Method and system for cooling user fluid flow

Abstract

The invention relates to a method and a system for cooling a user fluid flow using a system comprising a chiller (1) comprising a cooling exchanger (8), the chiller configured to generate a given cold power, the invention relates to a method for cooling a user fluid stream in a cooling exchanger (8) for a given cold power for extracting heat from the user fluid stream by exchanging heat with a circulating fluid circulating in a working circuit (10), comprising the step of reducing the temperature of the user fluid stream in the cooling exchanger (8) by a given amount, the method comprises a step of detecting any potential fouling of the cooling exchanger (8) due to solidification of a user fluid component in the cooling exchanger (8), and a step of reducing a decrease in the temperature of the user fluid flow in the cooling exchanger (8) if such fouling is detected, the step of reducing the reduction in temperature is performed by increasing the flow and / or temperature of the user fluid stream allowed to circulate in the cooling exchanger (8).

Description

[0001] The present invention relates to a method and apparatus for cooling a user fluid flow.

[0002] More particularly, the invention relates to a method for cooling a user fluid stream, in particular a liquefied natural gas stream, using a device comprising a cryogenic refrigerator, i.e. a cryogenic refrigerator operating at a temperature between minus 100 degrees Celsius and minus 273 degrees Celsius, the cryogenic refrigerator being of the circulating fluid type and comprising a working circuit forming a loop and containing a circulating fluid, the refrigerator comprising a cooling exchanger and being configured to generate a determined cooling power for extracting heat from the user fluid stream by exchanging heat with a circulating fluid circulating in the working circuit, the working circuit forming a cycle comprising: a circulating fluid a compression mechanism, a circulating fluid cooling mechanism, a circulating fluid expansion mechanism and a circulating fluid heating mechanism, the device comprising at least one user fluid reservoir, a conduit for circulating the user fluid flow taken from the at least one reservoir so as to be in heat exchange relationship with a cooling exchanger of a refrigerator before being re-injected into the at least one reservoir, the method comprising the step of determining to reduce the temperature of the user fluid flow in the cooling exchanger, the method comprising the step of detecting possible fouling of the cooling exchanger caused by solidification of a component of the user fluid in the cooling exchanger, and the step of reducing the temperature drop of the user fluid flow in the cooling exchanger if such fouling is detected.

[0003] The invention may particularly relate to methods and apparatus for refrigerating or keeping cold liquefied natural gas on board ships known as LNG tankers.

[0004] Subcooling and / or liquefaction of the evaporated product of the stored liquefied cryogenic fluid is typically performed by transferring cold power from a refrigerator to the cryogenic fluid (by heat exchange to subcool the cryogenic fluid). The cooled fluid is then returned to the storage vessel (or an adjacent storage vessel) from which the fluid was taken. In other configurations, it is the boil-off gas that is reliquefied.

[0005] The cryogenic fluid to be cooled to a certain temperature is not necessarily a pure compound and may be in the form of a mixture, in particular a mixture of hydrocarbons of different lightness and gravity with different solidification temperatures. This means that some components of the mixture may solidify during the supercooling. These solid particles may foul the exchangers of the refrigerator, thereby reducing the performance of the device. In particular, when the refrigerator is fine-tuned, this fouling may produce changes in the operation of the working circuit of the refrigerator.

[0006] One known solution consists in temporarily reducing or eliminating the cooling power supplied by the refrigerator (see for example FR 3099816 A1, FR 3099817 A1, FR 3099818 A1).

[0007] However, these satisfactory solutions have the drawback of impairing the energy efficiency of the refrigerating machine.

[0008] An object of the present invention is to overcome all or some of the above-mentioned drawbacks of the prior art.

[0009] To this end, the essential feature of the method according to the present invention, which also conforms to the general definition given in the above preamble, is that the step of reducing the temperature drop is carried out by increasing the flow rate and / or the temperature of the user fluid flow permitted to circulate in the cooling exchanger.

[0010] In addition, embodiments of the present invention may include one or more of the following features:

[0011] - During the step of reducing the temperature drop, the cooling power generated by the cryogenic refrigerating machine and supplied to the cooling exchanger is kept constant.

[0012] - During the step of reducing the temperature drop, the cooling power generated by the cryogenic refrigerating machine and supplied to the cooling exchanger is reduced by a determined amount, and this reduction contributes to reducing the temperature drop of the fluid flow in the cooling exchanger.

[0013] - The circulating fluid expansion mechanism includes one or more expansion turbines, and the one or more expansion turbines include the coldest turbine, which expands and cools the circulating fluid before the circulating fluid passes through the cooling exchanger. Wherein, before the step of reducing the temperature drop, the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger is equal to or substantially equal to the temperature difference between the inlet and the outlet of the circulating fluid in the coldest turbine, and wherein, during the step of reducing the temperature drop, the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger decreases and is less than the temperature difference between the inlet and the outlet of the circulating fluid in the coldest turbine.

[0014] - The user fluid flow is circulated through the cooling exchanger by at least one pump, and the step of reducing the determined temperature drop of the user fluid flow is carried out by increasing the flow rate of the user fluid permitted to circulate in the cooling exchanger via increasing the flow rate of the pump and / or increasing the number of pumps used to circulate the user fluid in the cooling exchanger.

[0015] - The step of determining to reduce the temperature of the user fluid flow is carried out by increasing the flow rate of the user fluid permitted to circulate in the cooling exchanger via increasing the number of pumps used to circulate the user fluid in the cooling exchanger. The method includes the step of pumping the user fluid from two separate user fluid reservoirs via corresponding separate pumps, and the user fluid cooled in the cooling exchanger is returned to at least one of the reservoirs.

[0016] - The steps for detecting possible fouling of the cooling exchanger include at least one of the following: detecting an increase in the pressure drop in the passage of the cooling exchanger intended for the user fluid; detecting an increase in the pinch point of the cooling exchanger, that is, an increase in the temperature difference between the relatively hotter passage and the relatively colder passage of at least one fluid in the cooling exchanger, detecting a decrease in the flow rate of the user fluid in the passage of the cooling exchanger intended for the user fluid to below a threshold.

[0017] - The steps for detecting possible fouling of the cooling exchanger use at least one set of sensors from the following: a set of sensors for measuring the temperature of at least one fluid flow between the inlet and the outlet of the cooling exchanger; a set of sensors for measuring the pressure difference of the user fluid flow between the inlet and the outlet of the cooling exchanger; a set of sensors for measuring the flow rate of the user fluid flow in the cooling exchanger.

[0018] The present invention also relates to a device for cooling and / or liquefying a user fluid flow, in particular a liquefied natural gas flow. The device includes a cryogenic refrigerator, that is, a cryogenic refrigerator operating at a temperature between minus 100 degrees Celsius and minus 273 degrees Celsius. The cryogenic refrigerator is of the circulating fluid type and includes a working circuit that forms a loop and houses the circulating fluid. The refrigerator includes a cooling exchanger and is configured to generate a determined cooling power, which is used to extract heat from the user fluid flow by exchanging heat with the circulating fluid circulating in the working circuit. The working circuit forms a cycle that sequentially includes: a circulating fluid compression mechanism, a circulating fluid cooling mechanism, a circulating fluid expansion mechanism, and a circulating fluid heating mechanism. The device includes at least one user fluid reservoir, a circulating conduit configured to guide the user fluid flow to be cooled from at least one reservoir to the cooling exchanger of the refrigerator for heat exchange. The device is configured to achieve a determined reduction in the temperature of the user fluid flow before the user fluid flow in the cooling exchanger returns to at least one reservoir. The device includes a system for detecting possible fouling of the cooling exchanger caused by solidification of the components of the user fluid in the cooling exchanger, and a device for controlling the degree of temperature drop of the user fluid flow in the cooling exchanger. The control device is configured to allow a reduction in the temperature drop in the case of detecting such fouling. The control device includes components for adjusting the flow rate and / or temperature of the user fluid flow permitted to circulate in the cooling exchanger.

[0019] According to other possible specific features:

[0020] - The circulation fluid expansion mechanism includes a group of one or more expansion turbines, the group of one or more expansion turbines including the coldest turbine which expands and cools the circulation fluid before the circulation fluid passes through the cooling exchanger. The device is configured such that, in the case where the cooling exchanger is not fouled, the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger is maintained equal to the temperature difference between the inlet and the outlet of the circulation fluid in the coldest turbine. And wherein, in the case where the cooling exchanger is fouled, the control means is configured to reduce the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger to a value lower than the temperature difference between the inlet and the outlet of the circulation fluid in the coldest turbine.

[0021] - The device includes at least one pump configured to convey the user fluid flow to be cooled from at least one reservoir to the cooling exchanger of the refrigerator for heat exchange purposes. Members for regulating the flow rate and / or temperature of the user fluid flow permitted to circulate in the cooling exchanger are configured to increase the flow rate of the at least one pump or the at least one pump and / or activate at least one additional pump to increase the flow rate of the said flow.

[0022] - The device includes two separate user fluid reservoirs and corresponding separate pumps.

[0023] - The system for detecting possible fouling of the cooling exchanger includes at least one set of sensors from the following: a set of sensors for measuring the temperature of at least one fluid flow between the inlet and the outlet of the cooling exchanger; a set of sensors for measuring the pressure difference of the user fluid flow between the inlet and the outlet of the cooling exchanger; a flowmeter sensor for measuring the flow rate of the user fluid flow circulating in the cooling exchanger.

[0024] The present invention may also relate to any alternative device or method including any combination of the above or below features within the scope of the claims.

[0025] Additional distinctive features and advantages will become apparent by reading the description provided below with reference to the accompanying drawings, in which: Description of the Drawings

[0026] The present invention will be better understood by reading the following description given by way of example only and with reference to the accompanying drawings, in which:

[0027] Figure 1 is a schematic partial view showing an example of the structure and operation of a device according to the present invention.

[0028] Figure 2 is a schematic partial view showing another example of the structure and possible operation of a device according to the present invention.

[0029] ​​​Figure 3 is a schematic partial view of the details of the device, showing an example of the arrangement of the heat exchanger of the device according to the present invention,

[0030] Figure 4 is a schematic partial view of the details of the device, showing an example of the arrangement for detecting fouling in the heat exchanger of the device according to the present invention,

[0031] Figure 5 is a schematic diagram showing an example of how the cooling power generated by the refrigerator, the heat loss, and the cooling power supplied by the device vary according to the delivery flow rate of the pump of the device. Detailed Description of the Invention

[0032] Throughout the drawings, the same reference numerals refer to the same elements.

[0033] In this detailed description, the following embodiments are examples. Although the description refers to one or more embodiments, this does not mean that these features are only applicable to a single embodiment. The various features of different embodiments can also be combined and / or interchanged to provide other embodiments.

[0034] The device 100 for cooling and / or liquefying a user fluid stream is designed, for example, to cool and / or subcool and / or liquefy natural gas from one or more reservoirs 5 on a ship, for example.

[0035] The device 100 includes a cryogenic refrigerator 1, i.e., a machine that generates cooling capacity at a temperature between minus 100 degrees Celsius and minus 273 degrees Celsius. The cryogenic refrigerator 1 is of the circulating fluid type and includes a working circuit 10 that forms a loop and houses the circulating fluid. The working circuit 10 is configured to subject the circulating fluid to a thermodynamic cycle that brings the circulating fluid to a low temperature at at least one cold end of the circuit, and the thermodynamic cycle is used to transfer cooling power to the application to be cooled. For example, the thermodynamic cycle is a Brayton cycle. For example, the circulating fluid contains at least one of the following: helium, hydrogen, nitrogen, argon.

[0036] To this end, the refrigerator 1 includes a cooling exchanger 8, and the refrigerator 1 is configured to generate a determined cooling power that is used to extract heat from the user fluid stream by exchanging heat (through heat exchange in the cooling exchanger 8) with the circulating fluid circulating in the working circuit 10.

[0037] ​​The working circuit 10 forms a cycle that includes: a cycle fluid compression mechanism 2 (e.g., including one or more compressors in parallel and / or in series), a cycle fluid cooling mechanism 3 (e.g., one or more heat exchangers in parallel and / or in series), a cycle fluid expansion mechanism 4 (e.g., one or more turbines and / or valves in series and / or in parallel), and a cycle fluid heating mechanism 8, 3 (e.g., one or more heat exchangers in parallel and / or in series). For example, the compression mechanism 2, the cycle fluid cooling mechanism 3, the expansion mechanism 4, and the heating mechanism 8, 3 are arranged in series in the working circuit.

[0038] As shown, the cycle fluid heating and cooling mechanism may include at least one countercurrent heat exchanger that ensures heat exchange between two portions 10 of the cycle circuit. As Figure 3 shown, the cooling exchanger 8 is connected to the heat exchanger 3 of the cycle circuit 10.

[0039] As Figure 2 schematically shown, one or more compressors may be driven by at least one motor 12 (e.g., an electric motor). Additionally, as shown in the figure, the turbine 4 (or at least one of the turbines 4) may be mounted on the same shaft 15 of the motor as the compressor 2 (motor - turbine - compressor).

[0040] The apparatus 100 includes at least one user fluid reservoir 5 (two in the example shown), a cycle conduit 6 that is configured to draw a user fluid flow from at least one reservoir 5 and convey the user fluid flow towards the cooling exchanger 8 of the refrigerator 1 for the purpose of heat exchange. The user fluid is pumped, for example, via at least one pump 7, which may be housed in the reservoir 5. The user fluid flow is cooled in the cooling exchanger 8 before returning to at least one reservoir 5 of the apparatus 100.

[0041] The apparatus 100 is preferably configured to achieve a determined reduction in the temperature of the user fluid.

[0042] The apparatus 100 includes a system for detecting any fouling of the cooling exchanger 8 caused by the solidification (frost formation) of the composition of the user fluid in the cooling exchanger 8.

[0043] The detection or determination of such fouling can be performed by at least one of the following measures: detecting an increase in the pressure drop in the passage of the cooling exchanger 8 intended for the user fluid; detecting an increase in the pinch point of the cooling exchanger 8, that is, an increase in the temperature difference between the relatively hotter passage and the relatively colder passage of at least one fluid in the cooling exchanger 8. The increase in the pinch point reduces the heat exchange area between the cold cycle fluid and the user fluid to be cooled.

[0044] For this purpose, and as Figure 2As schematically shown, the detection system may include a set of sensors 11 for measuring the pressure difference of the user fluid flow between the inlet and the outlet of the cooling exchanger 8. This is schematically shown in Figure 4 . The measured pressure difference may reveal the pressure drop in the cooling exchanger 8 caused by fouling due to the solidification of the compounds in the exchanger. For example, this measured pressure difference or the measured pressure drop is compared with a determined threshold.

[0045] As a variant or in combination, the detection system may include a sensor 13 (e.g., a flow meter) for measuring the flow rate of the user fluid flow circulating in the cooling exchanger 8. When the measured flow rate drops below a threshold, this may be a characteristic of fouling of the cooling exchanger 8.

[0046] As a variant or in combination, the detection system may include a set of sensors 9 for measuring the temperature of at least one of the fluid flows entering and leaving the cooling exchanger 8 in order to determine the pinch point of the exchanger. In fact, the pinch point (i.e., the temperature difference between the passages of the relatively hotter fluid and the relatively colder fluid of the cooling exchanger 8) is a parameter that can also be a characteristic of fouling of the cooling exchanger 8.

[0047] In normal operation, the device 100 is preferably configured such that the temperature difference of the user fluid flow between the inlet and the outlet of the cooling exchanger 8 is equal to or substantially equal to the temperature difference of the circulating fluid between the inlet and the outlet of the same cooling exchanger 8.

[0048] In the case where the cooling exchanger 8 is fouled in the passage for the user fluid flow, this balance of flow rate and heat balance is disturbed and the pinch point of the exchanger 8 is changed. An increase in the pinch point above a given threshold is a characteristic of such fouling. This can be measured or detected, for example, by a set of sensors (e.g., two sensors 9) that measure the temperature difference between the inlet and the outlet of one of the flows passing through the cooling exchanger 8. For example, the drift of the pinch point can be characterized by measuring the abnormal change over time of the temperature difference of the circulating fluid entering and leaving the cooling exchanger 8. This pinch point can also be monitored / measured by measuring the abnormal change over time of the temperature difference between the inlet and the outlet, and the temperature difference of the user fluid entering and leaving the cooling exchanger 8 (e.g., two suitable temperature sensors 9). Of course, four temperature sensors 9 for measuring at the inlets and outlets of the two fluid flows (circulating fluid and user fluid) can be envisaged.

[0049] Of course, any other system for detecting fouling (optical system or other systems) can be envisaged.

[0050] In the case of detecting such fouling, the device is configured to (preferably automatically) reduce the temperature drop of the user fluid flow in the cooling exchanger 8. This reduction in the temperature drop is achieved by increasing the flow rate and / or the temperature of the user fluid flow permitted to circulate in the cooling exchanger 8. In other words, in order to remove such fouling (dissolve the solidification of the material in the cooling exchanger 8), instead of reducing the cooling power supplied by the refrigerating machine at the cooling exchanger 8, the device alternatively acts on the user fluid flow (although a reduction in the cooling power supplied by the refrigerating machine can also be considered as a supplementary solution).

[0051] By at least temporarily increasing this flow rate of the user fluid in the cooling exchanger 8 (where the cooling power remains constant or slightly decreases), the user fluid will be less cooled, and the temperature in the cooling exchanger 8 will increase and will liquefy the solid part.

[0052] In the case where the device includes several systems for detecting fouling, when at least one of the systems for detecting fouling detects fouling, such removal can be initiated.

[0053] Thus, the device 100 includes at least one member 7, 14 for regulating the flow rate and / or the temperature of the user fluid flow permitted to circulate in the cooling exchanger 8, so that the exchanger 8 can be cleaned in the case of fouling.

[0054] The circulating fluid expansion mechanism 4 typically includes a set of expansion turbines, which includes at least one coldest turbine 4 that expands and cools the circulating fluid before the circulating fluid passes through the cooling exchanger 8.

[0055] In normal operation, i.e., in the case where the cooling exchanger (8) is not fouled, the device 100 is preferably configured such that the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger 8 is maintained equal to or substantially equal to the temperature difference between the inlet and the outlet of the circulating fluid in the coldest turbine 4. That is to say, the cooling of the user fluid corresponds to the cooling of the circulating fluid performed by the coldest turbine (substantially within a few degrees). In contrast, in the case where the cooling exchanger 8 is fouled, the device 100 includes control means configured to reduce the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger 8 to be lower than the temperature difference between the inlet and the outlet of the circulating fluid in the coldest turbine 4. That is to say, the cooling of the user fluid flow in the cooling exchanger 8 is relatively less than the cooling of the circulating fluid at the extreme of the coldest turbine 4.

[0056] As Figure 6 shown, the device may include a set of sensors 16 for measuring the temperature difference between the inlet and the outlet of the circulating fluid in the coldest turbine 4.

[0057] A user fluid flow circulates, for example, through at least one pump 7 in a cooling exchanger 8. A reduction in the determined temperature drop (i.e., its relative heating) of the user fluid flow in the cooling exchanger 8 can be achieved by increasing the flow rate of the user fluid permitted to circulate in the cooling exchanger 8 by increasing the delivery flow rate of the pump 7.

[0058] As a variant or in combination, this can be obtained by increasing the number of pumps 7 used to circulate the user fluid in the cooling exchanger 8.

[0059] This is shown in Figure 1 , in which the device 100 includes two pumps connected in parallel and respectively pumping from / to two separate reservoirs 5 from two separate reservoirs. An increase in the flow rate of the liquefied gas to be cooled can be achieved by operating at least one second pump that is not operating in a nominal or normal mode.

[0060] In normal operation, the pressure difference at the terminals of the cooling exchanger 8 for the user fluid can be on the order of, for example, 15 degrees (i.e., cooling by fifteen degrees). Some user fluids, especially some liquefied natural gas sources, can have a higher than average content of heavy hydrocarbons. These compounds tend to solidify in the exchanger during this (over) cooling.

[0061] The cold source (refrigerator 1) can be connected to the two reservoirs 5, but a single pump 7 using one of the reservoirs 5 is supplied. The flow rate of the user fluid to be cooled can be increased in order to reduce this cooling (reduce the temperature difference). This causes an increase in the heat loss due to the pump 7.

[0062] Alternatively or in combination, in the case of fouling, the flow rate of the user fluid to be cooled can be increased by starting or using an additional pump 7. Thus, the cooling exchanger 8 can be supplied temporarily via two pumps 7 (preferably pumping from different reservoirs 5). By doubling the flow rate of the user fluid to be cooled, the overcooling is halved (for a comparable cooling power). This reduces the solid heavy compounds in the cooling exchanger 8 and ensures defrosting of the solid heavy compounds.

[0063] Therefore, by increasing the flow rate of the user fluid to be cooled in the cooling exchanger 8 (which provides a constant cooling power), less user fluid is cooled, and in particular, the user fluid is made to be above the melting temperature of the solid compounds. This allows for the cleaning of the fouled cooling exchanger 8.

[0064] As a variant or in combination, in order to remove fouling, the device can use a specific control of one or more pumps 7. The pump 7 can be controlled by an electronic control member (such as a frequency converter that drives the pump motor (and thus controls its speed or the supplied flow rate)).

[0065] In the nominal mode (normal operation without fouling), the pump 7 can be controlled to operate at a delivery flow rate less than its maximum delivery flow rate. On the other hand, in the case of fouling, the device 100 can be configured such that the pump increases its delivery flow rate (e.g., the frequency converter increases its delivery flow rate).

[0066] In normal operation, the delivery flow rate of the pump 7 can be adjusted such that the temperature difference of the user fluid at the terminals (inlet / outlet) of the cooling exchanger 8 is equal to or substantially equal to the temperature difference at the terminals of the coldest turbine 4. That is, the cooling of the user fluid corresponds to the cooling of the circulating fluid at the terminals of this expansion turbine 4.

[0067] Furthermore, this delivery flow rate of the pump 7 is preferably selected as the lowest value (among the possible delivery flow rates of the pump 7) to achieve such a balance between the temperature differences (while maintaining the cooling power of the refrigerator 1). That is, the delivery flow rate of the pump 7 can be adjusted to ensure that the temperature difference between the inlet and outlet of the user fluid to be cooled in the cooling exchanger 8 is equal to (within a few degrees if necessary) the temperature difference between the inlet and outlet of the circulating fluid at the coldest turbine 4 of the refrigerator 1. Also preferably, this selected delivery flow rate of the pump 7 is the lowest delivery flow rate to achieve such equality.

[0068] In fact, the cooling power PF supplied by the refrigerator 1 is the product of the delivery flow rate DF of the circulating fluid, the heat capacity CC of the circulating fluid, and the temperature difference dT of this circulating fluid at the cooling exchanger 8 (PF = DF x CC x dT).

[0069] The useful cooling power PU (which is actually supplied to the user fluid) is the difference between the cooling power generated by the refrigerator PF and the losses associated with the equipment (pumps, pipelines, etc.) of the user fluid connecting the refrigerator to the reservoir 5.

[0070] The heat loss of the pump 7 is generally proportional to the delivery flow rate D of the pumped fluid. Therefore, setting the pumped delivery flow rate to the minimum value maximizes the available cooling power (see Figure 5 )).

[0071] Therefore, there is an optimal efficiency between pumping the lowest possible delivery flow rate while maintaining a sufficiently large temperature difference dT to be as close as possible to the temperature difference at the terminals of the coldest turbine 4.

[0072] Therefore, by temporarily increasing the delivery flow rate of the pump 7, it is also possible to reduce the cooling efficiency of the user fluid and cause less cooling, thereby enabling the removal of fouling solids from the cooling exchanger 8.

[0073] In a variant embodiment, the device 100 may be configured to use the circulating fluid flow rate delivered by the pump 7, which is always greater than the most energy-efficient flow rate. That is to say, the delivery flow rate of the pump 7 is always increased in order to avoid excessive cooling of the user fluid, thereby preventing (avoiding) the freezing of compounds in the cooling exchanger 8.

[0074] For example, the flow rate of the user fluid to be cooled may be maintained such that the temperature difference between the inlet and the outlet of the user fluid in the cooling exchanger 8 always remains less than the temperature difference between the inlet and the outlet of the circulating fluid in the coldest turbine 4.

[0075] The advantage of controlling the flow rate of the user fluid circulating in the cooling exchanger 8 rather than controlling the cooling power supplied by the refrigerating machine makes it possible to keep this cooling power constant. This allows for a very simple regulation that only affects the flow rate of the user fluid to be cooled. This makes it possible to optimize the efficiency in cases where the cooling exchanger 8 may become fouled due to the freezing of soluble compounds.

[0076] As Figure 1 shown, the device may include an electronic unit 14 (e.g., a controller), which includes a microprocessor configured to perform all or part of the regulation (flow rate and / or temperature of the user fluid flow). In particular, the electronic component 14 may receive measurements (temperature, pressure, flow rate, etc.) from all or some of the sensors and control the pump 7 or any other component of the device 100.

Claims

1. A method for cooling a user fluid flow, in particular a liquefied natural gas flow, the method using a device that includes a cryogenic refrigerator (1), i.e., a cryogenic refrigerator operating at a temperature between minus 100 degrees Celsius and minus 273 degrees Celsius, the cryogenic refrigerator (1) being of the circulating fluid type and including a working circuit (10) that forms a loop and houses the circulating fluid, the refrigerator (1) including a cooling exchanger (8) and being configured to generate a determined cooling power that is used to extract heat from the user fluid flow by exchanging heat with the circulating fluid circulating in the working circuit (10), the working circuit (10) forming a cycle that includes: A cyclic fluid compression mechanism (2), a cyclic fluid cooling mechanism (3), a cyclic fluid expansion mechanism (4), and a cyclic fluid heating mechanism (8, 3). The device includes at least one user fluid reservoir (5) and a conduit (6) for circulating the user fluid taken from at least one reservoir (5) so as to be in a heat exchange relationship with the cooling exchanger (8) of the refrigerator (1) before being re-injected into at least one reservoir (5). The method includes the step of determining to reduce the temperature of the user fluid flow in the cooling exchanger (8). The method includes the step of detecting possible fouling of the cooling exchanger (8) caused by solidification of the composition of the user fluid in the cooling exchanger (8), and the step of reducing the temperature drop of the user fluid flow in the cooling exchanger (8) if such fouling is detected. The step of reducing the temperature drop is performed by increasing the flow rate and / or temperature of the user fluid flow allowed to circulate in the cooling exchanger (8). It is characterized in that during the step of reducing the temperature drop, the cooling power generated by the cryogenic refrigerator (1) and supplied to the cooling exchanger (8) is kept constant.

2. The method according to any one of claims 1, characterized in that, The cyclic fluid expansion mechanism (4) includes one or more expansion turbines, and the one or more expansion turbines include the coldest turbine (4). The coldest turbine expands and cools the cyclic fluid before the cyclic fluid passes through the cooling exchanger (8). Wherein, before the step of reducing the temperature drop, the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger (8) is equal to or substantially equal to the temperature difference between the inlet and the outlet of the cyclic fluid in the coldest turbine (4), and wherein, during the step of reducing the temperature drop, the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger (8) decreases and is less than the temperature difference between the inlet and the outlet of the cyclic fluid in the coldest turbine (4).

3. The method according to any one of the preceding claims, wherein, The user fluid flow circulates through the cooling exchanger (8) by at least one pump (7). The step of reducing the determined temperature drop of the user fluid flow is performed by increasing the flow rate of the user fluid allowed to circulate in the cooling exchanger (8) by increasing the flow rate of the pump (7) and / or increasing the number of pumps for circulating the user fluid in the cooling exchanger (8).

4. The method according to claim 3, wherein, The step of determining to reduce the temperature of the user fluid flow is performed by increasing the flow rate of the user fluid allowed to circulate in the cooling exchanger (8) by increasing the number of pumps (7) for circulating the user fluid in the cooling exchanger (8). The method includes the step of pumping user fluid from two separate user fluid reservoirs (5) via respective separate pumps (7), and the user fluid cooled in the cooling exchanger (8) is returned to at least one of these reservoirs (5).

5. The method according to any one of claims 1 to 4, characterized in that, The steps for detecting possible fouling of the cooling exchanger (8) include at least one of the following: detecting an increase in the pressure drop in the passage of the cooling exchanger (8) intended for the user fluid; detecting an increase in the pinch point of the cooling exchanger (8), that is, an increase in the temperature difference between the relatively hotter passage and the relatively colder passage of at least one fluid in the cooling exchanger (8); detecting a decrease in the flow rate of the user fluid in the passage of the cooling exchanger (8) intended for the user fluid to below a threshold value.

6. The method according to any one of claims 1 to 5, characterized in that The steps for detecting possible fouling of the cooling exchanger (8) use at least one set of sensors from the following: a set of sensors (9) for measuring the temperature of at least one fluid flow between the inlet and the outlet of the cooling exchanger (8); a set of sensors (11) for measuring the pressure difference of the user fluid flow between the inlet and the outlet of the cooling exchanger (8); a set of sensors (13) for measuring the flow rate of the user fluid flow in the cooling exchanger (8).

7. An apparatus for cooling and / or liquefying a user fluid stream, in particular a liquefied natural gas stream, the apparatus comprising a cryogenic refrigerator (1), i.e. a cryogenic refrigerator operating at a temperature between minus 100 degrees Celsius and minus 273 degrees Celsius, the cryogenic refrigerator (1) being of the circulating fluid type and comprising a working circuit (10) which forms a loop and houses the circulating fluid, the refrigerator (1) comprising a cooling exchanger (8) and being configured to produce a determined cooling power which is used to extract heat from the user fluid stream by exchanging heat with the circulating fluid circulating in the working circuit (10), the working circuit (10) forming a cycle which successively comprises: A cyclic fluid compression mechanism (2), a cyclic fluid cooling mechanism (3), a cyclic fluid expansion mechanism (4), and a cyclic fluid heating mechanism (8, 3), the device includes at least one user fluid reservoir (5), a circulation conduit (6), the circulation conduit is configured to guide the user fluid flow to be cooled from at least one reservoir (5) to the cooling exchanger (8) of the refrigerator (1) for heat exchange, the device is configured to achieve a definite reduction in the temperature of the user fluid flow before the user fluid flow in the cooling exchanger (8) returns to at least one reservoir (5), the device includes a system for detecting possible fouling of the cooling exchanger (8) caused by solidification of the components of the user fluid in the cooling exchanger (8), and a device for controlling the degree of temperature drop of the user fluid flow in the cooling exchanger (8), the control device is configured to allow a reduction in the temperature drop in the case of detecting such fouling, the control device includes components (7, 14) for regulating the flow rate and / or temperature of the user fluid flow permitted to circulate in the cooling exchanger (8), and is characterized in that the device is configured to keep the cooling power generated by the cryogenic refrigerator (1) and supplied to the cooling exchanger (8) constant when the reduction in the temperature drop of the user fluid flow in the cooling exchanger (8) occurs.

8. The device according to claim 7, wherein, The circulating fluid expansion mechanism (4) includes a group of one or more expansion turbines, the group of one or more expansion turbines including the coldest turbine (4), which expands and cools the circulating fluid before the circulating fluid passes through the cooling exchanger (8), the device being configured such that, in the case where the cooling exchanger (8) is not fouled, the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger (8) is maintained equal to the temperature difference between the inlet and the outlet of the circulating fluid in the coldest turbine (4), and wherein, in the case where the cooling exchanger (8) is fouled, the control device is configured to reduce the temperature difference between the inlet and the outlet of the user fluid flow in the cooling exchanger (8) to a value lower than the temperature difference between the inlet and the outlet of the circulating fluid in the coldest turbine (4).

9. The device according to any one of claims 7 to 8, characterized in that, The device includes at least one pump (7), the at least one pump being configured to convey the user fluid flow to be cooled from at least one reservoir (5) to the cooling exchanger (8) of the refrigerating machine (1) for heat exchange purposes, and members (7, 14) for regulating the flow rate and / or the temperature of the user fluid flow permitted to circulate in the cooling exchanger (8) being configured to increase the flow rate of the at least one pump (7) or of at least one pump and / or to start at least one additional pump to increase the flow rate of said flow.

10. The device according to claim 9, characterized in that, The device includes two separate user fluid reservoirs (5) and corresponding separate pumps (7).

11. The device according to any one of claims 7 to 10, characterized in that, The system for detecting possible fouling of the cooling exchanger (8) includes at least one set of sensors selected from the following: a set of sensors (9) for measuring the temperature of at least one fluid flow between the inlet and the outlet of the cooling exchanger (8); a set of sensors (11) for measuring the pressure difference of the user fluid flow between the inlet and the outlet of the cooling exchanger (8); a flowmeter sensor (13) for measuring the flow rate of the user fluid flow circulating in the cooling exchanger (8).

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