FR2928991A1 - Fuel gas i.e. hydrogen, storing and delivering device for captive fleet of bus, has gas draw-off circuit comprising portion i.e. exchanger, set in direct or indirect heat exchange with cold environment in downstream of turbine - Google Patents

Abstract

The device has a reservoir (1) for storing high pressure gas, and a cold environment i.e. liquid nitrogen bath (6), formed around the stored gas so as to maintain the gas at a cryogenic temperature of 77 Kelvin. A gas draw-off circuit (5) draws-off the gas from the reservoir, and is connected to a user unit i.e. fuel cell (8), where the circuit comprises an expansion turbine (13) for expanding the pressurized gas to be drawn off. The circuit has a portion i.e. exchanger (15), set in direct or indirect heat exchange with the environment in downstream of turbine. An independent claim is also included for a method for storing and delivering a fuel gas.

Description

The present invention relates to a device and a method for storing and delivering a gas, in particular hydrogen gas, as well as their use. In order to allow the diffusion of hydrogen as a fuel for transportation or for the supply of isolated sites, it is necessary to treat safe storage systems with sufficient mass and volume densities. To do this, there are several options for increasing the density of stored hydrogen gas, for example: - gas storage at high or very high pressure which consist of a tank (bottle) that can be subjected to a pressure of several hundred bars - storage in liquid form (depending on the liquefaction temperature of the gas). Taking road transportation as an example, the range of a vehicle will depend on the amount of gas stored, and therefore the mass and volume of the high pressure storage. Conventionally, high pressure storage is used at room temperature. The tanks are cylindrical and the materials used can be: 20 - steel, - fiber reinforced steel (carbon or glass), - fully wound carbon fiber steel (steel used to make impervious storage and winding for structural strength) or carbon fiber wound plastic (plastic used for impermeability and winding for structural strength). Current storage pressures are of the order of 200 bar for steel storage and up to 350 or 700 bar or above for composite storage. The best mass densities obtained today are from 4% to 6.5% for composite hydrogen storage. The volume density of a hydrogen storage at high pressure at room temperature at 350 bar is 23 kg H2 / m3 and the compression energy at 350 bar is of the order of 0.25 kWh / Nm3 H2.

For even higher pressures, of the order of 700 bar, this density increases to 39 kg H2 / m3 and the compression energy at 700 bar is of the order of 0.29 kWh / Nm3 H2. However, this significant gain of 68% in volume density H2 is not yet really valued because of the increase in the weight of the structure serving as a reservoir. Depending on the targeted applications, this storage solution is still not very advantageous because the quantity of gas stored relative to the volume and the total weight of the storage is still low. Another form of storage envisaged is the use of liquefied hydrogen which offers a very high density (70.3 kg H2 / m3) but which requires the implementation of a reservoir capable of keeping a large amount of cold in the cold. liquid (at 20K) and this whatever the conditions of external temperature. This then requires to perfectly control the thermal insulation of the tank. Assuming this possible, the high liquefaction energy of hydrogen, which is 1.4 kWh / Nm3 LH2 for large liquefiers, becomes very penalizing.

Indeed, if we consider a fuel cell consuming 0.7 Nm3 H2 / kWe. It consumes 2.09 kWth / kWe H2 which corresponds to a conversion efficiency of 47.7%. In the same way, this fuel cell can be defined by saying that it produces 1.43 kWe / Nm3 / h of Hydrogen consumed. We then see that the electrical energy required for the liquefaction of 1 Nm3 / h of H2 corresponds almost to the energy produced by this same Nm3 / h of H2 by the fuel cell. Thus, to consume 1 kWe at the wheel of a vehicle, it is necessary to have consumed 0.98 kWe to liquefy hydrogen, this without counting the electrical production efficiency of the electricity used for liquefaction that does not exceed 50 % (assumed from fossil fuels). Thus, for a kWe at the wheel we will have consumed 1.96 kW thermal or a yield of 51%. Compared with a storage of 350 bars at room temperature, to have 1 kWe at the wheel of the vehicle, consumes 0.175 kWe to compress the H2. By taking an electrical conversion efficiency of 50%, the kWe wheel / kWth efficiency can be estimated at about 35.6%. In view of these elements, the most energy-efficient solutions for the storage of hydrogen are, at least for certain applications, those related to high pressure, but their storage density remains twice as low as the storage solution in form. liquid. An intermediate solution is to store pressurized gas at a relatively low temperature. The invention is therefore concerned with a solution that makes it possible to optimize mass and volume storage densities of hydrogen while maintaining an acceptable energy and storage structure. The invention may relate to high-pressure storage in a cryogenic liquid low pressure vessel. This second box is preferably itself isolated from the external environment, to limit heat loss. Thus, lowering the temperature of the gas stored under pressure at approximately 80 ° K makes it possible to multiply the mass density of the gas by 2.5 to 3 times. For hydrogen, this factor is 2.7 which is interesting since the necessary compression energy has only increased by a factor equal to 2.2. In addition, the storage density has risen to 63 kg / m3, which is close to the storage solution in liquid form (70.3 kg / m3) but with a lower energy consumption (0.55 kWh / Nm3 at instead of 1, 4 kWh / Nm3 for liquefaction). The maintenance in cold is maintained preferably by implementation of a refrigeration cycle to compensate for heat losses to the outside environment. This refrigeration cycle can use a compressor to liquefy the coolant (eg nitrogen) evaporated due to losses of frigories of the isolated system. The compressor shaft may be driven by a motor itself powered by an auxiliary power source, or a dedicated fuel cell or by a turbine powered by the expansion of a portion of the high pressure gas stored. A calculation corresponding to the supply of a 40-tonne bus running 200 km / day has been carried out and shows that, for a maximum output of 143 kWe, a flow rate of 100 Nm3 / h of hydrogen is sufficient and that displacement phase, the thermal loss of the box of liquid nitrogen (2m x 2.5m x 0.5m containing five high pressure tanks of 0.3 m3 each) corresponds to the vaporization of 5 Nm3 / h of nitrogen. This lost vaporized nitrogen can be reliqued via a cold cycle consuming only 0.25 kW, which represents only 0.18% of the energy provided by a typical fuel cell.

An object of the present invention is to overcome all or part of the disadvantages of the prior art noted above. To this end, the device according to the invention relates to a device for storing and delivering a gas, in particular hydrogen gas, comprising a gas storage tank in gaseous form, under pressure and at a cryogenic temperature, the device comprising a cold environment formed around the stored gas to maintain the latter at a cryogenic temperature below 100K and preferably between 60 and 80K and even more preferably at a temperature of 77K, a gas withdrawal circuit connected to an organ user of the gas withdrawn, the withdrawal circuit comprising an expansion turbine of the pressurized gas withdrawn, the tank gas withdrawal circuit comprising, downstream of the expansion turbine, a portion in direct or indirect thermal exchange with the atmosphere cold formed around the stored gas. This high-pressure cryogenic storage solution thus makes it possible to increase the range of vehicles using a combustible gas stored at high pressure, without increasing the weight or the volume of the storage while allowing a good control of the energy consumption of maintaining cold. According to other possible features: the device comprises a cold unit shaped to generate or maintain the cold environment around the gas stored at a cryogenic temperature via a thermodynamic compression / expansion cycle of a working fluid, the cold unit comprising a compressor mounted on an axis driven by a motor adapted to be electrically powered via a power supply, the compressor being able to be mechanically coupled to the axis of the turbine to selectively transfer mechanical energy generated by the expansion of the gas withdrawn to the cold unit compressor drive, - the tank gas withdrawal circuit comprises, downstream of the heat exchange portion with the cold environment, a gas reheating exchanger withdrawn and a fluidic connection to the inlet of the supply of the user organ, the device comprises an electrical connection able to connect the motor to a power supply. n electrical such as a network, - the user member comprises a fuel cell, - the tank comprises a double insulation envelope, the cold environment being formed in the jacket and comprising a liquefied cold gas bath such as liquid nitrogen, the cold group is shaped to generate or cool the bath of liquefied cold gas around the stored gas, to compensate for heat losses including vaporization. The invention also relates to a method for storing and delivering gas. For this purpose, the method for storing and delivering a gas, in particular hydrogen gas, comprises the following steps: - placing the gas in a storage tank in gaseous form and at a pressure of between 200 bar and 500 bar and preferably 350 bar, the gas in the tank being maintained at a cryogenic temperature below 100K and preferably between 60 and 80K, for example at a temperature of 77K, - maintain a cold atmosphere around the stored gas to maintain this last at the cryogenic temperature, - withdrawing and expanding gas from the tank, - maintaining the cold environment by performing a direct or indirect heat exchange between the expanded withdrawn gas and the cold environment. According to other possible particularities, the method comprises at least one of the following steps: - maintain the cold environment by using the mechanical energy of expansion of the gas withdrawn to produce cold, 25 - maintain the cold atmosphere by using a cold group electrically powered via a network and / or a fuel cell (8). The invention also relates to a use of said device or said method for storing and delivering hydrogen-type fuel gas on board a vehicle, in particular a bus. According to other possible particularities, the storage tank is filled with gas from a station comprising a first reserve of gas and a second reserve of liquefied cold gas intended to form the cold environment. The invention may also relate to any alternative device or method comprising any combination of the above or below features.

Other features and advantages will appear on reading the description below, made with reference to the single figure which schematically shows the structure and operation of a non-limiting embodiment of the invention.

In the embodiment of Figure 1 the storage and delivery device comprises a reservoir 1 of pressurized gas (high pressure storage for example about 350 bar). This tank 1 of high pressure gas is for example disposed in a low pressure chamber 60 cryogenic liquid (bath 6 of liquid nitrogen). This second box 60 is preferably itself isolated from the outside environment to limit heat losses (vacuum insulation for example). A circuit 5 makes it possible to withdraw the gas under pressure from the tank 1 via a turbine 13 for expansion. Downstream of the turbine 13, the withdrawal circuit 5 comprises a portion 15 capable of being put selectively in direct or indirect thermal exchange with the bath 6 of liquid nitrogen. In this way, the frigories produced during the expansion of the withdrawn gas are used to cool or keep cold the cryogenic bath 6 (cold environment). Still downstream, the withdrawal circuit 5 may include a heat exchanger 7 and a connection to a user member 8 such as a fuel cell.

In addition to (or instead of) the heat exchange 15 with the expanded gas, the device may comprise a cold unit 2 provided to ensure or maintain the cold environment 2 around the gas stored under pressure. Such a cold group 2 can conventionally use a refrigerant undergoing a thermodynamic cycle (compression in the gaseous state, condensation, expansion in the liquid state, evaporation) to produce cold (liquid nitrogen for example). The heat generated by the cold unit 2 is returned to the outside at a condenser. Mechanically compressed cold production systems are the most commonly encountered systems. This type of cold unit consumes mechanical energy, mainly supplied by electricity consumption in a compressor 3 (but also in auxiliaries: pumps, condenser fans ...). The compressor 3 is thus driven preferably by an electric motor 4 via a drive shaft.

Preferably, the axis of the expansion turbine 13 can be coupled to the drive shaft of the compressor 3 to transfer mechanical energy generated by the expansion to the compressor 3 of the cold unit 2. The device can be mounted on a vehicle 115 such as a bus for example.

A filling station 16 can fill the pressurized gas in the tank 1 from a gas reserve 11 under pressure. If necessary the station 6 comprises a compressor 14 (if the storage pressure of the reserve 11 is lower than the target pressure of the tank 1). The station 16 may also comprise a source 12 of cryogenic liquid (liquid nitrogen for example) intended to feed the box 60 to form the cold environment 6. The invention can be applied in particular to a captive fleet of vehicle having a need for storage of important fuel for their rotation (bus, garbage collection truck, etc.) and being filled in a large central filling station justifying storage of liquid nitrogen and high pressure hydrogen (for example 200bar). The hydrogen filling of the tank 1 at the temperature of 80 K and the pressure of 350 bar can be achieved via a cooling exchanger 17 supplied with liquid nitrogen. The cooling exchanger 17 is preferably located after the compression stage 14 (if the source 11 has insufficient pressure requiring compression during filling). To keep the hydrogen gas at a cryogenic temperature in the tank 1 embedded (80K for example), it is necessary to compensate for the heat loss of the tank (cold environment 6).

The maintenance of the cold (cold environment 6) to compensate for the heat losses of the storage can be achieved by the cold unit 2 whose compressor is driven by the axis of the turbine 13 supplied by the expansion of hydrogen stored at high pressure and / or by an electric motor 4 powered and / or by an external power supply 10 and / or by the fuel cell 8 of the bus 115. The frigories produced by the expansion 13 of the hydrogen are transmitted to the liquid nitrogen 6 by an exchanger 15. If the minimum speed of the fuel cell 8 (supply of auxiliaries) is sufficient, there is no need for a cold unit 2, the frigories generated by the expansion 13 of the minimum flow rate of gas are sufficient to maintain the cold.

The maintenance of the cold 6 when the system is stopped can be achieved in several ways. A first solution is to connect the bus 115 to the electrical network 10 to supply the electric motor 4 driving the compressor 3 of the cold unit 2. A second solution is to provide a direct connection of the cold environment 6 with a source 12 of nitrogen liquid to compensate for losses of evaporated nitrogen. Another solution may be to purge the tank 1 or 6. The invention thus provides a storage offering a good compromise weight / storage capacity / total energy efficiency. The invention makes it possible in particular to manage at a lower energy cost a cold storage having a good storage capacity. The invention allows a gain in terms of storage capacity (storage under pressure and maintenance in cold) greater than the loss due to the energy consumption required to maintain cold. In use, it is preferably the hydrogen leaving the storage that keeps the reservoir cold. Out of use, the storage can be connected to an electrical supply and / or a cold supply 12 (liquid nitrogen for example). The invention is advantageously applied in particular to captive fleets of vehicles.

The invention improves the safety of gas storage by reducing the pressure for the same amount stored. The invention makes it possible to valorize the cold of the withdrawn gas in order, for example, to reliquefy the holding nitrogen in cold conditions.

Claims (11)

1. Apparatus for storing and delivering a gas, in particular hydrogen gas, comprising a reservoir (1) for storing the gas in gaseous form, under pressure and at a cryogenic temperature, the device comprising a cold environment ( 6) formed around the stored gas to maintain the latter at a cryogenic temperature of less than 100K and preferably between 60 and 80K and even more preferably at a temperature of 77K, a circuit (5) for withdrawing the gas connected to an organ ( 8) user of the gas withdrawn, the withdrawal circuit (5) comprising a turbine (13) for expanding the pressurized gas withdrawn, the circuit (5) for withdrawing the gas from the tank (1) comprising, downstream of the turbine ( 13), a portion (15) in direct or indirect thermal exchange with the cold environment (6) formed around the stored gas. 2. Device according to claim 1, characterized in that it comprises a cold unit (2) shaped to generate or maintain the cold environment (6) around the gas stored at a cryogenic temperature via a thermodynamic compression / expansion cycle d a working fluid, the cold unit (2) comprising a compressor (3) mounted on an axis driven by a motor (4) adapted to be electrically powered via a power supply (10), the compressor (3) being adapted to be mechanically coupled to the axis of the turbine (13) for selectively transferring mechanical energy generated by expansion of the withdrawn gas to the compressor drive (3) of the refrigeration unit (2). 3. Device according to claim 1 or 2, characterized in that the circuit (5) for withdrawing the gas from the reservoir (1) comprises, downstream of the portion (15) in heat exchange with the cold environment (6), an exchanger (7) for heating the withdrawn gas and a fluidic connection (9) to the supply inlet of the user member (8). 4. Device according to any one of claims 1 to 3, characterized in that it comprises an electrical connection (10) adapted to connect the motor (4) to a power supply such as a network. 5. Device according to any one of claims 1 to 4, characterized in that the member (8) user comprises a fuel cell. 6. Device according to any one of claims 1 to 5, characterized in that the reservoir (1) comprises a double insulation envelope, the cold environment (6) being formed in the jacket and comprising a gas bath liquefied cold such as liquid nitrogen. 7. Device according to claims 2 and 6, taken in combination, characterized in that the cold unit (2) is shaped to generate or cool the bath (6) of liquefied cold gas around the stored gas, to compensate for heat losses including by vaporization. 8. A method for storing and delivering a gas, in particular hydrogen gas, comprising the following steps: - arranging the gas in a storage tank (1) in gaseous form and at a pressure of between 200 bar and 500 bar and preferably 350 bar, the gas in the tank (1) being maintained at a cryogenic temperature below 100K and preferably between 60 and 80K, for example at a temperature of 77K, - maintain a cold environment (6) around the gas stored to maintain the latter at the cryogenic temperature, - withdrawing and expanding gas from the tank (1), - maintaining the cold environment (6) by performing a direct or indirect heat exchange between the expanded off-gas and the cold environment ( 6). 9. The method of claim 8, characterized in that it comprises at least one of the following steps: - maintain the cold environment (6) using the mechanical energy of expansion of the gas withdrawn to produce cold, - maintaining the cold environment (6) by using a cold unit (2) electrically powered via a network and / or a fuel cell (8). 10. Use of the device according to any one of claims 1 to 7 or the method according to any one of claims 8 to 9 for the storage and delivery of hydrogen-type fuel gas on board a vehicle (15), including a bus. 11. Use according to claim 10, characterized in that the storage tank (1) is filled with gas from a station (16) comprising a first reserve (11) of gas and a second (12) reserve of gas liquefied cold to form the cold atmosphere (6).