 21 and the mobile platform 22 of the frame 2 each comprise an internal face 24, located opposite the plates 3, and an external face 25. The external face 25 of the fixed platform 21 is intended to receive the connections for fluid circulation.

A metal mesh sheet 26 is arranged on each of the internal faces 24 of the frame 2. The metal mesh sheet 26, of similar composition to that of the metal mesh plates 3, covers the surface of the internal face 24 which is intended to be in contact with the possibly corrosive process fluid. Each metal mesh sheet 26 is in turn covered by an anti-corrosion coating which, in the particular embodiment of the invention shown in Figure 1, is a thermoplastic resin coating 27 whose composition is similar to that of the metal mesh plates 3 The metal mesh sheet 26 and the thermoplastic resin coating 27 of the fixed platform 21 are intended to continuously cover the connections C and the internal face of the frame, thus protecting the fixed platform 21 against any corrosion due to passage of corrosive fluid.

The heat exchangers shown in Figures 1 to 9 comprise only metal mesh plates 3 comprising a single metal mesh sheet 31 and a coating 32 of thermoplastic resin that covers at least one face of the metal mesh sheet 31. In one embodiment not shown, a metal mesh plate can comprise several sheets of metal mesh, the length of the meshes being able to vary from one sheet to another, for example the length of the meshes can decrease in the thickness of the plate. In another embodiment not shown, only some of the plates of the heat exchanger are plates formed from sheets of metal mesh.

In the embodiments shown in Figures 1, 4, 6-9, the thermoplastic resin coatings 32 completely cover the face of the plate 3 that is intended to be in contact with the corrosive fluid, also called "process fluid". This face will be called the "process face" below, as opposed to the "service face" of the plate 3, intended to be in contact with the "service fluid" (for example water, steam or oil). Coatings 32 of thermoplastic resin also cover the edge of the metal mesh sheet 31 and a part of the service face.

Each metal mesh plate 3 has four through holes 33 (see figures 1, 6 and 7), provided for the passage and distribution of the two fluids inside the heat exchanger 1.

The arrangement of the metal mesh plates 3 inside the heat exchanger 1 is such that two plates 3 adjacent ones present, one opposite the other, either their process face or their service face, so as to allow the flow of the process fluid or the service fluid between them. In this way, an alternating distribution between the process fluid and the service fluid is carried out inside the plate heat exchanger 1.

As shown in Figure 4, the plates 3 form corrugations 36 arranged to generate turbulence during fluid flow between two adjacent plates 3. These corrugations 36 can be made during the drawing step of the metal mesh sheets 31. In the embodiments of figures 1 to 5, the corrugations 36 are formed by the two faces of the plates 3. In another embodiment, the corrugations are formed by a single face of the plate 3, for example by means of an overmoulding of material on the face. The plates can be arranged two by two so that the face of a first plate 3 that forms the corrugations is in tight contact with the substantially flat face of a second plate 3. In this way, the contact between two plates 3 extends by a more extended surface than that of a corrugation-corrugation contact in the case of figures 3-5 in which the corrugations are present on both faces of the plate 3 and allows to reduce the rate of friction of the coating on the metal.

To ensure tightness, specifically in order to prevent the flow of the process fluid along a surface devoid of coating 32 of thermosetting resin, gaskets 4 are arranged between two plates 3 or between a plate 3 and an internal surface of the frame 2, around the two holes 33 that guarantee the supply of the fluid whose flow is not required, as shown in detail in figures 6 and 7.

In order to guarantee a uniform compression of the gaskets 4 during the assembly of the heat exchanger 1 and to avoid deformation of the plates during compression due to the presence of gaps created by the gaskets 4, extra thicknesses can be provided in order to compensate for the absence of coating thickness when the latter is not present on the service face of the plate 3.

As shown in FIG. 5, tightness can also be guaranteed by welding 34 between two sheets of metal mesh 31 of adjacent plates 3 and by bringing two coatings 32 of adjacent plates 3 into contact. In the embodiment shown in Figure 5, the coatings 32 of the plates 3 do not cover the entire surface of the process face but are nevertheless sufficiently extended to cover the surface in contact with the process fluid and to allow contact with the cladding 32 of the adjacent plate 3.

The plate heat exchanger 1 works as follows.

The process fluid and the service fluid are circulated inside the heat exchanger 1 by means of connections fixed on the fixed platform 21. The fluids are distributed inside the plate heat exchanger 1, alternately between two faces of a similar type (process face or service face) of two adjacent metal mesh plates 3. The flow of these two fluids is disturbed by the corrugations 36 of the plates 3, which generates an exchange of thermal energy between a service face and a process face, through the thickness of the metal mesh plate 3. This energy exchange results in a balance between the temperatures of the two fluids on both sides of the two faces of the metal mesh plate 3.

In the case of the flow of the process fluid, represented in figure 6, a portion of the fluid flows, in the direction indicated by the arrows F, from an inlet hole 33 to an outlet hole 33, along the corrugations 36 formed by the process faces of two adjacent plates 3. The process face of the plate 3, shown in Figure 6, is completely covered by a coating 32 of thermoplastic resin in order to protect the metal mesh sheet 31 against corrosion. The fluid cannot escape through the other two holes 33 of the plate 3 due to the seals 4 that surround them. Conversely, the service face of the metal mesh plate 3, shown in Figure 6, is devoid of a coating 32 of thermoplastic resin in its portion in contact with the service fluid, thus favoring the transfer of thermal energy.

The invention is not limited to the presented embodiment and variants of this embodiment and other embodiments will clearly occur to the person skilled in the art. Another possible embodiment of the invention is specifically in which the two fluids used are corrosive and in which the entire surface of the plates in contact with the liquid is covered by a coating of thermosetting or thermoplastic resin.

Claims (15)

i. Plate heat exchanger (1) for fluid circulation, comprising: - plates (3) for fluid circulation, - a holding frame (2) for the plates (3) suitable for compressing the plates (3), the frame (2) and the plates (3) being connected two by two in a watertight manner, characterized in that the plate heat exchanger (1) comprises at least one metal mesh plate (3) comprising: - at least one sheet of metal mesh (31), and - a coating (32) of thermosetting or thermoplastic resin that covers at least one face of the metal mesh sheet (31). 2. Plate heat exchanger (1) according to claim 1, in which the metal mesh plate (3) is formed by drawing the metal mesh sheet (31). Plate heat exchanger (1) according to claim 1 or 2, in which the metal mesh plate (3) has a thickness of at least 0.8 mm, preferably 1.5 mm. 4. Plate heat exchanger (1) according to any one of the preceding claims, in which the metal mesh plate (3) comprises meshes with a length of 0.05 mm to 5 mm. 5. Plate heat exchanger (1) according to any one of the preceding claims, in which the coating (32) of thermosetting or thermoplastic resin is obtained by coating thermosetting or thermoplastic resin on the metal mesh sheet, or by impregnation of thermosetting or thermoplastic resin in the metal mesh sheet (31). 6. Plate heat exchanger (1) according to any one of the preceding claims, in which the frame (2) has an internal face (24), located opposite the plates (3), and an external face (25) which receives connections for the circulation of fluids, the frame (2) comprising an anti-corrosion coating (27), preferably of thermosetting or thermoplastic resin, which continuously covers the connections and the internal face (24) of the frame (2). 7. Plate heat exchanger (1) according to claim 6, in which the frame (2) comprises a metal mesh sheet (26) that covers at least partially the internal face and in which the anti-corrosion coating (27) covers the metal mesh sheet (26) of the frame (2). Plate heat exchanger (1) according to claim 7, in which the metal mesh sheet (26) of the frame (2) comprises meshes with a length of 0.05 mm to 5 mm. 9. Plate heat exchanger (1) according to any one of claims 7 and 8, in which the metal mesh sheet (31) of the metal mesh plate (3) and the metal mesh sheet (26) of the frame (2) are welded together along an area devoid of coating (27, 32) of thermosetting or thermoplastic resin, said area being surrounded by coating (27, 32) of thermosetting or thermoplastic resin so that it is isolated from at least one of the fluids. 10. Plate heat exchanger (1) according to any one of the preceding claims, in which the plates (3) form corrugations (36) arranged to generate turbulence during fluid flow and in which the corrugations (36) are formed by the two faces of the metal mesh plate, the plates being arranged in such a way that the contact between two adjacent plates is made outside of a vertex protruding from a corrugation. 11. Plate heat exchanger (1) according to any one of the preceding claims, in which the thermosetting or thermoplastic resin of at least one of the coatings (27, 32) of thermosetting or thermoplastic resin comprises powder loaded with silicon carbide , graphite, quartz, carbon or a mixture of these fillers. 12. Process for manufacturing a plate heat exchanger (1) comprising the following stages: - covering at least partially an internal face (24), located opposite the plates (3), of a holding frame (2) for the plates (3), by means of a metal mesh sheet (26), - welding together the metal mesh sheet (26) of the frame (2) and metal mesh sheets (31) of metal mesh plates (3) located opposite each other, along an area devoid of coating (27, 32) of thermosetting or thermoplastic resin, the area being surrounded by coating (27, 32) of thermosetting or thermoplastic resin so as to isolate it from at least one of the fluids. Method according to claim 12, in which several sheets of metal mesh (31) are superimposed and/or welded together before being drawn to form the corrugations (36) of a metal mesh plate (3). Method according to any one of claims 12 and 13, in which at least one metal mesh plate (3) is made by sintering metal powder. Method according to any one of claims 12 to 14, in which the coating (32) of thermosetting or thermoplastic resin includes, at the contact points between two plates (3), a load or a hard element that makes it possible to avoid wear due to friction of the plates during cycles of pressurization, decompression and movement of thermal expansions.