Abstract
Gas compression system having a compressor for compressing hydrogen, a recovery device(s) for recovering hydrogen escaping as leakage gas during compression, and a leakage gas return line to return recovered leakage gas into a stage in the gas compression system upstream of the compressor and/or into a suction line of a compressor stage of the compressor. The compressor has a leakage gas discharge line for discharging leakage gas. Each recovery device is fluidically connectable to the discharge and return lines and has a metal hydride reservoir(s) heat-coupled to a respective heat exchanger. Each hydride reservoir has a hydride-forming metal alloy(s) which, when heat is supplied or dissipated through the respective heat exchanger, provides cyclic de- or absorption of leakage gas. Each recovery device increases leakage gas pressure in the discharge line to at least the pressure in the upstream stage and/or the suction pressure in the suction line.
Claims
1. A gas compression system with a compressor for compressing hydrogen; at least one recovery device for recovering hydrogen which escapes from the compressor as leakage gas during compression; and a leakage gas return line which is designed to return the leakage gas recovered by the at least one recovery device into a stage in the gas compression system upstream of the compressor, or into a suction line of a compressor stage, or into the stage in the gas compression system upstream of the compressor and into the suction line of the compressor stage; wherein the compressor comprises a leakage gas discharge line for discharging the leakage gas from the compressor; wherein each recovery device can be fluidically connected to the leakage gas discharge line and the leakage gas return line and has at least one metal hydride reservoir, each of which is heat-coupled to a heat exchanger; wherein each metal hydride reservoir comprises at least one hydride-forming metal alloy which is designed for cyclic de- or absorption of the leakage gas with heat supply or removal through the respective heat exchanger; and wherein each recovery device is designed to increase a leakage gas pressure (p.sub.L) prevailing in the leakage gas discharge line to at least a pressure (p) prevailing in the stage of the gas compression system, or to at least a suction pressure (p.sub.S) prevailing in the suction line of the compressor stage, or both.
2. The gas compression system according to claim 1, wherein the at least one recovery device comprises a first recovery device and a second recovery device for loading and unloading the metal hydride reservoirs arranged in the respective recovery devices independently of one another in terms of time.
3. The gas compression system according to claim 1, wherein each recovery device has a plurality of metal hydride reservoirs which are connected in series with one another as viewed in the flow direction of the leakage gas stream and are each heat-coupled to a heat exchanger; wherein the metal hydride reservoirs connected in series each have at least one hydride-forming metal alloy, which are designed for the cyclic de- or absorption of hydrogen with heat supply or removal through the respective heat exchanger; wherein the first metal hydride reservoir arranged first in the direction of flow in each recovery device is designed to increase the pressure of the leakage gas from the leakage gas pressure (p.sub.L) to a first intermediate pressure (p.sub.1) which is higher than the leakage gas pressure (p.sub.L); wherein the last metal hydride reservoir arranged last in each recovery device in the direction of flow is designed to increase the pressure of the leakage gas to the suction pressure (p.sub.S); and wherein the metal hydride reservoirs arranged between the first and the last metal hydride reservoir are each designed to gradually increase the pressure of the leakage gas (2) to a higher intermediate pressure (p.sub.2, p.sub.3 . . . p.sub.n) relative to the first intermediate pressure (p.sub.1).
4. The gas compression system according to claim 1, wherein the compressor is designed as a piston compressor.
5. The gas compression system according to claim 1, wherein the metal alloys used have a dissociation pressure of at least 30 bar at a temperature of 60-100 C.
6. The gas compression system according to claim 1, wherein the metal alloys are selected from the group consisting of LaNi.sub.5, ZrV.sub.2, ZrMn.sub.2, TiMn.sub.2, FeTi, Zr.sub.2Co, and Ti.sub.2Ni.
7. The gas compression system according to claim 1, wherein the compressor has a housing which is designed to be pressure-resistant only up to 40 bar.
8. The gas compression system according to claim 1, wherein the gas compression system is free of containers for storing the leakage gas downstream of the at least one recovery device and before the leakage gas is returned to the stage in the gas compression system upstream of the compressor, or into the suction line of the compressor stage, or to the stage in the gas compression system upstream of the compressor and into the suction line of the compressor stage.
9. The gas compression system according to claim 1, wherein the respective heat exchangers contain a liquid with a boiling temperature at normal pressure of between 30 C. and 180 C. as heat transfer medium.
10. The gas compression system according to claim 1, wherein a gas cooler which can be cooled with cooling water is connected downstream of the compressor for cooling the hydrogen compressed by the compressor, wherein the gas cooler and the heat exchangers of the respective recovery devices are connected to one another in such a way that a cooling water heated during the cooling of the gas cooler can be used at least partially to supply heat to the respective metal hydride reservoirs.
11. The gas compression system according to claim 1, wherein the leakage gas discharge line has a pressure relief valve which opens at a pressure of more than 2 bar in the leakage gas discharge line.
12. The gas compression system according to claim 1, wherein each metal hydride reservoir comprises at least one combination valve or a valve pair consisting of an inlet valve upstream of the respective metal hydride reservoir in the direction of flow, and an outlet valve downstream in the direction of flow of the respective metal hydride reservoir for charging or discharging the respective metal hydride reservoir with leakage gas.
13. The gas compression system according to claim 12, further comprising an actuating device for actuating the inlet and outlet valves, wherein the inlet and outlet valves are actuated in such a way such that, in operational use, at least one of the adjacent valves is closed for each pair of valves adjacent in the direction of flow, in order to exclude a continuous fluid-conducting connection between the leakage gas discharge line and the leakage gas return line.
14. The gas compression system according to claim 1, wherein at least one non-return element closing against the direction of flow is arranged at a position selected from the group consisting of between the metal hydride reservoirs of the respective recovery device, in the leakage gas discharge line, and in the leakage gas return line.
15. A method for recovering hydrogen which emerges from a compressor as a leakage gas, carried out with the gas compression system according to claim 1, the method comprising the steps of: introducing the leakage gas into a recovery device with at least one metal hydride reservoir Ha containing at least one hydride-forming metal alloy; loading of the metal hydride reservoir with absorption of the introduced leakage gas by the metal alloy and formation of a metal hydride; removing of a heat released during the formation of the metal hydride by a heat exchanger, which is heat-coupled to the metal hydride reservoir; heating of the formed metal hydride to a predetermined temperature by the heat exchanger with desorption of at least part of the previously absorbed leakage gas; discharging the metal hydride reservoir and discharging the desorbed leakage gas from the recovery device to a leakage gas return line and into a stage in the gas compression system upstream of the compressor, or into a suction line of a compressor stage, or into the stage in the gas compression system upstream of the compressor and into the suction line of the compressor stage, of the compressor from which the leakage gas originates; wherein the pressure of the leakage gas is increased by the at least one metal hydride reservoir of the recovery device from a leakage gas pressure (p.sub.L) prevailing in the leakage gas discharge line to at least a pressure (p) prevailing in the stage of the gas compression system or at least a suction pressure (p.sub.S) prevailing in the suction line of the compressor stage, or both.
16. The method according to claim 15, wherein the pressure of the leakage gas is increased from the leakage gas pressure (p.sub.L) to the suction pressure (p.sub.S) in several stages using a plurality of metal hydride reservoirs connected in series with one another as viewed in the flow direction of the leakage gas flow; wherein the first metal hydride reservoir arranged first in the direction of flow in each recovery device increases the pressure of the leakage gas from the leakage gas pressure (p.sub.L) to a first intermediate pressure (p.sub.1) which is higher than the leakage gas pressure (p.sub.L); wherein the last metal hydride reservoir arranged last in the direction of flow in each recovery device increases the pressure of the leakage gas to the suction pressure (p.sub.S); and wherein the metal hydride reservoirs arranged between the first and the last metal hydride reservoir increase the pressure of the leakage gas in stages to a higher intermediate pressure (p.sub.2, p.sub.3 . . . p.sub.n) relative to the first intermediate pressure (p.sub.1).
17. The method according to claim 15, wherein the method is carried out continuously with cyclic charging and discharging of two recovery devices arranged in parallel in the flow direction and each comprising at least one first metal hydride reservoir.
18. The method according to claim 15, wherein the heating of the formed metal hydride in step d is carried out at least partially with water obtained from a cooling of a gas cooler downstream of the compressor.
19. The method according to claim 15, wherein the charging and discharging of each metal hydride reservoir takes place via at least one combination valve or a valve pair consisting of an inlet valve upstream of the respective metal hydride reservoir in the direction of flow, and an outlet valve downstream of the respective metal hydride reservoir in the direction of flow, wherein the respective inlet and outlet valves are actuated by an actuating device in such a way that a continuous fluid-conducting connection between the leakage gas discharge line and the leakage gas return line is excluded.
20. A hydrogen refueling station comprising a gas compression system according to claim 1.
Description
[0057] The problem is further solved by a hydrogen refueling station comprising a gas compression system as described herein, which is preferably operated by one of the methods described herein. Various embodiments of the invention are described below with reference to drawings, with identical or corresponding elements generally being provided with identical reference signs. It shows:
[0058] FIG. 1 Flow diagram showing a gas compression system according to the invention;
[0059] FIG. 2 Schematic representation of a metal hydride reservoir for use in a gas compression system according to the invention in cross-section;
[0060] FIG. 3 Flow diagram showing a further embodiment of a gas compression system according to the invention with two recovery devices connected in parallel;
[0061] FIG. 4a Flow diagram showing a gas compression system according to the invention in a loading step;
[0062] FIG. 4b Flow diagram showing the gas compression system from FIG. 4a in an unloading step;
[0063] FIG. 5a Flow diagram showing a further embodiment of a gas compression system according to the invention with recovery devices connected in parallel in a loading or unloading step;
[0064] FIG. 5b Flow diagram showing the gas compression system from FIG. 5a in an unloading or loading step.
[0065] FIG. 1 shows a flow diagram of a gas compression system 100 according to the invention with a compressor 1 for hydrogen. The compressor 1 can be fluidically connected to a hydrogen source Q via a line 3, so that the hydrogen to be compressed can be fed to the compressor 1 via the line 3. The gas compression system 100 also comprises a recovery device 10, described in more detail below, for recovering hydrogen which escapes from the compressor 1 as leakage gas during compression. To discharge the leakage gas from the compressor, a leakage gas discharge line 4 is provided, which can be fluidically connected to the compressor and the leakage gas flow produced during compression. The gas compression system 100 also has a leakage gas return line 2 for returning the leakage gas recovered by the recovery device 10 to a stage 5 in the gas compression system 100, which is located upstream of the compressor 1 from which the leakage gas originates. In the embodiment shown in FIG. 1, the leakage gas recovered by the recovery device 10 is introduced into the line 3, which fluidically connects the hydrogen source Q to the compressor 1, at the stage marked with the reference sign 5. The leakage gas return line 30 has a non-return element 31 which closes against the direction of flow S. In the embodiment shown, the recovery device comprises two metal hydride reservoirs 11a, 11b, which each contain a hydride-forming metal alloy and are each heat-coupled to a heat exchanger 12a, 12b. Cold cooling water, which can be supplied to the gas compression system 100 from a cooling water source W.sub.In via a cooling water pump 50, can be used to cool the two metal hydride reservoirs 11a, 11b. Preheated cooling water, i.e. cooling water which is obtained in the course of cooling the hydrogen compressed by the compressor 1 by a gas cooler 7, can be used to heat the two metal hydride reservoirs 11a, 11b. The cold or heated cooling water can be fed to the two metal hydride reservoirs 11a, 11b via three-way fittings 19a, 19b. Unused or spent cooling water is fed to cooling water drains W.sub.Out and preferably recycled. The recovery device 10 can be fluidically connected to the leakage gas discharge line 4 via the inlet valve 13a of the first metal hydride reservoir 11a and to the leakage gas return line 2 via the outlet valve 14b of the second metal hydride reservoir 11b. The two metal hydride reservoirs 11a, 11b can be fluidically connected to each other via a connecting line 16 and a valve 14a arranged in the connecting line 16 and, viewed in the flow direction S of the leakage gas flow, are connected in series. The metal hydride reservoir 11a arranged first in the direction of flow S is designed to increase the leakage gas pressure p.sub.L, which is for example 2 bar, in the leakage gas discharge line 4 to a higher first intermediate pressure p.sub.1, which is for example 15 bar, compared to the leakage gas pressure p.sub.L. The metal hydride reservoir 11b of the recovery device 10, which is arranged last in the direction of flow S, is designed to increase the first intermediate pressure p.sub.1, which is provided by the metal hydride reservoir 11a upstream thereof, to the pressure p prevailing in line 3, which is 30 bar, for example. The leakage gas thus recovered, i.e. raised from the leakage gas pressure p.sub.L to the pressure p, is fed back to the compressor 1 and ultimately delivered to a consumer V, for example a fuel cell vehicle.
[0066] FIG. 2 shows a schematic cross-sectional representation of a metal hydride reservoir 11a for use in a gas compression system according to the invention. In the embodiment shown, the metal hydride reservoir 11a comprises a total of twenty-five tubular containers 17a (shown in cross-section in FIG. 2), which are filled with a hydride-forming metal alloy 15a. The containers 17a are designed for the inlet and outlet of hydrogen leakage gas into the containers 17a, wherein in the case of tubular containers 17a the inlets and outlets are preferably arranged at the opposite ends of the tubes. The containers 17a containing the hydride-forming metal alloy 15a are surrounded by a heat transfer medium, in particular water or a thermal oil, so that the metal alloy 15a can desorb or adsorb leakage gas when heat is supplied or dissipated by the heat exchanger 12a. To improve the heat conduction between the heat transfer medium and the container wall, ribs made of material with good thermal conductivity can be arranged on the outer surface of the container 17a to increase the surface area, which are immersed in the heat transfer medium (not shown).
[0067] FIG. 3 shows a flow diagram of a further embodiment of a gas compression system 100 according to the invention, which comprises two recovery devices 10, 20 connected in parallel for recovering hydrogen which escapes from a compressor 1 as leakage gas. The first recovery device 10 comprises the two metal hydride reservoirs 11a and 11b connected in series, while the second recovery device 20 comprises the two metal hydride reservoirs 21a and 21b connected in series. The metal hydride reservoir 11a of the first recovery device 10, which is arranged first in the direction of flow S, can be fluidically connected to the metal hydride reservoir 11b arranged downstream in the direction of flow S via connecting line 16 and the valve 14a arranged therein. Similarly, the metal hydride reservoir 21a of the second recovery device 20, which is arranged first in the direction of flow S, can be fluidically connected to the metal hydride reservoir 21b arranged downstream in the direction of flow S via connecting line 26 and the valve 24a arranged therein. Hydrogen leakage gas, which is produced during compression by the compressor 1 of the gas compression system 100, is discharged from the compressor 1 through a leakage gas discharge line 4 and is connected to the first recovery device 10 or the second recovery device 20 via the inlet valve 13a or via the inlet valve 23a, which inlet valves 13a, 23a connect the first recovery device 10 or the second recovery device 20 to the inlet valve 23a. the second recovery device 20 with the leakage gas discharge line 4, alternating in time, i.e. the recovery devices 10, 20 arranged in parallel operate in push-pull mode. Within each recovery device 10, 20, the pressure of the leakage gas is increased from the leakage gas pressure p.sub.L prevailing in the leakage gas discharge line via a first intermediate pressure p.sub.1 to the suction pressure p.sub.S prevailing in the suction line 3b of the first compressor stage 5b of compressor 1, essentially as described above with respect to FIG. 1. The metal hydride reservoirs 11a, 11b, 21a, 21b are each heat-coupled to a heat exchanger 12a, 12b, 22a, 22b for this purpose, wherein the water used to cool or heat the metal hydride reservoirs can be fed to the heat exchangers 12a, 12b, 22a, 22b from a cooling water source W.sub.In with cooling water pump 50 or after prior heating by a gas cooler 7 via three-way fittings 19a, 19b, 29a, 29b. Unused or spent cooling water is fed to cooling water drains W.sub.Out and preferably recycled. The first recovery device 10 and the second recovery device 20 can be fluidically connected to a leakage gas return line 2 via the outlet valves 14b and 24b of the metal hydride reservoirs 11b, 21b arranged last in the respective recovery devices 10, 20 in the direction of flow S, wherein a non-return element 31, 32 is arranged downstream of each recovery device 10, 20 in the direction of flow S. Via the leakage gas return line 30, the leakage gas previously recovered and increased to the suction pressure p.sub.S is fed into the suction line 3b of the first compressor stage 5b of compressor 1 at the stage designated by the reference sign 5.
[0068] FIG. 4a shows a flow diagram of a gas compression system 100 according to the invention comprising a single recovery device 10 at the time of loading of the single metal hydride reservoir 11a contained therein. A portion of the hydrogen, which is supplied to the compressor 1 via a line 3 from a hydrogen source Q, is generated during compression as a leakage gas stream, which is discharged from the compressor via a leakage gas discharge line 4 and introduced into the metal hydride reservoir 11a of the recovery device 10 via the inlet valve 13a. To load the metal hydride reservoir 11a with leakage gas and form a metal hydride, the inlet valve 13a upstream of the metal hydride reservoir 11a in the flow direction S of the leakage gas is opened and the outlet valve 14a downstream of the metal hydride reservoir 11a in the flow direction S of the leakage gas flow is closed, as indicated in FIG. 4a. The heat released during the formation of the metal hydride is dissipated through a heat exchanger 12a, which is heat-coupled to the metal hydride reservoir 11a, wherein cold cooling water from a cooling water source W.sub.In is used for this purpose via a cooling water pump 50 and a three-way fitting 19a, which fluidically connects the cooling water source to the heat exchanger 12a (see dotted arrows in FIG. 4a to illustrate the flow of cold water). The used cooling water, which was heated in the heat exchanger 12a during the cooling of the hydride-forming metal alloy, is fed to a cooling water drain W.sub.out. Once the metal hydride reservoir 11a has been charged with leaked gas, the inlet valve 13a upstream of the metal hydride reservoir 11a in the flow direction S is closed (not shown).
[0069] FIG. 4b shows a flow diagram of the gas compression system 100 from FIG. 4a during the unloading of the metal hydride reservoir 11a of the recovery device 10. The metal hydride reservoir 11a was previously heated to a predetermined temperature by the heat exchanger 12a for desorption of at least a portion of the previously absorbed leakage gas with the inlet and outlet valves 13a, 14a closed, wherein a pressure relief valve present in the leakage gas discharge line continuously discharges leakage gas from the compressor 1 when a predetermined leakage gas pressure is exceeded (not shown). After the pressure inside the metal hydride reservoir 11a has been increased to the pressure p prevailing in the line 3, the outlet valve 14a of the metal hydride reservoir 11 downstream in the flow direction S of the leakage gas is opened and the metal hydride reservoir 11a is unloaded by the heat exchanger 12a with further heat input. In the present embodiment example, water from the cooling water source W.sub.In is used for this purpose, which was supplied to a gas cooler 7 by the cooling water pump 50 and heated by it (see dashed arrows in FIG. 4b to illustrate the flow of hot water). The three-way fitting 19a used, with which the heat exchanger 12a can be fluidically connected both to the cooling water source W.sub.In and to the gas cooler 7, can also be used to mix cold cooling water from the cooling water source W.sub.In and cooling water heated by the gas cooler 7 in order to adjust the temperature of the metal hydride reservoir 11a. The desorbed leakage gas under pressure p is discharged from the recovery device 10 via outlet valve 14a to a leakage gas return line 30, which comprises a non-return element 31 opening in the direction of flow S, and is introduced into line 3 at a stage marked with the reference sign 5. The recovered leakage gas is thus fed back to the compressor 1 and ultimately discharged to a consumer V.
[0070] FIG. 5a shows a flow diagram of a further embodiment of a gas compression system 100 according to the invention, comprising two recovery devices 10, 20 connected in parallel, each with a metal hydride reservoir 11a, 21a. In FIG. 5a, the first recovery device 10 is in a loading cycle and the second recovery device 20 operates in a counter-cycle to this in an unloading cycle. In other words, while the metal hydride reservoir 11a of the first recovery device 10 is being loaded, the metal hydride reservoir 21a of the second recovery device 20 is being unloaded. In contrast to the method described in FIGS. 4a and 4b, the recovery of leakage gas, which occurs during the compression of hydrogen in a compressor 1, can thus be carried out continuously with the method described in FIGS. 5a and 5b. For this reason, overpressure valves in the leakage gas discharge line 4, which open when a certain leakage gas pressure p.sub.L prevailing therein is exceeded, can generally be dispensed with. For safety reasons, however, the provision of such pressure relief elements to prevent pressure peaks and damage in the leakage gas discharge line 4 may still be advisable. In the embodiment of a gas compression system 100 according to the invention shown in FIGS. 5a and 5b, the leakage gas discharge line 4 branches into the two leakage gas discharge lines 4 and 4, of which one leakage gas discharge line 4 can be fluidically connected to the first recovery device 10 and the other leakage gas discharge line 4 can be fluidically connected to the second recovery device 20. The loading of the metal hydride reservoir 11a of the first recovery device 10 takes place with the inlet valve 13a open and the outlet valve 14a closed, which are arranged upstream and downstream of the metal hydride reservoir 11a in the flow direction S of the leakage gas, and with heat dissipation from the hydride-forming metal alloy contained in the metal hydride reservoir by a heat exchanger 12a, which is heat-coupled to the metal hydride reservoir 11a. The cold cooling water used for this purpose is provided by a cooling water source W.sub.In via a cooling water pump 50 and a three-way fitting 19a, which fluidically connects the cooling water source to the heat exchanger 12a (see dotted arrows in FIG. 5a to illustrate the flow of cold water). The used cooling water is discharged into a cooling water outlet W.sub.out. The metal hydride reservoir 21a of the second recovery device 20 is unloaded when the inlet valve 23a is closed and the outlet valve 24a is open and the metal hydride reservoir 21a is heated by the heat exchanger 22a assigned thereto. The heat exchanger 22a is fluidically connected to the cooling water source W.sub.In via the three-way fitting 29a, wherein the heated cooling water is obtained by a gas cooler 7, which cools the hydrogen compressed by the compressor 1 before it is discharged to a consumer V (see dashed arrows in FIG. 5a to illustrate the flow of hot water). The cooling water used in the heat exchanger 22a of the second recovery device 20 is also discharged into a cooling water outlet W.sub.Out and preferably recycled. The first recovery device 10 and the second recovery device 20 can be fluidically connected to a leakage gas return line 30 via the outlet valves 14a and 24a of the metal hydride reservoirs 11a, 21a arranged last in the respective recovery devices 10, 20 in the flow direction S, wherein a non-return element 31, 32 is arranged downstream of each recovery device 10, 20 in the flow direction S. The leakage gas, which has been compressed by the second recovery device 20 from the leakage gas pressure p.sub.L to the suction pressure p.sub.S, is fed into the first compressor stage 5b of the compressor 1 via the leakage gas return line 30 at the stage of the suction line 3b designated by the reference sign 5. The gas compression system, including the valves described above, is monitored and controlled by a freely programmable system control device not shown.
[0071] FIG. 5b shows a flow diagram of the gas compression system 100 from FIG. 5a, where the first recovery device 10 is now in the unloading cycle and the second recovery device 20 is in the loading cycle, merely to illustrate the counter-cycled operation of the two recovery devices 10 and 20 connected in parallel. The hot water flow in the gas compression system 100 is shown using dashed arrows and the cold water flow using dotted arrows. The assignment of the reference symbols used and the functional description of all the elements shown in FIG. 5b can be found in the description of FIG. 5a.
