DE10135625A1 - Hydrogen supply system for fuel cell arrangement has hydrogen recirculating pump driven by energy of pressure of hydrogen extracted from tank or coming from reforming unit - Google Patents

Abstract

A hydrogen feed system for a fuel cell arrangement in which hydrogen can be withdrawn from a pressurized storage tank or under pressure from a reforming device at a higher pressure and can be fed into the fuel cell arrangement after relaxation to a lower pressure, a feedback loop being provided in the hydrogen circuit so that part of it The unused hydrogen emerging from the fuel cell arrangement can be fed back into it, characterized in that a pump is provided which brings about the recirculation of the hydrogen and which can be driven by the pressure energy of the hydrogen removed from the tank or coming from a reformer unit.

Description

The present invention relates to a hydrogen feed system for a Fuel cell arrangement in which hydrogen from a pressurized standing storage tank or under pressure from a reforming direction can be removed at a higher pressure and after relaxation can be fed to the fuel cell arrangement at a lower pressure is, wherein a feedback loop is provided in the hydrogen circuit, thus a part of that emerging from the fuel cell arrangement unused hydrogen can be fed back into it.

Fuel cells are known in various embodiments. The However, the present invention is concerned only with such fuel cells, who work with hydrogen gas as fuel. Such fuel cells are in the form of so-called PEM fuel cells (Proton Exchange Membrane fuel cells) known. A fuel cell assembly ba Based on PEM fuel cells can be made from a single fuel consist of cell, but usually consists of a stack of over fuel cells arranged side by side or side by side, which together men form a so-called stack. Each fuel cell has one for Proton permeable membrane with electrodes on both sides, namely a cathode and an anode, both of which have a catalytic loading have stratification. The stack becomes hydrogen on the anode side fed at a certain pressure. This is on the cathode side Stack air is also supplied with a suitable positive pressure. In Be the fuel cell diffuses protons that pour out of hydrogen  finished, through the membrane and react on the Katho the side of the membrane with the supplied air. This will, on the one hand Water vapor is formed, which is discharged as exhaust gas on the cathode side and on the other hand generates electricity, for example for driving a Vehicle can be used in which the fuel cells order is installed.

Excess leaves on the anode side of the fuel cell arrangement low, still unused hydrogen the stack and becomes either Generation of heat burned or at least partially again Stack fed via a feedback loop, that is, recirculated. A Such an approach has certain advantages: On the one hand, it is economical Licher, on the other hand, the return of the hydrogen ensures that there is always sufficient moisture so that the membrane stay moist. This is an essential requirement for the stö operation of a fuel cell.

So it is known at least a part of that from the fuel cells emerging unused hydrogen of the fuel cell arrangement supply again. To achieve this, however, a printer must be used increase take place because of the pressure on the input side of the fuel cell arrangement is higher than on the output side.

However, this pressure increase is problematic. Because water substance molecules are small, pumping hydrogen is difficult and the risk of leakage is very high. Motor-driven pumps, at de NEN the engine is located outside the water cycle are in problematic in practice since it is extremely difficult to turn the rotating  to adequately seal the drive shaft of the pump. There are hydrogen leaks however extremely dangerous, especially when a vehicle is at a standstill, because it can lead to violent explosions.

To avoid the use of such pumps, is already in the international application with the publication number WO 99/05741 has been proposed to use so-called eductors the. These consist of a nozzle with a converging section and a divergent section and there will be hydrogen under one higher pressure in the constriction between the converging section and the diverging portion is injected, thereby causing suction with pressure increase, so that hydrogen at a lower Pressure sucked in on the converging side and using a printer elevation emerges on the diverging side. An eductor has the advantage that it can be sealed relatively easily since there are no moving the parts there. The problem, however, is that it only occurs with a certain Throughput works properly so a second eductor is required to maintain hydrogen circulation at low flow rates receive. In the second eductor, water is in the narrow point between injected into the converging and diverging section, what a water supply and a water pump are required for and it it is clear that the duration of the operating time is limited because the bare amount of water is limited. Through the various required Even such a system turns out to be relatively complex and components leakages are also to be feared here.

The object of the present invention is to provide a device which enables the pressure required for hydrogen recirculation  to get a relatively cheap increase without fear of leakage to have to.

In order to solve this problem, the type mentioned, provided according to the invention that a pump is provided, which causes the recirculation of the hydrogen and which from the pressure energy of the one taken from the tank or one Reformer unit coming hydrogen can be driven.

In other words, the solution according to the invention is that a Pump is provided to carry out the hydrogen recirculation connected to the fuel cell assembly, that of the supply stank or hydrogen coming from a reforming unit ben the pump this can be fed and by driving the pump relaxed hydrogen together with the recirculated hydrogen Fuel cell assembly is supplied.

Because the recirculation of hydrogen by one of the hydrogen itself operated pump, in particular in the form of a positive displacement pump, this pump can be completely within the hydrogen cycle brought so that the pump is completely inte is grated and no wave penetrates the wall of the pipe system, so that leakages on shaft bushings cannot occur. Though all pipe connections still have to be hydrogen-tight run, but this problem is much easier to solve, since there are no moving parts in the line connections during operation available. The pump is, so to speak, hermetic to the environment sealed.  

Because the drive energy comes from the already existing hydrogen pressure when it is released, no additional energy is required are supplied so that the power output by the fuel cells not diminished by the energy required to drive the pump is being learned.

Preferred embodiments of the invention are the subclaims as well as the further description and the attached drawing to take. Show it:

Figure 1 is a schematic representation of a first embodiment of a hydrogen feed system according to the invention with a piston pump.

Fig. 2 is a schematic representation of a diaphragm pump according to the invention during a first pump half cycle; and

FIG. 3 shows a schematic illustration of the diaphragm pump from FIG. 2 during a second pump half cycle.

Fig. 1 shows a double-acting piston pump 10 , which delivers hydrogen from a storage tank 35 or from a reforming unit 37 to the anode side via a schematically illustrated line 13 A of a fuel cell arrangement 11 and part of the excess, emerging from the fuel cells on the anode side Hydrogen is fed back into the fuel cells via a feedback loop. The feedback loop in this example includes schematically indicated lines 13 B and 13 C, which lead from the fuel cell arrangement 11 to connections 38 and 42 at the ends 30 and 32 of the pump 10 and lines 13 D and 13 E which lead from the connections 40 and 44 at the ends 30 and 32 of the pump 10 lead to the fuel cell arrangement. In a practical embodiment, the lines 13 B and 13 C or the lines 13 A, 13 D and 13 E can be realized as one line each, which lead via internal channels of the pump housing to the respective connections or openings of the pump. The pump 10 is therefore built into the feedback loop. The return loop 13 B, 13 C, 13 D, 13 E together with the line 13 A and the flow paths within the pump 10 and on the anode side of the fuel cell arrangement 11 form the hydrogen circuit.

In a manner known per se, the fuel cell arrangement 11 also has a cathode side to which air is supplied via the line 15 A. Protons that are supplied by the hydrogen on the anode side are transported to the cathode side by means of the membrane contained in the fuel cells and react there with oxygen from the supplied air to water, which in the form of water vapor forms the cathode side of the fuel cells with excess air or . in the reaction is not participating air components such as nitrogen leaves via the line 15 B.

The effect of the pump 10 is explained in more detail below. It has a double piston 12 which, depending on the prevailing pressure ratios, can be moved to the right according to arrow 14 or to the left accordingly arrow 16 within a cylinder housing 18 . The double piston 12 has two piston heads 20 and 22 which are connected to one another via a hollow connecting part 24 . A valve flap 26 is tiltably mounted on a pivot axis 28 on the cylinder housing 18 , so that it can be tilted between the oblique position shown in solid lines and a likewise inclined, broken lines schematically shown second position 26 '. The articulation axis 28 can be performed so that it either does not penetrate the cylinder housing at all or is realized by stub axles which are fixed during operation and are completely sealed off from the cylinder housing.

The tilting movement of the valve flap 26 takes place here by the reciprocating movement of the double piston 12 . If the piston is moved further to the right in the direction of arrow 14 , the valve flap 26 is tilted into the dashed position 26 'by a stop 27 provided on the connecting part 24 , while with a subsequent movement of the double piston 12 to the left according to the arrow 16, the valve flap 26 is moved back into the position shown in solid lines in FIG. 1 by the further stop 29 present on the connecting part.

In the arrangement shown, four pressure chambers I, II, III and IV are present, the pressure chamber I between the valve flap 26 and the piston head 22 , the pressure chamber II between the valve flap 26 and the piston head 20 , the pressure chamber III between the piston head 20 and the left end 30 of the cylinder 18 and the pressure chamber IV between the piston head 22 and the right end 32 of the cylinder 18 is formed.

Between the valve flap 26 and the connecting part or between the valve flap 26 and the cylinder housing 18 there are seals (not shown) in order to seal the chamber I against the chamber II in both positions of the valve flap 26 . Between the piston head 20 and the cylinder housing 18 or between the piston head 22 and the cylinder housing 18 there are further seals (not shown) which seal the chamber II against the chamber III and chamber I against the chamber IV.

The double piston pump 10 has six connections 34 , 36 , 38 , 40 , 42 and 44 in this example. The port 34 is connected to a storage tank 35 which contains hydrogen (H ₂ ) and supplies this to the port 34 with a constant driving pressure. In order to achieve this constant drive pressure, a pressure regulator valve 33 is provided between the before tank 35 and the port 34 . In the position shown in FIG. 1, the hydrogen reaches the pressure chamber I under the delivery pressure P _delivery and flows into the hollow connecting part 24 via a throttle point 46 adjacent to the piston head 22 . The hydrogen leaves the hollow connecting part 24 again via a second throttle point 48 and is then in the pressure chamber II.

The throttling points 46 and 48 do not have to be provided in the hollow connecting part 24 , they can be provided, for example, in the valve flap 26 or in a suitable flow passage in the cylinder housing 18 . Furthermore, it is not absolutely necessary to provide two throttling points; a single throttling point is sufficient.

In the position shown in Fig. 1, the hydrogen is now with reduced pressure according to the arrow 13 A leads to the fuel cells 11 ge. This pressure is referred to here as P _food .

You can thus write a first equation, namely:

P _food = P _delivery - ΔP _46.48 (1)

where ΔP _{46,48 represents} the pressure loss across the throttling points 46 and 48 .

In the fuel cells, part of the H ₂ fed to the anode side migrates in the form of protons through the membrane there, so that the rest of the hydrogen supplied is present as H ₂ -containing exhaust gases at the outlet of the fuel cells on the anode side (the exhaust gases also include water vapor , which originates from the anode side of the membrane), which have a pressure which is lower than the pressure P _feed and a part of these exhaust gases is supplied with a pressure, here referred to as P _back , to the terminal 38 and the terminal 42 .

Another part of the H ₂ -containing exhaust gases is removed via a pressure regulator valve 39 as exhaust gases from the hydrogen circuit and further used in a manner known per se, for example for heat generation or for safety reasons.

Now it is assumed that the double piston 12 moves according to arrow 14 , a check valve 52 adjacent to port 42 is closed and a check valve 54 adjacent to port 44 is opened by the corresponding pressure build-up in chamber IV, the exhaust gases located in chamber IV , which previously had the pressure P _Rück , are now compressed and leave the port 54 with an increased pressure P _food , so that they can be supplied with the gases from the port 36 to the fuel cells.

At the end of the movement corresponding to the direction of the arrow 14 , the Ven tilklappe 26 tilts by touching the stop 27 in the dashed position 26 'and the pressure conditions ensure, as will be explained in more detail later, that the double piston 12 moves to the left according to the arrow 16 . The III in the chamber located gasses with the initial pressure P due to the _return movement of the double piston with an increased _feed pressure P are from the terminal 40 arranged adjacent non-return valve 56 pushed out. At the same time, the check valve 58 , which is arranged adjacent to the connection 38 , blocks and prevents further H ₂ -containing exhaust gases from flowing into the chamber III and compressed H ₂ -containing exhaust gases from the connection 38 being forced out again. The exhaust gases, the cylinder 18 at port 40 , are then in turn fed back to the fuel cells with the H ₂ coming from port 36 .

During the movement of the double piston 12 to the left, according to arrow 16, a vacuum is created in the chamber IV whereby the return check valve 54 closes and the check valve 52 opens to he neut H ₂ -containing exhaust gases of the fuel cell at the pressure P _back in admit chamber IV. When the double piston 12 has reached its extreme lin ke setting, the valve flap 26 tilts again when it comes into contact with the stop 29 and the piston begins to move again under the prevailing pressure conditions to the right, according to the arrow 14 , which causes the Duty cycle repeats itself. The pressure ratios are selected by the design of the check valves 52 , 54 , 56 and 58 and the throttling points 46 , 48 so that we We repetitively constantly and hydrogen gas with the pressure P _{food is} always fed to the fuel cells 11 . A part of these gases consisting of H ₂ presents itself, so to speak, as fresh hydrogen coming from the tank (or from a reformer unit), while another part of the hydrogen supplied to the fuel cells consists of exhaust gases from the fuel cells consisting of H ₂ and hydrogen.

It is important in this arrangement that the pump is operated solely by the drive pressure P _Liefer and is completely contained in the hydrogen circuit or in the feedback loop. There is no outside of the hydrogen cycle, ie outside the wall of the. Hydrogen lead the line system positioned motor, which is somewhere on a shaft which has to drive in the H ₂ circuit, so that the entire H ₂ circuit can be carried out in a closed manner. There is therefore no danger that H ₂ can escape from leaks, since, as said, there is no shaft leading into the pump system from the outside, so that leakage from such a shaft cannot occur.

In order to explain the pressure forces that lead to the movement of the double piston 12 and are responsible for the implementation of the work cycle, a mathematical treatment of the movement sequences is now given.

We first assume that the double piston 12 moves to the right accordingly arrow 14 and the valve flap 26 , which has the position shown in solid lines in Fig. 1. It is also believed that the piston heads 20 and 22 have an effective area A on both sides. Thereafter, a force K _IR directed to the right acts on the piston 12 in the chamber I, from:

K _IR = P _delivery × A

In chamber II, a force acts on piston 12 in the opposite direction, ie to the left, from:

K _IIL = P _food × A.

A pressure P _back prevails in chamber III and this acts on piston 12 to the right with a force of:

K _IIIR = P _back × A

In turn, prevails chamber IV of the feed pressure P _feed, so that in Kam mer IV a leftward force on the double piston 12 acts of:

K _IVL = P _food × A

Now all forces that act on the double piston 12 in the right direction are added up. This means that the total force to the right K _GR results from the force K _IR + coming from chamber I + the force K _IIIR coming from chamber III ie:

K _GR = K _IR + K _IIIR = P _delivery × A + PRück × A (2)

The total force to the left K _GL is:

K _GL = K _IIL + K _IVL = P _dish × A + P _dish × A = 2P _dish × A (3)

Still applies

P _BACK = P _food - ΔP _Br (4)

where ΔP _{Br is} the pressure loss of the hydrogen on the anode side of the fuel cell system (measured between inlet and outlet), this pressure or pressure difference also being determined by the pressure regulator valve 39 , which ultimately ensures that the pressure at the outlet of the anode side of the fuel cells P _back lies.

Consequently, the total force K _G , which acts on the piston 12 to the right, is given by the following equation:

K _G = K _GR - K _GL = (P _delivery × A + P _return × A) - 2P _food × A (5)

considering equation (4) one can write:

K _G = A (P _delivery + (P _food - APBr) - 2P _food ) = A (P _delivery - P _food - ΔP _Br ) (6)

Taking equation (1) into account, this equation can be simplified as follows:

K _G = A ((P _dish + ΔP _46.48 ) - P _dish - ΔP _Br ) = A (ΔP _46.48 - ΔP _Br ) (7)

After A represents a constant, it can be seen that the condition for a positive rightward total force on piston 12 is that

ΔP _46.48 <ΔP _Br

That is, the total pressure loss at the throttle points 46 , 48 must be greater than the pressure loss between the inlet and the outlet of the hydrogen circuit in the fuel cell arrangement.

Although this equation is not entirely correct, since the effective area of the piston heads 20 , 22 in the chambers I and II is somewhat smaller than A, since the connecting part 24 has a finite cross-sectional area, the correction required is nevertheless relatively small, so that the one listed Condition at least roughly applies.

The above discussion applies to the rightward movement of the double piston 12 . At the end of this movement, the valve flap 26 is reversed or pivoted and the same relationship then applies to the movement of the double piston to the left. A continuous back and forth movement of the double piston is thus achieved, which is largely independent of the flow rate of the hydrogen and therefore still works even at low loads or with low power output of the fuel cell system.

As an alternative to the piston pump 10 , a diaphragm pump 100 can also be used in the hydrogen feed system shown in FIG. 1, as shown for example in FIGS. 2 and 3.

The diaphragm pump 100 has a first and a second diaphragm chamber 102 , 104 , between which a gas channel 106 is located. The membrane chambers 102 , 104 have identical, in the direction parallel to the gas channel 106 stretched and symmetrical diamond-shaped cross sections.

By a first membrane 108 , the first membrane chamber 102 in a first outer chamber chamber 110 and a first inner chamber chamber 112 and by a second membrane 114 , the second membrane chamber 104 is divided into a second inner chamber chamber 116 and a second outer chamber chamber 118 , The membranes 108 , 114 run essentially parallel to one another on both sides of the gas channel 106 .

A coupling element 166 mechanically couples the membranes 108 , 114 to one another, the ends 168 , 170 of the coupling element 166 being attached to the membranes 108 , 114 in the region of the membrane centers. The coupling element 166 has a degree of freedom of movement at least in the direction perpendicular to the plane of the membrane 108 , 114 .

The outer chamber spaces 110 , 118 are each provided with an inlet 120 , 122 in a storage tank-side end region, each inlet being equipped with a check valve 124 , 126 and serving for supplying unused hydrogen from the fuel cell arrangement. Furthermore, the outer chamber spaces 110 , 118 in their fuel cell-side end region each have an outlet 132 , 134 provided with a corresponding check valve 128 , 130 , in order to supply pressure-increased hydrogen in a manifold 136 to the fuel cell arrangement again.

Furthermore, a bushing 138 , 140 is provided in each case, which connects the end regions of the inner chamber spaces 112 , 116 on the storage tank side to the gas channel 106 . The gas channel-side feedthrough openings 142 , 144 of the feedthroughs 138 , 140 are in this example at the same height and on opposite sides of the gas channel 106 .

In the region of through openings 142, 144 is a tilt valve 146 is provided in the gas channel 106, which divides the gas passage 106 in a facing the front of rats tank portion 148 and one of the order Brennstoffzellenan facing portion 150th

The tilt valve 146 has two sealing legs 152 , 154 and a tilt leg 156 , which are arranged in a Y-like manner and are connected to one another. At the point where all three legs are adjacent to each other, the tilt valve 146 is rotatably supported. The sealing legs 152 , 154 are designed such that they can close the passage openings 142 , 144 either towards the section 148 facing the storage tank or the section 150 of the gas cell facing the fuel cell arrangement.

The toggle valve 146 can only assume two stable positions, ie switching states: in the first position ( FIG. 2), the first passage opening 142 is sealed off from the section 148 of the gas channel 106 facing the storage tank and to the section 150 facing the fuel cell arrangement open, while the second passage opening 144 is open to the section 148 of the gas channel 106 facing the storage tank and is sealed off from the section 150 facing the fuel cell arrangement. Gas flowing from the storage tank into the gas channel 106 can thus only get into the second inner chamber space 116 , while gas can flow from the first inner chamber space 112 into the section 150 of the gas channel 106 facing the fuel cell arrangement.

In the second position, which is shown in FIG. 3, the flow conditions are exactly the opposite, ie gas flowing from the storage tank into the gas channel 106 can only get into the first inner chamber space 112 , while gas from the second inner chamber space 116 into the section 150 of the gas channel 106 facing the fuel cell arrangement is able to flow.

The tilt valve 146 is switched with the aid of its tilt leg 156 , which is actuated by a drive element 158 . The drive element 158 has a V-shaped fork section formed by a first and second fork leg 160 , 162 , into which the tilt leg 156 engages. After a displacement of the fork section in a direction perpendicular to the Gaska nal 106 by a distance which corresponds to the distance between the free ends of the fork legs 160 , 162 , one of the fork legs 160 , 162 comes into contact with the tilt leg 156 and applies this to it a force that causes the rocker valve 146 to flip over and assume its other position.

The fork section is rigidly connected to the rod-like coupling element 166 by means of a rod section 164 . Coupling element 166 results in a synchronous deflection of first and second diaphragms 108 , 114 . A sufficient deflection of the diaphragm 108 , 114 leads to an actuation of the tilt valve 146 .

The operation of the diaphragm pump 100 is as follows:
At the beginning of the first pump half cycle shown in FIG. 2, the diaphragms 108 , 114 have a maximum deflection to the left, ie the coupling element 166 and thus also the fork section and the tilt leg 156 are in their left position. The tilt valve 146 assumes a position, which is hereby referred to as the first position, in which the passage 138 forms a flow connection from the first inner chamber space 112 to the section 150 facing the fuel cell arrangement and the passage 140 forms a flow connection from the storage tank section 148 of the gas channel 106 facing the second inner chamber space 116 .

Hydrogen from the storage tank therefore flows through the gas channel 106 and the open second passage opening 144 into the second inner chamber space 116 . This increases the pressure in the second inner chamber space 116 and leads to a deflection of the diaphragm 108 , 114 to the right. As a result, the volume of the second outer chamber space 118 is reduced and the gas present therein is compressed and displaced by the check valve 130 and the outlet 134 into the collecting line 136 .

Furthermore, the check valve 126 is closed by the increased pressure, so that no additional hydrogen returned from the fuel cell arrangement can flow into the second outer chamber space 118 .

At the same time, the deflection of the membrane 108 , 114 reduces the volume of the first inner chamber space 112 . Gas located therein is displaced through the open duct 138 into the section 150 of the gas channel 106 facing the fuel cell arrangement and also reaches the manifold 136 .

In addition, the movement of the diaphragm 108 , 114 increases the volume of the first outer chamber space 110 , in which a negative pressure is consequently generated. Due to the negative pressure, the check valve 128 is closed at the outlet 132 so that no hydrogen can flow back from the manifold 136 into the first outer chamber space 110 . Instead, the vacuum develops a suction effect, which leads to an opening of the check valve 124 at the inlet 120 of the first outer chamber space 110 and sucks in hydrogen returned by the fuel cell arrangement.

With the membranes 108 , 114 , the coupling element 166 and with it the drive element 158 , ie the fork section, also move to the right. If the outermost deflection of the diaphragm 108 , 114 is reached, the left fork leg 160 of the drive element 158 takes the tilt leg 156 and actuates the tilt valve 146 in this way.

The rocker valve 146 then tips over and assumes its second position. The second pump half cycle thus begins, in which the first inner chamber space 112 is filled with a flowing hydrogen from the storage tank through the gas channel 106 . The process described above takes place in the opposite direction.

The pressure (P _supply), which is introduced from the storage tank or from the reforming unit coming hydrogen in the gas channel 106 is about 300 kPa, while the relaxed hydrogen with egg nem feed pressure (P _feed) of about 220 kPa Overpressure is supplied to the fuel cells. The H ₂ -containing exhaust gases, which are partially returned to the membrane pump 100 by the fuel cells, are present at the inlets 120 , 122 with a pressure (P _Rück ) of approximately 180 kPa overpressure.

In a modified embodiment, the driving element 158 116 wech selwirkendes spring or lever member 2 can be formed by using the tilting valve 146 and the coupling element are formed, the two stable positions shown in Fig. And Fig. 3 assumes or defined.

In the diaphragm pump 100 , a continuous back and forth movement of the diaphragm 108 , 114 driven solely by the gas flow is sufficient, which is largely independent of the flow rate of the hydrogen and therefore also at low loads or at low power output of the fuel cell system works.

Claims (28)

1. Hydrogen supply system for a fuel cell arrangement ( 11 ) in which hydrogen (H ₂ ) from a pressurized storage tank ( 35 ) or under pressure from a reformer ( 37 ) at a higher pressure and after relaxation to a lower pressure in the A fuel cell arrangement ( 11 ) can be fed, a feedback loop ( 13 B, 13 C, 13 D, 13 E) in the hydrogen circuit (comprising 10 , 11 , 13 A, 13 B , 13 C, 13 D, 13 E) being seen before , so that a part of the unused hydrogen coming out of the fuel cell arrangement ( 11 ) can be fed back into it, characterized in that a pump ( 10 ) is provided which causes the recirculation of the hydrogen and what the pressure energy of the from the tank ( 35 ) removed or coming from a reformer unit ( 37 ) coming hydrogen. 2. Hydrogen feed system for a fuel cell arrangement ( 11 ), in which hydrogen (H ₂ ) from a pressurized storage tank ( 35 ) or under pressure from a reformer ( 37 ) can be removed at a higher pressure and after relaxation to a lower pressure in the Fuel cell arrangement ( 11 ) can be fed, a feedback loop ( 13 A, 13 B, 13 C, 13 D, 13 E) being provided in the hydrogen circuit (comprising 10 , 11 , 13 A , 13 B, 13 C, 13 D, 13 E) is so that a part of the unused hydrogen emerging from the fuel cell arrangement can be fed back into the latter, characterized in that a pump ( 10 ) is provided which is connected to the fuel cell arrangement ( 11 ) for carrying out the hydrogen recirculation, that the from the storage tank ( 35 ) or from a refor ming unit ( 37 ) coming hydrogen to drive the pump this can be supplied and the relaxed water by driving the pump off (H ₂ ) is fed together with the recirculated hydrogen to the fuel cell arrangement ( 11 ). 3. Hydrogen feed system according to one of the preceding claims, characterized in that the pump ( 10 ) is a positive displacement pump. 4. Hydrogen feed system according to claim 3, characterized in that it is a piston pump ( 10 ) in the displacement pump. 5. Hydrogen feed system according to claim 3 or 4, characterized in that it is a double-acting piston pump ( 10 ) in the displacement pump. 6. Hydrogen feed system according to claim 5, characterized in that the piston ( 12 ) of the double-acting piston pump has two coupled but spaced piston heads ( 20 , 22 ) which are movable back and forth in a cylinder ( 18 ) that a first cylinder space (III) is formed between the one piston head ( 20 ) and one end face ( 30 ) of the cylinder ( 18 ), that a second cylinder space (IV) between the second piston head ( 22 ) and the second end face ( 30 ) of the cylinder ( 18 ) is formed, and that each cylinder chamber (III, IV) has an outlet leading to the fuel cells outlet ( 40 , 44 ) and one of the fuel cells coming inlet ( 38 , 42 ), each inlet ( 38 , 42 ) and outlet ( 40 , 44 ) a respective check valve ( 52 , 54 , 54 , 56 ) is assigned. 7. hydrogen supply system according to claim 6, characterized in that the piston heads ( 20 , 22 ) are attached to each other via a hollow connec tion part ( 24 ), that a reversible valve member ( 26 ) is provided to the reciprocation of the piston heads ( 20 , 22 ) under the pressure of the hydrogen supplied to the piston pump ( 10 ), coming from the storage tank ( 35 ) or from the reformer unit ( 37 ). 8. Hydrogen feed system according to claim 7, characterized in that the valve member ( 26 ) has the shape of a valve flap which is pivotally arranged on the cylinder housing ( 18 ) and the Zylin derraum between the two piston heads ( 20 , 22 ) in two further chambers (I , II) divided, depending on the position of the valve member ( 26 ) with the pressure of the hydrogen from the storage tank ( 35 ) or from the refor mation unit ( 37 ) coming (H ₂ ). 9. hydrogen feed system according to claim 8, characterized in that the hollow connecting part ( 24 ) through the valve flap ( 26 ) is carried out and is sealed against this. 10. Hydrogen feed system according to claim 8 or 9, characterized in that the hollow connecting part ( 24 ) has a, at least one throttle point ( 46 , 48 ) comprising, between the two further chambers (I, II) extending flow path. 11. Hydrogen feed system according to one of claims 6 to 10, characterized in that the reversal of the valve flap ( 26 ) by the back and forth movement of the piston ( 12 ) can be effected. 12. Hydrogen feed system according to claim 11, characterized in that the reversal of the valve flap ( 26 ) by the piston ( 12 ) or on the connecting member ( 24 ) provided stops. 13 hydrogen feed system according to one of the preceding Ansprü che, characterized in that the pressure (P _supply) of is from the storage tank (35) or from the Refo rmiereinheit (37) coming hydrogen at 200 kPa pressure and the feed pressure (P _feed) for the fuel cells is about 130 kPa overpressure. 14. Hydrogen feed system according to claim 3, characterized in that the displacement pump is a diaphragm pump t ( 100 ). 15. Hydrogen feed system according to claim 14, characterized in that the diaphragm pump ( 100 ) has a first and second Membrankam mer ( 102 , 104 ), between which a grass channel ( 106 ) is arranged, the one facing the storage tank or the reforming section ( 148 ) and a section ( 150 ) facing the fuel cell arrangement. 16. Hydrogen feed system according to claim 15, characterized in that the first and second membrane chamber ( 102 , 104 ) through a ste and second gas-impermeable membrane ( 108 , 114 ) in a he most outer and inner chamber space ( 110 , 112 ) and a second inner and outer chamber space ( 116 , 118 ) are divided. 17. Hydrogen feed system according to claim 16, characterized in that the outer chamber spaces ( 110 , 118 ) each have an inlet coming from the fuel cells ( 120 , 122 ) and an outlet leading to the fuel cells ( 132 , 134 ), each with the inlet and Outlet a correspondingly designed check valve ( 124 , 126 , 128 , 130 ) is assigned, and that the inner chamber spaces ( 112 , 116 ) are connected by corresponding first and second bushings ( 138 , 140 ) to the gas channel ( 106 ). 18. Hydrogen feed system according to claim 16 or 17, characterized in that the membrane ( 108 , 114 ) are mechanically coupled to one another by a coupling element ( 166 ) mounted in the center of the membrane in such a way that they are synchronous in a gas channel ( 106 ) in substantially vertical direction can be deflected. 19. Hydrogen feed system according to one of claims 16 to 18, characterized in that in the gas channel ( 160 ) a tilt valve ( 146 ) is arranged with first and second positions, through which depending on its position either the first inner chamber space ( 112 ) against the the storage smelled facing portion (148) and the second inner chamber space (116) against which the fuel cell assembly facing portion (150) of the gas duct (106) or the second inner chamber space (116) opposite the side facing the stock tank section (148) and the first inner chamber space ( 112 ) can be closed with respect to the section ( 150 ) of the gas channel ( 106 ) facing the fuel cell arrangement. 20. Hydrogen feed system according to claim 19, characterized in that the tilt valve ( 146 ) has two sealing legs ( 160 , 162 ) and a tilt leg ( 156 ) which are arranged in a Y-like manner and are firmly connected to one another and are rotatably mounted in the region of their connection point , 21. Hydrogen feed system according to claim 19 or 20, characterized in that the tilt valve ( 146 ) can be actuated by a drive element ( 158 ) connected to the coupling element ( 166 ). 22. Hydrogen feed system according to claim 21, characterized in that the drive element ( 158 ) has a substantially rigidly connected to the coupling element ( 166 ) connected to the rod section ( 164 ), at its free end by two fork legs ( 160 , 162 ) a V-shaped Fork section is formed such that a force can be applied to the tilting leg ( 156 ) through the free ends of the fork leg ( 160 , 162 ). 23. Hydrogen feed system according to claim 21, characterized in that the drive element ( 158 ) is formed by a spring or lever element interacting with the tilt valve ( 146 ) and the coupling element ( 166 ). 24. Hydrogen feed system according to one of claims 15 to 23, characterized in that the gas flowing through the outlets from the membrane chambers ( 102 , 104 ) and from the gas channel ( 106 ) is brought together in a manifold ( 136 ) and can be fed into the fuel cell arrangement , 25, hydrogen feed system according to any one of claims 14 to 24, characterized in that the pressure (P _supply) of is from the storage tank or from the reforming unit coming hydrogen at 300 kPa excess pressure, the feed pressure (P _supply) for the fuel cell at about 220 kPa overpressure and the pressure (P _Rück ) of the H ₂ -containing exhaust gases supplied from the fuel cells of the membrane pump is about 180 kPa overpressure. 26. Hydrogen feed system according to one of the preceding claims, characterized in that the hydrogen circuit downstream of the fuel cell arrangement ( 11 ) has an outlet ( 17 ) through which excess H ₂ -containing exhaust gases can be removed. 27. Hydrogen feed system according to claim 26, characterized in that a pressure regulator valve ( 39 ) is provided at the outlet ( 17 ). 28. Hydrogen feed system according to one of the preceding claims, characterized in that the pump ( 10 ) is hermetically sealed from the environment.