Hydrogen storage device equipped with a liquid piston

Abstract

The present invention relates to a hydrogen compressor and / or hydrogen displacer, and more particularly to a hydrogen reservoir (1) for storing hydrogen (2). The apparatus comprises a hydrogen volume filled with hydrogen (2) and a working fluid volume filled with a working fluid (3), wherein the working fluid (3) is designed as a liquid piston for changing the hydrogen volume, characterized in that the working fluid (3) contains poly-α-olefin. The present invention further relates to a method for replacing and / or compressing hydrogen (2). The method includes (a) providing a hydrogen compressor and / or hydrogen displacer according to the present invention, and (b) replenishing the hydrogen compressor and / or hydrogen displacer with the working fluid (3) to increase the working fluid volume of the hydrogen compressor and / or hydrogen displacer and to decrease the hydrogen volume of the hydrogen compressor and / or hydrogen displacer.

Description

Technical Field

[0001] The present invention relates to a hydrogen compressor or a hydrogen displacer, preferably to a hydrogen reservoir for storing hydrogen or a housing - piston unit, and this hydrogen compressor and / or hydrogen displacer comprises a hydrogen volume filled with hydrogen, and a working fluid volume filled with a working fluid, the working fluid being designed as a liquid piston for changing, i.e., expanding and / or contracting, the hydrogen volume. and comprises.

[0002] The present invention further relates to a method for replacing and / or compressing hydrogen.

[0003] The present invention further relates to a housing - piston assembly, the housing - piston assembly comprising a housing, preferably a cylinder, the housing including an operating volume for containing hydrogen, and a solid piston movable relative to the housing for changing the operating volume, and a seal for sealing the movement of the solid piston relative to the housing, a seal fluid being provided as the seal. and comprises.

[0004] The present invention further relates to a rotor, the rotor comprising a rotation axis, and a rotational drive device, and the above - mentioned housing - piston assembly. and comprises.

[0005] Finally, the present invention relates to a method for sealing the movement of the solid piston relative to the housing.

Summary of the Invention

[0006] In a first embodiment of the present invention, a hydrogen compressor or hydrogen displacer and a corresponding method are provided. In this method, hydrogen is compressed or replaced by a working fluid (hereinafter referred to as the “working fluid”) that is in direct contact with the hydrogen. In a first modification of the present invention, the hydrogen compressor or hydrogen displacer can be designed as a hydrogen reservoir from which hydrogen can be transferred, for example, to a hydrogen tank in an automobile. In the hydrogen reservoir, the working fluid acts as a liquid piston, compressing or replacing the hydrogen in direct contact with it. In a second modification of the present invention, the hydrogen compressor or hydrogen displacer can be designed as a housing-piston unit, particularly with a cylindrical housing. Within this housing, the working fluid is also in the form of a liquid piston in direct contact with the hydrogen, and is moved back and forth, particularly axially, in order to compress or replace the hydrogen.

[0007] U.S. Patent Application Publication 2007 / 258828 describes a hydrogen reservoir in which the working fluid is used as a liquid piston. In this prior art, the working fluid is preferably an ionic fluid, a high boiling point hydraulic fluid, or a fluid with a very low vapor pressure. Examples include vacuum pump oil, low melting point molten salts or metals, and gases with a solubility of 10 -4 Examples include fluids with a concentration of less than mol / l bar (U.S. Patent Application Publication No. 2007 / 258828, paragraph

[0017] ).

[0008] U.S. Patent Application Publication 2007 / 258828 focuses on ionic fluids, which are consistently described as advantageous, for example, in paragraphs

[0018] ,

[0019] ,

[0021] through

[0023] ,

[0047] and

[0050] . On the other hand, the use of vacuum pump oil is mentioned only once in U.S. Patent Application Publication 2007 / 258828, in paragraph

[0017] , and no particularly relevant advantages are highlighted. Therefore, if a person skilled in the art were to select a working fluid based on U.S. Patent Application Publication 2007 / 258828, it would likely be an ionic fluid.

[0009] U.S. Patent Application Publication 2007 / 258828 does not specify which ionic fluids can be used. Those skilled in the art will recognize from U.S. Patent Application Publication 2010 / 154924 that not all ionic fluids are suitable as liquid pistons (U.S. Patent Application Publication 2010 / 154924, paragraph

[0017] ). In the search for a suitable ionic fluid, those skilled in the art will refer to Kermani et al., Journal of Hydrogen Energy, 45(33), 2020, which has been studied to determine ionic fluids suitable as liquid pistons. Based on the cited literature, those skilled in the art will select the ionic fluid identified as suitable in Kermani et al., Int. Journal of Hydrogen Energy, 45(33), 2020, as the working fluid for the reservoir.

[0010] However, because ionic fluids are conductive, when different metals may come into contact, as in the applications of the present invention, the problem of electrochemically effective potential difference series arises. This can lead to unintended changes in the metal film (coating flow) between metals via the ionic fluid.

[0011] U.S. Patent No. 6066604 discloses a vacuum pump oil in which the base oil can be a synthetic oil or a mineral oil. As the synthetic oil, a poly-α-olefin having 4 to 14 carbon atoms in one molecule can be used. The mineral oil used is, for example, a paraffinic mineral oil (especially isoparaffin) or a naphthenic mineral oil (U.S. Patent No. 6066604, Column 1, Row 59 to Column 2, Row 41).

[0012] European Patent Application Publication No. 3508559 also relates to vacuum pump oil, and the use of synthetic oils (e.g., poly-α-olefins) in vacuum pump oil is mentioned only in combination with mineral oil. According to European Patent Application Publication No. 3508559, care must be taken to ensure that the presence of synthetic oil does not adversely affect the effect. Therefore, according to European Patent Application Publication No. 3508559, it is preferable to include only a small amount of synthetic oil in the vacuum pump oil, or to include none at all (European Patent Application Publication No. 3508559,

[0134] to

[0136] ).

[0013] However, it would not be obvious to a person skilled in the art that the vacuum pump oil using poly-α-olefin as described in U.S. Patent Application Publication 6,066,604 or European Patent Application Publication 3,508,559 is used as the working fluid in U.S. Patent Application Publication 2007 / 258828.

[0014] While U.S. Patent No. 6066604 refers to the use of poly-α-olefins as vacuum pump oil, it focuses on achieving good vacuum quality and simplifying pump starting in low-temperature applications (U.S. Patent No. 6066604, column 1, lines 4-7). Because the application areas are so different, a person skilled in the art would have no reason to consider U.S. Patent No. 6066604 for hydrogen reservoir applications.

[0015] Vacuum pump oil is subjected to entirely different loads than the working fluid of a hydrogen compressor or displacer according to the present invention. Vacuum pumps use a rotor sealed by vacuum pump oil. Such rotary pumps require high processing capacity at low operating pressure to achieve a vacuum. The opposite is true for hydrogen compressors and displacers. Typically, hydraulically driven hydrogen compressors (as opposed to crank-driven piston compressors) use axial or radial piston pumps, which imposes high requirements on the oil film and its load-bearing capacity, as it is subjected to considerable surface pressure. In contrast, vacuum pumps do not experience high surface pressure, and therefore have much lower requirements for wear protection.

[0016] On the other hand, in vacuum pumps, vapor pressure is important at moderate ambient temperatures, and even operating temperatures, particularly in the range of -20°C to +60°C, and especially 0°C to 30°C, because boiling at low pressures must be avoided. On the other hand, in hydrogen compressors, the working fluid is required to evaporate very little even at high temperatures or high pressures. This is particularly due to the fact that hydrogen gas for technical applications often requires high purity and, due to its low density, is usually compressed to high pressures.

[0017] Considering that the requirements for vacuum pump oil (high throughput, low pressure, and sealing performance at low temperatures) differ from those for the hydrogen compressor according to the present invention (relatively low volume throughput, sealing performance under high pressure with considerable surface pressure and high temperature), those skilled in the art would not use known vacuum pump oils in a hydrogen compressor for the applications of the present invention.

[0018] A second embodiment of the present invention provides a cylinder-piston assembly and a corresponding method in which the movement of a solid piston within the housing of the housing-piston assembly is sealed by a sealing fluid.

[0019] U.S. Patent No. 4,750,409 discloses a device for compressing gas. For this purpose, a piston having a seal groove moves within a bore. Lubricating oil is located on the top of the piston and enters the seal groove through a groove running from the top of the piston to the seal groove. The lubricant smooths the movement of the piston and lubricates the seal in the seal groove, reducing wear. Hydraulic fluid is used as the lubricating oil.

[0020] U.S. Patent Application Publication 2016 / 145523 discloses compressor oil and a method for producing the same. The compressor oil contains hydrocarbon oil with a sulfur content of 0.1% by weight or less and an aromatic content of 1% by weight or less, and the proportion of hydrocarbons with 10 or fewer carbon atoms is less than 100 ppm by mass. U.S. Patent Application Publication 2016 / 145523 cites an experiment in which poly-α-olefin was mixed with the defoaming agent dimethylpolysiloxane and prepared according to the disclosed method. This mixture is used for hydrogen compression. However, the decomposition temperature of dimethylpolysiloxane has already reached about 200°C, limiting the achievable pressure conditions. Furthermore, the addition of the defoaming additive adversely affects the surface tension and thus the lubrication properties of axial and radial piston pumps. Therefore, this fluid is not suitable for the applications according to the present invention.

[0021] As explained at the beginning of International Publication No. 2006 / 034748, piston compressors are commonly used when compressing gaseous media to keep the media being compressed separate from the media driving the piston (e.g., hydraulic fluid). Compressing hydrogen requires a precise cylinder with a piston and an effective dynamic sealing system. These lead to high production and maintenance costs. Therefore, more expensive compression technologies, such as diaphragm compressors and lubrication-free piston compressors, are often used for such applications. Against this backdrop, International Publication No. 2006 / 034748 discloses a method and apparatus for compressing hydrogen, in which compression is performed using a working fluid that does not dissolve the gas and / or can be separated from the gas without leaving any residue. Thus, the piston, which is made of a solid material, is replaced by an incompressible liquid column. The working fluid can be an ionic liquid, a high-boiling-point hydraulic oil, a liquid with a very low vapor pressure (e.g., vacuum pump oil, molten salt, low-melting-point metal), or a gas with a solubility of 10 -4 It may also be a liquid with a concentration of less than mol / l bar.

[0022] International Publication No. 2006 / 120145 also describes how to directly transmit the force required for compression to the gas, and how to achieve a vapor pressure of 10 -3Relates to a working fluid for compressing hydrogen below mbar. The working fluid may be a molecular fluid, such as mineral oil, silicone oil, or synthetic oil.

[0023] German Patent Application Publication No. 102011101504 discloses a further method for compressing hydrogen with a working fluid. As the working fluid, an ionic liquid, a perfluoropolyether, or a thermal oil may be used.

[0024] German Patent Application Publication No. 19848234 relates to a method for compressing a gas and a compressor. In this case, the gas and the working fluid are arranged in a container, and the gas is compressed by increasing the filling level of the working fluid. The working fluid used is a liquid with a low vapor pressure and / or that does not contact the gas, such as silicone oil, water, hydrocarbons, etc.

[0025] Finally, German Patent Application Publication No. 102015016327 describes a filling station for filling hydrogen into a storage container of a moving vehicle. Hydrogen is stored in one or more constant-pressure accumulators, and the gas is available at a specific, constant pressure. For this purpose, the constant-pressure accumulator has a cylinder, which is divided into two regions by a movable separating piston. The first region absorbs hydrogen. The second region receives a fluid, such as a working fluid. During the storage phase, by displacing the separating piston, the pressure of the hydrogen in the first region is kept constant, the first region expands, and the second region contracts. During the extraction phase, the volume of the first region decreases by pumping more liquid into the second region and increasing the volume of the second region so that the pressure in the first region is kept constant.

[0026] As described in European Patent Application Publication No. 3514380, sealing the piston of a conventional compressor from a solid body is very cumbersome and complex. This is especially true for hydrogen compression, where hydrogen places the highest requirements on sealing. Therefore, frequent seal replacements are required. European Patent Application Publication No. 3514380 proposes a compressor with automated seal replacement. When the high-pressure seal becomes unable to ensure the sealing of the high-pressure piston due to wear or damage, the replacement device is activated, and the high-pressure seal is replaced by a replacement high-pressure seal by the replacement device. If all (replacement) high-pressure seals are worn, the entire magazine can be replaced with a corresponding magazine equipped with unused replacement high-pressure seals, or new replacement high-pressure seals can be inserted into the magazine. Therefore, the use of this seal replacement device greatly facilitates seal replacement. However, in contrast, it is desirable to further improve the sealing of the compressor piston during hydrogen compression so that seal replacement is either unnecessary in the first place or at least rarely required.

[0027] International Publication No. 2013 / 079692 discloses a different type of ball valve with an external seal assembly using a seal fluid. The use of polyalkylene glycol as a seal fluid is described.

[0028] The working fluids mentioned in the prior art have proven unsuitable or unfavorable for the applications described above. Some working fluids known in the prior art, such as mineral oil, hydraulic oil, synthetic oil, and perfluoropolyether, have very high viscosity. High viscosity increases the tendency to foam and cavitate the working fluid, which can result in increased wear of system components. Carryover of the working fluid from the intended processing space can also occur. This problem is important, for example, when refueling a vehicle with hydrogen, specifically when transferring hydrogen from a hydrogen reservoir to the vehicle's hydrogen tank. In either case, contamination of the vehicle's hydrogen tank with the working fluid must be avoided. Other working fluids known in the prior art, such as thermal oil, water, and hydrocarbons, tend to migrate to the gas phase due to their high gas solubility or vapor pressure. Therefore, working fluids known in the prior art may be unfavorable for stable process control and plant lifespan in the applications described at the beginning.

[0029] Therefore, an object of the present invention is to mitigate or eliminate at least some of the drawbacks of the prior art. In particular, there is a need for working fluids and sealing fluids that ensure high process stability and minimize wear on system components in the applications described at the beginning.

[0030] This objective is achieved by the hydrogen compressor and / or hydrogen displacer described in claim 1, the hydrogen compression and / or replacement method described in claim 7, the housing-piston assembly described in claim 8, the rotor described in claim 12, and the method for sealing the movement of a solid piston relative to the housing described in claim 14.

[0031] In a first embodiment of the present invention, as a hydrogen compressor and / or hydrogen displacer, the work required to compress and / or replace hydrogen can be carried out via a working fluid containing poly-α-olefin. In a second embodiment of the present invention, as a housing-piston assembly, the movement of a solid piston relative to the housing can be sealed via a sealing fluid containing poly-α-olefin. In either embodiment, the use of poly-α-olefin (PAO) is remarkable because it provides special advantages without accepting the typical drawbacks of PAO.

[0032] Practical testing has shown that a special advantage of PAO in the applications of the present invention is that it is a dilute liquid, i.e., a low-viscosity liquid. This avoids the problem of foaming of the fluid when gases dissolved in the fluid re-expand due to pressure changes, for example. Such foaming can increase the cavitation tendency of pumps that replenish the working fluid, thereby increasing pump wear. When refueling a vehicle with hydrogen, foaming of the working fluid can further cause fluid carryover into the hydrogen tank, which should be avoided. In the prior art, high-viscosity working fluids, such as ionic liquids, have been proposed, but their strong foaming tendency requires compensating for this drawback by making the gas solubility very low. However, in practice, the required low gas solubility has not been achieved. Other working fluids, such as mineral oil, synthetic oil, and hydraulic fluid, are very viscous, so if foaming occurs, their use in the applications of the present invention becomes very unfavorable or impossible. On the other hand, thermal oil is prone to carryover and is therefore unsuitable for systems that supply hydrogen to fuel cell vehicles. The use of PAO according to the present invention is based on the understanding that foaming can be reliably avoided without requiring extremely low gas solubility, due to PAO's low foaming tendency. In the applications according to the present invention, even if the gas solubility of PAO is considerably low in absolute terms, but higher than that of ionic liquids, the low foaming properties of PAO can be optimally utilized.

[0033] "Poly-α-olefin" is understood to mean poly-1-olefin obtained by polymerization of α-olefins. The term "poly-α-olefin" includes poly-α-olefin homopolymers, polymers composed of two or more different monomer units (e.g., poly-α-olefin copolymers, poly-α-olefin terpolymers, and mixtures thereof).

[0034] The working fluid preferably contains 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and particularly preferably 99% by weight or more, of the total weight of the working fluid. This allows for effective utilization of the excellent properties of poly-α-olefin, such as low gas solubility and low foaming.

[0035] Depending on the design, the working fluid may contain only one type of poly-α-olefin. In preferred embodiments, the working fluid contains a mixture of two or more poly-α-olefins. The physical properties of the working fluid (e.g., viscosity, boiling point) can be adapted to the respective conditions.

[0036] Poly-α-olefins may have a linear or branched structure (n-alkane or isoalkane). Mixtures of linear poly-α-olefins with the same poly-α-olefin isomers, or mixtures of linear poly-α-olefins with poly-α-olefins having different numbers of carbon atoms, can also be used. This allows for adjustment of the boiling point of the working fluid. In particular, branched molecules have a significant effect on the viscosity of the working fluid.

[0037] In a preferred embodiment, at least 90% by weight of the poly-α-olefin has 19 or fewer carbon atoms per molecule, preferably 14 to 18 carbon atoms per molecule, and more preferably 16 to 18 carbon atoms per molecule, based on the total weight of the poly-α-olefin. Preferably, at least 95% by weight of the poly-α-olefin has such a number of carbon atoms, and more preferably at least 99% by weight has such a number of carbon atoms, based on the total weight of the poly-α-olefin. Poly-α-olefins having such a number of carbon atoms are suitable as working fluids because they tend to have particularly low gas solubility and are less prone to foaming. If the working fluid has two or more types of poly-α-olefins, preferably all of the poly-α-olefins have such a number of carbon atoms.

[0038] Preferably, up to 10% by weight of the poly-α-olefin has 20 or more carbon atoms, particularly 20 to 30 carbon atoms, based on the total weight of the poly-α-olefin. Preferably, up to 5% by weight of the poly-α-olefin has such a number of carbon atoms, and more preferably up to 3% by weight has such a number of carbon atoms, based on the total weight of the poly-α-olefin. As a result, viscosity can be kept low and foaming is less likely to occur.

[0039] The working fluid preferably has an aromatic hydrocarbon content of 1% by weight or less, and more preferably 0.5% by weight or less, based on the total weight of the working fluid. This helps to keep viscosity and, consequently, foaming tendency low.

[0040] The sulfur compound content in the working fluid is preferably 10,000 ppm or less, and more preferably 1,000 ppm or less, based on the total weight of the working fluid. This makes it possible to avoid the effects of sulfur compounds acting as cellular poison, especially in fuel cell-driven vehicles.

[0041] The working fluid preferably has a decomposition temperature of at least 250°C, preferably at least 280°C, under environmental conditions (temperature 293.15 Kelvin, atmospheric pressure 101325 Pascals) (i.e., the temperature at which the working fluid irreversibly decomposes). However, there is no problem if the working fluid reversibly boils below this decomposition temperature.

[0042] The working temperature of the working fluid is preferably in the range of at least 0°C to 210°C, or -50°C to +250°C, or 280°C or less, under environmental conditions.

[0043] In a more preferred embodiment, the working fluid does not contain defoaming agents, particularly dimethylpolysiloxane. The addition of defoaming agents or additives adversely affects surface tension and, in particular, lubrication characteristics in axial piston pumps and radial piston pumps.

[0044] The composition of the working fluid can be measured by two-dimensional gas chromatography (2D-GC-MS) with a mass spectrometer (Orbitrap Exploris GC 60K MSMs, Thermo Fisher Scientific). For this purpose, a sample containing 4 wt% of the working fluid in dichloromethane can be prepared. The parameters may be set as follows: • Gas chromatography (GC): Cold feed injector (PVT injector): 40°C to 300°C at 2.5°C / sec; Heat oven: 40°C to 150°C at 5°C / min, then 3°C / min to 300°C; Column flow rate 0.5 ml / min, transfer temperature 250°C, detector flow rate 20 ml / min. • Flame ionization detector (FID): 200Hz, 300℃, air 350ml / min, hydrogen supply 10ml / min, hydrogen 35ml / min. ·Mass spectrometer (MS): 200°C, solvent delay 7 minutes, m / z range 30-650, resolution 15k, cold trap offset 1.5V. This measurement can be used to determine the content of volatile poly-α-olefins having a specific number of carbon atoms, volatile aromatic hydrocarbons, and volatile sulfur compounds. To determine the quantitative content, it is necessary to perform the corresponding calibration of the analyte.

[0045] The device configuration is as follows: • Primary column: BPX5, 20m x 0.18mm x 0.18μm A flow modulator with a loop length of 23 cm × 0.53 mm and a bleed line length of 5 m × 0.1 mm; modulation period of 3 seconds, flashing time of 100 milliseconds. • Secondary column: BPX50, 5m x 0.25mm x 0.1μm • Detector: FID, TCD, Mass Spectrometer (Exploris: Electron Impact Ionization and Quadrupole + Orbitrap Method), Split Ratio MS 5:1 TCD / FID

[0046] Under a pressure of 50°C and 50 bar, the solubility of hydrogen in the working fluid is preferably selected from the range of 0.02 L to 0.15 L of hydrogen per liter (L) of working fluid, and preferably substantially 0.07 L of hydrogen per liter (L) of working fluid. At this time, there is a slight tendency for the working fluid to transition to the gas phase, or conversely, for hydrogen to dissolve in the working fluid. Therefore, good process stability can be achieved.

[0047] The viscosity of the working fluid is preferably selected from the range of 1 to 10 centistokes (cSt), more preferably 1 to 5 cSt, and more particularly 2.5 to 4 cSt, at 70°C. Such a low viscosity prevents, at least largely, the foaming of the working fluid caused by hydrogen dissolved in it due to pressure changes during re-expansion, thereby increasing the cavitation tendency of the working fluid and leading to wear of system components. Furthermore, because of the low viscosity of the working fluid, it is not transported mixed with gas. Due to such low viscosity, the working fluid according to the present invention certainly has inferior tribological properties, particularly low friction, compared to working fluids commonly used in the prior art, such as mineral oil or hydraulic oil. However, this can be adequately compensated for, for example, by hydrostatic lubrication and / or a suitable combination of materials.

[0048] Gas solubility can be measured under isothermal conditions using a known method employing the "pressure decay method."

[0049] The working fluid preferably has exactly one boiling point (when using one type of PAO) or an upper limit of 250°C in its boiling point range (when using two or more types of PAO). The working fluid preferably has a boiling point or boiling point range selected from 90°C to 200°C. Because of its low boiling point or boiling point range, the working fluid may evaporate due to temperature increases during operation. This is not disadvantageous if the working fluid is preferably used in a closed circuit, as the working fluid can then condense again, and evaporation of the working fluid due to pressurization can be avoided.

[0050] Within the hydrogen reservoir, the working fluid volume may be smaller than the hydrogen volume. This is because the density of the working fluid is higher than that of hydrogen. The working fluid and hydrogen are in direct contact with each other within the hydrogen reservoir, and the hydrogen volume and the working fluid volume are adjacent in layers. Due to gravity, these layers may be located in a horizontal plane.

[0051] A first opening may be located on the first side of the hydrogen reservoir for replenishing the working fluid into the hydrogen reservoir. A second opening may be provided on the second side of the hydrogen reservoir for discharging hydrogen from the hydrogen reservoir. The second side may be located opposite the first side. As a result, the volume of the hydrogen reservoir can be utilized efficiently, and the volume of the working fluid can be replaced as completely as possible with the volume of the working fluid when hydrogen is removed.

[0052] Preferably, the initial hydrogen pressure in the hydrogen reservoir, i.e., the nominal hydrogen pressure before hydrogen is discharged and before the working fluid is replenished, and therefore the hydrogen volume and working fluid volume are kept constant, is greater than 500 bar, preferably greater than 600 bar, particularly greater than 700 bar, for example, substantially 800 bar, and / or 875 bar or less. As a result of this pressurization, evaporation of the working fluid is reduced or completely avoided. Therefore, in a closed hydraulic system, there is little to no boiling loss, although there are time limitations.

[0053] The present invention further relates to a system for compressing and / or replacing hydrogen, the system being: A hydrogen compressor and / or hydrogen displacer according to any of the above embodiments, Pumps for replenishing the working fluid space with working fluid, especially axial piston pumps or radial piston pumps. Includes.

[0054] The hydrogen substitution and / or compression method according to the present invention comprises at least, (a) To provide a hydrogen compressor or hydrogen displacer according to any of the above embodiments, (b) Replenishing the working fluid in the hydrogen compressor and / or hydrogen displacer to increase the working fluid volume of the hydrogen compressor and / or hydrogen displacer and decrease the hydrogen volume of the hydrogen compressor and / or hydrogen displacer, Includes.

[0055] In step (b), the working fluid acts as a liquid piston, transmitting the force necessary to compress and / or replace the hydrogen. By replenishing the working fluid, i.e., by increasing the volume of the working fluid in the hydrogen compressor or hydrogen displacer, the hydrogen volume can be reduced so that the hydrogen is at least partially compressed and / or at least partially discharged from the gas reservoir. The degree of reduction in hydrogen volume may depend, among other things, on the pressure at which the working fluid is supplied to the gas reservoir and the density of the hydrogen in the supplied hydrogen reservoir.

[0056] The present invention further relates to a method for filling hydrogen tanks, particularly hydrogen tanks for vehicles, and this method is: (a) supplying a hydrogen volume filled with hydrogen to the hydrogen reservoir in one of the embodiments described above, (b) supplying working fluid to the working fluid reservoir, (c) Connect the hydrogen reservoir to the hydrogen tank so that hydrogen is transferred from the hydrogen reservoir to the hydrogen tank during the discharge phase, (d) Connecting the working fluid reservoir to the first hydrogen reservoir, preferably during a repressurization phase that coincides with the outflow phase, the working fluid is pumped from the working fluid reservoir to the first hydrogen reservoir, thereby reducing the hydrogen-filled hydrogen volume in the first hydrogen reservoir.

[0057] This replenishment method can also be carried out using at least one additional hydrogen reservoir. In that case, the hydrogen reservoirs can be connected sequentially to the hydrogen tank. By replenishing the working fluid in each hydrogen reservoir, the hydrogen in each reservoir can be repressurized, in particular, back to its initial pressure.

[0058] Furthermore, this disclosure relates to hydrogen tanks, in particular to refueling systems for supplying hydrogen to vehicles, in particular to mobile refueling systems, and this refueling system is A hydrogen reservoir that contains hydrogen, A working fluid reservoir that contains the working fluid, A control device, particularly equipped with a valve controller, for controlling the discharge connection for discharging hydrogen from the hydrogen reservoir to the hydrogen tank, and for controlling the inflow connection between the working fluid storage tank and the hydrogen reservoir, A pump that pressurizes the working fluid from the working fluid reservoir to the first hydrogen reservoir and It is equipped with.

[0059] Furthermore, this disclosure also relates to a refueling system having the refueling equipment and vehicle as described above, wherein the hydrogen tank of the vehicle is connected to the hydrogen reservoir of the refueling equipment.

[0060] In the housing-piston assembly according to the present invention, the sealing fluid contains poly-α-olefin.

[0061] For the advantages and effects of the sealing fluid, as well as preferred compositions, please refer to the above description of the working fluid.

[0062] In a preferred embodiment, a solid piston, preferably moving linearly in a reciprocating manner, has a circumferentially extending recess on the end face facing the sealing fluid. In this embodiment, the distance between the end face of the solid piston facing the sealing fluid and the housing face opposite this end face is greater in the recess region than in the radially inward region. As a result, the working volume in the recess region can be increased, thus achieving particularly good sealing performance.

[0063] In the longitudinal cross-section of the solid piston, the recess may be curved. This increases the contact area between the sealing fluid and the solid piston, thereby pressing the sealing fluid against the inner wall of the solid piston. As a result, the sealing effect can be further enhanced.

[0064] In a preferred embodiment, the housing comprises an outer housing portion and a cylindrical insert or running sleeve located inside the outer housing portion. The insert sleeve may be made of, for example, a ceramic material. Alternatively, the inside of the insert sleeve may be coated with DLC ("diamond-like carbon," i.e., an amorphous carbon layer).

[0065] In a preferred embodiment, the piston has at least one circumferential seal groove, preferably a plurality of seal grooves spaced apart in the axial direction of the piston. At least one seal groove creates a pressure reduction that prevents the working fluid from flowing out of the working space along the outer circumference of the piston. Furthermore, additional mechanical seals can be housed in the seal grooves.

[0066] The present invention further relates to an axial or radial piston pump having a cylinder-piston assembly, which is one of the embodiments described above.

[0067] In the rotor according to the present invention, the rotary drive device is configured to rotate the housing-piston assembly around the axis of rotation.

[0068] In a preferred embodiment, the axis of rotation is substantially perpendicular to the longitudinal axis of the solid piston.

[0069] In an alternative embodiment, the axis of rotation may extend along the longitudinal axis of the piston.

[0070] The method for sealing the movement of a piston relative to a housing according to the present invention includes at least, (a) To provide a housing-piston assembly according to any of the above embodiments, with the solid piston positioned in a first position relative to the housing, (b) Moving a solid piston relative to the housing from a first position to a second position, thereby changing the working volume enclosed by the housing, The relative movement of the solid piston with respect to the housing is sealed by a sealing fluid.

[0071] In the first position, the end face of the solid piston facing the sealing fluid may be at a greater distance from the housing surface opposite this end face than in the second position. Next, by moving the solid piston to the second position, the working volume is reduced.

[0072] The housing-piston assembly is preferably rotated around the axis of rotation. As a result of inertia, centrifugal force acts on the sealing fluid, pushing it outwards and further strengthening the seal.

[0073] Hydrogen can be supplied into the working volume, and by moving the solid piston in step (b), the hydrogen can be at least partially compressed and / or at least partially discharged through an opening located in the housing. The opening can be located on a surface of the housing in the direction in which the piston moves in order to reduce the working volume.

[0074] The present invention will be described in more detail below with reference to preferred exemplary embodiments shown in the drawings.

[0075] In this disclosure, "hydrogen" always refers to a hydrogen molecule (H2). [Brief explanation of the drawing]

[0076] [Figure 1] Figure 1 is a longitudinal section showing one state of a hydrogen reservoir in two different states, where poly-α-olefin is used as a liquid piston for substituted and / or compressing hydrogen. [Figure 2] Figure 2 is a longitudinal section showing the other state of the hydrogen reservoir, where poly-α-olefin is used as a liquid piston for substituted and / or compressing hydrogen. [Figure 3]Figure 3 is a longitudinal section showing one state of the housing-piston assembly in two different configurations, where poly-α-olefin is used as a circumferential seal to seal the reciprocating motion of a solid piston along the housing, which is designed as a cylinder. [Figure 4] Figure 4 is a longitudinal section showing the other state of the housing-piston assembly in two different states, where poly-α-olefin is used as a circumferential seal to seal the reciprocating motion of a solid piston along a housing designed as a cylinder. [Modes for carrying out the invention]

[0077] Figures 1 and 2 show a hydrogen compressor or hydrogen displacer. Here, the hydrogen compressor or hydrogen displacer is designed as a hydrogen reservoir 1 that stores, extracts, and recompresses hydrogen remaining in the hydrogen reservoir 1. According to Figure 1, the hydrogen reservoir is in a first state. The hydrogen reservoir 1 has a hydrogen volume filled with hydrogen 2 and a working fluid volume filled with working fluid 3, which together constitute the filled space of the hydrogen reservoir. The working fluid 3 contains a mixture of poly-α-olefins having 16 to 18 carbon atoms per molecule. The working fluid 3 is designed as a liquid piston and is in direct contact with the hydrogen (i.e., there is no solid piston in between), so the interface with the hydrogen can be displaced by the working fluid 3. The hydrogen reservoir 1 has a first opening 4 through which the working fluid 3 can be replenished from a working fluid reservoir (not shown). Furthermore, the hydrogen reservoir 1 has a second opening 5 through which hydrogen 2 can be discharged from the hydrogen reservoir 1. In the illustrated embodiment, the first opening 4 is formed at the bottom of the hydrogen reservoir 1, and the second opening 5 is formed on the upper side of the hydrogen reservoir 1.

[0078] For the purposes of this disclosure, indications of position or direction such as "up" or "down" are based on the intended usage state of hydrogen reservoir 1.

[0079] In a preferred embodiment, the hydrogen reservoir 1 is a component of a refueling system that can be connected to a hydrogen vehicle to fill the hydrogen tank of the hydrogen vehicle with hydrogen (not shown).

[0080] According to Figure 1, the working fluid occupies a first working fluid volume in the hydrogen reservoir 1. Therefore, in the first state, the working fluid has a first filling level.

[0081] By replenishing the hydrogen reservoir 1 with working fluid 3, the working fluid volume can be increased, and the hydrogen volume can be decreased accordingly. In this case, some of the hydrogen 2 is compressed within the hydrogen volume, and the other portion is discharged from the hydrogen reservoir 1 and can be supplied to a hydrogen vehicle tank in a preferred application.

[0082] Figure 2 shows the second state of the hydrogen reservoir 1 in Figure 1, which is the state in which the working fluid 3 has been replenished. The working fluid occupies a second working fluid volume that is larger than the first working fluid volume. Therefore, in the second state, the working fluid has a second filling level that is higher than the first filling level.

[0083] Figures 3 and 4 show a second embodiment of the present invention, in which poly-α-olefin is used as the sealing fluid.

[0084] Figure 3 shows a first state of the housing-piston assembly 6. The housing-piston assembly 6 has a housing 7, which in the illustrated embodiment has an outer housing portion and a cylindrical insert or running sleeve that fills a cylindrical recess in the outer housing portion. The insert sleeve may be made of, for example, a ceramic material. Alternatively, the insert sleeve may have a DLC coating on its inside. The housing 7 may enclose an operating volume in which hydrogen 8 is contained. Furthermore, the housing-piston assembly 6 has a solid piston 9, which is axially movable in a substantially precise fitted state along the inner wall of the housing 7 to change the operating volume. Unlike the previous embodiment, according to Figures 3 and 4, there is no liquid piston, and the solid piston 9 is provided as a mechanical part whose shape does not change substantially. A sealing fluid 10 is provided to seal the movement of the solid piston 9 relative to the housing 7. This sealing fluid 10 prevents hydrogen 8 from passing from the operating volume to the opposite side of the piston 9 which is facing away from the operating volume. Furthermore, at least one circumferential seal groove, preferably multiple seal grooves spaced apart in the axial direction of the piston 9, can be provided on the outer circumferential surface of the piston 9. At least one seal groove provides a pressure reduction, thereby preventing the working fluid from flowing out of the working space along the piston 9. In addition, additional mechanical seals can be provided within the seal grooves.

[0085] In the illustrated embodiment, the sealing fluid 10 is composed of a mixture of poly-α-olefins having 16 to 18 carbon atoms per molecule. The solid piston 9 has a recess 11 extending circumferentially at the end face facing the sealing fluid 10, and this recess 11 is curved in the longitudinal cross-section of the solid piston 9. An opening 12 is located on one side of the housing 7, and as the piston 9 moves in that direction, the operating volume decreases and hydrogen 8 is discharged.

[0086] In Figure 3, the piston 9 is positioned in a first position relative to the housing 7. In this first position, the end face of the solid piston 9 facing the sealing fluid 10 is at a relatively large distance from the opposite surface of the housing 7. Therefore, the working volume is relatively large. By moving the solid piston 9 axially toward a second position, the working volume enclosed by the housing 7 can be reduced. This compresses some of the hydrogen 8, while other parts are discharged from the housing 7 through the opening 12.

[0087] Figure 4 shows the housing-piston assembly 6 of Figure 3 in the second state. The solid piston 9 is positioned in the second position, where the working volume is smaller than in the first state of the housing-piston assembly 6. The sealing fluid 10 fills the adjacent sealing area inside the housing 7, thereby sealing the movement of the solid piston 9 relative to the housing 7. By rotating the housing-piston assembly 6 around a rotation axis 14 perpendicular to the longitudinal axis of the solid piston 9, centrifugal force can be applied to the sealing fluid 10, thereby pressing the sealing fluid 10 more effectively against the inside of the housing 7, and thus further improving the sealing performance.

Claims

1. A hydrogen compressor and / or hydrogen displacer, which is a hydrogen reservoir (1) or housing-piston unit for storing hydrogen (2), The hydrogen volume filled with hydrogen (2) and A working fluid volume filled with working fluid (3), wherein the working fluid (3) is designed as a liquid piston for changing the hydrogen volume, and Equipped with, The working fluid (3) is characterized by containing poly-α-olefin. Hydrogen compressor and / or hydrogen displacer.

2. The hydrogen compressor and / or hydrogen displacer according to claim 1, characterized in that the working fluid (3) contains poly-α-olefin in a proportion of at least 80% by weight, based on the total weight of the working fluid (3).

3. A hydrogen compressor and / or hydrogen displacer according to claim 1 or 2, characterized in that, based on the total weight of the poly-α-olefin, at least 90% by weight of the poly-α-olefin has 14 to 18 carbon atoms per molecule.

4. A hydrogen compressor and / or hydrogen displacer according to any one of claims 1 to 3, characterized in that, based on the total weight of the poly-α-olefin, up to 10% by weight of the poly-α-olefin has 20 or more carbon atoms per molecule.

5. A hydrogen compressor and / or hydrogen displacer according to any one of claims 1 to 4, characterized in that the working fluid (3) has an aromatic hydrocarbon content of 1% by weight or less based on the total weight of the working fluid (3).

6. The hydrogen compressor and / or hydrogen displacer according to any one of claims 1 to 5, characterized in that the working fluid has a viscosity selected from 1 cSt to 5 cSt, particularly from 2.5 cSt to 4 cSt, at 70°C.

7. A method for replacing and / or compressing hydrogen (2), (a) To provide a hydrogen compressor and / or hydrogen displacer according to any one of claims 1 to 6, (b) Preferably using an axial piston pump or a radial piston pump to replenish the working fluid (3) to the hydrogen compressor and / or hydrogen displacer, thereby increasing the working fluid volume of the hydrogen compressor and / or hydrogen displacer and decreasing the hydrogen volume of the hydrogen compressor and / or hydrogen displacer. A method that includes this.

8. Housing-piston assembly (6), A housing (7), preferably a cylinder, wherein the housing (7) includes an operating volume for receiving hydrogen (8), To change the operating volume, a solid piston (9) is provided that is movable relative to the housing (7), A seal for sealing the movement of the solid piston (9) relative to the housing (7), wherein a sealing fluid (10) is provided as the seal, Equipped with, The sealing fluid (10) is characterized by containing poly-α-olefin. Housing-piston assembly (6).

9. The housing-piston assembly (6) according to claim 8, characterized in that, based on the total weight of the poly-α-olefin, at least 90% by weight of the poly-α-olefin has 14 to 18 carbon atoms per molecule.

10. The housing-piston assembly (6) according to claim 8 or 9, characterized in that the solid piston (9) has a recess extending circumferentially on the end face facing the sealing fluid (10).

11. The housing-piston assembly (6) according to any one of claims 8 to 10, characterized in that the recess is curved in the longitudinal cross-section of the solid piston (9).

12. The axis of rotation (13, 14) and Rotary drive device and A housing-piston assembly (6) according to any one of claims 8 to 11, Equipped with, The rotary drive device is configured to rotate the housing-piston assembly (6) around the rotation shafts (13, 14). Rotor.

13. The rotor according to claim 12, characterized in that the rotating shaft (14) is perpendicular to the longitudinal axis of the solid piston (9).

14. A method for sealing the movement of a piston (9) relative to a housing (7), (a) To provide the housing-piston assembly (6) according to any one of claims 8 to 11, with the solid piston (9) positioned in a first position relative to the housing (7), (b) Moving the solid piston (9) relative to the housing (7) from the first position to the second position, thereby changing the operating volume enclosed by the housing (7), Includes, The relative movement of the solid piston (9) with respect to the housing (7) is sealed by the sealing fluid (10). method.

15. The method according to claim 14, characterized in that the housing-piston assembly (6) is rotated around the rotation axis (13, 14).

16. An axial or radial piston pump comprising the cylinder piston assembly according to any one of claims 8 to 11.

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