Gas supply system for high- and low-pressure gas-consuming apparatuses and method of controlling such system

Abstract

To provide a gas supply system for consumer devices included in ships, and a method for controlling such a system.SOLUTION: The invention relates to a system (1) for supplying a gas to a high-pressure gas-consuming apparatus (4) and a low-pressure gas-consuming apparatus (5) of a floating structure including a tank (8). The supply system includes a first supply circuit (2), a second supply circuit (3), a return line (14), a first heat exchanger (6), and a second heat exchanger (7). The return line includes a flow-regulating member (15). The supply system includes a device (80) for managing the supply system which includes a control module (86) configured to control the flow-regulating member on the basis of the characteristics of the gas.SELECTED DRAWING: Figure 1

Description

Technical Field

[0004] , , ,

[0001] The present invention relates to the field of storage and / or transportation vessels for gases in a liquid state, and more particularly to a gas supply system for a consumption device contained within such a vessel, as well as a method for controlling such a system.

Background Art

[0002] During a journey by a vessel equipped with a tank for a gas in a liquid state intended to be consumed and / or delivered to a destination, the vessel may be able to use at least a portion of the gas in a liquid state via a gas supply system for the supply of at least one of its engines. This is the case of a vessel having a high-pressure propulsion engine of the ME-GI type. For the supply of this type of engine, it is necessary to compress the gas to a very high pressure by a special compressor capable of compressing the gas up to an absolute pressure of 300 bar. However, such compressors are expensive, involve considerable maintenance costs, and induce vibrations in the vessel.

[0003] An alternative to the installation of such a high-pressure compressor is to vaporize the liquid gas at an absolute pressure of 300 bar using, in particular, a high-pressure pump before sending the gas to the propulsion engine. In such a solution, it is not possible to remove the vaporous gas (or BOG (Boil-Off Gas, abbreviation for boil-off gas)) that is naturally formed within the tank that at least partially houses the cargo. A low-pressure compressor can be installed for the supply of an auxiliary engine capable of consuming the low-pressure vaporous gas. The surplus boil-off gas can flow into the tank by being recondensed by the gas in a liquid state supplied to the high-pressure gas consumption device.

[0004] However, this type of system has limitations in its internal operation. Therefore, the high-pressure pump can only pump gas in liquid form and may be damaged if the gas turns into vapor. For this reason, care must be taken to prevent the liquid gas from evaporating during heat exchange with the vapor gas. However, the latter needs to be recondensed to ensure the system's effectiveness. [Overview of the Initiative]

[0005] This invention addresses such problems. A system for at least one high-pressure gas consumption device and at least one low-pressure gas consumption device of a floating structure comprising at least one tank configured to contain gas, wherein the supply system is - At least one first circuit that supplies gas to the high-pressure gas consumption device, - At least one high-pressure evaporator configured to evaporate the gas flowing through the first gas supply circuit, - A second circuit for supplying gas to the low-pressure gas consumption device, comprising at least one compressor configured to compress the gas that has entered the tank in vapor form to a pressure that meets the requirements of the low-pressure gas consumption device, - The second supply circuit includes at least one gas return line connected downstream of the compressor and extending to the tank, -At least one first heat exchanger and at least one second heat exchanger, respectively, configured to exchange heat between the gas flowing in a vapor state through the return line and the gas flowing in a liquid state through the first supply circuit. Equipped with, The first supply circuit includes a pump positioned between the first heat exchanger and the second heat exchanger. The return line is in a supply system that includes a flow rate adjustment member positioned between the first heat exchanger and the tank, The supply system includes a device for managing the supply system, The apparatus comprises at least one first sensor and a first detector configured to determine the temperature and pressure of the gas present between the first heat exchanger and the pump in the first supply circuit, a second sensor configured to determine the temperature of the gas present between the tank and the first heat exchanger in the first supply circuit, and a third sensor configured to determine the temperature of the gas present between the first heat exchanger and the flow rate adjustment member in the return line. The control device includes a control module configured to control the flow rate adjustment member according to the characteristics of the gas identified by the first sensor, the second sensor, the third sensor, and the first detector. The objective is to solve the problem by proposing a supply system characterized by the following features.

[0006] Therefore, the presence of this control device allows for the adjustment of the gas flowing through different parts of the supply system to maximize the condensation of the vaporized gas flowing through the return line, while avoiding premature evaporation of the liquid gas flowing through the first supply circuit. Since the gas temperature and / or pressure are thus identified or measured at different points in the supply system, it is possible to determine when it is possible to act on the adjustment member, thereby improving the performance of the supply system.

[0007] The first gas supply circuit can meet the fuel needs of the high-pressure gas consumption device. The first circuit supplying gas to the high-pressure gas consumption device is understood to be configured to supply gas to the high-pressure gas consumption device. The device could be, for example, a means for propelling a floating structure, such as an ME-GI engine. The first supply circuit extends from the tank to the high-pressure gas consumption device.

[0008] For a gas to be supplied to a high-pressure gas consumption device, it must be in a vapor state; therefore, a high-pressure evaporator ensures that the gas is reliably boiled off (gasified) before it can be supplied to the device. The high-pressure evaporator is where heat exchange takes place between the liquid gas flowing through the first supply circuit and a heat transfer fluid, such as glycol water, seawater, or steam. This heat transfer fluid, regardless of its form, needs to be hot enough to change the state of the gas so that it becomes vapor or supercritical before being supplied to the high-pressure gas consumption device.

[0009] Preferably, the second heat exchanger and the high-pressure evaporator form a single heat exchanger. Such a configuration may be advantageous, for example, to reduce the mechanical bulk of the supply system. The liquid gas passing through the single heat exchanger exchanges its heat with the vapor gas flowing in the return line, and simultaneously, or afterward, evaporates.

[0010] Alternatively, the second heat exchanger and the high-pressure evaporator could be two separate heat exchangers.

[0011] The pump is positioned between the first and second heat exchangers. It is the pump that increases the pressure of the liquid gas flowing through the first supply circuit, ensuring the gas has a pressure suitable for supply to the high-pressure gas consumption device. The optimal configuration is to position the pump between the two heat exchangers. Therefore, it is essential that the gas flowing through the first supply circuit and passing through the first heat exchanger remains in a liquid state at its outlet.

[0012] Generally, gases contained in a tank can turn into vapor naturally or by force through a suspended structure. Gases that have turned into vapor within a tank must be released to avoid the development of overpressure within the tank.

[0013] Such functions are provided by a second gas supply circuit of the low-pressure gas consumption device. Such a second supply circuit extends from the tank to the low-pressure gas consumption device. The expression "second circuit supplying gas to low-pressure gas consumption" is understood to mean that the second supply circuit is configured to supply gas to the low-pressure gas consumption device. The device may be, for example, an auxiliary motor such as a generator. A compressor installed in the second supply circuit is responsible for drawing in the gas present in the tank space. This is intended to both enable low-pressure power supply to the gas consumption device and to allow for the regulation of the pressure within the tank.

[0014] At the compressor outlet, the vaporized gas can be supplied to a low-pressure gas consumption device, or, if the low-pressure gas consumption device does not require or requires little fuel intake, it can flow through the return line. Since the return line is connected downstream of the compressor, the vaporized gas drawn in by the compressor can flow through it.

[0015] The vaporized gas flowing through the return line passes first through the second heat exchanger and then through the first heat exchanger before returning to the tank. In this configuration, the heat exchange between the liquid gas flowing through the first supply circuit and the vaporized gas flowing through the return line reduces the temperature of the vaporized gas as it passes through the two heat exchangers, until the gas condenses and returns to a liquid state substantially downstream of the first heat exchanger. Thus, the gas condenses, becomes liquid, and flows into the tank.

[0016] The return line includes a flow control member located downstream of the first heat exchanger. The flow control member can be partially or completely opened and closed to control the flow rate of gas flowing through the return line. The flow rate is controlled so that the maximum amount of gas in vapor state is recondensed. However, this is limited to prevent cavitation in the pump from occurring due to the evaporation of liquid gas flowing through the first supply circuit during the heat exchange taking place in the first heat exchanger.

[0017] The supply system control device can control the flow rate adjustment member, particularly in response to measurements taken by various sensors and detectors at various points within the supply system. By definition, the sensor is configured to determine the temperature of the gas, and the detector is configured to determine the pressure of the gas.

[0018] The first sensor is positioned in the first supply circuit to identify or measure the gas temperature at the outlet of the first heat exchanger. Controlling this temperature helps determine whether the gas remains in a liquid state at the outlet of the first heat exchanger, even when the gas temperature flowing through the first supply circuit rises due to heat exchange occurring within the first heat exchanger. The temperature is also identified upstream of the pump. This is done, for example, by immersing the first sensor in the gas at a location between the outlet of the first heat exchanger and the inlet of the pump.

[0019] The first detector identifies the pressure of the gas flowing similarly between the first heat exchanger and the pump in the first supply circuit. Identifying the pressure is equally important because the boil-off temperature of the gas changes depending on that pressure.

[0020] The second sensor is similarly positioned to determine the temperature of the gas flowing through the first supply circuit, but unlike the first sensor, it is positioned upstream of the first heat exchanger. The third sensor is positioned in the return line to determine the temperature of the gas upstream of the first heat exchanger and downstream of the flow rate adjustment member.

[0021] All data from the sensors and detectors is transmitted to the control module. Depending on the received data, the control module can control the regulating member to maximize the amount of condensed gas flowing through the return line without causing a boil-off of the liquid gas flowing through the first supply circuit and passing through the first heat exchanger.

[0022] According to the features of the present invention, the supply system includes a fluid analyzer configured to identify the composition of the gas in the liquid state contained in the tank. In the above-mentioned tank, several types of gases in the liquid state can be transported and / or stored. These gases all have different boil-off temperatures according to their respective compositions, for example, different types and proportions of hydrocarbons constituting the gas, and according to the changes during the transportation of the cargo. Therefore, in order to optimally control the supply system of the present invention, it is important to know the composition of the gas as the cargo, and thus its boil-off temperature.

[0023] The fluid analyzer can identify the composition of the gas when it is in the liquid state. The fluid analyzer can also identify the composition of the gas by forcibly vaporizing the gas in the liquid state.

[0024] According to one feature of the present invention, the management device includes a second detector configured to identify the pressure of the gas present in the tank, and the control module is configured to control the flow rate adjustment member according to the pressure of the gas identified by the second detector. This second detector identifies the pressure of the gas flowing through the second supply circuit. This pressure is the same as the pressure of the gas in the tank space. In other words, the second detector helps to monitor the internal pressure of the tank. Such monitoring is important to avoid the situation where the pressure in the tank is too low and the membrane of the tank may be deformed or damaged.

[0025] According to one feature of the present invention, the return line includes a flow meter configured to identify the flow rate of the gas in the vapor state flowing through the return line, and the control module is configured to control the flow rate adjustment member according to the gas flow rate identified by the flow meter. The flow meter can be controlled by the operator to limit the flow rate of the gas flowing through the return line. In this example, the flow rate adjustment member is controlled by the operator through the flow meter and the control module. The latter ensures the connection between the flow meter and the flow rate adjustment member.

[0026] According to one feature of the present invention, the first supply circuit includes at least one pumping member configured to pump the gas taken out from the liquid state in the tank. A pump, also known as a separate pumping member, is installed at the bottom of the tank to ensure that the gas in the liquid state can be pumped and flow through the first supply circuit. The pumping member is preferably a submerged pump arranged at the bottom of the tank to pump the gas in the liquid state and flow it through the first supply circuit. When the gas in the liquid state is pumped by the submerged pump, its absolute pressure rises to a value of 6 to 17 bar.

[0027] The present invention is also a method for controlling the above-described supply system, comprising: - comparing the temperature of the gas existing between the first heat exchanger and the pump in the first supply circuit with the pressure of the gas existing between the first heat exchanger and the pump in the first supply circuit, the composition of the gas flowing through the supply system, and a maximum temperature threshold specified as a function of a safety margin; - when the temperature of the gas existing between the first heat exchanger and the pump in the first supply circuit is higher than the maximum temperature threshold, reducing the passage cross-section of the flow rate adjusting member; - when the temperature of the gas existing between the first heat exchanger and the pump in the first supply circuit is lower than the maximum temperature threshold, the comparison step is performed between the temperature of the gas existing between the first heat exchanger and the flow rate adjusting member in the return line and an optimum temperature threshold specified according to the temperature and temperature difference of the gas existing between the tank and the first heat exchanger in the first supply circuit; - when the temperature of the gas existing between the first heat exchanger and the flow rate adjusting member in the return line is higher than the optimum temperature threshold, reducing the passage cross-section of the flow rate adjusting member; - when the temperature of the gas existing between the first heat exchanger and the flow rate adjusting member in the return line is lower than the optimum temperature threshold, expanding the passage cross-section of the flow rate adjusting member. Regarding the control method.

[0028] This control method adjusts the supply system to optimize the condensation of vaporized gas without compromising the proper operation of the pump.

[0029] The comparison step can ensure that the temperature of the gas flowing through the first supply circuit does not become too high at the outlet of the first heat exchanger. For this purpose, the temperature of the gas is determined by a first sensor. At this stage, the temperature of the gas at the outlet of the first heat exchanger is thus determined.

[0030] Simultaneously, or afterward, a maximum temperature threshold is determined. The purpose is to maintain the gas temperature, as raised by the first sensor, below this maximum temperature threshold. This threshold is calculated from the gas pressure identified by the first detector and the gas composition, which is somehow determined. A safety margin is then subtracted from the result. This safety margin ensures, for example, that the gas does not boil off even if it slightly exceeds the maximum temperature threshold. Such a safety margin depends on the net suction height of the pump and the identified safety threshold. Net suction height is one of the data points to be monitored. The purpose is to prevent cavitation from occurring inside the pump due to the vaporization of the liquid gas by the suction of the liquid gas at the pump inlet. The net suction height depends on the pump model used. The safety threshold can be identified by the operator and forms an additional level of safety to ensure the achievement of the objective.

[0031] Once the maximum temperature threshold and the temperature recorded by the first sensor are obtained, these two values ​​are compared to each other in the comparison step.

[0032] If the temperature recorded by the first sensor is higher than the maximum temperature threshold, this means that the gas flowing through the first supply circuit is flowing out of the first heat exchanger at an excessively high temperature. This could cause some of the gas to evaporate, and the vapor portion of the gas flowing out of the first heat exchanger could impair the operation of the pump.

[0033] An excessively high temperature at the outlet of the first heat exchanger in the first supply circuit is equivalent to excessive heat exchange within the first heat exchanger. This level of heat exchange can be reduced by limiting the flow rate of vaporized gas flowing through the return line. The control module controls the flow rate adjustment member to reduce the flow rate of vaporized gas flowing through the return line.

[0034] This reduction in flow rate results in less heat exchange in the first heat exchanger, and the gas flowing through the first supply circuit flows out of the first heat exchanger at a lower temperature, thus remaining in a liquid state.

[0035] If the gas temperature identified by the first sensor is below the maximum temperature threshold, the method proceeds to the comparison step. At this stage, it is ensured that, under the conditions of the supply system at time t, there is no risk of the liquid gas evaporating at the outlet of the first heat exchanger. Therefore, it is potentially possible to increase the flow rate of the vapor gas flowing through the return line to maximize the amount of gas condensed by the supply system.

[0036] For this purpose, the comparison step consists of first determining the temperature of the gas present between the first heat exchanger and the flow rate adjustment member in the return line via a third sensor, and simultaneously, or afterward, determining an optimal temperature threshold.

[0037] The optimal temperature threshold is the temperature identified by the second sensor, i.e., the temperature of the gas flowing through the first supply circuit, which corresponds to the temperature between the tank and the first heat exchanger, preferably the temperature measured at the inlet of the first heat exchanger plus a temperature difference. The temperature difference corresponds, for example, to pinching of the first heat exchanger. Thus, the gas temperature identified by the third sensor is compared with the optimal temperature threshold.

[0038] The objective here is to maximize the efficiency of condensation performed by the supply system. This maximization is achieved by converging the temperature identified by the third sensor to an optimal temperature threshold. Therefore, if the temperature identified by the third sensor is lower than the optimal temperature threshold, this means that more vaporized gas flowing through the return line can be condensed. Thus, the control module expands the passage cross-section of the flow control member to increase the amount of gas flowing through the return line until the gas temperature identified by the third sensor converges to the optimal temperature threshold.

[0039] If the temperature identified by the third sensor is higher than the optimal temperature threshold, this means that the condensation of vaporized gas present in the return line is not optimal. The control module then reduces the passage cross-section of the flow control member to decrease the amount of gas flowing through the return line until the gas temperature identified by the third sensor converges to the optimal temperature threshold. Since the optimal temperature threshold depends on the measured temperature, this threshold changes depending on the operating conditions of the supply system.

[0040] As described above, the comparison step follows the comparison step. However, the control method can also perform the comparison step and the comparison step simultaneously. Potential adjustment of the passage cross-section of the flow control member is performed according to the priority step, i.e., according to the comparison step, or according to the comparison step if it is determined in the comparison step that it is not necessary to reduce the passage cross-section of the flow control member.

[0041] According to one feature of this method, it can be repeated over time. The method can be repeated starting from the comparison step if the steps are consecutive, or from those steps if the comparison and contrast steps are performed simultaneously. The method can be repeated after the control of the passage cross-section of the adjustment member by the comparison or contrast step has been performed.

[0042] According to one feature of this method, the composition of the gas can be determined by the fluid analyzer. Determination of the gas composition is available at least when the step of comparing control methods has been carried out, making it possible to define a maximum temperature threshold. The fluid analyzer described above provides a solution for obtaining the gas composition, and this analysis can be performed during the loading of the cargo or thereafter, i.e., during the movement of the floating structure.

[0043] According to one feature of this method, the composition of the gas can be determined by technical documentation. This is an alternative solution to determination via a fluid analyzer, for example, when the supply system does not have such a fluid analyzer. The technical documentation is provided with the cargo and includes several characteristics of the cargo, such as the boil-off temperature of the gas as cargo. This technical documentation may include, for example, a chart that correlates the boil-off temperature with a specific pressure of the gas contained in the cargo.

[0044] According to one feature of this method, the maximum temperature threshold can be determined by a data table for several types of gases. If gas analyzers or technical documentation are unavailable, the data table can be relied upon. Such a table contains boil-off temperatures as a function of pressure for most types of natural gas known to date that are transported and / or stored by ship. Therefore, by increasing the pressure identified by the first detector, the lowest boil-off temperature among the various types of gases at the identified pressure is used to set the maximum temperature threshold, while taking safety margins into consideration. Such a data table can be read manually or entered into the memory of the control device to automate the determination of the maximum temperature threshold.

[0045] According to the features of this method, the safety margin and temperature difference correspond to values ​​of 1°C to 3°C. These are relatively close to the actual temperature limit and are sufficient so as not to impair the optimization of the supply system's operation.

[0046] According to the features of this method, the pressure of the gas identified by the second detector is compared with a pressure threshold. This identification is performed in parallel with the steps described above. The second detector can identify the pressure of the gas flowing through the second supply circuit, and consequently, the dominant pressure in the tank space. This identification can ensure that the internal pressure of the tank does not become excessively low. Excessively low internal tank pressure can lead to membrane deformation. Therefore, it is necessary to maintain the internal pressure of the tank above the pressure threshold. The pressure threshold corresponds to a fixed value, below which it is assumed that the internal pressure of the tank may cause deformation of the tank membrane. For example, the pressure threshold may be -60 millibars or -30 millibars relative to the external pressure.

[0047] According to one feature of the present invention, the method includes the step of interrupting the gas flow in the return line when the pressure of the gas identified by the second detector is lower than the pressure threshold. The gas flow in the second supply circuit and the return line is a result of drawing vaporized gas into the tank space, which leads to a decrease in the internal pressure of the tank. Therefore, if the pressure in the tank space falls below the pressure threshold, the tank membrane may be damaged. To prevent this pressure drop, the control member completely closes the flow rate adjustment member.

[0048] Other features and advantages of the present invention will become apparent from both the following description and several exemplary embodiments, which are made for illustrative purposes only and not limited thereto, with reference to the accompanying schematic drawings. [Brief explanation of the drawing]

[0049] [Figure 1] Figure 1 is a schematic diagram of the supply system according to the present invention. [Figure 2] Figure 2 is a flowchart of the control method for the supply system according to the present invention. [Figure 3] Figure 3 is a flowchart of a control method for monitoring the amount of gas in vapor state. [Figure 4]Figure 4 shows examples of data tables for several types of gases that can be used to implement the control method. [Figure 5] Figure 5 is a schematic cutout of a floating structure tank and a terminal for loading and / or unloading this tank. [Modes for carrying out the invention]

[0050] In the following description, the terms “upstream” and “downstream” are used to indicate the position of an element within a circuit of a gas in a liquid or vapor state, and refer to the direction in which the gas flows within the circuit.

[0051] Figure 1 shows a gas supply system 1 located on a floating structure. This supply system 1 can supply gas, which may be in a liquid, vapor, two-phase, or supercritical state, from a storage tank and / or transport tank 8 to a high-pressure gas consumption device 4 and a low-pressure gas consumption device 5 for the purpose of fueling them.

[0052] The floating structure may be, for example, a ship capable of storing and / or transporting gas in liquid form, particularly natural gas. In this example, the supply system 1 can use the liquid gas stored and / or transported by the floating structure to supply a high-pressure gas consumption device 4, which may be, for example, a propulsion engine, and a low-pressure gas consumption device 5, which may be, for example, a generator that supplies electricity to the floating structure.

[0053] To ensure that the gas contained in the tank 8 is reliably delivered to the high-pressure gas consumption device 4, the supply system 1 has a first gas supply circuit 2. The first supply circuit 2 includes a pressurizing member 9, preferably a submersible pump 9, located inside the tank 8. The submersible pump 9 can pressurize the gas in liquid form and, in particular, deliver it into the first supply circuit 2. By pumping up the gas in liquid form, the pressurizing member 9 raises its absolute pressure to a value of 6 to 17 bar.

[0054] The liquid gas flows from the tank 8 to the high-pressure gas consumption device 4, passing through the first heat exchanger 6 and being pressurized by the pump 10. The liquid gas then passes through a single heat exchanger 21, which combines the second heat exchanger 7 and the high-pressure evaporator 11. However, the second heat exchanger 7 and the high-pressure evaporator 11 can be separate components. Further details regarding the heat exchangers are described below.

[0055] A single heat exchanger 21 can change the state of the gas flowing through the first supply circuit 2 via the high-pressure evaporator 11, transforming it into a vapor state or a supercritical state. In such a state, the gas can be adapted for supply to the high-pressure gas consumption device 4. Evaporation of the liquid gas can be carried out, for example, by heat exchange with a heat transfer fluid having a temperature sufficiently high to evaporate the liquid gas, in this example glycol water, seawater, or steam.

[0056] The increase in gas pressure is guaranteed by the pump 10 when it pumps the gas in liquid state. The pump 10 can increase the absolute pressure of the gas in liquid state to a value of 30 to 400 bar, especially when using ammonia or hydrogen; to a value of 30 to 70 bar when using liquefied petroleum gas; and preferably to a value of 150 to 400 bar when using liquefied natural gas consisting mainly of ethane, ethylene, or methane.

[0057] The combination of pump 10 and a single heat exchanger 21 ensures that the gas is pressurized and suitable for supply to the high-pressure consumption device 4. This configuration avoids the need to install a high-pressure compressor in the first supply circuit 2, which is subject to cost constraints and generates strong vibrations.

[0058] Within tank 8, some of the gas cargo may spontaneously change into vapor and diffuse into the tank's space 12. To avoid overpressure within tank 8, the vaporized gas contained in tank space 12 must be discharged.

[0059] Therefore, the supply system 1 includes a second gas supply circuit 3 that supplies vaporized gas to the low-pressure gas consumption device 5. The second supply circuit 3 extends between the tank space 12 and the low-pressure gas consumption device 5. The second supply circuit 3 is equipped with a compressor 13 to draw in vaporized gas contained in the tank space 12. The compressor 13 not only draws in vaporized gas but can also compress the vaporized gas flowing through the second supply circuit 3 to an absolute pressure of 6 to 20 bar. This brings the vaporized gas to a pressure suitable for supply to the low-pressure gas consumption device 5. Thus, the second supply circuit 3 enables supply to the low-pressure gas consumption device 5 while adjusting the pressure in the tank 8 by drawing in vaporized gas present in the tank space 12.

[0060] If an excess amount of vaporized gas is present in the tank space 12, overpressure will occur in the tank 8. Therefore, it is necessary to discharge the vaporized gas to reduce the pressure in the tank 8. The excess vaporized gas can be removed, for example, by a burner (combustor) 18, or discharged into the atmosphere in an embodiment not shown, which may result in cargo loss. However, the supply system 1 according to the present invention includes a return line 14 extending from the second supply circuit 3 to the tank 8.

[0061] The return line 14 is connected to the second supply circuit 3 downstream of the compressor 13 in the direction of flow of the vaporized gas flowing through the second supply circuit 3. The return line 14 passes through a single heat exchanger 21 in the first step. For this reason, the single heat exchanger 21 comprises a first pass 24 through which liquid gas flows from the first supply circuit 2, a second pass 28 through which vaporized gas flows from the return line 14, and a third pass 29 through which a heat transfer fluid flows that evaporates the liquid gas flowing through the first pass 24.

[0062] At the outlet of the second pass 28 of the single heat exchanger 21, the vaporized gas flows until it passes through the first heat exchanger 6. The inlet of the first heat exchanger 6 is where the liquid gas in the first supply circuit 2 has the lowest temperature. Therefore, the gas flowing through the return line 14 condenses after passing through the first heat exchanger 6. As a result, the gas from the return line 14 is in a vaporized state at the inlet of the first heat exchanger 6, but flows out in a liquid state after the heat exchange that takes place in the first heat exchanger 6.

[0063] The return line 14 also includes a flow rate adjustment member 15 that controls the flow rate of the fluid flowing through the return line 14. This flow rate adjustment member 15 has a changeable passage cross-section. The gas flows to the tank 8 after condensation. Thus, the first heat exchanger 6 functions as a condenser. Meanwhile, the flow rate adjustment member 15 controls the heat exchange that takes place in the first heat exchanger 6 and the single heat exchanger 21.

[0064] The supply system 1 is further equipped with an auxiliary supply line 16. The auxiliary supply line 16 extends from the first supply circuit 2, through a cock located between the pressurizing member 9 and the first heat exchanger 6, to the second supply circuit 3, which is connected between the compressor 13 and the low-pressure gas consumption device 5. The auxiliary supply line 16 can supply power to the low-pressure gas consumption device 5 when the flow rate of vaporized gas formed in the tank space 12 is insufficient.

[0065] If there is not a sufficient amount of vaporized gas in the tank space 12, liquid gas pumped by the submersible pump 9 may flow into this auxiliary supply line 16 for supply to the low-pressure gas consumption device 5. For this purpose, the auxiliary supply line 16 passes through the low-pressure evaporator 17. This causes the liquid gas flowing through the auxiliary supply line 16 to become vaporized. The operation of the low-pressure evaporator 17 may be identical to that of, for example, the high-pressure evaporator 11. That is, it evaporates the gas to a temperature high enough to boil off the liquid gas by heat exchange with a heat transfer fluid. At the outlet of the low-pressure evaporator 17, the vaporized gas flows through the auxiliary supply line 16 and then joins the second supply circuit 3 for supply to the low-pressure gas consumption device 5.

[0066] From the above, it is understood that the auxiliary supply line 16 is used only when there is insufficient vaporized gas in the tank space 12. Therefore, the auxiliary supply line 16 is equipped with a valve 19 that restricts the flow of gas in the auxiliary supply line 16 when its use is not required.

[0067] The pump 10 is advantageously positioned between the first heat exchanger 6 and the single heat exchanger 21. The pump 10 can only pump gas in a liquid state. To avoid impairing its proper operation, it is important to maintain the gas flowing through the first supply circuit 2 in a liquid state at the outlet of the first heat exchanger 6.

[0068] Furthermore, one of the objectives of the supply system 1 according to the present invention is to re-condense the maximum amount of vaporized gas formed in the tank space 12 and not consumed by the low-pressure gas consumption device 5, without the gas flowing through the first supply circuit 2 boiling off as it passes through the first heat exchanger 6.

[0069] For this purpose, the supply system 1 is equipped with a control device 80 that ensures control of the various parameters described above. The control device 80 is equipped with, in particular, a first sensor 81, a second sensor 82, a third sensor 83, a first detector 84, and a second detector 85. The fact that sensors 81, 82, and 83 determine the gas temperature and detectors 84 and 85 determine the gas pressure will be discussed below. The control device 80 also includes a control module 86 that receives various data determined by sensors 81, 82, 83 and detectors 84 and 85. In response to this data, the control module 86 can act on a flow rate adjustment member 15 to change the flow rate of the gas flowing through the return line 14.

[0070] The first sensor 81 is located in the first supply circuit 2 between the first heat exchanger 6 and the pump 10. The second sensor 82 is located in the first supply circuit 2 between the tank 8 and the first heat exchanger 6. The third sensor 83 is located in the return line 14 between the first heat exchanger 6 and the flow rate adjustment member 15. Each of the sensors 81, 82, and 83 is configured to determine the temperature of the gas flowing at each of the respective locations of the sensors 81, 82, and 83. The temperature of the gas flowing through these different sections of the supply system 1 is used to control the flow rate adjustment member 15. The same applies to the pressure determined by the detector 84 located in the first supply circuit 2 between the first heat exchanger 6 and the pump 10, and the second detector 85 located in the second supply circuit 3 between the tank 8 and the compressor 13.

[0071] The control device 80 may also include a fluid analyzer 87 capable of determining the composition of the liquid gas contained in the tank 8. The fluid analyzer 87 may be able to directly determine the composition of the liquid gas, or it may be necessary to vaporize the gas to determine its composition. Knowing the gas composition is advantageous for determining the gas's boil-off temperature, as will be described in detail below. The gas composition determined by the fluid analyzer 87, as well as the temperature and pressure values, is transmitted to the control module 86. However, the gas composition may be given through technical documentation regarding the gas as cargo, or it may correspond to the type of gas whose characteristics are listed in a data sheet, as shown below.

[0072] The return line 14 may also include a flow meter 88. The flow meter is configured to determine the gas flow rate through the return line 14. Advantageously, the gas flow rate is determined between the connection point with the second supply circuit 3 and the single heat exchanger 21. The flow meter 88 is also connected to a control module 86 which can act on a flow rate adjustment member 15. Thus, the operator can act on the flow meter 88 so that the control module 86 receives information from the flow meter 88 and acts on the flow rate adjustment member 15 in accordance with this information from the flow meter 88.

[0073] Figure 2 is a flowchart that illustrates the various steps of the control method 100 according to the present invention, for example, when implemented by the control device described above.

[0074] The control method 100 begins with a comparison step 101 between the gas temperature measured by the first sensor 81 and the maximum temperature threshold Tmax. The gas temperature identified by the first sensor 81 corresponds to the temperature of the gas flowing through the first supply circuit at the outlet of the first heat exchanger. In particular, this may be a field measurement by placing the first sensor 81 at any position between the outlet of the first heat exchanger path, which forms part of the first supply circuit, and the inlet of the pump, as shown in Figure 1. Alternatively, this may be an estimate or calculated value created from other data of the system.

[0075] Prior to, or simultaneously with, the determination of the gas temperature by the first sensor 81, or afterward, the maximum temperature threshold Tmax is defined from the gas pressure, gas composition, and safety margin determined by the first detector. The gas pressure used when determining the maximum temperature threshold Tmax corresponds to the pressure at the outlet of the first heat exchanger of the gas flowing through the first supply circuit.

[0076] Similar to the first sensor 81, the first detector may measure the pressure in situ or obtain it from an estimate or calculation created from other data in the system.

[0077] Once the gas pressure and composition are known, the gas boil-off temperature can be determined. The pressure is determined by the first detector 84, while the gas composition can be obtained by the fluid analyzer 87 shown in Figure 1. If the supply system does not include a fluid analyzer, the gas composition can be obtained from technical documentation about the cargo, particularly provided at the time of cargo loading. If neither of these is available, the maximum temperature threshold Tmax can be determined using a data table shown in Figure 4, which groups different types of gases and has different boil-off temperatures corresponding to the pressure of each gas. Since the pressure determined by the first detector 84 is known, the data table is read from this pressure by selecting the lowest boil-off temperature. The purpose of this is to ensure that, regardless of the type of gas contained in the tank, this gas has at least this selected temperature as its boil-off temperature.

[0078] The maximum temperature threshold Tmax is finally obtained by subtracting a safety margin from the previously obtained gas boil-off temperature. The safety margin depends on the pump's net suction height and safety threshold. The net suction height is specific to the pump used in the first supply circuit and corresponds to the limit at which the pump may boil off the gas by pumping the gas in a liquid state. The safety threshold can be selected by the operator. The safety margin may be, for example, 1°C to 3°C to obtain a maximum temperature threshold Tmax that is slightly lower than the actual gas boil-off temperature.

[0079] After the maximum temperature threshold is obtained, a comparison can be made between this threshold and the gas temperature identified by the first sensor 81.

[0080] If the gas temperature identified by the first sensor 81 is higher than the maximum temperature threshold, this means that at least part of the gas flowing through the first supply circuit may boil off due to excessively high temperatures flowing out of the first heat exchanger, potentially damaging the pump.

[0081] If the gas temperature between the first heat exchanger and the pump is too high, it means that excessive heat exchange is occurring within the first heat exchanger. To suppress this heat exchange, the flow rate of gas in the return line must be reduced.

[0082] Therefore, if the temperature identified by the first sensor 81 is greater than the maximum temperature threshold, the control method 100 proceeds to step 103 of reducing the passage cross-section. In this reduction step 103, the control module shown in Figure 1 acts on the flow rate adjustment member 15 to reduce its passage cross-section. The purpose of this is to reduce the flow rate of gas flowing in the return line, thereby limiting the rise in heat exchange in the first heat exchanger and, consequently, the temperature rise of the gas flowing in the first supply circuit. This prevents the gas from boiling off upstream of the pump.

[0083] Once the reduction step 103 is complete, the control method 100 may be repeated from the comparison step 101, for example, to verify whether the temperature of the gas flowing between the first heat exchanger and the pump has actually decreased.

[0084] If the gas temperature identified by the first sensor 81 is lower than the maximum temperature threshold Tmax, the control method 100 proceeds to the comparison step 102.

[0085] The comparison step 102 is performed between the gas temperature measured by the third sensor 83, i.e., the temperature of the gas flowing in the return line after passing through the first heat exchanger, and the optimal temperature threshold Topt. The optimal temperature threshold Topt corresponds to the temperature at which a temperature difference is added to the gas temperature identified by the second sensor, i.e., the temperature of the gas flowing in the first supply circuit upstream of the first heat exchanger. This difference can be +1°C to +3°C, as well as a safety margin. The temperature difference is the minimum difference between the temperature of the liquid gas coming from the tank and flowing into the first heat exchanger 6, for example, measured by the second sensor 82, and the temperature of the gas flowing in the return line 14, measured at the outlet of the first heat exchanger 6, for example, measured by the third sensor. This temperature difference can correspond to pinching of the first heat exchanger 6.

[0086] The second and third sensors 83 may measure temperature on-site, i.e., at the locations described above, or they may be obtained from estimates or calculations created from other data of the system.

[0087] The comparison step 102 optimizes the condensation of the gas flowing through the return line. The objective is to converge the temperature value of the gas flowing through the return line at the outlet of the first heat exchanger to the optimal temperature threshold Topt in order to achieve optimal condensation at the maximum amount. If the gas flowing through the return line and out of the first heat exchanger has an excessively high temperature, this means that too much gas is flowing for effective condensation. Conversely, if the gas flowing through the return line and out of the first heat exchanger has an excessively low temperature, this means that the gas flow rate can be increased to condense a larger amount of gas in a given time.

[0088] Next, the temperature identified by the third sensor 83 is compared with the optimal temperature threshold Topt. Whether the gas temperature identified by the third sensor 83 is higher or lower than the optimal temperature threshold Topt, the control method 100 proceeds to a step in which the control module adjusts the passage cross-section of the flow rate adjustment member. More specifically, if the gas temperature identified by the third sensor 83 is higher than the optimal temperature threshold Topt, the control method 100 proceeds to a step 103 in which the passage cross-section of the flow rate adjustment member is reduced. This reduction step 103 is similar to the steps that may arise from the comparison step 101. Conversely, if the gas temperature identified by the third sensor 83 is higher than the optimal temperature threshold Topt, the control method 100 proceeds to a step 104 in which the passage cross-section of the flow rate adjustment member is reduced.

[0089] In Figure 2, the comparison step 101 and the contrast step 102 are performed sequentially, but note that the comparison step 101 is performed first. However, the control method 100 may be configured to perform the comparison step 101 and the contrast step 102 simultaneously. Even then, the comparison step 101 still takes precedence over the contrast step 102.

[0090] After a reduction step 103 or expansion step 104 is performed according to the comparison step 101 or comparison step 102, the control method 100 may be repeated starting from the comparison step 101 if the steps are consecutive, or from two simultaneous steps as described above. It is a priority to ensure that the liquid gas flowing through the first supply circuit does not flow out in a state of at least partial evaporation. Therefore, the comparison step 101 takes precedence over the condensation optimization operation of the vapor-state gas flowing through the return line, which corresponds to the comparison step 102.

[0091] Figure 3 is a flowchart of part of the control method for monitoring the internal pressure of the tank space. This part of the control method is carried out in parallel with what was described in Figure 2 and, in particular, consists of a monitoring step 105 in which a specific pressure in the tank space is compared with a pressure threshold Pref. The pressure threshold Pref may correspond to a value of, for example, -30 millibars or -60 millibars relative to the external pressure. A second detector 85 identifies, for example, the pressure of the gas flowing through the second supply circuit between the tank and the compressor, and generally the internal pressure of the tank space.

[0092] Next, the pressure identified by the second detector 85 is compared with a pressure threshold Pref. The threshold is fixed below the pressure value at which the tank wall may be damaged, and corresponds to this value.

[0093] Therefore, if the pressure identified by the second detector 85 is below the pressure threshold Pref, this means that if the pressure in the tank space drops further, the tank walls may be damaged. A suspension step 110 is performed in which the control module completely closes the flow control member. In such a situation, the supply system can be deployed while waiting for the pressure in the tank space to rise. Alternatively, a low-pressure gas consumption device may be powered by the auxiliary supply line 16 shown in Figure 1.

[0094] If the pressure identified by the second detector 85 is higher than the pressure threshold, the control method may proceed while continuing to monitor the pressure value identified by the second detector 85.

[0095] Figure 4 shows data table 106, which allows us to identify the maximum temperature threshold Tmax mentioned in Figure 2. This data table 106 shows the boil-off temperature as a function of pressure identified by the first detector for five different types of gases A, B, C, D, and E.

[0096] Therefore, if the composition of the gas contained in the tank is unknown, the theoretical boil-off temperature as a function of the pressure identified by the first detector is determined using data table 106. The selected boil-off temperature is as low as possible, more so than the gas composition, to ensure that the gas contained in the tank remains in a liquid state at the outlet of the first heat exchanger in the first supply circuit. Thus, in Figure 4, the first type of gas A is selected. After applying a safety margin, the maximum temperature threshold is then determined.

[0097] Figure 5 is a cutaway view of a floating structure 20 showing a tank 8 containing gas in liquid and vapor states. The tank 8 has an overall prismatic shape and is mounted on the double hull 22 of the floating structure 20. The walls of the tank 8 include a primary seal membrane intended to come into contact with the liquid gas contained in the tank 8, a secondary seal membrane positioned between the primary seal membrane and the double hull 22 of the floating structure 20, and two thermal insulation barriers positioned between the primary seal membrane and the secondary seal membrane, and between the secondary seal membrane and the double hull 22, respectively.

[0098] A pipe 23 for loading and / or unloading liquid gas is located on the upper deck of the floating structure 20. The loading and / or unloading pipe 23 can be connected to an offshore or port terminal by appropriate connectors to transfer liquid gas as cargo to or from tank 8.

[0099] Figure 5 also shows an example of a marine terminal comprising a port or distribution terminal loading and / or unloading station 25, an underwater duct 26, and land-based and / or port facilities 27. The land-based and / or port facilities 27 may be located, for example, on a port dock, or, according to another example, on a concrete gravity platform. The land-based and / or port facilities 27 include a storage tank 30 for gas in liquid state and a connecting pipe 31 connected to the loading and / or unloading facilities 25 by an underwater pipe 26.

[0100] Pumps installed on land and / or port facilities 27, and / or pumps equipped on floating structures 20 are implemented to generate the pressure necessary for transferring the gas in liquid form.

[0101] Naturally, the present invention is not limited to the embodiments described above, and many modifications can be made to these embodiments without departing from the scope of the present invention.

[0102] As described above, the present invention can propose a gas supply system equipped with a control device that clearly achieves its intended purpose and ensures control of the temperature and condensation of the gas. Modifications not described herein can be carried out without departing from the context of the present invention, because, according to the present invention, the modifications comprise a gas supply system according to the present invention.

Claims

1. A system (1) for supplying gas to at least one high-pressure gas consumption device (4) and at least one low-pressure gas consumption device (5) of a floating structure (20) comprising at least one tank (8) configured to contain the gas, wherein the supply system (1) - At least one first circuit (2) that supplies gas to the high-pressure gas consumption device (4), - At least one high-pressure evaporator (11) configured to evaporate the gas flowing through the first gas supply circuit (2), - A second circuit (3) that supplies gas to the low-pressure gas consumption device (5), comprising at least one compressor (13) configured to compress the gas that enters the tank (8) in vapor form to a pressure that meets the requirements of the low-pressure gas consumption device (5), - The second supply circuit (3) is connected downstream of the compressor (13) and includes at least one gas return line (14) that extends to the tank (8), - At least one first heat exchanger (6) and at least one second heat exchanger (7) are configured to exchange heat between the gas flowing in a vapor state through the return line (14) and the gas flowing in a liquid state through the first supply circuit (2), Equipped with, The first supply circuit (2) includes a pump (10) positioned between the first heat exchanger (6) and the second heat exchanger (7). The return line (14) is located in a supply system (1) that includes a flow rate adjustment member (15) positioned between the first heat exchanger (6) and the tank (8), The supply system (1) includes a device (80) for managing the supply system (1), The apparatus (80) comprises at least one first sensor (81) and a first detector (84) configured to determine the temperature and pressure of the gas present between the first heat exchanger (6) and the pump (10) in the first supply circuit (2), a second sensor (82) configured to determine the temperature of the gas present between the tank (8) and the first heat exchanger (6) in the first supply circuit (2), and a third sensor (83) configured to determine the temperature of the gas present between the first heat exchanger (6) and the flow rate adjustment member (15) in the return line (14), The control device (80) includes a control module (86) configured to control the flow rate adjustment member (15) according to the characteristics of the gas identified by the first sensor (81), the second sensor (82), the third sensor (83), and the first detector (84). A supply system characterized by (1).

2. The system includes a fluid analyzer (87) configured to identify the composition of the gas in liquid state contained in the tank (8), The supply system (1) according to claim 1.

3. The control device (80) includes a second detector (85) configured to identify the pressure of the gas present in the tank (8), The control module (86) is configured to control the flow rate adjustment member (15) according to the pressure of the gas identified by the second detector (85). The supply system (1) according to claim 1 or 2.

4. The return line (14) includes a flow meter (88) configured to determine the flow rate of the vaporized gas flowing through the return line (14), The control module (86) is configured to control the flow rate adjustment member (15) according to the gas flow rate identified by the flow meter (88). The supply system (1) according to claim 1 or 2.

5. The first supply circuit (2) includes at least one pumping member (9) configured to pump the gas extracted from the liquid state in the tank (8). The supply system (1) according to claim 1 or 2.

6. A method (100) for controlling the supply system (1) according to claim 1, - The procedure includes a step (101) of comparing the temperature of the gas present between the first heat exchanger (6) and the pump (10) in the first supply circuit (2) with the pressure of the gas present between the first heat exchanger (6) and the pump (10) in the first supply circuit (2), the composition of the gas flowing through the supply system (1), and a maximum temperature threshold (Tmax) which is specified as a function of a safety margin. - If the temperature of the gas present between the first heat exchanger (6) and the pump (10) in the first supply circuit (2) is higher than the maximum temperature threshold (Tmax), the passage cross-section of the flow rate adjustment member (15) is reduced. - If the temperature of the gas present between the first heat exchanger (6) and the pump (10) in the first supply circuit (2) is lower than the maximum temperature threshold (Tmax), the comparison step (102) is performed between the temperature of the gas present between the first heat exchanger (6) and the flow rate adjustment member (15) in the return line (14) and the optimal temperature threshold (Topt) which is determined according to the temperature and temperature difference of the gas (2) present between the tank (8) and the first heat exchanger (6) in the first supply circuit. - If the temperature of the gas present between the first heat exchanger (6) and the flow rate adjustment member (15) in the return line (14) is higher than the optimal temperature threshold (Topt), the passage cross-section of the flow rate adjustment member (15) is reduced. - If the temperature of the gas present between the first heat exchanger (6) and the flow rate adjustment member (15) in the return line (14) is lower than the optimal temperature threshold (Topt), the passage cross-section of the flow rate adjustment member (15) is enlarged. Control method (100).

7. The control method (100) according to claim 6, which can be repeated over time.

8. The composition of the gas is determined by the fluid analyzer (87). A control method (100) according to claim 6 or 7 for controlling a supply system (1) comprising a fluid analyzer (87) configured to identify the composition of the liquid gas contained in the tank (8).

9. The composition of the aforementioned gas is specified in the technical documentation. The control method (100) according to claim 6 or 7.

10. The aforementioned maximum temperature threshold is determined by a data table (106) for several types of gases. The control method (100) according to claim 6 or 7.

11. The safety margin and temperature difference correspond to values ​​between 1°C and 3°C. The control method (100) according to claim 6 or 7.

12. The pressure of the gas identified by the second detector (85) is compared with a pressure threshold (Pref). The control device (80) comprises a second detector (85) configured to identify the pressure of the gas present in the tank (8), and the control module (86) controls a supply system (1) configured to control the flow rate adjustment member (15) according to claim 6 or 7.

13. The system includes a step (110) of interrupting the gas flow in the return line (14) if the pressure of the gas identified by the second detector (85) is lower than the pressure threshold (Pref), The control method (100) according to claim 12.

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