EP3830511B1 - Method for exchanging heat - Google Patents

Description

The present invention relates to a heat exchange method. A heat exchanger for such a process comprises series of passages for the flow of at least one refrigerant fluid to be put into heat exchange relationship with a heat-producing fluid, the exchanger comprising at least one passage configured for the 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 along two dimensions, length and width, thus constituting a stack of vaporization passages and condensation passages, some intended for example to vaporize refrigerant liquid and others to condense a gas calorigen. Note that heat exchanges between fluids can take place with or without phase change.

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

Several heat-producing and refrigerant fluids, of distinct nature and/or characteristics, can circulate in the exchanger. These fluids form distinct currents or flow rates which are introduced and evacuated from the exchanger by groups of inlets and outlets dedicated to a type of fluid.

We know in particular of the document US-A-2004255617 a liquefaction process using two successive refrigeration cycles to liquefy natural gas by heat exchange with two refrigerant fluids.

Conventionally, in the case where several refrigerants circulate in the exchanger, the inlets and outlets of the different refrigerants are arranged successively, along the length of the exchanger, in order of increasing temperature starting from the cold end of the exchanger, that is to say the entry point into the exchanger where a fluid is introduced at the temperature the lowest of all the exchanger temperatures.

Thus, when the outlet temperature of a 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 the refrigerant outlet.

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

The term pinch refers to the minimum difference between the temperature of the refrigerants, that is to say the fluids which heat up in the exchanger, and the temperature of the calorifying fluids, that is to say the fluids which cool in the exchanger, at a given point of the exchanger. To visualize this pinch, we evaluate the difference between two composite curves of a Heat exchanged - Temperature diagram, as illustrated by the Figure 3B(a) , one being associated with the flows to be heated, the other to 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 pinch between the curves of the exchange diagram resulting from the pinch 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 different type passages are not formed between the same pair of adjacent plates of the exchanger.

This results in a complexity of the exchanger and a significant increase in the dimensioning of the exchanger. In addition, each type of passage then presents a significant portion in which no fluid circulates, that is to say an inactive zone in terms of exchange with the heat-producing fluid.

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

The solution according to the invention is then a heat exchange process according to claim 1.

• plusieurs passages de la première série comprennent chacun au moins une entrée, une sortie, une première autre entrée et une première autre sortie de fluide frigorigène, lesdites entrées étant reliées fluidiquement à un même collecteur d'entrée, lesdites premières autres entrées étant reliées fluidiquement à un même premier autre collecteur d'entrée, lesdites premières sorties étant reliées fluidiquement à un même collecteur de sortie et lesdites premières autres sorties étant reliées fluidiquement à un même premier autre collecteur de sortie.
• au moins un passage de la deuxième série est adjacent audit au moins un passage de la première série et est configuré de sorte que, lorqu'un courant de fluide calorigène circule dans ledit passage, ledit courant de fluide calorigène échange de la chaleur avec le fluide frigorigène au niveau d'au moins une partie de la portion et avec le premier autre fluide frigorigène au niveau d'au moins une partie de la première autre portion.
• au moins un passage de la deuxième série comprend, au niveau de la seconde extrémité de l'échangeur, une entrée de fluide calorigène configurée pour distribuer le fluide calorigène dans ledit au moins un passage et, au niveau de la première extrémité de l'échangeur, une sortie de fluide calorigène configurée pour évacuer le fluide calorigène dudit au moins un passage.
• ledit au moins un passage de la première série comprend en outre au moins une deuxième autre entrée configurée pour introduire au moins un deuxième autre fluide frigorigène dans au moins une deuxième autre portion dudit passage et au moins une deuxième autre sortie configurée pour évacuer le au moins deuxième autre fluide frigorigène de la au moins deuxième autre portion, lesdites au moins première et deuxième autres entrées et au moins première et deuxième autres sorties étant agencées de sorte que ledit au moins un passage de la première série est divisé, suivant la direction longitudinale, en au moins trois portions successives.

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, an outlet, a first other inlet and a first other outlet of refrigerant, said inlets being fluidly connected to the same inlet manifold, said first other inlets being fluidly connected to the same first other input collector, said first outputs being fluidly connected to the same output collector and said first other outputs being fluidly connected to the same first other output collector.
• at least one passage of the second series is adjacent to said at least one passage of the first series and is configured so that, when a current of circulating fluid flows through said passage, said current of circulating fluid exchanges heat with the fluid refrigerant at at least part of the portion and with the first other refrigerant at at least part of the first other portion.
• at least one passage of the second series comprises, at the second end of the exchanger, a heating fluid inlet configured to distribute the heating fluid in said at least one passage and, at the first end of the exchanger , a circulating fluid outlet configured to evacuate the circulating fluid from said at least one passage.
• said at least one passage of the first series further comprises at least one second other inlet configured to introduce at least one second other refrigerant into at least one second other portion of said passage and at least one second other outlet configured to evacuate the at least second other refrigerant from the at least second other portion, said at least first and second other inlets and at least first and second other outlets being arranged so that said at least one other outlet at least one passage of the first series is divided, in the longitudinal direction, into at least three successive portions.

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 liquefied natural gas (LNG) production process.

The expression "natural gas" refers to any composition containing hydrocarbons including at least methane. This includes a “raw” 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 certain heavy and aromatic hydrocarbons.

1. a) introduction du courant d'hydrocarbures dans l'échangeur de chaleur,
2. b) introduction d'un premier courant réfrigérant dans l'échangeur de chaleur,
3. c) extraction de l'échangeur de chaleur d'un courant partiel réfrigérant et d'au moins un autre courant partiel réfrigérant issus du premier courant réfrigérant,
4. d) détente du courant partiel réfrigérant et de l'autre courant partiel réfrigérant à des niveaux de pression différents pour produire respectivement le fluide frigorigène et le premier autre fluide frigorigène,
5. e) réintroduction du fluide frigorigène produit à l'étape d) par l'entrée d'au moins un passage de la première série,
6. f) réintroduction du premier autre fluide frigorigène produit à l'étape d) par la première autre entrée dudit passage,
7. g) refroidissement du courant d'hydrocarbures par échange de chaleur avec au moins le fluide frigorigène et le premier autre fluide frigorigène.

Thus, the invention also relates to a process for cooling a stream of hydrocarbons such as natural gas as a stream of circulating fluid, said process implementing a heat exchange process according to the invention and comprising the following steps :

1. a) introduction of the hydrocarbon stream into the heat exchanger,
2. b) introduction of a first refrigerant current into the heat exchanger,
3. c) extraction from the heat exchanger of a partial refrigerant current and at least one other partial refrigerant current coming from the first refrigerant current,
4. d) expansion of the partial refrigerant current and the other partial refrigerant current at different pressure levels to respectively produce the refrigerant and the first other refrigerant,
5. e) reintroduction of the refrigerant produced in step d) by the entry of at least one passage of the first series,
6. f) reintroduction of the first other refrigerant produced in step d) through the first other inlet of said passage,
7. g) cooling the hydrocarbon stream by heat exchange with at least the refrigerant and the first other refrigerant.

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

Optionally, the hydrocarbon stream cooled and/or at least partially liquefied 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 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 may 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 first other refrigerant produced in step d) has a second pressure, the second pressure being greater than the first pressure.

• la Figure 1 est une vue schématique en coupe, dans un plan parallèle aux plaques de l'échangeur, d'un passage de fluide frigorigène d'un l'échangeur de chaleur selon l'art antérieur ;
• la Figure 2 est une vue schématique en coupe, dans un plan orthogonal aux plaques et parallèle à la direction longitudinale de l'échangeur, de séries de passages de l'échangeur de chaleur de la Figure 1 ;
• la Figure 3A est une autre vue schématique en coupe, dans un plan parallèle aux plaques de l'échangeur, d'un passage d'un échangeur de chaleur mis en oeuvre dans un procédé d'échange selon un mode de réalisation de l'invention ;
• la Figure 3B illustre d'une part les courbes de diagramme d'échange d'un échangeur classique tel qu'illustré sur la Figure 1 et d'autre part les courbes de diagramme d'échange d'un procédé d'échange selon l'invention tel qu'illustré sur la Figure 3A ;
• la Figure 4 schématise un mode de réalisation d'un procédé d'échange de chaleur selon un mode de réalisation de l'invention,
• la Figure 5 est une vue schématique en coupe, dans un plan parallèle aux plaques de l'échangeur, d'un passage d'un échangeur de chaleur mis en oeuvre dans un procédé d'échange selon un autre mode de réalisation de l'invention .

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 diagrams, among which:

• there 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;
• there 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 the Figure 1 ;
• there Figure 3A is another schematic sectional view, in a plane parallel to the plates of the exchanger, of a passage of a heat exchanger used in an exchange process according to one embodiment of the invention;
• there Figure 3B illustrates on the one hand the exchange diagram curves of a classic exchanger as illustrated on the Figure 1 and on the other hand the exchange diagram curves of an exchange method according to the invention as illustrated in the Figure 3A ;
• there Figure 4 schematizes an embodiment of a heat exchange process according to one embodiment of the invention,
• there Figure 5 is a schematic sectional view, in a plane parallel to the plates of the exchanger, of a passage of a heat exchanger used in an exchange process according to another embodiment of the invention.

There Figure 1 illustrates passages 10a, 10b of a heat exchanger according to the prior art comprising several plates 2 which extend along 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 stacking direction x, thus forming a plurality of passages for fluids in indirect heat exchange relationship via the plates. Preferably, each passage of the exchanger has a parallelepiped and flat shape. The gap between two successive plates is small compared to the length and width of each successive plate.

There Figure 1 schematizes the passages of an exchanger configured to vaporize a refrigerant F1 and a first other refrigerant F2 by heat exchange with a calorigen fluid C.

Note that the first other refrigerant F2 may be a fluid having a composition different from the refrigerant F1 or 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 on the Figure 2 ) arranged, in whole or in part, alternately or adjacently with 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 case illustrated, vertical during operation of the exchanger.

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

In a manner known per se, the exchanger comprises distribution members 51, 61, 52, 62 which extend from and towards the entrances and exits 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 flows by conduction to the adjacent plates.

The heat exchange structures also have a function as spacers between the plates 2, in particular during assembly by brazing of the exchanger and to avoid any deformation of the plates during installation. works with fluids under pressure. They also ensure the guidance of fluid flows in the passages of the exchanger.

Preferably, these structures comprise heat exchange waves which advantageously extend along the width and 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 heat exchange zone itself, which is bordered by distribution zones furnished with members 51, 61, 52, 62.

Such an arrangement of passages according to the Figure 1 is encountered in particular in an exchanger used 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 the natural gas to its dew point using at least two different expansion levels to increase cycle efficiency. The second cycle liquefies and subcools the natural gas and only has one expansion level.

In the first expansion cycle, the first refrigerant mixture from a compressor is subcooled in a first exchanger. At least two partial streams from the first refrigerant mixture are withdrawn from the exchanger at two distinct outlet points then expanded at different pressure levels, thus forming at least two distinct refrigerant fluids F1 and F2 reintroduced into the exchanger via inlets 31, 32 separate selectively supplying the passages 10a, 10b to be vaporized then evacuated through 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 leaves through the outlet 41 at a temperature higher than the entry temperature through the inlet. 32 of the first other refrigerant expanded to another pressure level.

To respect the arrangement of the inlets and outlets in an increasing order of fluid temperature, the inlet of the other refrigerant is conventionally located, in the longitudinal direction z, at a position closer to the cold end of the exchanger than is the outlet of the refrigerant at lower pressure.

As seen on the Figure 1 , the exchanger includes two types of refrigerant passages, one 10a for the refrigerant F1 and the other 10b for the first other refrigerant F2. The heat-producing fluid C flowing in passages 11 adjacent to the passages of a type 10a and/or another type 10b therefore exchanges heat at the level of the active exchange zone A1 with the fluid F1 and at the level of the active exchange zone A2 for the first other fluid F2. Zones I1 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 different refrigerant fluids there.

There Figure 3A is a schematic sectional view, in a plane parallel to that of the Figure 1 , of a passage of an interchange. In the example illustrated, the number of refrigerant fluids of different types is limited to 2 for the sake of simplification, it being noted that a greater number of types of fluid could circulate in such a passage according to the same principle.

As seen on the Figure 3A , at least one passage 10 of the first series of refrigerant passages comprises at least one first other inlet 32 and at least one first other outlet 42 for another refrigerant fluid F2.

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

In this way, during operation of the exchanger, several refrigerant fluids F1, F2 of different types circulate within the same passage, that is to say between two same plates of the exchanger, on portions of 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 first other fluid refrigerant F2 successively exchange heat with the circulating fluid C.

Almost all, or even the entirety 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 collectors. The dimensioning of the exchanger can be reduced, thus reducing the cost of the exchanger and the cold box in which it is integrated. Reducing 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 outlet of the first fluid is greater than that of entry of the second fluid. To do this, it is necessary to simulate the exchanger, not in a single section with two refrigerating fluids arriving at different temperatures, as is the case with the known pinch method, 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 to the real pinches that the exchanger will present.

This is illustrated on the Figure 3B , which shows a comparison between the exchange diagrams Heat exchanged - Temperature (ΔH - T), or enthalpy curves, obtained on the one hand with an exchanger simulated according to the classic pinch method (in (a)) and on the other hand leaves 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 classic pinch method, the refrigerant F1 according to the invention and the first 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 first other inlet and one first other outlet 32, 42 for the first other refrigerant F2.

Advantageously, the exchanger of the process according to the invention has a single type of passage 10 for refrigerant fluids, which greatly simplifies the design. By passages of the same type we mean 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 inlets and outlets 31, 41, 32, 42 are arranged at 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 coincidentally one above the other, following the stacking direction x of the passages. The inlets 31, 32 and outlets 41, 42 thus placed one above the other are united respectively 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 an upward direction. The circulating fluid C preferably circulates against the current. Other directions and senses flow of fluids F1, F2 are of course possible, 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 uniformly direct and 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 first 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 known wave types such as straight waves, partial offset waves (of the “serrated ” type in English), waves or herring bones (of the “herringbone ” type in English), 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 to each other and the first other inlets 32 and outlets 42 to each other.

According to the invention, the exchanger comprises a first end 1a at which, in operation, the temperature is the lowest of the exchanger, and a second end 1b at which, in operation, the temperature is the lowest. high of the exchanger.

Preferably, the second end 1b is arranged downstream of the first end 1a following 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 1a and the first other portion 200 for the flow of the first other refrigerant F2 is arranged between the portion 100 and the second end 1b.

Thus, in the representation given on the Figure 3 , the first 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 the Figure 3 , which makes it possible to best optimize the space within passage 10 by maximizing the extent of the active zones.

According to a variant embodiment, illustrated on the 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 inlets 32, 33 configured to respectively introduce two other refrigerant fluids F2, F3 into two other respective portions 200, 300 of the passage 10, and two other outlets 42, 43 configured to respectively evacuate the two other refrigerant fluids F2, F3 from the two other 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 through the inlet 31 of at least one passage 10 at a so-called initial temperature T0 and is evacuated 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 first other refrigerant F2 enters the passage 10 through the first other inlet 32 at a second temperature T2 and leaves through the first 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 fluid F1 at the outlet of portion 100 of the exchanger (high T1), while ensuring effective cooling of the calorific fluid in the first other portion 200 of the exchanger. thanks to a sufficiently low vaporization start temperature, T2, of the fluid F2 (lower than T1).

More preferably, the second temperature T2 is lower by at least 1°C compared to 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, than the first temperature T1. This is to avoid excessive mechanical stresses in the exchanger.

Let us 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 through the inlet 31 of at least one passage 10 at an initial temperature T0 of between -55 and -75°C and is evacuated 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 the passage 10 through a first other inlet 32 at a second temperature T2 and leaves through the first 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 the passage 10 via a second other inlet 33 at a fourth temperature T4 and leaves via 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 effective cooling of the calorific fluid in the second other portion 300 of the exchanger thanks to a starting temperature of vaporization, T4, of fluid F3 sufficiently low (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, than the first temperature T1.

Advantageously, the fourth temperature T4 is lower by at least 1°C relative to the third temperature T3, preferably the fourth temperature T4 is lower by at most 15°C, than the third temperature T3, more preferably, in order to to avoid excessive mechanical stresses in the exchanger, of at most 10°C, and preferably of 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 into the exchanger at a first pressure P1 and the other refrigerant F2 flows into 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 refrigerant fluids of different types, particularly 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 hydrocarbon stream such as natural gas. An example of such a process is partially schematized on the Figure 4 .

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

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

In the exchanger E1, three fractions, also called flow rates or partial currents, 301, 302, 303 of the first refrigerant current in the liquid phase are successively withdrawn. The fractions are expanded through the expansion valves V11, V12 and V13 at three different pressure levels, forming a refrigerant F1 and two other refrigerants F2, F3. These three refrigerant fluids 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 the natural gas, the second refrigerant current and part of the first refrigerant current.

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

The first refrigerant stream may be formed by a mixture of hydrocarbons such as a mixture of ethane and propane, but may also contain methane, butane and/or pentane. The proportions in mole fractions (%) 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 C ₂₊ hydrocarbons containing at least two carbon atoms is separated from the natural gas using a device known to those skilled in the art of art. The fractionated natural gas is sent via line 102 to another exchanger E2. The C2+ hydrocarbons collected are sent to fractionation columns including a deethanizer. The light fraction collected at the top of the deethanizer can be mixed with the natural gas circulating in conduit 102. The liquid fraction collected at the bottom of the deethanizer is sent to a depropanizer.

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

The second refrigerant current leaving the exchanger E2 via 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 via conduit 203 into the exchanger E2 to be vaporized by counter-current refrigeration of the natural gas and the second refrigerant stream.

At the outlet of the exchanger E2, the second vaporized refrigerant current 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 coming from the exchanger C2 is sent to the exchanger E1 via line 20. The pressure of the second refrigerant stream leaving the compressor K2 can be between 2 MPa and 8 MPa. The temperature of the second refrigerant stream at the outlet of 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 pressure level different then sent to different stages of the K2 compressor.

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 can also contain propane and/or butane. The proportions in mole 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 the heat exchanger E2 liquefied via 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 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, except for pressure losses. For example, natural gas leaves exchanger E2 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 particular examples described and illustrated in the present application. Other variants or embodiments within the reach of those skilled in the art 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 fluid flow, other types of fluids, etc. are of course possible, depending on the constraints. imposed by the process to be implemented.

Claims (8)

1. Method for exchanging heat implementing a heat exchanger (E1) comprising a plurality of plates (2) parallel to a longitudinal direction (z) and defining between one another a first series of passages (10) for the flow of at least one refrigerant fluid (F1) and one first other refrigerant fluid (F2) that are intended to exchange heat with at least one calorigenic fluid (C) and a second series of passages (11) for the flow of said calorigenic fluid (C), at least one passage (10) of the first series that is defined between two adjacent plates (2) comprising:

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

   - at least one first other refrigerant fluid inlet (32) configured to introduce the first other refrigerant fluid (F2) into a first other portion (200) of said passage (10) and at least one first other refrigerant fluid outlet (42) configured to discharge the first other refrigerant fluid (F2) from the first other portion (200),

   said first other inlet and outlet (32, 42) being arranged such 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 the flow of the refrigerant fluid (F1) and said first other portion (200) for the flow of the first other refrigerant fluid (F2), the exchanger (E1) comprising a first end (1a) at which, during operation, the temperature is the lowest of the exchanger, and a second end (1b) at which, during operation, the temperature is the highest of the exchanger, said second end (1b) being arranged downstream of the first end (1a) in the longitudinal direction (z), the portion (100) for the flow of the refrigerant fluid (F1) being arranged alongside the first end (1a) and the first other portion (200) for the flow of the first other refrigerant fluid (F2) being arranged between the portion (100) and the second end (1b),

   said method comprising the following steps:

   i) introducing the calorigenic fluid (C) into at least one passage (11) of the second series,

   ii) introducing the refrigerant fluid (F1) via the inlet (31) of at least one passage (10) of the first series and causing said refrigerant fluid (F1) to flow in the first portion (100) in the longitudinal direction (z),

   iii) discharging the refrigerant fluid (F1) introduced in step ii) via the outlet (41) of said passage (10),

   iv) introducing the first other refrigerant fluid (F2) via the first other inlet (32) of said passage (10) and causing said other first refrigerant fluid (F2) to flow in the first other portion (200) in the longitudinal direction (z),

   v) discharging the first other refrigerant fluid (F2) introduced in step iv) via the first other outlet (42) of said passage (10),

   said stream of calorigenic fluid (C) being cooled successively by the refrigerant fluid (F1) and the first other refrigerant fluid (F2), which form two distinct streams of refrigerant fluids, the refrigerant fluid (F1) being discharged in step iii) from the exchanger (E1) at a first temperature (T1) and the first other refrigerant fluid (F2) being introduced in step iv) into the exchanger (E1) at a second temperature (T2), the second temperature (T2) being lower than the first temperature (T1) .
2. Method according to Claim 1, characterized in that a plurality of passages (10) of the first series each comprise at least one inlet (31), one outlet (41), one first other inlet (32) and one second other outlet (42) for refrigerant fluid, said inlets (31) being fluidically connected to one and the same inlet manifold (71), said first other inlets (32) being fluidically connected to one and the same first other inlet manifold (72), said outlets (41) being fluidically connected to one and the same outlet manifold (81) and said first other outlets (42) being fluidically connected to one and the same first other outlet manifold (82).
3. Method according to either of the preceding claims, characterized in that at least one passage (11) of the second series comprises, at the second end (1b) of the exchanger, a calorigenic fluid inlet configured to distribute the calorigenic fluid (C) in said at least one passage (11) of the second series and, at the first end (1a) of the exchanger, a calorigenic fluid outlet configured to discharge the calorigenic fluid (C) from said at least one passage (11) of the second series.
4. Method according to one of the preceding claims, characterized in that said at least one passage (10) of the first series also comprises at least one second other inlet (33) configured to introduce at least one second other refrigerant fluid (F3) into at least one second other portion (300) of said passage (10) and one second other outlet (43) configured to discharge the at least one second other refrigerant fluid (F3) from the at least one second other portion (300), said first and second other inlets (32, 33) and first and second other outlets (42, 43) being arranged such that said at least one passage (10) of the first series is divided, in the longitudinal direction (z), into at least said portion (100) and into said first and second other portions (200, 300) .
5. Method according to one of the preceding claims, characterized in that the second temperature (T2) is at least 1°C lower than the first temperature (T1).
6. Method for cooling a stream of hydrocarbons such as natural gas as stream of calorigenic fluid (C), said method implementing a method for exchanging heat according to one of Claims 1 to 5 and comprising the following steps:

   a) introducing the stream of hydrocarbons (C) into the heat exchanger (E1),

   b) introducing a first cooling stream (30) into the heat exchanger (E1),

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

   d) expanding the partial cooling stream (301) and the other partial cooling stream (302) to different pressure levels in order to respectively produce the refrigerant fluid (F1) and the first other refrigerant fluid (F2),

   e) reintroducing the refrigerant fluid (F1) into the heat exchanger (E1) via the inlet (31) of at least one passage (10) of the first series,

   f) reintroducing the first other refrigerant fluid (F2) into the heat exchanger (E1) via the first other inlet (32) of said passage (10),

   g) cooling the stream of hydrocarbons (C) by exchanging heat with at least the refrigerant fluid (F1) and the first other refrigerant fluid (F2).
7. Method according to Claim 6, characterized in that the first cooling stream (30) is a mixture of hydrocarbons, for example, a mixture containing ethane and propane.
8. Method according to either of Claims 6 and 7, characterized in that the refrigerant fluid (F1) produced in step d) has a first pressure (P1) and the first other refrigerant fluid (F2) produced in step d) has a second pressure (P2), the second pressure (P2) being higher than the first pressure (P1).

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