Heat Exchanger

This application claims priority to Belgian Patent Application No. BE 2024/5296 filed May 22, 2024, the disclosure of which is hereby incorporated by reference in its entirety.

The present disclosure relates to a “heat exchanger” (also referred to herein as an “exchanger”) for preheating combustion air from a compressor of a micro-turbine of an energy production and/or cogeneration apparatus.

A heat exchanger, particularly in cogeneration systems equipped with gas micro-turbines, plays a decisive role in improving overall efficiency. It performs the essential function of preheating the combustion air by recovering the thermal energy still present in the exhaust gases from the turbine. For example, such a heat exchanger can be made by means of a structure conventionally composed of an arrangement of exchange plates arranged between distribution frames and reinforced by metallic lattices inserted into the frames. This configuration facilitates efficient alternating exchange between hot and cold fluids, optimizing heat transfer. However, the manufacture of such a heat exchanger can encounter a number of difficulties, particularly when it comes to making metallic lattices, which can take on complex shapes.

The international publication WO 2016/124472 A1 presents such a heat exchanger design, integrated in an energy cogeneration system equipped with a gas micro-turbine. The publication WO 2022/074078 A1 discloses a heat exchanger in which central leakage zones are formed for a leakage fluid in distribution frames. Two adjacent distribution frames are separated by two separating plates and a leakage passage between these plates is defined by a frame with ribs facing a turbulator to direct any fluid from the leakage zones towards it. The leakage fluid can be evacuated through lateral orifices in these frames or through specific end inlets and outlets provided in the exchanger.

One object, among others, of this disclosure is to provide a heat exchanger that is more robust and simpler to manufacture than the prior art.

To this end, a heat exchanger is proposed for an energy production and/or cogeneration apparatus. In an embodiment, the apparatus comprises:

The exchanger according to embodiments of the disclosure is robust and simpler to manufacture. This is because, for example, the support projections, which extend from the internal contour of the frames towards the zones where the fluids flow, act as an internal structural support for the metal sheets. By projecting into the zones where the fluid circulates, these protrusions help to maintain the integrity of the sheets against mechanical stresses, particularly the pressure differential between the hot and cold zones.

In addition, integrating the projections directly into the distribution frames can help eliminate the need for additional components such as metallic lattices or other forms of external reinforcement. They can therefore help to simplify the manufacturing process by reducing the number of separate parts to be manufactured and assembled. By reducing the complexity of the components required to assemble the exchanger, the production costs are reduced. The manufacturing process becomes more straightforward, allowing for standardization, easier logistics, and potential economies of scale during mass production.

As anyone skilled in the art will appreciate, the distribution frames guiding the flux of hot and cold fluids are arranged in such a way as to enable them to be stacked in an orderly fashion. The metal sheets are arranged alternately with these distribution frames so that each metal sheet is placed between two successive frames. In other words, the exchanger stack is designed with an alternating arrangement where each distribution frame (delimiting a hot or cold fluid zone) is followed by a metal sheet, then by another distribution frame (delimiting a cold or hot fluid zone), and so on along the thickness of the exchanger. The arrangement of the metal sheets follows this sequence, so as to achieve thermal contact between the alternating zones of hot and cold fluids.

The term “fluid zone” refers to the region specifically delimited by the internal contour of each of the distribution frames where the hot or cold fluids circulate for the heat transfer. Each fluid zone communicates with specific openings that are used to let fluids in and out. The “inlet orifices” allow the fluid to enter the fluid zone for heat transfer, and the “outlet orifices” allow the fluid to leave the zone after exchanging heat. These orifices are integrated or incorporated into the distribution frames, which are positioned next to each other (i.e. adjacent to each other) in the structure of the exchanger. Each frame has its own orifices for the passage of the fluids, allowing continuous circulation with those of neighboring frames through the exchanger.

It should be noted that for purposes of this disclosure, the use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Similarly, the use in this document of the indefinite article “a”, “an”, or the definite article “the” to introduce an element does not exclude the presence of a plurality of these elements. The present specification may reference quantities and numbers. Unless specifically stated, such quantities and numbers are not to be considered restrictive. Unless limited otherwise, the terms “connected,” “coupled,” and “mounted” and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings. Generally, throughout the specification, terms of art may be used. These terms are to take on their ordinary meaning in the art from which they come, unless specifically defined herein or the context of their use would clearly suggest otherwise.

In an embodiment of the present disclosure, the projections comprise a plurality of fingers connected to a common base. More specifically, the protrusions are grouped in sets, each formed by a plurality of fingers connected to a common base. Advantageously, the fingers add extra strength to the structure of the heat exchanger. This configuration of projections also allows to increase the support surface for metal sheets. There is sufficient spacing between the fingers to allow hot and cold fluids to circulate. This improves the robustness and efficiency of the exchanger. The fingers can have a rectangular cross-section (in the direction in which they extend) because they are projections from a flat frame. For the purposes of this document, the term “fingers” may be replaced by “elongated bodies” or “elongated elements”.

In an embodiment, the common base can extend from the internal contour towards the fluid zone so as to form a bridge. This means that the common base connecting the fingers, extends from the internal contour through the fluid zone to reach the opposite side, thus forming a bridge across this zone. The common base therefore extends into the fluid zone.

In an embodiment, the fingers are parallel and of equal length. Advantageously, this allows the mechanical forces to be distributed evenly across the metal sheets, reducing the risk of deformation or breakage. This also facilitates the design and manufacture of the distribution frames. The fingers can be identical.

In an embodiment, the common base is arranged according to a projection of an edge of one of the inlet or outlet orifices of one of the adjacent distribution frames in the stack. As the skilled person will understand, the common base can be more precisely an orthogonal projection along the stack (or equivalently along the thickness of the exchanger), at the level of the frame in which the projections are. The common base then provides support for the adjacent distribution frame when assembling the exchanger, in particular by brazing or diffusion welding as explained below, contributing to better sealing and strength of the exchanger.

Alternatively or additionally, part of each finger is arranged in such a projection. In other words, each finger can intersect such a projection. The fingers (and in both cases, the projections) support the distribution frames when assembling the above-mentioned exchanger, which improves the exchanger's tightness and robustness.

In an embodiment, the fingers extend at the fluid zone from the common base and normally with respect to it. Advantageously, this embodiment ensures that hot and cold fluid flux are directed more efficiently into and out of the fluid zone. This means that the hot or cold fluid is guided into the fluid zone, without unnecessary dispersion that could reduce heat transfer efficiency. This finger configuration also helps to stabilize the flux of fluids in and out, reducing the turbulence that can occur as fluids move from one fluid zone to another. The disclosure thus provides a more orderly and less resistive fluid path, which can contribute to the overall efficiency of heat exchange.

In an embodiment, the distribution frames are essentially polygonal in shape. Polygonal shapes are angular shapes made up of a finite sequence of consecutive line segments. Advantageously, this shape is easy to manufacture. For example, the distribution frames may incorporate rectangular inlet and/or outlet orifices (the term “rectangular” also covering the case of “square”) and have internal contours that are rectangular or comprise zigzag shapes. These shapes are easier to cut and integrate into metal structures than rounded or irregular shapes. This can reduce production costs and simplify the assembly of the components of the exchanger.

In this case, the common base (possibly of each set of projections as aforesaid) is rectilinear and has fingers connected thereto which are parallel and of the same length. This is a particularly simple and robust design, with all the frame elements being straight. The mechanical forces are distributed evenly across the metal sheets thanks to the configuration of the fingers.

A distal end of each finger can be arranged according to a projection of an edge of one of the inlet or outlet orifices of one of the adjacent distribution frames in the stack. As the fingers connected to the same common rectilinear base are parallel and of the same length, the aforementioned distal ends are aligned along a straight segment corresponding to the projection of the edge of an inlet or outlet orifice. The design stands out for its simplicity, watertightness and robustness, because the (distal ends of the) fingers support the distribution frames with the metal sheets interposed during assembly of the exchanger.

In an embodiment, the exchanger also comprises a metallic lattice arranged in at least part of the fluid zone. Advantageously, the lattice is arranged to act as a separating element between the hot and cold fluid zones. This lattice allows a constant gap to be maintained between these zones. The metallic lattice also makes a significant contribution to reinforcing the metal sheets between the distribution frames. It offers increased structural strength, protecting sheets from deformation due to pressure variations and turbulence from circulating fluids. The mesh of the lattice is dimensioned to provide minimum resistance to flow while ensuring effective separation, which enhances the overall stability of the exchanger.

This integration of the metallic lattice into the exchanger design also facilitates installation and maintenance, while guaranteeing the durability of the internal components. The metallic lattice can adopt a rectangular shape, which may be better suited to distribution frames with polygonal shapes, in particular with an essentially rectangular internal contour. This shape can be easily adjusted to match the right angles of the internal contour. The lattice can be easily cut to fit exactly into the frame, maximizing the use of space in the fluid zone.

In another embodiment, each metal sheet has corrugations. The corrugations considerably increase the total surface area available for heat transfer compared with a flat surface. This allows a greater heat transfer capacity in a given volume, which improves the efficiency of the exchanger. In addition, the corrugations in the metal sheets disrupt the flow of fluids, inducing the turbulence. In addition, this method reinforces the metal sheets, making them less likely to deform under the effect of pressure or temperature. This rigidity also contributes to greater durability and a longer life for the exchanger. The use of a metal sheet with corrugations also makes the use of a metallic lattice as described above optional. The role of the metallic lattice can be transferred to the metal sheet by the corrugations, reducing the number of separate parts in the exchanger and simplifying its manufacture.

In an embodiment, the corrugations can be inclined with respect to a direction of fluid flow at said metal sheet. This disrupts the fluid flux more effectively by creating vortices and increased turbulence, helping to improve heat transfer between the fluids at the metal sheets.

In an embodiment, the angle of inclination of the corrugations is configured so as not to induce great resistance to flow, which can increase the pressure drop. The angle of inclination is configured to optimally maximize the rate of heat transfer between the two fluids. For example, it is between 30° and 60°, more precisely between 30° and 40°. The corrugations can be sinusoidal, e.g. with a more specific amplitude of 1.0 to 2.0 mm, these profiles being suitable for good heat exchange.

In an embodiment, the internal contour of each of the distribution frames comprises alternating convex and concave portions. The convex portions refer to sections of the contour that bulge towards the inside of the fluid zone. They therefore look like bumps on the contour. In addition, the concave portions are curved externally with respect to the fluid zone, forming hollows with respect to the plane of the frame. Advantageously, by adopting an alternating shape for the internal contour, such as a wavy or zigzag shape, the fluid zone of each distribution frame can be increased. This extends the surface area available for heat transfer, improving the heat exchanger's thermal efficiency.

In an embodiment, each of the inlet and outlet orifices in at least one distribution frame is disposed between a convex portion of the internal contour and an external contour of the distribution frame. This allows optimum use to be made of the frame material, which becomes maximum in front of the convex portions. The inlet and outlet orifices are thus staggered in pairs. When the frames are stacked, the offset created at the orifices is designed to ensure that they align correctly with those of neighboring frames. This precision is essential to ensure that fluids flow efficiently throughout the structure without obstruction. According to embodiments, all or part of each distribution frame has an external contour of the same rectangular shape and each distribution frame fits within this contour, forming the visible outer sides of the heat exchanger.

The heat exchanger according to this embodiment, but also generally according to the disclosure, including one or more aspects thereof, has the advantage of being modular in the sense that it can comprise a plurality of inlet and outlet orifices per distribution frame without the need for major structural changes to the exchanger, unlike the exchangers described in WO 2022/074078 A1 which are provided with an inlet and outlet orifice. This effect is particularly apparent in the previous embodiment and in the embodiments described below (see, for example, the fluid flow arrows in, introduced below) because the alternation of convex and concave portions can be extended as required, making the heat exchanger modular and more efficient.

In an embodiment, at least one distribution frame (and possibly one distribution frame in every two depending on the stacking; i.e. distribution frames having an internal contour delimiting a fluid zone of the same “type”, i.e. hot or cold) comprises inlet and outlet orifices in the form of open slots, each having an edge from which distribution projections extend externally with respect to the fluid zone of said distribution frame. The distribution projections can comprise fingers (or, in other words, can have the shape of a straight segment) extending externally with respect to the fluid zone.

Advantageously, this embodiment, for example, allows uniform distribution of the fluids thanks to the pressure drop generated by the fingers. In fact, the fingers modify the space available for the fluid to pass through, causing a localized restriction of the flux. This restriction increases the local velocity of the fluid, resulting in a drop in pressure. This pressure drop is useful for controlling velocity of the fluid, ensuring that the fluid spends sufficient time in contact with the surfaces of the metal sheets at the fluid zones.

In an embodiment, the distribution projections can be parallel and of similar length. Each can have the shape of a straight segment with a free end at the external contour of one of the adjacent distribution frames in the stack. Equivalently, the free ends are therefore aligned with the projection of the external contour of one of the adjacent distribution frames in the stack. The above-mentioned advantages for similar characteristics applied, in certain embodiments, to fingers connected to a common base also apply to these distribution projections, contributing in particular to an exchanger that is easy to manufacture and more watertight and robust.

For example, the (free ends of the) distribution projections effectively support the external contour of the adjacent distribution frame with the interposed metal sheets during assembly of the exchanger. Each metal sheet, for example, the edge of or edges of, can thus be locally crushed between two portions of the external contours of distribution frames or between such a portion and the free ends of such distribution projections, which contributes to more robust manufacture of the exchanger and to its sealing without losing the advantages of alternating convex and concave portions for the internal contour. As the distribution projections are also similar, their contribution in terms of support and holding is harmoniously distributed, reducing the risk of deformation or breakage in the wall of the exchanger.

In an embodiment, the flow of the fluids in the exchanger move parallel to each other in opposite directions, advantageously allowing for a larger thermal contact surface between the fluids, potentially improving the heat transfer coefficient. The fluids can have different pressures. The hot and cold fluids at different pressures can have varying flow velocities, directly influencing turbulence and therefore heat transfer efficiency. A fluid under higher pressure can pass through the exchanger more quickly, increasing the rate of heat transfer.

In an embodiment, the exchanger can comprise a main inlet from the outside to the inside of the exchanger for the hot fluid and a main inlet from the outside to the inside of the exchanger for the cold fluid. One of these main inlets is for instance lateral and the other is for instance axial in the stacking direction. The configuration described in the previous six paragraphs is particularly well-suited to such inlets, which enable flows to be crossed more effectively and thus heat to be exchanged.

The disclosure further provides an energy production and/or cogeneration apparatus comprising an exchanger according to any of the aforementioned embodiments. All the embodiments as well as all the advantages of the exchanger according to the disclosure are transposed mutatis mutandis to the present apparatus. In an embodiment, the apparatus comprises:

In an embodiment, combustion chamber can be of the “flameless” type. According to an embodiment, the combustion chamber mainly comprises a cylindrical chamber. The preheated combustion air leaving the heat exchanger is typically introduced at one end of the combustion chamber. The publication WO 2016/124472 A1 gives an example of such combustion chamber and its coupling with the heat exchanger.

Generally speaking, the person skilled in the art will understand that all the embodiments relating to the exchanger apply to the energy production and/or cogeneration apparatus by positioning the exchanger in the manner provided by the disclosure.

The disclosure also proposes a method for manufacturing a heat exchanger according to the disclosure, wherein the distribution frames and metal sheets are assembled by high-temperature brazing under vacuum. As is known to a person skilled in the art, “high-temperature” brazing is carried out at a temperature of around 600 to 1100° C., e.g. 900° to 1000° C. in the context of the disclosure. It is produced by adding a brazing alloy that impregnates the surfaces of the distribution frames and the metal sheets, enabling them to be assembled by atomic diffusion.

Advantageously, brazing is perfectly suited to the manufacture of the exchanger according to the disclosure because it allows rapid and robust manufacture of the heat exchanger without requiring fusion of the edges of the distribution frames and metal sheets. This ensures a strong, watertight bond between the distribution frames and the metal sheets, while maintaining the structural integrity of the heat exchanger and minimizing the risk of heat distortion. It should be noted that the distribution frames and metal sheets can also be assembled by vacuum diffusion bonding, which allows adhesion between the diffusion frames and metal sheets to be created by atomic diffusion under high temperature pressure. Alternatively, laser welding can be used, given its precision and ability to target small zone.

The disclosed subject matter is further introduced in the claims. As it will be understood by a skilled person from the present disclosure, any one of the embodiments presented in these claims can be considered alone or in combination. In particular, the dependency of the claims can be considered in a broader manner so that any one of the possible combinations of the claims—as far as they are technically possible and understood by the person skilled in the art, in particular in view of the present disclosure—are part of the present application.

The drawings in the FIGURES are not to scale. Similar elements are generally denoted by similar references in the FIGURES. In the scope of this document, the same or similar elements may have the same references. Furthermore, the presence of reference numbers or letters in the drawings may not be considered as limiting, even when these numbers or letters are indicated in the claims

This section provides a detailed description of certain embodiments of the present disclosure. The latter is described with particular embodiments and references to FIGURES but the disclosure is not limited by them. In particular, the drawings and FIGURES described below are only schematic and are not limiting.

In the following description, details are set forth to provide a thorough understanding of representative embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that the embodiments disclosed herein may be practiced without embodying all of the specific details. In some instances, well-known process steps or structural elements have not been described in detail in order not to unnecessarily obscure various aspects of the present disclosure. Further, it will be appreciated that embodiments of the disclosure may employ any combination of features described herein.

shows a view of a heat exchangeraccording to an embodiment of the disclosure. The heat exchangercomprises a stack of flat distribution frames,′. Each of these distribution frames,′ is characterized by an internal contour which delimits a hollow fluid zonededicated to the passage of a fluid, hot or cold. The hot and cold fluid zonesalternate along the length of the heat exchanger. By “along a thickness” is meant along a stacking axis along which this thickness is measured, the axis being noted and represented by X in. The stack is also considered along the stacking axis X. The term “thickness” is considered along this axis for the purposes of this document.

The distribution frames,′ can be made in one piece or assembled from several metal elements. The distribution frames,′ are each provided with inlet orificesand outlet orificesfor the passage of fluids. As shown in, these orificesare circular, for example, and are aligned to ensure continuous fluid flow through the stack. Two adjacent distribution frames,′ can be identical in design but turned 180° in relation to each other, or positioned so that one is the image of the other by mirror symmetry.

Between each pair of adjacent distribution frames,′, thin metal sheetsare arranged to create thermal contact between the hot and cold fluid zones. These sheets are very thin, for example around 1 to 2 mm thick. They have orifices aligned with those 11 in the distribution frames,′ to allow fluids to pass through the exchangerwithout interruption.

The distribution frames,′ are each fitted with projectionsproviding local support for the metal sheets. The projectionsextend from the internal contour towards the fluid zone. As illustrated in, these projectionscomprise fingers connected to a common base. The fingers are parallel and of the same length, reminiscent of the shape of a comb. The fingers at the projectionsprovide local support for the metal sheets, following assembly of the exchanger. This support helps to maintain the integrity of the metal sheetsby preventing them from sagging or vibrating excessively.

The structural integrity and tightness of the heat exchangercan be ensured by the addition of lower and upper cover plates,as shown in. The plates,can be thicker and welded to the edges of the exchanger. These plates,guarantee rigidity and complete sealing of the exchanger.

The heat exchangeralso comprises main inlets and/or outlets,,for cold and hot fluids arranged at the cover plates,. These structural elements are known to a person skilled in the art.

The materials used to manufacture heat exchangerare selected for their resistance to corrosion and high temperatures. For example, steels with a high chromium and nickel content or special nickel-based alloys can be used, enabling the heat exchangerto operate efficiently up to maximum temperatures of around 800° C.