WO2020025873A1

WO2020025873A1 - Heat exchanger with an improved configuration of passages, associated methods for exchanging heat

Info

Publication number: WO2020025873A1
Application number: PCT/FR2019/051779
Authority: WO
Inventors: Natacha Haik-Beraud; Sophie LAZZARINI
Original assignee: L'air Liquide, Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude
Priority date: 2018-07-31
Filing date: 2019-07-16
Publication date: 2020-02-06
Also published as: EP3830511B1; FR3084739A1; JP2021534362A; RU2755968C1; CN112601925A; US20210164734A1; FR3084739B1; JP7399938B2; EP3830511A1

Abstract

The invention relates to a heat exchanger (E1) comprising a plurality of plates (2) parallel to a longitudinal direction (z) and together defining a first series of passages (10) for the flow of at least one refrigerant (F1) intended to exchange heat with at least one calorigenic fluid (C), at least one passage (10) of the first series defined between two adjacent plates (2) comprising a refrigerant inlet (31) configured to introduce the refrigerant (F1) into a portion (100) of said passage (10) and a refrigerant outlet (41) configured to discharge the refrigerant (F1) from the portion (100). According to the invention, said at least one passage (10) of the first series further comprises at least one other refrigerant inlet (32) configured to introduce another refrigerant (F2) into another portion (200) of said passage (10) and at least one other refrigerant outlet (42) configured to discharge the other refrigerant (F2) from the other portion (200), said other inlets and outlets (32, 42) being arranged so that said at least one passage (10) is divided, in the longitudinal direction (z), into at least said portion (100) and said other portion (200).

Description

HEAT EXCHANGER WITH IMPROVED PATHWAY CONFIGURATION, METHODS OF EXCHANGING HEAT

The present invention relates to a heat exchanger comprising series of passages for the flow of at least one refrigerant to be put in heat exchange relationship with a circulating fluid, the exchanger comprising at least one passage configured for flow said refrigerant and at least one other refrigerant.

The technology commonly used for an exchanger is that of aluminum exchangers with brazed plates and fins, which make it possible to obtain very compact devices offering a large exchange surface.

These exchangers comprise a stack of plates which extend in two dimensions, length and width, thus constituting a stack of vaporization passages and condensation passages, some intended for example to vaporize refrigerant and the others to condense a gas. calorigenically. Note that heat exchanges between fluids can take place with or without phase change.

In order to introduce and evacuate the fluids from the exchanger, the passages are provided with fluid inlet and outlet openings. The inlets and outlets placed one above the other in the stacking direction of the exchanger passages are combined respectively in generally semi-tubular inlet and outlet manifolds, through which the distribution and evacuation of fluids.

Several circulating and refrigerant fluids, of different types and / or characteristics, can circulate in the exchanger. These fluids form separate currents or flows which are introduced and evacuated from the exchanger by groups of inlets and outlets dedicated to a type of fluid.

Conventionally, in the case where several refrigerants circulate in the exchanger, the inputs and outputs of the various refrigerants are arranged successively, along the length of the exchanger, in increasing temperature order starting from the cold end of the exchanger, that is to say the point of entry into the exchanger where a fluid is introduced at the lowest temperature of all the temperatures of the exchanger. Thus, when the outlet temperature of one refrigerant is higher than the inlet temperature of another refrigerant, the other refrigerant must enter the exchanger, following the length of the exchanger, at a position closer to the cold end than is the outlet of the refrigerant.

In known manner, the pinch method is used to plan the way in which the fluids circulate in relation to heat exchange in the exchanger and to maximize the energy efficiency of the installation.

The term pinch refers to the minimum difference between the temperature of the refrigerants, i.e. the fluids which heat up in the exchanger, and the temperature of the circulating fluids, i.e. fluids which cool in the exchanger, and this at a given point in the exchanger. To visualize this pinching, we evaluate the difference between two composite curves of a Heat exchanged - Temperature diagram, as illustrated in Figure 3B (a), one being associated with the flows to be heated, the other with the flows to be cooled . As long as this minimum deviation is positive, there is theoretically a way to reduce energy consumption.

Conventionally, in order to optimize the pinching between the curves of the exchange diagram resulting from the pinching method, at least two different types of refrigerant passages are provided, a type of passage dedicated to the circulation of a refrigerant and at least one other type of passage dedicated to the circulation of the other refrigerant. These passages of different types are not formed between the same pair of adjacent plates of the exchanger.

This results in a complexification of the exchanger and a significant increase in the dimensioning of the exchanger. In addition, each type of passageway then has a large portion in which no fluid circulates, that is to say an inactive zone in terms of exchange with the circulating fluid.

The object of the present invention is to solve all or part of the problems mentioned above, in particular by proposing a heat exchanger. heat with greater compactness and whose thermal efficiency and mechanical strength are improved.

The solution according to the invention is then a heat exchanger comprising several plates parallel to a longitudinal direction and defining between them a first series of passages for the flow of at least one refrigerant intended for exchanging heat with at least one circulating fluid, at least one passage of the first series defined between two adjacent plates comprising:

a refrigerant inlet configured to introduce the refrigerant into a portion of said passage and a refrigerant outlet configured to evacuate the refrigerant from the portion,

characterized in that said at least one passage of the first series further comprises:

- at least one other refrigerant inlet configured to introduce another refrigerant into another portion of said passage and at least one other refrigerant outlet configured to evacuate the other refrigerant from the other portion,

said other inlet and outlet being arranged so that said at least one passage of the first series is divided, in the longitudinal direction, into at least said portion for the flow of the refrigerant and said other portion for the flow of the other refrigerant.

Depending on the case, the invention may include one or more of the following characteristics:

- Several passages of the first series each comprise at least one inlet, one outlet, another inlet and another outlet for refrigerant, said inlets being fluidly connected to the same inlet manifold, said other inlets being fluidly connected to the same another inlet manifold, said outlets being fluidly connected to the same outlet manifold and said other outlets being fluidly connected to the same other outlet manifold.

- The exchanger includes a first end at which, during operation, the temperature is the lowest in the exchanger, and a second end at which, during operation, the temperature is the highest of the exchanger, said second end being arranged downstream of the first end in the longitudinal direction, the portion for the flow of the refrigerant being arranged on the side of the first end and the other portion for the flow of the other refrigerant being arranged between the portion and the second end.

- The plates define between them a second series of passages for the flow of at least one circulating fluid, at least one passage of the second series being adjacent to said at least one passage of the first series and being configured so that, when a current of circulating fluid circulates in said passage, said current of circulating fluid exchanges heat with the refrigerant at at least part of the portion and with the other refrigerant at at least part on the other portion.

- At least one passage of the second series comprises, at the second end of the exchanger, an inlet for circulating fluid configured to distribute the circulating fluid in said at least one passage and, at the level of the first end of the exchanger, an outlet configured to evacuate the circulating fluid from said at least one passage.

- Said at least one passage of the first series comprises at least two other inlets configured to introduce respectively at least two other refrigerants in at least two other respective portions of said passage and at least two other outlets configured to evacuate the at least two others respectively refrigerants of at least two other portions, said at least two other inlets and at least two other outlets being arranged such that said at least one passage of the first series is divided, in the longitudinal direction, into at least three successive portions.

The invention also relates to a heat exchange method using a heat exchanger according to the invention, said method comprising the following steps:

i) introduction of a flow of circulating fluid into at least one passage of a second series of passages defined between the plates of the exchanger, ii) introduction of a refrigerant through the inlet of at least one passage of the first series,

iii) evacuation of the refrigerant introduced in step ii) by the outlet of said passage,

iv) introduction of at least one other refrigerant through said other inlet of said passage,

v) evacuation of the other refrigerant introduced in step iv) by the other outlet of said passage,

said circulating fluid stream exchanging heat at least with the refrigerant and with the other refrigerant.

Preferably, the refrigerant discharged in step iii) has a first temperature and the other refrigerant introduced in step iv) has a second temperature, the second temperature being lower than the first temperature.

Advantageously, the second temperature is at least 1 ° C lower than the first temperature.

The present invention can be applied to a heat exchanger which vaporizes at least two partial streams of a fluid with two liquid-gas phases as refrigerants, in particular at least two partial streams of a mixture with several constituents, for example a mixture of hydrocarbons, by heat exchange with at least one circulating fluid, for example natural gas.

In particular, the invention can be applied to a process for cooling, or even liquefying, a mixture of hydrocarbons such as natural gas. In particular, the liquefaction process is implemented in a process for the production of liquefied natural gas (LNG).

The expression "natural gas" refers to any composition containing hydrocarbons, including at least methane. This includes a "crude" composition (prior to any treatment or washing), as well as any composition that has been partially, substantially or entirely treated for the reduction and / or elimination of one or more compounds, including, but not limited to limit, sulfur, carbon dioxide, water, mercury and some heavy and aromatic hydrocarbons. Thus, the invention relates to a process for cooling a stream of hydrocarbons such as natural gas as a stream of circulating fluid, said process using a heat exchanger according to the invention or a process for exchanging heat according to the invention and comprising the following stages:

a) introduction of the hydrocarbon stream into the heat exchanger,

b) introduction of a first refrigerant current into the heat exchanger,

c) extraction of the heat exchanger from a partial refrigerant stream and from at least one other partial refrigerant stream from the first refrigerant stream,

d) expansion of the partial refrigerant stream and of the other partial refrigerant stream at different pressure levels to produce the refrigerant and the other refrigerant respectively,

e) reintroduction of the refrigerant produced in step d) by the entry of at least one passage from the first series,

f) reintroduction of the other refrigerant produced in step d) through the other inlet of said passage,

g) cooling of the hydrocarbon stream by heat exchange with at least the refrigerant and the other refrigerant.

Note that the hydrocarbon stream from step g) can be at least partially liquefied.

Optionally, the cooled and / or at least partially liquefied hydrocarbon stream in step g) is introduced into another exchanger into which a second refrigerant stream is introduced. Preferably, the second refrigerant stream leaving the other exchanger is expanded and then reintroduced into said other exchanger to be vaporized there by refrigerating the hydrocarbon stream and the second refrigerant stream, so that the hydrocarbon stream leaves liquefied and under - cooled from the other exchanger.

The first refrigerant stream can be a mixture of hydrocarbons, for example a mixture containing ethane and propane. Preferably, the refrigerant produced in step d) has a first pressure and the other refrigerant produced in step d) has a second pressure, the second pressure being greater than the first pressure.

The present invention will now be better understood thanks to the following description, given solely by way of nonlimiting example and made with reference to the attached diagrams, among which:

Figure 1 is a schematic sectional view, in a plane parallel to the plates of the exchanger, of a refrigerant passage of a heat exchanger according to the prior art;

Figure 2 is a schematic sectional view, in a plane orthogonal to the plates and parallel to the longitudinal direction of the exchanger, of series of passages of the heat exchanger of Figure 1;

Figure 3A is another schematic sectional view, in a plane parallel to the plates of the exchanger, of a passage of a heat exchanger according to another embodiment of the invention;

Figure 3B illustrates on the one hand the exchange diagram curves of a conventional exchanger as illustrated in Figure 1 and on the other hand the exchange diagram curves of an exchanger according to the invention as 'illustrated in Figure 3A;

FIG. 4 diagrammatically shows an embodiment of a heat exchange method implementing an exchanger according to an embodiment of the invention,

Figure 5 is a schematic sectional view, in a plane parallel to the plates of the exchanger, of a passage of a heat exchanger according to another embodiment of the invention.

Figure 1 illustrates passages 10a, 10b of a heat exchanger according to the prior art comprising several plates 2 which extend in two dimensions, length and width, respectively in a longitudinal direction z and a lateral direction y orthogonal to z and parallel to the plates 2.

The plates are arranged parallel one above the other with spacing in a direction of stacking x, thus forming a plurality of passages for fluids in relation to indirect heat exchange via the plates. Preferably, each passage of the exchanger has a parallelepiped and flat shape. The difference between two successive plates is small compared to the length and the width of each successive plate.

Figure 1 shows schematically passages of an exchanger configured to vaporize a refrigerant F1 and another refrigerant F2 by heat exchange with circulating fluid C.

Note that the other refrigerant F2 may be a fluid having a composition different from the refrigerant F1 or else a refrigerant having the same composition as the refrigerant F1 but at least one physical characteristic, in particular pressure, temperature, different from that of the refrigerant F1.

The circulating fluid C circulates in a second series of passages 11 (visible in FIG. 2) arranged, in whole or in part, alternately or adjacent to all or part of the passages 10a, 10b of the first series. The flow of fluids in the passages takes place generally parallel to the longitudinal direction z which is preferably, as in the illustrated case, vertical during the operation of the exchanger.

The passages 10a, 10b along the edges of the plates are generally sealed by lateral and longitudinal sealing strips 4 fixed to the plates. The lateral sealing strips 4 do not completely block the passages 10a, 10b but leave fluid inlet openings 31, 32 and outlet 41, 42.

In a manner known per se, the exchanger comprises distribution members 51, 61, 52, 62 which extend from and to the inlets and outlets of the passages. These organs, for example waves or distribution channels are configured to direct and ensure uniform distribution and recovery of fluids over the entire width of the passages.

In addition, the passages 10a, 10b advantageously comprise heat exchange structures arranged between the plates. These structures have the function of increasing the heat exchange surface of the exchanger. In fact, the heat exchange structures are in contact with the fluids circulating in the passages and transfer heat fluxes by conduction to the adjacent plates.

The heat exchange structures also have a function of spacers between the plates 2, in particular during assembly by brazing the exchanger and to avoid any deformation of the plates during the use of pressurized fluids. They also guide the flow of fluid in the exchanger passages.

Preferably, these structures include heat exchange waves which advantageously extend along the width and the length of the passages 10a, 10b, parallel to the plates 2, in the extension of the distribution members 51, 61, 52, 62 according to the length of passages 10a, 10b. The passages of the exchanger thus have a main part of their length constituting the actual heat exchange zone, which is bordered by distribution zones furnished with members 51, 61, 52, 62.

Such an arrangement of passages according to FIG. 1 is encountered in particular in an exchanger implemented in a natural gas liquefaction process. One of the known methods for obtaining liquefied natural gas is based on the use of two natural gas refrigeration cycles using respectively a first and a second mixture of refrigerant hydrocarbons. The first refrigeration cycle cools natural gas to its dew point using at least two different expansion levels to increase the efficiency of the cycle. The second cycle liquefies and sub-cools natural gas and has only one level of expansion.

In the first expansion cycle, the first refrigerant mixture from a compressor is sub-cooled in a first exchanger. At least two partial streams from the first refrigerant mixture are withdrawn from the exchanger at two separate outlet points and then expanded to different pressure levels, thus forming at least two distinct refrigerants F1 and F2 reintroduced into the exchanger through inlets. 31, 32 separate selectively supplying the passages 10a, 10b to be vaporized there and then evacuated by separate outlets 41, 42. According to the known method, the refrigerant F1 expanded at a given pressure level enters through the inlet 31 located at the cold end of the exchanger and exits through the outlet 41 at a temperature higher than the inlet temperature by the inlet 32 of the other refrigerant expanded to another pressure level.

To respect the arrangement of the inputs and outputs in an increasing order of temperature of the fluids, the input of the other refrigerant is conventionally located, in the longitudinal direction z, at a position closer to the cold end of the exchanger than neither is the outlet of the refrigerant at lower pressure.

As shown in Figure 1, the exchanger includes two types of refrigerant passages, one 10a for the refrigerant F1 and the other 10b for the other refrigerant F2. The circulating fluid C flowing in passages 11 adjacent to the passages of a type 10a and / or of another type 10b therefore exchanges heat at the active exchange zone A1 with the fluid F1 and at the level of the active exchange zone A2 for the other fluid F2. Zones 11 and I2 are not supplied with fluid and therefore constitute thermally inactive zones.

The present invention aims to reduce the longitudinal extent of these inactive zones, or even to eliminate them completely by proposing to share longitudinally at least one passage formed between two plates 2 of the exchanger and to circulate therein different refrigerants.

Figure 3 is a schematic sectional view, in a plane parallel to that of Figure 1, of a passage of an exchanger according to an embodiment of the invention. In the example illustrated, the number of refrigerants of different types is limited to 2 for the sake of simplification, it being noted that a greater number of types of fluid could flow in such a passage according to the same principle.

As can be seen in FIG. 3, at least one passage 10 of the first series of refrigerant passages comprises at least one other inlet 32 and at least one other outlet 42 for another refrigerant F2.

Said other inlet and outlet 32, 42 being arranged so that said passage 10 of the first series is divided, in the direction longitudinal z, in at least one portion 100 for the flow of the refrigerant F1 and another portion 200 for the flow of the other refrigerant F2.

In this way, during the operation of the exchanger, several refrigerants F1, F2 of different types circulate within the same passage, that is to say between two same plates of the exchanger, on portions d 'dedicated flows which follow one another along the longitudinal direction z.

In this way, the proportion of inactive zones in the exchanger is greatly reduced, or even eliminated, the same passage having at least two active exchange zones A1, A2 at the level of which the refrigerant F1 and said at least one other refrigerant. F2 successively exchange heat with circulating fluid C.

Almost all or even all of a calorigenic passage 11 of the second series is thus in contact with a refrigerant passage 10 of the first series, which promotes heat exchange and drastically reduces the thermal and mechanical stresses exerted on the plates and the exchanger inlet / outlet manifolds. The size of the exchanger can be reduced, thereby reducing the cost of the exchanger and the cold box in which it is integrated. The reduction of inactive zones within the exchanger also increases its mechanical strength.

In fact, the inventors of the present invention have demonstrated that by taking into account the temperature overlaps from the design phase of the process, it is possible to circulate the refrigerants in the same passage, even if the temperature of output of the first fluid is greater than that of input of the second fluid. This requires simulating the exchanger, not in a single section with two firgorigenic fluids arriving at different temperatures, as is the case with the known method of pinching, but in different consecutive sections (two in the example cited ), each of these sections comprising a single refrigerant, arriving at its inlet temperature, to get as close as possible to the real geometry and therefore the real pinches that the exchanger will present. This is illustrated in Figure 3B, which shows a comparison between the Heat exchanged - Temperature (DH - T) exchange diagrams, or enthalpy curves, obtained on the one hand with a simulated exchanger according to the classic pinch method (in ( a)) and on the other hand with an exchanger in which the fluids circulate in accordance with the invention (in (b)), the curves C, F, F1, F2 illustrate the evolution of the quantity of heat exchanged as a function of the temperature, respectively for the circulating fluid, a composite refrigerant constructed according to the conventional pinch method, the refrigerant F1 according to the invention and the other refrigerant F2 according to the invention.

Preferably, the majority, more preferably at least 80% of the total number of passages 10 of the first series, or even all of the passages 10 of the first series, each comprise an inlet and an outlet 31, 41 for the refrigerant F1 and at least one other inlet and another outlet 32, 42 for the other refrigerant F2.

Advantageously, the exchanger according to the invention has a single type of passage 10 for refrigerants, which greatly simplifies the design thereof. The term “passages of the same type” means passages which have an identical configuration or structure, in particular in terms of dimensions of the passages, arrangements of the fluid inlets and outlets.

Preferably, the majority, preferably at least 80%, or even all, of the total number of passages 10 of the first series have an identical configuration. In particular, the inputs and outputs 31, 41, 32, 42 are arranged in substantially identical positions in the longitudinal direction z.

Thus, the inputs and outputs 31, 41, 32, 42 of the passages 10 of the first series are arranged in coincidence one above the other, following the stacking direction x of the passages. The inputs 31, 32 and outputs 41, 42 thus placed one above the other are respectively united in collectors of semi-tubular shape 71, 72, 81, 82, through which the distribution and the evacuation of fluids.

Preferably, the longitudinal direction is vertical when the exchanger is in operation. The refrigerants F1, F2 generally flow vertically and in the upward direction. Circulating fluid C preferably flows against the current. Other directions and directions of flow of the fluids F1, F2 are of course conceivable, without departing from the scope of the present invention.

Preferably, the passage 10 of the exchanger comprises distribution zones 51, 61, 52, 62, preferably furnished with distribution members, which extend from and towards the inlets 31, 32 and outlets 41, 42 of the passage 10. These distribution zones are configured to direct and uniformly recover the fluids F1 and F2 over the entire width of the exchange zones A1 and A2 respectively.

Advantageously, the portion 100 of the passage 10 comprises the distribution zones 51, 61 and the exchange zone A1 and the other portion 200 comprises the distribution zones 52, 62 and the exchange zone A2.

Advantageously, heat exchange structures are arranged in the exchange zones A1 and A2. We can use the different types of waves usually used in exchangers of the brazed plate and fin type to form the heat exchange structures of the exchange zones A1, A2. The waves can be chosen from the known wave types such as straight waves, partial shift waves (of the "serrated" type in English), wave waves or herringbone (of the "herringbone" type), perforated or not.

Advantageously, the distribution members and the heat exchange structures form within the passage 10 a plurality of channels fluidly connecting the inlet 31 and outlet 41 therebetween and the other inlets 32 and outlets 42 therebetween.

Advantageously, the exchanger comprises a first end 1 a at which, during operation, the temperature is the lowest of the exchanger, and a second end 1 b at which, during operation, the temperature is the highest of the exchanger.

Preferably, the second end 1b is arranged downstream of the first end 1a in the longitudinal direction z, so that the direction of flow of the fluids F1, F2 in the passage 10 is generally ascending. Preferably, the portion 100 for the flow of the refrigerant F1 being arranged on the side of the first end 1 a and the other portion 200 for the flow of the other refrigerant F2 is arranged between the portion 100 and the second end 1 b.

Thus, in the representation given in FIG. 3, the other portion 200 extends, following the longitudinal direction z, downstream of the portion 100.

Preferably, the portions 100, 200 are juxtaposed in the longitudinal direction z, as illustrated in Figure 3, which optimizes the space within the passage 10 by maximizing the extent of the active areas.

According to an alternative embodiment, illustrated in Figure 5, two other refrigerants F2, F3 flow in the same passage 10 according to the invention.

In this case, at least one refrigerant passage 10 of the first series comprises two other inputs 32, 33 configured to introduce two other refrigerants F2, F3 respectively into two other respective portions 200, 300 of the passage 10, and two other outputs 42, 43 configured to evacuate the other two refrigerants F2, F3 respectively from the other two portions 200, 300. The passage 10 is divided, in the longitudinal direction z, into three successive portions 100, 200, 300.

Advantageously, when the exchanger is operating, the refrigerant F1 enters via the inlet 31 of at least one passage 10 at a temperature called initial T0 and is discharged through the outlet 41 at a first temperature T1 greater than T0. Preferably, the temperature T0 is between -55 and - 75 ° C and the temperature T1 is between -10 and -30 ° C.

Preferably, the other refrigerant F2 enters passage 10 via the other inlet 32 at a second temperature T2 and leaves it through the other outlet 42 at a third temperature T3, T3 being greater than T2. Preferably, the temperature T2 is between -15 and -35 ° C and the temperature T3 is between 35 and 0 ° C.

Preferably, the second temperature T2 is lower than the first temperature T1. This makes it possible to have a superheated F1 fluid at the outlet of the portion 100 of the exchanger (high T1), while ensuring cooling. effective circulating fluid in the other portion 200 of the exchanger thanks to a vaporization start temperature, T2, of the fluid F2 sufficiently low (lower than T1).

More preferably, the second temperature T2 is at least 1 ° C lower than the first temperature T1. Preferably, the second temperature T2 is at most 15 ° C lower, more preferably at most 10 ° C, and preferably at most 5 ° C, at the first temperature T 1. This is to avoid excessive mechanical stress in the exchanger.

Now consider the variant where two other refrigerants F2, F3 flow in the same passage 10.

Advantageously, when the exchanger is operating, the refrigerant F1 enters via the inlet 31 of at least one passage 10 at an initial temperature T0 between -55 and -75 ° C and is discharged through the outlet 41 at a first temperature T1 greater than T0, T1 being between -25 and -45 ° C.

Preferably, the first other refrigerant F2 enters passage 10 through a first other inlet 32 at a second temperature T2 and leaves it through the other outlet 42 at a temperature T3, T3 being greater than T2. Preferably, the temperature T2 is between -30 and -50 ° C and the temperature T3 is between 0 and -20 ° C.

Preferably, the second other refrigerant F3 enters passage 10 via a second other inlet 33 at a fourth temperature T4 and leaves it through a second other outlet 43 at a fifth temperature T5, T5 being greater than T4. Preferably, the temperature T4 is between -5 and -25 ° C and the temperature T5 is between 30 and 0 ° C.

Advantageously, the fourth temperature T4 is lower than the third temperature T3. This makes it possible to have a superheated fluid F2 at the outlet of the portion 200 of the exchanger (high T3), while ensuring efficient cooling of the circulating fluid in the other portion 300 of the exchanger thanks to a start temperature of sufficiently low vaporization, T4, of the fluid F3 (less than T3).

Preferably, the fourth temperature T4 is at least 1 ° C lower than the third temperature T3. Preferably, the second temperature T2 is at most 15 ° C lower, more preferably at most 10 ° C, and preferably at most 5 ° C, at the first temperature T1.

Advantageously, the fourth temperature T4 is at least 1 ° C lower than the third temperature T3, preferably the fourth temperature T4 is at least 15 ° C lower than the third temperature T3, more preferably in order to avoid excessive mechanical stresses in the exchanger, at most 10 ° C, and preferably at most 5 ° C, at the third temperature T4.

According to a particular embodiment, the refrigerant F1 and the at least one other refrigerant F2 are fluids having different pressures. In particular, the refrigerant F1 flows in the exchanger at a first pressure P1 and the other refrigerant F2 flows in the exchanger at a second pressure P2 which is preferably greater than the first pressure P1. Fluids F1, F2 can have the same composition.

An exchanger according to the invention can be used in any process using several refrigerants of different types, in particular in terms of composition and / or characteristics such as pressure, temperature, physical state, etc.

The use of an exchanger according to the invention is particularly advantageous in a process for liquefying a stream of hydrocarbons such as natural gas. An example of such a process is partially shown in Figure 4.

According to the natural gas liquefaction process shown diagrammatically in FIG. 4, the natural gas arrives via line 1 10 for example at a pressure between 4 MPa and 7 MPa and at a temperature between 30 ° C and 60 ° C. The natural gas circulating in the conduit 110, the first refrigerant current circulating in the conduit 30 and the second refrigerant current circulating in the conduit 20 enter the exchanger E1 according to the invention to circulate there in parallel and co-directions. current.

The natural gas comes out cooled from the exchanger E1 via the conduit 102, for example at a temperature between - 35 ° C and - 70 ° C. The second refrigerant current comes out completely condensed from the exchanger E1 via the conduit 202, for example at a temperature between - 35 ° C and - 70 ° C.

In the exchanger E1, three fractions, also called partial flows or currents, 301, 302, 303 of the first refrigerant current in the liquid phase are successively withdrawn. The fractions are expanded through the expansion valves V1 1, V12 and V13 at three different pressure levels, forming a refrigerant F1 and two other refrigerants F2, F3. These three refrigerants F1, F2, F3 of different types are reintroduced into the exchanger E1 having refrigerant passages provided with three separate inlets 31, 32, 33 in accordance with the invention, then vaporized by heat exchange with natural gas, the second refrigerant stream and part of the first refrigerant stream.

The three vaporized refrigerants F1, F2, F3 are sent to different stages of the compressor K1, compressed and then condensed in the condenser C1 by heat exchange with an external cooling fluid, for example water or air. The first refrigerant stream from the condenser C1 is sent to the exchanger E1 through the conduit 30. 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 first refrigerant stream at the outlet of the condenser C1 can be between 10 ° C and 45 ° C.

The first refrigerant stream can be formed by a mixture of hydrocarbons such as a mixture of ethane and propane, but can also contain methane, butane and / or pentane. The proportions in molar fraction (%) of the components of the first refrigerant mixture can be:

Ethane: 30% to 70%

Propane: 30% to 70%

Butane: 0% to 20%

The natural gas circulating in the conduit 102 can be fractionated, that is to say that a part of the C2 ₊ hydrocarbons containing at least two carbon atoms is separated from the natural gas using a device known to those skilled in the art. 'art. The fractionated natural gas is sent via line 102 to another exchanger E2. The C2 + hydrocarbons collected are sent to fractionation columns comprising a deethanizer. The light fraction collected at the top of the deethanizer can be mixed with the natural gas circulating in the conduit 102. The liquid fraction collected at the bottom of the deethanizer is sent to a depropanizer.

The gas circulating in the conduit 102 and the second refrigerant current circulating in the conduit 202 enter the other exchanger E2 to circulate there in parallel and co-current directions.

The second refrigerant stream leaving the exchanger E2 via the conduit 201 is expanded by the expansion member T3. The expansion member T3 can be a turbine, a valve or a combination of a turbine and a valve. The second expanded refrigerant stream from the turbine T3 is sent through the conduit 203 in the exchanger E2 to be vaporized by counter-current refrigerant natural gas and the second refrigerant stream.

At the outlet of the exchanger E2, the second vaporized refrigerant stream is compressed by the compressor K2 then cools in the indirect heat exchanger C2 by heat exchange with an external cooling fluid, for example water or air. The second refrigerant stream from the exchanger C2 is sent to the exchanger E1 via the conduit 20. The pressure of the second refrigerant stream at the outlet of the compressor K2 can be between 2 MPa and 8 MPa. The temperature of the second refrigerant stream at the outlet of the exchanger C2 can be between 10 ° C and 45 ° C.

In the process described with reference to Figure 4, the second refrigerant stream is not split into separate fractions, but, to optimize the approach in the exchanger E2, the second 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 compressor K2.

The second refrigerant stream 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 and / or butane. The proportions in molar fractions (%) of the components of the second refrigerant mixture can be:

Nitrogen: 0% to 10%

Methane: 30% to 70% Ethane: 30% to 70%

Propane: 0% to 10%

The natural gas leaves liquefied from the heat exchanger E2 via the conduit 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 denotes the temperature at which the first bubbles of vapor form in a liquid natural gas at a given pressure) and at a pressure identical to the inlet pressure of natural gas, except for pressure drops. For example, natural gas leaves the E2 exchanger at a temperature between - 105 ° C and - 145 ° C and at a pressure between 4 MPa and 7 MPa. Under these temperature and pressure conditions, natural gas does not remain entirely liquid after expansion to atmospheric pressure.

Of course, the invention is not limited to the specific examples described and illustrated in the present application. Other variants or embodiments within the reach of the skilled person can 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 fluids, other types of fluids, etc. are of course conceivable, depending on the constraints. imposed by the process to be implemented.

Claims

1. Heat exchanger (E1) comprising several plates (2) parallel to a longitudinal direction (z) and defining between them a first series of passages (10) for the flow of at least one refrigerant (F1) intended to exchange heat with at least one circulating fluid (C), at least one passage (10) of the first series defined between two adjacent plates (2) comprising:

- a refrigerant inlet (31) configured to introduce the refrigerant (F1) into a portion (100) of said passage (10) and a refrigerant outlet (41) configured to evacuate the refrigerant (F1) from the portion (100)

characterized in that said at least one passage (10) of the first series further comprises:

- at least one other inlet (32) of refrigerant configured to introduce another refrigerant (F2) into another portion (200) of said passage (10) and at least one other outlet (42) of refrigerant configured to evacuate the '' other refrigerant (F2) from the other portion (200),

said other inlet and outlet (32, 42) being arranged so that said at least one passage (10) of the first series is divided, in the longitudinal direction (z), into at least said portion (100) for flow refrigerant (F1) and said other portion (200) for the flow of the other refrigerant (F2).

2. Exchanger according to claim 1, characterized in that several passages (10) of the first series each comprise at least one inlet (31), one outlet (41), another inlet (32) and another outlet (42) refrigerant, said inlets (31) being fluidly connected to the same inlet manifold (71), said other inlets (32) being fluidly connected to the same other inlet manifold (72), said outlets (41) being related fluidly to the same outlet manifold (81) and said other outlets (42) being fluidly connected to the same other outlet manifold (82).

3. Exchanger according to one of claims 1 or 2, characterized in that it comprises a first end (1 a) at which, in operation, the temperature is the lowest of the exchanger, and a second end (1 b) at which, in operation, the temperature is the highest of the exchanger, said second end (1 b) being arranged downstream of the first end (1 a) in the longitudinal direction (z) , the portion (100) for the flow of the refrigerant (F1) being arranged on the side of the first end (1 a) and the other portion (200) for the flow of the other refrigerant (F2) being arranged between the portion (100) and the second end (1b).

4. Exchanger according to one of the preceding claims, characterized in that the plates (2) define between them a second series of passages (1 1) for the flow of at least one circulating fluid (C), at least one passage (11) of the second series being adjacent to said at least one passage (10) of the first series and being configured so that, when a flow of circulating fluid (C) flows in said passage (20), said flow of circulating fluid (C) heat exchange with the refrigerant (F1) at at least part of the portion (100) and with the other refrigerant (F2) at at least part of the '' other portion (200).

5. Exchanger according to claim 4, characterized in that at least one passage (11) of the second series comprises, at the second end (1b) of the exchanger, a circulating fluid inlet configured to distribute the circulating fluid (C) in said at least one passage (11) and, at the first end (1 a) of the exchanger, an outlet configured to evacuate circulating fluid (C) from said at least one passage (11) .

6. Exchanger according to one of the preceding claims, characterized in that said at least one passage (10) of the first series comprises at least two other inlets (32, 33) configured to introduce respectively at least two other refrigerants (F2 , F3) in at least two other respective portions (200, 300) of said passage (10) and two other outlets (42, 43) configured to evacuate the at least two other refrigerants (F2, F3) from the at least two others respectively portions (200, 300), said two other inlets (32, 33) and two other outlets (42, 43) being arranged so that said at least one passage (10) of the first series is divided, in the longitudinal direction ( z), in at least said portion (100) and in said two other portions (200, 300).

7. Heat exchange method using a heat exchanger (E1) according to one of the preceding claims, said method comprising the following steps:

i) introduction of a circulating fluid stream (C) into at least one passage (1 1) of a second series of passages defined between the plates (2) of the exchanger (E1),

ii) introduction of a refrigerant (F1) through the inlet (31) of at least one passage (10) of the first series,

iii) evacuation of the refrigerant (F1) introduced in step ii) through the outlet (41) of said passage (10),

iv) introduction of at least one other refrigerant (F2) through the other inlet (32) of said passage (10),

v) evacuation of the other refrigerant (F2) introduced in step iv) through the other outlet (41) of said passage (10),

said circulating fluid stream (C) exchanging heat at least with the refrigerant (F1) and with the other refrigerant (F2).

8. Method according to claim 7, characterized in that the refrigerant (F1) discharged in step iii) leaves the exchanger (E1) at a first temperature (T1) and the other refrigerant (F2) introduced in step iv) enters the exchanger (E1) at a second temperature (T2), the second temperature (T2) being lower than the first temperature (T1).

9. Method according to claim 8, characterized in that the second temperature (T2) is at least 1 ° C lower than the first temperature (T1).

10. A method of cooling a stream of hydrocarbons such as natural gas as a circulating fluid stream (C), said process using a heat exchanger (E1) according to one of claims 1 to 5 or a heat exchange process according to one of claims 6 to 8 and comprising the following steps:

a) introduction of the hydrocarbon stream (C) into the heat exchanger (E1),

b) introduction of a first cooling current (30) into the heat exchanger (E1),

c) extracting the heat exchanger (E1) from a partial refrigerant stream (301) and from at least one other refrigerant partial stream (302) from the first refrigerant stream (30),

d) expansion of the refrigerant partial stream (301) and of the other refrigerant partial stream (302) at different pressure levels to produce the refrigerant (F1) and the other refrigerant (F2) respectively,

e) reintroduction of the refrigerant (F1) into the heat exchanger (E1) through the inlet (31) of at least one passage (10) from the first series,

f) reintroduction of the other refrigerant (F2) into the heat exchanger (E1) through the other inlet (32) of said passage (10),

g) cooling of the hydrocarbon stream (C) by heat exchange with at least the refrigerant (F1) and the other refrigerant (F2).

1 1. Method according to claim 10, characterized in that the first refrigerant stream (30) is a mixture of hydrocarbons, for example a mixture containing ethane and propane.

12. Method according to one of claim 10 or 1 1, characterized in that the refrigerant (F1) produced in step d) has a first pressure (P1) and the other refrigerant (F2) produced in step d) has a second pressure (P2), the second pressure (P2) being greater than the first pressure (P1).