Process and device for hydrogen purification and compression

Abstract

The present invention relates to a method for purifying at least one impurity and compressing hydrogen, comprising at least one thermal compression and cooling of the hydrogen to a temperature strictly below 0°C, either simultaneously or starting with one of the two, to a temperature and pressure combination such that said at least one impurity condenses sufficiently so that the remaining quantity of the impurity in the hydrogen is less than a predetermined value. The present invention also relates to a device specially designed to implement the method according to the invention. Abstract figure: Figure 1

Description

Title of the invention: Method and device for purifying and compressing hydrogen

[0001] The present invention relates to a method and a device for purifying and compressing hydrogen.

[0002] To use hydrogen, for example as fuel in a vehicle, it must be pure, a threshold for several impurities being defined according to standards. Such impurities are in particular water, but also nitrogen, ammonia, carbon dioxide, for example.

[0003] The hydrogen must in particular be “dry”, that is to say, it must contain less than 5 ppm of water.

[0004] Hydrogen production is very often carried out at low pressure, of the order of a few bars, and can also be subject to significant water concentrations.

[0005] Hydrogen can conventionally be dried by chemical means or by liquid / gas separation means. However, this requires significant resources in terms of energy, equipment and time.

[0006] For example, document US20040042957 describes a method and a device in which the hydrogen which has just been produced passes over a surface activated by a direct current source where water is evacuated through a pipe; the hydrogen then contains less water, and can be compressed by mechanical compressors which do not tolerate the presence of water in the hydrogen well.

[0007] Hydrogen can also be dried by lowering the temperature sufficiently for the water to condense. But to achieve, for example, 5 ppm of water in hydrogen, it would be necessary to go down to temperatures below -71°C, which is industrially difficult and expensive.

[0008] The present invention aims to at least partially overcome these drawbacks. To this end, it proposes a process for purifying at least one impurity, and compressing hydrogen. This process is particular in that it comprises at least one thermal compression and cooling of the hydrogen at least to a temperature strictly below 0°C, simultaneously or starting with one of the two, to a combination of temperature and pressure such that said at least one impurity condenses sufficiently so that the remaining quantity of the impurity in the hydrogen is less than a predetermined value.

[0009] Thanks to these arrangements, “pure” hydrogen is obtained in the sense that the impurity is no longer present except in quantities lower than the predetermined value, which

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[0013] may be a value imposed by a standard to consider hydrogen as pure compared to said impurity. According to other characteristics: - the impurity may be water, and said combination may consist of a temperature below -10°C, preferably below -30°C and a pressure above 20 bar, preferably above 60 bar; such values ​​make it possible to obtain interesting levels of purity, - the first thermal compression can be a purely thermal compression, without added chemical reaction, allowing compression of hydrogen loaded with impurities without any drawbacks, - said method may further comprise a second thermal compression including a thermochemical compression sub-step, followed by a solely thermal compression sub-step, without added chemical reaction; such an arrangement advantageously makes it possible to reach high pressures, for example of the order of 900 bar. The present invention also relates to an installation for purifying at least one impurity, and for compressing hydrogen, comprising: • a hydrogen production facility, • a thermal compressor connected to a heat source and a cold source, at a temperature strictly below 0°C, • a means of recovering condensate, • a compressed hydrogen refrigeration installation, and / or a refrigeration installation associated with the production of hydrogen. This installation is special in that the heat source consists of the heat released by the hydrogen production installation, and / or the cold source consists of the compressed hydrogen refrigeration installation and / or the refrigeration installation associated with the production of hydrogen. Thanks to these provisions, pure hydrogen is obtained with very little means and reduced costs.

[0014] According to other characteristics: - said thermal compressor may comprise a first thermal-only compression unit, a second thermochemical compression unit, and a third thermal-only compression unit, and the first thermal-only compression unit is connected to the cold source at a temperature strictly below 0°C; such arrangements allow optimal implementation of the method according to the invention, with a first thermal-only compression, supporting the impurities in the hydrogen, prior, simultaneous or immediately after cooling,

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[0021] until sufficient condensation of impurities, and compression up to high pressure values, - the first thermal compression unit can be configured to compress hydrogen from a pressure between 1 and 35 bar to a pressure between 20 and 300 bar; such values ​​allow good hydrogen purity results to be obtained, - said installation can be connected downstream to a service station comprising cold generation equipment, and the cold source can comprise at least part of this cold generation equipment, thus making it possible to offer simplified equipment at the service station, - said installation can be connected downstream to a pipeline dedicated to the transport of hydrogen at a pressure between 50 and 200 bar. The advantage provided by the present invention lies mainly in the fact that it becomes possible to propose simple and inexpensive equipment for hydrogen service station installations while simultaneously addressing at least in part two challenges of such an installation: • on the one hand the purification of hydrogen intended for vehicles, in order to meet industrial standards • on the other hand the compression of the first bars of pressure, which consumes a lot of energy. The present invention will be better understood upon reading the detailed description which follows, given with reference to the appended figures in which - [Fig.l] is a schematic view of a device according to the invention. The method according to the invention is a method which consists of purifying hydrogen of at least one impurity, and compressing the hydrogen. The process is particularly advantageous for removing hydrogen from the water it contains in gaseous state, but can also be suitable for other impurities, such as nitrogen, ammonia or carbon dioxide for example. Below is a detailed description of the process applied to water as an impurity. We will therefore speak of drying hydrogen, since drying hydrogen is a purification of the "water" impurity from hydrogen. However, this in no way reduces the scope of the present invention to water as an impurity, and can be applied to other impurities, with adaptations in particular of temperature and pressure values ​​to the impurity concerned, which adaptations are within the reach of those skilled in the art. Throughout the following, we will talk about drying and compressing hydrogen. The purpose of such drying and compression is, for example, the use of purified and compressed hydrogen as fuel, particularly for vehicles. Hydrogen in question may include other impurities, either because these other impurities are present in proportions considered acceptable, or because they are present in higher proportions, for example because purification of such impurities is envisaged at a stage subsequent to drying.

[0022] The drying process according to the invention comprises at least a first step of thermal compression and cooling of the hydrogen.

[0023] For example, one can start by compressing the hydrogen using thermal compression to a pressure of 50 bar. Choosing thermal compression has the advantage of not being concerned about the water contained in the hydrogen at this stage of the process. The hydrogen can then be cooled, for example, to a temperature of -37°C while maintaining the pressure.

[0024] Under these temperature and pressure conditions, the water condenses until the hydrogen contains less than 5 ppm of water in the gaseous state.

[0025] In the context of the present invention, it will be considered that a condensation is either a transformation from the gaseous state to the liquid state, or a transformation from the gaseous state directly to the solid state; the condensate obtained can therefore be either a liquid or a solid; the condensation therefore allows a removal of the liquid or solid water, and only the part of water in the gaseous state in the hydrogen remains.

[0026] This combination of compression and cooling makes it possible to obtain sufficiently dry hydrogen, without having to lower the temperature to -71°C, a temperature which is very difficult to achieve.

[0027] It is therefore possible, according to the invention, to obtain dry hydrogen without having to lower the temperature to levels that are difficult to achieve, and without prior purification which would be costly and time-consuming.

[0028] Alternatively, the hydrogen can be cooled to a temperature of -37°C and then compressed to a pressure of 50 bar using thermal compression. The choice of thermal compression here has the same advantage as above.

[0029] Other combinations of temperature and pressure can be chosen, for example a temperature of -10°C, and a pressure of 565 bar. The choice of the combination of temperature and pressure will depend on the available cold source, and on the initial pressure of the hydrogen in particular. Other factors may be involved, as will be explained later.

[0030] For combinations of temperature and pressure in which the temperature rises above -10°C, or approaches 0°C, the necessary pressures are such that the interest of the method according to the invention decreases significantly.

[0031] One could imagine that the first stage of thermal compression is configured to rise to approximately 900 bar by a purely thermal compressor; even at such a pressure, the temperature to obtain sufficiently dry hydrogen would be of the order of -5°C. Such a process is therefore also in accordance with the present invention, but it makes it impossible to use other types of compressor, such as a thermochemical compressor, or a mechanical compressor, which may be useful for a significant part of the pressure increase.

[0032] According to a particular embodiment of the invention, the method according to the invention can be implemented in a service station type installation, comprising a hydrogen production device 1, a hydrogen compression device 2, 3, 5 up to approximately 950 bar, a tank 6 at approximately 950 bar, ready to be introduced into the tank of a vehicle, where it must have a pressure of approximately 700 bar.

[0033] As the hydrogen expands when introduced into the vehicle tank, it releases heat and heats up. A cold source 7 is therefore generally added, which can typically be at around -40°C. Thus, the hydrogen loaded into the tank cools down under the effect of the cold source, before it heats up, in particular under the effect of its expansion, and ends up balancing at a temperature close to ambient, around 20°C in the vehicle tank.

[0034] The hydrogen production device 1 may be a thermolyser, an electrolyser, or even a device for desorbing hydrogen which has been adsorbed onto another product for the purpose of its storage and transport.

[0035] In the context of the present invention, a hydrogen desorption device is considered to be a hydrogen production device, in the sense that it makes it possible to obtain hydrogen which can be introduced into said compression device.

[0036] All these hydrogen production devices release heat. According to the invention, this heat can be used by a first thermal compressor 2 of the hydrogen compression device, and can in certain circumstances be sufficient to raise the pressure to several tens of bar up to a pressure PI, for example equal to 60 bar.

[0037] A first thermal compressor 2 is thus obtained, the heat requirement of which is partly, and preferably entirely, covered by the heat release from the hydrogen production device 1.

[0038] The cold source 7 can be connected to the first thermal compressor 2 to form a cooling device 9, configured to reduce the temperature to T1, for example equal to -35°C.

[0039] A cooling device 9 is thus obtained powered by said cold source, without needing to provide a cold source specifically for said cooling device.

[0040] At 60 bar and -35°C, the saturated vapor pressure of water in hydrogen is such that there is less than 5 ppm of water left in the hydrogen, the remaining water has condensed and it is sufficient to recover it at the bottom of the device.

[0041] The hydrogen compression device may comprise a second thermal compressor 3, 5, configured to increase the pressure to a pressure P3 which may be 950 bar for example.

[0042] The hydrogen compression device may also comprise a thermochemical compressor 3, to raise the pressure of P1 to a pressure P2 for example equal to 450 bar and an intermediate tank 4 in which the hydrogen is stored at this pressure, and a thermal compressor 5 configured to raise the pressure from P2 to P3. The hydrogen is then stored at the pressure P3 in the tank 6.

[0043] The hydrogen stored in the tank 6 is at a pressure P3, for example 950 bar, higher than the pressure at which it is intended to be in the vehicle's tank.

[0044] A vehicle can then arrive at the service station to fill up its tank; a full tank is formed when the hydrogen in this vehicle tank is, for example, at 700 bar at ambient temperature. The hydrogen distribution terminal 8 of the service station then connects the vehicle tank, which generally contains a residual quantity of hydrogen, for example at 200 bar, with the tank 6 and opens a valve; the pressure in the tank 6 being higher, for example 950 bar, the hydrogen flows towards the vehicle tank, while expanding. The hydrogen which expands, heats up, and if no additional precautions are taken, can be found in the tank at temperatures above 85°C, the temperature limit that standard tanks are capable of withstanding.

[0045] To avoid this, a cold source 7 is almost systematically present on a hydrogen service station. The cold source 7 acts on the flowing hydrogen to cool it, before it is introduced into the vehicle's tank; the cold source 7 can typically be at a temperature of around -40°C; the construction details for obtaining this cooling of the hydrogen are within the reach of those skilled in the art, and do not need to be described in the context of the present application.

[0046] When a pressure of, for example, 875 bar is reached in the tank, the valve is closed and the tank is filled; the hydrogen can then be at a temperature of approximately 85°C thanks to the prior cooling, a temperature that the tank is capable of withstanding, whereas at 140°C, the tank would deteriorate.

[0047] By natural heat exchanges, the temperature then drops to ambient temperature, which lowers the pressure to around 700 bar, which corresponds to a full tank pressure.

[0048] 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 characteristics developed above.

Claims

Claims

1. Method for purifying at least one impurity, and for compressing hydrogen, characterized in that it comprises at least one thermal compression and one cooling of the hydrogen at least to a temperature strictly below 0°C, simultaneously or starting with one of the two, to a combination of temperature and pressure such that said at least one impurity condenses sufficiently so that the remaining quantity of the impurity in the hydrogen is less than a predetermined value.

2. Method according to the preceding claim in which the impurity is water in the gaseous state, and said combination consists of a temperature lower than -10°C, preferably lower than -30°C and a pressure higher than 20 bar, preferably higher than 60 bar.

3. Method according to one of the preceding claims, in which the first thermal compression is a purely thermal compression, without added chemical reaction.

4. Method according to one of the preceding claims, further comprising a second thermal compression including a thermochemical compression sub-step, followed by a thermal compression sub-step only, without added chemical reaction.

5. Installation for purifying at least one impurity, and for compressing hydrogen, comprising: • a hydrogen production installation, • a thermal compressor connected to a heat source and to a cold source at a temperature strictly below 0°C, • a means for recovering a condensate, • a compressed hydrogen refrigeration installation, and / or a refrigeration installation associated with the production of hydrogen, characterized in that the heat source consists at least in part of the heat released by the hydrogen production installation, and / or the cold source consists at least in part of the compressed hydrogen refrigeration installation and / or the refrigeration installation associated with the production of hydrogen.

6. Installation according to the preceding claim in which said thermal compressor comprises a first thermal-only compression unit, a second thermochemical compression unit, and a third thermal-only compression unit, and the first thermal-only compression unit is connected to the cold source at a temperature strictly below 0°C.

7. Installation according to the preceding claim, in which the first thermal compression unit is configured to compress hydrogen from a pressure of between 1 and 35 bar to a pressure of between 20 and 300 bar.

8. Installation according to one of claims 5 to 7, connected downstream to a service station comprising cold generation equipment, and the cold source comprises at least part of this cold generation equipment.

9. Installation according to one of claims 5 to 7, connected downstream to a pipeline dedicated to the transport of hydrogen at a pressure between 50 and 200 bar.

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