CN113629271A

CN113629271A - Hydrogen supply and return system and fuel cell system

Info

Publication number: CN113629271A
Application number: CN202010376517.6A
Authority: CN
Inventors: 孔丽超; 王飞; 赵猛; 廖至钢; 刘杨
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2020-05-07
Filing date: 2020-05-07
Publication date: 2021-11-09

Abstract

The application discloses hydrogen supply and return-flow system includes: a hydrogen supply passage for supplying hydrogen to an anode of the fuel cell stack; a hydrogen return passage for returning hydrogen from an anode of the fuel cell stack; a first supply return assembly comprising a first hydrogen injector, a first nozzle in fluid communication therewith, and a first ejector pump receiving the first nozzle; a second supply return assembly comprising a second hydrogen injector, a second nozzle in fluid communication therewith, and a second ejector pump receiving the second nozzle; and a switching valve disposed in the hydrogen return passage, wherein the output end of the first module and the output end of the second module are connected in parallel to the hydrogen supply passage, the return end of the first module and the return end of the second module are connected in parallel to the hydrogen return passage via the switching valve, hydrogen returning from the anode can selectively return to any one of the return ends, and the outlet cross section of the first nozzle is different from the outlet cross section of the second nozzle. The present application also discloses a fuel cell system.

Description

Hydrogen supply and return system and fuel cell system

Technical Field

The present application relates to the field of fuel cells, and in particular to a hydrogen supply and return system for a fuel cell.

Background

With the current stricter environmental regulations, fuel cells are increasingly used as an energy supply unit, especially as a power unit in a motor vehicle. Typically, the anode of the fuel cell will be supplied with hydrogen using a hydrogen supply and return system so that the supplied hydrogen reacts chemically at the anode accordingly and thus produces an electrical power output within the fuel cell. Since excess hydrogen gas is typically present at the anode of the fuel cell, this excess hydrogen gas must be vented along with the moisture produced at the anode. Therefore, the discharged hydrogen tends to react with the anode, which is fed back to the fuel cell by the recirculation system via the hydrogen supply.

With conventional hydrogen supply and return systems, variations in the power output of the fuel cell can result in either an insufficient amount of hydrogen being normally supplied or an insufficient amount of hydrogen being recirculated, both of which can affect the power output of the fuel cell. For this reason, in the prior art, an Anode Recycle Blower (ARB) is often used to recycle the excess hydrogen from the anode into the anode. However, the anode circulating fan firstly causes the whole system to be bulky and overweight, and is not beneficial to the application in the motor vehicle; secondly, the running reliability of the whole system is reduced; finally, this also leads to an increase in the production costs of the overall system.

For this reason, there is a strong need to find a solution that is simple and reliable and does not cause the system to increase too much weight.

Disclosure of Invention

In view of the above problems, the present application is directed to providing an improved hydrogen supply and return system for a fuel cell, whereby it is possible to ensure that an appropriate amount of hydrogen is supplied to the fuel cell and an excessive amount of hydrogen is discharged from an anode and recirculated to the anode for reaction, depending on the power output variation of the fuel cell.

According to an aspect of the present application, there is provided a hydrogen supply and return system for a fuel cell stack, including:

a hydrogen supply passage for supplying hydrogen to an anode of the fuel cell stack;

a hydrogen return passage for returning hydrogen from an anode of the fuel cell stack;

a first supply return assembly comprising a first hydrogen injector, a first nozzle in fluid communication with the first hydrogen injector, and a first jet pump receiving the first nozzle;

a second supply return assembly comprising a second hydrogen injector, a second nozzle in fluid communication with the second hydrogen injector, and a second jet pump receiving the second nozzle;

a switching valve provided in the hydrogen return passage; wherein the content of the first and second substances,

the output end of the first supply backflow component and the output end of the second supply backflow component are connected in parallel in the hydrogen supply channel, the backflow end of the first supply backflow component and the backflow end of the second supply backflow component are connected in parallel in the hydrogen backflow channel through the switching valve, so that hydrogen flowing back from the anode can selectively flow back into one of the backflow ends, and the cross section of an outlet of the first nozzle, which leads into the first ejector pump, is different from the cross section of an outlet of the second nozzle, which leads into the second ejector pump. Thus, the two supply and return assemblies in parallel with each other can be selectively activated to match the power output requirements of the fuel cell stack to properly supply and return hydrogen without adversely affecting the power output of the fuel cell stack.

Optionally, an internal hollow plenum is defined in each of the first and second ejector pumps such that the respective output end and the respective return end are in fluid communication with the internal hollow plenum, the outlet of the respective nozzle being proximate the respective return end in the internal hollow plenum. In this way, it is ensured that the siphon effect required for the hydrogen gas to flow back is produced in each ejector pump.

Optionally, the output of the first supply return assembly is defined by an orifice formed in the first jet pump; the output end of the second supply return assembly is defined by an orifice formed in the first jet pump; the return end of the first supply return assembly is defined by another orifice formed in the first jet pump; the return end of the second supply return assembly is defined by another orifice formed in the second jet pump.

Alternatively, the first or second supply return assemblies may be alternatively operative under different power output operating conditions of the fuel cell stack.

Optionally, an outlet cross section of the first nozzle leading into the first ejector pump is smaller than an outlet cross section of the second nozzle leading into the second ejector pump.

Optionally, the first supply return assembly is active when the fuel cell stack is operating at low power in the range of 5 to 30kw power; the second supply return assembly is active when the fuel cell stack is operating at high power in the power range of 30 to 150 kw.

Optionally, the aperture size of an outlet of the first nozzle, which leads into the first ejector pump, is in a range of 0.8-1.8 mm; and the aperture size of an outlet of the second nozzle, which is communicated with the second ejector pump, is within the range of 1.8-3.5 mm.

Optionally, the inner hollow plenum is formed progressively flared from adjacent the outlet of the first nozzle towards an aperture defining the output end.

According to another aspect of the present application, there is also provided a fuel cell system comprising a fuel cell stack and a hydrogen supply and return system according to the foregoing, wherein the hydrogen supply and return system is fluidly connected to an anode of the fuel cell stack to supply hydrogen to the anode and return hydrogen from the anode.

With the technical measures of the present application, the hydrogen supply and return system can be switched to operate with different supply and return assemblies according to the power requirement of the fuel cell stack, thereby ensuring that the proper amount of hydrogen is supplied and returned, improving the working efficiency of the fuel cell stack, simultaneously not excessively increasing the volume and weight of the hydrogen supply and return system, and reducing the burden of system improvement.

Drawings

The principles and aspects of the present application will be more fully understood from the following detailed description, taken in conjunction with the accompanying drawings. It is noted that the drawings may not be to scale for clarity of illustration and will not detract from the understanding of the present application. In the drawings:

FIG. 1 is a circuit diagram schematically illustrating a hydrogen supply and return system in operative connection with a fuel cell stack according to the prior art;

FIG. 2 is an enlarged fragmentary view schematically illustrating a supply return assembly of the hydrogen injector and ejector pump of the hydrogen supply and return system of FIG. 1;

FIG. 3 is a circuit diagram schematically illustrating a hydrogen supply and return system in operative connection with a fuel cell stack according to an embodiment of the present application; and is

FIG. 4 schematically illustrates a supply return assembly consisting of a hydrogen injector, a nozzle, and a jet pump according to one embodiment of the present application.

Detailed Description

In the various figures of the present application, features that are structurally identical or functionally similar are denoted by the same reference numerals.

Fig. 1 schematically shows a circuit diagram of a hydrogen supply and return system according to the prior art, wherein the hydrogen supply and return system generally comprises a hydrogen injector 100, a jet pump 200, a shut-off valve 300, a water separator 400 and a vent valve 700. The hydrogen injector 100, the ejector pump 200, and the shut-off valve 300 are in direct fluid communication or in fluid communication via piping, thereby forming a hydrogen supply passage, and the hydrogen supply passage is in fluid communication with the anode 510 of the fuel cell 500 to supply hydrogen to the anode 510 of the fuel cell 500 and thus chemically react therein. The water separator 400 is in fluid communication with the ejector pump 200 via tubing to form a hydrogen return passage, which is also in fluid communication with the anode 510 of the fuel cell 500 to enable excess hydrogen and other gas, particularly water vapor, mixture at the anode to be returned to the ejector pump 200 via the hydrogen return passage. In the process of gas backflow, the mixed gas passes through the water separator 400 to remove water vapor, and then the backflow hydrogen is supplied to the ejector pump 200 through the hydrogen backflow channel and supplied to the anode 510 of the fuel cell 500 through the hydrogen backflow channel to participate in the chemical reaction again.

In the hydrogen return passage section from the water separator 400 to the ejector pump 200, an exhaust valve 700 is connected in series via a pipe so as to discharge excess gas outside the system as needed. As shown in fig. 1, a hydrogen supply port 100a is provided at one end of the hydrogen supply passage, and a hydrogen output port 300a is provided at the opposite end, so that the hydrogen injector 100, the ejector pump 200, and the shutoff valve 300 are connected in series in the hydrogen supply passage between the hydrogen supply port 100a and the hydrogen output port 300a in this order. The hydrogen supply port 100a is adapted to be connected to a hydrogen tank (not shown), and the hydrogen output port 300a is adapted to be connected to the anode 510 of the fuel cell 500. As further shown in fig. 1, a hydrogen return port 400a is provided at one end of the hydrogen return channel such that the water separator 400 is located downstream of the hydrogen return port 400a in the hydrogen return channel. The hydrogen return passage is fluidly connected to the ejector pump 200 at an end 200a opposite the hydrogen return port 400 a.

As shown in fig. 2, the hydrogen injector 100 may be connected to a nozzle 600 due to structural design considerations, such that the fluid output port (not shown) of the hydrogen injector 100 is in fluid communication with the internal passage (not shown) of the nozzle 600. The internal passage of the nozzle 600 has a fixed-bore outlet communicating with the outside. The jet pump 200 includes a body 210 with an internal hollow cavity 220 formed in the body 210. The nozzle 600 may extend into the interior hollow volume 220 of the eductor pump 200 after the hydrogen injector 100 is in contact with the body 210 of the eductor pump 200 and secured in place. An orifice is formed in the body 210 and defines an end 200a of the hydrogen return passage opposite the hydrogen return port 400 a. Therefore, for clarity, the aperture of the body 210 is also designated by the same reference numeral 200 a. For example, a screw thread is formed in the orifice 200a so as to be connected to a corresponding pipe defining a hydrogen return passage. The orifice 200a of the body 210 is in fluid communication with the inner hollow volume 220 and the cross-section 610 of the nozzle 600 at which the exit of the fixed aperture is located just adjacent the interface of the orifice 200a with the inner hollow volume 220 after the nozzle 600 is in place extending into the inner hollow volume 220.

Further, an orifice is formed in the body 210 of the ejector pump 200, which defines the above-described hydrogen gas supply port 100a, and thus is denoted by the same reference numeral 100 a. For example, a screw thread is also formed in the orifice 100a for connection to a pipe communicating with a hydrogen tank (not shown in the drawings). After the hydrogen injector 100, the ejector pump 200 and the nozzle 600 form a supply return assembly, hydrogen from the hydrogen tank can first enter the hydrogen injector 100 via the orifice 100a (which serves as the input of the supply return assembly) and then be injected into the internal hollow volume 220 of the ejector pump 200 via the nozzle 600 connected to the hydrogen injector 100. An outlet orifice 200b is also formed in the body 210, the outlet orifice 200b being for fluid communication with the shut-off valve 300 and the hydrogen gas outlet 300a through piping. In order to ensure that the hydrogen gas flowing back from the hydrogen return channel to the ejector pump 200 via the orifice 200a can be fed again to the hydrogen outlet 300a via the outlet orifice 200b, the inner hollow volume 220 is formed with a cross-sectional enlargement, preferably a cross-sectional gradual enlargement, from the vicinity of a cross-section 610 of the outlet of the fixed bore of the nozzle 600, taken perpendicularly to the longitudinal axis of the body 210 of the ejector pump 200, towards the outlet orifice 200 b.

Under normal operation of the hydrogen supply and return system, as hydrogen is sequentially supplied from the hydrogen tank to the anode 510 of the fuel cell 500 through the hydrogen injector 100, the nozzle 600, the ejector pump 200, and the shutoff valve 300, excess hydrogen that has not undergone chemical reaction is generated at the anode. As excess hydrogen gas accumulates, the gas pressure on the side of the outlet orifice 200b will be higher than the gas pressure on the side of the nozzle 600 (i.e., the side of the orifice 200 a) as viewed in the internal hollow volume 220 of the body 210 of the jet pump 200. However, due to the above-mentioned enlarged cross-sectional design of the inner hollow volume 220, gas is drawn into the inner hollow volume 220 from the orifice 200a by a siphon effect and supplied to the outlet orifice 200b together with the hydrogen jet ejected from the outlet of the nozzle 600 under the action of the hydrogen jet at the outlet of the nozzle 600, thereby achieving recycling of the excess hydrogen.

As shown in fig. 2, the hydrogen injector 100 is provided with a solenoid valve 110 capable of controlling the flow of hydrogen gas output through a fluid output port of the hydrogen injector 100 itself, for example, controlling the flow rate and flow rate of the hydrogen gas flow. However, since the fluid outlet port of the hydrogen injector 100 itself is in fluid communication with the internal passage (not shown) of the nozzle 600 and the internal passage has a fixed-aperture outlet (at 610 in fig. 2) communicating with the outside, in the case where the self-jet flow of the hydrogen injector 100 controlled by the solenoid valve 110 is higher than the jet flow allowed by the outlet of the nozzle 600, the flow of hydrogen gas injected from the hydrogen tank into the ejector 200 via the hydrogen injector 100 and the nozzle 600 will be limited mainly by the aperture size of the outlet of the nozzle 600. Generally, the operating power condition of the fuel cell stack 500 is related to the flow rate of the hydrogen gas stream emitted from the nozzle 600. For example, during operation of fuel cell stack 500 at low power, as hydrogen injector 100 reduces the flow rate of the jets, the flow rate of the jets from nozzles 600 is correspondingly reduced, but such a reduction may cause the above-described siphon effect to be reduced, resulting in an obstruction or lack of hydrogen backflow from the anodes of fuel cell stack 500, and thus further causing excess hydrogen to accumulate at the anodes of fuel cell stack 500 and causing the power output of fuel cell stack 500 to be inconsistent with expectations. As another example, during operation of fuel cell stack 500 at high power, the flow rate of the jet from nozzle 600 increases, but due to the increased siphon effect, more hydrogen is caused to be recirculated from the anode of fuel cell stack 500, resulting in an undesirable power output of fuel cell stack 500.

In view of the above problems, the present application aims to improve such a hydrogen supply and return system by an elaborate wording. FIG. 3 schematically illustrates a hydrogen supply and return system according to one embodiment of the present application. As shown in fig. 3, the hydrogen supply and return system of the present application generally includes two

hydrogen injectors

1010 and 1011 and two

ejector pumps

2010 and 2011, a stop valve 300, a water separator 400, and a vent valve 700, wherein each

hydrogen injector

1010 or 1011 and a

corresponding ejector pump

2010 or 2011 form a supply return assembly via a corresponding nozzle 6010 or 6011 (only the supply return assembly formed by the

hydrogen injector

1010 or 1011, the

nozzle

6010 or 6011, and the

ejector pump

2010 or 2011 is shown in fig. 4). Similarly to that shown in fig. 1, two such formed supply return assemblies (shown in phantom) as a whole are in direct fluid communication or in fluid communication via piping with the shut-off valve 300, thereby forming a hydrogen supply channel, and the hydrogen supply channel is in fluid communication with the anode 510 of the fuel cell 500 via the hydrogen output terminal 300a to supply hydrogen to the anode 510 of the fuel cell 500 and thus to undergo a chemical reaction therein. In addition, the two thus formed supply return assemblies (shown in phantom) as a whole are in fluid communication with the water separator 400 via tubing to form a hydrogen return channel that is also in fluid communication with the anode 510 of the fuel cell 500 via the hydrogen return port 400a, so that excess hydrogen gas at the anode and a mixture of other gases, particularly water vapor, can be returned to the two supply return assemblies via the hydrogen return channel.

As further shown in fig. 3, the output orifices 2000b of the two ejector pumps 2010 and 2011 (which serve as the output ends of the respective supply and return assemblies) are respectively coupled in parallel into the hydrogen supply passages of the hydrogen supply and return system, and the return orifices 2000a of the two ejector pumps 2010 and 2011 (which serve as the return ends of the respective supply and return assemblies) are also respectively coupled in parallel into the hydrogen return passages of the hydrogen supply and return system, in particular, an electromagnetic switching valve 800 is provided in the hydrogen return passages of the hydrogen supply and return system, so that the returned gas, in particular, the returned hydrogen gas, can be selectively returned to one of the ejector pumps 2010 and 2011 under the control of the electromagnetic switching valve 800.

While fig. 4 schematically illustrates a supply return assembly of the hydrogen injector 1010 and the ejector pump 2010 via the nozzle 6010, it will be apparent to those skilled in the art that another hydrogen injector 1011 may also form a supply return assembly corresponding to the ejector pump 2011 in the same manner as described below.

As shown in fig. 4, the hydrogen injector 1010 is connected to the nozzle 6010 such that a fluid output port (not shown) of the hydrogen injector 1010 is in fluid communication with an internal passage (not shown) of the nozzle 6010. The internal passage of the nozzle 6010 has an outlet with a fixed aperture communicating with the outside. The ejector pump 2010 includes a body 2100 with an internal hollow cavity 2200 formed in the body 2100. After the hydrogen injector 1010 is in contact with the body 2100 of the eductor pump 2010 and secured in place, the nozzle 6010 may extend into the interior hollow cavity 2200 of the eductor pump 2010. A backflow orifice 2000a is formed in the body 2100. For example, threads are machined into the return orifice 2000a to connect with corresponding tubing defining the hydrogen return passage. The return orifice 2000a of body 2100 is in fluid communication with inner hollow volume 2200 and, with nozzle 6010 in place extending into inner hollow volume 2200, the fixed-bore exit of nozzle 6010 is at a cross-section that is just near the intersection of orifice 2000a with inner hollow volume 2200.

Also formed in the body 2100 is an input orifice 1000a representation. For example, a screw thread is also formed in the orifice 1000a for connection to a pipe communicating with a hydrogen tank (not shown). After the hydrogen injector 1100, the ejector 2010 and the nozzle 6010 form a supply return assembly, hydrogen from the hydrogen tank can first enter the hydrogen injector 1010 through the inlet port 1000a and then be injected into the hollow interior cavity 2200 of the ejector 2010 through the nozzle 6010 connected to the hydrogen injector 1010. An outlet port 2000b is formed in the body 2100, the outlet port 2000b for fluid communication with the shut-off valve 300 and the hydrogen gas outlet 300a via tubing. In order to ensure that the hydrogen gas flowing back from the hydrogen return channel to the ejector pump 2010 through the orifice 2000a can be fed again through the outlet orifice 2000b to the hydrogen gas outlet 300a, the inner hollow volume 2200 is formed with a cross-sectional enlargement, preferably a cross-sectional gradual enlargement, from the vicinity of the cross-sectional plane of the outlet of the fixed bore of the nozzle 6010, which is taken perpendicular to the longitudinal axis of the body 2100 of the ejector pump 2010, towards the outlet orifice 2000 b.

In the normal operation of the hydrogen supply and return system, as hydrogen is sequentially supplied from the hydrogen tank to the anode 510 of the fuel cell 500 through the hydrogen injector 1010, the nozzle 6010, the ejector pump 2010, and the shutoff valve 300, excess hydrogen that has not undergone chemical reaction is generated at the anode. As excess hydrogen gas accumulates, the gas pressure on the side of the outlet orifice 2000b will be higher than the gas pressure on the side of the nozzle 6010 (i.e., the side of the orifice 2000a) as viewed in the internal hollow cavity 2200 of the body 2100 of the eductor pump 2010. However, due to the above-described enlarged cross-sectional design of inner hollow volume 2200, gas is drawn into inner hollow volume 2200 from orifice 2000a by a siphon effect and supplied to outlet orifice 2000b with the hydrogen jet from the outlet of nozzle 6010 under the action of the hydrogen jet at the outlet of nozzle 6010, thereby achieving recycling of excess hydrogen.

According to the present application, the

hydrogen injectors

1010 and 1011 respectively employ

nozzles

6010 and 6011 having different outlet cross-sections or bore sizes in combination with the ejector pumps 2010 and 2011. For example, the outlet cross-section or pore size of nozzle 6010 is smaller than the outlet cross-section or pore size of nozzle 6011. This allows the

hydrogen injectors

1010 and 1011 to be controlled to output hydrogen only via the hydrogen injector 1010 while the electromagnetic switching valve 800 controls such that the returned hydrogen is supplied only to the return port 2000a of the ejector pump 2010 at the time of low power operation of the fuel cell stack 500. Therefore, due to the small exit aperture size of the nozzle 6010 design in the hydrogen injector 1010, even at low flow rates, a sufficient siphon effect is generated to cause sufficient hydrogen to be returned from the anodes 510 of the fuel cell stack 500. Whereas, at the time of high power operation of the fuel cell stack 500, the

hydrogen injectors

1010 and 1011 are controlled to output hydrogen only via the hydrogen injector 1011, while the electromagnetic switching valve 800 is controlled such that the returned hydrogen is supplied only to the return port 2000a of the ejector pump 2011. Therefore, due to the design of the nozzle 6011 with the larger outlet aperture size in the hydrogen injector 1011 at this time, the siphon effect is not excessively enhanced even at high flow rates, thereby affecting the power output of the fuel cell stack 500.

In the embodiment of the present application, in the case where the fuel cell stack 500 is operated in a power range of 5 to 30kw (low power), the size of the outlet aperture of the nozzle 6010 that allows the injection of hydrogen gas is in the range of 0.8 to 1.8 mm, preferably 1 mm; the size of the outlet aperture of the nozzle 6010, which allows the injection of hydrogen gas, is in the range of 1.8 to 3.5 mm, preferably 3 mm, for the case where the fuel cell stack 500 is operated at a power range of 30 to 150kw (high power).

By adopting the technical scheme, the hydrogen reasonable supply and backflow of the fuel cell stack under the low and high power operation conditions can be realized only by combining the hydrogen injector and the ejector pump which are relatively small in volume and weight through the nozzles with different outlet sizes without arranging a large and heavy anode circulating fan, so that the working efficiency of the fuel cell stack is improved, and the design of a hydrogen supply and backflow system is simplified.

It should be clear to those skilled in the art that in an alternative embodiment, the input port 1000a of the hydrogen supply and return system may also be designed as a single port in the corresponding hydrogen injector. Further, it will be apparent to those skilled in the art that an appropriate pressure gauge and/or temperature gauge may be connected in series in the hydrogen supply path and/or the hydrogen reflux path of the hydrogen supply and reflux system, respectively, according to the need.

Although specific embodiments of the present application have been described herein in detail, they have been presented for purposes of illustration only and are not to be construed as limiting the scope of the application. Further, it should be clear to those skilled in the art that the various embodiments described in this specification can be used in combination with each other. Various substitutions, alterations, and modifications may be conceived without departing from the spirit and scope of the present application.

Claims

1. A hydrogen supply and return system for a fuel cell stack, comprising:

a hydrogen supply channel for supplying hydrogen to an anode (510) of the fuel cell stack (500);

a hydrogen return passage for returning hydrogen from an anode (510) of the fuel cell stack (500);

a first supply return assembly consisting of a first hydrogen injector (1010), a first nozzle (6010) in fluid communication with the first hydrogen injector (1010), and a first ejector pump (2010) receiving the first nozzle (6010);

a second supply return assembly consisting of a second hydrogen injector (1011), a second nozzle (6011) in fluid communication with the second hydrogen injector (1011), a second ejector pump (2011) receiving the second nozzle (6011);

a switching valve (800) provided in the hydrogen return passage; wherein the content of the first and second substances,

the output end (2000b) of the first supply backflow assembly and the output end (2000b) of the second supply backflow assembly are connected in parallel in the hydrogen supply channel, the backflow end (2000a) of the first supply backflow assembly and the backflow end (2000a) of the second supply backflow assembly are connected in parallel in the hydrogen backflow channel through the switching valve (800) so that hydrogen gas flowing back from the anode (510) can selectively flow back into one of the backflow ends (2000a), and the outlet cross section of the first nozzle (6010) leading into the first ejector pump (2010) is different from the outlet cross section of the second nozzle (6011) leading into the second ejector pump (2011).

2. The hydrogen supply and return system according to claim 1, wherein an internal hollow volume (2200) is defined in each of the first ejector pump (2010) and the second ejector pump (2011) so that the respective output end (2000b) and the respective return end (2000a) are in fluid communication with the internal hollow volume (2200), the outlet of the respective nozzle (6010 or 6011) being located in the internal hollow volume (2200) near the respective return end (2000 a).

3. The hydrogen supply and return system of claim 1 or 2, wherein the output (2000b) of the first supply return assembly is defined by an orifice (2000b) formed in the first jet pump (2010); the output end (2000b) of the second supply/return assembly is defined by an orifice (2000b) formed in the first jet pump (2011); the return end (2000a) of the first supply return assembly is defined by another orifice (2000a) formed in the first jet pump (2010); the return end (2000a) of the second supply return assembly is defined by another orifice (2000a) formed in the second jet pump (2011).

4. The hydrogen supply and return system of claim 1 or 2, wherein the first or second supply return assemblies are alternatively active under different power output operating conditions of the fuel cell stack (500).

5. The hydrogen supply and return system according to claim 4, characterized in that the outlet cross section of the first nozzle (6010) into the first ejector pump (2010) is smaller than the outlet cross section of the second nozzle (6011) into the second ejector pump (2011).

6. The hydrogen supply and return system of claim 5, wherein the first supply return assembly is active when the fuel cell stack (500) is operating at low power in the 5 to 30kw power range; the second supply return assembly is active when the fuel cell stack (500) is operating at high power in the power range of 30 to 150 kw.

7. The hydrogen supply and return system of claim 6, wherein the orifice size of the outlet of the first nozzle (6010) into the first ejector pump (2010) is in the range of 0.8-1.8 mm; the aperture size of an outlet of the second nozzle (6011) leading into the second ejector pump (2011) is within the range of 1.8-3.5 mm.

8. The hydrogen supply and return system according to claim 7, wherein the aperture size of the outlet of the first nozzle (6010) into the first ejector pump (2010) is 1 mm; the aperture size of the outlet of the second nozzle (6011) leading into the second ejector pump (2011) is 3 mm.

9. A hydrogen gas supply and return system according to claim 3, wherein said inner hollow volume (2200) is formed flaring gradually from near an outlet of said first nozzle (6010 or 6011) towards an orifice (2000b) defining said output end (2000 b).

10. A fuel cell system comprising a fuel cell stack (500) and a hydrogen supply and return system according to any one of the preceding claims, wherein the hydrogen supply and return system is in fluid connection with an anode (510) of the fuel cell stack (500) for supplying hydrogen to the anode (510) and returning hydrogen from the anode (510).