Mixing device for promoting homogeneous distribution of a two-phase mixture, heat exchange device and associated mixing process

Description

[0001] The present invention relates to a mixing device for distributing a mixture of two liquid / gas phases more homogeneously in at least one passage of a heat exchanger as well as a heat exchange installation comprising such a mixing device.

[0002] In particular, the present invention can be applied to a heat exchanger which vaporizes at least one flow of liquid-gas mixture, in particular a flow of liquid-gas mixture with several constituents, for example a mixture comprising hydrocarbons, by heat exchange with at least one other fluid, for example natural gas, which cools, or even liquefies at least in part, or even liquefied natural gas which subcools.

[0003] Among the processes using one or more fluid refrigeration cycles with two-phase refrigerant, i.e. in the state of liquid / gas mixture, several methods are known for liquefying a natural gas stream to obtain liquefied natural gas (LNG). Typically, a refrigerant stream, generally a mixture of several constituents, such as a mixture containing hydrocarbons, is compressed by a compressor and then introduced into an exchanger or a succession of exchangers where it is completely liquefied and sub-cooled to the coldest temperature of the process reached by the fluids which are cooled, typically that of the liquefied natural gas stream. At the coldest outlet of the exchanger, the refrigerant stream is expanded to form a first phase and a second phase. These two phases are separated by means of a phase separator and then reintroduced into the exchanger and remixed before being reintroduced into the exchanger.The refrigerant stream introduced in a two-phase state into the exchanger is vaporized there against the stream of hydrocarbons which liquefies and against the natural gas. Document WO-A-2017081374 describes one of these known methods.

[0004] The use of brazed plate and fin aluminum exchangers makes it possible to obtain very compact devices offering a large exchange surface, which improves the energy performance of the process, and this in a limited volume.

[0005] These exchangers comprise a stack of plates which extend in two dimensions, length and width, thus constituting a stack of several sets of passages positioned one on top of the other, some being intended for the circulation of a heat-generating fluid, for example the stream of hydrocarbons to be liquefied, others being intended for the circulation of a refrigerant fluid, for example the two-phase refrigerant stream to be vaporized.

[0006] Heat exchange structures, such as heat exchange waves, are generally arranged in the exchanger passages. These structures include fins that extend between the exchanger plates and increase the heat exchange surface area of the exchanger. They also act as spacers and contribute to the mechanical strength of the passages.

[0007] Certain problems arise in exchangers using two-phase refrigerant flows, particularly when their vaporization takes place in an upward vertical flow.

[0008] Indeed, in order to ensure the proper functioning of the exchanger, that is to say in particular to maximize the use of its exchange surface, in particular for an exchanger using a liquid-gas mixture, the proportion of liquid phase and gas phase must be the same in all passages and must be uniform within the same passage.

[0009] The sizing of the exchanger is calculated assuming a uniform distribution of the phases, and therefore a single end of vaporization temperature of the liquid phase per passage, equal to the dew point temperature of the mixture.

[0010] For a mixture with several components in particular, the end of vaporization temperature will depend on the proportion of liquid phase and gas phase in the passages given that the two phases do not have the same compositions.

[0011] In the case of an unequal distribution of the two phases, the temperature profile of the first fluid will therefore vary according to the passages and / or within the same passage. Due to this non-uniform distribution, it may then happen that the fluid(s) in exchange relationship with the two-phase mixture have a temperature at the outlet of the exchanger higher than that expected, which consequently degrades the performance of the heat exchanger.

[0012] One solution to distribute the liquid and gas phases of the mixture as evenly as possible is to introduce them separately into the exchanger, then mix them together only inside the exchanger.

[0013] Documents FR-A-2563620 or WO-A-2018172644 describe such exchangers in which a grooved bar is inserted into the series of passages intended to channel the two-phase mixture. This mixing device comprises a series of separate channels or grooves for the flow of the liquid phase of the refrigerant and another series of separate channels for the flow of the gaseous phase of the refrigerant. The channels of one series are fluidically connected to channels of the other series by orifices so that a liquid-gas mixture, i.e. a two-phase flow, is distributed at the outlet of the mixing device to the heat exchange zone. Each refrigerant passage of the exchanger is provided with such a device.

[0014] A problem that arises with this type of mixing device concerns the uneven distribution of the liquid-gas mixture across the width of the exchanger passages.

[0015] Indeed, the two-phase mixture is distributed at the outlet of the channels opening into the passage. As the channels are arranged at a certain distance from each other, the introduction of the liquid-gas mixture into the exchange zone is done discretely over the width of the passage. As the fluid flows along the overall flow direction in the exchanger, a distribution can take place in the direction orthogonal to the overall flow direction, in particular thanks to the exchange waves generally used in this type of exchanger such as perforated or serrated waves (from the term "serrated" in English). Thus, "serrated" waves tend to deflect part of the fluid from its flow direction and the perforated waves put the channels formed by the waves into fluidic relation.

[0016] However, homogenization of the fluid distribution across the width of the exchanger is only achieved after a certain distance traveled by the mixture after leaving the mixing device. Over this distance, the fluid feeds the exchange zone with unequal mass flow rates depending on the position considered across the width of the exchanger; some channels of the exchange waves may be poorly or even not fed at all. The performance of the exchanger is degraded. In addition, such distribution by lateral deflection of the fluid is not possible with non-perforated straight waves.

[0017] Exchangers operating under small temperature differences between the heat-transferring and refrigerating fluids are all the more sensitive to this phenomenon of maldistribution. In addition, the phenomenon of inhomogeneous distribution is accentuated in the case of a refrigerant mixture with several components.

[0018] Document FR 3 064 346 describes a mixing device in which the channels all have downstream portions with external profiles forming an angle, measured between the tangent to said external profile at the point of intersection with the downstream face of the downstream portion and the axis of symmetry of the longitudinal channel, equal to 0°.

[0019] None of the existing solutions are satisfactory. Thus, the arrangement of a free space at the outlet of the mixing device poses problems in terms of mechanical strength of the exchanger and can lead to an accumulation of the first phase in this area. Increasing the number of channels following one another in the width of the exchanger leads to a reduction in the flow rate of the first phase through each orifice of each channel and is detrimental to the good distribution of the two-phase mixture at the outlet of the mixing device. Finally, the arrangement of "hardway" type waves at the outlet of the mixing device or the arrangement of mixing devices with more complex geometry increases the pressure losses, which degrades the performance of the process.

[0020] The present invention aims to solve all or part of the problems mentioned above, in particular by proposing a mixing device allowing a more homogeneous distribution of a two-phase mixture in the width of a heat exchanger passage while limiting the pressure losses that the two-phase mixture can undergo at the outlet of the mixing device.

[0021] The solution according to the invention is then a mixing device for distributing a mixture of a first phase and a second phase of a first fluid generally in a longitudinal direction in at least one passage of a heat exchanger, said mixing device comprising: at least one lateral channel configured for the flow of a first phase of the first fluid from at least one first inlet, a series of longitudinal channels extending in the longitudinal direction and each configured for the flow of a second phase of the first fluid from a second inlet to a second outlet, said longitudinal channels succeeding one another in a lateral direction orthogonal to the longitudinal direction, at least one orifice fluidically connecting said lateral channel to at least one longitudinal channel so that the mixing device is configured to distribute a mixture of the first phase and the second phase through the second outlet of said at least one longitudinal channel, characterized in that said at least one longitudinal channel is divided, in the longitudinal direction,in at least one upstream portion and one downstream portion each having a length measured in the longitudinal direction and a width measured in the lateral direction, the downstream portion being arranged between the upstream portion and the second outlet, said downstream portion having, at any point along its length, a width greater than the width of the upstream portion, , the downstream portion opens at a downstream face of the mixing device, the second outlet being arranged at the downstream face, and in longitudinal section in a plane parallel to the longitudinal direction and to the lateral direction, the external profile forming an angle, measured between the tangent to said external profile at the point of intersection with the downstream face and the axis of symmetry of the longitudinal channel, of between 5 and 85°.

[0022] Depending on the case, the invention may comprise one or more of the following characteristics: the downstream portion has an increasing width, preferably continuously increasing, along its length towards the second outlet. the downstream portion has a minimum width and a maximum width with the ratio DM / D m greater than or equal to 1.1, preferably greater than or equal to 1.8 and / or less than or equal to 4. all or part of the downstream portion has, in longitudinal section in a plane parallel to the longitudinal direction and to the lateral direction, an external profile in the shape of an isosceles trapezoid. all or part of the downstream portion has, in longitudinal section in a plane parallel to the longitudinal direction and to the lateral direction, a curvilinear external profile.the upstream portion of the longitudinal channel is connected to the downstream portion by one end, said at least one orifice opening into said longitudinal channel at the upstream portion at a distance from the end, preferably greater than or equal to 4% and preferably between 7 and 90% of the length of the upstream portion. the at least one orifice is arranged so that, when the first phase flows from the first inlet of the lateral channel and the second phase flows from the second inlet of the longitudinal channel, the mixing of the first phase and the second phase takes place upstream of the downstream portion. the orifice(s) of the mixing device all open at the upstream portion of a longitudinal channel. each longitudinal channel of the series of longitudinal channels comprises at least one orifice opening at its upstream portion, the position of the at least one orifice in the longitudinal direction varying between the longitudinal channels.the length of the upstream portion and the length of the downstream portion are such that the ratio L 3 / L 4 is between 1 and 15, preferably between 3 and 12. all or part of the upstream portion has, in longitudinal section in a plane parallel to the longitudinal direction and to the lateral direction, a rectilinear external profile with a constant width which is preferably equal to the minimum width of the downstream portion. the downstream portion has a depth, measured in a so-called stacking direction which is perpendicular to the longitudinal direction and perpendicular to the lateral direction, increasing in the direction of the second outlet. the longitudinal channel comprises at least one obstacle arranged so as to subdivide the downstream portion into several intermediate channels opening out at the second outlet, preferably said intermediate channels are arranged symmetrically with respect to the axis of symmetry of the longitudinal channel.at the second outlet, the total surface area of said at least one obstacle measured in a cross-sectional plane perpendicular to the longitudinal direction represents between 20 and 80%, preferably between 30 and 70%, of the total fluid passage section of the surface area of the downstream portion measured in said cross-sectional plane. the at least one obstacle has a width, measured in the lateral direction, increasing towards the second outlet, with preferably at least one obstacle having, according to a longitudinal sectional plane, a curvilinear external profile. the longitudinal channel further comprises at least one balancing channel putting the intermediate channels into fluid communication.

[0023] Furthermore, the invention relates to a heat exchanger comprising several plates arranged parallel to each other and in a longitudinal direction, said plates being stacked with spacing so as to define between them at least a first set of passages configured for the flow of the first fluid generally in the longitudinal direction and at least a second set of passages configured for the flow of a second fluid to be put into heat exchange relationship with the first fluid, at least one passage of the first set comprising a mixing device according to the invention.

[0024] Furthermore, the invention relates to a heat exchange installation comprising: a heat exchanger comprising several plates arranged parallel to each other and in a longitudinal direction, said plates being stacked with spacing so as to define between them at least a first set of passages configured for the flow of a first fluid generally in the longitudinal direction and at least a second set of passages configured for the flow of a second fluid to be put into heat exchange relation with the first fluid, a source of a first phase of the first fluid fluidically connected to at least a first collector of the heat exchanger, a source of a second phase of the first fluid fluidically connected to at least a second collector of the heat exchanger, a mixing device according to the invention,said mixing device being arranged in at least one passage of the first series and configured to distribute the first fluid formed from a mixture of the first phase and the second phase in said passage of the first series, the first inlet of the lateral channel being in fluid communication with said first collector, and the second inlet being in fluid communication with the second collector, the first phase being a liquid phase and the second phase being a gaseous phase.

[0025] Preferably, the first phase is a liquid phase. The second phase is a gaseous phase.

[0026] According to another aspect, the invention relates to a method of mixing a first phase and a second phase of a first fluid in a mixing device according to the invention, said method comprising the following steps: i) introducing the first phase of the first fluid through at least a first inlet of the lateral channel, ii) introducing the second phase of the first fluid through a second inlet of each longitudinal channel, the second phase flowing in each longitudinal channel in the longitudinal direction to a second outlet of said longitudinal channel, iii) flowing at least a portion of the first phase from the lateral channel to the longitudinal channel through the orifice so as to mix the first phase with the second phase in the longitudinal channel, iv) distributing the mixture of the first phase and the second phase through the second outlet of each longitudinal channel.

[0027] Preferably, the mixing of the first phase with the second phase is carried out upstream of the downstream portion.

[0028] Furthermore, the invention relates to a method for liquefying a hydrocarbon stream such as natural gas as a second fluid by heat exchange with at least one two-phase refrigerant stream as a first fluid, said method implementing a mixing method according to the invention and comprising the following steps: a) introducing the hydrocarbon stream into a second set of passages of a heat exchanger, b) introducing a refrigerant stream into a third set of passages of the heat exchanger, c) leaving the refrigerant stream from the heat exchanger and expanding the refrigerant stream to at least one pressure level so as to produce at least one two-phase refrigerant stream, d) separating at least a portion of the two-phase refrigerant stream from step c) into a second phase and a first phase, e) arranging a mixing device in at least one passage of a first set of passages of the heat exchanger, f) introducing at least a portion of the second phase and at least a portion of the first phase into the mixing device so as to obtain a first fluid formed from a mixture of the first phase and the second phase at the outlet of the mixing device,g) vaporization of at least a portion of the first fluid from step f) in the passage by heat exchange with at least the hydrocarbon stream so as to obtain a cooled and / or at least partially liquefied hydrocarbon stream at the outlet of the exchanger.

[0029] The term "natural gas" refers to any composition containing hydrocarbons including at least methane. This includes a "raw" composition (prior to any processing or washing), as well as any composition that has been partially, substantially or completely processed for the reduction and / or removal of one or more compounds, including, but not limited to, sulfur, carbon dioxide, water, mercury and certain heavy and aromatic hydrocarbons.

[0030] The present invention will now be better understood thanks to the following description, given solely by way of non-limiting example and made with reference to the appended figures, among which: Fig. 1 schematizes a heat exchange installation according to one embodiment of the invention. Fig. 2 is a three-dimensional schematic view of a mixing device according to one embodiment of the invention. Fig. 3 is a schematic cross-sectional view in a plane perpendicular to the plates of the exchanger, of a first mixing device according to an embodiment of the invention. Fig. 4 is a schematic view in longitudinal section in a plane parallel to the longitudinal direction z and to the lateral direction y of a mixing device according to one embodiment of the invention. Fig. 5 is a schematic view in longitudinal section in a plane parallel to the longitudinal direction z and to the lateral direction y of a mixing device according to another embodiment of the invention. Fig. 6 is a schematic view in longitudinal section in a plane parallel to the longitudinal direction z and to the lateral direction y of a mixing device according to another embodiment of the invention. Fig. 7 is a schematic view in longitudinal section in a plane parallel to the longitudinal direction z and to the lateral direction y of a mixing device according to another embodiment of the invention. Fig. 8 is a schematic view in longitudinal section in a plane parallel to the longitudinal direction z and to the lateral direction y of a mixing device according to another embodiment of the invention. Fig. 9 is a schematic view in longitudinal section in a plane parallel to the longitudinal direction z and to the lateral direction y of a mixing device according to another embodiment of the invention. Fig. 10 represents a configuration of a mixing device and exchanger according to the invention used to carry out fluid flow simulations. Fig.11 represents the results of fluid flow simulations with a mixing device configured according to the prior art and with a mixing device according to an embodiment of the invention. Fig. 12 schematizes a process for liquefying a hydrocarbon stream according to one embodiment of the invention. Fig. 13 schematizes a process for liquefying a hydrocarbon stream according to another embodiment of the invention.

[0031] Fig. 1 is a sectional view of a heat exchanger 1 comprising a mixing device 3 according to the invention. The exchanger 1 is preferably of the brazed plate and fin type. It comprises a stack of plates 2 (not visible) which extend in two dimensions, parallel to a plane defined by a longitudinal direction z and a lateral direction y. The plates 2 are arranged parallel to one another with a spacing between each plate and thus form a superposition of passages for the flow of fluids in indirect heat exchange relationship via said plates.

[0032] Preferably, each passage has a parallelepiped and flat shape. The gap between two successive plates is small compared to the length, measured along the longitudinal direction z, and the width, measured along the lateral direction y, of each passage.

[0033] The exchanger 1 may comprise a number of plates greater than 20, or even greater than 100, defining between them a first set of passages 10 (only one passage is visible on Fig. 1 ) to channel at least a first fluid F1, and a second set of passages 20 (not visible on Fig. 1 ) to channel at least one second fluid F2, the flow of said fluids taking place generally in the direction z. The passages 10 may be arranged, in whole or in part, alternating and / or adjacent to all or part of the passages 20. The exchanger 1 may comprise a third set of passages, or even more, for the flow of one or more additional fluids. These sets of passages are superimposed on each other forming a stack of passages.

[0034] The sealing of the passages 10, 20 along the edges of the plates 2 is generally ensured by lateral and longitudinal sealing strips 4 fixed to the plates 2. The lateral sealing strips 4 do not completely close the passages 10, 20 but advantageously leave fluid inlet and outlet openings located in the diagonally opposite corners of the passages.

[0035] The openings of the passages 10 of the first set are arranged coincidentally one above the other in the stacking direction x of the passages, which is perpendicular to the directions y and z, while the openings of the passages 20 of the second set are arranged in the other corners of the exchanger located on Fig. 1 by the arrows F2, with the inlet and outlet for the second fluid F2 located respectively at the top left and bottom right. The openings placed one above the other are joined respectively in semi-tubular collectors 40, 45, 52, 55, through which the distribution and evacuation of the fluids in and from the passages 10, 20 are carried out.

[0036] Note that fluid introduction and outlet configurations other than that according to Fig. 1 can be used. The passage openings can thus be arranged at other positions within the width of the exchanger, in particular in the center of the width of the exchanger, and / or at other positions within the length of the exchanger.

[0037] In the representation of Fig. 1 , the semi-tubular collectors 52 and 45 are used for introducing fluids into the exchanger 1 and the semi-tubular collectors 40, 55 are used for evacuating these fluids from the exchanger 1.

[0038] In this embodiment variant, the supply manifold for one of the fluids and the discharge manifold for the other fluid are located at the same end of the exchanger, the fluids F1, F2 thus circulating counter-currently in the exchanger 1.

[0039] According to another embodiment, the first and second fluids can also circulate co-currently, the means for supplying one of the fluids and the means for discharging the other fluid then being located at opposite ends of the exchanger 1.

[0040] Preferably, the direction z is oriented vertically when the exchanger 1 is in operation. The first fluid F1 flows generally vertically and in an upward direction. Other directions and flow directions of the fluids F1, F2 are of course conceivable, without departing from the scope of the present invention.

[0041] It should be noted that within the framework of the invention, one or more second fluids F2 of different natures can flow within the passages 20 of the second assembly.

[0042] Preferably, the first fluid F1 is a refrigerant fluid and the second fluid F2 is a heat-transfer fluid.

[0043] The exchanger advantageously comprises distribution waves 51, 54, arranged between two successive plates 2 in the form of corrugated sheets, which extend from the inlet and outlet openings. The distribution waves 51, 54 ensure the uniform distribution and recovery of the fluids over the entire width of the passages 10, 20.

[0044] Furthermore, the passages 10, 20 advantageously comprise heat exchange structures arranged between the plates 2. These structures have the function of increasing the heat exchange surface of the exchanger and increasing the exchange coefficients between the fluids by making the flows more turbulent. Indeed, the heat exchange structures are in contact with the fluids circulating in the passages and transfer heat flows by conduction to the adjacent plates 2, to which they can be fixed by brazing, which increases the mechanical strength of the exchanger.

[0045] The heat exchange structures also have a spacer function between the plates 2, in particular during assembly by brazing of the exchanger and to avoid any deformation of the plates during the implementation of pressurized fluids. They also ensure the guidance of fluid flows in the passages of the exchanger.

[0046] Preferably, these structures comprise heat exchange waves 11 which advantageously extend along the width and length of the passages 10, 20, parallel to the plates 2, in the extension of the distribution waves along the length of the passages. The passages 10, 20 of the exchanger thus have a main part of their length constituting the heat exchange part itself, which is lined with a heat exchange structure, said main part being bordered by distribution parts lined with the distribution waves 51, 54.

[0047] Fig. 1 shows a passage 10 of the first assembly configured for the flow of a first fluid F1 in the form of a mixture of two phases, also called a two-phase mixture. The first assembly comprises several passages 10 of this type superimposed on each other. The first fluid F1 is separated in a separator device 6 into a first phase 61 and a second phase 62 introduced separately into the exchanger 1 via a first collector 30 and a second collector 52 which are separate. The separator 6 then forms a source of first phase and second phase. By “source” of fluid is meant any means suitable for supplying the channels of the mixing device with a fluid.

[0048] Preferably, the first phase 61 is liquid and the second phase 62 is gaseous. In the case where the longitudinal channel is configured for a vertical and upward flow of the first phase and the two-phase mixture at the second outlet, gravity has a lesser impact on the flow of the gaseous phase compared to that of the liquid phase. The entrainment of the liquid phase in the orifice 34 is facilitated by the higher speed of the gaseous phase. In addition, the presence of the gaseous phase facilitates the flow of the liquid phase once said liquid phase has been introduced into the longitudinal channel through the orifice 34.

[0049] The phases 61, 62 are then mixed with each other by means of a mixing device 3 arranged in at least one passage 10. Advantageously, several passages 10, or even all of the passages 10 of the first set, comprise a mixing device 3. The semi-tubular collectors 52 and 55 are fluidically connected to the inlets and outlets of the passages 10. The first collector 30 is fluidically connected to at least a first inlet 311 of the mixing device 3. The second collector 52 is fluidically connected to at least a second inlet 321 of the mixing device 3. The first and second collectors may be any collecting means suitable for collecting a fluid from a fluid source and introducing said fluid into one or more passages of a heat exchanger.

[0050] Note that Fig. 1 illustrates a mixing device 3 positioned at a certain distance from the distribution zone 51 of the exchanger 1. According to an alternative embodiment, the mixing device 3 can be positioned directly after the distribution zone, either juxtaposed to said zone, or by being formed in one piece with the distribution zone. According to the latter possibility, the mixing device forms a monolithic part, which can be manufactured by conventional machining or by additive manufacturing, i.e. by 3D printing, for example by laser sintering

[0051] Fig. 2 is a three-dimensional view of a mixing device 3 advantageously consisting of a bar, or rod, housed in a passage 10.

[0052] The mixing device 3 preferably extends in the section of the passage 10 over almost all, or even all, of the height of the passage 10, so that the mixing device is in contact with each plate 2 forming the passage 10.

[0053] The mixing device 3 is advantageously fixed to the plates 2 by brazing.

[0054] The mixing device 3 is advantageously of generally parallelepiped shape.

[0055] Preferably, the mixing device 3 is a monolithic part, i.e. formed from a block or a single piece. The mixing device 3 may be manufactured by conventional machining or by additive manufacturing. The mixing device 3 may have, parallel to the longitudinal direction z, a first dimension of between 20 and 200 mm and, parallel to the lateral direction y, a second dimension of between 100 and 1400 mm.

[0056] The mixing device 3 comprises at least one lateral channel 31 configured for the flow of the first phase 61 of the first fluid F1 from at least one first inlet 311. Preferably, the lateral channel 31 extends parallel to the lateral direction y.

[0057] It further comprises a series of longitudinal channels 32 extending parallel to the longitudinal direction z and configured for the flow of the second phase 62 of the first fluid F1 from a second inlet 321 to a second outlet 322, said longitudinal channels 32 being arranged at successive positions yi, y i+1,... along the lateral direction y.

[0058] Preferably, the lateral channel 31 extends over the entire second dimension and / or the longitudinal channel 32 extends over the entire first dimension.

[0059] Preferably, the mixing device 3 comprises at least one first inlet 311 in fluid communication with the first collector 30 and a second inlet 321, separate, i.e. distinct, from the first inlet 311, in fluid communication with the second collector 52. The first collector 30 is fluidly connected to a source of first phase 61 and the second collector 52 is fluidly connected to another source of second phase 62. Said at least one first inlet 311 and said at least one second inlet 321 are placed in fluid communication via at least one orifice 34. In fact, the mixing device is configured for a separate introduction of the first phase and the second phase, the first inlet 311 being adapted for a supply of the first phase 61 to the lateral channel 31 and said at least one second inlet 321 being adapted to supply the longitudinal channels 32 with the second phase 62.

[0060] The first and second inlets are advantageously formed by opening the lateral and longitudinal channels at the lateral and longitudinal peripheral edges of the device 3.

[0061] Fig. 2 shows an introduction of the first phase 61 through one end of the device 3 comprising several first inlets 311. According to an advantageous embodiment, the mixing device 3 comprises at least one other first inlet for the first phase 61 located at an opposite end of the device 3. Advantageously, these other inlets are obtained by extending the lateral channels 31 until they open at an opposite lateral edge of the exchanger 1. In this case, another first collector 30 is arranged on an opposite side of the exchanger 1. The introduction of the first phase 61 on either side of the mixing device makes it possible to reduce the effect of pressure losses during the flow of the first phase in the lateral channels, which promotes a more homogeneous distribution of the two-phase mixture over the width of the exchanger.

[0062] Preferably, the mixing device 3 comprises a mixing volume located in the longitudinal channel 32, downstream of the orifice 34 following the direction of flow of the first phase 61 in the orifice 34.

[0063] The lateral channel 31 is fluidically connected to at least one longitudinal channel 32 so that, when the first phase 61 flows in the lateral channel 31 and the second phase 62 flows in the longitudinal channel 32, the mixing device 3 distributes through a second outlet 322 of the channel 32 a mixture of the first phase 61 and the second phase 62, preferably a two-phase liquid / gas mixture F1, also called a two-phase mixture. Preferably, the longitudinal channel and / or the lateral channel have generally rectilinear shapes.

[0064] The channels 31, 32 are advantageously in the form of longitudinal recesses provided in the mixing device 3. They preferably open out at the level of the upper 3a and lower 3b surfaces of the mixing device 3.

[0065] Preferably, the channels 31, 32 have a square or rectangular cross-section but may possibly have other shapes (round, portion of round, etc.).

[0066] The orifices 34 are advantageously holes 34 made in the material of the device 3 and extending between the first channel 31 and the second channel 32, preferably in the plane formed by the directions x and y, the orifices 34 being able to be inclined relative to the direction x or, preferably, being aligned with the vertical direction x. Preferably, the orifices 34 are cylindrically symmetrical, more preferably cylindrical in shape.

[0067] Preferably, said at least one lateral channel 31 comprises a bottom wall 3c and said at least one longitudinal channel 32 comprises a top wall 3d which extends opposite the bottom wall 3c, the orifices 34 being pierced in the bottom wall of the first channel 31 and opening into the top wall of the longitudinal channel 32.

[0068] Fig. 3 is a view of the mixing device 3 of Fig. 2 in a section plane orthogonal to the lateral direction y and passing through an orifice 34.

[0069] According to the prior art, mixing devices 3 having longitudinal channels whose width, measured in the lateral direction y, remains constant along the longitudinal direction z are arranged in the passages 10 of the first set, in particular longitudinal channels of parallelepipedal shape such as the shape of the lateral channels 31 visible on Fig. 2 .

[0070] At the outlet of each longitudinal channel 32, the flow of the two-phase mixture of the first fluid F1 takes place preferentially along the longitudinal direction z, with a progressive expansion of the flow in the width of the passage 10. The homogenization of the flows in each passage is only obtained beyond a certain distance traveled by the mixture. This lack of homogenization of the mixture F1 takes place throughout the stack of passages 10 of the first set.

[0071] In order to solve these problems, the present invention proposes to arrange in a passage 10 of the first assembly, a mixing device 3 of which at least one longitudinal channel 32 is divided, along the longitudinal direction z, into an upstream portion 323 and a downstream portion 324 each having a length L 3 , L 4 measured in the longitudinal direction z and a width D 3 , D y measured parallel to the lateral direction y, the downstream portion 324 being arranged between the upstream portion 323 and the second outlet 322. According to the invention, the downstream portion 324 has, at any point along its length L 4 , a width D y greater (strictly) than the width D 3 of the upstream portion 323.

[0072] Note that the term "width" means the distance measured between the edges delimiting the longitudinal channel 32 in a predetermined longitudinal section plane which is parallel to the longitudinal direction z and parallel to the lateral direction y, i.e. the width of the external profile of the channel in said section plane, as shown for example in Fig. 4 à Fig. 9 .

[0073] The arrangement of a downstream portion having a widening in the lateral direction y promotes the lateral expansion of the two-phase mixture leaving the longitudinal channel 32. The inventors of the present invention have demonstrated that the fluid jet forms a wider base cone at the outlet of the longitudinal channel, which allows the fluid leaving the longitudinal channel 32 to irrigate a greater number of exchange channels of an exchange wave positioned, in operation, downstream of the mixing device 3. It is thus possible to obtain faster homogenization with the fluid jets leaving the neighboring longitudinal channels.

[0074] The disparities in the flow rate of the mixture in the width of the passage 10 are thus reduced, or even eliminated, after a shorter propagation distance of the mixture downstream of the mixing device 3. The heat exchanges between the two-phase mixture and the second fluid F2, and hence the operation of the exchanger, are improved.

[0075] Furthermore, the widening of the downstream portion in the lateral direction offers the possibility, in cases where the mass flow rate of two-phase mixture in the longitudinal channel 32 is relatively high, of inducing a slowing down of the flow of the mixture at the downstream portion, and thus of reducing the pressure losses undergone by the two-phase mixture at the outlet of the longitudinal channel 32, when it irrigates the exchange waves located downstream of the mixing device 3.

[0076] Preferably, several channels of the series of longitudinal channels 32, more preferably all of them, are configured according to the invention and may include all or part of the characteristics described below.

[0077] Preferably, the downstream portion 324 opens at a downstream face 326 of the mixing device 3, the second outlet 322 being arranged at the downstream face 326. At least a portion of the first phase 61 flowing in the lateral channel 31 feeds the orifice 34 to flow into the longitudinal channel where the mixing takes place. The second phase 62 flows successively in the upstream 323 and downstream 324 portions. The mixture is distributed through the second outlet 322.

[0078] Preferably, the downstream portion 324 has a width D y increasing along the length L 4 in the direction of the second outlet 322, preferably increasing over the entire length L 4 .

[0079] Note that the widening of the downstream portion along the longitudinal direction z can be induced punctually, in one or more times, or in a progressive manner, i.e. be continuously increasing, along all or part of the downstream portion 324.

[0080] Preferably, the width D y of the downstream portion 324 increases continuously, i.e. progressively, over the entire length L 4 in the direction of the second outlet 322. This limits the disturbances that could be caused by sudden variations in channel width in the flow of the mixture.

[0081] Preferably, the downstream portion 324 has a minimum width D m and a maximum width DM with the ratio DM / D m greater than or equal to 1.1, preferably greater than or equal to 1.8 and / or less than or equal to 4. Such a dimensional ratio makes it possible to sufficiently increase the width of the longitudinal channel 32 at the end 322 without, however, excessively increasing the length of the longitudinal channel 32 in the z direction and while maintaining simplicity of machining of the longitudinal channel 32.

[0082] In particular, the DM width can be between 6 and 25 mm, preferably between 8 and 20 mm.

[0083] It should also be noted that a mixing device according to the invention may be intended to be arranged in a passage 10 provided, downstream of the mixing device, with at least one exchange wave comprising exchange channels each having a width of between 0.6 and 2 mm, preferably a width of at least 0.7 mm and / or at most 1.5 mm.

[0084] Preferably, the minimum width D m is measured at the end 324a of the downstream portion 324 and the maximum width DM is measured at the second outlet 322.

[0085] Advantageously, the longitudinal channel 32 is delimited by side walls 325 forming, in a longitudinal section plane which is parallel to the longitudinal direction z and to the lateral direction y, an external profile of said channel 32 with axis of symmetry AA' parallel to the longitudinal direction z.

[0086] Note that the side walls 325 of the channel are preferably erected in a direction which is orthogonal to the longitudinal z and lateral y directions. The walls 325 advantageously have a height, measured along the x direction, constant over the entire length of the channel 32.

[0087] Alternatively, it is possible to envisage a variation in the height of the walls 325, in particular an increase in said height in the direction of the second outlet 322, that is to say a downstream portion 324 whose depth increases in the direction of the second outlet 322, until possibly reaching the height of the passage 10 at the level of the second outlet 322. This provides an additional degree of freedom to increase the fluid passage section of the downstream portion 324 and thus slow down the fluid in order to homogenize it also in the height of the passage 10.

[0088] Advantageously, at least part of the downstream portion 324 has a curvilinear external profile, preferably an external profile of convex shape. Fig. 4 schematizes an exemplary embodiment of a longitudinal channel 32 comprising such a downstream portion 324. The presence of a curvilinear external profile at the downstream portion ensures better guidance of the flow of the fluid in the downstream portion until its exit from the mixing device, in particular it avoids possible phenomena of detachment, recirculation of fluid or turbulence which could result from sharp edges on the walls and would cause additional undesirable pressure losses on the fluid.

[0089] It is also possible that all or part of the downstream portion 324 has, in longitudinal section in a plane parallel to the longitudinal direction z and to the lateral direction y, an external profile in the shape of an isosceles trapezoid, the side walls at the level of this portion being rectilinear walls. Fig. 5 schematizes an example in which the entire downstream portion 324 has such an external profile.

[0090] According to the invention, considering a downstream face 326 of the mixing device 3 at which the downstream portion 324 opens, the external profile forms an angle θ, measured between the tangent T to said external profile at the point of intersection with the downstream face 326 and the axis of symmetry AA', between 5 and 85°. These values make it possible to sufficiently increase the width of the channel 32 at the second outlet 322 to promote better distribution of the two-phase fluid F1 across the width of the exchanger in the direction y, without however creating too rapid a widening which could cause pressure losses of the fluid F1 and without excessively increasing the length L 4 and therefore the length of the mixing device 3.

[0091] Fig. 9 represents an embodiment in which the widening of the downstream portion along the longitudinal direction z is induced punctually, in one go, at the end 324a.

[0092] Preferably, the upstream portion 323 is connected to the downstream portion 324 by its end 324a.

[0093] Advantageously, the upstream portion 323 has a length L 3 measured along the longitudinal direction z with the ratio L 3 / L 4 between 1 and 15, preferably between 3 and 12.

[0094] For example, the length L 4 can be between 5 and 40 mm. The length L 3 can be between 30 and 70 mm.

[0095] Advantageously, said at least one orifice 34 opens into the longitudinal channel 32 at its upstream portion 323, preferably at a distance L z from the end 324a of the downstream portion 324 with L z at least equal to 4%, more preferably between 7 and 90%, and even more preferably ranging from 10 to 50%, of the length L 3 of the upstream portion (323). In particular, the orifice 34 may open at a distance L z between 3 and 70 mm from the end 324a of the downstream portion 324. Advantageously, the orifice(s) 34 of a longitudinal channel 32 all open at its upstream portion 323. The mixing device is advantageously free of orifice 34 opening at its upstream portion 324.

[0096] This ensures that the first phase 61 and the second phase 62 are mixed sufficiently upstream of the downstream portion 324 so that, on the one hand, the two-phase fluid has time to homogenize well before entering the downstream portion 324 and, on the other hand, so that any zones of recirculation of the fluid in the downstream portion 324 do not disturb the flow of the first phase 61 via the orifice 34 of the lateral channel 31 to the longitudinal channel 32, which could cause maldistribution. The higher speed of the second phase 62 in the portion 323 of the channel 32 compared to the speed of the fluid F1 in the portion 324 also makes it easier to pass the phase 61 from the channel 31 to the channel 32 via the orifice 34 due to the high inertia of the phase 61 by the phase 62 and the resulting entrainment.

[0097] Note that, preferably, the position of the at least one orifice 34 along the longitudinal direction z varies between the longitudinal channels. This is particularly for cette raison that some ports 34 may be closer to the end 324a than others.

[0098] Furthermore, it should be noted that within the framework of the invention, the longitudinal channels advantageously have identical dimensional characteristics, i.e. the same external profile, the same depth, the same ratio L 3 / L 4 , the same distance L z , although it is possible in certain configurations to vary at least one characteristic of at least one channel relative to the others, in particular the ratio of lengths of the downstream and upstream portions.

[0099] Preferably, and as illustrated for example on Fig. 4 in particular, all or part of the upstream portion 323 has a rectilinear external profile with a constant width D 3 , preferably equal to the minimum width D m of the downstream portion 324. According to one possibility, it can be envisaged that the upstream portion 323 has a variable width D 3 over all or part of its length, D y being greater than the maximum value that can be reached by D 3 .

[0100] Fig. 6 And Fig. 7 schematize embodiments according to which the longitudinal channel 32 comprises at least one obstacle 327 arranged so as to subdivide the downstream portion 324 into several intermediate channels 328 opening at the level of the second outlet 322.

[0101] This prevents the mixture from flowing completely in the longitudinal z direction and forces the flow to widen in the lateral y direction. The creation of intermediate channels is particularly advantageous when the mass flow rate in the longitudinal channel 32 is relatively high because in this case the mixture has significant inertia in the longitudinal z direction, i.e. it tends to continue to flow in the z direction even when the longitudinal channel widens.

[0102] The installation of one or more obstacles makes it possible to modify the flow direction of the two-phase mixture by giving a component along the y direction to its speed. This increases the angular opening of the fluid jet at the outlet of the longitudinal channel, which makes it possible to supply a greater number of exchange channels positioned downstream of the mixing device.

[0103] Obstacles can also be used to keep the fluid passage section constant or almost constant, or possibly reduce it, in the downstream portion, despite its widening. Note that "fluid passage section" means the surface through which the fluid flows measured perpendicular to the longitudinal direction z. This is to ensure lateral expansion of the mixture, without increasing the fluid passage section.

[0104] This rebalances the pressure losses along the longitudinal channel.

[0105] Preferably, at the level of the second outlet 322, the total surface area of said obstacle 327 measured in a cross-sectional plane perpendicular to the longitudinal direction z, represents between 20 and 80%, preferably between 30 and 70%, of the total fluid passage section of the downstream portion (324) measured in said cross-sectional plane.

[0106] In the case of several obstacles, the total surface area is understood as the sum of the surfaces of each obstacle.

[0107] In particular, it may be provided that the surface of the obstacle, measured at a distance of 1 mm along the longitudinal direction z, in the direction of the flow of the fluid, after the point of appearance in the channel 32, that is to say at a so-called impact position located 1 mm after the point of appearance of the obstacle where the fluid impacts on the obstacle, represents between 1% and 80% of the fluid passage section of the channel 32 determined in a cross-sectional plane positioned at the impact position.

[0108] According to a particular embodiment, the longitudinal channel 32 further comprises at least one balancing channel 329 placing the intermediate channels 328 in fluid communication. This makes it possible to rebalance the fluid pressures between the intermediate channels 328, in the case where there are disparities in flow rate and fluid pressure between the intermediate channels. Fig. 8 represents an example of such a configuration.

[0109] Advantageously, an even number of intermediate channels is provided in order to maintain a distribution symmetry along the AA' axis of the mixture within the longitudinal channel.

[0110] The obstacle(s) can be manufactured with the longitudinal channel by milling, metal injection molding, electro-erosion or laser machining. An additive manufacturing method can also be considered.

[0111] Preferably, the obstacles 327 have a height equal to those of the side walls of the longitudinal channel.

[0112] Preferably, said at least one obstacle 327 has a width dy, measured in the lateral direction y, increasing towards the second outlet 322, preferably with a curvilinear, convex and / or concave external profile. This makes it possible to conform the obstacle so as to avoid additional pressure losses of the fluid F1 in the downstream portion 324 of the channel 32 by detachment of the fluid at the walls of the obstacle or due to fluid recirculation zones.

[0113] Preferably, several passages 10 of the first set, advantageously all of the passages 10, comprise a mixing device according to the invention.

[0114] Preferably, at least one passage 20 of the second set is arranged between at least one pair of consecutive passages 10 of the first set.

[0115] Preferably, the longitudinal channels 32 of the mixing device 3 are separated from each other by a constant distance DA measured parallel to the longitudinal direction y.

[0116] Note that the positions yi , y i+1 , y i+2 ... of each channel along the lateral direction y can be determined by considering the position of the center of each channel along the lateral direction y. For example, by considering channels in the form of parallelepiped grooves as shown in Fig. 2 , the position of a channel along the y direction corresponds to the position of the axis of symmetry of the channel located at an equal distance from the side walls of the channel, as seen in Fig. 2 .

[0117] The distance DA can be between 10 and 40 mm, preferably greater than or equal to 20 mm and less than or equal to 30 mm.

[0118] In order to illustrate the homogenization effect obtained with the invention, Fig. 11 shows the results of a simulation of the propagation of a two-phase mixture in a longitudinal channel of a conventional mixing device (configuration A) and in a longitudinal channel of a mixing device according to an embodiment of the invention (configuration B).

[0119] In configuration A, the mixing device was in the form of a grooved bar having, as longitudinal channels, a series of parallelepipedal grooves succeeding one another at regular intervals of 30 mm. Each groove measured 7 mm in width, 70 mm in length and 7 mm in height.

[0120] In configuration B, partially schematized in Fig. 10 , the mixing devices were in the form of grooved bars with grooves succeeding each other at regular intervals of 30 mm. Each groove was in the form of a longitudinal channel with an upstream portion 323 having dimensions of 7 mm in width, 63 mm in length and 7 mm in height. The downstream portion 324 was of truncated cone shape with a width of 7 mm at the end 324a and 14 mm at the second outlet 322. The upstream portion 323 had a length of 7 mm and a height of 7 mm. An obstacle in the form of an isosceles triangle was placed in the downstream portion 324, symmetrically with respect to the axis of symmetry AA', with a height of 7 mm in the z direction and a base width of 7 mm at the second outlet 322. The width DM was twice as high as D 3 . The ratio L 3 / L 4 was 8 and the length L z was 5 mm. The angle θ was 45°.Note that configuration B corresponds to the particular case in which the fluid passage section of the downstream portion is kept constant in the longitudinal direction z due to the presence of the obstacle although the width of said portion increases in the direction of the second outlet 322.

[0121] The longitudinal channels of the mixing devices of configurations A and B were arranged in the same number and at identical positions yi , y i+1 ,... along the lateral direction y.

[0122] In configurations A and B, waves 11 of the "serrated" type, i.e. with partial offset, were arranged at the outlet of the mixing devices in each passage. These waves were of the "1 / 8 " serrated" type (1" = 1 inch = 25.4 mm), i.e. with a serration length of 25.4 / 8 = 3.18 mm and presented corrugations with a density of 23 fins per inch (1 inch = 25.4 millimeters), measured in the lateral direction y.

[0123] Simulation is a three-dimensional CFD-type calculation using the finite element method, which is the English acronym for "Computational Fluid Dynamics".

[0124] Fig. 11 shows the evolution of the value of the smallest dimensionless velocity of the fluid along the longitudinal direction z (denoted V z ) measured on successive sections of the waves located after the outlet 322 in planes parallel to the x and y directions, for several distance values between the outlet 322 and said planes. These velocity values are representative of the quality of the distribution of the fluid in the waves: a negative value indicates the presence of a recirculation zone, with stagnant fluid in the center of the zone. A zero value indicates the presence of stagnant fluid. Since the stagnant fluid is not renewed, it does not participate in the heat exchange and reduces the overall efficiency of the exchanger.

[0125] A performance indicator of fluid distribution is the minimum distance required along the longitudinal z direction from which all fluid has a positive velocity along the longitudinal z direction.

[0126] It can be seen that the minimum distance required is reduced from 45 to 31 mm, i.e. a reduction of 35% in configuration B according to the invention compared to the classic configuration A. Thanks to the invention, the homogenization of the two-phase mixture distributed by a mixing device is therefore significantly improved and the efficiency of the exchanger is improved.

[0127] Fig. 12 And Fig. 13 show examples of methods implementing one or more exchangers according to the invention.

[0128] Fig. 12 schematizes a process for liquefying a hydrocarbon stream 102 as a second fluid F2, which may be natural gas, possibly pretreated, for example having undergone separation of at least one of the following constituents: water, carbon dioxide, sulfur compounds, methanol, mercury, before its introduction into the heat exchanger 1.

[0129] Preferably, the hydrocarbon stream comprises, in mole fraction, at least 60% methane, preferably at least 80%.

[0130] The hydrocarbon stream 102 and the refrigerant stream 202 enter the exchanger 1 respectively through a third inlet 25 and a fourth inlet 21 to circulate in dedicated passages of the exchanger in directions parallel to the longitudinal direction z, which is substantially vertical in operation. The hydrocarbon stream 102 circulates in the passages 20 of the second assembly supplied by the third inlet 25. The refrigerant stream 202 circulates in a third set of passages arranged within the stack forming the exchanger 1. These streams exit through a third outlet 22 and a first outlet 23. The passages of the second and third sets are arranged, in whole or in part, alternating and / or adjacent to all or part of the passages 10 of the first set.

[0131] Advantageously, the fourth inlet 21 for the refrigerant stream 202 and the third inlet 25 for the hydrocarbon stream 102 are arranged so that the refrigerant stream 202, and possibly the hydrocarbon stream 102, flow co-currently in the downward direction, towards a second end 1b of the exchanger which is located at a level lower than that of a first end 1a of said exchanger. Preferably, the first end 1a corresponds to the hot end of the exchanger 1, i.e. the inlet point of the exchanger where a fluid is introduced at the highest temperature of the temperatures of the exchanger, this inlet point possibly being the fourth inlet 21 or the third inlet 25, depending on the method considered.

[0132] The hydrocarbon stream 102 can be introduced into the exchanger 1 at a temperature between -130 and 40°C.

[0133] According to one possibility, the hydrocarbon stream 102 is introduced in a completely gaseous or partially liquefied state into the exchanger 1 at a temperature between -80 and -35°C.

[0134] Alternatively, the hydrocarbon stream 102 is introduced fully liquefied into the exchanger 1 at a temperature between -130 and -100°C.

[0135] The refrigerant stream 201 leaving the exchanger 1 is expanded by an expansion member T3, such as a turbine, a valve or a combination of a turbine and a valve, so as to form a two-phase refrigerant stream 203 comprising a first phase and a second phase. The two-phase refrigerant stream 203 forms the first fluid F1 considered previously. At least a portion of the two-phase refrigerant stream 203 resulting from the expansion is introduced into a separating member 27. The separating member may be any device suitable for separating a two-phase fluid into a predominantly gaseous stream on the one hand and a predominantly liquid stream on the other hand.

[0136] The second phase 62 is introduced by the collector 52 which feeds the second inlets 321 of mixing devices 3 arranged in the passages 10 of the first set. The first phase 61 is introduced by the first collector 30 which feeds the first inlets 311 of mixing devices 3 arranged in each passage 10 (not shown in Fig. 9 ).

[0137] Preferably, the second phase is introduced through an inlet located in the region of the second end 1b corresponding to the cold end of the exchanger 1, i.e. the entry point into the exchanger where a fluid is introduced at the lowest temperature of the temperatures of the fluids in the exchanger.

[0138] The two phases 61, 62 of the two-phase current 203 are recombined within the exchanger 1 and distributed in the liquid-gas mixture state in the passages 10 of the exchanger 1 each provided with mixing devices 3 according to the invention.

[0139] Preferably, the two-phase refrigerant stream 203 is introduced into the heat exchanger 1 at a first temperature T1 between -120 and -160°C and leaves the heat exchanger 1 at a second temperature T2 higher than the first temperature T1, preferably with T2 between -35 and -130°C.

[0140] Alternatively, the two-phase refrigerant stream 203 is introduced into the heat exchanger 1 at a first temperature T1 of between -130 and -80°C and exits the heat exchanger 1 at a second temperature T2 higher than the first temperature T1, preferably with T2 of between -10 and 50°C.

[0141] Said at least a portion of the two-phase refrigerant stream 203 flows in the passages 10 in an upward direction and is vaporized by counter-cooling the natural gas 102 and the refrigerant stream 202. A cooled and / or at least partially liquefied hydrocarbon stream 101 is thus obtained at the outlet of the exchanger 1.

[0142] The vaporized refrigerant stream leaves the exchanger 1 through a second outlet 42 connected to the collector 55 to be compressed by a compressor then cooled in an indirect heat exchanger by heat exchange with an external cooling fluid, for example water or air (at 26 on Fig. 12 ). The pressure of the refrigerant stream at the compressor outlet can be between 2 MPa and 9 MPa. The temperature of the refrigerant stream at the outlet of the indirect heat exchanger can be between 10 °C and 45 °C.

[0143] In the process described by Fig. 12 , the refrigerant stream is not split into separate fractions, but, to optimize the approach in exchanger 1, the refrigerant stream can also be separated into two or three fractions, each fraction being expanded to a different pressure level and then sent to different stages of the compressor.

[0144] Preferably, the refrigerant stream 202 contains hydrocarbons having a number of carbon atoms of at most 5, preferably at most three, more preferably at most two.

[0145] Preferably, the refrigerant stream 202 is formed for example by a mixture of hydrocarbons and nitrogen such as a mixture of methane, ethane and nitrogen but may also contain propane, butane, isobutane, n-butane, pentane, isopentane, n-pentane and / or ethylene.

[0146] The proportions in molar fractions (%) of the components of the refrigerant stream can be: Nitrogen: 0% to 10% Methane: 20% to 70% Ethane: 30% to 70% Ethylene: 20 to 70% Propane: 0% to 20% n-butane: 0% to 30% Isopentane: 0% to 20%

[0147] Optionally, the refrigerant stream may include, as a replacement for ethane, ethylene and, as a replacement for all or part of the propane, compounds of the C4, C5 type.

[0148] Preferably, the natural gas leaves the exchanger 1 at least partially liquefied 101 at a temperature preferably at least 10°C higher than the bubble temperature of the liquefied natural gas produced at atmospheric pressure (the bubble temperature designates the temperature at which the first vapor bubbles form in a liquid natural gas at a given pressure) and at a pressure identical to the inlet pressure of the natural gas, apart from the pressure drops. For example, the natural gas leaves the exchanger 1 at a temperature between -100°C and -162°C and at a pressure between 2 MPa and 7 MPa. Under these temperature and pressure conditions, and depending on its composition, the natural gas generally does not remain liquid after expansion to atmospheric pressure.

[0149] Advantageously, the method for liquefying a hydrocarbon stream according to the invention can implement one or more additional refrigeration cycles carried out upstream of the main refrigeration cycle described above, so as to carry out pre-cooling of the hydrocarbon stream.

[0150] Fig. 13 schematizes a process for liquefying a hydrocarbon stream such as natural gas comprising an additional refrigeration cycle in which the natural gas is cooled to a temperature close to its dew point using at least two different expansion levels to increase the efficiency of the cycle. This additional refrigeration cycle is operated by means of an additional refrigerant stream 300 in an additional heat exchanger 2, called a pre-cooling exchanger, arranged upstream of the heat exchanger 1 in the direction of flow of the hydrocarbon stream 110, which then forms the liquefaction exchanger.

[0151] In this embodiment, a feed stream 110 arrives for example at a pressure of between 2.5 MPa and 7 MPa and at a temperature of between 20°C and 60°C. The feed stream 110 comprising a mixture of hydrocarbons such as natural gas, the refrigerant stream 202, an additional refrigerant stream 300 enter the additional exchanger 2 to circulate therein in parallel directions and co-currently in the downward direction.

[0152] A cooled, or at least partially liquefied, hydrocarbon stream 102 leaves the pre-cooling exchanger 2. Preferably, the hydrocarbon stream 102 leaves in the gaseous or partially liquefied state, for example at a temperature between -35°C and -70°C. The refrigerant stream 202 can also leave the exchanger 2 completely condensed, for example at a temperature between -35°C and -70°C. The stream 102 is then introduced into the exchanger 1.

[0153] As seen on Fig. 13 , the stream 203 is vaporized in the exchanger 1 and leaves to be compressed by the compressor K2 then cooled in the indirect heat exchanger C2 by heat exchange with an external cooling fluid, for example water or air. The refrigerant stream from the exchanger C2 is then returned to the additional exchanger 2.

[0154] The additional refrigerant stream 300 may be formed by a mixture of hydrocarbons such as a mixture of ethane and propane, but may also contain methane, ethylene, propylene, butane and / or pentane. The proportions in molar fraction (%) of the components of the first refrigerant mixture may be: Ethane: 30% to 70% Propane: 30% to 70% Butane: 0% to 20%

[0155] In the additional exchanger 2, which is also of the brazed plate and fin type, at least two partial streams from the additional refrigerant stream 300 are withdrawn from the exchanger at at least two separate outlet points and then expanded to different pressure levels, giving rise to expanded two-phase partial streams each comprising a first phase and a second phase. At least a portion of these two-phase partial streams is introduced into respective separator members 24, 25, 26.

[0156] In the embodiment according to Fig. 13 , three fractions, also called partial flows or streams, 301, 302, 303 of the additional refrigerant stream 300 in the first phase are successively withdrawn.

[0157] The gaseous and liquid phases separated by each separating member are introduced through separate inlets of the additional exchanger 2 and recombined within mixing devices (not shown) so as to form at least two refrigerants introduced in the liquid-gas mixture state into dedicated refrigerant passages. Alternatively, only the first phase is injected into the exchanger 2 and the gas phase is directed towards the inlet of the compression stages of the compressor K1. These refrigerants are vaporized in the additional exchanger 2 by heat exchange with the feed stream 110 and the refrigerant stream 202 and the additional refrigerant stream 300.

[0158] Advantageously, at least two types of mixing devices 2 are arranged in the additional exchanger 2, such as those which can be arranged within the exchanger 1 according to the invention. Thus, the additional exchanger comprises at least two refrigerant fluid passages, each comprising a mixing device, these devices comprising one or more of the characteristics previously described for the first and second mixing devices 3A, 3B.

[0159] The refrigerants vaporized in their respective refrigerant passages are sent to different stages of the compressor K1, compressed and then condensed in a condenser by heat exchange with an external cooling fluid, for example water or air. The stream from the condenser is returned to the additional exchanger 2. The pressure of the first refrigerant stream at the outlet of the compressor K1 can be between 2 MPa and 6 MPa. The temperature of the additional refrigerant stream at the outlet of the condenser C1 can be between 10 °C and 45 °C.

[0160] Preferably, the refrigerants flow from one end 2b of the additional exchanger 2 to another end 2a along the longitudinal direction z, in the upward direction. The end 2b corresponds to the cold end of the additional exchanger 2 where the refrigerant is introduced at the lowest temperature of the temperatures of the additional exchanger 2.

[0161] 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. For example, other configurations for injecting and extracting fluids from the exchanger, other directions and directions of flow of the fluids, other types of fluids, other forms of mixing devices, lateral and longitudinal channels, etc. are of course conceivable, depending on the constraints imposed by the method to be implemented.

Claims

1. A mixing device (3) for distributing a mixture of a first phase (61) and a second phase (62) of a first fluid (F1) generally along a longitudinal direction (z) in at least one passage (10) of a heat exchanger (1), said mixing device (3) comprising: at least one lateral channel (31) configured for the flow of the first phase (61) from at least one first inlet (311), a series of longitudinal channels (32) extending along the longitudinal direction (z) and each configured for the flow of the second phase (62) from a second inlet (321) to a second outlet (322), said longitudinal channels succeeding one another along a lateral direction (y) orthogonal to the longitudinal direction (z), and at least one orifice (34) fluidly connecting said lateral channel (31) to at least one longitudinal channel (32) so that the mixing device (3) is configured to distribute a mixture of the first phase (61) and the second phase (62) through the second outlet (322) of said longitudinal channel (32), said at least one longitudinal channel (32) of the mixing device (3) is divided, along the longitudinal direction (z), into an upstream portion (323) and a downstream portion (324) each having a length (L3, L4) measured in the longitudinal direction (z) and a width (D3, Dy) measured in the lateral direction (y), the downstream portion (324) being arranged between the upstream portion (323) and the second outlet (322), said downstream portion (324) having, at any point of its length (L4), a width (Dy) greater than the width (D3) of the upstream portion (323), the downstream portion (324) opening out at the level of a downstream face (326) of the mixing device (3), the second outlet (322) being arranged at the level of the downstream face (326), characterized in that the downstream portion (324) has, in a longitudinal cross-section in a plane (P) parallel to the longitudinal direction (z) and to the lateral direction (y), an external profile forming an angle (θ), measured between the tangent (T) to said external profile at the intersection point with the downstream face (326) and the axis of symmetry (AA') of the longitudinal channel (32), comprised between 5 and 85°.

2. The device according to claim 1, characterized in that the downstream portion (324) has a continuously increasing width (Dy) over its entire length (L4) towards the second outlet (322).

3. The device according to one of the preceding claims, characterized in that all or part of the downstream portion (324) has, in a longitudinal cross-section in a plane (P) parallel to the longitudinal direction (z) and to the lateral direction (y), an external profile in the shape of an isosceles trapezoid.

4. The device according to one of the preceding claims, characterized in that the upstream portion (323) of the longitudinal channel (32) is connected to the downstream portion by an end (324a), said at least one orifice (34) opening into said longitudinal channel (32) at the level of the upstream portion (323) at a distance (Lz) from the end (324a), preferably (Lz) is greater than or equal to 4% and preferably comprised between 7 and 90% of the length (L3) of the upstream portion (323).

5. The device according to one of the preceding claims, characterized in that the at least one orifice (34) is arranged so that, when the first phase (61) flows from the first inlet of the lateral channel (31) and the second phase (62) flows from the second inlet (321) of the longitudinal channel (32), the mixture of the first phase (61) and the second phase (62) takes place upstream of the downstream portion (324).

6. The device according to one of the preceding claims, characterized in that the orifice or orifices (34) of the mixing device (3) all open out at the level of the upstream portion (324) of a longitudinal channel (32).

7. The device according to one of the preceding claims, characterized in that each longitudinal channel of the series of longitudinal channels (32) comprises at least one orifice (34) opening out at the level of its upstream portion (323), the position of the at least one orifice (34) along the longitudinal direction (z) varying between the longitudinal channels (32).

8. The device according to one of the preceding claims, characterized in that the length (L3) of the upstream portion (323) and the length (L4) of the downstream portion (324) are such that the ratio L3 / L4 is comprised between 1 and 15, preferably between 3 and 12.

9. The device according to one of the preceding claims, characterized in that the downstream portion (324) has a depth, measured in a so-called stacking direction (x) which is perpendicular to the longitudinal direction (z) and perpendicular to the lateral direction (y), increasing towards the second outlet (322).

10. The device according to one of the preceding claims, characterized in that the longitudinal channel (32) comprises at least one obstacle (327) arranged so as to subdivide the downstream portion (324) into several intermediate channels (328) opening out at the level of the second outlet (322), preferably said intermediate channels (328) are arranged symmetrically with respect to the axis of symmetry (AA') of the longitudinal channel (32).

11. A heat exchange installation comprising: - a heat exchanger (1) comprising several plates (2) arranged parallel to each other and to a longitudinal direction (z), said plates (2) being stacked with spacing so as to define between them at least a first set of passages (10) configured for the flow of a first fluid (F1) generally along the longitudinal direction (z) and at least a second set of passages (20) configured for the flow of a second fluid (F2) to be brought into heat exchange relationship with the first fluid (F1), - a source of a first phase (61) of the first fluid (F1) fluidly connected to at least one first header (30) of the heat exchanger (1), - a source of a second phase (62) of the first fluid (F1) fluidly connected to at least one second header (52) of the heat exchanger (1), - a mixing device (3) as defined by one of claims 1 to 10, said mixing device (3) being arranged in at least one passage (10) of the first set and configured to distribute the first fluid (F1) formed of a mixture of the first phase (61) and the second phase (62) in said passage (10) of the first set, the first inlet (311) of the lateral channel (31) being in fluid communication with said first header (30), and the second inlet (321) being in fluid communication with the second header (52), the first phase (61) being a liquid phase and the second phase (62) being a gaseous phase.

12. A method for mixing a first phase (61) and a second phase (62) of a first fluid (F1) in a mixing device (3) as defined by one of claims 1 to 10, said method comprising the following steps: i) introduction of the first phase (61) of the first fluid (F1) through at least one first inlet (311) of the lateral channel (31), ii) introduction of the second phase (62) of the first fluid (F1) through a second inlet (321) of each longitudinal channel (32), the second phase (62) flowing in each longitudinal channel (32) along the longitudinal direction (z) to a second outlet (322) of said longitudinal channel (32), iii) flow of at least a part of the first phase (61) from the lateral channel (31) towards the longitudinal channel (32) through the orifice (34) so as to mix the first phase (61) with the second phase (62) in the longitudinal channel (32), iv) distribution of the mixture of the first phase (61) and the second phase (62) through the second outlet (322) of each longitudinal channel (32).

13. The mixing method according to claim 12, characterized in that the mixture of the first phase (61) with the second phase (62) is carried out upstream of the downstream portion (324).

14. A method for liquefaction of a hydrocarbon stream (102) such as natural gas as a second fluid (F2) by heat exchange with at least one two-phase refrigerant stream (203) as a first fluid (F1), said method implementing a mixing method according to one of claims 12 or 13 in a mixing device (3) as defined by one of claims 1 to 10, and comprising the following steps: a) introduction of the hydrocarbon stream (102) into a second set of passages (20) of a heat exchanger (1), b) introduction of a refrigerant stream (202) into a third set of passages of the heat exchanger (1), c) exit of the refrigerant stream (201) from the heat exchanger (1) and expansion of the refrigerant stream (201) at at least one pressure level so as to produce at least one two-phase refrigerant stream (203), d) separation of at least a part of the two-phase refrigerant stream (203) resulting from step c) into a second phase (62) and a first phase (61), e) arrangement of the mixing device (3) in at least one passage (10) of a first set of passages of the heat exchanger (1), f) introduction of at least a part of the second phase (62) and at least a part of the first phase (61) into the mixing device (3) so as to obtain a first fluid (F1) formed of a mixture of the first phase (61) and the second phase (62) at the outlet of the mixing device (3), g) vaporization of at least a part of the first fluid (F1) resulting from step f) in the passage (10) by heat exchange with at least the hydrocarbon stream (102) so as to obtain a cooled and / or at least partially liquefied hydrocarbon stream (101) at the outlet of the exchanger (1).