Gas treatment system including a control unit

Abstract

Title of the invention: Gas treatment system comprising a control unit. The present invention relates to a gas treatment system (2) comprising at least a first line (10) through which a gas flows in the vapor state and a second line (40) through which at least part of the gas flows in the liquid state, the first line (10) comprising at least one compression device (20), the second line (40) comprising at least one pumping element (42) configured to supply the second line (40) with gas in the liquid state, characterized in that the gas treatment system (2) comprises a control unit (44) which controls the operation of the pumping element (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, particularly LNG carriers, and to the field of cooling equipment. More specifically, the invention concerns a gas treatment system intended to power the engines of such vessels, and whose cooling at the inlet of a compression device is optimized.

[0002] Such vessels include a hold designed to contain one or more tanks for transporting gas in a liquid state, these tanks having a capacity of several thousand or even tens of thousands of cubic meters. When natural gas is involved, it is maintained in the tanks at approximately -163°C (degrees Celsius), at atmospheric pressure. The tanks are therefore leak-proof and thermally insulated by a double layer of insulation. However, since liquefied natural gas (LNG) tends to evaporate, for example due to a decrease in 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 head, is filled with gas in a vapor state.

[0003] LNG that evaporates naturally and accumulates in the headspace is also called NBOG (for "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 NBOG pressure in the headspace and at a given temperature. To this end, these ships are equipped with one or more compression devices designed to supply the ship's engines with NBOG at a pressure suitable for those engines. However, these compression devices, during their operation, contribute to heating the NBOG to temperatures higher than the engines' intake temperature.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 motors is at a temperature permissible for the latter.

[0004] The cooling of the NBOG at the inlet of the compression device is conventionally achieved by injecting natural gas in a liquid state from a tank and circulating in a dedicated line, using a pumping element immersed in the tank. In the prior art system, the pumping element operates continuously so as to continuously cool the NBOG. However, the operation of The pumping unit generates heat within the tank, which increases the amount of NBOG generated in the tank. Such uninterrupted operation of the pumping unit helps to reduce the energy balance of operational losses of evaporated gas during a ship's voyage, also known as the ship's operational Boil-Off Rate (BOR).

[0005] The present invention falls within this context and aims to overcome at least some of the drawbacks of the prior art. In particular, the present invention proposes a gas treatment system in which the generation of NBOG in the tank resulting from the heat generated by the pumping element is limited by controlled operation of said pumping element.

[0006] Thus, the present invention relates to a gas treatment system comprising at least a first line through which a gas in vapor state contained in a storage tank circulates and a second line through which at least part of said gas in liquid state contained in the storage tank circulates, the first line being configured to connect at least one gas head of said storage tank to a gas-consuming device and comprising at least one compression device for supplying gas to the gas-consuming device and a phase separator disposed between the gas head and the compression device, the second line comprising at least one pumping element configured to supply the second line with gas in liquid state from the storage tank, said second line extending at least between said pumping element and the first line,the second line being fluidly connected to the first line between the gaseous head 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 provides an operating indication and / or controls the operation of the pumping element 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 allows the activity of the pumping unit to be modulated according to the cooling requirements of the gas in vapor form circulating in the first line. This gas in vapor form results from the natural evaporation of the gas contained in liquid form in the storage tank.

[0008] The temperature of the gas in its 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 its vapor state is compressed for delivery to the gas-consuming appliance. In particular, when the gas at the inlet of the compression device is too hot, the control unit is capable of activating the pumping element to ensure the cooling of the gas in its vapor state by spraying gas in its liquid state. It should be noted that The control unit can provide an indication to activate the pumping unit. This indication could, for example, be a signal to an operator to manually activate the pumping unit. This injection is performed before the cooled gas reaches the phase separator. Thus, although the gas in its vapor state has been cooled by the injection of liquid gas, it is ensured that only the gaseous phase of the gas circulating in the first line reaches the compression device.

[0009] The encounter 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 on 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 unit running continuously but to control its operation according to the need for cooling of the gas in the vapor state circulating in the first line.

[0011] According to one feature of the invention, the compression device is a compression device comprising a maximum of two compression stages. In two-stage compression devices, cooling the gas compressed by the compression device between the two compression stages is complex. Thus, the gas must be cooled before entering the compression device.

[0012] According to one feature of the invention, the pumping element is configured to assume at least a first operating state in which the pumping element generates the circulation of the gas in the liquid state in the second line and to assume a second operating state in which the pumping element does not generate the circulation of the gas in the liquid state in the second line, the control unit being capable of switching the pumping element from one of said operating states to the other. The control of the pumping element allows for the generation of gas circulation in the liquid state in the second line or for the generation of no circulation. By switching the pumping element from one operating state to the other, the control unit is capable of controlling, by means of the pumping element, the cooling of the gas in the vapor state circulating in the first line.

[0013] According to one feature of the invention, the control unit is capable of defining a threshold temperature value, the pumping element being in its first operating state when the gas temperature determined at the inlet of the compression device is greater than the threshold temperature value, and the pumping element being in its second operating state when the gas temperature determined at the inlet of the compression device is less 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 unit and when to deactivate the pumping unit.

[0014] According to one feature of the invention, the threshold temperature value is variable. The threshold temperature value is a dynamic parameter dependent on the conditions of the gas treatment system. It is understood that the threshold temperature value is not a predetermined fixed value but a value that fluctuates over time.

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

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

[0017] According to an alternative or complementary feature of the invention, the threshold temperature value is a function, at least in part, of the movement of the liquid gas contained in the storage tank. The greater the movement of the liquid gas in the tank, the more vapor gas will be generated. Also, the greater the volume of vapor gas in the headspace of the storage tank, the greater the volume of vapor gas flowing towards the compression device. Furthermore, the greater the volume of vapor gas, the lower its temperature. Thus, the pumping unit's control and / or the pumping unit's operating indication are adapted to the volume of vapor gas generated in the headspace of the storage tank.

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

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

[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 data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device and gives an operating indication and / or controls the pumping unit according to said data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device.

[0022] According to one feature 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 unit according to said comparison.

[0023] According to a feature 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 element so that the pumping element 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 element so that the pumping element is in its second operating state.

[0024] According to one feature of the invention, the treatment method implements at least one additional step in which the control unit collects at least one data point relating to the temperature of the gas in the vapor state present in the gaseous headspace of the storage tank to determine the threshold temperature value.

[0025] According to one feature of the invention, the treatment method implements at least one additional step in which the control unit collects at least one data point 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 one feature of the invention, the treatment method implements at least one additional step during which the control unit collects at least one data point 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 prior to or simultaneously with the second step.

[0028] Other features and advantages of the invention will become apparent from the following description on the one hand, and from several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0029] [Fig.1] schematically represents a general view of a treatment system for cooling a gas in the vapor state by a gas in the liquid state by means of a pumping device controlled by a control unit;

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

[0031] [Fig.3] schematically represents the gas treatment system visible on the [Fig.1] when the pumping unit is in its first operating state and generates a circulation of a gas;

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

[0033] The features, variants, and different embodiments of the invention can be combined in various ways, provided they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features, described hereafter in isolation from the other described features, 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 through which a gas flows are shown with a thicker line when a gas flows through said conduits and with a thinner line when no gas flows through said conduits. Furthermore, the dashed lines represent an exchange of information between the control unit and an associated element of the system according to the invention.

[0036] Figure 1 schematically illustrates a gas treatment system 2 according to an embodiment of the invention. As seen in Figure 1, the gas treatment system 2 is integrated within a floating structure 4, such a floating structure 4 being shown in Figure 4. This floating structure 4 is intended to provide storage temporary storage and / or transport of liquefied gas. In what follows, the invention is described in a non-limiting manner with regard to the storage and / or transport of liquefied natural gas, which will be referred to in the following description by the acronym "LNG". For this purpose, the floating structure 4 comprises at least one LNG storage tank 6, in this case three storage tanks 6. It should be noted that the description relating to one storage tank 6 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 a liquid state at atmospheric pressure. The storage tank 6 includes a gas head 8 in which the gas resulting from the natural evaporation of the gas contained in liquid form 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 gas head 8. This gas head 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 NBOG to be contained at a safe pressure.

[0038] This gaseous headspace 8 is fluidly connected to a first line 10 in which the gas in the vapor state from the natural evaporation of the gas contained in the liquid state in the storage tank 6 circulates. It is remarkable in [Fig. 1] that the first line 10 is connected to the gaseous headspace 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 can be a propulsion engine 14 participating in moving the floating structure 4, a generator 16 intended to generate an electric current or a gas combustion unit 18, commonly referred to as a "burner".

[0040] In the embodiment shown, the first line 10 is connected to the propulsion engine 14, the generator 16 and 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 space 8 and the gas-consuming device 12, a compression device 20 for compressing the gas flowing in the first line 10 before it reaches the gas-consuming device 12 at a given pressure. In the embodiment shown, the compression device 20 consists of a main line 22 comprising a first compressor 24 and an auxiliary line 26, arranged parallel to 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 joining the gas-consuming device 12. The first compressor 24 and the second compressor 30 operate in redundancy, with the second compressor 30 taking over in case of malfunction of the first compressor 24.

[0042] The compression device 20, here the first compressor 24 or the second compressor 30, comprises a maximum of 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, cooling the compressed gas between two compression stages is complex to implement.

[0043] The main line 22 includes a first valve 32 and the auxiliary line 26 includes a second valve 34. The first valve 32 and the second valve 34 allow the gas supply from the first line 10 to the inlet of the first compressor 24 or the second compressor 30 to be controlled independently respectively.

[0044] Between the gaseous space 8 of the storage tank 6 and the compression device 20, the first line 10 includes 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 ensures that only the gaseous phase of said gas is 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 includes a second line 40 extending between a pumping element 42 and the first line 10. The second line 40 allows gas in liquid state contained in the storage tank 6 to circulate to the first line 10.

[0046] This second line 40 ensures the cooling of the NBOG, i.e. the gas resulting from the natural evaporation of the gas contained in 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 to, for example, 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 the operation of the compression device 20, the compressed gas heats up as a result of the compression performed by the compression device 20.

[0048] Furthermore, the gas resulting from the natural evaporation of the gas contained in liquid form in the storage tank 6 and accumulating in the gaseous headspace 8 is at a temperature of approximately -120°C. However, during the circulation of the NBOG from the gaseous space 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 no more than -120°C.

[0049] For this purpose, the second line 40 allows the NBOG circulating in the first line 10 to be cooled 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 admissible 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 fluid flow, i.e., between the gaseous space and the phase separator 36, allows the gas in the liquid state circulating in the second line 40 to be distributed into the first line 10.

[0051] It should be noted that the second line 40 can 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 encounter 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 a phenomenon of expansion, also known by the English designation "flash", of the gas in the liquid state which, in contact with a hotter gas, vaporizes and allows the temperature of the gas in the vapor state contained in the second line 40 to be lowered.

[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 provide an operating indication and / or control the operation of the pumping element 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 "providing 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 can control the pumping element 42 himself 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 element 42, so as to activate or deactivate it. The control unit 44 is also connected, for example electrically, to the temperature sensor 64 located at the inlet of the compression device 20 and / or a temperature probe 66 located in the top 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 located at the inlet of the compression device 20 and / or from the temperature probe 66 located in the top 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 element 42, according to a strategy implemented by the process of the invention.

[0055] Figures 2 and 3 show in more detail the management of gas circulation 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 element 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 element 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 element 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 in which the control unit 44 collects at least one data point relating to the temperature of the gas in the vapor state determined at the inlet of the compression device 20 and provides an operating indication and / or controls the pumping element 42 based on said data point 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 to measure or determine 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 positioned at the inlet of the compression device 20.

[0058] The treatment method also implements a second step in which the control unit 44 determines a threshold temperature value and a third step in 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 to the threshold temperature value and gives an operating indication and / or controls the pumping element 42 according to said comparison.

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

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

[0061] It is understood that in the embodiment shown, the pumping element 42 is an on / off type pump. Of course, in an alternative embodiment of the invention, the pumping element 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 these operating states to the other of the pumping element 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 above the threshold temperature value, then the control unit 44 provides an operating signal and / or controls the pumping element 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 below the threshold temperature value, then the control unit provides an operating signal and / or controls the pumping element 42 so that it is in its second operating state, the latter preventing the generation of heat transferred to the natural gas in the liquid state.

[0063] It is understood from the above that during the third step of the method of 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 element 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 evolving, 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 located.

[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 space 8 during an additional step of the treatment 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 gas head 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 gas head 8 and communicating them with the control unit 44. Also, depending on the temperature of the gas present in the gas head 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 no more than -110°C.

[0066] The control unit 44 is capable of collecting information relating to the flow rate of vaporized gas 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 velocity of the vaporized gas 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 vaporized gas circulating in the first line 10. Thus, depending on the measured gas flow rate, the control unit 44 adjusts the threshold temperature value so that the vaporized gas at the inlet of the compression device 20 is at a temperature of no more than -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 allows the operation of the pumping element 42 to be interrupted.

[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 its temperature. Thus, the control of the pumping element 42 and / or the operating indication of the pumping element 42 are adapted to the volume of gas in the vapor state generated in the gas head 8 of the storage tank 6.More specifically, when the amount of NBOG generated in the storage tank 6 is significant, the temperature of the NBOG at the inlet of the compression device 20 is low enough that the pumping element 42 does not need to be activated.

[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 by a conduit in which the gas in the vapor state is capable of moving from the gaseous space 8 to the compression device 20. This conduit may be subjected to external temperature constraints due to its location on the ship's deck. Its temperature therefore varies according to these external constraints.

[0070] The control unit 44 is configured to collect at least one data point relating to the temperature of the first line of the conduit so as to adjust the threshold temperature value according to the temperature of said conduit during an additional step of the treatment method. Indeed, the temperature of the gas in its vapor state circulating in the first line 10 varies according to the temperature of said conduit. A temperature sensor 68 is therefore positioned against the conduit to measure its surface temperature. More precisely, the higher the temperature of the conduit, the higher the temperature of the gas circulating in said conduit, which necessitates the activation of the pumping element 42. Conversely, if the temperature of the conduit constituting the first line decreases, then the pumping element 42 can be switched off.

[0071] Figure 4 represents the floating structure 4 comprising the storage tank 6, which is Watertight and thermally insulated, it is generally prismatic in shape and mounted in a double hull 46 of the floating structure 4, which may be a ship or a floating platform. One wall of the storage tank 6 comprises a primary watertight membrane intended to be in contact with a liquefied gas, here LNG, contained in the storage tank 6, a secondary watertight membrane arranged between the primary watertight membrane and the double hull 46 of the floating structure 4, and two thermally insulating barriers arranged respectively between the primary watertight membrane and the secondary watertight membrane and between the secondary watertight 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 suitable connectors, to a storage terminal 50 to transfer a cargo of liquefied gas and / or gas from the evaporation of liquefied gas from or to the storage tank 6.

[0073] Figure 4 also illustrates a storage terminal 50 comprising a station loading and / or unloading station 52, a subsea pipeline 54 and an onshore installation 56. The loading and / or unloading station 52 is a fixed offshore installation comprising a movable arm 58 and a tower that supports the movable arm 58. The movable arm 58 carries a bundle of insulated flexible pipes 60 that can be connected to the loading / unloading pipelines 48. The movable arm 58 is steerable and adapts to all dimensions of floating structures 4. A connecting pipeline (not shown) extends inside the tower. The loading and / or unloading station 52 enables the loading and / or unloading of the floating structure 4 from or to the storage terminal 50, which includes storage tanks for liquefied gas and / or gas from the evaporation of liquefied gas as well as connecting pipelines 62 linked by the subsea pipeline 54 to the loading and / or unloading station 52. The subsea pipeline 54 enables the transfer of liquefied gas and / or gas from the evaporation of liquefied gas between the loading and / or unloading station 52 and the floating structure 4 over a large distance, for example five kilometers, which makes it possible to keep the floating structure 4 a large distance from the coast during 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 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 its objective by proposing a treatment system that allows the operation of a pumping device to be controlled according to the cooling requirements of the gas admitted into the compression device, so as to optimize the energy balance during a ship's journey and limit operational gas losses.

[0077] The present invention is not limited to the means and configurations described and illustrated herein and also extends to any equivalent means and configuration as well as to any technically operative combination of such means.

Claims

Demands

1. A gas processing system (2) comprising at least a first line (10) through which flows a gas in the vapor state contained in a storage tank (6) and a second line (40) through which flows at least part of said gas in the liquid state contained in the storage tank (6), the first line (10) being configured to connect at least one gaseous outlet (8) of said storage tank (6) to a gas-consuming device (12) and comprising at least one compression device (20) for supplying gas to the gas-consuming device (12) and a phase separator (36) disposed between the gaseous outlet (8) and the compression device (20), the second line (40) comprising at least one pumping element (42) configured to supply the second line (40) with gas in the liquid state from the storage tank (6), said second line extending at least between said pumping element (42) and the first line (10),the second line (40) being fluidly connected to the first line (10) between the gaseous space (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 provides an operating indication and / or controls the operation of the pumping element (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 a maximum of two compression stages.

3. A gas treatment system (2) according to any one of claims 1 and 2, wherein the pumping element (42) is configured to take at least a first operating state in which the pumping element (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 element (42) does not generate the circulation of the gas in the liquid state in the second line (40), the control unit (44) being capable of switching the pumping element (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 element (42) being in its first operating state when the temperature of the gas determined at the inlet of the compression device (20) is greater than the threshold temperature value, the pumping element (42) being in its second operating state when the temperature of the gas determined at the inlet of the compression device (20) is less than the threshold temperature value.

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

6. A gas treatment system (2) according to any one of claims 4 and 5, wherein 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 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 displacement 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 processing assembly comprising a storage tank (6) and a processing system (2) according to any one of claims 1 to 9, wherein the pumping member (42) is immersed in the gas contained in liquid form 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. A 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 in which the control unit (44) collects at least one data point relating to the temperature of the gas in the state determined vapor at the inlet of the compression device (20) and gives an indication of operation and / or controls the pumping unit (42) according to said data relating to the temperature of the gas in the vapor state determined at the inlet of the compression device (20).

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

14. A treatment method according to claim 13, wherein 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 (20) is greater than the threshold temperature value then the control unit (44) gives an operating indication and / or controls the pumping element (42) so that the pumping element (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 inlet of the compression device (20) is less than the threshold temperature value then the control unit (44) gives an operating indication and / or controls the pumping element (42) so that the pumping element (42) is in its second operating state.

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

16. A treatment method according to any one of claims 13 to 15, implementing at least one additional step in which the control unit (44) collects at least one data point 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. A processing method according to any one of claims 13 to 16, implementing at least one additional step in 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.

Images