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 hydrogen purification and compression

[0001] The present invention relates to a method and device for the purification and compression of hydrogen.

[0002] To use hydrogen, for example as fuel in a vehicle, it must be pure, with a threshold for several impurities being defined according to standards. Such impurities include, in particular, water, but also nitrogen, ammonia, and 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, on the order of a few bars, and can also be subject to non-negligible water concentrations.

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

[0006] For example, document US20040042957 describes a process and a device in which the hydrogen that has just been produced passes over a surface activated by a direct current source where water is discharged 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 hydrogen well.

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

[0008] The present invention aims to overcome, at least in part, these drawbacks. To this end, it proposes a method for purifying at least one impurity and compressing hydrogen. This method is particular in that it comprises at least one thermal compression and cooling of the hydrogen to at least a temperature strictly below 0°C, simultaneously or starting with one of the two, until a combination of temperature and pressure is reached 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 present only in quantities lower than the predetermined value, which may be a value imposed by a standard to consider hydrogen as pure relative to said impurity.

[0010] 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 purely thermal, without any added chemical reaction, allowing for the compression of hydrogen laden with impurities without drawbacks. - said process may further include a second thermal compression including a sub-step of thermochemical compression, followed by a sub-step of purely thermal compression, without added chemical reaction; such an arrangement advantageously allows to rise to high pressures, for example of the order of 900 bar.

[0011] The present invention also relates to an installation for purifying at least one impurity and 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 a condensate, • a compressed hydrogen refrigeration installation, and / or a refrigeration installation associated with hydrogen production,

[0012] This installation is particular 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 hydrogen production.

[0013] Thanks to these arrangements, pure hydrogen can be obtained with very few means and reduced costs.

[0014] According to other characteristics: - said thermal compressor may comprise a first thermal compression unit, a second thermochemical compression unit, and a third thermal compression unit, and the first thermal compression unit is connected to the cold source at a temperature strictly below 0°C; such arrangements allow for the optimal implementation of the process according to the invention, with a first thermal compression, tolerating impurities in hydrogen, and prior cooling, simultaneous or immediately afterwards, 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 up to a pressure between 20 and 300 bar; such values ​​allow for good results in hydrogen purity. - said installation may be connected downstream to a service station including refrigeration generation equipment, and the refrigeration source may include at least part of this refrigeration generation equipment, thus allowing for simplified equipment to be offered at service stations, - said installation can be connected downstream to a pipeline dedicated to the transport of hydrogen at a pressure between 50 and 200 bar.

[0015] The main advantage of the present invention lies in the fact that it becomes possible to offer simple and inexpensive equipment for hydrogen service station installations, simultaneously addressing at least partially 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 few bars of pressure, which is very energy-intensive.

[0016] The present invention will be better understood upon reading the following detailed description made with reference to the accompanying figures in which - Fig. 1 is a schematic view of a device according to the invention.

[0017] The process according to the invention is a process which consists of purifying hydrogen of at least one impurity, and compressing the hydrogen.

[0018] The process is particularly advantageous for removing hydrogen from the water it contains in gaseous form, but can also be suitable for other impurities, such as nitrogen, ammonia or carbon dioxide for example.

[0019] A detailed description of the process applied to water as an impurity is given below. This will be referred to as hydrogen drying, hydrogen drying being a purification of the "water" impurity from hydrogen.

[0020] However, this does not in any way limit 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 a person skilled in the art.

[0021] In what follows, we will refer to the drying and compression of hydrogen. The objective of such drying and compression is, for example, the use of purified and compressed hydrogen as a fuel, particularly for vehicles. Hydrogen the matter in question may include other impurities, either that these other impurities are present in proportions considered acceptable, or that they are present in higher proportions, for example because purification of such impurities is envisaged at a stage after drying.

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

[0023] One can, for example, begin by compressing the hydrogen by thermal compression up to a pressure of 50 bar. The choice of thermal compression has the advantage of not being affected by 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, condensation will be considered to be 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; condensation thus allows the removal of liquid or solid water, and only the water remains in the gaseous state in the hydrogen.

[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 reach.

[0027] According to the invention, it is therefore possible 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 by thermal compression. The choice of thermal compression offers the same advantage as above.

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

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

[0031] One could imagine that the first thermal compression stage is configured to rise to approximately 900 bar by a purely thermal compressor; even At such a pressure, the temperature required to obtain sufficiently dry hydrogen would be around -5°C. Such a process is therefore also consistent with the present invention, but it precludes the use of other types of compressors, such as a thermochemical compressor or a mechanical compressor, which can be useful for a significant portion of the pressure increase.

[0032] According to a particular embodiment of the invention, the process 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 about 950 bar, a tank 6 at about 950 bar, ready to be introduced into the tank of a vehicle, where it must present a pressure of about 700 bar.

[0033] As hydrogen expands when introduced into the vehicle's tank, it releases heat and therefore heats up. A cooling source 7 is therefore generally added, typically at around -40°C. The hydrogen in the tank is thus cooled by the cooling source before heating up, particularly due to its expansion, and eventually reaches equilibrium at a temperature close to ambient, approximately 20°C in the vehicle's tank.

[0034] The hydrogen production device 1 can be a thermolyser, an electrolyser, or a hydrogen desorption device 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 allows hydrogen to be obtained 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] This gives us a first thermal compressor 2 whose heat requirement is partly, and preferably entirely, covered by the heat released 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 down to Tl for example equal to -35°C.

[0039] This gives us a cooling device 9 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 less than 5 ppm of water remains in the hydrogen, the rest of the water has condensed and it is enough to recover it at the bottom of the device.

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

[0042] The hydrogen compression device may also include a thermochemical compressor 3, to raise the pressure of PI 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 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 refuel; a full tank is considered complete when the hydrogen in the vehicle's tank reaches, for example, 700 bar at ambient temperature. The hydrogen dispensing terminal 8 at the service station then connects the vehicle's tank, which generally contains a residual amount of hydrogen, for example at 200 bar, to tank 6 and opens a valve; the pressure in tank 6 being higher, for example 950 bar, the hydrogen flows into the vehicle's tank, while expanding. The expanding hydrogen heats up, and if no additional precautions are taken, can reach temperatures in the tank exceeding 85°C, the maximum temperature that standard tanks are capable of withstanding.

[0045] To avoid this, a cooling source 7 is almost always present at a hydrogen refueling station. The cooling source 7 acts on the flowing hydrogen to cool it before it enters the vehicle's tank; the cooling source 7 can typically be at a temperature of around -40°C; the construction details for achieving this hydrogen cooling are within the grasp of those skilled in the art and do not need to be described in this 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 about 85°C thanks to the prior cooling, a temperature that the tank is able to withstand, whereas at 140°C, the tank would deteriorate.

[0047] Through natural heat exchange, the temperature then drops to ambient, 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 features developed above.

Claims

Demands

1. A method for purifying at least one impurity and compressing hydrogen, said impurity being selected from the following list: water, nitrogen, ammonia, carbon dioxide, characterized in that it comprises at least one thermal compression and cooling of hydrogen to at least 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, and in that the first thermal compression is a purely thermal compression, without any added chemical reaction.

2. A process according to the preceding claim wherein the impurity is water in the gaseous state, and said combination consists of a temperature below -10°C, preferably below -30°C, and a pressure above 20 bar, preferably above 60 bar.

3. A method according to any one of the preceding claims, further comprising a second thermal compression including a thermochemical compression substep, followed by a purely thermal compression substep, without any added chemical reaction.

4. A hydrogen purification and compression installation for at least one impurity, comprising: • a hydrogen production unit, • a thermal compressor connected to a heat source and a cold source at a temperature strictly below 0°C, • a condensate recovery means, • a compressed hydrogen refrigeration unit, and / or a refrigeration unit associated with hydrogen production, characterized in that the heat source consists at least in part of the heat released by the hydrogen production unit, and / or the cold source consists at least in part of the compressed hydrogen refrigeration unit and / or the refrigeration unit associated with production of hydrogen, and in that said thermal compressor comprises a first thermal compression unit only, without any added chemical reaction.

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

6. Installation according to the preceding claim, wherein the first thermal compression unit is configured to compress hydrogen from a pressure between 1 and 35 bar up to a pressure between 20 and 300 bar.

7. Installation according to any one of claims 4 to 6, connected downstream to a service station comprising refrigeration generation equipment, and the refrigeration source comprises at least a portion of this refrigeration generation equipment.

8. Installation according to any one of claims 4 to 6, connected downstream to a pipeline dedicated to the transport of hydrogen at a pressure between 50 and 200 bar.