Heat exchanger with leak detection system

Abstract

The invention relates to a brazed plate heat exchanger comprising a stack (1) of plates (2) arranged parallel to each other so as to define between said plates (2) a plurality of passages (3) for the flow of one or more fluids, the plates (2) each comprising at least a first edge (4) extending parallel to a first direction (z), at least one sealing bar (6) being arranged in at least one passage (3) defined between two consecutive plates (2) so as to delimit at least partially one or more internal volumes in the passage (3), the sealing bar (6) comprising at least one longitudinal recess (12), the sealing bar (6) and the longitudinal recess (12) extending, in their length direction, parallel to the first direction (z).According to the invention, at least one measuring element (14) is arranged in the longitudinal recess (12) and configured to measure at least one physical quantity, in particular at least one temperature, in said longitudinal recess (12). Figure for the abstract: 2.

Description

Title of the invention: Heat exchanger with leak detection system

[0001] The present invention relates to a brazed plate heat exchanger comprising at least one measuring device for detecting a leak in the exchanger.

[0002] The present invention finds particular application in the field of cryogenic gas separation, especially cryogenic air separation (known by the English acronym "ASU" for air separation unit) for the production of pressurized gaseous oxygen. In particular, the present invention can be applied to a heat exchanger that cools or liquefies a flow of gaseous oxygen from an ASU by exchanging heat with a flow of liquid nitrogen, or to a heat exchanger that heats or vaporizes a flow of liquid oxygen by exchanging heat with a flow of gaseous nitrogen. Alternatively, the present invention can be applied to a heat exchanger that cools or liquefies a flow of gaseous oxygen from an ASU by exchanging heat with a flow of liquid argon, which is then heated or vaporized.

[0003] The present invention can also be applied to a heat exchanger that heats or vaporizes at least one flow of liquid-gas mixture, in particular a flow of a multi-component mixture, for example a mixture of hydrocarbons, by exchanging heat with at least one other fluid, for example natural gas or nitrogen gas. An exchanger according to the invention can also be used to vaporize or heat liquefied natural gas against nitrogen gas, which is then cooled or liquefied.

[0004] More generally, the invention can be applied to a heat exchanger in which at least one fluid circulates at a pressure of at least 20 bar.

[0005] The exchanger according to the invention can also be a reactor-exchanger or catalytic exchanger configured for carrying out chemical reactions with the fluid or fluids circulating in the exchanger.

[0006] A commonly used technology for heat exchangers is that of brazed plate heat exchangers, which allow for very compact units offering a large exchange surface area and low pressure losses. These exchangers are formed from a series of parallel plates between which intercalated elements, such as corrugated structures or waves, can be inserted, forming finned heat exchange structures. The stacked plates form a stack of flat passages for different fluids to be exchanged. thermal.

[0007] During the manufacture of the exchanger, the plates, the finned interlayer elements and the other constituent elements of the exchanger are pressed together and then joined together by brazing in a vacuum furnace at temperatures which can be between 550 and 900 °C.

[0008] Due to their compact size and monolithic construction, it is difficult to measure physical quantities, particularly temperatures, within these plate heat exchangers. Thus, in most of the processes in which they are used, the operator only has access to the total thermal power exchanged between fluids, thanks to an energy balance performed between the inlet and outlet of each fluid. This greatly complicates the characterization and monitoring of the operation of these exchangers and does not allow, for example, the isolated measurement of physical quantities relating to the fluid circulating in each passage.

[0009] In use, the lack of local data limits the possibilities for process control. In particular, certain specific physical phenomena that may occur within the heat exchanger, such as phase changes or chemical reactions, result in a local variation in temperature, which also depends on the position considered within the heat exchanger.

[0010] Local temperature measurements would allow for the in-situ detection of poor operating conditions in heat exchangers: poor fluid distribution, reduced performance in certain areas of the exchanger due, for example, to clogging or local distillation. Local temperature or heat flux measurements are also useful for monitoring the performance evolution of plate and fin heat exchangers over their service life.

[0011] Methods for measuring "in situ" temperatures exist, but they are relatively intrusive because they alter the fluid flow within the heat exchange passages. And because they are not planned from the initial construction of the heat exchanger, their implementation is relatively complex, costly, and not very robust.

[0012] Furthermore, in the case of brazed plate heat exchangers, the geometry and microstructure of the brazing material connecting the constituent elements of the exchanger make the brazed areas susceptible to fatigue damage, the appearance and propagation of cracks, and therefore a risk of fluid leakage. This risk increases in the case of exchangers operating in cyclic mode, i.e., undergoing cyclic variations in the pressures of the fluids circulating in the exchanger, and / or in the case of exchangers where the fluids circulate at high pressures, typically more than 30 bar, or even more than 50 bar.

[0013] In certain processes, leaks can generate significant local concentrations of certain fluids and represent a risk inherent to the nature of the fluid or A change in the quality of the fluid exiting the heat exchanger. Potential leaks can also degrade the operating conditions and performance of the heat exchangers and the associated process.

[0014] A plate heat exchanger with doubled passage sealing bars is known from document FR-A-2929369, such that the space between them forms a dead zone open to the atmosphere through a vent through which any fluid leak can escape. However, this solution does not allow for the detection of a leak, in particular to allow for adjusting or stopping the operation of the heat exchanger if necessary, nor does it allow for locating the leak, in particular to facilitate subsequent inspection of the heat exchanger.

[0015] An alternative to limit these risks is to use wound-type exchangers, but these exchangers are nevertheless much less efficient than plate exchangers, whose large exchange surface and low pressure losses offer better thermal efficiency.

[0016] The present invention aims in particular to solve all or part of the problems mentioned above, by proposing a plate heat exchanger in which fluid leaks can be detected and located precisely and quickly, without disturbing the operation of the exchanger or the flow of fluids, and without increasing its size.

[0017] To this end, the invention relates to a brazed plate heat exchanger comprising a stack of plates arranged parallel to each other so as to define between said plates a plurality of passages, each plate comprising at least one first edge extending parallel to a first direction, at least one passage defined between two consecutive plates comprising at least one sealing bar arranged so as to delimit at least partially one or more internal volumes for the flow of one or more fluids within said passage, the sealing bar comprising at least one longitudinal recess, the sealing bar and the longitudinal recess extending, in their lengthwise, parallel to the first direction (z), characterized in that at least one measuring element is arranged in the longitudinal recess and configured to measure at least one physical quantity, in particular at least one temperature,in said longitudinal recess.

[0018] Depending on the case, the exchanger according to the invention may include one or more of the features below.

[0019] Said at least one sealing bar is arranged at the first edge so as to at least partially separate an internal volume from the outside of the stack or in that said at least one sealing bar is arranged at a predetermined distance from the first edge so as to at least partially separate a internal volume of another internal volume within the passage.

[0020] Said at least one measuring element is long-sloping and extends, in its length, parallel to the first direction in the longitudinal recess, the measuring element preferably being configured to measure several values ​​of said physical quantity along the first direction.

[0021] Said at least one measuring element comprises at least one optical waveguide, in particular at least one optical fiber.

[0022] The sealing bar comprises a first part of a bar and a second part of a bar, each extending parallel to the first direction and spaced apart from each other along a second direction orthogonal to the first direction and parallel to the plates, such that the longitudinal recess is formed by the space between the first part of the bar and the second part of the bar, or in that the longitudinal recess is formed by a groove in a monolithic sealing bar comprising two lateral faces facing each of the adjacent plates, the groove opening into one or the other of the lateral faces of the bar.

[0023] The exchanger comprises at least two sealing bars arranged in opposition between two adjacent plates, each bar extending lengthwise parallel to the first direction and comprising at least one longitudinal recess extending lengthwise parallel to the first direction and equipped with at least one measuring device.

[0024] The longitudinal recess and the measuring member extend over at least 50%, preferably at least 75%, preferably even the entire length, of the sealing bar.

[0025] The sealing bar comprises at least one longitudinal face parallel to the first direction and at least one transverse face orthogonal to the first direction, the longitudinal recess opening outwards to the outside of the stack through at least one opening located on the transverse face of the sealing bar, preferably the sealing bar comprises two opposite transverse faces and the longitudinal recess opens outwards to the outside of the stack through two openings located on each of the opposite transverse faces.

[0026] The exchanger comprises at least one set of sealing bars extending, in their length, parallel to the first direction and arranged one above the other in a stacking direction orthogonal to the plates, each sealing bar of said set comprising at least one longitudinal recess extending, in the length, parallel to the first direction and equipped with at least one measuring device.

[0027] The sealing bars of said assembly each comprise at least one Ion- face longitudinal recess parallel to the first direction, at least one transverse face orthogonal to the first direction and at least one longitudinal recess extending, lengthwise, parallel to the first direction and equipped with at least one measuring device, the longitudinal recesses of each sealing bar opening outwards to the outside of the stack through respective openings located at the level of the transverse faces of each bar, at least one measuring device extending outwards from a longitudinal recess through one of the openings and then entering into an adjacent longitudinal recess through another of said openings.

[0028] The measuring element comprises at least two internal portions arranged each in a longitudinal recess of a sealing bar and connected in one piece by an external curvilinear portion arranged outside the stack, preferably the external portion has a radius of curvature of at least 10 cm, preferably at least 20 cm.

[0029] The plates have two second opposite edges arranged parallel to a second direction orthogonal to the first direction, the measuring member comprising a plurality of internal portions connected by external portions located alternately on the side of one or the other of the second opposite edges.

[0030] The stack has a total height measured along the stacking direction, the sealing bars of said assembly being separated from each other by intermediate heights measured along the stacking direction, the ratio between the intermediate heights and the total height being between 5 and 50%.

[0031] Said at least one longitudinal recess and said at least one measuring member have, along at least one direction orthogonal to the first direction if the sealing bar is arranged parallel to the first direction or parallel to the first direction if the sealing bar is arranged orthogonally to said second direction, an internal dimension and an external dimension respectively, the ratio between the external dimension of the measuring member and the internal dimension of the longitudinal recess being at most 95%, preferably between 70 and 90%.

[0032] In addition, the invention relates to a heat exchange installation comprising a heat exchanger according to one of the preceding claims and comprising at least one distribution line configured to distribute one or more fluids into one or more internal volumes of at least one passage, at least one fluid control device configured to allow, modify and / or stop the distribution of at least one fluid through the distribution line, the measuring element being configured to generate at least one leak signal in response to a variation of said physical quantity and the control device being configured to modify or stop the distribution of said fluid through the distribution line in response to said leak signal.

[0033] According to another aspect, the invention relates to the use of an exchanger according to the invention or an installation according to the invention for connecting at least one fluid with at least one other fluid for heat exchange, the fluid and / or the other fluid comprising one of: neon, krypton, xenon, nitrogen, argon, oxygen, hydrogen, helium, carbon monoxide, carbon dioxide, methane, in particular for liquefying or cooling gaseous oxygen by heat exchange with liquid nitrogen or liquid argon.

[0034] The invention also relates to a cryogenic air separation unit comprising at least one exchanger according to the invention or an installation according to the invention, unit in which said exchanger operates a liquefaction or cooling of a flow of gaseous oxygen coming from the cryogenic air separation unit with liquid nitrogen or liquid argon which heats up or vaporizes.

[0035] The invention will now be better understood from the following description, given by way of non-limiting example and with reference to the attached figures, among which:

[0036] [Fig-1] is a three-dimensional view of a heat exchanger according to an embodiment of the invention,

[0037] [Fig.2] is a longitudinal cross-sectional view of a passage of an exchanger according to an embodiment of the invention,

[0038] [Fig.3] is another longitudinal cross-sectional view of a passage of an exchanger according to an embodiment of the invention,

[0039] [Fig.4] is another longitudinal cross-sectional view of passages of an exchanger according to an embodiment of the invention, in a cutting plane orthogonal to the cutting plane of [Fig.2] and [Fig.3],

[0040] [Fig.5] is a cross-sectional view of a measuring device according to an embodiment of the invention,

[0041] [Fig.6] is a longitudinal cross-sectional view of a measuring device according to an embodiment of the invention.

[0042] Figure 1 illustrates an embodiment in which the heat exchanger is of the brazed plate and fin type, comprising a stack 1 of plates 2 extending in two dimensions, length and width, respectively along a first direction z and a second direction x. Preferably, the stack 1 is parallelepiped in shape. The plates 2 are arranged one above the other, parallel to each other, and with spacing between them. They thus form several sets of passages 3, some passages being provided for the flow of a first fluid Fl, and other passages being provided for the flow of at least one other fluid F2, F3 to be connected for indirect heat exchange with Fl via the plates 2. Preferably, the second direction x is perpendicular to the first direction z and parallel to the plates. The fluids preferably flow along the length of the exchanger, the length being much greater than the width of the exchanger. In the illustrated case, the first direction z corresponds to the longitudinal extent of the exchanger, and the fluids flow generally parallel to the first direction z. Other flow directions are, of course, possible within the scope of the invention, in particular fluid flow directions that are generally parallel to the first direction x.

[0043] Preferably, each passage has a flat, parallelepiped shape. The gap between two successive plates 2, corresponding to the height of the passage, measured along the stacking direction y of the plates 2, is small compared to the length and width of each successive plate. The stacking direction y is orthogonal to the plates 2.

[0044] Each plate 2 comprises at least one first edge 4 extending parallel to the first direction z. Preferably, each plate 2 comprises a pair of first edges 4 arranged parallel to the first direction z and opposite each other. According to the embodiment illustrated in [Fig. 1], the plates 2 are further delimited by a pair of second edges 5 arranged parallel to the second direction x and opposite each other.

[0045] The passages 3 are delimited by sealing bars 6 arranged between the plates 2, around the periphery of the passages 3. These bars 6 ensure spacing between the plates 2 and define an internal volume suitable for the flow of one or more fluids within each passage 3, and ensure the sealing of the passages 3 against the outside of the stack. Preferably, at least one sealing bar 6 extends along the first direction z; more preferably, one passage 3 is delimited between a pair of bars 6 parallel to the first direction z. The passages 3 may also be delimited by at least one sealing bar 6 extending along the second direction x; preferably, one passage 3 is delimited between a pair of bars 6 parallel to the second direction x.

[0046] Depending on the location of the fluid inlet and outlet areas of the heat exchanger, the sealing bars 6 may not completely close the passages, but leave openings for the inlet or outlet of the corresponding fluids. The heat exchanger 1 includes semi-tubular manifolds 7, 9 equipped with inlets and outlets 10 for introducing fluids into the heat exchanger and expelling fluids from the heat exchanger. Distribution zones arranged downstream of the inlet manifolds and upstream of the outlet manifolds serve to channel the fluids homogeneously to or from the entire width of the passages.

[0047] Alternatively or additionally, at least a portion of the passages 3 may include at least one sealing bar 6 arranged to delimit at least in part several internal volumes within passage 3. Different fluids can flow into these internal volumes, the sealing bar being configured to prevent the circulation of these fluids from one internal volume to another.

[0048] Preferably, at least a portion of the passages 3 comprises finned interlayer elements 8 that advantageously extend along the width and length of the exchanger passages, parallel to the plates 2. In the illustrated example, the interlayer elements 8 comprise heat exchange waves in the form of corrugated sheets. In this case, the wave legs connecting successive crests and bases of the wave are called "fins." The interlayer elements 8 may also have other specific shapes defined according to the desired fluid flow characteristics. More generally, the term "fins" covers blades or other secondary heat exchange surfaces that extend from the primary heat exchange surfaces, i.e., the exchanger plates, into the exchanger passages.

[0049] Preferably, waves are used as an intercalated element 8. In particular, waves are used whose fins extend parallel to the first z direction, with a general undulation direction that is perpendicular to the first z direction and parallel to the plates 2.

[0050] Preferably, during the manufacture of the heat exchanger 1, a set of plates 2 is supplied and stacked parallel to each other and in the first direction z. The plates 2 are spaced from each other by sealing bars 6. After assembly of the other constituent elements of the heat exchanger, in particular the heat exchange waves, the distribution waves, etc., the stack is brazed to secure the heat exchanger elements together. A filler metal, called brazing alloy or brazing agent, is placed between the heat exchanger elements. Preferably, the plates and all or part of the other constituent elements of the heat exchanger are made of aluminum or an aluminum alloy.

[0051] Within the stack, adjacent plates 2 are separated by sealing bars 6 arranged between each pair of adjacent plates. These bars 6, together with the adjacent plates 2, delimit at least one internal volume in which at least one fluid can circulate. The sealing bars 6 are arranged to prevent the fluid from escaping from an internal volume of the passage 3 to the outside of the stack and / or to prevent the fluid from circulating between several internal volumes of the same passage 3, if applicable. Sealed joint zones are formed between the sealing bars and the adjacent plates, in particular by brazing the bars to the plates. However, due to the thermal and mechanical stresses experienced by the heat exchanger over time, the sealing of the passages may degrade, and the first fluid may seep between the sealing bars and the plates. adjacent.

[0052] According to the invention, at least one sealing bar 6 extending along the first direction z is provided with at least one longitudinal recess 12 arranged so as to be able to collect said first fluid in the event of a leak from a passage 3 delimited by said sealing bar 6. The sealing bar 6 and the longitudinal recess 12 extend, in the length direction, parallel to the first direction z. A measuring element 14 is arranged in the longitudinal recess 12 and configured to detect a variation of at least one physical quantity, in particular a variation of temperature, in the longitudinal recess 12.

[0053] The invention thus makes it possible to detect a potential fluid leak at the sealing bar 6 from the adjacent internal volume by detecting a change in a physical quantity caused in the longitudinal recess 12 by the introduction of fluid into the longitudinal recess 12. Depending on the positioning of the sealing bar, the invention makes it possible to detect leaks occurring from passage 3 to the outside of the stack or leaks occurring between internal volumes of a passage separated by the bar 6. In the event of leak detection, the operation of the heat exchanger can therefore be stopped to ensure the safety of operators and to reduce the risk of contamination of the fluids used. As a physical quantity representative of a leak in the circuit 12, the temperature in the longitudinal recess 12 can be measured.Advantageously, the measuring device is configured to detect a temperature variation in the longitudinal recess 12 or to measure the temporal evolution of the temperature in the longitudinal recess 12. Measuring the temperature makes it possible to detect abrupt variations in the latter which are characteristic of a leak.

[0054] The arrangement of the measuring element 14 within a sealing bar 6 does not increase the overall size of the heat exchanger. Local temperature measurements can be taken by choosing the positioning of the measuring element. Furthermore, the measuring element can be inserted after the stacking step, which reduces the risk of damage to the probe and allows the use of a wider variety of technologies, not just high-temperature resistant probes.

[0055] The invention also makes it possible to measure characteristics of the fluid flowing in the passage 3 delimited by the sealing bar 6, which includes the longitudinal recess, such as temperature, without disturbing the fluid flow. Such measurements make it possible to detect any malfunctions of the heat exchanger or to dynamically monitor the fluid characteristics and, in particular, to assess the thermal shocks experienced by the heat exchanger.

[0056] Figure 2 represents an embodiment in which a longitudinal recess 12 is formed in a bar 6 extending parallel to the first direction z, which This defines an overall direction of fluid flow Fl. In addition to leak detection, this configuration allows for the local measurement of the fluid temperature, and therefore its evolution, at different positions along the length of the heat exchanger, as it exchanges heat with another fluid flowing in an adjacent passage. This provides information on the physical phenomena that may occur within the heat exchanger, including phase changes and chemical reactions, and their location within the exchanger.

[0057] In the context of the invention, one or more sealing bars 6 may be provided with one or more respective longitudinal recesses 12 equipped with measuring elements 14. It is also conceivable that one or more longitudinal recesses 12 may be provided in other sealing bars, in particular sealing bars 6 parallel to the second direction x. Thus, at least one sealing bar 6 and the associated longitudinal recess 12 may extend parallel to the second direction x.

[0058] With reference to [Fig.3], the plates 2 may further each include at least one second edge 5 extending perpendicularly to the first direction z, at least one sealing bar 6 being arranged, in the length direction, parallel to the second edge 5 and including at least one longitudinal recess 12 extending, in the length direction, parallel to the second edge 5 and provided with at least one measuring member 14.

[0059] In the context of the invention, at least one sealing bar 6 can be arranged at a first edge 4 or a second edge 5 so as to form a peripheral bar separating at least partially an internal volume from the outside of the stack. The sealing bar thus delimits at least partially the periphery of a passage 3. At least one sealing bar 6 can also be arranged at a predetermined distance from a first edge 4 or a second edge 5 so as to form a separating bar separating one internal volume from another internal volume within the passage 3. The sealing bar thus delimits at least partially an internal volume 3A with respect to another volume 3B inside the stack. Combinations of these embodiments are conceivable; in particular, at least one passage 3 may comprise at least one peripheral bar and at least one separating bar.

[0060] According to one embodiment, at least two sealing bars 6 are arranged oppositely between two adjacent plates 2, parallel to the first direction z or the second direction x, so as to delimit the same passage 3. Each of the two opposing sealing bars 6 includes at least one measuring element 14 arranged in a fluid circuit 12.

[0061] Arranging measuring devices 14 on the bars located on either side of the passage 3 makes it possible to detect leaks even more effectively. This also makes it possible to It is essential to verify that the fluid is evenly distributed across the width of the passage, specifically ensuring that the measured physical quantity is identical on both sides. In particular, taking temperature measurements on each side of the passage allows for the effective detection of any uneven distribution. The heat exchange within the passage, which determines the fluid and bar temperatures, is linked to the fluid flow rate near the probes. Temperature differences between the two sides therefore reflect differences in flow rate. Furthermore, the probes enable the dynamic monitoring of transient temperature regimes over time and the assessment of thermal shocks experienced by the heat exchanger.

[0062] Preferably, the longitudinal recess 12 and the measuring element 14 extend over at least 50%, preferably at least 75%, and preferably the entire length, of the sealing bar 6. It should be noted that the length of the bar 6 is measured along its longitudinal direction, in particular along the first direction z in the case where the bar extends lengthwise along the first direction z. Thus, it is possible to arrange one or more measuring elements along a significant proportion of the length or width of passages 3 and therefore improve the efficiency and accuracy of leak detection. The arrangement of several recesses makes it possible to measure changes in physical quantities at different positions along the length and / or width of the heat exchanger, in order to determine where leaks occur.

[0063] According to one embodiment, the heat exchanger comprises at least one set of sealing bars 6 arranged parallel to the first direction z and one above the other along the stacking direction y. At least one measuring element 14 is arranged in the longitudinal recess 12 of each of the sealing bars 6 in the set. This allows for the detection of any fluid leaks at different positions in the stack height and the identification of the passage(s) concerned. Each recess 12 in a bar 6 makes it possible to detect a leak originating from the passage 3 arranged opposite the bar 6.

[0064] In particular, the stack has a total height H measured along the stacking direction y and the sealing bars 6 provided with recesses 12 and members 14 are separated from each other by intermediate heights h measured along the stacking direction y, the ratio between the intermediate heights h and the total height H being between 5 and 50%.

[0065] According to an embodiment in which the measuring element comprises an optical fiber, the intermediate height h is greater than twice the minimum radius of curvature of the fiber or of the protective sheath in which said fiber is located.

[0066] In particular, the intermediate height h is at least equal to 5 cm, preferably at least equal to 10 cm, and even more preferably at least equal to 20 cm.

[0067] According to one embodiment, the ratio between the total number of passages 3 of the stack and the number of passages 3 equipped with at least one sealing bar according to the invention is between 1 and 10, preferably greater than or equal to 5.

[0068] It being specified that the bars 6 can be arranged equidistantly in the height of the stack, but not necessarily.

[0069] Preferably, the longitudinal recess 12 opens to the outside of the stack 1 through at least one opening 11. This allows a leak of the first fluid to escape to the outside of the stack. The opening 11 can optionally be connected to the atmosphere by a vent or to a leak recovery circuit. The opening 11 also serves for the insertion and / or removal of the measuring element 14. In particular, the longitudinal recess is through-hole and opens into two openings 11 located across the length of the bar 6, which allows for a more flexible arrangement of the measuring element. Preferably, the measuring element 14 protrudes from the outside of the stack 1 through at least one opening 11.

[0070] In particular, the sealing bar 6 comprises at least one longitudinal face 64 parallel to the first direction z and at least one transverse face 65 orthogonal to the first direction z.

[0071] According to one embodiment, said at least one sealing bar 6 is parallelepiped in shape. The cross-section of said bar may be square or rectangular. The sealing bar 6 comprises two opposing longitudinal faces 64 that are parallel to the first z-direction and the stacking direction y. Depending on the positioning of the bar in the heat exchanger, one longitudinal face 64 is oriented towards an internal volume for fluid circulation and another longitudinal face 64 is oriented towards the outside of the stack, or each longitudinal face 64 is oriented towards a respective internal fluid circulation volume. The sealing bar 6 comprises two opposing lateral faces 63 that are parallel to the first z-direction and orthogonal to the stacking direction y. The opposing lateral faces 63 face the adjacent plates 2.

[0072] As can be seen in [Fig. 2], the sealing bar 6 can comprise a first bar portion 61 and a second bar portion 62 that are physically distinct from each other. The first bar portion 61 and the second bar portion 62 each extend parallel to the longitudinal direction z and to the plates 2. The longitudinal recess 12 then results from the spacing formed along the second direction x between the first bar portion 61 and the second bar portion 62. In the event of at least a partial loss of the seal provided by one or the other of the first and second bar portions, fluid can flow and be collected in the recess 12.

[0073] According to another possibility, the longitudinal recess 12 is formed by a groove cut into a monolithic sealing bar 6. In particular, the groove may The groove may have any suitable cross-sectional shape, including square, rectangular, and semi-circular. It preferably opens onto one of the lateral faces 63 of the bar 6 that face one or more of the adjacent plates 2. The groove has a second width, measured along the second x-direction, that is less than the total width of the sealing bar. In the event of at least a partial loss of the seal provided by the sealing bar, fluid may flow out and be collected in the recess 12.

[0074] Preferably, the longitudinal recess 12 opens outwards through at least one opening 11 located on the transverse face 65. As shown in the example of [Fig.2], the sealing bar 6 preferably comprises two opposite transverse faces 65 and the longitudinal recess 12 opens outwards from the stack 1 through two openings 11 located on each of the opposite transverse faces.

[0075] According to a particular embodiment, the sealing bar 6 comprises an external longitudinal face 64e parallel to the first direction z and aligned with the first edge 4 of an adjacent plate 2. In this configuration, the external longitudinal face 64e forms part of a peripheral surface of the stack.

[0076] In particular, the sealing bar 6 may include at least one transverse face 65 parallel to the second direction x and aligned with a second edge 5 of an adjacent plate 2. In this configuration, the transverse face 65 forms part of a peripheral surface of the stack.

[0077] Preferably, the stack 1 has at least one first face parallel to the first direction z on which are located the first edges 4 of the plates 2 and the external longitudinal faces 64e of the bars 6. In addition, the stack 1 may have at least one second face, parallel to the second direction x, where are located the second edges 5 of the plates 2 and the transverse faces 65 of the bars 6.

[0078] Figure 4 illustrates an embodiment in which the heat exchanger comprises at least a first set of sealing bars 6 parallel to the first direction z and arranged one above the other, each with at least one longitudinal recess 12 provided with at least one measuring element 14. In particular, the sealing bars 6 of the set each comprise at least one transverse face 65 provided with an opening 11 through which the longitudinal recesses 12 open to the outside of the stack 1.

[0079] According to one possibility, the exchanger may include at least one pair of first sets of bars arranged in opposition on either side of the passages 3.

[0080] Preferably, at least one measuring element 14 extends outwards from a longitudinal recess 12 through one of the openings 11 and then enters an adjacent longitudinal recess 12 through another of said openings 11. Thus, the same measuring element can equip distinct recesses 12 and therefore detect leaks from 3 distinct passages.

[0081] In particular, the measuring member 14 comprises at least two internal portions 14a arranged each in a longitudinal recess 12 of a sealing bar 6 and connected in one piece by a curvilinear external portion 14b arranged outside the stack, preferably the external portion 14b has a radius greater than 5 cm, preferably greater than 10 cm.

[0082] In particular, the plates 2 have two opposing second edges 5 arranged parallel to the second direction x, the measuring element 14 comprising a plurality of internal portions 14a connected by external portions 14b located alternately on the side of one or the other of the second edges 5. A single measuring element can thus extend by meandering within the stack. This arrangement makes it possible to have only one measuring element and therefore only one signal transmission and acquisition system. This simplifies the operation and facilitates the maintenance of the exchanger. The associated investment costs are reduced.

[0083] Alternatively or complementarily, but not shown, the heat exchanger may include at least one second set of sealing bars parallel to the second x-direction and arranged one above the other along the stacking direction y, each with at least one longitudinal recess equipped with at least one measuring element. In particular, the sealing bars of the second set each include at least one opening through which the longitudinal recesses open to the outside of the stack. This second set of bars may have all or part of the characteristics described above for the first set, except that the longitudinal faces of the bars 6 are parallel to the second x-direction and the openings 11 open to the side of the first edges 4 and are arranged on transverse faces of the bars 6 arranged parallel to the first z-direction.

[0084] Preferably, with reference to the example in [Fig.5], the measuring member 14 comprises an internal part 15 sensitive to a variation of said at least one physical quantity in the longitudinal recess 12 and a protective sheath 16 arranged around the internal part 15.

[0085] Preferably, the measuring element is long-sloping so that it can be easily inserted into the recess and does not increase the size of the exchanger.

[0086] Preferably, a single measuring element is arranged in the recesses of a set of bars as described above, or even a single measuring element is arranged in the recesses of several sets of bars, whether they are arranged parallel to the first direction z or the second direction x.

[0087] Preferably, said at least one measuring element 14 comprises a plurality of sensitive zones arranged along the measuring element 14 and at the level of which the A physical quantity is measured. These sensitive areas may be arranged equidistant from each other, but not necessarily. In particular, the sensitive areas may be separated from each other by distances of between 5 and 100 mm, preferably distances ranging from 10 to 50 mm.

[0088] According to an advantageous embodiment, said at least one measuring element 14 comprises at least one optical waveguide, in particular at least one optical fiber. It should be noted that the term "optical fiber" can be understood to mean either a single optical fiber or an array of several optical fibers in series or in parallel.

[0089] An optical waveguide is defined as a structure that confines and guides light. This waveguide consists of two or more layers of transparent dielectric materials, for example, silica glass or plastic, with different refractive indices, ensuring that the light is confined near the center. An optical fiber is a circularly symmetrical optical waveguide. The optical fiber generally consists of a dielectric medium called the fiber core, covered with a material called the optical cladding, which has a lower refractive index than the core. The entire assembly is itself surrounded by a sheath, usually made of plastic, which has the dual role of protecting the fiber mechanically and trapping the light propagating in the optical cladding, which is generally undesirable. Optical fiber measuring devices are both sensors and the transmission channel for the light signal.They are sensitive to variations in physical quantities in the surrounding environment, including temperature, deformation... .

[0090] Optical fibers have the advantages of requiring only limited instrumentation and little or no power supply and of being very compact, which makes their implementation less intrusive, easier and compatible with regulations relating to explosive atmospheres (ATEX regulations).

[0091] In the case of an optical fiber 14, the protective sheath 16 can be the fiber's outer casing, or a tubular sleeve arranged around the outer casing, preferably made of metallic material.

[0092] Preferably, the optical fiber measuring device is connected to a system for measuring the profile of the physical quantity, in particular the temperature, measured along said optical fiber. The principle of the measurement system may, in particular, be based on Raman, Rayleigh, or Brillouin spectroscopy of at least one light pulse and the influence of the physical quantity on light absorption. After digital processing, the variations in intensity and the acquisition times of the reflected signals make it possible to record any change in the physical quantity at different points along the fiber and to translate them into a detailed temperature profile along the fiber. This temperature profile then makes it possible to identify, in real time, the areas of the sealing bar where variations appear, indicating the presence of leaks. Figure 6 schematically illustrates an embodiment in which a measuring element 14 comprising at least one optical fiber is connected to an emitting device 23 of at least one light pulse 23 configured to determine the physical quantity at different points or sensitive areas 22a, 22b... along the optical fiber.

[0093] The temperature profile measured along the optical fiber is generally a discontinuous profile, that is to say, made up of a series of temperatures, each of them corresponding to a finite element of said optical fiber.

[0094] Advantageously, two categories of optical waveguide measuring devices 14 can be used. The first category includes, on the one hand, distributed measuring devices, i.e., continuously sensitive, based on the Raman, Brillouin, or Rayleigh effects, and on the other hand, distributed sensors, i.e., locally sensitive, with Bragg gratings photo-inscribed within the fiber core itself. The second category is that of extrinsic measuring devices, which use several methods based on connecting microtransducers to the optical fiber. Whether it is a semiconductor, a Fabry-Perot type interferometric cavity, or a phosphorescent compound, each of them functions to modify one of the parameters of the guided optical wave, in particular intensity, spectrum, phase, etc.Depending on the temperature or another physical quantity, measuring the evolution of this optical parameter allows us to trace back to the inducing thermal variations. In the case of distributed sensors, the principle of measurement using optical fiber is based on the interaction between light and matter. When the fiber material is traversed by a light pulse, it emits a backscattered spectrum composed of three types of components: Raman backscattering, Rayleigh backscattering, and Brillouin backscattering. At least one of these components can be used.

[0095] In particular, it is possible to use Rayleigh backscattering, which results from the interaction between impurities in the fiber and an electromagnetic field. The local variation in the refractive index, linked to variations in temperature and / or deformation, alters the intensity of the backscattered wave, making it possible to retrieve the desired information.

[0096] It is also possible to use the Raman effect to determine the fiber temperature at different points (spatial and regular discretization of the fiber). The Raman effect is a nonlinear effect based on the principle of energy exchange between the optical wave and the vibration of the material. This results in a shift in the lines representing the light spectrum. Shifted frequencies, both lower and higher, are observed. Since temperature only affects the higher shifted frequencies, it is therefore possible to use this spectrum to create a temperature sensor.

[0097] Preferably, these phenomena are implemented by means of a device of the type OTDR (Optical Time Domain Reflectometry) involves sending a long light pulse. Knowing the speed of light propagation in the material allows us to determine the position of the measurement point or sensitive area. The spatial resolution depends on the length of the pulse sent.

[0098] According to another possibility, a measuring device 14 comprising at least one Bragg grating optical fiber may be used. A fiber Bragg grating is an optical fiber whose core has a refractive index that varies according to an alternation between a relatively high index and a relatively low index along the length of the fiber. This variation allows the fiber to reflect certain wavelengths and transmit others. The reflected wavelength depends on the distance between a section with a high refractive index and sections with a low refractive index. The distance between two sections with a high refractive index is called the Bragg grating period. Each measuring point or sensitive area reflects a wavelength thanks to a pattern "printed on the fiber." The reflected wavelength varies according to the temperature and deformation.

[0099] It should be noted that it is also possible to use a temperature measuring element 14 based on resistance, for example a resistance probe, in particular a platinum resistance probe of the PT 100 type, or a temperature measuring element 14 based on a thermocouple or thermistor. In particular, the measuring element 14 may include a protective sheath 16 in which several resistance, thermocouple, or thermistor measuring elements are arranged discreetly along the sheath, thus allowing measurements to be taken at different positions along the measuring element, and therefore at different positions in the heat exchanger.

[0100] The transverse dimension(s) of the longitudinal recess 12 can be adapted according to those of the bar 6 and / or those of the measuring member 14.

[0101] In particular, said at least one longitudinal recess 12 and said at least one measuring member 14 have, along at least one direction parallel to the second direction x if the sealing bar 6 is arranged parallel to a longitudinal edge 4 or measured in a direction parallel to the first direction z if the sealing bar 6 is arranged parallel to a lateral edge 5, an internal dimension and an external dimension respectively, the ratio between the external dimension of the measuring member 14 and the internal dimension of the longitudinal recess 12 being at most 95%, preferably between 70 and 90%. These values ​​are defined so that the measuring member can slide in the recess and deviate slightly from its overall direction of extension in the recess, in order to prevent the measuring member from being placed under tension due to differential expansions between the measuring member and the material surrounding this recess.This reduces the risk of rupture. the measuring element. The external dimension of element 14 refers to the external dimension of the protective sheath, if applicable.

[0102] In the case where the longitudinal recess 12 is formed by the space between two distinct parts of bar 61, 62, the depth of the longitudinal recess 12, measured in the stacking direction y, corresponds to the height of the passage 3 in which the bar 6 is located. Preferably, the internal dimension of the longitudinal recess 12 is equal to the height of the passage, the ratio between the external dimension of the measuring member 14 and the height of the passage being at most 95%, preferably between 70 and 90%.

[0103] In the case where the longitudinal recess 12 is formed by a groove cut into a monolithic bar 6, the depth of the longitudinal recess 12, measured in the stacking direction y, is less than the height of the passage 3 in which the bar is located. Preferably, the internal dimension of the longitudinal recess 12 is equal to the depth of the recess, the ratio between the external dimension of the measuring member 14 and the depth of the recess being at most 95%, preferably between 70 and 90%.

[0104] In the context of a leak measurement, the external surface of the measuring element 14 is preferably not in contact with the surface of the internal walls of the recess 12. By contact, we mean a direct or indirect thermal contact, in particular a thermal contact through a material allowing heat transfer between the external surface of the measuring element 14 and the walls of the recess 12. This absence of contact makes it possible to improve the response of the system by avoiding the thermal inertia of the material.

[0105] Alternatively, the external surface of the measuring element 14 is in thermal contact with at least part of the surface of the internal walls of the recess 12. Such a configuration can be used in particular in the context of measuring the characteristics of the fluids flowing in the exchanger in order to monitor or characterize its operation.

[0106] The measuring element may optionally be fixed in the recess, on the bar 6 or on a part of the stack 1, for example glued with a cement or an adhesive having good thermal conductivity.

[0107] Preferably, with reference to a partial schematic representation in [Fig. 5], the heat exchanger according to the invention comprises a cold box having walls 20 forming a closed enclosure around the stack 1. The measuring element 14 extends between a first end 14c and a second end 14d located outside the cold box, and circulates inside the cold box by passing through at least one opening provided in at least one wall of the cold box. This allows the instrumentation necessary for the detection and processing of the measurement signals to be placed, and the where appropriate to the fluid supply control systems of the exchanger, outside the cold box in order to limit the constraints on this type of equipment which can therefore be positioned in the control area of ​​the unit.

[0108] Of course, the invention is not limited to the specific examples described and illustrated in this application. Other variations or embodiments within the scope of the person skilled in the art may also be considered without departing from the scope of the invention defined by the following claims.

Claims

Demands

1. A brazed plate heat exchanger comprising a stack (1) of plates (2) arranged parallel to each other so as to define between said plates (2) a plurality of passages (3), the plates (2) each comprising at least one first edge (4) extending parallel to a first direction (z), at least one passage (3) defined between two consecutive plates (2) comprising at least one sealing bar (6) arranged so as to delimit at least partially one or more internal volumes for the flow of one or more fluids within said passage (3), the sealing bar (6) comprising at least one longitudinal recess (12), the sealing bar (6) and the longitudinal recess (12) extending, in their length, parallel to the first direction (z), characterized in that at least one measuring element (14) is arranged in the longitudinal recess (12) and configured to measure at least one physical quantity,in particular at least one temperature, in said longitudinal recess (12).

2. Exchanger according to claim 1, characterized in that said at least one sealing bar (6) is arranged at the first edge (4) so ​​as to separate at least partially an internal volume from the outside of the stack or in that said at least one sealing bar (6) is arranged at a predetermined distance from the first edge (4) so ​​as to separate at least partially one internal volume from another internal volume within the passage (3).

3. Exchanger according to any one of claims 1 or 2, characterized in that said at least one measuring member (14) is long-sloping and extends, in its length, parallel to the first direction (z) in the longitudinal recess (12), the measuring member preferably being configured to measure several values ​​of said physical quantity along the first direction (z).

4. Exchanger according to any one of the preceding claims, characterized in that said at least one measuring element (14) comprises at least one optical waveguide, in particular at least one optical fiber.

5. Heat exchanger according to any one of the preceding claims, characterized in that the sealing bar (6) comprises a first bar portion (61) and a second bar portion (62) that are physically distinct, each extending parallel to the first direction (z) and spaced apart by the other following a second direction (x) orthogonal to the first direction (z) and parallel to the plates (2) so that the longitudinal recess (12) is formed by the space provided between the first part of bar (61) and the second part of bar (62) or in that the longitudinal recess (12) is formed by a groove provided in a monolithic sealing bar (6) comprising two lateral faces (63) facing each of the adjacent plates (2), the groove (12) opening onto one or the other of the lateral faces (63) of the bar (6).

6. Heat exchanger according to any one of the preceding claims, characterized in that it comprises at least two sealing bars (6) arranged in opposition between two adjacent plates (2), each bar extending, in the length direction, parallel to the first direction (z) and comprising at least one longitudinal recess (12) extending, in the length direction, parallel to the first direction (z) and provided with at least one measuring element (14).

7. Heat exchanger according to any one of the preceding claims, characterized in that the longitudinal recess (12) and the measuring member (14) extend over at least 50%, preferably at least 75%, preferably even the whole, of the length of the sealing bar (6).

8. Heat exchanger according to any one of the preceding claims, characterized in that the sealing bar (6) comprises at least one longitudinal face (64) parallel to the first direction (z) and at least one transverse face (65) orthogonal to the first direction (z), the longitudinal recess (12) opening outwards from the stack (1) through at least one opening (11) located on the transverse face (65) of the sealing bar (6), preferably the sealing bar (6) comprises two opposite transverse faces (65) and the longitudinal recess (12) opening outwards from the stack (1) through two openings (11) located on each of the opposite transverse faces.

9. Heat exchanger according to any one of the preceding claims, characterized in that it comprises at least one set of sealing bars (6) extending, in their length direction, parallel to the first direction (z) and arranged one above the other in a stacking direction (y) orthogonal to the plates (2), each sealing bar (6) of said set comprising at least one longitudinal recess (12) extending, in the length direction, parallel to the first direction (z) and provided with at least one measuring element (14).

10. Heat exchanger according to claim 9, characterized in that the bars sealing bars (6) of said assembly each comprise at least one longitudinal face (64) parallel to the first direction (z), at least one transverse face (65) orthogonal to the first direction (z) and at least one longitudinal recess (12) extending, in the length direction, parallel to the first direction (z) and provided with at least one measuring element (14), the longitudinal recesses (12) of each sealing bar (6) opening outwards to the outside of the stack (1) through respective openings (11) located at the level of the transverse faces (65) of each bar, at least one measuring element (14) extending outwards from a longitudinal recess (12) through one of the openings (11) and then entering into an adjacent longitudinal recess (12) through another of said openings (11).

11. Exchanger according to any one of claims 9 or 10, characterized in that the measuring member (14) comprises at least two internal portions (14a) each arranged in a longitudinal recess (12) of a sealing bar (6) and connected in one piece by a curvilinear external portion (14b) arranged outside the stack (1), preferably the external portion (14b) has a radius of curvature of at least 10 cm, preferably of at least 20 cm.

12. Exchanger according to claim 11, characterized in that the plates (2) have two second opposite edges (5) arranged parallel to a second direction (x) orthogonal to the first direction (z), the measuring member (14) comprising a plurality of internal portions (14a) connected by external portions (14b) situated alternately on the side of one or the other of the second opposite edges (5).

13. Heat exchanger according to any one of claims 9 to 12, characterized in that the stack has a total height (H) measured along the stacking direction (y), the sealing bars (6) of said assembly being separated from each other by intermediate heights (h) measured along the stacking direction (y), the ratio between the intermediate heights (h) and the total height (H) being between 5 and 50%.

14. Heat exchanger according to any one of the preceding claims, characterized in that said at least one longitudinal recess (12) and said at least one measuring member (14) have, along at least one direction orthogonal to the first direction (z) if the sealing bar (6) is arranged parallel to the first direction (z) or parallel to the first direction (z) if the sealing bar (6) is arranged orthogonally afinally to said second direction (x), an inner dimension an outer dimension respectively, the ratio between the outer dimension of the measuring member (14) and the inner dimension of the longitudinal recess (12) being at most 95%, preferably between 70 and 90%.

15. Heat exchange installation comprising a heat exchanger according to any one of the preceding claims and comprising at least one distribution line configured to distribute one or more fluids into one or more internal volumes of at least one passage (3), at least one fluid control device configured to allow, modify and / or stop the distribution of at least one fluid through the distribution line, the measuring element (14) being configured to generate at least one leak signal in response to a variation of said physical quantity and the control device being configured to modify or stop the distribution of said fluid through the distribution line in response to said leak signal.

16. Use of a heat exchanger according to any one of claims 1 to 14 or of an installation according to claim 15 for heat exchange connection at least one fluid with at least one other fluid, the fluid and / or the other fluid comprising one of: neon, krypton, xenon, nitrogen, argon, oxygen, hydrogen, helium, carbon monoxide, carbon dioxide, methane, in particular for liquefying or cooling gaseous oxygen by heat exchange with liquid nitrogen or liquid argon.

17. Cryogenic air separation unit comprising at least one exchanger according to any one of claims 1 to 14 or an installation according to claim 15, unit in which said exchanger liquefies or cools a flow of gaseous oxygen from the cryogenic air separation unit with liquid nitrogen or liquid argon which heats or vaporizes.

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