FR3099234A1 - Process for recovering refrigeration energy with production of electricity or liquefaction of a gas stream - Google Patents

Abstract

The invention relates to a method for recovering refrigerating energy from a cold stream (F), in a system comprising a storage tank (203), at least one electric generator (G) and at least one device. heat exchange comprising several passages configured for the flow of fluids to be placed in a heat exchange relationship, said method comprising, in a first mode of operation, the vaporization of at least a part of said first working fluid (W1) in at least a first passage against at least a first hot current (C1), the expansion of the first working fluid (W1) from step a) of the first passage (1) in a first expansion member cooperating with a first generator electrical so as to produce electrical energy, the condensation of at least a part of said first working fluid (W1) expanded against at least the cold current (F), raising the pressure of said first working fluid ( W1) and the reintroduction of the first working fluid (W1) in the first pass. According to the invention comprises, in a second mode of operation, the following steps: introduction of a supply current (200), condensation of at least part of said supply current (200) against the cold current (F ) so as to produce an at least partially liquefied feed stream (201), and filling the storage tank (203) with the at least partially liquefied feed stream (201). Abstract figure: Fig. 1

Description

Process for recovering refrigeration energy with production of electricity or liquefaction of a gas stream

The present invention relates to a method for recovering refrigerating energy from a cold current making it possible to produce electrical energy from at least one Rankine cycle or to liquefy a supply current. In the case where the cold stream is a stream of cryogenic liquid such as liquefied natural gas, the stream can be regasified to be distributed in distribution networks while recovering its refrigeration content.

It is customary for natural gas from fields far from places of consumption to be liquefied before being stored on board specially adapted vessels, LNG carriers, to be transported over long distances. Indeed, natural gas occupies, in the liquid state, a smaller volume for a given mass and does not need to be stored at high pressure.

Before supplying the distribution networks, the liquefied natural gas (LNG) must be regasified, or in other words revaporized, at a pressure of around 10 to 90 bar depending on the network. This revaporization is carried out in LNG terminals, generally at ambient temperature by exchanging heat with seawater, possibly seawater heated with natural gas. The refrigeration content of the liquefied natural gas is then not valued in any way.

There are different methods for generating electricity from the cold temperatures of liquefied natural gas and thus recovering its energy content.

A known method is based on direct expansion of natural gas. The liquefied natural gas is pumped at a pressure higher than that of the distribution network, vaporized by heat exchange with a hot source such as seawater, then expanded to network pressure in an expansion turbine associated with an electric generator.

Other methods are based on thermodynamic cycles using an intermediate fluid, or working fluid. Among these methods, the Rankine cycle is known, in which a working fluid is vaporized under pressure against a hot source such as sea water in a first heat exchanger, then expanded in a turbine coupled to an electric generator. . The expanded working fluid is then condensed in a second exchanger against LNG which is used as the cold source of the cycle. This results in a low pressure liquid working fluid which is pumped and returned at high pressure to the first exchanger, thus closing the cycle.

While the Rankine cycle can operate with water as the working fluid for applications such as geothermal heat recovery, the use of organic fluids evaporating at low temperatures makes it possible to exploit cold sources at low temperature. We then speak of the organic Rankine cycle or ORC cycle (for Organic Rankine Cycle).

ORC cycles are conventionally industrialized using LNG as the cold source and seawater as the hot source. These cycles make it possible to regasify a stream of LNG while producing electricity with energy yields of the order of 20 kWh per ton of vaporized LNG, that is to say 0.015 kWh/Nm ³ .

In addition, the demand for electricity is not constant and the methods of electricity production must be increasingly flexible. This is mainly due to the fact that electricity is difficult to store. It is therefore necessary to constantly balance supply and demand in order to avoid causing tensions on the electricity network resulting in significant fluctuations in electricity prices.

The purpose of the present invention is to solve all or part of the problems mentioned above, in particular by proposing a process for recovering cooling energy offering increased flexibility in order to be able to adapt to fluctuations in electricity demand.

The solution according to the invention is then a method for recovering cooling energy from a cold stream, in a system comprising a storage tank, at least one electric generator and at least one heat exchange device comprising several passages configured for the flow of fluids to be placed in a heat exchange relationship, said method comprising, in a first mode of operation, the following steps:

a) introducing a first working fluid having a first high pressure into at least a first passage and vaporizing at least a part of said first working fluid against at least a first hot stream circulating in at least a second passage in relation heat exchange with said at least one first passage,

b) outlet of the first working fluid from step a) of the first passage and expansion to a first low pressure lower than the first high pressure, in a first expansion member cooperating with a first electric generator so as to produce electrical energy,

c) introduction of the first working fluid expanded in step b) into at least a third passage and condensation of at least a part of said first working fluid against at least the cold current circulating in at least a fourth passage in relation d heat exchange with at least the third pass,

d) exit of the first working fluid at least partially condensed in step c) of the third passage, raising the pressure of the said first working fluid to the first pressure and reintroducing it into the first passage, characterized in that, in a second mode of operation, said method comprises the following steps:

e) introduction of a supply current in at least a tenth passage in heat exchange relationship with at least the fourth passage,

f) condensing at least part of said feed stream against the cold stream so as to produce, at the output of the tenth pass, an at least partially liquefied feed stream, and

g) filling the storage tank with the feed stream produced in step f). Depending on the case, the invention may include one or more of the following characteristics:

- the method further comprises the following steps:

h) introduction of the feed stream from step f) into a supercooler,

i) output of the feed stream from the supercooler and expansion in a third expansion device so as to form a gaseous phase and a liquid phase of said feed stream,

j) introducing said gaseous and liquid phases into the storage tank,

k) extraction, from the storage tank, of at least part of the gaseous phase and introduction into the supercooler so as to cool the feed stream circulating in the supercooler by heat exchange with the phase carbonated,

l) compressing the gas phase in a compression device to form a compressed gas phase and introducing said compressed gas phase into the feed stream before introduction into the tenth pass.

- the cold current leaving the fourth passage is introduced into at least an eighth passage, the method comprising, in the first mode of operation, the following additional steps:

m) introducing a second working fluid having a second high pressure into at least a fifth passage and vaporizing at least a part of said second working fluid against at least a second hot stream circulating in at least a sixth passage in relation heat exchange with at least the fifth pass,

n) output of the second working fluid at least partially vaporized in step m) of the fifth passage and expansion to a second low pressure, with Pb2 lower than Ph2, in a second expansion member cooperating with a second electric generator of how to produce electrical energy,

o) introduction of the second working fluid expanded in step n) into at least a seventh passage in heat exchange relationship with at least the eighth passage, and condensation of at least a part of said second working fluid against the current cold circulating in the eighth passage,

p) outlet of the second working fluid at least partially condensed in step g) of the seventh passage, raising the pressure of said second working fluid to the second high pressure and reintroducing said second working fluid at least partially condensed at step g) in the fifth pass.

and the method comprising, in the second mode of operation, the following additional steps:

q) prior to step f), introduction of the supply current into at least an eleventh passage in heat exchange relationship with the eighth passage,

r) cooling, possibly with condensation of at least a part, of said feed stream against the cold stream so as to obtain, at the output of the eleventh pass, a cooled feed stream, and introduction of said cooled feed stream into the tenth pass.

- the cold current leaving the fourth passage is introduced into at least an eighth passage, the method comprising, in the first mode of operation, the following additional steps:

s) introducing a second working fluid having a second high pressure into at least a fifth passage and vaporizing at least a part of said second working fluid against at least a second hot stream circulating in at least a sixth passage (6 ) in heat exchange relationship with at least the fifth passage,

t) output of the second working fluid at least partially vaporized in step s) of the fifth passage and expansion to a second low pressure, with Pb2 lower than Ph2, in a second expansion member cooperating with a second electric generator of how to produce electrical energy,

u) introduction of the second working fluid expanded in step t) into the second passage and condensation of at least a part of said second working fluid against at least the cold stream circulating in the eighth passage,

v) outlet of the second working fluid at least partially condensed in step w) of the second passage, raising the pressure of said second working fluid to the second high pressure and reintroducing said second working fluid at least partially condensed at step w) in the fifth pass,

the first hot stream circulating in step a) being formed at least in part by the second working fluid circulating in step u) in the passage,

and the method comprising, in the second mode of operation, the following additional steps:

w) prior to step f), introduction of the supply current into at least an eleventh passage in heat exchange relationship with at least the eighth passage,

x) cooling, possibly with condensation of at least a part, of said feed stream against the cold stream so as to obtain, at the output of the eleventh pass, a cooled feed stream, and introduction of said cooled feed stream into the tenth pass.

- the first working fluid and the second working fluid are organic fluids, the first working fluid and the second working fluid respectively comprising a first mixture of hydrocarbons and a second mixture of hydrocarbons, preferably the first and the second mixture of hydrocarbons each contain at least two hydrocarbons selected from methane, ethane, propane, butane, ethylene, propylene, butene, isobutane, optionally with the addition of at least one additional component selected among nitrogen, argon, helium, carbon dioxide, neon.

- the first working fluid and the second working fluid are organic fluids, the first working fluid and the second working fluid being pure substances consisting respectively of a first hydrocarbon and a second hydrocarbon.

- the feed stream is formed mainly, preferably entirely or almost entirely, of an air gas, preferably nitrogen, oxygen or argon.

- the cold stream is a stream of liquefied hydrocarbons such as liquefied natural gas or a stream of cryogenic liquid chosen from: a stream of liquefied nitrogen, a stream of liquefied oxygen, a stream of liquefied hydrogen.

- the first hot stream, the second hot stream and/or the third stream are formed from seawater, preferably seawater introduced at a temperature strictly above 0°C, preferably between 10 and 30 °C, the seawater possibly having undergone a prior heating stage.

- the method is operated selectively according to the first mode of operation or the second mode of operation.

- the selection of the first or the second mode of operation is carried out according to the value of at least one parameter representative of a demand for electricity, preferably, the method comprises at least one step of determining at least one value instantaneous electric power and/or electric energy consumed on an electricity supply network and/or by an industrial installation, the method being operated in the first mode of operation when said value is greater than or equal to a predetermined threshold or in the second operating mode when said value is lower than the predetermined threshold.

- in the second mode of operation, the flow rates of at least one of: the first hot stream, the second hot stream, the first working fluid and/or the second work.

- the method is operated simultaneously according to the first mode of operation and the second mode of operation so as to simultaneously produce electrical energy and an at least partially liquefied supply current, said method including at least one step of adjusting the operation by means of a variation of the flow rate of at least the first working fluid and/or the second working fluid (W2).

- the feed stream from step f) has a pressure of at least 5 bar, preferably at least 20 bar, more preferably at least 30 bar.

- the cold stream leaving the eighth passage is introduced into at least a ninth passage to be heated there against the second hot stream, the second working fluid and/or a third hot stream and the feed stream is introduced, prior to its introduction in the eleventh passage, in at least a thirteenth passage in heat exchange relationship with at least the ninth passage.

- the cold current and the supply current circulate against the current.

- the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth and/or thirteenth passages are part of at least one heat exchanger of the brazed plate type, said exchanger comprising a stack of several parallel plates spaced apart from each other so as to delimit between them several series of several passages within said exchanger.

- the feed stream is introduced in the gaseous state into the tenth passage, the eleventh passage and/or the thirteenth passage and leaves the tenth passage fully condensed, preferably at a temperature between -200 and -130°C, preferably between -170°C and -130°C, more preferably between -160°C and -140°C.

According to another aspect, the invention relates to an installation for recovering refrigeration energy from a cold stream, in a system comprising a storage tank, at least one electric generator and at least one heat exchange device comprising several passages configured for the flow of fluids to be placed in heat exchange relationship, said installation comprising:

- at least a first passage configured for the flow of a first working fluid,

- at least one second passage configured for the flow of a first hot stream, said second passage being in heat exchange relation with said first passage so that, in a first mode of operation, the first working fluid introduced into the first pass is vaporized in less part against the first hot stream,

- a first expansion device arranged downstream of said first passage and configured to reduce the pressure of the first working fluid leaving the first passage from a first high pressure to a first low pressure,

- an electric generator coupled to the first expansion device,

- at least one third passage arranged downstream of the first expansion member and configured for the flow of the first working fluid expanded by the first expansion member,

- at least a fourth passage configured for the flow of a cold current, said fourth passage being in heat exchange relation with said third passage so that, in the first operating mode, the first working fluid introduced into the third passage is condensed at least in part against the cold current which vaporizes at least in part,

- a first pressure-raising device arranged downstream of said third passage and configured to increase the pressure of the first working fluid leaving the third passage from the first low pressure to the first high pressure, said installation further comprising:

- at least a tenth passage configured for the flow of a supply current, said passage being in heat exchange relation with the passage, so that, in a second mode of operation, the supply current introduced into the tenth pass is condensed at least in part against the cold stream, and

- a storage tank fluidly connected to the tenth passage.

Furthermore, the invention relates to a system formed by an installation according to the invention, a production unit, such as an air separation unit by cryogenic distillation, capable of producing a feed stream at at least an output of said production unit, said at least one output being fluidly connected to said installation.

The expression “natural gas” relates 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 including limit, sulfur, carbon dioxide, water, mercury and certain heavy and aromatic hydrocarbons.

The present invention will now be better understood thanks to the following description, given solely by way of non-limiting example and made with reference to the appended figures, among which:

schematizes a method for recovering cooling energy according to one embodiment of the invention.

schematizes a method for recovering cooling energy according to another embodiment of the invention.

schematizes a method for recovering cooling energy according to another embodiment of the invention.

schematizes a method for recovering cooling energy according to another embodiment of the invention.

schematizes a method for recovering cooling energy according to another embodiment of the invention.

represents exchange diagrams obtained in methods according to embodiments of the invention.

The method according to the invention is implemented in particular by means of at least one heat exchange device, which can be any device comprising passages adapted to the flow of several fluids and allowing direct or indirect heat exchange between said fluids.

In the embodiments detailed below, the various fluids of the process circulate in one or more heat exchangers of the brazed plate and fin type, advantageously made of aluminum. These exchangers make it possible to work under low temperature differences and with reduced pressure drops, which improves the energy performance of the liquefaction process described above. Plate heat exchangers also offer the advantage of obtaining very compact devices offering a large exchange surface in a limited volume.

These exchangers comprise a stack of plates which extend along two dimensions, length and width, thus constituting a stack of several series of passages, some being intended for the circulation of a circulating fluid, in this case the working fluid of the cycle, others being intended for the circulation of a refrigerant fluid, in this case cryogenic liquid such as liquefied natural gas to be vaporized.

Heat exchange structures, such as heat exchange waves or fins, are generally arranged in the passages of the exchanger. These structures include fins which extend between the plates of the exchanger and make it possible to increase the heat exchange surface of the exchanger.

It should be noted that other types of exchangers can however be used, such as plate exchangers, shell and tube exchangers, or assemblies of the "core in kettle" type. that is to say plate or plate and fin exchangers embedded in a calender in which the refrigerant vaporizes. In the case where the exchangers are tube exchangers, the passages can be formed by the spaces in, around and between the tubes.

schematizes a process for recovering cold from a cold stream F of hydrocarbons. In particular, the cold stream F can be natural gas.

In this embodiment, a single Rankine cycle is implemented by means of a first exchanger E1 and a second exchanger E2.

Advantageously, the exchangers E1, E2 each comprise a stack of several plates (not visible) arranged parallel to each other with spacing along a so-called stacking direction, which is orthogonal to the plates. A plurality of passages for the process fluids are thus obtained which are placed in a heat exchange relationship via the plates. A passage is formed between two adjacent plates. Preferably, the gap between two successive plates is small compared to the length and the width of each successive plate, so that each passage of the exchanger has a parallelepiped and flat shape. The passages intended for the circulation of the same fluid form a series of passages. Each exchanger comprises several series of passages configured to channel the various fluids of the process parallel to an overall direction of flow z, the passages of a series being arranged, in whole or in part, alternately and/or adjacent to all or part of the passages of another series.

The sealing of the passages along the edges of the plates is generally ensured by lateral and longitudinal sealing bars fixed to the plates. The lateral sealing bars do not completely block the passages but leave inlet and outlet openings used for the introduction and evacuation of fluids. These inlet and outlet openings are joined by collectors, generally of semi-tubular shape, ensuring a uniform distribution and recovery of the fluid on all the passages of the same series.

In the following, we will speak of one or at least one passage, it being understood that the passage can be part of a series of several passages intended for the flow of the same fluid.

It being understood that these structural characteristics are applicable in whole or in part to the other exchangers described in the present application.

The first exchanger E1 acts as a vaporizer in the Rankine cycle. As seen on , a first working fluid W1 circulates in at least a first passage 1 from an inlet 1a to an outlet 1b. A first hot stream is introduced into the first exchanger from an inlet 21 to an outlet 22. The first working fluid W1 is vaporized at least partially by heat exchange with the first hot stream C1.

After leaving the first exchanger E1, the first vaporized working fluid W1 is expanded in a first expansion device, preferably a turbine, coupled to an electric generator G converting the kinetic energy produced by the expanded fluid into electrical energy.

After its expansion, the first working fluid W1 enters the second heat exchanger E2 from an inlet 31 to an outlet 32 of at least a third passage 3.

It should be noted that the first working fluid W1 resulting from the expansion in the first member can optionally be in the two-phase state and be introduced with or without separation of the liquid and gaseous phases upstream of the second exchanger E2.

The first working fluid W1 is placed in heat exchange relationship with the cold stream F flowing in at least a fourth passage 4 of the second exchanger E2 from an inlet 41 to an outlet 42. The first working fluid W1 is condensed by heating the first cold stream F1 and exits in the liquid state through outlet 32 to then be returned to the first exchanger E1, after pressurization by a pressure-raising device such as a pump, which closes the Rankine cycle .

Preferably, the cold stream F is introduced through the inlet 41 of the second exchanger E2 in the liquid state, preferably completely liquid, and leaves at least partially, preferably completely vaporized, through the outlet 42.

By “hot current” or “cold current”, we mean a current formed by one or more fluids providing a source of heat or cold by heat exchange with another fluid.

According to the invention, the Rankine cycle described above is implemented in a first mode of operation in which the method according to the invention ensures recovery of the refrigerating content of the cold stream F in order to produce electricity.

According to the invention, the method also has a second mode of operation, in which the refrigerating content of the cold stream F is recovered not to produce electricity but to liquefy a supply stream.

In this second mode of operation, a supply current 200 is introduced into at least a tenth passage 10 of the second exchanger E2 which is in heat exchange relationship with at least the fourth passage 4 in which the cold current F flows. at least part of the feed stream 200 condenses against the cold stream F, giving rise, at the outlet of passage 10, to a feed stream 201 that is at least partially liquefied, preferably completely liquefied. Preferably, the cold stream F circulates in counter-current with the supply stream 200 in the first mode of operation and/or in counter-current with the working fluid W1 condensed in the second exchanger E2 in the second mode of operation. The cold stream F can be vaporized in whole or in part in the passage 4 against the working fluid W1, that is to say by heat exchange with the working fluid W1.

The feed stream 201 thus obtained is sent to a storage tank 203. The at least partially liquefied stream 201 can thus be stored at a storage pressure preferably between 1 and 10 bar, preferably between 1 and 5 bar and at a cryogenic temperature of the order of the equilibrium temperature of the fluid at the storage pressure.

Note that the feed stream 201 can optionally be expanded in a third expansion member 202 so as to form a gaseous phase and a liquid phase of said feed stream 201. Such an expansion of the at least partially liquefied feed stream 201 is operated when the storage in the tank 203 is carried out at atmospheric pressure or at least at a relatively low pressure compared to that of the liquefaction network which can be up to 20 bar, or even up to 40 bar. Indeed, the liquefaction of the feed stream 200 takes place more efficiently in the exchanger when working at these high pressures.

The process of the invention allows effective recovery of the negative calories from the cold stream F with increased flexibility since the negative calories can be used to generate electricity or to liquefy a supply current, the choice of the mode of operation being made according to the current needs. In the case where the cold stream is a cryogenic liquid, in particular natural gas, the method makes it possible to regasify the cold stream while enhancing its refrigerating content. Switching from one operating mode to another is relatively simple and does not require modifying the industrial installation. In addition, the liquefaction of feed streams makes it possible to build up stocks of fluid in the liquid state at reduced costs in order to ensure continuity of gas supply, for example when a production plant is shut down. .

It is to highlight that illustrates a configuration in which, optionally, the feed stream 201 originating from the passages 10 circulates in an overcooler 205 prior to its expansion and its introduction into the storage tank 203. By “overcooler”, is meant any heat exchange device configured to produce at its outlet a liquid at a temperature below its equilibrium temperature at the operating pressure.

On leaving supercooler 205, feed stream 201 is expanded in third expansion member 202, forming a gaseous phase and a liquid phase (phenomenon known as “flash”) which are introduced together into reservoir 203. recovers, at the top of the storage tank 203, a gas flow 204 resulting from the flash which is introduced into the supercooler 205 so as to further cool the feed stream 201 by heat exchange in the supercooler 205 , preferably against the current. This configuration offers the advantage of recovering the negative calories of the gas stream 204 which are usually evacuated from storage and lost. After leaving the supercooler 205, the gas stream 204 can be compressed in a compression device to form a compressed gas stream 206 which can be recycled in the feed stream 200 before introduction into the tenth passage 10.

It is also possible for the at least partially liquefied feed stream 201 to be introduced directly into the reservoir 203.

Preferably, the method according to the invention operates alternately between the first and the second mode of operation. The selection between the first and the second mode is carried out according to the determination of at least one parameter representative of an electricity demand. The method can be operated in the first mode of operation when the parameter is greater than or equal to a predetermined threshold or in the second mode of operation when the parameter is less than the predetermined threshold.

Preferably, in the second mode of operation, the flow rates are stopped in the heat exchange passages of at least one of: the first hot stream C1, the second hot stream C2, the first working fluid W1 and/or the second working fluid W2.

In particular, the method may comprise at least one step of determining at least one value of instantaneous electrical power and/or electrical energy which may be predetermined or indeed measured on an electricity supply network or an industrial installation, for example from direct measurements of the physical parameters of the installation, such as the electric supply voltage, the intensity of the delivered electric current, etc. or even from a consumption history of said installation. Similarly for an electrical network, consumption can be determined instantly or from historical data, depending for example on the time of day or the time of year.

The method is operated in the first mode of operation when said value is greater than or equal to a predetermined threshold or in the second mode of operation when said value is less than the predetermined threshold. This makes it possible to erase the consumption peaks of the said installation and thus reduce the tensions on the electrical network.

It is thus possible to react more effectively to variations in energy demand and avoid a phenomenon of overproduction in relation to the actual electricity consumption of users of the electricity supply network, while continuing to valorize the cooling energy of the cold current by a other use.

Alternatively or additionally, the method may comprise a step of determining at least one other value of instantaneous electrical power and/or electrical energy produced by a separate electricity production unit. The method is operated in the first mode of operation when said value is less than or equal to another predetermined threshold or in the second mode of operation when said value is greater than the other predetermined threshold. It is thus possible to adapt to intermittent production of electricity, as is the case for example in photovoltaic or wind power production, in particular by choosing to use the negative calories of the cold current to liquefy the supply current when a excess energy is produced by the generating unit.

It is also possible to envisage simultaneous operation of the method according to the first and second modes. In this case, part of the negative calories of the cold current is recovered to produce electrical energy and another part of the negative calories of the cold current is used to liquefy the supply current. The first mode and the second mode are adapted so as to produce more liquefied feed current and less electrical energy when the demand for electricity decreases and vice versa when the demand for electricity increases.

A mode of adaptation can be to vary the flow rate of circulation of at least the first working fluid W1 and/or the second working fluid W2 in their respective passages By reducing the flow rate of the working fluid(s), less refrigeration is needed from the cold stream to condense the working fluids, which increases the refrigeration available to liquefy the feedstream 200. More liquid feedstream and less electricity are thus produced. An increase in the flow rate of the working fluid(s) produces the opposite phenomenon and therefore favors the production of electricity when demand requires it, while continuing to produce a reduced quantity of liquid current. Preferably, the method according to the invention operates so as to produce either electrical energy only, or both electrical energy in a substantially reduced step and liquid supply current. To operate the second mode of operation, it is thus possible to implement drops in fluid flow rates for the first fluid W1 and/or the second fluid W2 of between 2 and 50%, preferably at least 5% and/or at most 20%, more preferably between 5 and 15%. Preferably, in combined two-cycle operation, the flow reduction applied to the first fluid is greater than the reduction applied to the second fluid.

Advantageously, the method according to the invention can implement in the first mode of operation, a combination of several Rankine cycles in order to increase the energy yield of the method.

illustrates the combination of a first and a second Rankine cycle according to a first variant embodiment. It being understood that a method according to the invention may comprise a number greater than two Rankine cycles combined according to the same principles as those set out below in the case of two Rankine cycles, whether in the first variant or the second variant described below.

The first Rankine cycle is implemented by means of a first exchanger E1 and a second exchanger E2, in accordance with the description of the simple cycle given above.

The second Rankine cycle uses a second working fluid W2, preferably of a composition different from that of the first working fluid W1. The second working fluid W2 is introduced into a third exchanger E3 through an inlet 51 to an outlet 52 and circulates in at least a fifth passage 5 in which it is at least partially vaporized by heat exchange with a second hot stream C2 circulating in at least a sixth passage 6 between an inlet 61 and an outlet 62.

The second working fluid W2 is expanded according to the same principles as the first cycle and introduced, optionally in the diphasic state and optionally with separation of the phases before introduction, into a fourth heat exchanger E4 from an inlet 71 up to at an outlet 72 of at least a seventh passage 7 in which it is condensed by heating a second cold stream F2 circulating in at least an eighth passage 8. The fourth exchanger E4 forms the condenser of the second cycle. The second working fluid W2 from outlet 72 in the liquid state is pumped and reintroduced through inlet 51 of passages 5, which closes the second cycle.

Note that the cold stream F can be vaporized in whole or in part and/or reheated in the first Rankine cycle (passage 4) by heat exchange with the first fluid W1. The cold stream F can be vaporized in whole or in part in the second Rankine cycle (passage 8) by heat exchange with the second fluid W2.

According to one possibility, the cold stream F is only reheated in the at least one fourth pass 4 and it is vaporized only in the eighth pass 8. The first cycle has as its cold source only the sensible heat of de-subcooling of the cold stream.

According to another possibility, the cold stream is partially vaporized in the fourth passage 4. The first cycle has as its cold source the sensible heat of de-subcooling of the cold stream and part of the latent heat of vaporization of the cold stream.

According to another possibility, the cold stream F is vaporized only in the at least one fourth passage 4, i. e. emerges totally vaporized from the fourth pass 4. The first cycle has as its cold source the sensible heat of de-subcooling of the cold stream and all the latent heat of vaporization of the cold stream, possibly with a sensible heat of reheating of the vaporized cold stream.

The cold stream F can also be partially vaporized in the fourth passage 4 and be partially vaporized in the eighth passage 8.

It should be noted that it is possible, in the context of the invention, for the first working fluid W1 leaving condensed from the third passage 3 to be reintroduced into the second exchanger E2 to circulate there before being reintroduced into the first exchanger E1. This configuration is preferred when the first working fluid W1 is not a pure substance but a mixture of several constituents, because it offers the advantage of further heating the temperature at which the first working fluid W1 leaves the second exchanger E2. According to the same principle, the second working fluid W2 leaving the passages 7 condensed can also be reintroduced into the fourth exchanger E4, before being reintroduced into the third exchanger E3. represents this type of configuration.

This principle of additional passes in the condensation exchanger(s) is applicable to the other embodiments described in the present application (see for example , passages 14, 15).

Alternatively, it is possible to envisage introducing the first and second working fluids W1, W2 directly into the first and third exchangers respectively, without an additional pass through the second and fourth exchangers.

In the first mode of operation, the cold stream F feeds in series the first Rankine cycle and the second Rankine cycle in which it is vaporized and gradually heated against the second and first working fluids W2, W1. As such, F can therefore possibly be in the diphasic state. The first Rankine cycle and the second Rankine cycle are used to generate electricity.

In the second mode of operation, the cold stream F supplies the second exchanger E2 and the fourth exchanger E4 in series, in which it is vaporized and gradually heated against the supply stream 200. The supply stream 200 supplies the fourth exchanger E4 and the second exchanger E2 in which it is gradually cooled and condensed.

Such an arrangement makes it possible to regasify the cold stream by ensuring a more effective recovery of the cold over the whole of the temperature gradient between the inlet temperature of the cold stream F in the fourth passage 4 and the temperature of the cold stream F at the outlet of the eighth passage 8. In fact, the recovery of the negative calories of the cold stream is carried out separately on portions of passages 4, 8 where it has different temperature levels. It is then possible to best adapt the characteristics of each of the first and second working fluids, so that they have boiling temperatures adapted to these temperature levels, to the high and low pressure levels that will be chosen for each of the two cycles. There is thus a very large degree of freedom to increase the energy efficiency of the process, in particular by adjusting the temperatures, the pressures and/or the compositions of the working fluids according to the characteristics of the cold stream F to be heated, in particular its pressure. , its temperature, its composition...

Advantageously, the cold current F exiting at 82 from the eighth passage 8 is introduced into at least a ninth passage 9 of a fifth exchanger E5, in order to continue its heating there against a third hot current C3 in the first mode of operation or against the supply current 200 in the second mode of operation. This is advantageous in cases where the temperature obtained at the outlet 82 of the exchanger E4 is too low and incompatible with the material forming the pipes of the natural gas distribution network. In this case, the supply current is introduced into at least a thirteenth passage 13 upstream of its introduction into the passages 11, which makes it possible, in the second mode of operation, to cool the supply current 200 even more effectively. .

Preferably, the feed stream 200 is introduced into the process, that is to say into the exchanger first passed through by the stream 200, which can be E2, E5, E4, E3 depending on the configuration selected, at a temperature between 0 and 30°C. Preferably, feed stream 200 is introduced into the process in an all-gaseous state.

Advantageously, the feed stream 200 is formed mainly, preferably entirely or almost entirely, of an air gas, preferably nitrogen, oxygen or argon.

By air gas, we mean a gas entering into the composition of the air such as argon, carbon dioxide, helium, nitrogen and oxygen.

In particular, the installation implementing the method according to the invention can be integrated into a system comprising at least one production unit of said feed stream, for example an air separation unit (or ASU for "Air Separation Unit”), preferably by cryogenic distillation, fluidly connected to said installation, in particular to passages 10, 11 and/or 13 according to the embodiment considered, preferably via at least one pipe. In the second mode of operation, the installation can thus be used to liquefy, before storage, the feed stream from the production unit. The installation implementing the method according to the invention can also be fluidically connected to an air gas distribution network.

Depending on the configuration adopted, the cold current F recovered at the end of the outlets 82 or 92 supplies at least one pipe of a fluid distribution network (at 100), in particular a hydrocarbon distribution network such as gas natural.

Preferably, the inlets and outlets of the condensation passages 3, 7 are arranged so that the first and second working fluids W1, W2 are condensed in countercurrent with the cold current F. Preferably, the hot currents C1, C2 cycles flow countercurrently to the working fluids vaporized in each cycle. Preferably, the third current C3 circulates counter-current to the cold current F possibly circulating in the passages 9. It should be noted that the same hot current can form C1, C2 or even C3 by circulating in series in the third exchanger, the first exchanger and possibly the fifth exchanger.

These fluid flow directions make it possible to maximize the outlet temperature of the working fluids W1 and W2, and therefore to maximize the power delivered by the turbines during expansion.

and following illustrate configurations in which the Rankine cycles are operated in exchangers forming entities that are physically separate from each other, ie each forming at least one separate stack of plates and passages.

In the context of the invention, it is also possible to arrange some of the fluid passages within the same stack. This can be envisaged in particular with exchangers of the brazed plate type and makes it possible to reduce the complexity and manufacturing costs of the installation implementing several combined Rankine cycles.

Thus, the first exchanger E1, the third exchanger E3, possibly with the fifth exchanger E5, can form the same common exchanger and/or the second exchanger E2 and the fourth exchanger E4 can form another common exchanger.

In the case of pooled exchangers, when passages of one series and passages of another series in which a fluid circulates in series are considered, each passage of said series forms an extension of a corresponding passage of the other series, and therefore one and the same passage of the exchanger E formed between two same plates. Thus, if we consider E1 and E3 forming the same exchanger, the passages 2 of the second series and the passages 6 of the sixth series are formed between the same plates of the exchanger E and are arranged in continuity with each other. A passage 2 and a passage 6 thus form a single passage of the exchanger E delimited between two same plates of the exchanger E and in which the hot current C2 circulates from the inlet 61 to the outlet 22.

When considering passages from one series and passages from another series in which different fluids circulate, these passages are superimposed within the same stack, adjacent or not.

and [Fig.5] illustrate the combination of a first cycle and a second Rankine cycle according to a second variant embodiment.

In the first mode of operation of this variant, a second working fluid W2 having a second high pressure Ph2 is introduced into at least a fifth passage 5 of a third exchanger E3 and vaporized at least in part against at least a second hot stream C2 circulating in at least a sixth passage 6. The second working fluid W2 leaving the passages (5) is expanded to a second low pressure (Pb2) in a second expansion member cooperating with a second electric generator so as to produce electrical energy.

The second working fluid W2 thus expanded is introduced, optionally in the diphasic state, into the second passage 2 and thus forms, at least in part, the hot current in the first cycle to vaporize the first working fluid W1 circulating in the first pass 1.

The second working fluid W2 is condensed against at least the cold stream F flowing in the eighth passage 8. After leaving the passages 2, the pressure of the second working fluid W2 is raised to the second high pressure Ph2 and the second working fluid W2 in passage 5.

In the second mode of operation, the supply current 200 is introduced, prior to its introduction into the tenth passage, into at least an eleventh passage 11 in heat exchange relationship with at least the eighth passage 8. supply 200 is cooled, possibly with at least partial condensation, against the cold current F. There is thus obtained, at the output of the eleventh passage 11, a cooled supply current 200 which is then introduced into the tenth passage 10.

The supply current 200 can optionally be introduced into at least a thirteenth passage 13 upstream of its introduction into the passages 11, which makes it possible, in the second mode of operation, to cool the supply current 200 even more effectively.

Note that the cold stream F can be vaporized in whole or in part and/or reheated in the second Rankine cycle (passage 4) by heat exchange with the second fluid W2. The cold stream F can be vaporized in whole or in part and/or reheated (passage 8) in the first Rankine cycle by heat exchange with the first fluid W1.

shows a combination of cycles in which the condensed working fluids are reintroduced into the condenser part before being reintroduced into the vaporizer part and [Fig. 5] shows a combination in which the condensed working fluids are reintroduced directly into the vaporizer part.

It is also possible to implement such a combination of cycles but without additional pass of the condensed working fluid(s) in the condensation exchangers, as illustrated in .

According to a particular embodiment, applicable to the first or to the second variant, it is possible to use the same generator coupled both to the first expansion device of the first cycle and to the second expansion device of the second cycle (not illustrated). The first generator and the second generator are therefore coincident. This saves a generator and simplifies installation. This arrangement is possible because the two electricity generation cycles have a generally simultaneous mode of operation.

In the context of the present invention, the cold stream F can be a stream of liquefied hydrocarbons such as liquefied natural gas or a stream of cryogenic liquid such as a stream of liquefied nitrogen, a stream of liquefied oxygen, a stream of liquefied hydrogen.

Preferably, the temperature at which the cold stream F is introduced into the fourth passage 4 is less than -100°C.

Advantageously, the cold stream F is formed from a stream of hydrocarbons, in particular natural gas, preferably comprising, in molar fraction, at least 60% of methane (CH ₄ ), preferably at least 80%. The natural gas may optionally include ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), butane (nC ₄ H ₁₀ ) or isobutane (iC ₄ H ₁₀ ), nitrogen , preferably in contents between 0 and 10% (mol %). Thanks to the method of the invention, the necessary regasification is carried out before injecting the natural gas into the distribution network, while recovering the cold temperatures of the liquefied natural gas.

Cold currents of another nature can advantageously supply the method according to the invention to be revaporized before use. In particular, a cryogenic liquid, for example liquid oxygen, liquid nitrogen, or even liquid hydrogen can be used. The vaporization of such liquids can ensure continuity of gas supply when a production plant is shut down and save some of the energy spent on building up liquid stocks. Since the vaporization temperatures of these constituents are much lower than those of natural gas, it may be advantageous to implement a process combining three Rankine cycles, or even more, in the continuity of one of the previous descriptions.

The cold stream to be revaporized can be a cryogenic liquid at very low temperature, i.e. a temperature which can be lower than -170°C, or even lower than -200°C. The implementation of three or more cycles will then be advantageous.

Preferably, and when the fluid to be vaporized is LNG, the first working fluid W1 and the second working fluid W2 are organic fluids, that is to say fluids comprising one or more organic components. It is also possible that the Rankine cycles of the process according to the invention are not organic cycles.

With vaporizing cryogenic liquids having lower boiling constituents than LNG, the working fluid of the cycle operating at the lowest temperature may include one or more components such as hydrogen, nitrogen, argon, helium, neon, in addition or substitution of all or part of the organic compounds. It will thus be possible to envisage working with working fluids free of organic components.

According to a first possibility, it is possible to use pure substances of a different nature to form the first fluid W1 and/or the second fluid W2. In particular, it is possible to use ethylene as the first working fluid W1 and ethane as the second working fluid W2. This choice is explained by the physical properties of these constituents, which have saturating vapor pressures for the temperature range swept by the vaporization of LNG, compatible with good mechanical strength of the brazed aluminum exchangers and the components of the expansion turbines. Thus, the use of such components in ORC cycles makes it possible to design compact and efficient systems.

In the context of the invention, working fluids of different compositions are preferably used in the different Rankine cycles, but it remains possible to use working fluids of the same composition, by then adjusting the operating pressures of these fluids. This is possible for relatively small temperature differences between the cold and hot currents of the cycles, for example when the second cold current is a liquefied gas at very high pressure and the first hot current is sea water at a sufficiently low temperature. .

According to another possibility, it is possible to use mixed working fluids comprising mixtures of hydrocarbons, preferably mixtures of hydrocarbons each containing at least two hydrocarbons chosen from methane, ethylene (C ₂ H ₄ ), propane , ethane, butane or isobutane, butene. The first working fluid W1 and the second working fluid W2 may optionally comprise at least one additional component chosen from hydrogen, nitrogen, argon, helium, neon, in addition to or substitution for the organic components, and this in particular if the cryogenic liquid to be vaporized has a boiling point lower than that of methane.

The use of mixed working fluids makes it possible to reduce the energy losses linked to the irreversibility of heat exchanges between cold and hot fluids by reducing the temperature differences between the cold currents and the working fluids at each point according to the length of the the exchanger. The compositions, pressures before and after expansion and/or temperatures of each fluid can be adapted to ensure the best possible energy recovery.

It should be noted that in the case where the working fluids are mixed, i.e. are mixtures, these come out of the liquid exchanger(s) at very low temperature and that it is then advantageous to operate a reintroduction of the condensed fluids into the heat exchangers concerned in order to heat them and maximize their exit temperature at the hot end and therefore the production of electricity during their expansion in the turbine.

In particular, the proportions in molar fractions (%) of the components of the first mixture of hydrocarbons can be (% molar):

Methane: 20 to 60%, preferably 30 to 50%

Propane: 0 to 20%, preferably 0 to 10%

Ethylene: 20 to 70%, preferably 30 to 60%

The proportions in mole fractions (%) of the components of the second hydrocarbon mixture can be:

Methane: 0 to 20%, preferably 0 to 10%

Propane: 20 to 60%, preferably 30 to 50%

Ethylene: 20 to 60%, preferably 30 to 50%

Isobutane: 0 to 20%, preferably 0 to 10%

Preferably, the first hot stream C1, the second hot stream C2 and/or the third hot stream C3 are formed from sea water, preferably at an inlet temperature in the exchanger above 0°C, from preferably between 10 and 30°C.

Preferably, the cold stream F is a stream of hydrocarbons introduced totally liquefied at the inlet 41 at a temperature between -140 and -170°C.

In the case where the cold current F is formed by a liquid of another nature, such as oxygen, nitrogen, liquid hydrogen, the temperature of the fluid at the inlet 41 is preferably 1 order from its equilibrium temperature to the storage pressure.

Preferably, the cold stream F has a temperature between -85 and -105°C at the outlet 42, a temperature between -10 and -20°C at the outlet 82 and/or a temperature between 5 and 50°C. C at the outlet 92, to be introduced at this temperature into a distribution network 100. Preferably, the cold stream F leaves completely vaporized by the outlets 42, 82 or 92 as the case may be.

Preferably, the cold stream has a pressure of between 10 and 100 bar throughout the passages in which it flows.

Preferably, in the context of the invention, the supply stream 200 has a temperature of between -170 and -140°C at the outlet of the fourth passage 4, a temperature of between -110 and -80°C at the outlet of the eighth passage 8 and/or a temperature between -20 and -10°C at the outlet of the ninth passage 9.

Preferably, the first working fluid W1 has, after its condensation in the third passage 3, a first temperature T1. The second working fluid W2 has, after its condensation in the seventh passage 7, a second temperature T2, with T2 greater than T1.

Preferably, T2 is between -60 and -30°C and T1 is between -110 and -70°C. Alternatively, T2 is between -110 and -80°C and T1 is between -160 and -120°C.

Preferably, the first working fluid W1 leaves vaporized from at least a first passage 1 at a temperature between 0 and -30°C and/or the second working fluid W2 leaves vaporized from the fifth passage 5 at a temperature between 5 and 25°C.

Preferably, the first working fluid W1 and the second working fluid W2 leave the third passage 3 and the seventh passage 7 respectively at first and second so-called low pressures Pb1, Pb2, and enter the first passage 1 and the fifth passage 5 respectively to first and second so-called high pressures Ph1, Ph2.

Preferably, the first and/or second high pressures Ph1, Ph2 are between 10 and 40 bar and/or the first and/or second low pressures Pb1, Pb2 are between 1 and 5 bar. Preferably again, the first high pressure Ph1 is greater than the first low pressure Pb1 by a multiplying factor of between 2.5 and 15 and/or the second high pressure Ph2 is greater than the second low pressure Pb2 by a multiplying factor between 2.5 and 15. These values and pressure ratios make it possible to adapt the process to the enthalpy curves of the fluids and to adjust the equilibrium temperatures as well as possible. The higher the pressure, the greater the amount of energy recovered. A multiplier factor of at least 2.5 makes it possible to recover a sufficiently interesting quantity of energy. In practice, the pressures are limited by the capacity of the expansion devices.

Of course, all or part of the characteristics mentioned above for the first working fluid and the second working fluid are applicable in the case where a single working fluid is implemented, for example as on .

In order to demonstrate the effectiveness of the invention, simulations were carried out to calculate the energy yields obtained with a simple Rankine cycle (simulation No. 1) and combinations of Rankine cycles according to embodiments of the invention. (simulations n°2 n°3 and n°4).

Cold streams were natural gas comprising 90.5% methane, 7.3% ethane, 1.5% propane, 0.2% butane, 0.3% isobutane, 0.2% d nitrogen (% molar).

Simulation n°1:

The configuration of exchangers used was according to . The only working fluid was propane. The pressure of the working fluid W1 was 7.5 bar at the inlet of the vaporization exchanger and 1.5 bar at the outlet 32 of the condensation exchanger. The hot stream was seawater at a pressure of 5 bar and a temperature of 23°C at the inlet of the vaporization exchanger.

Simulation n°2:

The configuration of exchangers used was according to . The working fluids were pure bodies. The first W1 working fluid was ethylene. The second working fluid was ethane. The pressure of the first working fluid W1 was 32 bar at inlet 1a and 2 bar at outlet 32. The pressure of the second working fluid W2 was 27 bar at inlet 51 and 5.8 bar at outlet 72. The natural gas pressure was 90 bar at inlet 41 and 89 bar at outlet 92. The hot streams C1, C2, C3 were sea water at a pressure of 5 bar at the inlet and at the outlet of passages 2, 6, 12. [Table 1] indicates the fluid temperatures calculated at the inlet or outlet of various passages.

Simulation n°3:

The configuration of exchangers used was according to , The first working fluid W1 was a mixture of hydrocarbons comprising 53% ethylene, 41% methane, 6% propane (molar%). The second working fluid W2 was a mixture of hydrocarbons comprising 46% ethylene, 38% propane, 8% methane, 8% isobutane (mole%). The pressure of the first working fluid W1 was 31.0 bar at inlet 23 and 1.8 bar at outlet 32. The pressure of the second working fluid W2 was 12.4 bar at inlet 43 and 4.6 bar at outlet 72. The natural gas pressure was 90 bar at inlet 41 and 89.5 bar at outlet 82. Hot streams C1, C2, C3 were sea water at a pressure of 5 bar at the inlet and outlet of passages 2, 6 and 12. [Table 2] indicates the fluid temperatures calculated at the inlet or outlet of various passages.

Simulation #4:

The configuration of exchangers used was according to . The working fluids were pure bodies. The first W1 working fluid was ethylene. The second working fluid was ethane. The pressure of the first working fluid W1 was 8.1 bar at inlet 1a and 2.1 bar at outlet 32. The pressure of the second working fluid W2 was 27 bar at inlet 51 and 5 .8 bar at outlet 22. The natural gas pressure was 90 bar at inlet 41 and 89 bar at outlet 92. The hot stream C2 was sea water at a pressure of 5 bar at the inlet and at the outlet of the passages 6. [Table 3] indicates the fluid temperatures calculated at the inlet or outlet of the various passages.

Simulation n°5:

The configuration of exchangers used was according to . The first working fluid W1 was a mixture of hydrocarbons comprising 55.4% ethylene, 41% methane, 3.6% propane (mole%). The second working fluid was a hydrocarbon mixture comprising 46% ethylene, 38% propane, 8% methane, 8% isobutane. The pressure of the first working fluid W1 was 16.7 bar at the inlet 141 and 1.7 bar at the outlet 32. The pressure of the second working fluid W2 was 12 bar at the inlet 151 and 4 .2 bar at outlet 22. The natural gas pressure was 90 bar at inlet 41 and 89.5 bar at outlet 82. The hot stream C1 was sea water at a pressure of 5 bar at the inlet and outlet of the passages 2. [Table 3] indicates the fluid temperatures calculated at the inlet or outlet of the various passages.

With simulation n°1, the energy yield obtained in the first operating mode of the process was 0.016 kWh/Nm ³ .

With simulation n°2, the energy yield obtained in the first operating mode of the first cycle was 0.0114 kWh/Nm ³ and the energy yield of the second Rankine cycle was 0.0049 kWh/Nm ³ , i.e. a total yield of the process of 0.01634 kWh/Nm ³ , representing a gain of the order of 2% compared to simulation n°1.

With simulation n°3, the energy efficiency of the first Rankine cycle was 0.016 kWh/Nm ³ and the energy efficiency of the second Rankine cycle was 0.011 kWh/Nm ³ , giving a total efficiency of 0.027 kWh/Nm ³ , representing a gain of the order of 68% compared to simulation n°1.

With simulation n°4, the energy yield of the first Rankine cycle was 0.0045 kWh/Nm ³ and the energy yield of the second Rankine cycle was 0.0134 kWh/Nm ³ , giving a total efficiency of 0, 0179 kWh/Nm ³ , representing a gain of the order of 12% compared to simulation n°1. With simulation n°5, the energy efficiency of the first Rankine cycle was 0.012 kWh/Nm ³ and the energy efficiency of the second Rankine cycle was 0.021 kWh/Nm ³ , giving a total efficiency of 0.033 kWh/Nm ³ , representing a gain of the order of 106% compared to simulation n°1.

In each case, the process was simulated in both operating modes. Consider as an example the process according to simulation No. 5. In the first operating mode, the flow rate of the first working fluid was 1055 Nm ³ /h and the flow rate of the second working fluid was 3617 Nm ³ /h.

In the second mode of operation, the flow rate of the first working fluid was 927 Nm ³ /h, a reduction of 12% (relative deviation) compared to the first mode of operation, and the flow rate of the second working fluid was 3400 Nm ³ /h, ie a reduction of 6% (relative difference) compared to the first mode of operation. A feed stream 200 formed of nitrogen was introduced into the exchanger E3. It had a pressure of around 35 bar and a temperature of around 20° C. at the inlet of the second exchanger E2.

A liquefied feed stream 201 was obtained at the outlet of the second exchanger, said stream 201 having a temperature of the order of -150°C and a pressure of the order of 34.5 bar.

With a flow rate of around 3000 Nm ³ /h of LNG, it was possible to store around 175 Nm ³ /h of nitrogen in tank 203, at a storage pressure of 10 bar after prior flash expansion and at a storage temperature of -170°C. This production of liquid nitrogen was also accompanied by a generation of electricity of the order of 0.029 kWh/Nm ³ _LNG , i.e. a reduction in the electrical energy produced of 0.004 kWh/Nm ³ compared to the simulation n °5 in the first operating mode alone.

It will be noted that the use of a first working fluid and a second mixed working fluid makes it possible to significantly increase the performance of the process, thanks to the improvement of the exchange diagrams between the liquefied natural gas and the fluids of work.

By way of illustration, shows a comparison of the exchange diagrams Heat exchanged - Temperature (ΔH – T), or enthalpy curves, obtained on the one hand with a combination of cycles with pure working fluids according to simulation n°4 (in (a)) and on the other hand with a combination of cycles with mixed working fluids according to simulation n°5 (in (b)). The diagrams shown are obtained for a flow rate of 3000 Nm3/h of treated LNG (i.e. approximately a scale of 1/100 of an industrial unit). Curves A, B, C, D illustrate the change in the quantity of heat exchanged as a function of temperature, respectively for natural gas and all the refrigerants which heat up and/or vaporize in the processes, including the LNG (curves A and C) and all the circulating fluids which cool and/or condense in the processes, including the first and second working fluids (curves B and D), for each of the two simulated configurations . It can be seen in [Fig. 6] b) that the average temperature difference is significantly reduced by the use of working fluids composed of a mixture of constituents, which explains the better efficiency of this cycle.

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 those skilled in the art can also be envisaged without departing from the scope of the invention. For example, other fluid injection and extraction configurations from the exchanger(s), other fluid flow directions and directions, other types of fluids, etc. are possible.

Claims (20)

Method for recovering cooling energy from a cold stream (F), in a system comprising a storage tank (203), at least one electrical generator (G) and at least one heat exchange device comprising several passages configured for the flow of fluids to be placed in a heat exchange relationship, said method comprising, in a first mode of operation, the following steps:
a) introduction of a first working fluid (W1) having a first high pressure (Ph1) into at least a first passage (1) and vaporization of at least a part of said first working fluid (W1) against at least one first hot stream (C1) flowing in at least one second passage (2) in heat exchange relationship with said at least one first passage (1),
b) exit of the first working fluid (W1) from step a) from the first passage (1) and expansion to a first low pressure (Pb1), Pb1 being lower than Ph1, in a first cooperating expansion member with a first electrical generator so as to produce electrical energy,
c) introduction of the first working fluid (W1) expanded in step b) into at least one third passage (3) and condensation of at least part of the said first working fluid (W1) against at least the cold stream ( F) circulating in at least a fourth passage (4) in heat exchange relationship with at least the third passage (3),
d) outlet of the first working fluid (W1) at least partially condensed in step c) from the third passage (3), raising the pressure of said first working fluid (W1) to the first high pressure (Ph1) and reintroduction into the first passage (1), characterized in that, in a second operating mode, said method comprises the following steps:
e) introducing a supply current (200) into at least a tenth passage (10) in heat exchange relation with at least the fourth passage (4),
f) condensation of at least part of said feed stream (200) against the cold stream (F) so as to produce, at the output of the tenth passage (10), a feed stream (201) at least partially liquefied , And
g) filling the storage tank (203) with the feed stream (201) produced in step f). Method according to claim 1, characterized in that it further comprises the following steps:
h) introduction of the feed stream (201) from step f) into a supercooler (205),
i) output of the feed stream (201) from the supercooler (205) and expansion in a third expansion member (202) so as to form a gaseous phase (204) and a liquid phase of said feed stream (201 ),
j) introducing said gaseous (204) and liquid phases into the storage tank (203),
k) extraction, from the storage tank (203), of at least part of the gaseous phase (204) and introduction into the supercooler (205) so as to cool the feed stream (201) circulating in the supercooler (205) by heat exchange with the gaseous phase (204),
l) compressing the gas phase (204) in a compression device to form a compressed gas phase (206) and introducing said compressed gas phase (206) into the feed stream (200) before introduction into the tenth passage ( 10). Method according to one of the preceding claims, characterized in that the cold stream (F) leaving the fourth passage (4) is introduced into at least an eighth passage (8), the method comprising, in the first operating mode, the following additional steps:
m) introducing a second working fluid (W2) having a second high pressure (Ph2) into at least a fifth passage (5) and vaporizing at least a part of said second working fluid (W2) against at least a second hot stream (C2) flowing in at least a sixth passage (6) in heat exchange relationship with at least the fifth passage (5),
n) outlet of the second working fluid (W2) at least partially vaporized in step m) of the fifth passage (5) and expansion to a second low pressure (Pb2), with Pb2 lower than Ph2, in a second organ of expansion cooperating with a second electrical generator so as to produce electrical energy,
o) introduction of the second working fluid (W2) expanded in step n) into at least one seventh passage (7) in heat exchange relationship with at least the eighth passage (8), and condensation of at least one part of said second working fluid (W2) against the cold current (F) circulating in the eighth passage (8),
p) outlet of the second working fluid (W2) at least partially condensed in step g) from the seventh passage (7), raising the pressure of said second working fluid (W2) up to the second high pressure (Ph2) and reintroducing said second working fluid (W2) at least partially condensed in step g) into the fifth passage (5).
and the method comprising, in the second mode of operation, the following additional steps:
q) prior to step f), introduction of the supply current (200) into at least an eleventh passage (11) in heat exchange relationship with the eighth passage (8),
r) cooling, possibly with condensation of at least a part, of said feed stream (200) against the cold stream (F) so as to obtain, at the output of the eleventh pass (11), a feed stream (200 ) cooled, and introducing said cooled feed stream (200) into the tenth passage (10). Method according to one of Claims 1 to 2, characterized in that the cold stream (F) leaving the fourth passage (4) is introduced into at least an eighth passage (8), the method comprising, in the first operating mode , the following additional steps:
s) introducing a second working fluid (W2) having a second high pressure (Ph2) into at least a fifth passage (5) and vaporizing at least part of said second working fluid (W2) against at least one second hot stream (C2) flowing in at least a sixth passage (6) in heat exchange relationship with at least the fifth passage (5),
t) outlet of the second working fluid (W2) at least partially vaporized in step s) of the fifth passage (5) and expansion to a second low pressure (Pb2), with Pb2 lower than Ph2, in a second organ of expansion cooperating with a second electrical generator so as to produce electrical energy,
u) introduction of the second working fluid (W2) expanded in step t) into the second passage (2) and condensation of at least part of said second working fluid (W2) against at least the cold stream (F) circulating in the eighth passage (8),
v) outlet of the second working fluid (W2) at least partially condensed in step w) from the second passage (2), raising the pressure of said second working fluid (W2) to the second high pressure (Ph2) and reintroducing said second working fluid (W2) at least partially condensed in step w) into the fifth passage (5),
the first hot stream (C1) circulating in step a) being formed at least in part by the second working fluid (W2) circulating in step u) in the passage (2),
and the method comprising, in the second mode of operation, the following additional steps:
w) prior to step f), introduction of the supply current (200) into at least one eleventh passage (11) in heat exchange relationship with at least the eighth passage (8),
x) cooling, possibly with condensation of at least a part, of said supply stream (200) against the cold stream (F) so as to obtain, at the output of the eleventh pass (11), a supply stream (200 ) cooled, and introducing said cooled feed stream (200) into the tenth passage (10). Method according to one of the preceding claims, characterized in that the first working fluid (W1) and/or the second working fluid (W2) are organic fluids, the first working fluid (W1) and/or the second working fluid (W2) comprising respectively a first mixture of hydrocarbons and a second mixture of hydrocarbons, preferably the first and the second mixture of hydrocarbons each contain at least two hydrocarbons chosen from methane, ethane, propane , butane, ethylene, propylene, butene, isobutane, optionally added with at least one additional component chosen from nitrogen, argon, helium, carbon dioxide, neon. Method according to one of Claims 1 to 4, characterized in that the first working fluid (W1) and/or the second working fluid (W2) are organic fluids, the first working fluid (W1) and/or the second working fluid (W2) being pure bodies consisting respectively of a first hydrocarbon and a second hydrocarbon. Method according to one of the preceding claims, characterized in that the feed stream (200) consists mainly, preferably entirely or almost entirely, of an air gas, preferably nitrogen , oxygen or argon. Process according to one of the preceding claims, characterized in that the cold stream (F) is a stream of liquefied hydrocarbons such as liquefied natural gas or a stream of cryogenic liquid chosen from: a stream of liquefied nitrogen, a stream of liquefied oxygen, a stream of liquefied hydrogen. Method according to one of the preceding claims, characterized in that the first hot stream (C1), the second hot stream (C2) and/or the third stream (C3) are formed from sea water, preferably sea water introduced at a temperature strictly above 0° C., preferably between 10 and 30° C., the sea water possibly having undergone a prior heating stage. Method according to one of the preceding claims, characterized in that the method is operated selectively according to the first mode of operation or the second mode of operation. Method according to Claim 10, characterized in that the selection of the first or of the second mode of operation is carried out according to the value of at least one parameter representative of a demand for electricity, preferably, the method comprises at least one step of determining at least one value of instantaneous electrical power and/or electrical energy consumed on an electricity supply network and/or by an industrial installation, the method being operated in the first mode of operation when said value is greater than or equal to a predetermined threshold or in the second operating mode when said value is less than the predetermined threshold. Method according to one of the preceding claims, characterized in that, in the second operating mode, the flow rates of circulation of at least one of: the first hot stream (C1), the second hot stream (C2), the first working fluid (W1) and/or the second working fluid (W2). Method according to one of Claims 1 to 9, characterized in that the method is operated simultaneously according to the first mode of operation and the second mode of operation so as to simultaneously produce electrical energy and a supply current (201 ) at least partially liquefied, said method including at least one step of adjusting the operation by means of a variation of the circulation rate of at least the first working fluid (W1) and/or the second working fluid (W2 ). Method according to one of the preceding claims, characterized in that the feed stream (201) from step f) has a pressure of at least 5 bar, preferably at least 20 bar, more preferably at least 30 bar. Method according to one of the preceding claims, characterized in that the cold stream (F) leaving the eighth passage (8) is introduced into at least a ninth passage (9) to be heated there against the second hot stream (C2), the second working fluid (W2) and/or a third hot stream (C3) and the supply stream (200) is introduced, prior to its introduction into the eleventh passage (11), into at least a thirteenth passage (13 ) in heat exchange relationship with at least the ninth passage (9). Method according to one of the preceding claims, characterized in that the cold current (F) and the supply current (200) flow in countercurrent. Method according to one of the preceding claims, characterized in that the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth and/or thirteenth passages form part of at least one brazed plate type heat exchanger, said exchanger comprising a stack of several parallel plates spaced apart from each other so as to delimit between them several series of several passages within said exchanger. Method according to one of the preceding claims, characterized in that the feed stream (200) is introduced in gaseous state into the tenth passage (10), the eleventh passage (11) and/or the thirteenth passage (13 ) and emerges totally condensed from the tenth passage (10), preferably at a temperature between -200 and -130°C, preferably between -170°C and -130°C, more preferably between -160°C and - 140°C. Installation for recovering refrigerating energy from a cold stream (F), in a system comprising a storage tank (203), at least one electric generator and at least one heat exchange device comprising several passages configured to the flow of fluids to be placed in heat exchange relationship, said installation comprising:
- at least a first passage (1) configured for the flow of a first working fluid (W1),
- at least one second passage (2) configured for the flow of a first hot current (C1), said second passage (2) being in heat exchange relation with said first passage (1) so that, in a first mode of operation, the first working fluid (W1) introduced into the first passage (1) is at least partially vaporized against the first hot stream (C1),
- a first expansion device arranged downstream of said first passage (1) and configured to reduce the pressure of the first working fluid (W1) leaving the first passage (1) from a first high pressure (Ph1) to a first pressure bass (Pb1),
- an electric generator coupled to the first expansion device,
- at least one third passage (3) arranged downstream of the first expansion member and configured for the flow of the first working fluid (W1) expanded by the first expansion member,
- at least a fourth passage (4) configured for the flow of a cold current (F), said fourth passage (4) being in heat exchange relation with said third passage (3) so that, in the first operating mode, the first working fluid (W1) introduced into the third passage (3) is condensed at least in part against the cold stream (F) which vaporizes at least in part,
- a first pressure-raising device arranged downstream of said third passage (3) and configured to increase the pressure of the first working fluid (W1) leaving the third passage (3) from the first low pressure (Pb1) to the first high pressure (Ph1),
characterized in that it further comprises:
- at least a tenth passage (10) configured for the flow of a supply current (200), said passage (10) being in heat exchange relation with the passage (4), so that, in a second mode of operation, the supply current (200) introduced into the tenth passage (10) is condensed at least in part against the cold current (F), and
- a storage tank (203) fluidically connected to the tenth passage (10). System formed by an installation according to claim 19, a production unit, such as an air separation unit by cryogenic distillation, capable of producing a feed stream (200) at at least one output of said production unit , said at least one outlet being fluidly connected to said installation.