Device and method for filling a space with a pressurized fluid and then emptying said space with recovery of the fluid

Description

Designation of the technical field concerned

[0001] The invention relates to methods requiring temporary filling of an enclosure with a pressurized fluid for which it is necessary to recover all or part of the fluid after emptying the enclosure. For example, the fluid may be recovered because it is dangerous, polluting or expensive.

[0002] The enclosure may be of any nature, for example it may be a hydrogen storage tank for an electric vehicle. The method may also be of any nature, for example a method for testing the gas tightness of said hydrogen storage tank.

[0003] The invention applies to any type of fluid, whether liquid, gaseous or composed of a mixture of a gas and a liquid.

[0004] It is described below for the particular case of a method for testing the gas tightness of a hydrogen tank using a tracer gas without this limiting the scope of the invention. Technical problems addressed by the invention

[0005] The leak test of a hydrogen tank with a tracer gas consists of filling it with the tracer gas, for example a mixture of nitrogen and helium with 2% helium under a pressure of 600 bars. The leaktightness of the tank is then checked with a sensor that detects the presence of helium near the tank in the event of a leak.

[0006] According to the state of the art, the filling can be carried out from a first tank whose tracer gas pressure is higher than that desired in the tank to be tested and whose volume is sufficient so that this pressure remains higher than that of the tank to be tested when the latter has reached the target pressure. During emptying, the gas is transferred from the tank to be tested into a second tank. A compressor then returns the tracer gas from the second tank to the first and a tracer gas top-up is carried out in the first tank.

[0007] This solution is not very energy efficient, as it requires a high pressure increase of the tracer gas. It also leads to significant frost formation around valves and pipes due to the significant expansion of the tracer gas during filling and emptying of the tank to be tested. CN104 075 106 B relates to a method and a device for filling and emptying an enclosure.

[0008] The invention provides a new solution to these problems. Summary of the invention

[0009] According to a first aspect of the invention, there is provided a method of filling an enclosure with a fluid until a target pressure is reached and then emptying said enclosure when the time comes, characterized in that the filling is carried out from a first plurality of reservoirs of different pressures, successively from the lowest pressure reservoir to the highest pressure reservoir, and in that the emptying is carried out by transferring contents of the reservoir of the enclosure to a second plurality of reservoirs, successively from the highest pressure reservoir to the lowest pressure reservoir.

[0010] The invention makes it possible to limit fluid consumption by recovering a large portion of it and reusing it again for a new filling cycle. It also makes it possible to optimize the filling process energetically, the fluid being recovered under pressure, thus limiting the energy required to raise its pressure to the desired level at the end of filling.

[0011] After emptying, fluid can be added to the second plurality of reservoirs, which is then used as the first plurality of reservoirs for refilling an enclosure.

[0012] Advantageously, the emptying is carried out in a second plurality of tanks composed of tanks from the first plurality of tanks. Carrying out the emptying in the same plurality of tanks makes it possible to limit the number of tanks, thus reducing the cost of the machine and its size.

[0013] According to a second aspect, which is not claimed, there is provided a machine for filling an enclosure with a fluid until a target pressure is reached and then emptying said enclosure when the time comes, comprising a first plurality of reservoirs of different pressures from which the enclosure is filled and a second plurality of reservoirs into which the fluid from the enclosure is transferred during emptying and in that it is suitable for implementing the method according to the first aspect of the invention.

[0014] Preferably, the second plurality of reservoirs is comprised of reservoirs from the first plurality of reservoirs. Brief description of the figures

[0015] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which one will refer to the attached drawing in which:

[0016] [ Fig. 1] is a schematic view of a machine according to an exemplary embodiment of the invention.

[0017] The hydrogen tank to be tested 30 is first subjected to a pressure resistance test under water. It is then dried and then flushed with nitrogen to remove all traces of oxygen from the tank. At the end of this operation, it is under a residual pressure of approximately 5 bars of nitrogen.

[0018] It is then filled with tracer gas until the desired pressure is reached. It is maintained at this pressure while the gas leak test is carried out. Finally, the tank, once tested, is drained. The filling and emptying of the tank are carried out by implementing the method according to the invention and by means of a machine according to the invention.

[0019] Machine 1 represented in [ Fig. 1] comprises a first tank R2 supplied with a mixture of nitrogen and helium at 2% helium under a pressure of 40 bars from a supply circuit 3 comprising a pump 4 and a mixer 5 supplied by a nitrogen circuit 6 and a helium circuit 7. The helium content at the outlet of the mixer is measured by an analyzer 8 and the proportions of nitrogen and helium are adjusted with regulating valves 9, 10.

[0020] Valve 11 is closed during the filling phase of tank R2, as is valve 13 located at the tank outlet.

[0021] Machine 1 includes a set of complementary tanks, six tanks R3 to R8 in this exemplary embodiment, intended to receive the tracer gas at different and higher pressures.

[0022] A compressor 12 makes it possible to supply these tanks with tracer gas from that available in tank R2 by raising its pressure from 40 bars to 718 bars. Tanks R3 to R8 are supplied with gas by opening an inlet valve 14 connected to an outlet of the compressor 12, the inlet valve 14 being closed when the target pressure is reached in the tank, the tank pressure being measured by a pressure gauge 15.

[0023] For example, the last tank R8 is at a nominal pressure of 718 bars, higher than that of 600 bars of tank 30 to be tested, the others are at decreasing intermediate nominal pressures, down to 40 bars for tank R2.

[0024] To fill the test tank 30 with tracer gas at 600 bars, it is successively connected to each of the tanks R3 to R8 using a transfer circuit 16 connected to the outlets of the tanks R3 to R8, by opening an outlet valve 17 of the tank concerned, starting with the lowest pressure tank R3. Once a desired pressure is reached in the tank 30 to be tested, the valve 17 of the tank concerned is closed and that of the next tank is opened to increase the pressure in the tank to be tested. When the last tank R8 reaches 718 bars, its outlet valve 17 is opened until the pressure in the test tank 30 is 600 bars. Once this pressure is reached, the tank R8 is isolated by closing its outlet valve 17.

[0025] The helium content in the tank to be tested is checked with an analyzer 28 and helium is topped up if necessary from a helium buffer tank 18 at 750 bars. The buffer tank 18 is supplied with helium from a helium supply tank 19 by means of a booster 20.

[0026] Once the leak test is complete, the outlet valve 17 of the tank R7 is opened in order to connect it to the test tank by means of the transfer circuit 16. Due to a higher pressure in the test tank 30, part of the tracer gas which was in this tank is transferred into the tank R7. It is possible to wait until the pressures between the test tank 30 and the tank R7 are equalized, but this may take too long, which is detrimental to the machine cycle time. It is therefore advantageous to stop the transfer between the two tanks when the pressure difference between them has reached a target value. The tank R7 is then isolated by closing its outlet valve 17 and the test tank 30 is connected to the tank R6 by means of the transfer circuit 16 by opening its outlet valve 17.Once the target pressure difference is reached between these two tanks, tank R6 is isolated by closing its outlet valve 17 and the same is done successively for tanks R5 to R2 so as to successively transfer tracer gas contained in the test tank 30 into these tanks.

[0027] To limit the loss of tracer gas and further improve the energy efficiency of the machine, the machine 1 may include a return circuit 24 connecting the tank to be tested 30 and the suction of the pump 4 allowing the tracer gas remaining in the tank 30 to be transferred to the tank R2. A valve 22 is arranged on the side of the machine to be tested 30 to isolate the return circuit 24. During this step, the mixer 5 is isolated by a valve 25. At the end of this operation, after closing the valve 22, a valve 26 allows the tank 30 to be returned to atmospheric pressure before it is separated from the machine.

[0028] Alternatively, the machine may not include the return circuit 24 and opening the valve 22 may simply discharge the remainder of the test gas contained in the tested tank to the atmosphere and return its pressure to atmospheric pressure.

[0029] Then, the pressure supplement is applied to tanks R3 to R8 to bring them back to their nominal pressure with compressor 12 and a new tank 30 is connected to the machine to be tested before starting a second test cycle. Tracer gas is also added to tank R2 when its pressure gauge 15 detects that its pressure has reached a low threshold.

[0030] The table below illustrates an example of operating points of a machine according to the [ Fig. 1], in which the nominal pressures of the tanks at the start of the test cycle of a tank 30 are indicated in column A, the pressures of the tanks after filling the tank 30 to be tested in column B, the volume supplied to the tank 30 by each tank in column C, the pressures of the tanks after recovery of gas from the tested tank in column D, the volume recovered from the tank 30 by each tank in column E, and the volume of gas to be supplied to the tanks to return to the initial state and start a new test cycle in column F. Reserves Volume (liters) A (bars) B (bars) C (Nm3) D (bars) E (Nm 3< ) F (Nm 3< ) R8 300 718 621 29,0 621 - 29,0 R7 300 600 500 24,0 554 13,3 16,7 R6 300 500 400 24,0 464 19,3 10,7 R5 300 400 300 24,0 373 21,9 8,1 R4 300 300 200 20,9 277 23,1 6,9 R3 300 200 113 20,9 186 21,9 4,2 R2 1000 40 40 - 68 28,2 - 30 240 5 600 - 68 - -

[0031] Test tank 30 was filled from tanks R3 to R8 with a total tracer gas volume of 142.8 Nm 3< . After the test was completed, 127.7 Nm 3< of tracer gas was recovered from test tank 30, representing 89% of the tracer gas. A top-up of 75.6 Nm 3< of tracer gas was required in tanks R3 to R8 from tank R2, but only 47.4 Nm 3< was supplied by mixing station 5, the difference having been recovered in tank R2 when the test tank was emptied. Only 16.4 Nm 3< would be lost if the tank were to be connected to the atmosphere by opening valve 26, corresponding to the 68 bar remaining in the test tank after emptying. However, it is advantageous to recover this gas through the return circuit 24.

[0032] Several 30 tank models can be tested on the machine, with varying volumes and / or test pressures. When switching to a new tank model to be tested, the pressure levels in tanks R3 to R8 can be adjusted according to the test pressure of the new tank.

[0033] Advantageously, for the test of the first tank of a new model, depending on the pressure required for its test, its filling with tracer gas can follow a strategy defined according to the pressures available in tanks R3 to R8. Thus, if the test pressure is low, for example 400 bars, only the first tanks R3 to R6 will be used and the gas top-up of these tanks after the test can be carried out from tank R7. The same procedure will be followed for the following tests as long as the pressure in tank R7 allows it. When it becomes insufficient, the top-up of tanks R3 to R6 will be carried out from tank R8. As soon as a tank R7 and R8 has insufficient pressure for top-up, it is included in the batch of tanks used for filling the tank to be tested.The pressure distribution in these tanks is adjusted each time a new tank joins the batch of tanks used for filling in order to optimize the energy efficiency of the test process.

[0034] The number of tanks R2 to R8 is optimized in particular according to the tank test pressure, according to the variety of tanks to be tested in terms of test pressure and volume and according to the cycle time required for testing a tank. Pressure losses in the circuits and the Kv values ​​of the valves are also taken into account, as these have an impact on the tracer gas flows. Kv expresses the flow rate in a valve with a pressure drop of one bar; if it is a control valve, the Kv value will be different depending on the opening level of the valve. Hydrogen tanks 30 are generally equipped with an "overflow" type valve 27. For safety reasons, this valve closes when the flow rate exceeds a defined value. The maximum flow rate allowed when emptying a tested tank is thus limited by this valve and must be considered for the sizing of the machine.Similarly, the volume of tanks R2 to R8 is chosen based on these parameters, as not all tanks necessarily have the same volume.

[0035] These choices are made after a numerical simulation of the machine's operation in order to retain the best compromise between the machine's operating cost and its purchase cost. Indeed, adding an additional tank can be advantageous for the machine's energy efficiency, but it loses its interest if the savings made on the machine's operation do not compensate for the additional cost resulting from the additional tank.

Claims

1. Method for filling an enclosure (30) with a fluid until a target pressure is reached and then emptying said enclosure when the time comes, characterized in that the filling is carried out from a first plurality of tanks (R3, R4, R5, R6, R7, R8) of different pressures, successively from the lowest-pressure tank (R3) up to the highest-pressure tank (R8), and in that the emptying is carried out by transferring the contents of the of the enclosure (30) to a second plurality of tanks (R2, R3, R4, R5, R6, R7), successively to the highest-pressure tank (R7) up to the lowest-pressure tank (R2).

2. Method according to claim 1, characterized in that the emptying is carried out in a second plurality of tanks made up of tanks from the first plurality of tanks.

3. Method according to claim 2, characterized in that after emptying, fluid is topped up in the second plurality of tanks, which is then used as the first plurality of tanks for refilling an enclosure.