Method for recovering a compressed gas stored under pressure in a tank

Abstract

The recovery method comprises the following steps: - providing at least one at least partially empty recovery container (28) for recovering the compressed gas, - placing the intermediate tank (6) in fluid communication with the recovery container (28), - transferring at least some of the compressed gas from the intermediate tank (6) to the recovery container (28) by equalising the internal pressure of the intermediate tank (6) and the recovery container (28) during a transfer step.

Description

[0001] Process for recovering a compressed gas stored under pressure in a tank

[0002] The present invention relates to a method for recovering a compressed gas stored under pressure in an intermediate tank.

[0003] The invention also relates to a method for metrological control of a device for distributing a compressed gas to a motor vehicle implementing such a recovery method.

[0004] It is planned to subject a station for supplying compressed gas to motor vehicles to regular metrological checks in order to ensure the proper functioning of the various elements of this station. More specifically, each device for distributing compressed gas to a motor vehicle is regularly checked to ensure that the transfer of compressed gas from a source of compressed gas to a motor vehicle is carried out under good conditions.

[0005] To achieve this, it is intended to use each dispensing device to transfer compressed gas from the compressed gas source to one or more test tanks, the operation of the dispensing device and certain characteristics of the dispensed compressed gas being monitored or measured during this transfer operation.

[0006] Once filled, the test tank(s) must be emptied of the compressed gas they contain in order to be reused. This is usually done by flaring the compressed gas contained in the mobile test tanks, i.e. burning the gas.

[0007] However, such a flaring process is polluting in that it releases combustion gases directly into the atmosphere. In addition, the compressed gas is "wasted," meaning that it is only used to conduct metrological control and is not used to fuel a motor vehicle. Given that a compressed gas supply station generally includes several distribution devices and that each must be controlled, the amount of wasted gas quickly becomes significant.

[0008] Alternatively, in the case of a non-combustible gas, the emptying of the intermediate tanks is done, for example, by simply releasing the gas into the atmosphere, which results in significant waste, and can even lead to toxic emissions.

[0009] One of the aims of the invention is to overcome these drawbacks by proposing a method for recovering a compressed gas which has been previously transferred into an intermediate tank making it possible to recover this gas so that it can be reused and not flared, or released as is into the atmosphere. To this end, the invention relates to a method for recovering a compressed gas stored under pressure in an intermediate tank, comprising the following steps: providing at least one container for recovering the compressed gas which is at least partly empty, placing the intermediate tank in fluid communication with the recovery container, transferring at least a portion of the compressed gas from the intermediate tank to the recovery container by balancing the internal pressure between the intermediate tank and the recovery container during a transfer step,wherein the recovery method further comprises the following step if a volume remains available in the recovery container and if a volume of gas remains present in the intermediate tank: placing a compressor in fluid communication with the intermediate tank on the one hand and with the recovery container on the other hand, transferring at least a portion of the gas remaining in the intermediate tank into the recovery container by means of said compressor.,

[0010] The invention allows the intermediate tank to be emptied so that it can be reused for another metrological check, the compressed gas being transferred into a recovery container which can be stored for the purpose of subsequent reuse of the compressed gas. Thus, the compressed gas is recovered and not flared and can be reused, for example, to power a motor vehicle or to replenish the source of compressed gas.

[0011] The recovery method according to the invention may further comprise one or more of the following features, considered alone or in any technically conceivable combination: the compressed gas is a natural gas; the recovery method further comprises the following step if the recovery container is filled with the gas transferred from the intermediate tank and if a volume of gas remains present in the intermediate tank: breaking the fluid communication between the intermediate tank and the recovery container, placing the intermediate tank in fluid communication with another at least partly empty recovery container, transferring at least a portion of the gas remaining in the intermediate tank into the other recovery container;the compressed gas is transferred from the intermediate tank to one or more recovery containers until the pressure in the intermediate tank is close to atmospheric pressure, more particularly less than or equal to 1 bar; the recovery method further comprises at least one step of re-injecting the compressed gas present in at least one compressed gas exploitation installation recovery container by placing said recovery container in fluid communication with the exploitation installation by transferring said compressed gas from the recovery container to said exploitation installation; said re-injection step is carried out by means of a compressor arranged in the fluid communication between the recovery container and the exploitation installation; the compressed gas pressure in the intermediate tank (6) is substantially between atmospheric pressure and 300 bars before the transfer step.;

[0012] According to another aspect, the invention also relates to a method for metrological control of a device for distributing a compressed gas to a motor vehicle, comprising the following steps: placing the distribution device in fluid communication with a source of compressed gas on the one hand and with at least one intermediate tank on the other hand, actuating the distribution device to fill the intermediate tank from the gas source, measuring at least the quantity and the flow rate of the gas distributed by the distribution device during its actuation, after filling the intermediate tank, implementing a recovery method as described above to transfer the gas from the intermediate tank to at least one recovery container.

[0013] The control method according to the invention may further comprise one or more of the following features, considered alone or in any technically conceivable combination: the source of compressed gas comprises a plurality of storage containers distributed in at least two transfer levels to the intermediate tank, the distribution device being arranged: to transfer the compressed gas stored in at least one storage container from one level to the intermediate tank and when the pressure differential between said storage container and the intermediate tank is less than a predetermined value, to transfer the compressed gas stored in at least one storage container from the other level to said intermediate tank;the compressed gas injection point of a gas supply station is in fluid communication with the gas source, the compressed gas reinjected into said injection point being used to resupply said compressed gas source with compressed gas.;

[0014] Other aspects and advantages of the invention will appear on reading the following description, given by way of example and with reference to the appended drawings, in which: Fig. 1 is a schematic representation of a device for distributing a compressed gas, and Fig. 2 is a schematic representation of the different stages of a method for recovering a compressed gas stored in an intermediate tank.

[0015] With reference to Fig. 1, a distribution device 1 for dispensing a compressed gas from a compressed gas source 2 is described for transferring the compressed gas from the compressed gas source 2 to a vehicle tank 4 or to an intermediate tank 6. Such a distribution device 1 is intended to be part of a station for supplying compressed gas to motor vehicles using the compressed gas as fuel. The compressed gas is, for example, a natural gas. This is then referred to as compressed natural gas or CNG.

[0016] The distribution device 1 comprises in particular a device 8 for injecting compressed gas into a vehicle tank 4 or into the intermediate tank 6, the injection device 8 being in fluid communication with the source of compressed gas 2, possibly via a control device 10 and a valve device 12.

[0017] The injection device 8 is for example formed by a conventional gun for this type of application which can be placed in fluid communication with the internal volume of the vehicle tank 4 or the intermediate tank 6, as shown schematically in Fig. 1.

[0018] The compressed gas source 2 is for example formed by a plurality of storage containers 14 each containing compressed gas at a pressure substantially between 250 and 300 bars. The compressed gas contained in the storage containers is gas having been compressed from the national gas distribution network. The storage containers 14 are for example distributed between at least two, preferably three, transfer levels to the injection device 8, the gas pressure being different in the storage containers 14 of each transfer level. More particularly, the storage containers 14 are distributed between at least one lower bank 16 and one upper bank 18, the compressed gas in the lower bank being supplied to a tank before the compressed gas in the upper bank when the compressed gas is supplied to a vehicle tank.Preferably, the storage containers 14 are equally distributed in an intermediate bank 20, the compressed gas in the intermediate bank 20 being supplied to a tank before the compressed gas in the upper bank and after the compressed gas in the lower bank when the compressed gas is supplied to a vehicle tank, as will be described in more detail below.

[0019] The valve device 12 makes it possible to open and close the fluid communication between the compressed gas source 2 and the injection device 8. When the storage containers 14 are distributed in several transfer levels, the valve device 12 makes it possible to select the bank from which the compressed gas is transferred from the compressed gas source 2 to the injection device 8, by opening the fluid communication between one of the banks and the injection device 8 and by closing the fluid communication between the other banks and the injection device 8. Thus, the valve device 12 comprises for example three valves 22 arranged respectively in the fluid communication between the lower bank 16 and the injection device 8, the intermediate bank 20 and the injection device 8 and the upper bank 18 and the injection device 8.

[0020] The control device 10 makes it possible to control the valve device 12 to open and close the fluid communication between the compressed gas source 2 and the injection device 8 when a user actuates the injection device 8. The control device 10 is in particular arranged to select the valve 22 to be opened in the valve device in order to open the fluid communication between one of the transfer levels and the injection device 8 as a function of the pressure at which the gas can be injected into a vehicle tank 4 during normal operation of the distribution device 1.Thus, the control device 10 is arranged to measure the gas flow rate upstream of the injection device 8 by means of a flow sensor 24 and to control the valve device 12 in order to guarantee an optimum filling flow rate as a function of the pressure differential between a storage tank 14 and a vehicle tank 4, by means of a computer 26.

[0021] More particularly, when a user places the injection device 8 in fluid communication with a vehicle tank 4, the control device 10 is arranged to begin the transfer of compressed gas between the lower bank 16 of the compressed gas source 2 and the vehicle tank 4 by pressure balancing when the pressure differential between the lower bank 16 and the vehicle tank 4 makes it possible to obtain a satisfactory filling flow rate. When the pressure differential does not make it possible to obtain such a filling flow rate, the control device 10 closes the fluid communication between the lower bank 16 and the injection device 8 and opens the fluid communication between the intermediate bank 20 and the injection device 8.Likewise, when the pressure differential between the intermediate bank 20 and the vehicle tank 4 does not allow a satisfactory filling flow rate to be obtained, the control device 10 closes the fluid communication between the intermediate bank 20 and the injection device 8 and opens the fluid communication between the upper bank 18 and the injection device 8. The filling of the vehicle tank 4 continues by pressure balancing until a pressure of approximately 200 bar is obtained in the vehicle tank 4.

[0022] When the pressure in the storage containers 14 of the different transfer levels becomes lower than a predetermined threshold, which is different for each transfer level, the storage containers 14 are resupplied with compressed gas from the distribution network.

[0023] The invention can for example be implemented within the framework of a metrological control of the distribution device. Indeed, in order to ensure that the distribution device 1 described above is functioning correctly, it is regularly subjected to a metrological control during which the distribution device 1 is used as described above to fill the intermediate tank 6 instead of a vehicle tank 4. This filling makes it possible to measure at least the quantity and the flow rate of the gas distributed by the distribution device 1 when the injection device 8 is actuated. It is understood that other parameters can also be measured during the metrological control. When the results of the control are not satisfactory, the distribution device 1 is made unavailable until the anomalies are overcome.

[0024] The intermediate tank 6 is a container, for example of the steel cylinder type, capable of containing compressed gas. The intermediate tank 6 is, for example, a test tank intended to enable metrological control of the compressed gas distribution device. The intermediate tank 6 is, for example, a mobile intermediate tank, for example a mobile test tank. By mobile, it is meant that the intermediate tank 6 can be transported, for example by being placed in a vehicle, between different distribution devices and between different compressed gas supply stations so that the intermediate tank 6 can be used for different metrological control sessions. The intermediate tank 6 has, for example, a volume of 70 liters and a diameter of 30 cm.During the test, the intermediate tank 6 is filled by placing it in fluid communication with the injection device 8 and actuating the latter until a filling flow rate of approximately 9 to 10 kg / min and a pressure of approximately 220 bar is reached. Such filling corresponds to approximately 12 kg of compressed gas in the intermediate tank 6. After filling the intermediate tank 6, the pressure in the intermediate tank 6 is substantially between atmospheric pressure and 300 bar, more particularly in the case of compressed natural gas. The operation of filling the intermediate tank 6 is carried out several times in order to validate the control. Thus, for example, it is planned to completely fill the intermediate tank 6 three times and half-fill it twice. Consequently, a metrological control session of a compressed gas distribution device 1 consumes almost 50 kg of CNG.Knowing that a distribution station generally comprises three to five distribution devices 1 , we understand that the consumption of compressed gas to carry out metrological controls of the distribution devices is very significant.

[0025] The invention makes it possible to recover the compressed gas used during these checks so that this significant quantity of compressed gas can be reused and not flared, as is currently done. This recovery method will now be described with reference to Fig. 2.

[0026] When the intermediate tank 6 has been filled during a metrological control phase as described above, the intermediate tank 6 is placed in fluid communication with a compressed gas recovery container 28 which is at least partly empty, as shown at the top of Fig. 2. The recovery container 28 has, for example, at this stage an internal pressure lower than the compressed gas pressure in the intermediate tank 6. It is however understood that the internal pressure of the recovery container 28 could be equal to or greater than that of the intermediate tank 6.The recovery container 28 is for example of the same type as the intermediate tank 6 and has for example a capacity similar to or greater than that of the intermediate tank 6 so that the compressed gas contained in the intermediate tank 6 can be completely emptied into the recovery container 28 if the latter is empty at the start of the implementation of the recovery method.

[0027] During this step, the recovery container 28 is in direct fluid communication with the intermediate tank 6, that is to say that the recovery container 28 and the intermediate tank 6 are connected directly by a gas line so that the compressed gas contained in the intermediate tank 6 is transferred to the recovery container 28 without its characteristics being modified. Thus, during this step, at least a portion of the compressed gas contained in the intermediate container 6 is transferred to the recovery container 28, for example by balancing the internal pressure between the intermediate tank 6 and the recovery container 28 when the internal pressure of the recovery container 28 is lower than that of the intermediate tank 6.

[0028] At the end of this step, if the intermediate tank 6 still contains compressed gas and if the recovery container 28 still contains an empty volume, the direct fluid communication between the intermediate tank 6 and the recovery container 28 is undone and a compressor 30 is placed between the intermediate tank 6 and the recovery container 28. In other words, the compressor 30 is placed in fluid communication with the intermediate tank 6 on the one hand and with the recovery container 28 on the other hand, as shown in the middle of Fig. 2. The compressor 30 makes it possible to finish emptying the intermediate tank 6 into the recovery container 28 despite the zero or negative pressure difference between the pressure in the intermediate tank 6 and the pressure in the recovery container 28 at the end of the filling step.The compressor 30 is, for example, a mobile compressed gas compressor which can be transported with the intermediate reservoir container 6 from one distribution device 1 to another and from one distribution station to another.

[0029] The compressor 30 and the recovery container 28 form, for example, a mobile assembly making it possible to recover compressed gas from one or more intermediate tanks 6. The mobile assembly can then be transported between the different intermediate tanks 6 and / or the different operating installations.

[0030] When the intermediate tank 6 still contains compressed gas and when the recovery container 28 is full following the transfer steps described above, the compressed gas remaining in the intermediate tank 6 is transferred into another recovery container. To do this, the fluid communication between the intermediate tank 6 and the recovery container 28 is broken and the intermediate tank 6 is placed in fluid communication with another at least partially empty recovery container, either directly or via the compressor 30. The compressed gas remaining in the intermediate tank 6 is then transferred into the other recovery container either by pressure balancing or by means of the compressor 30 depending on the pressure difference between the intermediate tank 6 and the other recovery container.

[0031] The compressed gas contained in the intermediate tank 6 is transferred into one or more recovery containers 28 until the pressure inside the intermediate tank 6 is close to atmospheric pressure. Atmospheric pressure means that the pressure inside the intermediate tank 6 is less than or equal to 1 bar. The intermediate tank 6 can then be reused for a new metrological inspection. Thus, the recovery method according to the invention makes it possible to recover the compressed gas transferred into an intermediate tank 6 during a metrological inspection of a compressed gas distribution device 1 without having to flare this compressed gas to empty the intermediate tank 6. This recovery avoids a significant release of compressed gas into the atmosphere and avoids polluting and costly waste.

[0032] According to one embodiment, the compressed gas contained in the recovery container 28 can be reused, for example by being transferred to a compressed gas exploitation installation. Such an exploitation installation can be formed by one or more vehicle tanks 4 or by a compressed gas injection point 32 of a gas supply station in fluid communication with the compressed gas source 2, as shown at the bottom of Fig. 2. The injection point 32 thus makes it possible to resupply the compressed gas source 2, by filling one or more of the storage containers 14. The transfer of the compressed gas contained in the recovery container 28 to the exploitation installation is done for example by means of the compressor 30 described previously.

[0033] The compressed gas contained in the recovery container(s) 28, used to carry out one or more metrological checks, can thus be recovered to be consumed as motor vehicle fuel after these metrological checks.

[0034] The description has been made with reference to an intermediate tank forming more particularly a test tank for the metrological control of a compressed gas distribution device. It is however understood that the invention applies to any type of intermediate tank which can be filled from a distribution device and which it is desired to empty into a recovery container, for example a truck tank or other.

Claims

CLAIMS 1. A method for recovering a compressed gas stored under pressure in an intermediate tank (6), comprising the following steps: providing at least one recovery container (28) for the compressed gas which is at least partly empty, placing the intermediate tank (6) in fluid communication with the recovery container (28), transferring at least a portion of the compressed gas from the intermediate tank (6) to the recovery container (28) by balancing the internal pressure between the intermediate tank (6) and the recovery container (28) during a transfer step, the recovery method being characterized in that it further comprises the following step if a volume remains available in the recovery container (28) and if a volume of gas remains present in the intermediate tank (6): placing a compressor (30) in fluid communication with the intermediate tank (6) on the one hand and with the recovery container (28) on the other hand,transferring at least part of the gas remaining in the intermediate tank (6) into the recovery container (28) by means of said compressor (30)., 2. A recovery method according to claim 1, wherein the compressed gas is a natural gas.

3. A recovery method according to claim 1 or 2, further comprising the following step if the recovery container (28) is filled with the gas transferred from the intermediate tank (6) and if a volume of gas remains present in the intermediate tank (6): breaking the fluid communication between the intermediate tank (6) and the recovery container (28), placing the intermediate tank (6) in fluid communication with another at least partly empty recovery container, transferring at least a portion of the gas remaining in the intermediate tank (6) into the other recovery container (28).

4. Recovery method according to any one of claims 1 to 3, wherein the compressed gas is transferred from the intermediate tank (6) to one or more recovery containers (28) until the pressure in the intermediate tank (6) is close to atmospheric pressure, more particularly less than or equal to 1 bar.

5. A recovery method according to any one of claims 1 to 4, further comprising at least one step of re-injecting the compressed gas present in at least one recovery container (28) by placing said recovery container (28) in fluid communication with a compressed gas operating installation and transferring said compressed gas from the recovery container (28) to said operating installation.

6. Recovery method according to claim 5, wherein said reinjection step is carried out by means of a compressor (30) arranged in the fluid communication between the recovery container (28) and the operating installation.

7. Recovery method according to any one of claims 1 to 6, in which the compressed gas pressure in the intermediate tank^) is substantially between atmospheric pressure and 300 bars before the transfer step.

8. Method for metrological control of a distribution device (1) for a compressed gas to a motor vehicle, comprising the following steps: placing the distribution device (1) in fluid communication with a source (2) of compressed gas on the one hand and with at least one intermediate tank (6) on the other hand, actuating the distribution device (1) to fill the intermediate tank (6) from the gas source (2), measuring at least the quantity and the flow rate of the gas distributed by the distribution device (1) during its actuation, after filling the intermediate tank (6), implementing a recovery method according to any one of claims 1 to 7 to transfer the gas from the intermediate tank (6) to at least one recovery container (28).

9. Metrological control method according to claim 8, wherein the source (2) of compressed gas comprises a plurality of storage containers (14) distributed in at least two transfer levels towards the intermediate tank (6), the distribution device (1) being arranged: - to transfer the compressed gas stored in at least one storage container (14) from one level to the intermediate tank (6) and when the pressure differential between said storage container (14) and the intermediate tank (6) is less than a predetermined value, to transfer the compressed gas stored in at least one storage container (14) from the other level to said intermediate tank (6).

10. Metrological control method according to claim 8 or 9, implementing a recovery method according to claim 5, in which said operating installation is a compressed gas injection point (32) of a gas supply station, said injection point (32) being in fluid communication with the source (2) of compressed gas, the compressed gas reinjected into said injection point (32) being used to resupply said source (2) of compressed gas with compressed gas.

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