Gas treatment system comprising a control unit

Abstract

Title of the invention: System for treating a gas comprising a control unit The present invention relates to a system for treating a gas (2) comprising at least a first line (10) in which a gas in the vapor state circulates and a second line (40) in which at least part of the gas in the liquid state circulates, the first line (10) comprising at least one compression device (20), the second line (40) comprising at least one pumping member (42) configured to supply the second line (40) with gas in the liquid state, characterized in that the system for treating a gas (2) comprises a control unit (44) which controls the operation of the pumping member (42) according to at least one temperature of the gas in the vapor state determined at the inlet of the compression device (20). (Figure 1)

Description

Title of the invention: Gas treatment system comprising a control unit

[0001] The present invention relates to the field of liquefied gas transport vessels, in particular methane carriers, and to the field of cooling equipment. More specifically, the invention relates to a system for treating a gas intended to supply the engines of such vessels and the cooling of which at the inlet of a compression device is optimized.

[0002] Such ships include a hold designed to contain one or more tanks for transporting gas in the liquid state, these tanks having a capacity of several thousand or even several tens of thousands of cubic meters. When it comes to natural gas, it is kept in the tanks at approximately -163°C (degrees Celsius), at atmospheric pressure. The tanks are therefore sealed and thermally insulated by a double layer of insulation. However, since liquefied natural gas (LNG) tends to evaporate, for example due to a reduction in the gas pressure in the tanks or a heat flow passing through the tank walls despite the double insulation, the upper part of each tank, called the tank gas ceiling, is filled with gas in the vapor state.

[0003] LNG that evaporates naturally and accumulates in the gaseous headspace is also called NBOG (for the English "Natural Boil-Off Gas"). This NBOG is generally used as fuel for one or more of the ship's engines. The engines of these ships must be supplied with NBOG at pressures higher than the pressure of the NBOG in the tank gaseous headspace and at a given temperature. For this purpose, these ships are equipped with one or more compression devices intended to supply the ship's engines with NBOG at a pressure suitable for these engines. However, these compression devices participate, during their operation, in heating the NBOG to temperatures higher than the intake temperature of the engines.Among these compression devices, two-stage compression devices are implemented and it is known to cool the NBOG at the inlet of such compression devices so that the NBOG at the inlet of the engines is at a temperature admissible for the latter.

[0004] Cooling of the NBOG at the inlet of the compression device is conventionally obtained by the projection of natural gas in the liquid state coming from a tank and circulating in a specific line, by means of a pumping member immersed in the tank. In the system of the prior art, the pumping member operates continuously so as to continuously cool the NBOG. However, the operation of The pumping device generates heat within the tank, which increases the amount of NBOG generated in the tank. Such uninterrupted operation of the pumping device helps to reduce the energy balance of operational losses of evaporated gas during a ship's journey, also called the operational BOR (for English "Boil-Off Rate") of a ship.

[0005] The present invention falls within this context and proposes to overcome at least some of the drawbacks of the prior art. The present invention proposes in particular a system for treating a gas in which the generation of NBOG in the tank following the calories generated by the pumping member is limited by controlled operation of said pumping member.

[0006] Thus, the present invention relates to a system for treating a gas comprising at least a first line in which a gas in the vapor state contained in a storage tank circulates and a second line in which at least partly said gas in the liquid state contained in the storage tank circulates, the first line being configured to connect at least one gaseous canopy of said storage tank to a gas-consuming device and comprising at least one compression device intended to supply gas to the gas-consuming device and a phase separator arranged between the gaseous canopy and the compression device, the second line comprising at least one pumping member configured to supply the second line with gas in the liquid state coming from the storage tank, said second line extending at least between said pumping member and the first line,the second line being fluidically connected to the first line between the gaseous airspace and the phase separator, the second line being configured to deliver gas in the liquid state into the first line so as to lower the temperature of the gas in the vapor state circulating in the first line, characterized in that the gas treatment system comprises a control unit which gives an operating indication and / or controls the operation of the pumping member according to at least one temperature of the gas in the vapor state determined at the inlet of the compression device.

[0007] The gas treatment system makes it possible to modulate the activity of the pumping member according to the cooling requirement of the gas in the vapor state circulating in the first line. This gas in the vapor state comes from the natural evaporation of the gas contained in the liquid state in the storage tank.

[0008] The temperature of the gas in the vapor state at the inlet of the compression device determines the temperature of said gas at the outlet of the compression device when the gas in the vapor state is compressed to be sent to the gas consuming device. In particular when the gas at the inlet of the compression device is too hot, the control unit is able to activate the pumping member to ensure the cooling of the gas in the vapor state by projection of gas in the liquid state. It should be noted that the control unit can give an indication to activate the pumping member. This indication can, for example, be a signal to an operator to manually control the activation of the pumping member. This projection is carried out before said gas thus cooled reaches the phase separator. Thus, although the gas in the vapor state has been cooled by the projection of gas in the liquid state, it is ensured that only the gaseous phase of the gas circulating in the first line reaches the compression device.

[0009] The meeting of the gas in the liquid state circulating in the second line with the gas in the vapor state circulating in the first line can generate an expansion of the gas in the liquid state which vaporizes in contact with the gas in the vapor state circulating in the first line, while lowering the temperature of the latter.

[0010] The treatment system thus makes it possible not to leave the pumping member operating permanently but to control its operation according to the cooling requirement of the gas in the vapor state circulating in the first line.

[0011] According to a characteristic of the invention, the compression device is a compression device comprising at most two compression stages. Within compression devices with two compression stages, the cooling of the compressed gas by the compression device between two compression stages is complex. Thus, the gas must be cooled before entering the compression device.

[0012] According to a characteristic of the invention, the pumping member is configured to take at least a first operating state in which the pumping member generates the circulation of the gas in the liquid state in the second line and to take a second operating state in which the pumping member does not generate circulation of the gas in the liquid state in the second line, the control unit being able to switch the pumping member from one of said operating states to the other. Controlling the pumping member makes it possible to generate a circulation of gas in the liquid state in the second line or not to generate circulation. By switching the pumping member from one operating state to the other, the control unit is able to control, by means of the pumping member, the cooling of the gas in the vapor state circulating in the first line.

[0013] According to a characteristic of the invention, the control unit is capable of defining a threshold temperature value, the pumping member being in its first operating state when the temperature of the gas determined at the inlet of the compression device is higher than the threshold temperature value, the pumping member being in its second operating state when the temperature of the gas determined at the inlet of the compression device is lower than the threshold temperature value. The threshold temperature value is a value determined by the control unit and compared to the temperature of the gas in the vapor state at the inlet of the compression device to choose when to activate the pumping member and when to deactivate the pumping member.

[0014] According to a characteristic of the invention, the threshold temperature value is variable. The threshold temperature value is an evolving parameter depending on the conditions in which the gas treatment system is located. It is understood that the threshold temperature value is not a predetermined fixed value but a value which fluctuates over time.

[0015] According to a characteristic of the invention, the threshold temperature value is a function at least of the temperature of the gas present in the gaseous headspace of the storage tank. The gas in the vapor state circulating in the first line comes from the gaseous headspace of the storage tank, the temperature value thus adapts to the temperature of the gas in the gaseous headspace.

[0016] According to an alternative or complementary characteristic of the invention, the threshold temperature value is a function at least of the flow rate of gas circulating in the first line between the phase separator and the compression device. The greater the circulation of gas in the first line, the lower the temperature of said gas will tend to be, which limits the use of the pumping member.

[0017] According to an alternative or complementary characteristic of the invention, the threshold temperature value is a function at least of the movement of the gas in the liquid state contained in the storage tank. The greater the movements of the gas contained in the liquid state in the tank, the more gas in the vapor state will be generated. Also, the greater the volume of gas in the vapor state in the gaseous headspace of the storage tank, the greater the volume of gas in the vapor state flowing towards the compression device. Furthermore, the greater the volume of gas in the vapor state, the lower the temperature of the latter. Thus, the control of the pumping member and / or the indication of operation of the pumping member are adapted to the volume of gas in the vapor state generated in the gaseous headspace of the storage tank.

[0018] According to an alternative or complementary characteristic of the invention, the threshold temperature value is a function of at least one temperature of at least one conduit forming the first line. The higher the temperature of the conduit forming the first line, the higher the temperature of the gas circulating within this conduit will also be. Thus, by taking into account the temperature of the conduit, the control unit can determine the impact of this parameter on the increase in the temperature of the gas contained in said conduit, and thus decide whether or not to operate the pumping member.

[0019] The present invention also relates to a gas treatment assembly comprising a storage tank and a treatment system, the pumping member being immersed in the gas contained in the liquid state in the storage tank.

[0020] The present invention also relates to a floating structure comprising a gas treatment system or a gas treatment assembly, as described herein.

[0021] The present invention also relates to a method of treating a gas by a gas treatment system implementing at least: - a first step during which the control unit collects at least one piece of data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device and gives an indication of operation and / or controls the pumping member as a function of said data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device.

[0022] According to a characteristic of the invention, the treatment method implements at least: - a second step during which the control unit determines a threshold temperature value, - a third step during which the control unit compares the data to the threshold temperature value and gives an operating indication and / or controls the pumping device according to said comparison.

[0023] According to a characteristic of the invention, during the third step, if the data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device is greater than the threshold temperature value then the control unit gives an operating indication and / or controls the pumping member so that the pumping member is in its first operating state and if the data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device is less than the threshold temperature value then the control unit gives an operating indication and / or controls the pumping member so that the pumping member is in its second operating state.

[0024] According to a characteristic of the invention, the processing method implements at least one additional step during which the control unit collects at least one piece of data relating to the temperature of the gas in the vapor state present in the gaseous ceiling of the storage tank to determine the threshold temperature value.

[0025] According to a characteristic of the invention, the processing method implements at least one additional step during which the control unit collects at least one piece of data relating to the flow rate of gas in the vapor state circulating in the first line between the phase separator and the compression device to determine the threshold temperature value.

[0026] According to a characteristic of the invention, the processing method implements at least one additional step during which the control unit collects at least one piece of data relating to the temperature of at least one conduit forming the first line to determine the threshold temperature value.

[0027] It should be noted that these additional steps can be carried out before or simultaneously with the second step.

[0028] Other characteristics and advantages of the invention will become apparent from the following description on the one hand, and from several examples of embodiment given for informational and non-limiting purposes with reference to the appended schematic drawings on the other hand, in which:

[0029] [Fig.l] schematically represents a general view of a treatment system making it possible to cool a gas in the vapor state by a gas in the liquid state by means of a pumping member controlled by a control unit;

[0030] [Fig.2] schematically represents the system for treating a gas visible on the [Fig.l] when the pumping member is in its second operating state and does not generate circulation of a gas;

[0031] [Fig.3] schematically represents the system for treating a gas visible on the [Fig.l] when the pumping member is in its first operating state and generates a circulation of a gas;

[0032] [Fig.4] represents a floating structure comprising a system for treating a gas ;

[0033] The features, variants and the different embodiments of the invention may be combined with each other, in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be imagined comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage and / or to differentiate the invention from the prior art.

[0034] In the figures, the elements common to several figures retain the same reference.

[0035] It should be noted that in the attached figures 1 to 3, the lines representing conduits in which a gas circulates are represented with a strong thickness when a gas circulates in said conduits and in a lesser thickness when no gas circulates in said conduits. Furthermore, the dotted lines represent an exchange of information between the control unit and an associated element of the system according to the invention.

[0036] [Fig.l] schematically illustrates a gas treatment system 2 according to an embodiment of the invention. As seen in [Fig.l], the gas treatment system 2 is integrated within a floating structure 4, such a floating structure 4 being shown in [Fig.4]. This floating structure 4 is intended to ensure the storage temporary storage and / or transport of liquefied gas. In the following, the invention is described in a non-limiting manner in the context of the storage and / or transport of liquefied natural gas, which will be designated in the description which follows by the acronym “LNG”. For this purpose, the floating structure 4 comprises at least one LNG storage tank 6, in the present case three storage tanks 6. It should be noted that the description in connection with a storage tank 6 which will be made applies mutatis mutandis to the other storage tanks 6.

[0037] The LNG is stored in a storage tank 6 at a temperature of approximately -163°C (degrees Celsius) allowing it to be maintained in the liquid state at atmospheric pressure. The storage tank 6 comprises a gaseous canopy 8 within which the gas resulting from the natural evaporation of the gas contained in the liquid state in the storage tank 6, which will be designated in the following description by the acronym NBOG for "Natural Boil-Off Gas", accumulates in the gaseous canopy 8. This gaseous canopy 8 represents, when the storage tank 6 is full, approximately 15% of the volume of the storage tank 6 and allows the pressure changes within the storage tank 6 resulting from the formation of the NBOG to be contained at a safe pressure.

[0038] This gaseous sky 8 is fluidically connected to a first line 10 in which circulates the gas in the vapor state resulting from the natural evaporation of the gas contained in the liquid state in the storage tank 6. It is remarkable in [Fig.l] that the first line 10 is connected to the gaseous sky 8 of each of the storage tanks 6. Thus, all of the NBOG generated in the storage tanks 6 is able to circulate in the first line 10.

[0039] The first line 10 connects the gaseous sky 8 to at least one gas-consuming device 12. The gas-consuming device 12 may be a propulsion engine 14 participating in setting the floating structure 4 in motion, a generator 16 intended to generate an electric current or even a combustion unit 18 of a gas, commonly designated by the term “burner”.

[0040] In the embodiment shown, the first line 10 is connected to the propulsion engine 14, to the generator 16 and to the combustion unit 18. For this purpose, each of said gas-consuming devices 12 is associated with a supply valve 19 to independently control the gas supply to each of these gas-consuming devices 12.

[0041] The first line 10 comprises, between the gaseous ceiling 8 and the gas consuming device 12, a compression device 20 intended to compress the gas circulating in the first line 10 before reaching the gas consuming device 12 at a given pressure. In the embodiment shown, the compression device 20 is formed of a main line 22 comprising a first compressor 24 and an auxiliary line 26, arranged in parallel with the main line 28, comprising a second compressor 30. The main line 22 and the auxiliary line 26 join at the outlet of the first compressor 24 and the second compressor 30 before reaching the gas-consuming device 12. The first compressor 24 and the second compressor 30 operate redundantly, the second compressor 30 taking over in the event of a malfunction of the first compressor 24.

[0042] The compression device 20, here the first compressor 24 or the second compressor 30, comprises at most two compression stages. In the embodiment shown, the first compressor 24 and the second compressor 30 each comprise two compression stages. In such a configuration of the compression device, the cooling of the compressed gas between two compression stages is complex to implement.

[0043] The main line 22 comprises a first valve 32 and the auxiliary line 26 comprises a second valve 34. The first valve 32 and the second valve 34 respectively make it possible to independently control the arrival of gas from the first line 10 at the inlet of the first compressor 24 or the second compressor 30.

[0044] Between the gaseous sky 8 of the storage tank 6 and the compression device 20, the first line 10 comprises a phase separator 36 intended to separate the liquid phase from the gaseous phase of the gas circulating in the first line 10. This phase separator 36 allows only the gaseous phase of said gas to be sent to the compression device 20 while the liquid phase returns to the storage tank 6 by means of a return line 38.

[0045] The gas treatment system 2 also comprises a second line 40 extending between a pumping member 42 and the first line 10. The second line 40 makes it possible to circulate gas in the liquid state contained in the storage tank 6 to the first line 10.

[0046] This second line 40 makes it possible to ensure the cooling of the NBOG, that is to say the gas resulting from the natural evaporation of the gas contained in the liquid state in the storage tank 6, circulating in the first line 10.

[0047] Indeed, at least a portion of the NBOG compressed by the compression device is intended to power the propulsion engine 14 so as, for example, to set the floating structure 4 in motion. The propulsion engine 14 requires that the gas compressed by the compression device 20 and entering the propulsion engine 14 be sufficiently cold. However, during operation of the compression device 20, the compressed gas heats up under the effect of the compression carried out by the compression device 20.

[0048] In addition, the gas resulting from the natural evaporation of the gas contained in the liquid state in the storage tank 6 and accumulating in the gaseous atmosphere 8 is at a temperature of approximately -120°C. However, during the circulation of the NBOG from the gaseous headspace 8 to the inlet of the compression device 20, the temperature of the NBOG increases to approximately -110°C. At such a temperature of the NBOG at the inlet of the compression device 20 the compressed gas cannot be admitted to the propulsion engine. The NBOG then needs to be cooled to a temperature of at most -120°C.

[0049] For this purpose, the second line 40 makes it possible to cool the NBOG circulating in the first line 10 so that the temperature of the gas at the inlet of the compression device 20 is sufficiently cold, i.e. at most -120°C, so that the gas compressed by the compression device 20 can be at a temperature acceptable by the propulsion engine 14.

[0050] The gas in the liquid state contained in the second line 40 is at a temperature of approximately -160°C. It should be noted that this gas may, depending on the application, heat up during its circulation in the second line 40. However, the temperature of the gas circulating in the second line 40 remains strictly lower than the temperature of the gas circulating in the first line 10. The junction between the second line 40 and the first line 10 upstream of the phase separator 36, considering the direction of circulation of the fluid, that is to say between the gaseous ceiling and the phase separator 36, makes it possible to distribute the gas in the liquid state circulating in the second line 40 in the first line 10.

[0051] It should be noted that the second line 40 may be provided with a non-return valve, not shown here, to prevent the passage of gas from the first line 10 to the second line 40.

[0052] The meeting of the gas in the liquid state circulating in the second line 40 with the gas in the vapor state circulating in the first line 10 generates an expansion phenomenon, also known by the English term "flash", of the gas in the liquid state which, in contact with a hotter gas, vaporizes and makes it possible to lower the temperature of the gas in the vapor state contained in the second line 40.

[0053] This cooling of the gas circulating in the vapor state in the first line 10 is controlled by a control unit 44. In the embodiment shown, the control unit 44 is configured to give an operating indication and / or control the operation of the pumping member 42 so that at least the circulation of the gas in the liquid state in the second line 40 can be controlled by the control unit 44. It should be noted that “giving an operating indication” means that the control unit 44 is capable of generating a signal or transmitting information to the operator so that the latter himself controls the pumping member 42 in accordance with the information transmitted by the control unit 44.

[0054] The control unit 44 is thus connected, for example electrically, at least to the pumping member 42, so as to activate or stop it. The control unit 44 is also connected, for example electrically, to the temperature sensor 64 arranged at the inlet of the compression device 20 and / or a temperature probe 66 arranged in the roof of the tank and / or to a temperature detector 68 of a pipe of the first line 10 and / or to a flow meter 46 and / or to the valves 32 and 34. The control unit 44 thus receives information from the temperature sensor 64 arranged at the inlet of the compression device 20 and / or from the temperature probe 66 arranged in the roof of the tank and / or from the temperature detector 68 of the pipe of the first line 10 and / or from the flow meter 46, and activates or deactivates the pumping member 42, depending on a strategy implemented by the method which is the subject of the invention.

[0055] Figures 2 and 3 show in more detail the management of the circulation of the gas within the gas treatment system 2 as controlled by the control unit 44. More specifically, [Fig.2] represents the gas treatment system 2 when the pumping member 42 does not generate circulation of the gas in the liquid state in the second line 40 and [Fig.3] represents the gas treatment system 2 when the pumping member 42 generates circulation of the gas in the liquid state contained in the storage tank 6 in the second line 40.

[0056] The present invention integrates the control of the pumping member 42 by the control unit 44 within a method of treating a gas by the gas treatment system 2.

[0057] The processing method implements a first step during which the control unit 44 collects at least one piece of data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device 20 and gives an indication of operation and / or controls the pumping member 42 as a function of said data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device. For this purpose, the first line 10 may be provided, for example, with a temperature sensor 64 for measuring or determining in situ the temperature of the gas in the vapor state circulating in the first line 10, and more specifically at the inlet of the compression device 20. Alternatively, the temperature sensor 66 may be associated with the first or second compressor 24, 30. Such a temperature sensor 66 is immersed in the gas in the vapor state circulating in the first line 10.It is advantageously arranged at the entrance to the compression device 20.

[0058] The processing method also implements a second step during which the control unit 44 determines a threshold temperature value and a third step during which the control unit 44 compares the data relating to the temperature of the gas in the vapor state at the inlet of the compression device with the threshold temperature value and gives an operating indication and / or controls the pumping member 42 as a function of said comparison.

[0059] The threshold temperature value is a variable temperature which takes into account at least least one parameter. In the embodiment shown, the threshold temperature value is a function of a plurality of parameters which influence each other.

[0060] The pumping member 42 is, in the embodiment shown, capable of taking a first operating state in which the pumping member 42 generates the circulation of the gas in the liquid state in the second line 40, as visible in [Fig. 3], and a second operating state in which the pumping member 42 does not generate circulation of the gas in the liquid state in the second line 40, visible in [Fig. 2],

[0061] It is understood that in the embodiment shown, the pumping member 42 is an on / off type pump. Of course, in an alternative embodiment of the invention, the pumping member 42 can be completely controlled by the control unit 44 so as to adapt the flow rate of gas in the liquid state circulating in the second line 40 according to the cooling requirement of the gas in the vapor state circulating in the first line 10.

[0062] The transition from one of said operating states to the other of the pumping member 42 is controlled by the control unit 44 such that if the temperature of the gas in the vapor state circulating in the first line 10 and measured at the inlet of the compression device 20 is higher than the threshold temperature value, then the control unit 44 gives an operating indication and / or controls the pumping member 42 so that it is in its first operating state. Conversely, if the temperature of the gas in the vapor state circulating in the first line 10 and measured at the inlet of the compression device 20 is lower than the threshold temperature value, then the control unit gives an operating indication and / or controls the pumping member 42 so that it is in its second operating state, the latter avoiding the generation of calories transmitted to the natural gas in the liquid state.

[0063] It is understood from the above that during the third step of the method for treating a gas, the control unit 44 compares the temperature of the gas at the inlet of the compression device 20 with the threshold temperature value and gives an operating indication and / or controls the pumping member 42 so as to make it pass from one of said operating states to the other.

[0064] As mentioned previously, the threshold temperature value is determined by the control unit 44. This threshold temperature value is scalable, that is to say that the threshold temperature value is not defined by a given temperature value but by a temperature value evolving according to the parameters and / or conditions in which the LNG is found.

[0065] In the embodiment shown, the control unit 44 is configured to collect data relating to the temperature of the gas present in the gaseous ceiling 8 during an additional step of the processing method. By collecting this data, the control unit 44 is capable of determining the temperature of the NBOG and thus the temperature of the gas in the vapor state circulating in the first line 10. For this purpose, the gaseous canopy 8 of the storage tank 6 is provided, for example, with a temperature probe 66 capable of collecting data relating to the temperature of the gas present in the gaseous canopy 8 and communicating them with the control unit 44. Also, depending on the temperature of the gas present in the gaseous canopy 8, the control unit 44 can adapt the threshold temperature value so that the gas in the vapor state at the inlet of the compression device 20 is at a temperature of at most -110°C.

[0066] The control unit 44 is capable of collecting information relating to the flow rate of gas in the vapor state circulating in the first line 10 between the phase separator 36 and the compression device 20 during an additional step of the treatment method. This data is collected by a flow meter 46 which measures the flow rate of the gas in the vapor state between the phase separator 36 and the compression device 20. Indeed, the higher the flow rate of the gas circulating in the first line 10, the lower the temperature of the gas in the vapor state circulating in the first line 10. Thus, depending on the flow rate of the measured gas, the control unit 44 modulates the threshold temperature value so that the gas in the vapor state at the inlet of the compression device 20 is at a temperature of at most -110°C.When this flow rate is high, the temperature of the gas in the vapor state at the inlet of the compression device drops, which makes it possible to interrupt the operation of the pumping member 42.

[0067] The control unit 44 collects data relating to the movement of the gas contained in the liquid state in the storage tank 6 during an additional step of the treatment method. This data allows the control unit 44 to determine the quantity of NBOG generated in the storage tank 6 by these movements of the gas contained in the liquid state in the storage tank 6. Also, the greater the volume of NBOG generated in the storage tank 6, the greater the volume of gas compressed by the compression device 20. Also, the greater the volume of gas in the vapor state, the lower the temperature of the latter. Thus, the control of the pumping member 42 and / or the indication of operation of the pumping member 42 are adapted to the volume of gas in the vapor state generated in the gaseous canopy 8 of the storage tank 6.More specifically, when the quantity of NBOG generated in the storage tank 6 is large, the temperature of the NBOG at the inlet of the compression device 20 is low enough to avoid having to activate the pumping member 42.

[0068] It should be noted that the control unit 44 is also capable of controlling the first valve 32 and the second valve 34 so as to manage the redundancy between the first compressor 24 and the second compressor 30.

[0069] The first line 10 is formed of a conduit in which the gas in the vapor state is able to move from the gaseous airspace 8 to the compression device 20. This conduit may be subject to external temperature constraints due to the fact that it circulates on the deck of the ship. It then has a temperature which varies according to these external constraints.

[0070] The control unit 44 is configured to collect at least one piece of data relating to the temperature of this conduit forming the first line so as to adapt the threshold temperature value as a function of the temperature of said conduit during an additional step of the treatment method. Indeed, the temperature of the gas in the vapor state circulating in the first line 10 varies as a function of the temperature of said conduit. A temperature detector 68 is thus arranged against the conduit, so as to measure its surface temperature. More precisely, the higher the temperature of the conduit, the more the gas circulating in said conduit will see its temperature increase, which requires the activation of the pumping member 42. Conversely, if the temperature of the conduit constituting the first line drops, then the pumping member 42 can be stopped.

[0071] [Fig.4] represents the floating structure 4 comprising the storage tank 6, which is sealed and thermally insulated. It is generally prismatic in shape and is mounted in a double hull 46 of the floating structure 4, which may be a ship or a floating platform. A wall of the storage tank 6 comprises a primary sealed membrane intended to be in contact with a liquefied gas, here LNG, contained in the storage tank 6, a secondary sealed membrane arranged between the primary sealed membrane and the double hull 46 of the floating structure 4, and two thermally insulating barriers arranged respectively between the primary sealed membrane and the secondary sealed membrane and between the secondary sealed membrane and the double hull 46. In a simplified version, the floating structure 4 comprises a single hull.

[0072] Loading / unloading pipelines 48 arranged on an upper deck of the floating structure 4 can be connected, by means of appropriate connectors, to a storage terminal 50 to transfer a cargo of liquefied gas and / or gas resulting from the evaporation of the liquefied gas from or to the storage tank 6.

[0073] [Fig.4] also illustrates a storage terminal 50 comprising a station loading and / or unloading station 52, an underwater pipe 54 and a land-based installation 56. The loading and / or unloading station 52 is a fixed offshore installation comprising a mobile arm 58 and a tower which supports the mobile arm 58. The mobile arm 58 carries a bundle of insulated flexible pipes 60 which can be connected to the loading / unloading pipes 48. The mobile arm 58 is orientable and adapts to all sizes of floating structure 4. A connecting pipe not shown extends inside the tower. The loading and / or unloading station 52 allows the loading and / or unloading of the floating structure 4 from or to the storage terminal 50, which comprises storage tanks for the liquefied gas and / or the gas resulting from the evaporation of the liquefied gas as well as connecting pipes 62 connected by the underwater pipe 54 to the loading and / or unloading station 52. The underwater pipe 54 allows the transfer of the liquefied gas and / or the gas resulting from the evaporation of the liquefied gas between the loading and / or unloading station 52 and the floating structure 4 over a long distance, for example five kilometers, which makes it possible to keep the floating structure 4 at a long distance from the coast during the loading and / or unloading operations.

[0074] To generate the pressure necessary for the transfer of the liquefied gas and / or the gas resulting from the evaporation of the liquefied gas, pumps on board the floating structure 4 and / or pumps equipping the land-based installation 56 and / or pumps equipping the loading and unloading station 52 are used.

[0075] The examples have been described for a floating structure 4; however, they are also applicable to a land-based structure.

[0076] The present invention achieves the aim it set itself by proposing a treatment system making it possible to control the operation of a pumping member according to the cooling requirements of the gas admitted into the compression device, so as to optimize the energy balance during a voyage of the ship and limit operational gas losses.

[0077] The present invention cannot, however, be limited to the means and configurations described and illustrated here and it also extends to any equivalent means and configuration as well as to any technically operative combination of such means.

Claims

Claims

1. System for treating a gas (2) comprising at least a first line (10) in which circulates a gas in the vapor state contained in a storage tank (6) and a second line (40) in which circulates at least in part said gas in the liquid state contained in the storage tank (6), the first line (10) being configured to connect at least one gaseous canopy (8) of said storage tank (6) to a gas-consuming device (12) and comprising at least one compression device (20) intended to supply gas to the gas-consuming device (12) and a phase separator (36) arranged between the gaseous canopy (8) and the compression device (20), the second line (40) comprising at least one pumping member (42) configured to supply the second line (40) with gas in the liquid state coming from the storage tank (6), said second line extending at least between said pumping member (42) and the first line (10),the second line (40) being fluidically connected to the first line (10) between the gaseous headspace (8) and the phase separator (36), the second line (40) being configured to deliver gas in the liquid state into the first line (10) so as to lower the temperature of the gas in the vapor state circulating in the first line (10), characterized in that the gas treatment system (2) comprises a control unit (44) which gives an operating indication and / or controls the operation of the pumping member (42) according to at least one temperature of the gas in the vapor state determined at the inlet of the compression device (20).,

2. A gas treatment system (2) according to claim 1, wherein the compression device (20) is a compression device (20) comprising at most two compression stages.

3. A gas treatment system (2) according to any one of claims 1 and 2, wherein the pumping member (42) is configured to take at least a first operating state in which the pumping member (42) generates the circulation of the gas in the liquid state in the second line (40) and to take a second operating state in which the pumping member (42) does not generate circulation of the gas in the liquid state in the second line (40), the control unit (44) being capable of switching the pumping member (42) from one of said operating states to the other.

4. A gas treatment system (2) according to claim 3, wherein the control unit (44) is capable of defining a threshold temperature value, the pumping member (42) being in its first operating state when the temperature of the gas determined at the inlet of the compression device (20) is higher than the threshold temperature value, the pumping member (42) being in its second operating state when the temperature of the gas determined at the inlet of the compression device (20) is lower than the threshold temperature value.

5. A gas treatment system (2) according to claim 4, wherein the threshold temperature value is variable.

6. Gas treatment system (2) according to any one of claims 4 and 5, in which the threshold temperature value is a function at least of the temperature of the gas present in the gaseous headspace (8) of the storage tank (6).

7. A gas treatment system (2) according to any one of claims 4 to 6, wherein the threshold temperature value is a function at least of the gas flow rate circulating in the first line (10) between the phase separator (36) and the compression device (20).

8. A gas treatment system (2) according to any one of claims 4 to 7, wherein the threshold temperature value is a function at least of the movement of the gas in the liquid state contained in the storage tank (6).

9. A gas treatment system (2) according to any one of claims 4 to 8, wherein the threshold temperature value is a function of at least one temperature of at least one conduit forming the first line (10).

10. A gas treatment assembly comprising a storage tank (6) and a treatment system (2) according to any one of claims 1 to 9, wherein the pumping member (42) is immersed in the gas contained in the liquid state in the storage tank (6).

11. Floating structure (4) comprising a gas treatment system (2) according to any one of claims 1 to 9 or a gas treatment assembly according to claim 10.

12. Method of treating a gas by a gas treatment system (2) according to any one of claims 1 to 9, the treatment method implementing at least: - a first step during which the control unit (44) collects at least one piece of data relating to the temperature of the gas in the vapor determined at the inlet of the compression device (20) and gives an indication of operation and / or controls the pumping member (42) as a function of said data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device (20).

13. Processing method according to claim 12 in combination with claim 4, implementing at least: - a second step during which the control unit (44) determines a threshold temperature value, - a third step during which the control unit (44) compares the data with the threshold temperature value and gives an operating indication and / or controls the pumping member (42) as a function of said comparison.

14. Treatment method according to claim 13, in which during the third step, if the data relating to the temperature of the gas in the vapor state determined at the input of the compression device (20) is greater than the threshold temperature value then the control unit (44) gives an indication of operation and / or controls the pumping member (42) so that the pumping member (42) is in its first operating state and if the data relating to the temperature of the gas in the vapor state determined at the input of the compression device (20) is less than the threshold temperature value then the control unit (44) gives an indication of operation and / or controls the pumping member (42) so that the pumping member (42) is in its second operating state.

15. Treatment method according to any one of claims 13 and 14, implementing at least one additional step during which the control unit (44) collects at least one piece of data relating to the temperature of the gas in the vapor state present in the gaseous ceiling (8) of the storage tank (6) to determine the threshold temperature value.

16. Treatment method according to any one of claims 13 to 15, implementing at least one additional step during which the control unit (44) collects at least one piece of data relating to the flow rate of gas in the vapor state circulating in the first line (10) between the phase separator (36) and the compression device (20) to determine the threshold temperature value.

17. Processing method according to any one of claims 13 to 16, implementing at least one additional step during which the control unit (44) collects at least one piece of data relating to the temperature of at least one conduit forming the first line (10) to determine the threshold temperature value.

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