GAS SUPPLY SYSTEM FOR HIGH PRESSURE AND LOW PRESSURE GAS CONSUMPTION DEVICES AND METHOD FOR CONTROLLING SUCH A SYSTEM - Patent application

Abstract

The present invention relates to a supply system (1) for supplying gas to a high pressure gas consumer (4) and a low pressure gas consumer (5). The supply system (1) comprises a first supply circuit (2), a second supply circuit (3), a return line (14) connected to the second supply circuit (3), a first heat exchanger (6) and a second heat exchanger (7). The supply system (1) comprises a heat treatment branch (33) connected to the second supply circuit (3). The supply system (1) comprises a third heat exchanger (36) configured to perform a heat exchange between the gas flowing through the heat treatment branch (33) and the gas flowing through the return line (14).

Description

[Technical field]

[0001] The present invention relates to the field of ships storing and / or transporting gas in liquid state, and more particularly to a gas supply system for gas consuming devices equipped on such ships, and to a method for controlling such a system. [Background technology]

[0002] During a voyage by a ship equipped with tanks for the consumption and / or delivery of gas in liquid state to a destination, said ship must be able to use at least a portion of said gas in liquid state to supply at least one of its motors via a gas supply system. This is the case for ships with ME-GI high pressure propulsion engines. To supply gas to such a motor, the gas needs to be compressed to very high pressures by dedicated compressors capable of compressing the gas up to 300 bar absolute, which are expensive, incur high maintenance costs and cause vibrations to the ship.

[0003] An alternative to installing such a high-pressure compressor is to boil off the gas in liquid state, in particular at a pressure of 300 bar absolute, in a high-pressure pump before sending it to the propulsion engine. Since such a solution does not allow the removal of the gaseous state (boil-off gas, BOG) that naturally occurs in the tanks that at least partially contain the cargo, low-pressure compression means can be installed that supply the gas to an auxiliary motor that can consume the gas as low-pressure steam. The surplus gaseous state can also be passed through the tanks by recondensation.

[0004] Although the efficiency of such systems is already high, there is room to further improve the overall system performance. One such improvement is to use the gas in the vapor state to improve condensation of the excess vapor state gas that is recirculated to the tank. Summary of the Invention

[0005] The present invention relates to a gas supply system for at least one high pressure gas consumer and at least one low pressure gas consumer for a floating structure, comprising at least one tank adapted to contain gas at least in a liquid state, The gas supply system includes: at least one first gas supply circuit for said high pressure gas consumer, at least one high-pressure evaporator configured to vaporize the gas flowing through said first gas supply circuit; at least one second gas supply circuit of said low-pressure gas consumer, said second gas supply circuit comprising at least one compression device configured to compress the gas withdrawn in gaseous state from said tank to a pressure suitable for the needs of said low-pressure gas consumer; at least one gas return line connected to said second supply circuit downstream of said compressor and extending to said tank; at least one first heat exchanger and at least one second heat exchanger, each configured to perform a heat exchange between gas in a gaseous state flowing through said gas return line and gas in a liquid state flowing through said first gas supply circuit; Equipped with the gas supply system includes a heat treatment branch for gaseous gas passing through the gas return line; the heat treatment branch is connected to the second gas supply circuit upstream of the compression device; the gas supply system comprises a third heat exchanger configured to perform a heat exchange between the gas in a gaseous state passing through the heat treatment branch and the gas in a gaseous state passing through the gas return line; It is the aim to achieve such an improvement by proposing a gas supply system which is characterized in that:

[0006] Thus, the gas supply system can use the gaseous gas from the tank, in particular the gaseous gas in the blanket of the tank, to condense the gaseous gas passing through the return line. The heat exchange in the third heat exchanger is an additional heat exchange that improves the condensation of the gaseous gas flowing through the return line. The heat exchange in the third heat exchanger is carried out under conditions in which the gaseous gas taken from the tank is at a suitable temperature, i.e. preferably at the inlet of the third heat exchanger, lower than the temperature of the gaseous gas flowing through the return line. If this condition is met, the gaseous gas flows through the heat treatment branch and into the third heat exchanger.

[0007] A first gas supply circuit can satisfy the fuel requirements of a high-pressure gas consumer. This can be, for example, a propulsion means of a floating structure, for example an ME-GI motor. The first supply circuit extends from the tank to the high-pressure gas consumer. Gas in liquid state can be taken from the tank by a submersible pump at the bottom of the tank. The submersible pump pumps the gas in liquid state through the first gas supply circuit.

[0008] Since the gas needs to be in a gaseous state to be supplied to the high-pressure gas consumer, a high-pressure evaporator vaporizes the gas before it is supplied to the high-pressure gas consumer. The high-pressure evaporator is where the heat exchange takes place between the liquid gas in the first gas supply circuit and a heat transfer fluid, e.g. water glycol, seawater, water vapor, etc. Whatever type of heat transfer fluid it is, it must have a sufficiently high temperature to cause a phase change in the gas so that the gas becomes in a gaseous or supercritical state and can be supplied to the high-pressure gas consumer.

[0009] Generally, gas within a tank may become a gas naturally or may be forced to become a gas by a floating structure. The gas that becomes a gas within the tank must be released to prevent excessive pressure within the tank.

[0010] This is done by a second gas supply circuit of the low-pressure gas consumer. Such a second gas supply circuit extends from the tank to the low-pressure gas consumer. This can be, for example, an auxiliary motor of an internal combustion engine of a generator or the like. The function of the compressor of the second gas supply circuit is to suck gas from the blanket of the tank and supply it to the low-pressure gas consumer while at the same time regulating the pressure in the tank.

[0011] At the outlet of the compressor, the gas in gaseous state can be supplied to a low pressure gas consuming device and / or can flow through a return line if the low pressure gas consuming device does not or hardly requires a fuel supply. The return line is connected downstream of the compressor, so that the gaseous state gas sucked into the compressor can flow through the return line.

[0012] The gas in the return line first flows through the second heat exchanger, then through the third heat exchanger, then through the first heat exchanger and back to the tank. The gas in the return line is gradually cooled as heat exchange is carried out in the three heat exchangers. The liquid gas flowing through the first gas supply circuit cools the gas in the return line by flowing through the first and second heat exchangers. The gas in the heat treatment branch cools the gas in the return line by flowing through the third heat exchanger.

[0013] Thus, the temperature of the gas in gaseous state is reduced as it flows through the three heat exchangers, and the gas condenses back into a liquid substantially downstream of the first heat exchanger, and the condensed liquid gas then flows into the tank.

[0014] Since the heat treatment branch is connected to the second gas supply circuit, the gas supply system can be configured such that the gas in gaseous state at the outlet of the tank can flow directly through the heat treatment branch, can flow through a third heat exchanger and then be compressed in a compressor and continue to a low-pressure gas consumer, or can continue to flow through a return line.

[0015] According to a feature of the present invention, the third heat exchanger comprises a first line located between the first and second heat exchangers in the gas return line and a second line located in the heat treatment branch. In other words, when the gas in a gaseous state flows through the gas return line, it flows substantially through the first line of the third heat exchanger, the line of the first heat exchanger, and the line of the second heat exchanger.

[0016] More specifically, the gas in the gaseous state is first pre-cooled by flowing through the line of the second heat exchanger, then the gaseous state is cooled by flowing through the first line of the third heat exchanger, and finally, the gas is condensed by flowing through the line of the first heat exchanger.

[0017] It will be appreciated that the heat exchange is performed in a precise sequence to optimize condensation of the gas in the gaseous state flowing through the return line.

[0018] According to a feature of the invention, the second supply circuit comprises a branching zone where the heat treatment branch and the second supply circuit branch off, and a merging zone where the heat treatment branch and the second supply circuit join, the heat treatment branch extending between the branching zone and the merging zone. Gas in the gaseous state leaves the tank and flows to the branching zone, then either to the second gas supply circuit or to the heat treatment branch, and then through the merging zone to reach the second gas supply circuit. The merging zone is located at the level of the second gas supply circuit, upstream of the compressor through which the gas in the gaseous state must flow.

[0019] According to a feature of the invention, the gas supply system comprises a monitor unit for the flow of gas through the second supply circuit, the heat treatment branch being mounted in parallel to the monitor unit. For example, the monitor unit may be a valve that can be opened or closed to respectively allow or prevent gas in gaseous state from flowing through the second gas supply circuit. When the monitor unit is closed, the gas in gaseous state bypasses the monitor unit by flowing to the heat treatment branch. For example, the monitor unit may be an on-off valve.

[0020] According to a feature of the invention, the heat treatment branch comprises a monitoring device configured to monitor the flow of gas in gaseous state through the heat treatment branch. Like the monitoring unit, the monitoring device can be opened or closed to allow or prevent gas in gaseous state from flowing through the heat treatment branch. The monitoring device can also be a valve.

[0021] According to a feature of the invention, the gas supply system comprises measuring means for the temperature of the gas withdrawn in gaseous state from said tank, and a management device for giving commands to said monitoring unit and to said monitoring device.

[0022] As mentioned above, whether the gas in gaseous state flows through the heat treatment branch depends in particular on the temperature of said gas. Therefore, the temperature of the gaseous gas in the tank has to be measured by a temperature measuring means, which can be for example a temperature sensor. Depending on the temperature of the gas, the management device controls the monitor unit and the monitor device to make the gaseous gas flow through the second gas supply circuit or through the heat treatment branch. The destination of the gaseous gas is managed by a pipe device that closes the monitor unit and opens the monitor device, or vice versa.

[0023] According to a feature of the invention, the third heat exchanger is configured to carry out a heat exchange between the gas in gaseous state passing through the gas return line, the gas in gaseous state passing through the heat treatment branch and the gas in liquid state passing through the first gas supply circuit. This is a variant of the structure of the third heat exchanger. This allows to better optimize the cooling of the gaseous state gas flowing through the return line. Thus, in this example, the heat exchange in the third heat exchanger is carried out between three lines through which the gas flows in gaseous or liquid state. The objective is always to cool the gaseous state gas flowing through the return line.

[0024] According to a feature of the invention, the third heat exchanger comprises a first line in the gas return line between the first and second heat exchangers, a second line in the heat treatment branch and a third line in the first gas supply circuit between the first and second heat exchangers. Heat exchange is thus performed between a number of lines so as to cool the gas in gaseous state passing through the first line. The structure of the third heat exchanger can be such that heat exchange is performed between a number of groups of lines grouped into two or between three lines simultaneously.

[0025] According to a feature of the invention, at least the second heat exchanger, the third heat exchanger and the high pressure evaporator constitute a single heat exchanger module. In other words, two or three units of the second heat exchanger, the third heat exchanger and / or the high pressure evaporator are combined in a single heat exchanger. The number of lines through a single heat exchanger module depends on the number of units combined therein. Such an arrangement can be advantageous, for example, to reduce the mechanical size of the gas supply system.

[0026] According to a feature of the invention, the gas supply system comprises at least one cooling branch for the gas withdrawn in gaseous state from the tank, said cooling branch being connected to the second supply circuit upstream of the compressor, and at least one heat exchanger arranged to carry out a heat exchange between the gas in gaseous state passing through said cooling branch and the gas in liquid state passing through the first supply circuit, which is a second embodiment of the gas supply system according to the invention, the above-mentioned gas supply system comprising a heat treatment branch but without a cooling branch being a first embodiment.

[0027] The function of the cooling branch is to cool the gas in the gaseous state intended to flow through the second gas supply circuit if this gas is at a high temperature. The cooling of the gaseous gas in the tank is achieved by a heat exchanger which performs a heat exchange between the gaseous gas and the liquid gas in the first gas supply circuit.

[0028] The cooling branch therefore has two advantages. On the one hand, the gas in gaseous state flowing through the heat exchanger is cooled, which limits the energy required for its subsequent compression by the compressor in the second gas supply circuit. On the other hand, the liquid gas passing through the first gas supply circuit is warmed, which makes its subsequent evaporation in the high-pressure evaporator easier, due to the reduced flow rate of heat transfer fluid required for its complete evaporation. This in turn limits the energy required for the operation of the gas supply system. It is estimated that up to 30% of the power consumption of the compressor can be saved if the gas in gaseous state flows through the condensation return line, and up to 45% can be saved if the gas in gaseous state flows through the second gas supply circuit and is provided to a low-pressure gas consumer. It is therefore understood that the gas supply system according to the invention can be made more versatile by simultaneously comprising both a heat treatment branch and a cooling branch.

[0029] According to a feature of the invention, the cooling branch comprises a monitor valve configured to monitor the flow of gas in gaseous state through the cooling branch, which, like the monitor unit for the second gas supply circuit and the monitor unit for the heat treatment branch, can be opened or closed to respectively allow or prevent the flow of gas in gaseous state through the cooling branch.

[0030] According to a feature of the invention, at least the second heat exchanger, the mass heat exchanger and the high-pressure evaporator form a single heat exchanger module, which is particularly advantageous since the three heat exchangers are configured to perform heat exchange under high pressure, i.e. they are suitable for being combined.

[0031] According to a feature of the invention, at least the second heat exchanger, the third heat exchanger, the mass heat exchanger and the high pressure evaporator form a single heat exchanger module. As mentioned above, combining two, three or four units of the second heat exchanger, the third heat exchanger, the mass heat exchanger and the high pressure evaporator into a single exchanger can, for example, limit the mechanical size and / or manufacturing costs of these units.

[0032] According to a feature of the invention, the first gas supply circuit comprises a pump between the first and second heat exchangers. The pump is arranged between the first and second heat exchangers. The pump makes it possible to increase the pressure of the gas in liquid state passing through the first gas supply circuit, so that the pressure is suitable for supplying to a high-pressure gas consumer. The ideal positioning is to place the pump between the two heat exchangers. Care must therefore be taken that the gas flowing through the first gas supply circuit and the first heat exchanger remains liquid at its outlet.

[0033] The present invention also relates to a control process for a gas supply system as described above, said control process comprising the steps of: - in a measuring step, the temperature of the gas in gaseous state removed from the tank is measured; - passing gas in gaseous state through the second gas supply circuit if the temperature of the gaseous state measured in the measuring step is higher than a temperature threshold, or - if the temperature of the gas in gaseous state measured in said measuring step is lower than said temperature threshold, then flowing the gas in gaseous state through said heat treatment branch;

[0034] From the various steps of the control process according to the invention, it can be seen that the destination of the gas in the gaseous state in the tank depends on its temperature, and the subsequent steps of the control process are therefore first dependent on the measurement of the temperature of the gas in the gaseous state, which can be measured by the measuring means mentioned above.

[0035] Once the temperature of the gaseous gas is measured, it is compared to a temperature threshold value that corresponds to a value at which the gaseous gas in the tank is or is not available to condense the gaseous gas passing through the return line.

[0036] If the temperature of the gaseous gas is below the temperature threshold, the temperature of the gaseous gas in the tank is low enough to cool the gas passing through the return line, and the gaseous gas is then caused to flow through the heat treatment branch to flow through the third heat exchanger and to cool the gaseous gas passing through the return line.

[0037] If the temperature of the gaseous gas is higher than the temperature threshold, the temperature of the gaseous gas in the tank will be too high to cool the gaseous gas passing through the return line. In this situation, it is pointless or even counterproductive to send the gaseous gas to the tank of the heat treatment branch so as to condense the gaseous gas passing through the return line. Therefore, the gaseous gas from the tank is sent to the second gas supply circuit to supply the low-pressure gas consumer or is condensed as it flows through the return line.

[0038] For example, the feeding of gas from the tank to the second gas supply circuit or to the heat treatment branch is performed by a management device which opens and / or closes the monitoring unit and / or the monitoring device depending on the temperature measured by the measuring means.

[0039] According to a feature of the process, the temperature threshold is −110° C. Thus, the gas in the gaseous state is passed through the heat treatment branch if its temperature is lower than −110° C., and through the second gas supply circuit if its temperature is higher than −110° C.

[0040] According to a feature of the present process, - passing gas in gaseous state through said heat treatment branch if the temperature of the gaseous state measured in said measuring step is lower than said temperature threshold, or - passing the gas in gaseous state through the cooling branch if the temperature of the gas in gaseous state measured in the measuring step is higher than a reference threshold value higher than the temperature threshold value, or - allowing gas in gaseous state to flow through said second gas supply circuit if the temperature of the gas in gaseous state measured in said measuring step is between said temperature threshold and said reference threshold.

[0041] This is the process for a second embodiment of the gas supply system according to the invention, namely a gas supply system with a heat treatment branch and a cooling branch. As in the first embodiment, the destination of the gaseous gas in the tank depends on its temperature. The temperature of the gaseous gas in the tank is measured and compared with a temperature threshold and a reference threshold. The reference threshold corresponds to a temperature value higher than the temperature threshold and at which the temperature of the liquid gas in the tank is so high that the compression device will consume excessive power when compressing the gaseous gas from the tank.

[0042] If the temperature of the gaseous gas is below the temperature threshold, the temperature of the gaseous gas in the tank is low enough to cool the gaseous gas passing through the return line, and the gaseous gas is then caused to flow through the heat treatment branch to flow through the third heat exchanger and to cool the gaseous gas passing through the return line.

[0043] If the temperature of the gaseous gas is greater than the reference threshold, then the gaseous gas in the tank has a temperature that will cause the compressor to over-consume during the compression process.

[0044] In this way, the gas in the gaseous state is made to flow through the cooling branch and flows through the heat exchanger so as to be cooled by the gas in the liquid state passing through the first gas supply circuit, thereby making the temperature suitable for compression by the compressor and preventing excessive consumption of electricity.

[0045] If the temperature of the gaseous gas in the tank is greater than the temperature threshold and less than the reference threshold, the temperature of the gaseous gas in the tank is too high to cool the gaseous gas passing through the return line, but low enough to be compressed by the compressor without consuming excessive power, and the gaseous gas from the tank is thus delivered to the second gas supply circuit.

[0046] As in the first embodiment, the management device manages the flow of liquid gas in the tank by opening or closing the monitor unit, the monitor device, and the monitor valve depending on the measured temperature of the gaseous gas in the tank.

[0047] According to a feature of the process, the reference threshold is -90°C and the control process comprises a step of condensing the gas in gaseous state passing through the gas return line. In other words, the gas in gaseous state is made to flow through the heat treatment branch if its temperature is lower than -110°C, through the cooling branch if its temperature is higher than -90°C and through the second gas supply circuit if its temperature is between -90°C and -110°C. The reference threshold of -90°C is used in case the compressed gas in gaseous state subsequently flows at least partially through the return line. In case the gas in gaseous state is intended to be supplied to a low-pressure gas consumer, the reference threshold may be -150°C or higher.

[0048] Other characteristics and advantages of the invention will become apparent from the following description on the one hand and from a number of embodiments given by way of guide and in a non-limiting manner with reference to the attached drawings, in which: [Brief description of the drawings]

[0049] [Figure 1] 1 is a schematic diagram of a first embodiment of a gas supply system according to the present invention; [Diagram 2] FIG. 4 is a schematic diagram of a first example of the operation of the first embodiment of the gas supply system. [Diagram 3] FIG. 4 is a schematic diagram of a second example of the operation of the first embodiment of the gas supply system. [Figure 4] FIG. 4 is a schematic diagram of a modified example of the first embodiment of the gas supply system. [Diagram 5] FIG. 4 is a schematic diagram of a second embodiment of a gas supply system according to the present invention. [Figure 6] FIG. 11 is a schematic diagram of a first example of a second embodiment of a gas supply system. [Figure 7] FIG. 11 is a schematic diagram of a second example of the operation of the second embodiment of the gas supply system. [Figure 8] FIG. 11 is a schematic diagram of a third example of the operation of the second embodiment of the gas supply system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] 1 shows a first embodiment of a gas supply system 1 mounted on a floating structure. The gas supply system 1 allows gas in a liquid, gaseous, two-phase or supercritical state to flow from a storage and / or transport tank 8 to high pressure gas consumers 4 and low pressure gas consumers 5 to fuel them.

[0051] The floating structure may for example be an LNG-carrying vessel capable of storing and / or transporting gas in liquid state, in particular natural gas. In this case, the gas supply system 1 may use the gas in liquid state stored and / or transported by the floating structure to supply a high-pressure gas consumer 4, which may for example be a propulsion engine, and a low-pressure gas consumer, which may for example be a generator for powering the floating structure.

[0052] To ensure the flow of gas from the tank 8 to the high-pressure gas consumer 4, the gas supply system 1 comprises a first gas supply circuit 2. The first gas supply circuit 2 comprises a submersible pump 9 arranged in the tank 8. The submersible pump 9 makes it possible to pump gas in liquid state and to pass this in particular through the first gas circuit 2. By sucking in the gas in liquid state, the submersible pump 9 increases its pressure to a value of 6-17 absolute pressure.

[0053] From the tank 8 to the high-pressure gas consumer 4, the gas in liquid state flows through a first heat exchanger 6 and is pressurized by a pump 10, also called high-pressure pump. The gas in liquid state then flows through a second heat exchanger 7 and then through a high-pressure evaporator 11 before reaching the high-pressure motor 4. The pump 10 is advantageously arranged between the first heat exchanger 6 and the second heat exchanger 7.

[0054] The high-pressure evaporator 11 can bring the gas flow through the first gas supply circuit 2 into a gaseous or supercritical state, which is suitable for supply to the high-pressure gas consumer 4. The vaporization of the liquid gas can be carried out, for example, by heat exchange between the liquid gas flowing into the high-pressure evaporator 11 and a heat transfer fluid, here water glycol, seawater or water vapor, which is at a temperature high enough to boil off the liquid gas.

[0055] The increase in gas pressure is brought about by the pump 10 when it pumps the gas in the liquid state. The pump 10 can increase the pressure of the gas in the liquid state to a value of 30-400 bar absolute, in particular when using ammonia or hydrogen, to a value of 30-70 bar absolute when using liquefied petroleum gas, and to a value of 150-400 bar absolute, preferably when using liquefied natural gas based on ethane, ethylene or methane.

[0056] The combination of the pump 10 and the high-pressure evaporator 11 brings the gas to a pressure and state suitable for supply to the high-pressure gas consuming device 4. This configuration eliminates the need to provide the first gas supply circuit 2 with a high-pressure compression device, which is cost-intensive and generates strong vibrations.

[0057] In the tank 8, some of the gas in the cargo may spontaneously become gaseous and spread to the tank blanket 12. To prevent excessive pressure in the tank 8, the gaseous state in the tank blanket 12 needs to be vented.

[0058] The gas supply system 1 therefore comprises a second gas supply circuit 3, which uses gas in a gaseous state to supply the low-pressure gas consuming device 5. The second gas supply circuit 3 extends between the tank blanket 12 and the low-pressure gas consuming device 5. In order to suck the gaseous gas contained in the tank blanket 12, the second gas supply circuit 3 comprises a compression device 13, in particular a compressor. Besides sucking the gaseous gas, the compression device 13 is capable of compressing the gaseous gas passing through the second gas supply circuit 3 to an absolute pressure of 6 to 200 bar. This allows the gaseous gas to reach a pressure suitable for supply to the low-pressure gas consuming device 5. The second gas supply circuit 3 allows the supply to the low-pressure gas consuming device 5 and also allows the pressure in the tank 8 to be adjusted by sucking the gaseous gas from the tank blanket 12.

[0059] The gas supply system 1 further comprises a heat treatment branch 33. The heat treatment branch 33 extends between a branch zone 52 downstream of the tank 8 in the second gas supply circuit and a confluence zone 53 downstream of the branch zone 52 and upstream of the compressor 13 in the second gas supply circuit 3. The heat treatment branch 33 is thus mounted in parallel to a portion 51 of the second gas supply circuit 3, the portion 51 extending between the branch zone 52 and the confluence zone 53. The gas supply system 1 further comprises a third heat exchanger 36 having one of the line portions of the heat treatment branch 33.

[0060] If there is an excess of gas in gaseous state in the tank blanket 12, the pressure in the tank 8 will be excessive. It is therefore necessary to reduce the pressure in the tank 8 by venting the gaseous state. For example, the excess gaseous state can then be removed by a burner 18 or, in a not shown embodiment, can be vented to the atmosphere. These solutions result in a loss of cargo. For this reason, the gas supply system 1 according to the invention comprises a gas return line 14 which runs from the second gas supply circuit 3 to the tank 8.

[0061] A gas return line 14 is connected to the second gas supply circuit 3 downstream of the compression device 13 in the flow direction of the gas in gaseous state through the second gas supply circuit 3. The return line 14 runs first through the second heat exchanger 7, then through the third heat exchanger 36 and finally through the first heat exchanger 6.

[0062] The first heat exchanger 6 comprises a first line 6a which is part of the first gas supply circuit 2. This first heat exchanger 6 comprises a second line 6b which is part of the return line 14. The direction of flow through the first line 6a is opposite to the direction of flow through the second line 6b of the first heat exchanger 6.

[0063] The second heat exchanger 7 is disposed in the first gas supply circuit 2 between the first heat exchanger 6 and the high-pressure evaporator 11 .

[0064] The second heat exchanger 7 comprises a first line 7a which is part of the first gas supply circuit 2. This second heat exchanger 7 comprises a second line 7b which is part of the return line 14. The direction of flow through the first line 7a is opposite to the direction of flow through the second line 7b of the second heat exchanger 7.

[0065] The third heat exchanger 36 is disposed in the return line 14 between the first heat exchanger 6 and the second heat exchanger 7. The third heat exchanger 36 includes a first line 36a which is a part of the return line 14, and a second line 36b which is a part of the heat treatment branch section 33. The first line 36a of the third heat exchanger 36 is mounted in the return line 14 between the second line 7b of the second heat exchanger 7 and the second line 6b of the first heat exchanger 6.

[0066] The heat treatment branch 33 is therefore designed to cool the gaseous gas flowing in the return line 14 to facilitate its condensation. In this situation, the heat treatment branch 33 allows the cold of the gaseous gas taken from the tank 8 to be recovered and utilized by sending it to the return line 14. Such an operation is only suitable if the gaseous gas in the tank 8 is at a sufficiently low temperature, more generally at a lower temperature at the inlet of the first line 36a of the third heat exchanger 36 than the temperature of the gaseous gas flowing in the return line 14.

[0067] In order to properly manage the second gas supply circuit 3 and the heat treatment branch 33 depending on the temperature of the gaseous gas in the tank 8, the flow is designed to be controlled by a monitor unit 46. The latter is, for example, a valve. The flow of the gaseous gas in the heat treatment branch 33 is designed to be controlled by a monitor device 38. The monitor unit 46 and / or the monitor device 38 is, for example, a valve or an on-off valve.

[0068] The heat treatment branch section 33 is mounted in parallel to the monitor unit 46. In other words, the branch zone 52 is disposed on the upstream side of the monitor unit 46 in the gas flow passing through the second gas supply circuit 3, and the confluence zone 53 is disposed on the downstream side of the monitor unit 46.

[0069] The gas supply system 1 also comprises a management device 49 and at least one measuring means 48 for the temperature of the gas in gaseous state taken from the tank 8. The measuring means 48 for temperature is, for example, a temperature sensor arranged in the second gas supply circuit 3 between the tank 8 and the branching zone 52. Alternatively, the measuring means 48 can be attached to the tank blanket 12. The measuring means 48 for temperature is electrically connected to the management device 49, since data from the measuring means 48 are used in the calculations carried out by the management device 49.

[0070] The management device 49 is an electronic control unit which receives data from the measuring means 48 and monitors the opening and closing of the monitoring unit 46 and / or the monitoring device 38. The management device 49 performs the method and its various steps, except for the step of measuring the temperature of the gas in gaseous state withdrawn from the tank 8.

[0071] The method of the present invention is illustrated in Figures 2 and 3. Figures 2 and 3 show two examples of destinations of gas in gaseous state from tank 8 depending on its temperature. In Figures 2 and 3, solid lines indicate lines through which gas flows, and dotted lines indicate lines through which there is no gas flow.

[0072] If the temperature of the gas in gaseous state withdrawn from the tank 8 and measured by the measuring means 48 is lower than a temperature threshold value, for example equal to -110°C, the management device 49 can allow the gas to flow through the heat treatment branch 33. For this, the management device 49 performs an opening of the monitor device 38. In this way, the monitor device 38 allows the gas in gaseous state withdrawn from the tank 8 to reach the third heat exchanger 36, in particular its second line 36b. In such a situation, the management device 49 prevents the gas in gaseous state from flowing through a portion 51 of the second gas supply circuit 3 extending between the branching zone 52 and the merging zone 53. For this, the management device 49 performs a closing of the monitor unit 46 mounted on the portion 51.

[0073] As shown in Fig. 3, the management device 49 can also prevent the gas from passing through the heat treatment branch 33 if the temperature measured by the measuring means 48 is higher than the above-mentioned temperature threshold. In this case, passing a gas flow at such a temperature through the heat treatment branch 33 would be counterproductive, since the gas in the gaseous state flowing through the return line would be heated instead of cooled. In this configuration, the management device 49 performs the closing of the monitor device 38 and the opening of the monitor unit 46, thereby allowing the gas in the gaseous state to flow through the part 51 of the second gas supply circuit 3. The gas in the gaseous state taken from the tank 8 can thus reach the compressor 13 directly.

[0074] Naturally, the management device 49 can be assigned to other computational processes necessary for the functioning of the gas supply system 1 according to the invention, for example monitoring of the flow regulating unit 15, or of the valve 19 controlling the flow of gas through the auxiliary gas supply line 16, or of the compressor 13, or of the submersible pump 9 or the pump 10.

[0075] The gas in gaseous state flowing through the return line 14 can therefore be cooled, if possible at its temperature, by the gaseous state contained in the tank. The gas in liquid state of the first gas supply circuit 2 then has its lowest temperature at the inlet of the first line 6a of the first heat exchanger 6. Thus, the gas flowing through the return line 14 condenses after flowing through the first heat exchanger 6. The fluid in the return line 14 is therefore in gaseous state at the inlet of the second line 6b of the first heat exchanger 6 and leaves in liquid state after the heat exchange in the first heat exchanger 6.

[0076] The return line 14 further comprises a flow regulation unit 15 which monitors the flow rate of the fluid through the return line 14. This flow regulation unit 15 has a variable flow area. As the gas condenses it flows into the tank 8. Thus, the first heat exchanger 6 is used as a condenser, while the flow regulation unit 15 monitors the heat exchange in the first heat exchanger 6, the second heat exchanger 7 and the high pressure evaporator 11.

[0077] The gas supply system 1 also includes an auxiliary gas supply line 16 that extends from the first gas supply circuit 2 through a nipple between the submersible pump 9 and the first heat exchanger 6 to the second gas supply circuit 3 and connects to the compressor 13 between the low-pressure gas consuming device 5. The auxiliary gas supply line 16 allows gas to be supplied to the low-pressure gas consuming device 5 even when the flow rate of gaseous gas from the tank blanket 12 is insufficient.

[0078] If there is not enough gas in the gaseous state in the tank blanket 12, gas in the liquid state from the submersible pump 9 can flow through this auxiliary gas supply line 16 and be supplied to the low-pressure gas consumer 5. For this purpose, the auxiliary gas supply line 16 extends through the low-pressure evaporator 17 so that the gas in the liquid state flowing through the auxiliary gas supply line 16 becomes gaseous. For example, the operation of the low-pressure evaporator 17 can be the same as that of the high-pressure evaporator 11. That is, the gas is boiled off by heat exchange with a heat transfer fluid having a temperature high enough to boil off the gas in the liquid state. At the outlet of the low-pressure evaporator 17, the gas in the gaseous state flows through the auxiliary gas supply line 16 and reaches the second gas supply circuit 3 and is supplied to the low-pressure gas consumer 5.

[0079] From the above, the auxiliary gas supply line 16 is used only when there is not enough gas in the gaseous state within the tank blanket 12.

[0080] Therefore, the auxiliary gas supply line 16 is equipped with a valve 19. The valve 19 monitors the gas flow through the auxiliary gas supply line 16 when its use is not required.

[0081] It should be noted that each heat exchange device described herein may be a two-line component, and the present invention also contemplates multiple heat exchangers grouped together to form a single heat exchanger, for example a three-line or four-line heat exchanger.

[0082] Thus, a combination of two or more of the second heat exchanger 7, the third heat exchanger 36, and the high pressure evaporator 11 may be configured into a single heat exchanger module 50. For example, by combining these into a single heat exchanger module 50, the size of multiple independent exchangers may be reduced.

[0083] FIG. 4 shows a variant of the first embodiment of the gas supply system 1 according to the invention. Compared to the one described in the previous figures, the variant differs in the structure of the third heat exchanger 36. The third heat exchanger 36 still comprises a first line 36a, which is part of the return line 14, and a second line 36b, which is part of the heat treatment branch 33, but also a third line 36c, which is part of the gas supply circuit 2. It is therefore understood that the third heat exchanger 36 according to the variant of FIG. 4 is configured to perform a heat exchange between the gas in the gas state passing through the return line 14, the gas in the gas state from the tank 8 flowing through the heat treatment branch 33, and the gas in the liquid state passing through the first gas supply circuit 2. Such a variant allows optimizing the cooling of the gas in the gas state passing through the first line 36a of the third heat exchanger 36 and through the return line 14 by utilizing the cold heat of the gas in the liquid state passing through the first gas supply circuit 2 and the third line 36c of the third heat exchanger 36. It is therefore a three-line heat exchanger which in combination with the second heat exchanger 7 and / or the high pressure evaporator 11 forms a single heat exchanger module 50 .

[0084] All these structural and functional elements are the same as those described above, except for the third heat exchanger 36, so please refer to the description of FIG. 1 for items common to the first embodiment and its variants.

[0085] 5 shows a second embodiment of a gas supply system 1 according to the invention, which corresponds to the first embodiment with the addition of further components.

[0086] This second embodiment of the gas supply system 1 therefore further comprises a cooling branch 40 for the gas in gaseous state withdrawn from the tank. Such a line allows the gas in gaseous state withdrawn from the tank 8 to flow through and be cooled.

[0087] The cooling branch 40 is connected to the second gas supply circuit 3 upstream of the compressor 13 via a branch point 44 and a junction point 45 specific to the cooling branch 40. Alternatively, both the cooling branch 40 and the heat treatment branch 33 may be connected to the branching zone 52 and the junction zone 53. In either connection manner, the heat treatment branch 33 and the cooling branch 40 are mounted in parallel with each other and with the portion 51 of the second gas supply circuit 3.

[0088] The gas supply system 1 shown in FIG. 5 also includes a heat exchanger 41 intended to cool the gaseous gas taken out of the tank by heat exchange with the liquid gas flowing through the first supply circuit 2.

[0089] The heat exchanger 41 includes a first line 42 that exchanges heat with a second line 43 that is a part of the heat exchanger 41. The first line 42 of the heat exchanger 41 is a part of the first gas supply circuit 2, and liquid gas flows through it. On the other hand, the second line 43 of the heat exchanger 41 is a part of the cooling branch section 40, and gas in a gaseous state from the tank 8 flows through it.

[0090] Originally, the first line 42 of the heat exchanger 41 is fluidly arranged between the first line 7 a of the second heat exchanger 7 and the first line 11 a of the high-pressure evaporator 11 .

[0091] Such an arrangement allows the gas in the gaseous state flowing through the cooling branch 40 to be cooled by heat exchange with the gas in the liquid state flowing through the first gas supply circuit 2, resulting in a reduction in the volumetric flow rate at the inlet of the compressor 13 and therefore in a reduction in its consumption, in particular in electricity consumption.

[0092] This arrangement also allows for a reduction in the flow rate of the heat transfer fluid passing through the second line 11b of the high pressure evaporator 11 to boil off the liquid gas from the tank 8. Since this is a heat source, the present invention allows for a reduction in the amount of heat provided by the heat transfer fluid, since part of the heat is provided by the gas in the gaseous state flowing through the cooling branch 40.

[0093] The cooling branch 40 further comprises a monitor valve 47 arranged to monitor the flow of gas in gaseous state through the cooling branch 40. This monitor valve 47 is designed to be controlled by a management device 49 and is in an open position if the temperature of the gaseous gas withdrawn from the tank 8, measured by the measuring means 48, when most or all of the gaseous gas flows through the return line 14, is higher than a reference threshold value, for example equal to -90°C. In this arrangement, the reference threshold value is higher than the temperature threshold value.

[0094] Alternatively, the reference threshold is above -150°C when most or all of the gas in gaseous state is sent to the low pressure gas consumer 5 via the second gas supply circuit 3. In such a case, the flow regulating unit 15 reduces, or possibly stops entirely, the flow of gas through the return line 14.

[0095] If the temperature of the gas in gaseous state measured by the measuring means 48 is lower than a reference threshold value, the control device 49 effects the closing of the monitor valve 47 .

[0096] In the case of the second embodiment, the above-mentioned single heat exchanger module 50 may be supplemented by a mass heat exchanger 41. Such a single heat exchanger module 50 may comprise at least five lines fluidly separated from one another. Advantageously, the single heat exchanger module 50 may combine the second heat exchanger 7, the mass heat exchanger 41 and the high-pressure evaporator 11. These three exchangers are high-pressure exchangers.

[0097] 6 to 8 show examples of the flow of gaseous gas from the tank 8 through the second gas supply circuit 3, the heat treatment branch 33 or the cooling branch 40 depending on the measured temperature of the gaseous gas in the tank 8. The flow of gaseous gas from the tank 8 is managed by the monitoring unit 46, the monitoring device 38 or the management device 49 managing the monitoring valve 47 depending on the temperature of the gaseous gas in the tank 8 measured by the temperature measuring means 48 and on the comparison of this temperature with the abovementioned temperature threshold and reference threshold. As in figures 2 and 3, the solid lines indicate lines through which gas flows and the dotted lines indicate lines through which there is no gas flow.

[0098] Thus, Figure 6 corresponds to the flow of gaseous gas from tank 8 when the measured temperature of the gaseous gas from tank 8 is below the temperature threshold, i.e., when the temperature of the gaseous gas from tank 8 is low enough to cool the gaseous gas passing through return line 14.

[0099] Depending on the measured temperature measured by the measuring means 48, the management device 49 closes the monitor unit 46 and the monitor valve 47 and opens the monitor device 38, so that the gaseous gas from the tank 8 flows through the heat treatment branch 33 and the second line 36b of the third heat exchanger 36 and cools the gaseous gas flowing through the return line 14 and the first line 36a of the third heat exchanger 36.

[0100] FIG. 7 corresponds to the passage of gaseous gas from the tank 8 when the measured temperature of the gaseous gas from the tank 8 is higher than the reference threshold, i.e. when the temperature of the gaseous gas from the tank 8 is too high and the compressor 13 cannot compress it without consuming excessive energy. To prevent this excessive energy consumption, the gaseous gas from the tank 8 must be cooled before compression. For this purpose, the management device 49 closes the monitor unit 46 and the monitor device 38 and opens the monitor valve 47, so that the gaseous gas from the tank 8 flows through the cooling branch 40 and the second line 43 of the heat exchanger 41 and is cooled by the gaseous gas flowing through the second gas supply circuit 2 and the first line 42 of the heat exchanger 41. The cooled gaseous gas in the heat exchanger 41 can flow to the compressor 13 and be compressed without excessive energy consumption.

[0101] FIG. 8 corresponds to the flow of gaseous gas from tank 8 when the measured temperature of the gaseous gas from tank 8 is between the temperature threshold and the reference threshold, i.e., above the temperature threshold and below the reference threshold.

[0102] Thus, in this configuration, the temperature of the gaseous gas in the tank 8 is low enough to be compressed in the compressor 13 without consuming excessive energy, but too high to cool the gaseous gas in the return line 14. It may be counterproductive to allow the gaseous gas in the tank to flow through the heat treatment branch 33.

[0103] In this configuration, the management device 49 closes the monitor device 38 and the monitor valve 47 and opens the monitor unit 46, so that the gas in gaseous state from the tank 8 flows directly through the second gas supply circuit 3 via a portion 51, is compressed directly by the compressor, and then is consumed in the low-pressure gas consumer 5 or is recondensed in the return line 14.

[0104] Naturally, the invention is not limited to the embodiments described above, and many modifications can be made to these within the framework of the invention.

[0105] As mentioned above, the present invention proposes a gas supply system which achieves the assigned objectives and which utilizes the cold of a gas in a tank to carry out condensation of said gas in a gaseous state. Variations not described in this specification are also possible within the framework of the present invention, provided that they comprise a gas supply system according to the invention.

Claims

1. A gas supply system (1) for at least one high pressure gas consumer (4) and at least one low pressure gas consumer (5) for a floating structure, comprising at least one tank (8) adapted to contain gas at least in a liquid state, The gas supply system (1) comprises: at least one first gas supply circuit (2) for said high pressure gas consumer (4), at least one high-pressure evaporator (11) configured to vaporize the gas flowing in said first gas supply circuit (2); at least one second gas supply circuit (3) for said low-pressure gas consumer (5), said second gas supply circuit (3) comprising at least one compression device (13) configured to compress the gas extracted in gaseous state from said tank (8) to a pressure suitable for the needs of said low-pressure gas consumer (5); at least one gas return line (14) connected to said second supply circuit (3) downstream of said compression device (13) and extending to said tank (8); at least one first heat exchanger (6) and at least one second heat exchanger (7), each configured to perform a heat exchange between the gas in gaseous state flowing in said gas return line (14) and the gas in liquid state flowing in said first gas supply circuit (2); Equipped with The gas supply system (1) comprises a heat treatment branch (33) for gas in a gaseous state passing through the gas return line (14), the heat treatment branch (33) is connected to the second supply circuit (3) upstream of the compression device (13); the gas supply system (1) comprises a third heat exchanger (36) configured to perform a heat exchange between the gas in gaseous state passing through the heat treatment branch (33) and the gas in gaseous state passing through the gas return line (14); A gas supply system (1).

2. the third heat exchanger (36) comprises a first line (36a) located between the first heat exchanger (6) and the second heat exchanger (7) in the gas return line (14) and a second line (36b) located in the heat treatment branch (33); A gas supply system (1) according to claim 1.

3. the second supply circuit (3) comprises a branching zone (52) where the heat treatment branching section (33) and the second supply circuit (3) branch off, and a merging zone (53) where the heat treatment branching section (33) and the second supply circuit (3) merge; The heat treatment branch (33) extends between the branching zone (52) and the confluence zone (53). A gas supply system (1) according to claim 1 or 2.

4. the gas supply system (1) comprises a monitoring unit (46) for the flow of gas through the second supply circuit (3), The heat treatment branch (33) is mounted in parallel to the monitor unit (46). A gas supply system (1) according to any one of the preceding claims.

5. the heat treatment branch (33) is provided with a monitoring device (38) configured to monitor the flow of gas in gaseous state through the heat treatment branch (33); A gas supply system (1) according to claim 4.

6. a measuring means (48) for the temperature of the gas withdrawn in gaseous state from said tank (8), and a management device (49) for giving commands to said monitor unit (46) and said monitor device (38), A gas supply system (1) according to claim 5.

7. the third heat exchanger (36) is configured to perform a heat exchange between the gas in gaseous state passing through the gas return line (14), the gas in gaseous state passing through the heat treatment branch (33) and the gas in liquid state passing through the first gas supply circuit (2); A gas supply system (1) according to any one of the preceding claims.

8. the third heat exchanger (36) comprises a first line (36a) located in the gas return line (14) between the first heat exchanger (6) and the second heat exchanger (7), a second line (36b) located in the heat treatment branch (33), and a third line (36c) located in the first gas supply circuit (2) between the first heat exchanger (6) and the second heat exchanger (7); A gas supply system (1) according to claim 7.

9. At least the second heat exchanger (7), the third heat exchanger (36) and the high pressure evaporator (11) constitute a single heat exchanger module (50). A gas supply system (1) according to any one of the preceding claims.

10. the gas supply system (1) comprises at least one cooling branch (40) for the gas withdrawn in gaseous state from the tank (8), said cooling branch (40) being connected to the second supply circuit (3) upstream of the compressor (13), the gas supply system (1) comprises at least one heat exchanger (41) configured to perform a heat exchange between gas in a gaseous state passing through the cooling branch (40) and gas in a liquid state passing through the first supply circuit (2), A gas supply system (1) according to any one of the preceding claims.

11. the cooling branch (40) is provided with a monitor valve (47) configured to monitor the flow of gas in a gaseous state through the cooling branch (40); A gas supply system (1) according to claim 10.

12. At least the second heat exchanger (7), the heat exchanger (41) and the high-pressure evaporator (11) constitute a single heat exchanger module. A gas supply system (1) according to claim 10 or 11.

13. At least the second heat exchanger (7), the third heat exchanger (36), the heat mass exchanger (41) and the high pressure evaporator (11) constitute a single heat exchanger module (50). A gas supply system (1) according to claim 12.

14. the first gas supply circuit (2) includes a pump (10) between the first heat exchanger (6) and the second heat exchanger (7); A gas supply system (1) according to any one of the preceding claims.

15. A control process for a gas supply system (1) according to any one of claims 1 to 14, comprising: - in a measuring step, measuring the temperature of the gas in gaseous state taken from said tank (8), and then - passing said gas in gaseous state through said second gas supply circuit (3) if the temperature of said gaseous state gas measured in said measuring step is higher than a temperature threshold value, or - passing said gaseous gas through said heat treatment branch (33) if the temperature of said gaseous gas measured in said measuring step is lower than said temperature threshold value; Control process.

16. The control process of claim 15, wherein the temperature threshold is -110°C.

17. - passing said gas in gaseous state through said heat treatment branch (33) if the temperature of said gaseous state measured in said measuring step is lower than said temperature threshold, or - passing said gas in gaseous state through said cooling branch (40) if the temperature of said gas in gaseous state measured in said measuring step is higher than a reference threshold value higher than said temperature threshold value, or - passing said gas in gaseous state through said second gas supply circuit (3) if the temperature of said gaseous gas measured in said measuring step is between said temperature threshold and said reference threshold; A control process according to claim 15 or 16 in combination with any one of claims 10 to 13.

18. The reference threshold is −90° C. The control process comprises the step of condensing the gas in the gaseous state passing through the gas return line (14).

20. A control process according to claim 17.

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