SYSTEM FOR THE THERMAL COMPRESSION OF A GAS

Description

[0001] The present invention relates to the field of gas compression. RU2509256C2 discloses a cyclic method for the thermal compression of a gas.

[0002] It concerns a thermal compression system for a gas, and in particular dihydrogen.

[0003] In a context of rapid development of low-carbon dioxide solutions for mobility and the transport of goods and passengers, hydrogen is emerging as a promising fuel. Its use, combined with a fuel cell and an electric motor in a vehicle, can represent an alternative to fossil fuels or the use of batteries commonly employed to power electric motors.

[0004] Due to its low density, dihydrogen must be compressed to a pressure of around 700 bar to be used as a fuel. It is usually delivered to service stations at a pressure of 200 bar, then compressed on-site in a compressor to pressures ranging from 450 to 1000 bar.

[0005] This compressor is usually a mechanical one, which has several drawbacks. The moving parts cause hydrogen leaks. The pistons are not lubricated because this would introduce impurities into the hydrogen, damaging the fuel cell; the pistons therefore wear out quickly. In addition, these compressors consume electricity, which represents a significant cost and worsens the environmental impact of hydrogen. Finally, the mechanical compressor generates significant noise, which is particularly problematic for service stations in cities.

[0006] To address these problems, thermochemical compressors using metal hydrides have been developed. Metal powders absorb dihydrogen at low pressure to form metal hydrides. These hydrides are then heated, releasing dihydrogen at high pressure. These compressors operate ideally between 20 bar and 500 bar. Outside this operating range, it is difficult to find metal powders capable of performing compression at temperatures compatible with industrial standards. In particular, for very high pressure levels, the energy required to further increase the pressure is too great compared to a mechanical compressor, which consumes energy on the order of the ratio between the outlet pressure and the inlet pressure. A thermochemical compressor can then be combined with a mechanical compressor to reach the highest pressure levels.

[0007] Alternatively, thermal compressors exist. Document US20120028140 proposes a compressor with multiple tanks connected in series, where the pressure rises between two consecutive tanks by heating the upstream tank. This method does not allow for high flow rates and consumes too much energy.

[0008] One object of the present invention is to provide a compressor that is efficient in terms of energy consumption, particularly for pressures above 500 bars, without the problems of wear, electrical consumption, noise and leaks of mechanical compressors.

[0009] The present invention aims to address, at least in part, the aforementioned objectives by proposing a cyclic method for the thermal compression of a gas in which several tanks of a group undergo a cycle during which they pressurize in contact with a hotter tank or series of hotter tanks, then depressurize in order to pressurize other, cooler tanks. To this end, it proposes a cyclic method for the thermal compression of a gas in a plurality of tanks of at least one group of a system according to the invention, each cycle comprising, for each tank of each group, the following steps: cooling of the gas contained in the tank and transfer of gas from the source to said tank, transfer of gas from a donor tank to said tank, said donor tank being the one whose gas is at the lowest pressure among the tanks of said group whose gas is at a pressure and temperature higher than the gas of said tank, until equalization of the pressures in said tank and said donor tank, if necessary, repetition of this step as long as there is another tank of said group whose gas is at a pressure and temperature higher than the gas of said tank, heating of the gas contained in the tank and transfer of gas from said tank to the target, transfer of gas from said tank to a receiving tank, said receiving tank being the one whose gas is at the highest pressure among the tanks of said group whose gas is at a pressure and temperature lower than the gas of said tank,until the pressures in said tank and said receiving tank are equalized, if necessary, this step is repeated as long as there is another tank in said group whose gas is at a pressure and temperature lower than the gas in said tank, the step of cooling the gas contained in the tank and transferring gas from the source to said tank being carried out successively for each tank in said group.

[0010] Thanks to these features, the gas can be compressed to high pressure by thermal compression, thus avoiding noise and wear on mechanical parts. This process is particularly energy-efficient, as the heat used to increase the pressure in one tank is then used to compress the contents of other tanks as the pressure drops, with the compression potentially occurring in a cascade.

[0011] According to other characteristics: The said process can take place in a plurality of tanks from two groups, the steps of cooling the gas contained in a tank and transferring the gas from the source being able to take place alternately to one of the tanks of one group, then to one of the tanks of the other group, which makes it possible to optimize the process, and in particular to allow continuous supply of the system and production of compressed gas, during the step of transferring gas from a donor tank of the same group, whose gas is at a higher pressure and temperature, to said tank, the transferred gas can be cooled to reduce the temperature rise of the contents of said tank, which makes it possible to maintain the temperature difference between a tank increasing in pressure and a tank decreasing in pressure, this difference making it possible to optimize the compression of the gas of said tank, each group of tanks can comprise at least three, preferably at least four tanks,and the two transfer stages are each repeated at least two, preferably at least three times, which allows the gas to be raised to several pressure stages, and thus to obtain a greater pressure rise for a given temperature difference; said process may further include a gas compression stage, before its transfer from the source to a tank, in a metal hydride compressor, which allows combining a first compression offering the advantages of the hydride compressor, then a thermal compression when the high pressure values ​​make the hydride compressor less suitable; during the stage of cooling the gas contained in a first tank, heat can be extracted from said first tank and used in the stage of heating the gas contained in a second tank, which allows the energy consumption of the process to be optimized.At least two steps can be carried out simultaneously: a first step involving a gas transfer between a first and a second entity, these two entities being the source and a tank, two tanks, or a tank and the target; and a second step involving a gas transfer between a third and a fourth entity, these two entities being the source and a tank, two tanks, or a tank and the target. The first, second, third, and fourth entities are four distinct entities, which optimizes the cycle. Several different steps can take place simultaneously in several different tanks of the system, or even within the same group. The gas transfer step from the source to a first tank can occur simultaneously with the gas transfer step from a second tank to a receiving tank or to the target, thus optimizing the cycle.several different stages taking place simultaneously in several different reservoirs of the system, or even within the same group.

[0012] The present invention also relates to a thermal compression system for a gas characterized in that it comprises a source, a target, and at least one group of tanks, each group comprising at least two tanks, said system comprising a heating means and a cooling means for the contents of each tank, each group further comprising: transfer means enabling the transfer of gas directly from said source to each tank and directly from each tank to said target, and for each tank of said group, bidirectional transfer means enabling the transfer of gas directly between that tank and at least one other tank of said group.

[0013] Thanks to these provisions, the gas can be compressed to a high pressure by thermal compression, which avoids problems of noise and wear of mechanical parts, while allowing an energy-efficient process.

[0014] According to other characteristics: said gas may be dihydrogen, which is a relevant embodiment of the invention, dihydrogen often having to be compressed to high pressures to be usable, particularly in transport;It can also be N2, O2, CH4 or Helium for example, the said system may include two groups of tanks, which allows to optimize its operation, and in particular to allow a continuous supply of the system and production of compressed gas, the said system may include at least three, preferably at least four tanks in each group, which allows to increase several stages of pressure to the gas, and therefore to obtain a greater pressure rise for a given temperature difference, the heating means may include a source of waste heat such as for example a dihydrogen production installation by biomass or an electrolyzer, which makes it possible to recover the heat produced, and thus reduce the costs of the energy consumed by the system, ; The cooling method may include a source of fatal cold, such as a liquefied gas storage or a return from a chilled water loop, which allows the available cold to be recovered, and thus reduce the energy consumed by the system. The source may include an evaporation gas outlet from a liquid dihydrogen storage, which allows cold dihydrogen to be supplied to the tank which must be fed by the source, and thus achieve a particularly efficient first compression stage. All the tanks of the same group may have the same volume, which simplifies the system.

[0015] The present invention will be better understood upon reading the detailed description that follows, with reference to the accompanying figures in which: [ Fig.1 ] There [ Fig.1 ] is a schematic view of a thermal compression system for a gas according to an embodiment of the invention, [ Fig.2 ] There [ Fig.2 ] is a schematic view of the steps in a thermal compression process of a gas according to the embodiment of the [ Fig.1 ], [ Fig.3 ] There [ Fig.3 ] is a schematic view of the first steps of a thermal compression process for a gas according to a preferred embodiment of the invention, [ Fig.4 ] There [ Fig.4 ] is a schematic view of the steps completing the process begun in [ Fig.3 ].

[0016] The thermal compression system for a gas according to the invention, illustrated in [ Fig.1 ], comprises a source 1, a target 2, and one or more groups of reservoirs 3.

[0017] The system according to the invention allows gas to be compressed from a source 1, at which the gas is at a pressure P 0, to a target pressure P.

[0018] The gas concerned by the invention is preferably dihydrogen. However, it may be another gas, such as oxygen or nitrogen for example.

[0019] The three tanks are suitable for containing a certain volume of said gas in a sealed manner. Within a group, the three tanks preferably all have the same volume, for example 50 liters.

[0020] The thermal compression system includes a heating means 4 and a cooling means 5 for the contents of each tank 3. The heating means 4 and cooling means 5 allow, for example, bringing a heat transfer fluid into contact with the contents of each tank 3. If the heat transfer fluid is hotter, respectively colder, than the contents of a tank 3, it can be used to heat, respectively cool, said contents.

[0021] Heating method 4 can also be an electric resistance immersed in the tank.

[0022] The heating means 4 can be connected to an electrolyzer or a biomass-fired hydrogen production unit. Thus, if the gas is hydrogen, the heat generated to produce this hydrogen can be recovered in the thermal compression system. Depending on the installation location of the system according to the invention, other locally available sources of waste heat can be connected to the heating means to reduce energy costs. These could include, for example, a waste collection site or any other industrial site where heat is generated.

[0023] The thermal compression system further includes transfer means 6a for transferring gas directly from source 1 to each reservoir 3 of a group, and transfer means 6b for transferring gas directly from each reservoir 3 of a group to target 2. A direct transfer here means a transfer which does not pass through another reservoir 3 of the same group or of another group, nor through source 1 or target 2.

[0024] The thermal compression system also includes bidirectional transfer means 7 for transferring gas directly from each tank in a group to each other tank in the same group. Direct transfer here refers to a transfer that does not pass through another tank 3 in the same group or another group, nor through the source 1 or the target 2. Thus, considering any pair of tanks 3 in the same group, it is possible to transfer gas directly between these two tanks 3 in both directions.

[0025] The present invention relates to a cyclic method for the thermal compression of a gas in a plurality of tanks 3 of at least one group. Each cycle comprises, for each tank 3a of each group, the following steps: Cooling of the gas contained in tank 3a to a cold temperature T1, and transfer of gas from source 1 to said tank 3a. At the end of this step, tank 3a contains gas at a pressure P0 and a temperature T1. Transfer of gas from another donor tank 3 to said tank 3a. The donor tank 3 is the one whose gas is at the lowest pressure among the tanks 3 in the same group whose gas is at a pressure and temperature higher than the gas contained in said tank 3a. The transfer takes place automatically upon opening of the bidirectional transfer means 7 between tank 3a and donor tank 3, until the pressures in tank 3a and donor tank 3 are equalized. It is during this step that the gas contained in said tank 3a is compressed. At the end of the first occurrence of this step, tank 3a contains gas at a pressure P1 and a temperature T1.This step can be repeated several times, as long as there is another tank 3 in said group whose gas is at a higher pressure and temperature than the gas contained in said tank 3a. For example, the step can be repeated twice if the group has three tanks 3, or three times if the group has four tanks 3. Each repetition of this step allows tank 3a to increase its pressure by one stage. At the end of this step, tank 3a contains gas at a pressure PK and a temperature T1, where K is equal to the number of repetitions of the transfer step. The gas contained in tank 3a is then heated to a higher temperature T2, allowing it to increase its pressure by one final stage, and the gas is transferred from said tank 3a to the target 2. At the end of this step, tank 3a contains gas at a pressure PK+1 and a temperature T2. The pressure PK+1 is close to, or equal to, the target pressure P.Gas transfer from said tank 3a to another receiving tank 3. The receiving tank 3 is the one whose gas is at the highest pressure among the tanks 3 in the same group whose gas is at a pressure and temperature lower than that of said tank 3a. The transfer occurs automatically upon opening the bidirectional transfer means 7 between tank 3a and receiving tank 3, until the pressures in said tank 3a and receiving tank 3 are equalized. At the end of the first occurrence of this step, tank 3a contains gas at a pressure close to or equal to PK and a temperature T2. This step can be repeated several times, as long as there is another tank 3 in said group whose gas is at a pressure and temperature lower than that of the gas in tank 3a. The step can, for example, be repeated twice if the group has three tanks 3, or three times if the group has four tanks 3.Each repetition of this step allows tank 3a to raise the pressure of another tank 3 in the same group by one stage. At the end of this step and its repetition to the end, tank 3a contains gas at a pressure close to or equal to P1 and a temperature T2.

[0026] In the case where all the tanks 3 in the group have the same volume, we can also determine the quantity of gas in tank 3 at each stage: At the end of the cooling and transfer step from source 1, reservoir 3a contains n 0 moles of gas; at the end of one occurrence of the transfer step from a donor reservoir 3 to said reservoir 3a, said reservoir 3a contains n 1 moles of gas; at the end of the entire transfer step from one or more donor reservoirs 3 to said reservoir 3a, said reservoir 3a contains n K moles of gas; at the end of the heating and transfer step to target 2, reservoir 3a contains n K-1 moles of gas. at the end of one occurrence of the transfer step of said tank 3a to a receiving tank 3, said tank 3a contains n K-2 moles of gas, at the end of the entire transfer step of said tank 3a to one or more receiving tanks, said tank 3a contains n -1 moles of gas.

[0027] The step of cooling the gas contained in the tank and transferring the gas from the source to said tank 3a is carried out successively for each tank 3 of said group, and not for several tanks 3 at the same time. Thus, the tanks 3 of the group each go through this step in turn, then follow the same cycle simultaneously, each with a time lag relative to the others.

[0028] During this process, the thermal compression of the gas is achieved by opening the transfer means between two reservoirs 3. The reservoir 3 in which the gas is most compressed allows the gas in the other reservoir to increase in pressure. The receiving reservoir is in a cold state, and the supplying reservoir is in a hot state. This ensures that, with an equivalent number of moles of gas in both reservoirs, the hot reservoir has a higher pressure and can supply gas, thus increasing the pressure in the cold reservoir. During each cycle, each reservoir 3 therefore undergoes a pressure increase in a cold state, followed by a pressure decrease in a hot state. Consequently, during a cycle, a reservoir 3 only needs to be heated and cooled once.

[0029] Preferably, during the gas transfer step from another tank 3 of the same group, containing gas at a higher pressure and temperature, to said tank, the transferred gas is cooled. This maintains a cold temperature in the tank 3 receiving the hot gas, thus preserving the temperature differential with the other hot tanks 3. The transferred gas can be cooled before arriving in tank 3, for example, in the bidirectional transfer means 7 between the two tanks 3. Alternatively, the transferred gas can be cooled after arriving in tank 3 by cooling the entire contents of tank 3, for example, by the cooling means 5. In a preferred embodiment of the invention, the contents of a tank 3 cooled to a cold temperature T1 are maintained at the cold temperature T1 until the reheating step.Similarly, the contents of a tank 3 heated to a hot temperature T2 are preferably kept at that hot temperature T2 until the cooling stage. This ensures that the temperature difference between T1 and T2 is always taken advantage of when a hot tank 3 is connected to a cold tank 3 to pressurize the latter.

[0030] In order to optimize the cycle of the process according to the invention, at least two steps of the process can be carried out simultaneously. A first step including a gas transfer between a first and a second entity, these two entities being the source 1 and a tank 3, two tanks 3, or a tank 3 and the target 2, and a second step including a gas transfer between a third and a fourth entity, these two entities being the source 1 and a tank 3, two tanks 3, or a tank 3 and the target 2, the first, second, third and fourth entities being four distinct entities.

[0031] For example, the gas transfer step from source 1 to a first tank 3a, ..., 3h takes place simultaneously with the gas transfer step from a second tank 3a, ..., 3h to a receiving tank 3 or to the target 2. Thus, when some tanks 3 of the system perform certain steps, other tanks 3 perform other steps of the process, which saves time.

[0032] In a preferred embodiment of the invention, in order to optimize the energy consumption of the process, during the step of cooling the gas contained in a first tank 3a, ..., 3h, it is possible to use heat extracted from said first tank 3a, ..., 3h in the step of heating the gas contained in a second tank 3a, ..., 3h. For example, a heat transfer fluid can be circulated from the first tank 3a, ..., 3h to the second tank 3a, ..., 3h.

[0033] A group of tanks 3 comprises at least two tanks 3, for example three, and preferably four tanks 3. The number of tanks 3 is chosen, along with the other system parameters, based on the number of stages required to compress the gas from pressure P0 at source 1 to the desired target pressure P at target 2. Other parameters to adjust include the volumes of the tanks 3 and the temperatures T1 and T2 at which the tanks 3 are heated and cooled. It is advantageous to have an even number of tanks 3 in a group. This ensures that at each stage of the process, one stage takes place in each tank 3.

[0034] The system may consist of a single group of tanks 3, but preferably it consists of two groups of tanks 3. Indeed, the total number of steps in the cycle described above, including repetitions of the second and fourth steps, is equal to twice the number of tanks 3 in a group. When the system comprises a single group, only half of the steps can therefore be performed simultaneously by one of the tanks 3. In particular, the gas transfer steps from source 1 to target 2 do not occur for a single group at each stage of the cycle. It is therefore possible to have two groups operating in parallel, which allows, at each stage of the cycle, gas to be transferred from source 1 to one of the system's tanks 3, and from one of the system's tanks 3 to target 2.The number of tanks in each group can be different, but in order to obtain the advantage mentioned above for two groups, it is necessary that both groups have either an even or an odd number of tanks.

[0035] In one particular embodiment, three additional tanks can be provided to allow for heating and cooling to be carried out in several stages. This is advantageous if the heating and cooling stages take longer than the transfer stages; typically, if these stages take twice as long as the transfer stages, it may be beneficial to perform the heating and cooling in two stages.

[0036] According to another specific embodiment, an installation can be provided that initially operates between a first source pressure P0 and a target pressure P1. Then, in a second stage, a portion of the gas at pressure P1 can be drawn and used as a source at pressure P1. The device then raises the pressure to pressure P2. This process can continue for as long as necessary to finally reach the desired target pressure.

[0037] In a preferred embodiment of the invention, the source gas pressure P0 is between 400 and 600 bar, for example, from a metal hydride compressor, and the target gas pressure Ptarget is between 800 and 1000 bar. In this embodiment, two groups of four tanks 3 can be provided, the pressure increase in a tank 3a being achieved, for example, in the following stages: 500 bar at the source, then 560 bar, 635 bar, 725 bar after the three transfer stages from another hot tank 3, and then a final stage leading to 810 bar during the heating of tank 3a. Preferably, the cooling temperature T1 and heating temperature T2 of the gas are between 280 and 310 K, for example 293.15 K, and between 360 and 390 K, for example 373.15 K, respectively. These temperatures can of course be used with other pressure values.

[0038] To optimize energy consumption, the cooling temperature T1 can be as low as possible, for example, the ambient temperature or the temperature of the lowest available cooling source at the site of use. If liquefied gases such as liquid nitrogen, a chilled water return line, or other cooling fluids are available on site, these can be used. A liquefied gas is defined as a product that is in a gaseous state at atmospheric pressure and ambient temperature, for example, 20°C, and is cooled to a liquid state.

[0039] Source 1 can also be connected to an evaporation gas outlet from a liquid hydrogen storage (boil-off gas), which is at a temperature of 15K, thus providing cold hydrogen to the reservoir which must be supplied by the source.

[0040] The system according to the invention is particularly advantageous for small installations, with a gas outlet flow rate at target 2 for example between 1 and 100 kg per hour.

[0041] Other applications are possible in terms of pressure / temperature: Source connected to an evaporation gas outlet of a liquid hydrogen storage (boil-off gas): pressure P0 at source 1: between 0.5 and 10 bar, target pressure P at target 2: between 5 and 450 bar, cooling temperature T1: between 15 and 300 K, heating temperature T2: between 300 and 400 K. Source connected to a waste hydrogen outlet, co-produced by an industrial installation: pressure P0 at source 1: between 0.5 and 3 bar, target pressure P at target 2: between 20 and 500 bar, cooling temperature T1: between 253 and 353 K, heating temperature T2: between 353 and 1000 K. Source connected to a low-temperature electrolyzer: pressure P0 at source 1: between 1 and 50 bar, target pressure P at target 2: between 2 and 200 bars, cooling temperature T 1: between 253 and 293 K, heating temperature T 2: between 333 and 393 K.Source connected to a high-temperature electrolyzer: pressure P0 at source 1: between 1 and 30 bar, target pressure P at target 2: between 2 and 200 bar, cooling temperature T1: between 253 and 293 K, heating temperature T2: between 333 and 1073 K. Source connected to a thermochemical compressor, for example, a metal hydride compressor: pressure P0 at source 1: between 200 and 500 bar, target pressure P at target 2: between 400 and 1000 bar, cooling temperature T1: between 253 and 293 K, heating temperature T2: between 353 and 423 K. Source connected to a gas cylinder outlet: pressure P0 at source 1: between 50 and 500 bar, target pressure P at target 2: between 100 and 1000 bar, cooling temperature T1: between 253 and 293 K, warming temperature T2: between 353 and 500 K.source connected to a biomass dihydrogen production unit: pressure P 0 at source 1: between 1 and 5 bars, pressure P target at target 2: between 2 and 50 bars, cooling temperature T 1: between 253 and 293 K, heating temperature T 2: between 353 and 1073 K. .

[0042] There [ Fig.2 ] illustrates an example of an embodiment in which the system according to the invention comprises a group of two tanks 3a, 3b. The volumes of the tanks 3a, 3b are equal. On the [ Fig.2 [ ], the arrows illustrate the gas flows. The state of each tank is noted after the gas transfers are complete.

[0043] The cycle consists of four stages: Step A: The gas in reservoir 3a is heated to temperature T2 and some of this gas is transferred to the target 2. At the end of this step, reservoir 3a contains n0 moles of gas, at pressure P2 = Ptarget, and at temperature T2. The gas in reservoir 3b is cooled to temperature T1 and some gas is transferred from source 1 to reservoir 3b. At the end of this step, reservoir 3b contains n0 moles of gas, at pressure P0, and at temperature T1. Step B: The bidirectional transfer means 7 is opened between reservoirs 3a and 3b, causing a transfer of gas from reservoir 3a to reservoir 3b. At the end of this step, tank 3a contains n -1 moles of gas, at pressure P 1 , and at temperature T 2 , and tank 3b contains n 1 moles of gas, at pressure P 1 , and at temperature T 1 .

[0044] Steps C and D are identical to steps A and B, except that tanks 3a and 3b are swapped. After step D, the cycle can restart at step A.

[0045] THE figures 3 And 4 illustrate an example of an embodiment in which the system according to the invention comprises two groups of four tanks 3a to 3d and 3e to 3h. The volumes of tanks 3a to 3d are equal. The volumes of tanks 3e to 3h are equal. On the figures 3 And 4 The arrows illustrate the gas flows. The state of each tank is noted after the gas transfers are complete.

[0046] The cycle consists of eight steps A to H. We will describe the cycle followed by reservoir 3a: Step A: The gas in reservoir 3a is cooled to temperature T1, and gas is transferred from source 1 to reservoir 3a. At the end of this step, reservoir 3a contains n0 moles of gas, at pressure P0 and temperature T1. Step B: The bidirectional transfer means 7 is opened between reservoirs 3a and 3b, causing a transfer of gas from reservoir 3b to reservoir 3a. At the end of this step, reservoir 3a contains n1 moles of gas, at pressure P1 and temperature T1. Step C: The bidirectional transfer means 7 is opened between reservoirs 3a and 3d, causing a transfer of gas from reservoir 3d to reservoir 3a. At the end of this step, reservoir 3a contains n2 moles of gas, at pressure P2 and temperature T1. Step D: The bidirectional transfer means 7 is opened between tanks 3a and 3c, causing a transfer of gas from tank 3c to tank 3a.At the end of this step, reservoir 3a contains n³ moles of gas, at pressure P₃, and at temperature T₁. Step E: The gas contained in reservoir 3a is heated to temperature T₂ and a portion of this gas is transferred to target 2. At the end of this step, reservoir 3a contains n² moles of gas, at pressure P₄ = Ptarget, and at temperature T₂. Step F: The bidirectional transfer means 7 is opened between reservoirs 3a and 3b, causing a transfer of gas from reservoir 3a to reservoir 3b. At the end of this step, reservoir 3a contains n¹ moles of gas, at pressure P₃, and at temperature T₂. Step G: The bidirectional transfer means 7 is opened between reservoirs 3a and 3d, causing a transfer of gas from reservoir 3a to reservoir 3d. At the end of this step, the reservoir 3a contains n 0 moles of gas, at pressure P 2 , and at temperature T 2 .Step H: The bidirectional transfer means 7 is opened between tanks 3a and 3c, causing a transfer of gas from tank 3a to tank 3c. At the end of this step, tank 3a contains n -1 moles of gas, at pressure P1, and at temperature T2. At the end of step H, the cycle can resume at step A.

[0047] All tanks 3a to 3h follow the cycle above, exchanging of course with the relevant tanks 3 at each transfer stage: Tank 3b starts the cycle above at step C, tank 3c starts the cycle above at step G, tank 3d starts the cycle above at step E, tank 3e starts the cycle above at step B, tank 3f starts the cycle above at step D, tank 3g starts the cycle above at step H, tank 3h starts the cycle above at step F.

[0048] The presence of two groups in the system allows for a reservoir 3 to receive gas from source 1 and a reservoir 3 to send gas to target 2 at each stage of the cycle. For example, at stage A, reservoir 3d of the first group of reservoirs 3 sends gas to target 2; at stage B, it is reservoir 3h of the second group of reservoirs 3; then at stage C, reservoir 3c of the first group of reservoirs 3, and so on. Furthermore, at stage A, reservoir 3a of the first group of reservoirs 3 receives gas from source 1; at stage B, it is reservoir 3e of the second group of reservoirs 3; then at stage C, it is reservoir 3b of the first group of reservoirs 3, and so on.

[0049] Considering this example of implementation, and carrying out the heating and cooling stages over the duration of two transfer stages, this leads to the requirement of ten 3-tanks instead of eight. The ten tanks then constitute a single group, and each 3-tank can be connected to three other 3-tanks among the ten, by bidirectional transfer means; each 3-tank must, of course, also be connected to the source and the target by transfer means.

[0050] Although the above description is based on particular embodiments, it is in no way limiting of the scope of the invention, and modifications may be made, in particular by substitution of technical equivalents or by different combination of all or part of the features developed above.

Claims

1. A cyclic process for the thermal compression of a gas in a plurality of reservoirs (3) of at least one group of reservoirs (3), each cycle comprising for each reservoir (3a, ..., 3h) of said plurality of reservoirs (3) the following steps: - cooling of the gas contained in the reservoir (3a, ..., 3h) and transfer of gas from the source (1) to said reservoir (3a, ..., 3h), - transfer of gas from a donor reservoir (3) to said reservoir (3a, ..., 3h), said donor reservoir (3) being at a higher pressure and temperature than the gas of said reservoir (3a, ..., 3h) and of the same group, preferably said donor reservoir (3) being the one whose gas is at the lowest pressure among the reservoirs (3) of said group whose gas is at a higher pressure and temperature than the gas of said reservoir (3a, ..., 3h), until equalization of the pressures in said reservoir (3a, ..., 3h) and said donor reservoir (3), if necessary repeating this step for as long as there is another reservoir (3) of said group whose gas is at a higher pressure and temperature than the gas in said reservoir (3a, ..., 3h), - heating of the gas contained in the reservoir (3a, ..., 3h) and transfer of gas from said reservoir (3a, ..., 3h) to the target (2), - transfer of gas from said reservoir (3a, ..., 3h) to a receiving reservoir (3), said receiving reservoir (3) being at a lower pressure and temperature than the gas from said reservoir (3a, ..., 3h), preferably said receiving reservoir (3) being that whose gas is at the highest pressure among the reservoirs (3) of said group whose gas is at a lower pressure and temperature than the gas from said reservoir (3a, ..., 3h), until equalization of the pressures in said reservoir (3a, ..., 3h) and said receiving reservoir (3), if necessary repeating this step for as long as there is another reservoir (3) of said group whose gas is at a lower pressure and temperature than the gas in said reservoir (3a, ..., 3h), the step of cooling the gas contained in the reservoir (3a, ..., 3h) and transferring gas from the source to said reservoir (3a, ..., 3h) being carried out successively for each reservoir (3) of said group.

2. Process according to the preceding claim, wherein during the step of transferring gas from a donor reservoir (3) of the same group whose gas is at a higher pressure and temperature to said reservoir (3), the transferred gas is cooled to reduce the temperature rise of the contents of said reservoir (3).

3. Process according to one of the preceding claims also comprising a gas compression step, prior to its transfer from the source (1) to a reservoir, in a metal hydride compressor.

4. Process according to one of the preceding claims, wherein during the step of cooling the gas contained in a first reservoir (3a, ..., 3h), heat is extracted from said first reservoir (3a, ..., 3h) and is used in the step of reheating the gas contained in a second reservoir (3a, ..., 3h).

5. Process according to one of the preceding claims, wherein at least two gas transfer steps are carried out in the same time, the first concerning two entities from among the source, the target and a reservoir, the second concerning two entities not concerned by the first.

6. Process according to one of the preceding claims, wherein the step of transferring gas from the source (1) to a first reservoir (3) takes place simultaneously with the step of transferring gas from a second reservoir (3) to a receiving reservoir (3) or to the target (2).

7. A system configured to implement a process for thermally compressing a gas according to claim 5, comprising a source (1), a target (2), and at least one group of reservoirs (3) each comprising at least two reservoirs (3), said system further comprising means for heating (4) and means for cooling (5) the contents of each reservoir, each group further comprising: - transfer means (6a, 6b) for transferring gas directly from said source (1) to each reservoir (3) and directly from each reservoir (3) to said target (2), and - for each reservoir (3) of said group, bidirectional transfer means (7) enabling gas to be transferred directly between this reservoir (3) and at least one other reservoir (3) of said group.

8. System according to the preceding claim, wherein said gas is dihydrogen.

9. System according to one of claims 7 to 8, comprising two groups of reservoirs (3).

10. System according to one of claims 7 to 9 with at least three, preferably at least four reservoirs (3) in each group.

11. System according to one of claims 7 to 10, wherein the heating means (4) comprises a source of waste heat, for example a biomass dihydrogen production plant or an electrolyzer.

12. System according to one of claims 7 to 11, wherein the cooling means (5) comprises a fatal cold source, for example a liquid nitrogen storage or a return from a chilled water loop.

13. System according to one of claims 7 to 12, wherein the source (1) comprises an evaporation gas outlet from a liquid dihydrogen storage.

14. System according to one of claims 7 to 13, wherein all reservoirs (3) in a group have the same volume.