Floating structure comprising a processing system for processing natural gas

Abstract

A floating structure comprising a treatment system (1) for natural gas stored in at least one tank (3) of the floating structure (100), the treatment system (1) comprising at least one closed circuit (4) through which passes a refrigerant comprising at least nitrogen and methane, the treatment system (1) being configured to supply gaseous natural gas from the tank (3) to at least one consumption unit (2) of the floating structure (100) as fuel, said treatment system (1) comprising at least one control system (9) for controlling the composition of the refrigerant, said control system (9) being configured to control at least a refrigerant flow rate adjustment member (125) of a sampling branch (120) and a flow rate adjustment device (165) for adjusting the flow rate of a fluid mainly comprising methane of said at least one injection branch (160, 1601, 1602).

Description

Technical Field

[0001] This invention relates to the field of floating structures in which at least one consumption unit is supplied with natural gas, and which also enables the containment or transport of liquefied natural gas. More specifically, this invention relates to a processing system for processing natural gas used as fuel by at least one consumption unit of a floating structure. Background Technology

[0002] To facilitate the long-distance transportation and / or storage of gases such as natural gas, they are typically liquefied by cooling the gas to a cryogenic temperature (e.g., -163°C at atmospheric pressure) to obtain liquefied natural gas, commonly referred to simply as "LNG". This liquefied natural gas is then loaded into specialized floating storage tanks.

[0003] However, these tanks are never perfectly insulated, so natural evaporation of the gas is inevitable; this phenomenon is known as BOG, an abbreviation for Boil-Off Gas. Floating tanks therefore contain both liquefied and gaseous natural gas, with the gaseous gas forming at the top of the tank.

[0004] It is well known that at least a portion of natural gas existing in gaseous form in a tank can be used to supply consumption units, such as motors, which are configured to meet the operating energy requirements of floating structures, particularly for their propulsion and / or for the generation of electricity for onboard equipment. For this purpose, a particularly known practice is to circulate the gaseous natural gas through at least one natural gas processing system to compress and heat it to a temperature suitable for use as fuel in the consumption unit. Such a processing system particularly includes a heat exchanger and a compression unit, both located upstream of the consumption unit and serving as superheaters, and at least one refrigerant circuit configured to exchange at least one type of heat with the natural gas circulating in the processing system.

[0005] Known refrigerant circuits incorporate a compressor. Because such circuits operate at low temperatures, the individual rotating bearings of the compressor must be sealed with a gas (e.g., nitrogen). In practice, at such temperatures, the use of oil in the compressor unit (multiple units) would result in at least partial solidification of the oil, which could affect the proper operation of the processing system. A disadvantage of using a compressor with hermetically sealed bearings is the inevitable leakage of nitrogen into the refrigerant flowing through the circuit, which alters the initial composition of the refrigerant and reduces the efficiency of the refrigerant circuit. Summary of the Invention

[0006] The present invention falls within this context and aims to address this deficiency by proposing a floating structure comprising at least one tank for transporting or storing liquefied natural gas, the floating structure comprising at least one processing system for natural gas stored in the at least one tank of the floating structure, and at least one consumption unit for consuming natural gas as fuel, the at least one consumption unit being supplied with fuel by gaseous natural gas circulating at least partially in the processing system, the processing system comprising at least one closed loop through which a refrigerant comprising at least nitrogen and methane passes, the processing system comprising at least one supply line configured to supply gaseous natural gas from the tank as fuel to the at least one consumption unit of the floating structure, the refrigerant loop comprising at least one main branch on which:

[0007] - A compression device configured to compress a refrigerant and including at least one nitrogen-sealed rotary bearing;

[0008] - The first heat exchanger performs at least one heat exchange between the refrigerant and the gaseous natural gas from the tank;

[0009] - Refrigerant expansion device;

[0010] - A second heat exchanger that exchanges heat between the refrigerant and liquefied natural gas;

[0011] The refrigerant circuit should include at least:

[0012] - A sampling branch for sampling a portion of the refrigerant flowing in the main branch, the sampling branch being arranged parallel to the expansion device and including at least one refrigerant flow rate regulating member and a phase separator, the flow of the portion of refrigerant depending on the refrigerant flow rate regulating member;

[0013] - At least one injection branch for injecting a fluid mainly containing methane, the injection branch including at least one flow rate regulating device for regulating the flow rate of the fluid mainly containing methane flowing in the injection branch, the injection branch being connected to the main branch of the refrigerant circuit at an injection point arranged between the first output of the second heat exchanger and the input of the compression device;

[0014] This processing system includes at least one control system for controlling the composition of the refrigerant, the control system being configured to control at least the refrigerant flow rate regulating member of the sampling branch and the flow rate regulating device in the injection branch for regulating the fluid that mainly contains methane.

[0015] It should be understood that in this document, the qualifiers “first,” “second,” or “primary,” “secondary” are used to distinguish similar elements of the processing system, but are not used to determine the priority or rank among these elements.

[0016] In this invention, the processing system is configured to exchange heat at low temperatures between the refrigerant flowing in the refrigerant circuit and natural gas from the tank, the natural gas being in a gaseous and / or liquid state. "Low temperature" should be understood to mean temperatures below -40°C, even below -90°C, and preferably below -160°C.

[0017] Understandably, the refrigerant circulates in a loop, thus entering the compressor, then the first heat exchanger, then the expansion device, then the second heat exchanger, and finally the compressor again. Therefore, the compressor is fluidly connected to the first heat exchanger, the first heat exchanger is fluidly connected to the expansion device, the expansion device is fluidly connected to the second heat exchanger, and the second heat exchanger is fluidly connected to the compressor. Thus, the refrigerant loop is self-contained.

[0018] Therefore, the initial composition of the refrigerant is suitable for optimizing the efficiency of this heat exchange. This refrigerant, in addition to containing nitrogen and methane, can also contain at least one hydrocarbon selected from ethane, ethylene, propane, propylene, and / or butane. Therefore, the object of the present invention is to correct the altered composition of the refrigerant, particularly as a consequence of nitrogen contamination following leakage from the rotating bearing of the compressor, thereby making the refrigerant composition, such as its initial composition, optimized for heat exchange with gaseous and / or liquid natural gas at low temperatures.

[0019] In particular, the present invention aims to reduce the proportion of nitrogen present in the altered refrigerant. Additionally, the present invention aims to adjust the proportion of methane in the refrigerant to compensate for any methane loss that may accompany a decrease in the nitrogen proportion in the refrigerant. The processing system is configured to ensure the adjustment of the refrigerant composition by injecting the fluid, which primarily contains methane, particularly via the at least one injection branch.

[0020] In the refrigerant circuit, the refrigerant is compressed by a compression device comprising at least one body in which a shaft supported by at least one nitrogen-sealed rotary bearing extends. Specifically, the compression device includes at least one second hermetically sealed rotary bearing.

[0021] In the refrigerant circuit, the main branch comprises two parts: the first part, contained between the output of the compressor and the input of the expander, in which the refrigerant is subjected to high pressure; and the second part, contained between the output of the expander and the input of the compressor, in which the refrigerant is subjected to low pressure, which is lower than the high pressure.

[0022] Advantageously, the refrigerant circuit may include an internal heat exchanger configured to exchange heat between the refrigerant flowing in the first section and the refrigerant flowing in the second section. Notably, the internal heat exchanger may be incorporated into the first heat exchanger. This then includes at least three channels to achieve at least two heat exchanges: a first heat exchange, as previously described, between the first refrigerant and gaseous natural gas from the tank, using the first heat exchanger as a superheater for the gaseous natural gas from the tank; and a second heat exchange specific to the internal heat exchanger.

[0023] Therefore, as the refrigerant flows through the various components of the refrigerant circuit, it undergoes a series of state and temperature changes through heat exchange, and these heat exchanges can accompany the processing of the flowing natural gas.

[0024] "Processing" should be understood as heating and / or cooling intended to cause the evaporation or condensation of natural gas, respectively. Therefore, a natural gas processing system includes at least a refrigerant circuit and at least several pipelines and / or installations that ensure the flow and / or processing of natural gas, particularly between tanks and floating structure consumption units.

[0025] "Consuming unit" should be understood as a unit equipped with an internal combustion engine, configured to cooperate with the processing system and capable of using gaseous natural gas as fuel. As an example, a consumption unit may include a DFDE (dual-fuel diesel-electric) type generator, that is, a gas consumption unit configured to ensure the electric drive of a floating structure, or a ship's propulsion engine, such as a ME-GI or XDF engine.

[0026] In the processing system, the supply to the consumption unit is ensured by a supply loop including a supply line. The supply line extends at least partially within the tank to lead to the gaseous top of the tank and thus draw in gaseous natural gas to bring it to the consumption unit. The temperature of this natural gas is above -160°C, for example, in the range of -130°C to -110°C.

[0027] Advantageously, gaseous natural gas can be extracted continuously or selectively, and the supply pipeline can then include at least one valve for controlling the discharge of gaseous natural gas.

[0028] According to the features of the invention, the processing system includes at least one compression device, referred to as a second compression device, which is different from the compression device of the refrigerant circuit (hereinafter referred to as the first compression device). The second compression device is arranged on a supply line between a first output of the first heat exchanger and the at least one consumption unit. The first compression device and the second compression device are configured to compress natural gas from the tank.

[0029] In other words, the processing system is configured to ensure redundancy of the second compression unit in the supply loop. Therefore, depending on the needs of the floating structure, the first compression unit can compress refrigerant or liquefied natural gas into a gaseous state, depending on whether it is used to circulate and compress refrigerant or to supply the consumption units of the floating structure. This is especially true in the event of a failure of the second compression unit, as the first compression unit can take over its function of supplying the consumption units. The first compression unit then becomes the backup compression unit.

[0030] This arrangement is implemented specifically for safety purposes and to ensure a continuous supply of gaseous natural gas as fuel to the consumption unit. Therefore, in the event of a failure of the second compression unit, the first compression unit can be used to ensure the compression of natural gas for the consumption unit.

[0031] Therefore, the supply loop of the processing system may include an alternative loop for at least a portion of the supply line, the alternative loop being configured to bypass the second compressor and including at least one alternative line comprising the first compressor. Additionally, the first and / or second compressor may be located before and / or after at least one isolation valve configured to allow or block the flow of refrigerant and / or natural gas.

[0032] The processing system according to the invention includes a control system configured to at least partially open and close a refrigerant flow rate regulating member included in a sampling branch and a flow rate regulating device included in the at least one injection branch for regulating the flow rate of the fluid, which mainly comprises methane.

[0033] According to the present invention, the control system includes at least one refrigerant temperature detector and / or one refrigerant composition detector arranged on the main branch of the refrigerant circuit.

[0034] The temperature detector is preferably located in the second part of the main branch, that is, downstream of the expansion device.

[0035] The refrigerant composition detector is preferably located in the first part of the main branch. Alternatively, the refrigerant composition detector may be located at the accumulation device, which is a component of the refrigerant circuit.

[0036] In reality, changes in refrigerant composition, especially nitrogen enrichment due to nitrogen sealing of bearings, are accompanied by changes in refrigerant state temperature. After heat exchange with gaseous and / or liquefied natural gas, the refrigerant can no longer change its state.

[0037] Temperature measurements or determinations performed by a refrigerant temperature detector and / or a refrigerant component detector are transmitted to an analytical unit included in the control system, which compares the measurements accordingly with at least one temperature threshold and / or at least one reference component. For example, the refrigerant component detector may include a chromatograph.

[0038] Based on the measured temperature of the refrigerant and / or based on the analyzed composition, the control system of the processing system, on the one hand, performs sampling of a portion of the refrigerant (essentially a liquid), which is directed to a sampling branch to reduce the proportion of nitrogen in the refrigerant; on the other hand, it performs the injection of the fluid, which mainly contains methane. In other words, the refrigerant flow rate regulating member of the sampling branch, operated by the control system, and the flow rate regulating device for regulating the flow rate of the main methane-containing fluid in the at least one injection branch, are at least partially opened or closed depending on the measurement of the refrigerant temperature and / or the measurement of the refrigerant composition.

[0039] Therefore, the control system ensures the measurement of the refrigerant's temperature and / or composition, the analysis of one or more recorded measurements, and the control of the refrigerant composition by sampling a portion of the refrigerant and injecting it into the fluid, which mainly contains methane.

[0040] According to the present invention, the sampling branch is connected to the main branch of the refrigerant circuit at the bifurcation point between the second output of the first heat exchanger and the input of the expansion device.

[0041] According to the invention, the processing system includes a primary branch connected to the lower part of the phase separator and connected to the main branch at a connection point between the output of the expansion device and the first input of the second heat exchanger.

[0042] When a portion of the primarily liquid refrigerant enters the phase separator, it is partially evaporated and separated into a liquid portion and a gaseous portion. The primary branch is configured to collect the hydrocarbon-rich liquid portion, which includes the least volatile components of the refrigerant and whose evaporation temperature is higher than that of nitrogen or even methane.

[0043] According to a feature of the invention, the primary branch may include a primary flow rate regulating device controlled by a control system between the phase separator and the junction, the primary flow rate regulating device being used to regulate the flow rate of refrigerant circulating in the primary branch.

[0044] In other words, the return of the liquid portion of the refrigerant to the main branch of the refrigerant circuit depends on the primary refrigerant flow rate regulator and therefore on the control system.

[0045] According to a feature of the invention, the processing system includes a secondary branch connected to the upper part of the phase separator.

[0046] The secondary branch is configured to collect the nitrogen-rich gaseous portion of the refrigerant.

[0047] According to the present invention, the secondary branch includes a secondary flow rate regulating device controlled by a control system, the secondary flow rate regulating device being used to regulate the flow rate of refrigerant flowing in the secondary branch.

[0048] According to the invention, the portion of refrigerant circulating in the secondary branch is at least partially discharged from and / or burned from the processing system, and / or injected into the gaseous natural gas supply line.

[0049] In other words, the nitrogen-rich gaseous portion of the refrigerant can be reused elsewhere in the processing system, and the injection of the gaseous portion is regulated by the control system.

[0050] As previously explained, the gaseous portion of the refrigerant flowing in the secondary branch can consist of a variable proportion of methane. Therefore, the purpose of injecting the fluid, which primarily contains methane, through the injection branch is to compensate for methane loss, which may be accompanied by the extraction of nitrogen from the refrigerant.

[0051] According to the invention, the processing system includes at least one third branch extending between a bypass point and a connection point, the bypass point being arranged on a secondary branch, and the connection point being arranged on a gaseous natural gas supply line between the tank output and the input of a first compression device or a second compression device.

[0052] In other words, the gaseous portion of the nitrogen-rich refrigerant can be mixed with gaseous natural gas and circulated in the fuel supply loop to serve at least partially as fuel for at least one consumption unit of the floating structure.

[0053] Advantageously, the flow of the gaseous portion of the refrigerant in the third branch can depend on a secondary refrigerant flow rate regulating device arranged in the secondary branch.

[0054] According to the invention, at least one injection branch can be supplied by at least one storage cylinder that stores a fluid that mainly contains methane, or advantageously, a fluid that is only methane.

[0055] According to a first alternative of the invention, the at least one injection branch may extend between a branch point and an injection point, the branch point being arranged between the at least one consumption unit and the second compression device of the floating structure on a supply pipeline for supplying gaseous natural gas.

[0056] According to the second alternative, the processing system may include multiple injection branches for injecting a fluid that primarily contains methane, at least one injection branch (hereinafter referred to as the first injection branch) extending between a branch point and an injection point, the branch point being arranged between the at least one consumption unit of the floating structure and the second compression device on a supply line for supplying gaseous natural gas, and the second injection branch being supplied by at least one storage cylinder storing the fluid that primarily contains methane.

[0057] Specifically, the first injection branch includes a flow rate regulating device for regulating the flow rate of the fluid mainly containing methane, hereinafter referred to as the first flow rate regulating device, and the second injection branch includes a second flow rate regulating device for regulating the flow rate of the fluid mainly containing methane from the storage cylinder, the opening and closing of at least part of the first regulating device and / or the second regulating device being controlled by a control system.

[0058] According to another alternative, the processing system may include a single injection branch configured to inject a primary methane-containing fluid from the storage tank and / or from the consumption unit of the floating structure (i.e., from the tank) into the main branch of the refrigerant circuit.

[0059] Specifically, regardless of the embodiment or the implemented alternative, the injection point may be located in a second portion of the main branch, which includes the area between the output of the expansion device and the input of the compression device, wherein the refrigerant is subjected to low pressure. As an example, the injection point may be located at the accumulator of the refrigerant circuit, located between the third output of the first heat exchanger and the input of the first compression device, or the injection point may be located on the main branch, between the third output of the first heat exchanger and the accumulator.

[0060] Advantageously, the processing system may include at least one condensing device. The "condensing device" of the processing system is understood to be a device configured to ensure the transformation of initially gaseous natural gas into a liquid state through heat exchange, such as BOG produced by the natural evaporation of natural gas in a tank. In particular, the condensing device may be configured to ensure the condensation of at least a portion of the gaseous natural gas flowing in the supply line, which is not essential for the operation of the consumption units (e.g., propulsion engines) of the floating structure.

[0061] According to the invention, the processing system includes at least one natural gas return pipeline through which compressed excess natural gas passes, and the processing system includes a third heat exchanger that performs heat exchange between the compressed excess natural gas and liquefied natural gas.

[0062] "Compressed excess natural gas" is understood as a compressed portion of gaseous natural gas flowing in the supply line of the fuel supply loop, for example, compressed by a second compression unit but not used by the consumption unit. For example, compressed excess natural gas may have a pressure of less than or equal to 13 bar.

[0063] Advantageously, the return line can, for example, discharge excess compressed natural gas between the second compression unit and the consumption unit of the floating structure at the branch point of the injection branch used for injecting the fluid that mainly contains methane.

[0064] In particular, according to the invention, the liquefied natural gas can be directly sourced from the tank so as to supply the liquefied natural gas to a third heat exchanger, which performs heat exchange between the compressed excess natural gas from the return line and the liquefied natural gas.

[0065] Additionally, liquefied natural gas can originate from a second heat exchanger, allowing the liquefied natural gas from the tank to flow sequentially through the second heat exchanger and then through a third heat exchanger, where the liquefied natural gas exchanges heat with compressed excess natural gas.

[0066] The present invention also proposes a floating structure comprising at least one tank for transporting or storing liquefied natural gas, the floating structure comprising at least one consumption unit that consumes natural gas as fuel and at least one processing system as described above, the at least one consumption unit being configured to be fueled by gaseous natural gas circulating at least partially in the processing system.

[0067] The present invention also relates to a system for loading or unloading liquefied natural gas, the system combining at least one onshore device and at least one floating structure for transporting liquefied natural gas, as described above.

[0068] According to the invention, the at least one onshore device includes a pipeline and a pump, the pipeline being arranged to connect a tank mounted in the hull of a floating structure to a floating or onshore storage device, and the pump being used to drive a flow of liquefied natural gas through the pipeline from the floating or onshore storage device to the tank of the floating structure or from the tank of the floating structure to the floating or onshore storage device.

[0069] The present invention also relates to a method for loading or unloading liquefied natural gas into or from a floating structure tank, wherein cold liquid products, particularly natural gas, are transported via pipeline from a floating or onshore storage facility to or from a floating structure tank to a floating or onshore storage facility.

[0070] Finally, the present invention relates to a method for adjusting the composition of a refrigerant flowing in a refrigerant circuit of a floating structure processing system as described above, the method comprising at least:

[0071] - The step of compressing the refrigerant in the first compression unit;

[0072] - The steps of determining the temperature of the refrigerant by means of a temperature detector in the control system and / or measuring the composition of the refrigerant by means of a composition detector in the control system;

[0073] - The steps of comparing a determined temperature relative to at least one threshold and / or comparing the composition of the refrigerant with at least one reference component;

[0074] - A step of sampling a portion of the refrigerant flowing in the main branch, wherein the portion of refrigerant is supplied to the sampling branch of the refrigerant circuit by at least a partial opening of the refrigerant flow rate regulating member;

[0075] - At least the step of separating the gaseous and liquid portions of the refrigerant flowing in the sampling branch by a phase separator;

[0076] - The steps of discharging and / or burning at least a portion of the gaseous portion of the refrigerant from the treatment system, and / or injecting at least a portion of the gaseous portion into the supply line.

[0077] - The step of returning at least a portion of the refrigerant to the main branch;

[0078] - A step of adjusting the composition of the refrigerant flowing in the refrigerant circuit by injecting a fluid that mainly contains methane.

[0079] Advantageously, the step of sampling the portion of the refrigerant may include the steps of calculating and controlling the mass flow rate of the refrigerant in the sampling branch.

[0080] According to the present invention, the injection of a fluid mainly containing methane is carried out through the at least one injection branch.

[0081] According to the invention, a method for adjusting the composition of a refrigerant includes a first sub-step between a step of sampling the portion of the refrigerant and a step of adjusting the composition of the refrigerant, the first sub-step determining the proportion of gaseous methane in the portion of the refrigerant flowing in the sampling branch and advantageously in a secondary branch of the processing system according to the invention.

[0082] According to the invention, the adjustment method includes a second sub-step following the first sub-step, which determines the amount of the main methane-containing fluid to be injected into the refrigerant flowing in the refrigerant circuit based on the proportion of gaseous methane measured in the sampling branch, for example, in a secondary branch.

[0083] Specifically, when the injection of a fluid primarily containing methane is carried out via the first injection branch and the fluid primarily containing methane is obtained from the supply line, the method for adjusting the refrigerant composition includes a sub-step prior to the second sub-step, which analyzes the composition of the gaseous natural gas from the tank to determine the proportion of the fluid primarily containing methane therein.

[0084] Specifically, the proportion of methane contained in gaseous natural gas can be measured between the output of the second compression unit and the consumption unit.

[0085] It is worth noting that the step of adjusting the refrigerant composition by injecting a fluid that mainly contains methane may include the step of calculating and controlling the mass flow rate of gaseous natural gas in the at least one injection branch. Attached Figure Description

[0086] Other features, details, and advantages of the invention will become more apparent, on the one hand, from the following description, and on the other hand, from several exemplary embodiments given in an indicative and non-limiting manner with reference to the accompanying drawings, in which:

[0087] Figure 1 A schematic diagram illustrates a processing system for liquefied natural gas stored in tanks in a floating structure for transporting or storing the natural gas, the system being configured to supply natural gas from the tanks as fuel to at least one consumption unit;

[0088] Figure 2 Indicates the first operating mode Figure 1 The natural gas processing system shown;

[0089] Figure 3 show when Figure 1 The natural gas processing system shown is a natural gas processing system when a method for adjusting the composition of the refrigerant flowing in the processing system is implemented.

[0090] Figure 4 yes Figure 3 A flowchart of the adjustment methods implemented in the process;

[0091] Figure 5 Implementation shown Figure 1 The natural gas processing system shown is in standby operating mode.

[0092] Figure 6 Indicates the second operating mode Figure 1 The natural gas processing system shown;

[0093] Figure 7 It is a schematic cross-sectional view of a floating tank and a dock for loading and / or unloading the tank. Detailed Implementation

[0094] Figure 1 A processing system 1 is shown for natural gas stored in at least one tank 3 of a floating natural gas transport and / or storage structure, the natural gas being used as fuel for at least one consumption unit 2 of the floating structure. The processing system 1 is configured to cooperate with the at least one consumption unit 2 and the tank 3 of the floating structure, the tank 3 being designed to store natural gas in liquefied form, and the processing system 1 thus ensuring the supply of natural gas from the tank 3 to the consumption unit 2. As an example, the at least one consumption unit may be a DFDE (dual-fuel diesel-electric) type generator, that is, a gas consumption unit configured to ensure the electrical supply to the floating structure, or a ship's propulsion engine, such as a ME-GI or XDF engine. It should be understood that this is merely an exemplary embodiment of the invention, and different gas consumption units may be provided for the apparatus without departing from the scope of the invention.

[0095] For this purpose, the processing system 1 includes at least one refrigerant circuit 4 and at least one fuel supply circuit 5 for the consumption unit 2. The refrigerant circuit 4 is a closed loop in which a refrigerant comprising at least nitrogen and methane flows. Furthermore, the refrigerant may include at least one hydrocarbon selected from ethane, ethylene, propane, propylene, and / or butane. The initial composition of the refrigerant is particularly suited to optimizing the efficiency of at least one cryogenic heat exchange between the refrigerant and liquid and / or gaseous natural gas, which may, for example, originate from tank 3.

[0096] The refrigerant circuit 4 includes at least one compression device referred to as the first compression device 41, a first heat exchanger 42, an expansion device 43 (e.g., a Joule-Thomson valve) and a second heat exchanger 44.

[0097] The processing system 1, particularly the fuel supply circuit 5, is used on the one hand to heat the gaseous natural gas from the tank 3, and on the other hand to increase its pressure so as to set the natural gas at pressure and temperature conditions compatible with the requirements of the consumption unit 2.

[0098] Furthermore, the processing system 1 may include at least one natural gas condensation unit 6 and / or subcooling unit 7, which may be used independently or in combination with each other. Depending on the requirements of the consuming unit 2 for gaseous natural gas, they ensure that at least a portion of the natural gas drawn from the tank 3 is processed to accordingly ensure the condensation of the gaseous natural gas or the subcooling of the liquefied natural gas. These various loops and devices 5, 6, 7, and their operating modes in the processing system 1, will be described in more detail below.

[0099] The processing system 1 according to the invention includes a control system 9 for controlling the composition of the refrigerant flowing in the refrigerant circuit 4. The control system 9 is configured to control and adjust the composition of the refrigerant as needed. Therefore, the control system 9 aims to optimize the efficiency of the processing system 1 by correcting the composition of the refrigerant, for example, returning it to the initial composition, when the composition of the refrigerant has changed relative to the initial composition.

[0100] Furthermore, the processing system 1 may include at least one backup system configured to ensure the supply of natural gas as fuel to the consumption unit 2 via an alternative loop 8, which is at least partially included in the supply loop 5. These systems will be described in further detail below.

[0101] Throughout the instruction manual, the terms "upstream," "downstream," "input," and "output" refer to the direction of refrigerant flow S1 in refrigerant circuit 4.

[0102] Within the processing system 1, the refrigerant circuit 4 includes a unit capable of transferring thermal energy at a low temperature close to the storage temperature at which natural gas is liquefied. It is noteworthy that, in this invention, the liquefied natural gas primarily comprises methane and has a state change temperature of approximately -163°C from gaseous to liquid state.

[0103] like Figure 1 and 2 As shown, the refrigerant circuit 4 includes at least one main branch 410 consisting of a first portion 411 and a second portion 412. The first portion 411 of the refrigerant circuit 4 extends between the output of the first compression device 41 and the input of the expansion device 43 in the refrigerant flow direction S1 of the refrigerant circuit 4. In the first portion 411 of the main branch 410, the refrigerant is subjected to a high pressure, which may be, for example, in the range of 18 bar to 36 bar. The second portion 412 of the refrigerant circuit 4 is included between the output of the expansion device 43 and the input of the first compression device 41. In the second portion 412, the refrigerant is subjected to a low pressure, which is lower than the high pressure observed in the first portion 411, and this low pressure may be on the order of 1.2 to 2.5 bar.

[0104] Therefore, in the refrigerant circuit 4, the refrigerant is first compressed by the first compression device 41 and then flows along the first portion 411 of the main branch 410 to the first channel 421 of the first heat exchanger 42. Specifically, in this invention, the first compression device 41 of the refrigerant circuit 4 includes at least one body within which a shaft supported by at least one nitrogen-sealed rotary bearing extends. The implementation of this rotary bearing is accompanied by leakage of sealing gas into the refrigerant, resulting in nitrogen contamination of the refrigerant and alteration of its initial composition. Therefore, the primary objective of this invention is to correct this alteration.

[0105] In addition, the first compression device 41 includes at least one second airtight rotary bearing, which may use nitrogen or a refrigerant as the sealing gas, for example.

[0106] As shown in the figure, the first heat exchanger 42 can be configured to operate at least partially as an internal heat exchanger that facilitates heat exchange between a so-called high-pressure first portion 411 and a so-called low-pressure second portion 412 of the refrigerant circuit 4. It includes at least three channels: a first channel 421, a second channel 422, and a third channel 423 of the first heat exchanger 42. A first input 4225 and a first output 4226 define the third channel 423 of the first heat exchanger 42. A second input 4221 and a second output 4224 define the first channel 421. A third input 4223 and a third output 4222 define the second channel 422.

[0107] Because of the temperature difference between the first portion 411 and the second portion 412, the internal heat exchanger facilitates heat exchange between the refrigerant flowing in the first portion 411 of the refrigerant circuit 4 (more specifically in the first channel 421 of the first heat exchanger 42) and the cooler refrigerant flowing in the second portion 412 of the circuit (more specifically in the second channel 422 of the first heat exchanger 42). In the example shown, the internal heat exchanger allows: on the one hand, the refrigerant flowing in the second channel 422 of the first heat exchanger 42 is heated upstream of the first compressor 41, such that the refrigerant is substantially in gaseous form when reintroduced into the input of the first compressor 41; on the other hand, the refrigerant flowing in the first channel 421 is cooled upstream of the expansion device 43 to reduce the pressure applied by the expansion device 43. The overall efficiency of the refrigerant circuit 4 is thus improved by the presence of this internal heat exchanger.

[0108] The cooled refrigerant leaving the first channel 421 of the first heat exchanger 42 is then carried to the input of the expansion device 43, where it is expanded and reduced to a low pressure. The expanded refrigerant has a temperature on the order of -168°C to -180°C, and then flows along the second portion 412 of the refrigerant circuit 4 to the first input 4411 of the first channel 441 of the second heat exchanger 44.

[0109] In the example shown, the second heat exchanger 44 facilitates heat exchange between the refrigerant flowing in the first channel 441 of the second heat exchanger 44 and the liquefied natural gas flowing through the second channel 442 of the second heat exchanger 44, which is included in the natural gas subcooling device 7. Since the temperature of the liquefied natural gas is higher than that of the refrigerant, for example, around -160°C, it releases heat to the refrigerant and thus becomes colder. The refrigerant rises to a temperature of, for example, -162°C in the first outlet 4412 of the first channel 441 of the second heat exchanger 44, while the liquefied natural gas is cooled, or even subcooled, to a temperature of -172°C.

[0110] The refrigerant then flows to the second channel 422 of the first heat exchanger 42, where, as previously described, the refrigerant absorbs the heat released by the refrigerant flowing in the first channel 421 of the first heat exchanger 42.

[0111] Furthermore, the first heat exchanger 42 is configured to achieve heat exchange between the refrigerant and the gaseous natural gas from the tank 3. Therefore, the refrigerant flowing in the second channel 422 of the first heat exchanger 42 releases heat to the cooler gaseous natural gas flowing in the third channel 423 of the first heat exchanger 42, which is included in the fuel supply circuit 5 of the consumption unit 2.

[0112] The refrigerant leaving the first heat exchanger 42 is essentially gaseous and therefore has a temperature of about -30 to 45°C, and is sent to the first compression unit 41. Advantageously, the refrigerant circuit 4 may include at least one accumulator 46 arranged between the third output 4222 of the first heat exchanger 42 and the input of the first compression unit 41, configured to form an accumulation zone for both liquid and gaseous refrigerant, and only supplying gaseous refrigerant to the first compression unit 41.

[0113] In the natural gas processing system 1, the fuel supply loop 5, the subcooling device 7, and the condensation device 6 are configured to ensure the processing of at least a portion of the natural gas taken from the tank 3 in liquid and / or gaseous form. The implementation of these different loops and devices depends on the fuel demand of the floating structure consumption unit 2, that is, the demand for gaseous natural gas.

[0114] As previously described, the processing system 1 is also configured to detect changes in the refrigerant composition and remedy such changes by implementing methods for adjusting the refrigerant composition.

[0115] Therefore, the control system 9 of the processing system 1 may include at least a temperature detector 91 and / or a refrigerant composition detector 92.

[0116] Temperature detector 91 can be arranged on the main branch 410 of refrigerant circuit 4, particularly in the second part 412 of main branch 42. In the case shown in the figure, temperature detector 91 is located between the output of expansion device 43 and the first input 4411 of second heat exchanger 44, but this only represents an exemplary embodiment, as it is important that temperature detector 91 is located downstream of expansion device 43.

[0117] Component detector 92 is located, for example, in the first portion 411 of the main branch 410 to sample the refrigerant to be analyzed after its compression phase. In the case shown in the figure, component detector 92 is located between the output of the first compression unit 41 and the second input 4221 of the first heat exchanger 42. For example, component detector 92 may include a chromatograph.

[0118] Alternatively, the refrigerant composition detector 92' can be arranged in the storage device 46 of the refrigerant circuit 4. Advantageously, as shown, the processing system 1 can include multiple refrigerant composition detectors 92, 92'.

[0119] The control system also includes at least one analysis unit 93, such as a computer, configured to receive measurements of the temperature and / or composition of the refrigerant and compare them, respectively, with at least one temperature threshold and / or at least one reference component.

[0120] To ensure the adjustment of the refrigerant composition, the processing system 1 includes at least one sampling branch 120 that samples a portion of the refrigerant flowing in the main branch 410.

[0121] More specifically, sampling branch 120 is connected at a bifurcation point 121 to the first portion 411 of main branch 410, which is arranged between the second output 4224 of the first heat exchanger 42 and the input of the expansion device 43, in order to extract refrigerant leaving the first heat exchanger 42, which is essentially a liquid, and flows at high pressure in the first portion 411 of the refrigerant circuit 4.

[0122] The sampling branch 120 includes at least one phase separator 12, which is thus arranged in parallel with an expansion device 43 that defines a first portion 411 relative to a second portion 412 of the refrigerant circuit 4. In this way, only a portion of the refrigerant flowing in the circuit 4 is fed to the phase separator 12 via the branch 120. The phase separator 12 is configured to separate the portion of refrigerant extracted by the sampling branch 120 into a hydrocarbon-rich liquid portion and a nitrogen-rich gaseous portion by gravity.

[0123] The processing system 1 includes at least one primary branch 130 and one secondary branch 140. The primary branch 130 is connected to the lower vertical portion of the phase separator 12 and to the main branch 410 at a junction 131, which is located between the output of the expansion device 43 and the first input 4411 of the second heat exchanger 44. Thus, the primary branch 130 collects the liquid portion of the refrigerant section and returns it to the main branch 410, entering the low-pressure second portion 412 of the refrigerant circuit 4.

[0124] Conversely, the secondary branch 140 is connected to the higher vertical portion of the phase separator 12 to collect the gaseous portion of the refrigerant. This gaseous portion can then be discharged from and / or burned off from the processing system 1, and / or injected at another point in the processing system 1.

[0125] The sampling branch 120 includes at least one refrigerant flow rate regulating member 125 arranged between the bifurcation point 121 and the phase separator 12, the flow of the refrigerant portion depending on the refrigerant flow rate regulating member 125.

[0126] Similarly, primary branch 130 may include a primary refrigerant flow rate regulating device 135 between phase separator 12 and junction 131. The same applies to secondary branch 140, which may include at least one secondary refrigerant flow rate regulating device 145.

[0127] In the processing system 1 according to the invention, the control system 9 is configured to control the opening of at least a portion of at least a refrigerant flow rate regulating member 125 included in the sampling branch 120, in order to control the sampling of the refrigerant portion to be separated. This control is schematically shown here by dashed line 901. Figure 3 As can be seen in the diagram. Advantageously, the control system 9 can also be configured to regulate at least partial opening of the primary flow rate regulator 135 and / or the secondary flow rate regulator 145, these controls being schematically shown by lines 902 and 903 respectively. Figure 3 This can also be seen in the text.

[0128] The processing system 1 also includes at least one injection branch 160 for injecting a fluid primarily containing methane. This injection branch 160 is connected at an injection point 161 to a main branch 410 of the refrigerant circuit 4, which is located between the first output 4412 of the second heat exchanger 44 and the input of the first compression unit 41. The proportion of methane in the primarily methane-containing fluid can be between 70% molar and 100% molar.

[0129] It is worth noting that the injection point 161 can be arranged at the storage device 46, or, according to an alternative not shown, on the main branch 410, for example, between the first output 4412 of the second heat exchanger 44 and the input of the first compression device 41. The injection branch 160 includes at least one flow rate regulating device 165 for regulating the flow rate of the fluid primarily containing methane, which is controlled by the control system 9. Figure 3 The middle line is shown by lines 904 and 905.

[0130] Figures 2 to 5 Different operating modes of the processing system 1 are shown, which can be implemented according to the requirements of the floating structure. (Refer to...) Figure 1 The processing system 1 shown describes these different operating modes.

[0131] In these diagrams, solid lines represent lines or branches of the heat treatment system 1 in which refrigerant or natural gas flows, while thick dashed lines represent lines or branches of the heat treatment system 1 in which neither refrigerant nor natural gas flows. As previously mentioned, the transmission of various measurements to the control system 9 and the control system's control over various components of the treatment system 1 are also schematically represented by thin dashed lines. Components, devices, or apparatuses used to regulate the flow rate of at least one fluid are shown as solid when they impede the flow of the relevant fluid and hollow when they allow the flow of said fluid.

[0132] Figure 2 A first operating mode of the processing system 1 is shown, in which the processing system 1 participates in supplying at least gaseous natural gas from the top of tank 3 to the consumption unit 2. This operating mode can be implemented when the demand of the consumption unit 2 in the floating structure is substantially equal to the amount of BOG naturally generated within tank 3. It is worth noting that when the first operating mode is implemented, the flow of refrigerant in loop 4 is restricted to the main branch 410, and the refrigerant route is the same as the route explained above.

[0133] In processing system 1, gaseous natural gas is obtained at a temperature ranging from -140°C to -90°C from a supply line 51 included in the fuel supply loop 5 of processing system 1. This supply line 51 leads to the top of tank 3 and connects tank 3 to consumption unit 2. The supply line 51 carries the gaseous natural gas to the first input 4225 of the first heat exchanger 42, and then into the third channel 423 of the first heat exchanger 42, where, as previously described, the gaseous natural gas absorbs heat from the refrigerant flowing in the second channel 422 of the first heat exchanger 42. Therefore, the first heat exchanger 42 serves at least partially as a superheater for the gaseous natural gas.

[0134] The heated gaseous natural gas leaves the first heat exchanger 42 at a temperature between -30°C and 45°C and is carried to the second compression unit 11 of the processing system 1. This second compression unit 11 is different from the first compression unit 41 included in the refrigerant circuit 4, in which the natural gas is compressed. The properly compressed natural gas leaves the second compression unit 11 at a temperature of approximately 43°C and is subjected to a pressure of less than or equal to 13 bar.

[0135] According to one possibility provided by the invention, the second compression device 11 includes at least one first nitrogen-sealed rotary bearing. Furthermore, the second compression device 11 may include a second gas-sealed rotary bearing, for example, sealed for gaseous natural gas or a gas primarily comprising nitrogen and methane. The second compression device 11 may also be an oil-lubricated compressor.

[0136] As an example, the second compression device 11 may have a compression ratio of at least 13 ± 20% and a throughput of 5000 m3 / h ± 10%.

[0137] Gaseous compressed natural gas is compatible with the use of consumption unit 2 as fuel, and can then be sent to the floating structure consumption unit 2 at least through the supply line 51 of supply loop 5.

[0138] Similarly, the processing system 1 shown in the figure includes at least one sampling conduit 71 configured to sample liquefied natural gas, which, depending on its composition, may have a temperature of -159°C or lower, in order to bring it to a second heat exchanger 44, specifically to the second input 4415 of the second heat exchanger 44. The sampling conduit 71 is at least partially submerged for sampling the liquefied natural gas and may include a pump 711, such as a submersion pump. Sampling of the liquefied natural gas can be controlled by at least one sampling valve 712 disposed on the sampling conduit 71 and arranged upstream of the second heat exchanger 44.

[0139] Advantageously, the heat exchange implemented in the second heat exchanger 44 ensures that at least a portion of the liquefied natural gas removed from the tank 3 is subcooled. In this mode of operation, the processing system 1 thus simultaneously implements the supply circuit 5 of the at least one consumption unit 2, the refrigerant circuit 4, and the subcooling device 7 including the second heat exchanger 44, which is configured to cool the liquefied natural gas to a temperature below -168°C.

[0140] The subcooled liquefied natural gas exiting the second heat exchanger 44 at the second outlet 4414 of the second heat exchanger 44 can then be sent directly to the lower part of the tank 3 via at least one return conduit 72 including at least one return valve 721 to form a storage layer of subcooled liquefied natural gas 31, which can then be reused.

[0141] Alternatively, see below. Figure 6 As further explained, the supercooled liquefied natural gas can be fed to a third heat exchanger 61 included in the condensation unit 6 of the processing system 1.

[0142] Figure 3 Showing similarities to the previous reference Figure 1 and 2 The processing system 1 is described. However, unlike it, it also implements, as... Figure 4 The method shown is for adjusting the composition of the refrigerant flowing in refrigerant circuit 4.

[0143] As previously mentioned, when the refrigerant is compressed in the first compression unit 41, nitrogen from the first rotating bearing contaminates the refrigerant. This leakage into the refrigerant alters its composition and causes a change in its state temperature, which, over time, renders it unsuitable for heat exchange with liquid and / or gaseous natural gas.

[0144] Therefore, the processing system 1 according to the invention is configured to detect such changes in the refrigerant composition and then remedy them by adjusting the composition of the refrigerant.

[0145] Therefore, as Figure 3 and Figure 4 As shown, when implementing the method for adjusting the composition of the refrigerant flowing in loop 4, the processing system 1 performs a measurement step 1000 to measure the refrigerant temperature and / or a measurement step 2000 to measure the composition of the refrigerant. As previously mentioned, the measurement of the refrigerant temperature 1000 is performed by a temperature detector 91, which transmits the measurement or determination to the analysis unit 93, the transmission of which is indicated here by the dashed line 1001.

[0146] Analysis unit 93 ensures a comparison step 1100 between the measured temperature and at least one threshold or reference range. If the measured temperature does not differ from the threshold or reference range, the method of adjusting the refrigerant composition is stopped, and then a new temperature measurement step 1000 can be subsequently performed.

[0147] Conversely, if the measured temperature differs from a threshold or a reference range, the control system 9 performs a sampling step 1200 to sample a portion of the refrigerant flowing between the second output 4224 of the first heat exchanger 42 and the input of the expansion device 43 of the refrigerant circuit 4. This refrigerant is substantially liquid and under high pressure. The control system 9 commands at least a partial opening of the refrigerant flow rate regulating member 125 on the sampling branch 120, and a portion of the refrigerant is sent through the sampling branch 120 to the phase separator 12, while the remaining refrigerant continues to flow on the main branch 410.

[0148] Similarly, component detector 92 performs component measurement step 2000 and ensures its transmission to the analysis unit, which is indicated here by dashed line 2001. Alternatively or additionally, component measurement step 2000 can be implemented by component detector 92' arranged in accumulation device 46, which transmits the measurement to analysis unit 93, indicated here by dashed line 2001'.

[0149] As previously described, the analysis unit 93 ensures step 1100, which compares the measured component with at least one reference component or reference component range. If the measured component is no different from the reference component or reference component range, the adjustment method stops, and a new component measurement step 2000 can then be performed. Conversely, if the measured component differs from the reference component or the reference component range, the control system 9 performs sampling step 1200 as previously described.

[0150] For example, sampling step 1200 can be performed when the measured composition of the refrigerant shows that the proportion of nitrogen is increased by at least 5% relative to a reference proportion of nitrogen included in the initial composition of the refrigerant.

[0151] Then, the method for adjusting the refrigerant composition includes a separation step 1300 of the refrigerant portion flowing on the sampling branch 120, wherein the refrigerant portion is evaporated upon entering the phase separator 12 to be separated into a nitrogen-rich gaseous portion and a hydrocarbon-rich liquid portion.

[0152] Following the refrigerant separation step 1300, the liquid portion of the refrigerant is returned to the main branch 410 via the third branch 130 in step 1400. This return occurs downstream of the expansion device 43, in the so-called low-pressure second section 412 of the main branch 410, along the refrigerant flow direction S1 in the loop 4. Specifically, this return occurs between the output of the expansion device 43 and the first input 4411 of the second heat exchanger 44, in which the liquid portion from the phase separator 12 combines with the expanded refrigerant flowing in the main branch 410.

[0153] As previously stated, the return of the liquid portion of the refrigerant to the main branch 410 is controlled by the control system 9, which regulates (shown here by dashed line 903) at least partially opening the primary flow rate regulating device 135.

[0154] Furthermore, as described above, after the separation step 1300, there may be steps of discharging 1450 from the processing system 1 and / or burning 1450 and / or injecting the gaseous portion of the refrigerant into the supply line 51 of the supply circuit 5. This step 1450 may be performed before, after, or simultaneously with step 1400, when the liquid portion of the refrigerant returns to the main branch 410, as shown in the figure.

[0155] As previously stated, the flow of the gaseous portion to the secondary branch 140 is controlled by the control system 9, as shown by the dashed line 902. The control system 9 adjusts at least a partial opening of the secondary flow rate regulating device 145.

[0156] In the illustrated example, secondary branch 140 allows a portion of the nitrogen-rich gas portion to be discharged from and / or burned from the treatment system 1, while a third branch 150 of the treatment system 1 connected to secondary branch 140 allows the remaining portion of the gaseous portion to be injected at different points in the supply loop 5.

[0157] In summary, after the refrigerant separation step 1300, based on the need to eliminate nitrogen present in the refrigerant, the secondary flow rate regulating device 145 controls a portion of the nitrogen-rich vapor to return to the discharge and / or supply loop 5. The liquid portion, and possibly a portion of the vapor, returns to the junction 131.

[0158] The third branch 150 extends between the bypass point 151 and the connection point 152, with the bypass point 151 located on the secondary branch 140 and the connection point 152 located on the gaseous natural gas supply line 51, between the output of tank 3 and the first input 4225 of the first heat exchanger 42, to inject a nitrogen-rich gaseous portion into the gaseous natural gas. The resulting gas mixture is then sent to the first heat exchanger 42, where it is heated and consumed by the consumption unit 2. Advantageously, a secondary refrigerant flow rate regulating device 145 can be arranged between the branch point 121 and the bypass point 151.

[0159] Therefore, step 1450 allows for a reduction in the proportion of nitrogen in the refrigerant circulating in loop 4. Since the gaseous portion of the refrigerant section may contain up to 20% methane, step 1450 is also accompanied by the discharge and / or combustion and / or injection of a non-negligible amount of methane initially contained in the refrigerant into the supply line 51 from the processing system.

[0160] To compensate for this loss, the method for adjusting the refrigerant composition according to the invention includes step 1500 of injecting a fluid mainly comprising methane at injection point 161. The injected fluid mainly comprising methane may obviously originate from storage tank 17 and / or from supply circuit 5 of processing system 1, that is, from gaseous natural gas from the tank.

[0161] To ensure that an appropriate amount of the fluid primarily containing methane is injected, the method for adjusting the refrigerant composition includes a first sub-step 1410 between the sampling step 1200 of the refrigerant section and the injection step 1500 of the fluid primarily containing methane, which determines the proportion of gaseous methane in the refrigerant section flowing in the secondary branch 140.

[0162] As an example, the processing system 1 may include at least one sensor 126 arranged on the secondary branch 140 and configured to measure the ratio and transmit the ratio to the analysis unit 93. This transmission is represented here by line 906.

[0163] Specifically, as shown in the figure, the first sub-step 1410 can be performed after returning to step 1400 and / or step 1450. Alternatively, the first sub-step 1410 can be performed before, simultaneously with, or after the refrigerant separation step 1300.

[0164] The adjustment method includes a second sub-step 1420 following the first sub-step 1410, which determines the amount of the main methane-containing fluid to be injected into the refrigerant flowing in the refrigerant circuit based on the proportion of gaseous methane measured in the secondary branch 140. This sub-step 1420 is specifically implemented by an analysis unit 93, which calculates the proportion of the main methane-containing fluid to be injected.

[0165] Therefore, step 1500, which involves injecting a fluid that primarily comprises methane, allows for the adjustment of the refrigerant's composition to obtain a suitable composition, such as one that is close to or similar to the initial composition of the refrigerant or even one of the reference compositions.

[0166] Therefore, as shown in the figure, the processing system 1 may include multiple injection branches 160. A first injection branch 1601 may extend between a branch point 162 and an injection point 161. Advantageously, the branch point 162 is arranged on the supply line 51 for supplying gaseous natural gas, located between the second compression unit 11 and the floating structure consumption unit 2, to obtain compressed gaseous natural gas under high pressure and rich in a fluid primarily containing methane, and inject it into the refrigerant circuit 4. For example, this gaseous natural gas may contain approximately 89% methane.

[0167] The diversion of the compressed natural gas in the supply circuit 5 and its injection into the refrigerant circuit 4 depends on at least partial opening of the flow rate regulating device 165, which is used by the control system 9 to regulate the flow rate of the fluid mainly containing methane, hereinafter referred to as the first flow rate regulating device 1651, schematically represented by the dashed line 904. Thus, the gaseous natural gas obtained at the output of the second compression unit 11 is subjected to high pressure and advantageously delivered to the second portion 412 of the main branch 410 of the refrigerant circuit 4, where the refrigerant is subjected to low pressure.

[0168] The second injection branch 1602 is supplied with a fluid primarily containing methane by at least a pressurized storage cylinder 17. The injection of the fluid primarily containing methane into the refrigerant circuit 4 depends on at least partial opening of a second flow rate regulating device 1652, which is used to regulate the flow rate of the fluid primarily containing methane via a control system 9, schematically represented by dashed line 905.

[0169] According to an alternative not shown, the processing system 1 may include a single injection branch 160 configured to be supplied at least by the storage cylinder 17 and / or extend between the injection point 161 and the branch point 162.

[0170] Furthermore, it should be understood that while the processing system 1 shown may include multiple injection branches 160, it may also include only one of injection branches 1651 or 1652. Injection branch 165 may be supplied with a fluid mainly containing methane by the storage cylinder 17, or injection branch 165 may extend between injection point 161 and branch point 162.

[0171] Therefore, when the processing system includes only the injection branch 1601, it is advantageous to utilize the main methane-containing fluid resources on the floating structure by obtaining gaseous natural gas from the supply line 51, and there is no need to equip the processing system 1 with any storage cylinder 17.

[0172] It should be noted that when the injection of a fluid primarily containing methane is performed via the first injection branch 1601, i.e., when the fluid primarily containing methane originates from gaseous natural gas flowing in supply line 51, the method for adjusting the refrigerant composition includes an additional sub-step 1430 prior to the second sub-step 1420, which analyzes the composition of the gaseous natural gas from tank 3 to determine the proportion of methane therein. Specifically, this analysis sub-step 1430 is performed between the sampling step 1200 of the refrigerant section and the injection step 1500 of the fluid primarily containing methane, and may be performed after the first sub-step 1410, or, as shown, simultaneously with the first sub-step 1410.

[0173] As an example, the processing system 1 may include at least one composition sensor 94, which is arranged on the supply line 51 and configured to measure the ratio and transmit the ratio to the analysis unit 93. This transmission is indicated here by the dashed line 907. This measurement is then considered during a second sub-step 1420, which determines the amount of the predominantly methane-containing fluid to be injected, for example, by combining it with a calculation step of the mass flow rate of gaseous natural gas to be implemented in the first injection branch 1601. In the example shown, the composition sensor 94 is arranged between the output of the second compression unit 11 and the consumption unit 2, but it could be arranged at any point on the supply line 51, including the output of the tank 3 and the input of the consumption unit 2.

[0174] Figure 5 This indicates an alternative operating mode for the backup system of the supply loop 5 of the processing system 1. The backup system includes redundant compression units 11 and 41, which supply at least one consumption unit 2 of the floating structure via the alternative loop 8 to avoid interruption of the supply to the consumption unit 2, even in the event of a failure of the second compression unit 11.

[0175] In fact, in the processing system 1 according to the invention, the first compression device 41 included in the refrigerant circuit 4 is configured to also compress gaseous natural gas flowing in the fuel supply circuit 5 and to supply gaseous natural gas as fuel to the consumption unit 2. The first compression device 41 needs to be able to compress natural gas from atmospheric pressure to a pressure of approximately 13 bar. For example, in order to be able to compress natural gas or refrigerant, the first compression device 41 preferably has a compression ratio of at least 13 ± 20% and a throughput of 5000 m³ / h ± 10%.

[0176] As mentioned above, the result of this structure is that the first compression device 41 can be substantially similar to the second compression device 11, that is, they can have similar compression ratios and / or throughputs and / or at least one identical sealed rotary bearing.

[0177] To allow the use of the first compressor 41 in the refrigerant circuit 4 or the fuel supply circuit 5, the alternative circuit 8 of the backup system includes at least one alternative line 81 that ensures bypass of the second compressor 11. The alternative line 81 includes the first compressor 41 and extends between a first point 811 and a second point 812 on the supply line 51 of the system, which includes the supply circuit 5. The first point 811 is located between the first output 4226 of the first heat exchanger 42 and the second compressor 11, while the second point 812 is located between the output of the second compressor 11 and the consumption unit 2.

[0178] To implement the standby mode, similar to the second compressor unit 11, at least one isolation valve 82 is provided before and / or after the first compressor unit 41 for directing the flow of gaseous natural gas and / or refrigerant. Specifically, at least one primary isolation valve 821 may be arranged on an alternative line 81 upstream and / or downstream of the first compressor unit 41, while at least one secondary isolation valve 822 may be arranged on a supply line 51 upstream and / or downstream of the second compressor unit 11.

[0179] In addition, the refrigerant circuit 4 may include at least one shut-off valve 45, which is arranged on the main branch 410 upstream and / or downstream of the first compression unit 41 along the refrigerant flow direction S1 in the circuit 4.

[0180] Therefore, by default, that is, in the reference above... Figure 2 In the explained operating mode, the second compression unit 11 is operable and used in the fuel supply circuit 5 to supply gaseous natural gas to the consumption unit 2. The primary isolation valve 821 is closed, and the shut-off valve 45 and the secondary isolation valve 822 are open to isolate the first compression unit 41 from the natural gas flow in the supply circuit 5 and to use it in the refrigerant circuit 4 to compress refrigerant.

[0181] Conversely, such as Figure 5 As shown, when the second compression unit 11 fails and the backup system is implemented, at least the second isolation valve 822 and the shut-off valve 45 are closed, while the first isolation valve 821 is open. Natural gas leaving the third channel 423 of the first heat exchanger 42 thus flows in the replacement loop 8, is drawn into the first compression unit 41, and then returns to the supply line 51 of the supply loop 5 to supply the consumption unit 2.

[0182] Figure 6 As shown in the previous reference Figure 1 and 2 The second operating mode of the processing system 1, as explained above, includes the implementation of the condensation device 6. It should be understood that when the processing system 1 operates according to the second operating mode of the present invention, as previously referred to... Figure 3 and Figure 4 The method for adjusting the refrigerant composition described above can also be implemented.

[0183] When excess BOG is generated relative to the demand of consumption unit 2, a second operating mode can be used. In this case, a portion of the gaseous natural gas that has been fed into fuel supply loop 5 but not used by consumption unit 2 of the floating structure is removed and sent to condensation unit 6 to liquefy it, and then returned to tank 3. The return line 62 of processing system 1 removes a portion of the natural gas from the supply line 51 of supply loop 5 between the output of second compression unit 11 and consumption unit 2.

[0184] As shown in the figure, the return line 62 can be connected to the fuel supply circuit 5 at the branch point 162. Alternatively, the return line can be connected to the supply circuit at a point other than the branch point 162 included between the second compression unit 11 and the consumption unit.

[0185] The temperature of the portion of natural gas that is extracted, compressed, and subjected to high pressure (e.g., less than or equal to 13 bar) is between 20°C and 45°C. Hereinafter, it will be referred to as compressed excess natural gas or excess natural gas. Advantageously, the diversion of compressed excess natural gas can be selective and can be controlled, for example, by a diversion valve 621 located on the return line 62.

[0186] In the condensation unit 6, the compressed excess natural gas is sent to the third heat exchanger 61, where it flows through the first channel 611 and releases heat to the liquefied natural gas flowing through the second channel 612 of the third heat exchanger 61. Advantageously, as shown, this liquefied natural gas can originate from the second heat exchanger 44, that is, it can be subcooled in the second heat exchanger 44 before entering the second channel 612 of the third heat exchanger 61, in order to optimize the condensation of the compressed excess natural gas.

[0187] According to an alternative not shown, liquefied natural gas can be obtained directly from tank 3.

[0188] At the output of the third heat exchanger 61, the temperature of the excess natural gas being cooled and condensed is between -152°C and -160°C. Liquid natural gas flowing in the second channel 612 of the third heat exchanger 61 and condensed natural gas from the first channel 611 of the same third heat exchanger 61 are sent to tank 3 via at least one common return conduit 63. Advantageously, the return conduit 63 may include at least one valve 631.

[0189] at last, Figure 7 This is a cross-sectional view of the floating structure 100, showing a natural gas storage tank 3 installed in a double shell of the floating structure 100. The double shell is formed by at least one primary sealing membrane, a secondary sealing membrane arranged between the primary sealing membrane of the floating structure 100 and the double shell, and two thermal barriers formed between the primary sealing membrane and the secondary sealing membrane and between the secondary sealing membrane and the double shell, respectively.

[0190] Loading and / or unloading pipelines 101 arranged on the top deck of the floating structure 100 can be connected to the sea or port terminal 102 via appropriate connectors to transfer liquefied natural gas cargo from or to the tank 3.

[0191] As can be understood from the foregoing, the present invention proposes a natural gas processing system 1 for supplying natural gas as fuel to at least one consumption unit of a floating structure. The processing system includes at least one refrigerant circuit whose composition is specifically optimized for heat exchange at low temperatures with the natural gas stored in and taken from at least one tank of the floating structure. The processing system also includes at least one system for controlling the refrigerant composition, and this at least one system is configured to allow adjustment of the composition to maintain optimal efficiency of the processing system.

[0192] However, the invention is not limited to the devices and constructions described and illustrated herein, and it extends to any equivalent devices or constructions and any operational combination of such devices. In particular, the number of heat exchangers can be modified, and especially the first heat exchanger can be divided into multiple heat exchangers, provided that the processing system ultimately achieves the same functionality as described in this document.

Claims

1. A floating structure (100) comprising at least one tank (3) for transporting or storing liquefied natural gas, the floating structure (100) comprising at least one processing system (1) for storing natural gas in the tank (3) and at least one consumption unit (2) for consuming natural gas as fuel, the at least one consumption unit (2) being configured to be fueled by gaseous natural gas circulating at least partially in the processing system (1), the processing system (1) comprising at least one closed loop (4) through which a refrigerant comprising at least nitrogen and methane passes, the processing system (1) comprising at least one supply line (51) configured to supply gaseous natural gas from the tank (3) as fuel to the at least one consumption unit (2) of the floating structure (100), the refrigerant loop (4) comprising at least one main branch (410) on which are arranged: The compression device (41) is configured to compress the refrigerant and includes at least one nitrogen-sealed rotary bearing; The first heat exchanger (42) performs at least one heat exchange between the refrigerant and the gaseous natural gas from the tank (3); Refrigerant expansion device (43); The second heat exchanger (44) performs heat exchange between the refrigerant and the liquefied natural gas; The refrigerant circuit (4) includes at least: A sampling branch (120) for sampling a portion of the refrigerant flowing in the main branch (410), the sampling branch (120) being arranged in parallel with the expansion device (43) and including at least one refrigerant flow rate regulating member (125) and a phase separator (12), the flow of the portion of the refrigerant depending on the refrigerant flow rate regulating member (125). At least one injection branch (160, 1601, 1602) for injecting a fluid mainly containing methane, the injection branch including at least one flow rate regulating device (65) regulating the flow rate of the fluid mainly containing methane flowing in the injection branch (160, 1601, 1602), the injection branch (160, 1601, 1602) being connected to the main branch (410) of the refrigerant circuit (4) at an injection point (161) arranged between the first output (4412) of the second heat exchanger (44) and the input of the compressor (41); The processing system (1) includes at least one control system (9) for controlling the composition of the refrigerant, the at least one control system being configured to control at least the refrigerant flow rate regulating member (125) of the sampling branch (120) and the flow rate regulating device (165) for regulating the flow rate of the fluid mainly containing methane in the injection branches (160, 1601, 1602).

2. The floating structure (100) according to claim 1, wherein, The processing system (1) includes at least one compression device, referred to as a second compression device (11), which is different from the compression device of the refrigerant circuit (4), referred to below as a first compression device (41). The second compression device (11) is arranged on the supply line (51) between the first output (4226) of the first heat exchanger (42) and the at least one consumption unit (2). The first compression device (41) and the second compression device (11) are configured to compress natural gas from the tank (3).

3. The floating structure (100) according to claim 1 or 2, wherein, The control system (9) includes at least a refrigerant temperature detector (91) and / or a refrigerant composition detector (92, 92') arranged on the main branch (410) of the refrigerant circuit (4).

4. The floating structure (100) according to claim 1 or 2, wherein, The sampling branch (120) connects to the main branch (410) of the refrigerant circuit (4) at the bifurcation point (121) between the second output (4224) of the first heat exchanger (42) and the input of the expansion device (43).

5. The floating structure (100) according to claim 1 or 2, wherein, The processing system (1) includes a primary branch (130) connected to the lower part of the phase separator (12), and the primary branch is connected to the main branch (410) at a junction (131), the junction being located between the output of the expansion device (43) and the first input (4411) of the second heat exchanger (44).

6. The floating structure (100) according to claim 5, wherein, The primary branch (130) includes a primary flow rate regulating device (135) controlled by the control system (9) between the phase separator (12) and the junction (131), the primary flow rate regulating device being used to regulate the flow rate of refrigerant flowing in the primary branch (130).

7. The floating structure (100) according to claim 2, wherein, The processing system (1) includes a secondary branch (140) connected to the upper part of the phase separator (12).

8. The floating structure (100) according to claim 7, wherein, The secondary branch (140) includes a secondary flow rate regulating device (145) controlled by the control system (9), the secondary flow rate regulating device being used to regulate the flow rate of refrigerant flowing in the secondary branch (140).

9. The floating structure (100) according to claim 7 or 8, wherein, The portion of the refrigerant circulating in the secondary branch (140) is at least partially discharged from and / or burned from the processing system (1), and / or injected into the supply line (51) of gaseous natural gas.

10. The floating structure (100) according to claim 7 or 8, wherein, The processing system (1) includes at least one third branch (150) extending between a bypass point (151) and a connection point (152), the bypass point (151) being arranged on the secondary branch (140), and the connection point (152) being arranged on the supply line (51) of gaseous natural gas, between the output of the tank (3) and the input of the first compression device (41) or the second compression device (11).

11. The floating structure (100) according to claim 1 or 2, wherein, The at least one injection branch (160, 1602) is supplied by at least one storage cylinder (17) storing the fluid which mainly contains methane.

12. The floating structure (100) according to claim 2, wherein, The at least one injection branch (160, 1601) extends between the branch point (162) and the injection point (161), the branch point (162) being arranged on the supply line (51) supplying gaseous natural gas between the at least one consumption unit (2) and the second compression device (11) of the floating structure (100).

13. The floating structure (100) according to claim 2, wherein, The processing system (1) includes a plurality of injection branches (160, 1601, 1602) for injecting the fluid which mainly contains methane. At least one injection branch (160), referred to below as the first injection branch (1601), extends between a branch point (162) and an injection point (161), the branch point being arranged on the supply line (51) for supplying gaseous natural gas between the at least one consumption unit (2) of the floating structure and the second compression device (11). The second injection branch (1602) is supplied by at least one storage cylinder (17) for storing the fluid which mainly contains methane.

14. The floating structure (100) according to claim 1 or 2, wherein, The processing system (1) includes at least one natural gas return pipeline (62) through which the compressed excess natural gas flows, and the processing system (1) includes a third heat exchanger (61) that performs heat exchange between the compressed excess natural gas and the liquefied natural gas.

15. A system for loading or unloading liquefied natural gas, comprising at least one onshore device and at least one floating structure (100) for transporting liquefied natural gas according to any one of the preceding claims, said at least one onshore device comprising a pipe (101) and a pump, said pipe (101) being arranged to connect a tank (3) mounted in the shell of said floating structure (100) to a floating or onshore storage device (102), said pump being used to drive a flow of liquefied natural gas through said pipe (101) from said floating or onshore storage device (102) to the tank (3) of said floating structure (100) or from the tank (3) of said floating structure (100) to said floating or onshore storage device (102).

16. A method for loading liquefied natural gas into or unloading from a tank (3) of a floating structure (100) according to any one of claims 1 to 14, wherein, Cold liquid products are transported via pipeline from the floating or onshore storage device to the tank (3) of the floating structure (100) or from the tank (3) of the floating structure (100) to the floating or onshore storage device.

17. A method for adjusting the composition of a refrigerant flowing in a refrigerant circuit (4) of a processing system (1) of a floating structure (100) according to any one of claims 1 to 14, the method comprising at least: The step of compressing the refrigerant in the first compression device (41); The steps (1000) of determining the temperature of the refrigerant by the temperature detector (91) of the control system (9) and / or the steps (2000) of determining the composition of the refrigerant by the composition detectors (92, 92') of the control system (9); The step (1100) of determining the temperature relative to at least one threshold and / or the step (1100) of comparing the composition of the refrigerant with at least one reference component; A sampling step (1200) for sampling a portion of the refrigerant flowing in the main branch (410), wherein the portion of the refrigerant is supplied to the sampling branch (120) of the refrigerant circuit (4) by at least a partial opening of the refrigerant flow rate regulating member (125); At least the separation step (1300) of separating the gaseous and liquid portions of the portion of refrigerant flowing in the sampling branch (120) by the phase separator (12); The steps of discharging (1450) and / or burning (1450) at least a portion of the gaseous portion of the refrigerant from the treatment system, and / or injecting (1450) at least a portion of the gaseous portion into the supply line (51), Step (1400) of returning at least a portion of the refrigerant to the main branch (410); The adjustment step (1500) involves adjusting the composition of the refrigerant flowing in the refrigerant circuit (4) by injecting the fluid, which mainly contains methane.

18. The method for adjusting the composition of a refrigerant according to claim 17, comprising a first sub-step (1410) between the sampling step (1200) of the portion of the refrigerant and the adjustment step (1500) of the refrigerant composition, the first sub-step determining the proportion of gaseous methane in the portion of the refrigerant flowing in the sampling branch (120).

19. The method for adjusting the composition of a refrigerant according to claim 18, comprising a second sub-step (1420) following the first sub-step (1410), the second sub-step determining the amount of the predominantly methane-containing fluid to be injected into the refrigerant flowing in the refrigerant circuit (4) based on the proportion of gaseous methane measured in the sampling branch (120).

20. The method for adjusting the composition of a refrigerant according to claim 19, comprising a sub-step (1430) prior to a second sub-step (1420) analyzing the composition of gaseous natural gas from tank (3) to determine the proportion of said fluid which is primarily methane-containing.

Images