Gas supply system for gas appliances with high and low pressure and method for controlling such a system

Description

[0001] The present invention relates to the field of ships for the storage and / or transport of gas in liquid form and more particularly concerns a gas supply system for consuming appliances included within such ships, as well as a method for controlling such a system.

[0002] During a voyage undertaken by a vessel carrying a tank of liquid gas intended for consumption and / or delivery to a destination, the vessel may be capable of using at least some of the liquid gas to power at least one of its engines via a gas supply system. This is the case for vessels equipped with a high-pressure propulsion engine of the ME-GI type. To power this type of engine, the gas must be compressed to very high pressure by special compressors capable of compressing the gas up to 300 bar absolute, but such compressors are expensive, incur significant maintenance costs, and induce vibrations within the vessel.

[0003] An alternative to installing these high-pressure compressors is to vaporize the gas in liquid form at 300 bar absolute, notably using a high-pressure pump, before it is sent to the propulsion engine. Since this solution does not eliminate the gas in vapor form (or BOG, which stands for Boil-Off Gas) that naturally forms within a tank containing at least part of the cargo, low-pressure compressors can be installed to power an auxiliary engine capable of consuming the gas in vapor form at low pressure. Excess gas vapor can be recirculated back to the tank, where it is recondensed by the liquid gas supplying the high-pressure gas-consuming equipment.

[0004] This type of system, however, has certain constraints that must be observed. For example, the high-pressure pump can only pump gas in its liquid state and risks being damaged if the gas passes through it in its vapor state. Therefore, care must be taken to ensure that the liquid gas does not evaporate during heat exchange with the vapor gas. The vapor gas must, however, be recondensed to guarantee the system's efficiency. Document EP3483419 describes a gas supply system for at least one high-pressure gas-consuming appliance and at least one low-pressure gas-consuming appliance of a floating structure, in accordance with the prior art.

[0005] The present invention aims to solve such problems by proposing a gas supply system for at least one high-pressure gas-consuming device and at least one low-pressure gas-consuming device of a floating structure comprising at least one tank configured to contain the gas, the supply system being as defined by claim 1.

[0006] The presence of this control device allows for the regulation of gas circulating within the various parts of the supply system in order to maximize the condensation of the gas in its vapor state circulating in the return line, while preventing premature evaporation of the gas in its liquid state circulating in the first supply circuit. The temperature and / or pressure of the gas is thus determined or measured at different points in the supply system, making it possible to determine the extent to which the control device can be adjusted and therefore improve the performance of the supply system.

[0007] The first gas supply circuit provides the fuel required by the high-pressure gas-consuming device. The first gas supply circuit for the high-pressure gas-consuming device is understood to be the first supply circuit configured to supply gas to the high-pressure gas-consuming device. This device could, for example, be the propulsion system for the floating structure, such as an ME-GI engine. The first supply circuit extends from the tank to the high-pressure gas-consuming device.

[0008] Since the gas must be in a vapor state to supply the high-pressure gas-consuming appliance, the high-pressure evaporator ensures the gas evaporates before being delivered to the appliance. The high-pressure evaporator is the site of a heat exchange between the liquid gas circulating in the first supply circuit and a heat transfer fluid, such as glycol water, seawater, or steam. This heat transfer fluid, regardless of its form, must be at a sufficiently high temperature to induce a phase change in the gas, causing it to transition to a vapor or supercritical state and supply the high-pressure gas-consuming appliance.

[0009] Preferably, the second heat exchanger and the high-pressure evaporator form a single heat exchanger. Such a configuration can be advantageous, for example, to reduce the mechanical footprint of the feed system. The liquid gas, passing through the single heat exchanger, exchanges its heat with the vapor gas circulating in the return line and is also evaporated simultaneously or successively.

[0010] Alternatively, the second heat exchanger and the high-pressure evaporator can 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 circulating in the first supply circuit, ensuring it reaches a pressure suitable for supplying the high-pressure gas-consuming appliance. The optimal arrangement is to place the pump between the two heat exchangers. Therefore, it is essential to ensure that the gas circulating in the first supply circuit and passing through the first heat exchanger remains in a liquid state upon exiting it.

[0012] Generally, the gas contained in the tank can naturally, or be forced by the floating structure, into a vapor state. The gas within the tank that vaporizes must be vented to prevent overpressure within the tank.

[0013] This function is performed by the second gas supply circuit of the low-pressure gas-consuming appliance. This second supply circuit extends from the tank to the low-pressure gas-consuming appliance. The second gas supply circuit of the low-pressure gas-consuming appliance is understood to be the circuit configured to supply gas to the low-pressure gas-consuming appliance. This appliance could, for example, be an auxiliary engine such as an electric generator. The compressor located on the second supply circuit is responsible for drawing gas from the top of the tank in order to both supply the low-pressure gas-consuming appliance and regulate the pressure within the tank.

[0014] At the compressor outlet, the vaporized gas can supply the low-pressure gas-consuming appliance and / or flow through the return line if the low-pressure gas-consuming appliance requires little or no fuel. Since the return line is connected downstream of the compressor, the vaporized gas drawn in by the compressor can therefore flow through it.

[0015] The gas in its vapor state circulating in the return line first passes through the second heat exchanger, then the first heat exchanger, before returning to the tank. According to this configuration, thanks to the heat exchange occurring between the gas and l'état With liquid circulating in the first supply circuit and gas in a vapor state circulating in the return line, the temperature of the vapor gas decreases 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. The condensed gas, that is, in a liquid state, then flows to the tank.

[0016] The return line includes a flow control device located downstream of the first heat exchanger. This flow control device is capable of opening or closing partially or fully to control the flow rate of the gas circulating in the return line. The flow rate is controlled to maximize the recondensation of the vaporized gas. However, it is limited to prevent evaporation of the liquid gas circulating in the first supply circuit during the heat exchange occurring in the first heat exchanger, which would cause pump cavitation.

[0017] The power supply system management device controls the flow regulator based on measurements taken by various sensors and detectors within the power supply system and at different locations within it. By definition, the sensors are configured to determine the gas temperature, while the detectors are configured to determine the gas pressure.

[0018] The first sensor is positioned to determine or measure the gas temperature in the first supply circuit at the outlet of the first heat exchanger. Monitoring this temperature helps determine whether the gas at the outlet of the first heat exchanger is maintained in a liquid state, as the heat exchange occurring within the first heat exchanger increases the temperature of the gas circulating in the first supply circuit. The temperature can also be determined upstream of the pump, for example, by immersing the first sensor in the gas at a point located between the outlet of the first heat exchanger and the inlet of the pump.

[0019] The first sensor determines the pressure of the gas circulating within the first supply circuit between the first heat exchanger and the pump. Determining the pressure is also important because the gas's evaporation temperature varies with its pressure.

[0020] The second sensor is also positioned to determine the temperature of the gas circulating in the first supply circuit, but upstream of the first heat exchanger, unlike the first sensor. The third sensor is positioned to determine the temperature of the gas on the return line, downstream of the first heat exchanger and upstream of the flow control device.

[0021] All data from the sensors and detector are transmitted to the control module. Based on the data received, the control module is able to control the regulating device in order to maximize the amount of condensed gas circulating in the return line, but without causing evaporation of the gas in a liquid state circulating in the first supply circuit and passing through the first heat exchanger.

[0022] According to one feature of the invention, the feeding system includes a fluid analyzer configured to determine the composition of the liquid gas contained in the tank. Several types of liquid gases can be transported and / or stored within the aforementioned tank. All these gases have different evaporation temperatures depending on their respective compositions, for example, the different types and proportions of hydrocarbons composing the gas and the evolution of the cargo during transport. It is therefore important to know the composition of the gas cargo and thus its evaporation temperature in order to optimally control the feeding system of the invention.

[0023] The fluid analyzer can determine the composition of a gas when it is in a liquid state. The gas in its liquid state can also be forcibly vaporized so that the fluid analyzer can determine its composition.

[0024] According to one feature of the invention, the control device includes a second sensor configured to determine the gas pressure present in the tank. The control module is configured to control the flow regulator based on the gas pressure determined by the second sensor. This second sensor determines the gas pressure circulating in the second supply circuit, this pressure being identical to the gas pressure in the tank head. In other words, the second sensor participates in monitoring the internal pressure of the tank. Such monitoring is important to prevent excessively low pressure within the tank, which can lead to deformation and damage of the tank membranes.

[0025] According to one feature of the invention, the return line includes a flow meter configured to determine the flow rate of gas in the vapor state circulating in the return line, the control module being configured to control the flow regulator based on the gas flow rate determined by the flow meter. The flow meter can be controlled by an operator to limit the gas flow rate circulating in the return line. In this case, the flow regulator is controlled by the operator via the flow meter and the control module, the latter providing the connection between the flow meter and the flow regulator.

[0026] According to one feature of the invention, the first supply circuit comprises at least one pumping element configured to pump the gas drawn from the tank in liquid form. The pump, also called the pumping element, is installed at the bottom of the tank and pumps the gas in liquid form so that it can circulate in the first supply circuit. The pumping element is advantageously a submersible pump arranged at the bottom of the tank to draw the gas in liquid form and circulate it within the first supply circuit. When the gas in liquid form is pumped by the submersible pump, its pressure is raised to between 6 and 17 bar absolute.

[0027] The invention also covers a method for controlling a power supply system as described above, comprising: a comparison step between the temperature of the gas present in the first supply circuit between the first heat exchanger and the pump, and a maximum temperature threshold determined according to the pressure of the gas present in the first supply circuit between the first heat exchanger and the pump, the composition of the gas circulating in the supply system and a safety margin; if the temperature of the gas present in the first supply circuit between the first heat exchanger and the pump is above the maximum temperature threshold, a passage section of the flow control device is reduced; if the temperature of the gas present in the first supply circuit between the first heat exchanger and the pump is below the maximum temperature threshold,A comparative step is implemented between the temperature of the gas present in the return line between the first heat exchanger and the flow control device and an optimal temperature threshold determined based on the temperature of the gas present in the first supply circuit between the tank and the first heat exchanger and a temperature difference. If the temperature of the gas present in the return line between the first heat exchanger and the flow control device is above the optimal temperature threshold, the flow control device's cross-sectional area is reduced. If the temperature of the gas present in the return line between the first heat exchanger and the flow control device is below the optimal temperature threshold, the flow control device's cross-sectional area is increased.

[0028] It is through this control process that the regulation of the supply system is achieved in order to optimize the condensation of the gas into a vapor state without harming the proper functioning of the pump.

[0029] The comparison step ensures that the temperature of the gas circulating in the first supply circuit is not too high at the outlet of the first heat exchanger. To do this, the temperature of the gas is determined by the first sensor. At this stage, the temperature of the gas at the outlet of the first heat exchanger is then known.

[0030] The maximum temperature threshold is determined simultaneously or successively. The objective is to keep the gas temperature measured by the first sensor below this maximum temperature threshold. This threshold is calculated based on the gas pressure determined by the first sensor and the gas composition, which is known in some way. A safety margin is then subtracted from the result. This safety margin ensures, for example, that the gas does not evaporate even if the maximum temperature threshold is slightly exceeded. This safety margin depends on the net positive suction head of the pump and a predetermined safety threshold. The net positive suction head is a parameter to monitor to prevent the suction of liquid gas at the pump inlet from causing vaporization of the liquid gas, which could create cavitation within the pump.The net positive suction head depends on the pump model used. The safety threshold, on the other hand, can be determined by an operator and provides an additional level of safety to ensure the target is met.

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

[0032] If the temperature reading from the first sensor exceeds the maximum temperature threshold, it means that the gas circulating in the first supply circuit is exiting the first heat exchanger at too high a temperature. This creates a risk of partial evaporation, as the vapor portion of the gas exiting the first heat exchanger could impair the pump's operation.

[0033] An excessively high temperature in the first supply circuit at the outlet of the first heat exchanger indicates excessive heat exchange within that heat exchanger. This heat exchange can be reduced by limiting the flow rate of vaporized gas circulating in the return line. The control module then regulates the flow control device to reduce the vaporized gas flow rate in the return line.

[0034] Thanks to this reduction in flow rate, the heat exchange produced in the first heat exchanger is less important and the gas circulating in the first supply circuit exits the first heat exchanger at a lower temperature and is therefore maintained in a liquid state.

[0035] If the gas temperature measured by the first sensor is below the maximum temperature threshold, the process continues with the comparative step. At this stage, it is ensured that, under the conditions of the feed system at time t, there is no risk of the gas evaporating into a liquid state at the outlet of the first heat exchanger. It is therefore possible to potentially increase the flow rate of vaporized gas circulating in the return line to maximize the amount of gas condensed by the feed system.

[0036] To do this, the comparative step consists first of all in determining the temperature of the gas present in the return line between the first heat exchanger and the flow control unit via the third sensor, and, simultaneously or successively, in determining the optimal temperature threshold.

[0037] The optimal temperature threshold corresponds to the temperature determined by the second sensor, that is, the temperature of the gas circulating within the first supply circuit and measured between the tank and the first heat exchanger, preferably at the inlet of the first heat exchanger, plus the temperature difference. This temperature difference corresponds, for example, to the pinch point of the first heat exchanger. The gas temperature determined by the third sensor is then compared to the optimal temperature threshold.

[0038] The goal here is to maximize the efficiency of the condensation performed by the feed system. This maximization is achieved by bringing the temperature determined by the third sensor closer to the optimal temperature threshold. Therefore, if the temperature determined by the third sensor is lower than the optimal temperature threshold, it means that a greater quantity of vapor gas circulating in the return line can be condensed. The control module then increases the flow area of ​​the flow regulator to increase the amount of gas circulating in the return line, until the gas temperature determined by the third sensor converges with the optimal temperature threshold.

[0039] If the temperature measured by the third sensor is above the optimal temperature threshold, this means that the condensation of the gas into vapor in the return line is not optimal. The control module then reduces the flow area of ​​the flow regulator to decrease the amount of gas flowing in the return line until the gas temperature measured by the third sensor converges with the optimal temperature threshold. Since the optimal temperature threshold depends on a measured temperature, this threshold varies according to the operating conditions of the supply system.

[0040] As described, the comparative step follows the comparison step. However, it is possible for the control procedure to implement the comparison step and the comparative step simultaneously. The potential adjustment of the flow control device's passage area is then carried out according to the priority step, i.e., the comparison step, or the comparative step if it was determined in the comparison step that the flow control device's passage area does not need to be reduced.

[0041] According to a characteristic of the process, it is repeatable over time. The process is repeatable from the comparison step if the steps are successive, or from the comparison step and the comparative step if they are implemented simultaneously. The process can be repeated once the control of the flow path of the regulating element following the comparison step or the comparative step has been carried out.

[0042] Depending on a characteristic of the process, the gas composition can be determined by the fluid analyzer. The gas composition determination is available at least at the time of implementation of the process comparison step and allows the maximum temperature threshold to be defined. The aforementioned fluid analyzer provides a solution for obtaining the gas composition, and this analysis can be performed during cargo loading or subsequently, i.e., during the movement of the floating structure.

[0043] Depending on a process characteristic, the gas composition can be determined using technical documentation. This is an alternative to determination via a fluid analyzer, for example, when the feed system does not include such a fluid analyzer. The technical documentation is supplied with the cargo and contains a variety of characteristics related to it, such as the vaporization temperature of the cargo gas. This technical documentation might include, for example, a chart relating the vaporization temperature to the specific pressure of the cargo gas.

[0044] According to a characteristic of the process, the maximum temperature threshold can be determined using a data table for several types of gas. In the absence of a gas analyzer and technical documentation, a data table can be relied upon. Such a table presents the evaporation temperature as a function of pressure for most types of natural gas transported and / or stored by ship and known to date. Thus, by noting the pressure determined by the first detector, the lowest evaporation temperature among the different gas types at the given pressure is used to set the maximum temperature threshold, also taking into account the safety margin. Such a data table can be read manually or entered into the memory of the management device to automate the determination of the maximum temperature threshold.

[0045] According to a characteristic of the process, the safety margin and temperature deviation correspond to a value between 1°C and 3°C. These values ​​are sufficient while remaining relatively close to the actual temperature limits, so as not to impair the optimization of the operation of the feeding system.

[0046] According to a characteristic of the process, the gas pressure determined by the second detector is compared to a pressure threshold. This determination is performed in parallel with the steps described previously. The second detector determines the pressure of the gas circulating in the second supply circuit, and therefore the pressure in the tank head. This determination ensures that the internal pressure of the tank is not too low. Insufficient internal pressure can lead to deformation of the membranes. The internal pressure of the tank must therefore be maintained above the pressure threshold. The pressure threshold is a fixed value below which the internal pressure of the tank is considered to cause deformation of the membranes. For example, the pressure threshold could be -60 mbar or -30 mbar relative to the external pressure.

[0047] According to a characteristic of the process, it includes a step of interrupting the gas flow in the return line when the gas pressure determined by the second detector is below the pressure threshold. The gas circulation within the second supply circuit and the return line results from the aspiration of gas in vapor form from the tank head, leading to a drop in the internal tank pressure. Thus, when the tank head pressure is below the pressure threshold, the tank diaphragm is at risk of being damaged. The control device then completely closes the flow control device to stop the pressure drop.

[0048] 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 attached schematic drawings on the other hand, in which: [ fig 1 ] is a schematic representation of a power supply system according to the invention, [ fig 2 ] is a logic diagram of a control method according to the invention, of the power supply system, [ fig 3 ] is a flowchart of a part of the control process monitoring a quantity of gas in the vapor state, [ fig 4 ] is an example of a data table for several types of gas, usable for implementing the control process, [ fig 5 ] is a schematic cutaway representation of a tank of a floating structure and a loading and / or unloading terminal for this tank.

[0049] The terms "upstream" and "downstream" used in the description below are used to express the positions of elements within circuits of gas in liquid or vapor state and refer to the direction of flow of said gas within said circuit.

[0050] There figure 1 represents a gas supply system 1 arranged on a floating structure. The supply system 1 allows gas to circulate, which may be in liquid, vapor, two-phase or supercritical state, from a storage and / or transport tank 8, to a high-pressure gas-consuming device 4 and a low-pressure gas-consuming device 5, in order to supply them with fuel.

[0051] The floating structure may, for example, be a vessel capable of storing and / or transporting gas in liquid form, particularly natural gas. The supply system 1 is then capable of using the gas in liquid form that the floating structure stores and / or transports to supply the high-pressure gas-consuming device 4, which may, for example, be a propulsion engine, and the low-pressure gas-consuming device 5, which may, for example, be an electric generator supplying the floating structure with electricity.

[0052] To ensure the circulation of the gas contained in the tank 8 to the high-pressure gas-consuming appliance 4, the supply system 1 is provided with a first gas supply circuit 2. The first supply circuit 2 includes a pumping element 9, advantageously a submersible pump 9 located within the tank 8. The submersible pump 9 pumps the gas in its liquid state and circulates it, in particular, within the first supply circuit 2. By drawing in the gas in its liquid state, the pumping element 9 increases its pressure to a value between 6 and 17 bar absolute.

[0053] The gas in its liquid state, flowing from tank 8 to the high-pressure gas-consuming unit 4, passes through a first heat exchanger 6 and is pressurized by a pump 10. Subsequently, the gas in its liquid state passes through a single heat exchanger 21, combining a second heat exchanger 7 and a high-pressure evaporator 11. However, it is possible that the second heat exchanger 7 and the high-pressure evaporator 11 are separate units. Details concerning the heat exchangers will be described later.

[0054] The single heat exchanger 21, via the high-pressure evaporator 11, allows the state of the gas circulating in the first supply circuit 2 to be changed to a vapor or supercritical state. This state makes the gas compatible for supplying the high-pressure gas-consuming device 4. The evaporation of the gas into a liquid state can, for example, be achieved by heat exchange with a heat transfer fluid at a temperature high enough to evaporate the gas into a liquid state, in this case glycol water, seawater, or steam.

[0055] The increase in gas pressure is ensured by pump 10 when it pumps the gas in its liquid state. Pump 10 makes it possible to raise the pressure of the gas in its liquid state to a value between 30 and 400 bar absolute, particularly for use with ammonia or hydrogen, between 30 and 70 bar absolute for use with liquefied petroleum gas, and preferably between 150 and 400 bar absolute for use with ethane, ethylene or liquefied natural gas consisting mainly of methane.

[0056] Thanks to the combination of the pump 10 and the single heat exchanger 21, the gas is at a pressure and in a state compatible for supplying the high-pressure consumer device 4. Such a configuration avoids the installation of high-pressure compressors on the first supply circuit 2 which present cost constraints and generate strong vibrations.

[0057] Within tank 8, part of the gas cargo can naturally turn into vapor and diffuse into a tank headspace 12. In order to avoid overpressure within tank 8, the gas in vapor form contained in the headspace of tank 12 must be evacuated.

[0058] The supply system 1 therefore includes a second gas supply circuit 3, which uses the gas in its vapor state to supply the low-pressure gas-consuming device 5. The second supply circuit 3 extends between the tank head 12 and the low-pressure gas-consuming device 5. In order to draw the gas in its vapor state from the tank head 12, the second supply circuit 3 includes a compressor 13. In addition to drawing the gas in its vapor state, the compressor 13 also compresses the gas to l'état steam circulating in the second supply circuit 3 at a pressure between 6 and 20 bar absolute, so that the gas in the vapor state is at a pressure compatible for supplying the low pressure gas consuming device 5. The second supply circuit 3 thus makes it possible to supply the low pressure gas consuming device 5, while regulating the pressure within the tank 8 by drawing the gas in the vapor state present in the tank head 12.

[0059] The presence of excessive vapor gas in the tank head 12 causes overpressure within the tank 8. It is therefore necessary to vent the vapor gas to reduce the pressure within the tank 8. The excess vapor gas can then be eliminated, for example, by a burner 18 or, as not shown, released into the atmosphere, thus resulting in cargo loss. However, the supply system 1 according to the invention includes a return line 14 extending from the second supply circuit 3 to the tank 8.

[0060] The return line 14 is connected to the second supply circuit 3 downstream of the compressor 13 with respect to a direction of flow of the gas in the vapor state circulating in the second supply circuit 3. The return line 14 initially passes through the single heat exchanger 21. As such, the single heat exchanger 21 therefore comprises a first pass 24 in which the gas in the liquid state from the first supply circuit 2 flows, a second pass 28 in which the gas in the vapor state from the return line 14 flows and a third pass 29 in which the heat transfer fluid evaporates the gas in the liquid state circulating in the first pass 24.

[0061] At the outlet of the second pass 28 of the single heat exchanger 21, the gas in its vapor state flows through the first heat exchanger 6. The liquid gas from the first feed circuit 2 has its lowest temperature at the inlet of the first heat exchanger 6. Consequently, the gas flowing in the return line 14 condenses after passing through the first heat exchanger 6. The gas in the return line 14 is therefore in a vapor state at the inlet of the first heat exchanger 6 and exits at l'état liquid following the exchange of calories taking place within the first heat exchanger 6.

[0062] The return line 14 also includes a flow control device 15 which controls the flow rate of the fluid circulating in the return line 14. This flow control device 15 has a variable cross-sectional area. Once the gas is condensed, it flows to the tank 8. The first heat exchanger 6 therefore acts as a condenser, while the flow control device 15 controls the heat exchange taking place in the first heat exchanger 6 and in the single heat exchanger 21.

[0063] The supply system 1 also includes an auxiliary supply line 16, extending from the first supply circuit 2, via a branch located between the pumping unit 9 and the first heat exchanger 6, to the second supply circuit 3, connecting to it between the compressor 13 and the low-pressure gas consuming device 5. The auxiliary supply line 16 allows the low-pressure gas consuming device 5 to be supplied in the event of insufficient flow of gas in vapor form formed within the tank head 12.

[0064] When there is not a sufficient quantity of vaporized gas in the tank head 12, liquid gas pumped by the submersible pump 9 can then circulate within this auxiliary supply line 16 to supply the low-pressure gas-consuming device 5. To achieve this, the auxiliary supply line 16 passes through a low-pressure evaporator 17 so that the liquid gas circulating in the auxiliary supply line 16 changes to a vapor state. The operation of the low-pressure evaporator 17 can, for example, be identical to that of the high-pressure evaporator 11, i.e., the gas is evaporated by heat exchange with a heat transfer fluid at a temperature high enough to evaporate the gas into a liquid state.At the outlet of the low-pressure evaporator 17, the gas in vapor state circulates within the auxiliary supply line 16, then joins the second supply circuit 3 in order to supply the low-pressure gas-consuming device 5.

[0065] It is understood from the above that the auxiliary supply line 16 is only used when there is no sufficient quantity of gas in the vapor state within the tank head 12. Thus, the auxiliary supply line 16 includes a valve 19 controlling the flow of gas within the auxiliary supply line 16 when its use is not required.

[0066] Pump 10 is advantageously positioned between the first heat exchanger 6 and the single heat exchanger 21. Pump 10 is only capable of pumping gas in its liquid state. To ensure its proper operation, it is important that the gas circulating in the first supply circuit 2 remains in a liquid state at the outlet of the first heat exchanger 6.

[0067] Furthermore, one of the objectives of the supply system 1 according to the invention is to recondense a maximum of gas in the vapor state formed in the tank head 12 and not consumed by the low pressure gas-consuming device 5, but without causing the evaporation of the gas circulating in the first supply circuit 2 when passing through the first heat exchanger 6.

[0068] To achieve this, the supply system 1 includes a control unit 80 that monitors the various parameters mentioned above. The control unit 80 includes, in particular, a first sensor 81, a second sensor 82, a third sensor 83, a first detector 84, and a second detector 85. It will be assumed hereafter that sensors 81, 82, and 83 determine the gas temperature, while detectors 84 and 85 determine the gas pressure. The control unit 80 also includes a control module 86 that receives the various data determined by sensors 81, 82, and 83, as well as by detectors 84 and 85. In response to this data, the control module 86 can act on the flow regulator 15 to vary the gas flow rate in the return line 14.

[0069] The first sensor 81 is positioned in the first supply circuit 2 between the first heat exchanger 6 and the pump 10. The second sensor 82 is positioned in the first supply circuit 2 between the tank 8 and the first heat exchanger 6. The third sensor 83 is positioned in the return line 14 between the first heat exchanger 6 and the flow control device 15. Each of the sensors 81, 82, 83 is configured to determine the temperature of the gas flowing at each of its respective positions. The temperature of the gas flowing in these different sections of the supply system 1 is used to control the flow control device 15.The same applies to the pressures determined by the first detector 84, positioned at the level of the first supply circuit 2 between the first heat exchanger 6 and the pump 10, and for the second detector 85, positioned at the level of the second supply circuit 3 between the tank 8 and the compressor 13.

[0070] The control unit 80 may also include a fluid analyzer 87 capable of determining the composition of the gas in its liquid state contained in the tank 8. The fluid analyzer 87 can determine the gas composition directly in its liquid state or may require vaporizing the gas to determine its composition. Knowing the gas composition is useful for determining the gas's vaporization temperature, as will be described in detail later. Like the temperature and pressure values, the gas composition determined by the fluid analyzer 87 is also transmitted to the control module 86. However, the gas composition may also be provided via technical documentation relating to the gas cargo or correspond to a gas type whose characteristics are listed in a data table, as will be illustrated later.

[0071] The return line 14 may also include a flow meter 88. The flow meter is configured to determine the gas flow rate in the return line 14. Advantageously, the gas flow rate is determined between the connection with the second supply circuit 3 and the single heat exchanger 21. The flow meter 88 is also connected to the control module 86, which can act on the flow control device 15. An operator can therefore act on the flow meter 88 so that the control device 86 receives information from the flow meter 88 and acts on the flow control device 15 in response to this information from the flow meter 88.

[0072] There figure 2 is a flowchart allowing the different steps of a control process 100 according to the invention to be described, for example when it is implemented by the management device described above.

[0073] The control process 100 begins with a comparison step 101 between the gas temperature measured by the first sensor 81 and a maximum temperature threshold Tmax. The gas temperature determined by the first sensor 81 corresponds to the temperature of the gas circulating in the first supply circuit at the outlet of the first heat exchanger. This may, in particular, be a measurement in situ, by positioning the first sensor 81 at any point located between an outlet of the first heat exchanger pass forming part of the first supply circuit and an inlet of the pump, as illustrated in figure 1 It can also be an estimate or a calculation made from other data in the system.

[0074] Prior to, simultaneously with, or following the determination of the gas temperature by the first sensor 81, the maximum temperature threshold Tmax is defined based on the gas pressure determined by the first detector, the gas composition, and a safety margin. The gas pressure used to determine the maximum temperature threshold Tmax corresponds to the pressure of the gas circulating in the first supply circuit, at the outlet of the first heat exchanger.

[0075] Just like the first sensor 81, the first detector can measure pressure in situ or result from an estimate or calculation made from other data in the system.

[0076] It is possible to find the evaporation temperature of the gas if its pressure and composition are known. The pressure is determined by the first detector 84, while the gas composition can be obtained using the fluid analyzer 87 shown in figure 1 If the fuel supply system does not include a fluid analyzer, the gas composition can be determined from the cargo's technical documentation, particularly that provided at the time of cargo loading. If neither is available, the maximum temperature threshold Tmax can be determined using a data table, as illustrated in figure 4 , grouping the different types of gas and showing the different evaporation temperatures according to the pressure of each gas. The pressure determined by the first detector 84 being known, the data table is therefore read from this pressure by selecting the lowest evaporation temperature to ensure that, regardless of the type of gas contained in the tank, it has at least this selected temperature as its evaporation temperature.

[0077] The maximum temperature threshold Tmax is ultimately obtained by subtracting the safety margin from the previously determined gas evaporation temperature. The safety margin depends on the pump's net positive suction head and a safety threshold. The net positive suction head is specific to the pump used in the first supply circuit and corresponds to a limit beyond which the pump risks evaporating the gas into a liquid state while pumping it. The safety threshold can be selected by the operator. For example, the safety margin can be between 1°C and 3°C to obtain a maximum temperature threshold Tmax slightly lower than the actual gas evaporation temperature.

[0078] Once the maximum temperature threshold has been obtained, the comparison between this and the gas temperature determined by the first sensor 81 can be implemented.

[0079] If the gas temperature determined by the first sensor 81 is above the maximum temperature threshold, this means that the gas circulating in the first supply circuit is leaving the first heat exchanger at too high a temperature, thus risking at least partial evaporation and subsequently damaging the pump.

[0080] An excessively high gas temperature between the first heat exchanger and the pump indicates that the heat exchange occurring within the first heat exchanger is too great. To reduce this heat exchange, the gas flow rate in the return line must be decreased.

[0081] Thus, when the gas temperature determined by the first sensor 81 exceeds the maximum temperature threshold, the control process 100 continues with a reduction step 103 of the passage cross-section. During this reduction step 103, the control module described in figure 1 It acts on the flow control device 15, reducing its cross-sectional area to decrease the gas flow rate in the return line, thus limiting heat exchange within the first heat exchanger and consequently the temperature rise of the gas circulating in the first supply circuit. This prevents gas evaporation upstream of the pump.

[0082] Once the reduction step 103 has been completed, the control process 100 can be repeated from the comparison step 101, for example to verify that the temperature of the gas circulating between the first heat exchanger and the pump has indeed decreased.

[0083] If the gas temperature determined by the first sensor 81 is below the maximum temperature threshold Tmax, the control process 100 continues with a comparative step 102.

[0084] Comparative step 102 is performed between the gas temperature measured by the third sensor 83, i.e., the gas flowing in the return line after passing through the first heat exchanger, and an optimal temperature threshold Topt, corresponding to the gas temperature determined by the second sensor, i.e., the gas flowing in the first supply circuit upstream of the first heat exchanger, plus a temperature difference. This difference, like the safety margin, can be between +1°C and +3°C. This temperature difference is the minimum difference between the temperature of the gas in its liquid state from the tank entering 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 83.This temperature difference may correspond to the pinching of the first heat exchanger 6.

[0085] The second sensor and the third sensor 83 can measure the temperature in situ, that is to say, to the positions described previously, or resulting from an estimate or calculation made from other data of the system.

[0086] Comparative step 102 optimizes the condensation of the gas circulating in the return line. The objective is to bring the temperature of the gas circulating in the return line at the outlet of the first heat exchanger towards the optimal temperature threshold, Topt, in order to achieve optimal condensation in the maximum quantity. If the gas circulating in the return line leaving the first heat exchanger is too hot, it means that too much gas is flowing to be condensed efficiently. Conversely, if the gas circulating in the return line leaving the first heat exchanger is too cold, it means that the gas flow rate can be increased to condense a greater quantity of gas in a given time.

[0087] The gas temperature determined by the third sensor 83 is therefore compared to the optimal temperature threshold Topt. Whether the gas temperature determined by the third sensor 83 is above or below the optimal temperature threshold Topt, the control process 100 continues with a step where the control module adjusts the flow control element's passage area. More specifically, the control process 100 continues with the reduction step 103 of the flow control element's passage area if the gas temperature determined by the third sensor 83 is above the optimal temperature threshold Topt. This reduction step 103 is similar to the one that can result from the comparison step 101.Conversely, the control process 100 continues with an increase step 104 of the passage section of the flow control device if the gas temperature determined by the third sensor 83 is below the optimal temperature threshold Topt.

[0088] It should be noted that on the figure 2 Comparison step 101 and comparison step 102 are performed sequentially, with comparison step 101 being performed first. However, the control procedure 100 can be configured to implement comparison step 101 and comparison step 102 simultaneously, although comparison step 101 takes precedence over comparison step 102.

[0089] Once the reduction step 103 or the increase step 104 has been carried out, depending on the comparison step 101 or the comparison step 102, the control process 100 can be repeated from the comparison step 101 if the steps are successive, or from both steps simultaneously as described previously. The priority is to ensure that the gas in the liquid state circulating in the first supply circuit does not exit at least partially evaporated. The comparison step 101 therefore takes precedence over the optimization operation of condensing the gas in the vapor state circulating in the return line, corresponding to the comparison step 102.

[0090] There figure 3 is a flowchart of a part of the control process monitoring the internal pressure of the tank head. This part of the control process runs in parallel with what was described in figure 2 This process includes a monitoring step 105 where the determined pressure in the tank head is compared to a pressure threshold Pref. The pressure threshold Pref can, for example, correspond to a value of -30 mbar or -60 mbar relative to the external pressure. The second detector 85 determines, for example, the pressure of the gas circulating in the second supply circuit between the tank and the compressor, and, more generally, the internal pressure in the tank head.

[0091] This pressure, determined by the second detector 85, is then compared to the pressure threshold Pref. This threshold is fixed and corresponds to a pressure value below which there is a risk of damage to the tank walls.

[0092] Thus, if the pressure determined by the second detector 85 is less than or equal to the pressure threshold Pref, this means there is a risk of damage to the tank walls if the tank head pressure decreases further. An interruption step 110 is implemented, where the control module completely closes the flow control device. In such a situation, the supply system can be shut down while waiting for the tank head pressure to increase. Alternatively, the low-pressure gas-consuming device can be supplied via the auxiliary supply line 16 shown in figure 1 .

[0093] If the pressure determined by the second detector 85 is above the pressure threshold, the control process can continue while continuing to monitor the pressure value determined by the second detector 85.

[0094] There figure 4 represents the data table 106 mentioned previously, and allows us to determine the maximum temperature threshold Tmax mentioned in figure 2 . This data table 106 represents the evaporation temperature as a function of the pressure determined by the first detector for five different types of gas A, B, C, D and E.

[0095] Thus, if the composition of the gas in the tank cannot be known, data table 106 is used to determine a theoretical evaporation temperature based on the pressure determined by the first detector. To ensure that the gas in the tank remains in a liquid state within the first feed circuit at the outlet of the first heat exchanger, regardless of its composition, the evaporation temperature chosen is the lowest possible. On the figure 4 Therefore, the first type of gas, A, is chosen. Once the safety margin has been applied, the maximum temperature threshold is then determined.

[0096] There figure 5 is a cutaway view of a floating structure 20 which shows the tank 8 which contains the gas in liquid and vapor state, this tank 8 being of general prismatic shape mounted in a double hull 22 of the floating structure 20. The wall of the tank 8 comprises a primary sealing membrane intended to be in contact with the gas in liquid state contained in the tank 8, a secondary sealing membrane arranged between the primary sealing membrane and the double hull 22 of the floating structure 20, and two thermally insulating barriers arranged respectively between the primary sealing membrane and the secondary sealing membrane and between the secondary sealing membrane and the double hull 22.

[0097] Liquid gas loading and / or unloading pipelines 23 arranged on the upper deck of the floating structure 20 can be connected, by means of suitable connectors, to a marine or port terminal to transfer the liquid gas cargo from or to the tank 8.

[0098] There figure 5 This also represents an example of a marine or port terminal comprising loading and / or unloading equipment 25, a subsea pipeline 26, and an onshore and / or port facility 27. The onshore and / or port facility 27 may, for example, be located on a port quay, or, as another example, be located on a concrete gravity platform. The onshore and / or port facility 27 includes liquid gas storage tanks 30 and connecting pipelines 31 linked by the subsea pipeline 26 to the loading and / or unloading equipment 25.

[0099] To generate the pressure necessary for the transfer of the gas in liquid form, pumps are used equipping the onshore and / or port installation 27 and / or pumps equipping the floating structure 20.

[0100] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

[0101] The invention, as described above, achieves its intended purpose and provides a gas supply system comprising a control device for temperature control and condensation of the gas. Variations not described here could be implemented without departing from the scope of the invention, provided that, in accordance with the invention, they include a supply system conforming to the invention.

Claims

1. A system (1) for supplying gas to at least one high-pressure gas-consuming apparatus (4) and at least one low-pressure gas-consuming apparatus (5) of a floating structure (20) comprising at least one tank (8) configured to contain the gas, the supply system (1) comprising: - at least one first circuit (2) supplying gas to the high-pressure gas-consuming apparatus (4), comprising at least one pumping member (9) configured to pump the gas taken from the liquid state in the tank (8), - at least one high-pressure evaporator (11) configured to evaporate the gas circulating in the first gas supply circuit (2), - at least one second circuit (3) supplying gas to the low-pressure gas-consuming apparatus (5), comprising at least one compressor (13) configured to compress gas taken in the vapor state into the tank (8) to a pressure compatible with the requirements of the low-pressure gas-consuming apparatus (5), - at least one gas return line (14) connected to the second supply circuit (3) downstream of the compressor (13) and extending to the tank (8), - at least one first heat exchanger (6) and one second heat exchanger (7), each configured to exchange heat between the gas circulating in the return line (14) in the vapor state and the gas circulating in the first supply circuit (2) in the liquid state, the return line (14) comprising a flow-regulating member (15) arranged between the first heat exchanger (6) and the tank (8), a third sensor (83) configured to determine a temperature of the gas present in the return line (14) between the first heat exchanger (6) and the flow-regulating member (15), characterized in that the first supply circuit (2) comprises a pump (10) interposed between the first heat exchanger (6) and the second heat exchanger (7), and in that the supply system (1) comprises a device (80) for managing said supply system (1) which comprises at least one first sensor (81) and a first detector (84) respectively configured to determine a temperature and pressure of the gas present in the first supply circuit (2) between the first heat exchanger (6) and the pump (10), a second sensor (82) configured to determine a temperature of the gas present in the first supply circuit (2) between the tank (8) and the first heat exchanger (6), the management device (80) comprising a control module (86) configured to control the flow-regulating member (15) according to the characteristics of the gas determined by the first sensor (81), the second sensor (82), the third sensor (83) and the first detector (84).

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

3. The supply system (1) according to claim 1 or 2, wherein the management device (80) comprises a second detector (85) configured to determine a pressure of the gas present in the tank (8), the control module (86) being configured to control the flow-regulating member (15) according to the pressure of the gas determined by the second detector (85).

4. The supply system (1) according to any of the preceding claims, wherein the return line (14) comprises a flowmeter (88) configured to determine the flow rate of gas in the vapor state circulating in the return line (14), the control module (86) being configured to control the flow-regulating member (15) according to the gas flow rate determined by the flowmeter (88).

5. A method for controlling (100) a supply system (1) according to any of the preceding claims, comprising: - a step of comparing (101) the temperature of the gas present in the first supply circuit (2) between the first heat exchanger (6) and the pump (10), and a maximum temperature threshold (Tmax) determined as a function of the pressure of the gas present in the first supply circuit (2) between the first heat exchanger (6) and the pump (10), a composition of the gas circulating in the supply system (1) and a safety margin, - if the temperature of the gas present in the first supply circuit (2) between the first heat exchanger (6) and the pump (10) is greater than the maximum temperature threshold (Tmax), a passage section of the flow-regulating member (15) is reduced, - if the temperature of the gas present in the first supply circuit (2) between the first heat exchanger (6) and the pump (10) is lower than the maximum temperature threshold (Tmax), a comparative step (102) is implemented between the temperature of the gas present in the return line (14) between the first heat exchanger (6) and the flow-regulating member (15) and an optimal temperature threshold (Topt) determined according to the temperature of the gas (2) present in the first supply circuit between the tank (8) and the first heat exchanger (6) and a temperature difference, - if the temperature of the gas present in the return line (14) between the first heat exchanger (6) and the flow-regulating member (15) is greater than the optimal temperature threshold (Topt), the passage section of the flow-regulating member (15) is reduced, - if the temperature of the gas present in the return line (14) between the first heat exchanger (6) and the flow-regulating member (15) is lower than the optimal temperature threshold (Topt), the passage section of the flow-regulating member (15) is increased.

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

7. The control method (100) according to claim 5 or 6, combined with claim 2, wherein the composition of the gas is determined by the fluid analyzer (87).

8. The control method (100) according to claim 5 or 6, wherein the composition of the gas is determined by means of technical documentation.

9. The control method (100) according to claim 5 or 6, wherein the maximum temperature threshold is determined by virtue of a data table (106) of several types of gas.

10. The control method (100) according to any of claims 5 to 9, wherein the safety margin and the temperature difference correspond to a value between 1°C and 3°C.

11. The control method (100) according to any of claims 5 to 10, combined with claim 3, wherein the pressure of the gas determined by the second detector (85) is compared to a pressure threshold (Pref).

12. The control method (100) according to the preceding claim, comprising a step of interrupting (110) the gas flow within the return line (14) when the pressure of the gas determined by the second detector (85) is lower than the pressure threshold (Pref).