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 one 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 at least partially delimit 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 the direction of their length, parallel to the first direction (z).According to the invention, at least one measuring member (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 abstract: 2.

Description

Title of the invention: Heat exchanger with leak detection system

[0001] The present invention relates to a heat exchanger of the brazed plate type comprising at least one measuring member making it possible to detect a leak in the exchanger.

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

[0003] The present invention may also be applied to a heat exchanger which heats or vaporizes at least one flow of liquid-gas mixture, in particular a flow of a mixture with several constituents, for example a mixture of hydrocarbons, by heat exchange with at least one other fluid, for example natural gas or nitrogen gas. An exchanger according to the invention may also be used to vaporize or heat liquefied natural gas against nitrogen gas which cools or liquefies.

[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 may also be an exchanger-reactor or catalytic exchanger configured for the implementation of chemical reactions with the fluid(s) circulating in the exchanger.

[0006] A commonly used technology for heat exchangers is brazed plate exchangers, which make it possible to obtain very compact components offering a large exchange surface area and low pressure losses. These exchangers are formed from a set of parallel plates between which can be inserted intercalary elements, such as corrugated or wave structures, which form finned heat exchange structures. The stacked plates form between them a stack of flat passages for different fluids to be put into exchange relation. thermal.

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

[0008] Due to their compactness and monolithic construction, it is difficult to carry out measurements of physical quantities, in particular temperatures, within these plate exchangers. Thus, in the majority of processes in which they are installed, the operator only has access to the total thermal power exchanged between fluids, thanks to an energy balance carried out 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 of the passages.

[0009] In use, the absence of local data limits the possibilities for controlling the process. In particular, certain particular physical phenomena which can take place within the exchanger, such as phase changes or chemical reactions, result in a local variation in temperature, which also depends on the position considered in the exchanger.

[0010] Local temperature measurement would make it possible to detect in situ poor operating conditions of the exchangers: poor distribution of fluids, reduction in the performance of certain areas of the exchanger due for example to blockage or local distillation phenomena. It is also useful to benefit from local temperature or heat flow measurements to monitor the evolution of the performance of plate and fin exchangers during their lifetime.

[0011] "In situ" temperature measurement methods exist, but they are relatively intrusive, because they modify the fluid flows within the exchange passages. And because they are not planned from the construction of the exchanger, their implementation is relatively complex, expensive and not very robust.

[0012] Furthermore, in the case of brazed plate exchangers, the geometry and microstructure of the brazing material connecting the constituent elements of the exchanger together make the brazed areas subject to fatigue damage, the appearance and propagation of cracks and therefore to a risk of fluid leaks. This risk increases in the case of exchangers operating in cycling, that is to say 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 an alteration in the quality of the fluid leaving the exchanger. Possible leaks can also degrade the operating conditions and performance of the exchangers and the associated process.

[0014] Document FR-A-2929369 discloses a plate exchanger having doubled passage sealing bars, so that the space between them forms a dead zone open to the atmosphere by a vent through which any possible fluid leak can escape. However, this solution does not make it possible to detect the appearance of a leak, in particular to be able to adjust or stop the operation of the exchanger if necessary, nor to locate the leak, in particular to facilitate inspection of the exchanger subsequently.

[0015] An alternative to limit these risks is to use coil-type exchangers, which is a possible alternative, but these exchangers nevertheless remain much less efficient than plate exchangers, whose large exchange surface area 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] For this purpose, the invention relates to a heat exchanger of the brazed plate type comprising a stack of plates arranged parallel to each other so as to define between said plates a plurality of passages, the plates each 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 at least partially delimit 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 the direction of their length, parallel to the first direction (z), characterized in that at least one measuring member 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 comprise one or more of the characteristics 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 exterior 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 member is of elongate shape and extends, in the direction of its length, parallel to the first direction in the longitudinal recess, the measuring member preferably being configured to measure several values ​​of said physical quantity along the first direction.

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

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

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

[0024] The longitudinal recess and the measuring member extend over at least 50%, preferably at least 75%, more preferably 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 from 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 from 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 the direction of their length, parallel to the first direction and arranged one above the other following a stacking direction orthogonal to the plates, each sealing bar of said set comprising at least one longitudinal recess extending, in the direction of the length, parallel to the first direction and provided with at least one measuring member.

[0027] The sealing bars of said assembly each comprise at least one Ion- face longitudinal parallel to the first direction, at least one transverse face orthogonal to the first direction and at least one longitudinal recess extending, in the lengthwise direction, parallel to the first direction and provided with at least one measuring member, the longitudinal recesses of each sealing bar opening out towards the outside of the stack through respective openings located at the level of the transverse faces of each bar, at least one measuring member extending outside a longitudinal recess through one of the openings then returning inside an adjacent longitudinal recess through another of said openings.

[0028] The measuring member comprises at least two internal portions each arranged in a longitudinal recess of a sealing bar and connected in one piece by a curvilinear external 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 situated 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, in 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 orthogonal 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] Furthermore, the invention relates to a heat exchange installation comprising an exchanger according to one of the preceding claims and comprising at least one distribution pipe configured to distribute one or more fluids in one or more internal volumes of at least one passage, at least one fluid control device configured to authorize, modify and / or stop the distribution of at least one fluid through the distribution pipe, the measuring member being configured to generate at least one leak signal in response to a variation in said physical quantity and the control device being configured to modify or stop the distribution of said fluid through the distribution pipe 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 of an installation according to the invention for putting at least one fluid into heat exchange relation 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.

[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, a unit in which said exchanger carries out a liquefaction or a 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 thanks to the description which follows, given by way of non-limiting example and made with reference to the appended figures among which:

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

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

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

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

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

[0041] [Fig.6] is a longitudinal sectional view of a measuring member according to one embodiment of the invention.

[0042] [Fig. 1] represents an embodiment in which the heat exchanger is of the brazed plate and fin type comprising a stack 1 of plates 2 which extend in two dimensions, length and width, respectively in a first direction z and a second direction x. Preferably, the stack 1 is of parallelepipedal shape. The plates 2 are arranged one above the other, parallel to each other, and with spacing. They thus form between them several sets of passages 3, certain passages being provided for the flow of a first fluid F1, and other passages provided for the flow of at least one other fluid F2, F3 to be put in indirect heat exchange relation with F1 via the plates 2. Preferably, the second direction x is perpendicular to the first direction z and parallel to the plates 2. The fluids preferably flow along the length of the exchanger, the length being large compared to the width of the exchanger. In the illustrated case, the first direction z corresponds to the longitudinal extension direction of the exchanger and the fluids flow generally parallel to the first direction z. Other flow directions are of course conceivable within the scope of the invention, in particular fluid flow directions generally parallel to the first direction x.

[0043] Preferably, each passage has a parallelepiped and flat 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] The plates 2 each comprise at least one first edge 4 extending parallel to the first direction z. Preferably, the plates 2 each comprise a pair of first edges 4 arranged parallel to the first direction z and in opposition to each other. According to the embodiment illustrated in [Fig.l], the plates 2 are further delimited by a pair of second edges 5 arranged parallel to the second direction x in opposition to each other.

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

[0046] Depending on the location of the fluid introduction and evacuation zones of the exchanger, the sealing bars 6 may not completely close the passages, but leave free openings for the entry or exit of the corresponding fluids. The exchanger 1 comprises semi-tubular shaped collectors 7, 9 provided with inlets and outlets 10 for the introduction of fluids into the exchanger and the evacuation of fluids from the exchanger. Distribution zones arranged downstream of the inlet collectors and upstream of the outlet collectors serve to channel the fluids homogeneously to or from the entire width of the passages.

[0047] Alternatively or additionally, at least part of the passages 3 may comprise at least one sealing bar 6 arranged so as to delimit at least partly several internal volumes within the passage 3. Different fluids can flow in 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 intermediate elements 8 which advantageously extend along the width and length of the passages of the exchanger, parallel to the plates 2. In the example illustrated, the intermediate elements 8 comprise heat exchange waves in the form of corrugated sheets. In this case, the wave legs which connect the successive peaks and bases of the wave are called "fins". The intermediate elements 8 may also have other particular shapes defined according to the desired fluid flow characteristics. More generally, the term "fins" covers blades or other secondary heat exchange surfaces, which extend from the primary heat exchange surfaces, i.e. the plates of the exchanger, into the passages of the exchanger.

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

[0050] Preferably, during the manufacture of the exchanger 1, a set of plates 2 is supplied and stacked parallel to each other and to the first direction z. The plates 2 are spaced from each other by the sealing bars 6. After assembly of the other constituent elements of the exchanger, in particular the exchange waves, the distribution waves, etc., the stack is brazed in order to secure the elements of the exchanger to each other. A filler metal, called brazing or brazing agent, is arranged between the elements of the exchanger. Preferably, the plates and all or part of the other constituent elements of the exchanger are made of aluminum or 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 delimit with the adjacent plates 2 at least one internal volume in which at least one fluid can circulate. The sealing bars 6 are arranged so as to prevent the fluid from escaping from an internal volume of the passage 3 to the outside of the stack and / or so as to prevent the fluid from circulating between several internal volumes of the same passage 3 where appropriate. Sealed junction zones are formed between the sealing bars and the adjacent plates, in particular by brazing the bars with the plates. However, due to the thermal and mechanical stresses undergone by the exchanger over time, the sealing of the passages can deteriorate and the first fluid can infiltrate between the sealing bars and the plates. adjacent.

[0052] According to the invention, at least one sealing bar 6 extending in 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 lengthwise direction, parallel to the first direction z. A measuring member 14 is arranged in the longitudinal recess 12 and configured to detect a variation of at least one physical quantity, in particular a temperature variation, in the longitudinal recess 12.

[0053] The invention thus makes it possible to detect a possible fluid leak at the sealing bar 6 from the neighboring 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 the 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 exchanger can therefore be stopped in order to ensure the safety of the operators and to reduce the risks of pollution 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 member 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 member 14 in a sealing bar 6 does not increase the size of the exchanger. It is possible to carry out temperature measurements locally by choosing the positioning of the measuring member. In addition, the measuring member can be inserted after the stack formation step, which reduces the risk of damage to the probe and allows the use of a wider variety of technologies without being limited to 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 comprises the longitudinal recess, such as the temperature, without disturbing the flow of the fluid. Such measurements make it possible to detect possible malfunctions of the exchanger or to dynamically monitor the characteristics of the fluid and in particular to assess the thermal shocks undergone by the exchanger.

[0056] [Fig.2] represents an embodiment in which a longitudinal recess 12 is provided in a bar 6 extending parallel to the first direction z, which defines an overall direction of flow of the fluid Fl. In addition to leak detection, this configuration makes it possible to locally measure the temperature of the fluid, and therefore its evolution, at different positions along the length of the exchanger, as it exchanges heat with another fluid circulating in an adjacent passage. This provides information on the physical phenomena that can take place within the exchanger, including phase changes, chemical reactions, and their location in 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 provided with measuring members 14. It is also conceivable that one or more longitudinal recesses 12 are 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 each further comprise at least one second edge 5 extending perpendicularly to the first direction z, at least one sealing bar 6 being arranged, in the lengthwise direction, parallel to the second edge 5 and comprising at least one longitudinal recess 12 extending, in the lengthwise 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 may be arranged at a first edge 4 or a second edge 5 so as to form a peripheral bar at least partially separating an internal volume from the exterior of the stack. The sealing bar thus at least partially delimits the periphery of a passage 3. At least one sealing bar 6 may also be arranged at a predetermined distance from a first edge 4 or a second edge 5 so as to form a separation bar separating an internal volume from another internal volume within the passage 3. The sealing bar thus at least partially delimits an internal volume 3A relative to another volume 3B within 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 separation bar.

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

[0061] Arranging measuring members 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 check whether the fluid is distributed evenly across the width of the passage, in particular to check that the physical quantity measured is identical on each side. In particular, taking temperature measurements on each side of the passage allows for effective detection of any maldistribution phenomena. The heat exchange in the passage, on which the fluid and bar temperatures depend, is linked to the fluid flow rate near the probes. The temperature differences between each side therefore reveal differences in flow rate. In addition, the probes allow for dynamic monitoring of transient temperature regimes over time and for assessing the thermal shocks experienced by the exchanger.

[0062] Preferably, the longitudinal recess 12 and the measuring member 14 extend over at least 50%, preferably at least 75%, more preferably the entire length of the sealing bar 6. It is noted that the length of the bar 6 is measured along its longitudinal extension direction, in particular along the first direction z in the case where the bar extends, in the direction of its length, along the first direction z. Thus, it is possible to arrange one or more measuring members along a significant proportion of the length or width of passages 3 and therefore to 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 in the length and / or width of the exchanger, to determine where leaks are occurring.

[0063] According to one embodiment, the exchanger comprises at least one set of sealing bars 6 arranged parallel to the first direction z and one above the other following the stacking direction y. At least one measuring member 14 is arranged in the longitudinal recess 12 of each of the sealing bars 6 of the set. It is thus possible to detect possible fluid leaks at different positions in the height of the stack and to identify the passage(s) concerned. Each recess 12 of a bar 6 makes it possible to detect a leak coming 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 member 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, 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 provided with at least one sealing bar according to the invention is between 1 and 10, preferably greater than or equal to 5.

[0068] It is 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 outwards from the stack 1 through at least one opening 11. This allows a leak of the first fluid to escape therein towards the outside of the stack. The opening 11 may 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 member 14. In particular, the longitudinal recess is through and opens onto two openings 11 located on either side of the length of the bar 6, which allows a more flexible arrangement of the measuring member. Preferably, the measuring member 14 projects outwards from 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 of parallelepipedal shape. The cross-section of said bar may be of square or rectangular shape. The sealing bar 6 comprises two opposite longitudinal faces 64 which are parallel to the first direction z and to the stacking direction y. Depending on the positioning of the bar in the exchanger, one longitudinal face 64 is oriented towards an internal volume for the circulation of a fluid 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 opposite lateral faces 63 which are parallel to the first direction z and orthogonal to the stacking direction y. The opposite lateral faces 63 face the adjacent plates 2.

[0072] As seen in [Fig.2], the sealing bar 6 may comprise a first bar portion 61 and a second bar portion 62 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 partial loss of the sealing provided by one or the other of the first and second bar portions, fluid may flow and be collected in the recess 12.

[0073] According to another possibility, the longitudinal recess 12 is formed by a groove provided in a monolithic sealing bar 6. In particular, the groove may have any suitable cross-sectional shape, in particular square, rectangular, semi-circular. The groove preferably opens onto one or other of the lateral faces 63 of the bar 6 which face one or the other of the adjacent plates 2. The groove has a second width measured along the second direction x less than the total width of the sealing bar. In the event of at least partial loss of the seal provided by the sealing bar, fluid can flow 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 comprise 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 the first edges 4 of the plates 2 and the external longitudinal faces 64e of the bars 6 are located. In addition, the stack 1 may have at least one second face, parallel to the second direction x, where the second edges 5 of the plates 2 and transverse faces 65 of the bars 6 are located.

[0078] [Fig.4] illustrates an embodiment in which the 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 member 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 out to the outside of the stack 1.

[0079] According to one possibility, the exchanger may comprise 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 member 14 extends towards the outside of a longitudinal recess 12 through one of the openings 11 and then returns inside an adjacent longitudinal recess 12 through another of said openings 11. Thus, the same measuring member can equip distinct recesses 12 and therefore detect leaks from 3 separate passages.

[0081] In particular, 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, 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 second opposite edges 5 arranged parallel to the second direction x, 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 edges 5. The same measuring member can thus extend in a serpentine fashion within the stack. This arrangement makes it possible to have only one measuring member and therefore only one signal transmission and acquisition system. This simplifies operation and facilitates maintenance of the exchanger. The associated investment costs are reduced.

[0083] Alternatively or additionally, not illustrated, the exchanger may comprise at least a second set of sealing bars parallel to the second direction x and arranged one above the other in the stacking direction y, each with at least one longitudinal recess provided with at least one measuring member. In particular, the sealing bars of the second set each comprise at least one opening through which the longitudinal recesses open to the outside of the stack. Said 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 direction x and that the openings 11 open on the side of the first edges 4 and are arranged on transverse faces of the bars 6 arranged parallel to the first direction z.

[0084] Preferably, with reference to the example of [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 member is of elongated shape so that it can be easily inserted into the recess and not increase the size of the exchanger.

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

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

[0088] According to an advantageous embodiment, said at least one measuring member 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 a network of several optical fibers in series or in parallel.

[0089] An optical waveguide is defined as a structure for confining and guiding light. This guide is made up of two or more layers of transparent dielectric materials, for example silica glass or plastic, with different refractive indices ensuring the confinement of light near the center. An optical fiber is an optical waveguide with circular symmetry. The optical fiber generally consists of a dielectric medium called the fiber core, covered with a material called optical cladding, with a refractive index lower than that of the core. The assembly is itself surrounded by an envelope, generally 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. Fiber optic 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, in particular temperature, deformation, etc.

[0090] Optical fibers have the advantages of requiring only limited instrumentation and little, if any, electrical 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 may be the envelope of the fiber, or a tubular sleeve arranged around the envelope, preferably made of metallic material.

[0092] Preferably, the fiber optic measuring member 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 measuring 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 the absorption of light. 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 of the fiber and to translate them in the form of 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. [Fig.6] shows a diagram of an embodiment in which a measuring member 14 comprising at least one optical fiber is connected to a device 23 for emitting at least one light pulse 23 configured to determine the physical quantity at different sensitive points or zones 22a, 22b, etc. along the optical fiber.

[0093] The temperature profile measured along the optical fiber is generally a discontinuous profile, that is to say consisting of a series of temperatures, each of which corresponds to a finite element of said optical fiber.

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

[0095] It is in particular possible to use Rayleigh backscattering which is the consequence of the interaction between the impurities of the fiber and an electromagnetic field. The local variation of the refractive index linked to the variation of temperature and / or deformation varying the intensity of the backscattered wave, it is possible to go back to the desired information.

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

[0097] Preferably, these phenomena are implemented by means of a device of the type OTDR (acronym for Optical Time Domain Reflectometry) which consists of sending a long light pulse, it is possible to go back to the position of the measuring point or sensitive area knowing the propagation speed of the light wave in the material. The spatial resolution is a function of the length of the pulse sent.

[0098] According to another possibility, a measuring member 14 comprising at least one optical fiber with Bragg gratings may be used. A fiber Bragg grating is an optical fiber whose core has a refractive index that varies alternately 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 to allow others to pass through. The reflected wavelength depends on the distance between a section with a high refractive index and the sections with a low refractive index. The distance between two sections with a high refractive index is called the period of the Bragg grating. Each measuring point or sensitive zone reflects a wavelength thanks to a pattern "printed on the fiber". The reflected wavelength varies according to the temperature and the deformation.

[0099] Note that it is also possible to use a resistance temperature measuring member 14, for example a resistance probe, in particular a platinum resistance probe of the PT 100 type, or a thermocouple or thermistor temperature measuring member 14. In particular, the measuring member 14 may comprise a protective sheath 16 in which several resistance, thermocouple or thermistor measuring elements are arranged discreetly along the sheath, thus making it possible to carry out measurements at different positions along the measuring member, and therefore at different positions in the exchanger.

[0100] The transverse dimension(s) of the longitudinal recess 12 may be adapted as a function of 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, in 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 inner dimension and 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%. 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 avoid the measuring member being in tension due to differential expansions between the measuring member and the material surrounding this recess.This reduces the risk of breakage. the measuring member. The external dimension of the member 14 is understood to be the external dimension of the protective sheath, if applicable.

[0102] In the case where the longitudinal recess 12 is formed by the space provided between two separate bar parts 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 formed in 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 member 14 is preferably not in contact with the surface of the internal walls of the recess 12. By contact is meant a direct or indirect thermal contact, in particular a thermal contact by means of a material allowing a thermal transfer between the external surface of the measuring member 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 member 14 is in thermal contact with at least a portion 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 with a view to monitoring or characterizing its operation.

[0106] The measuring member 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 diagram in [Fig.5], the exchanger according to the invention comprises a cold box comprising walls 20 forming a closed enclosure around the stack 1. The measuring member 14 extending between a first end 14c and a second end 14d located outside the cold box, and circulating inside the cold box passing through at least one orifice provided in at least one wall of the cold box. This makes it possible to place the instrumentation necessary for the detection and processing of the measurement signals, and the where appropriate to the exchanger fluid supply control systems, outside the cold box in order to limit the constraints on this type of equipment which can therefore be positioned in the unit control area.

[0108] Of course, the invention is not limited to the particular examples described and illustrated in the present application. Other variants or embodiments within the reach of those skilled in the art may also be envisaged without departing from the scope of the invention defined by the claims below.

Claims

Claims

1. Brazed plate type 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 at least partially delimit 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 the direction of their length, parallel to the first direction (z), characterized in that at least one measuring member (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 at least partially separate an internal volume from the exterior 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 at least partially separate an internal volume from another internal volume within the passage (3).

3. Exchanger according to one of claims 1 or 2, characterized in that said at least one measuring member (14) is of elongate shape and extends, in the direction of 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 one of the preceding claims, characterized in that said at least one measuring member (14) comprises at least one optical waveguide, in particular at least one optical fiber.

5. Exchanger according to one of the preceding claims, characterized in that the sealing bar (6) comprises a first bar part (61) and a second bar part (62) physically distinct each extending parallel to the first direction (z) and spaced apart from each other. 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 bar part (61) and the second bar part (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. Exchanger according to 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 member (14).

7. Exchanger according to 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%, more preferably the entire length, of the sealing bar (6).

8. Exchanger according to 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 towards the outside of the stack (1) by 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) opens towards the outside of the stack (1) by two openings (11) located on each of the opposite transverse faces.

9. Exchanger according to one of the preceding claims, characterized in that it comprises at least one set of sealing bars (6) extending, in the direction of their length, parallel to the first direction (z) and arranged one above the other following 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 direction of the length, parallel to the first direction (z) and provided with at least one measuring member (14).

10. Exchanger according to claim 9, characterized in that the bars sealing bar (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 lengthwise direction, parallel to the first direction (z) and provided with at least one measuring member (14), the longitudinal recesses (12) of each sealing bar (6) opening out towards the outside of the stack (1) by respective openings (11) located at the level of the transverse faces (65) of each bar, at least one measuring member (14) extending outside a longitudinal recess (12) by one of the openings (11) then returning inside an adjacent longitudinal recess (12) by another of said openings (11).

11. Exchanger according to 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 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 other of the second opposite edges (5).

13. Exchanger according to 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. Exchanger according to one of the preceding claims, characterized in that said at least one longitudinal recess (12) and said at least one measuring member (14) have, in 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 orthogo- finally 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 an exchanger according to one of the preceding claims and comprising at least one distribution pipe configured to distribute one or more fluids in one or more internal volumes of at least one passage (3), at least one fluid control device configured to authorize, modify and / or stop the distribution of at least one fluid via the distribution pipe, the measuring member (14) being configured to generate at least one leak signal in response to a variation in said physical quantity and the control device being configured to modify or stop the distribution of said fluid via the distribution pipe in response to said leak signal.

16. Use of an exchanger according to one of claims 1 to 14 or of an installation according to claim 15 for putting at least one fluid into heat exchange relation 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 one of claims 1 to 14 or an installation according to claim 15, unit in which said exchanger operates a liquefaction or a 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.

Images