Storage system and method for supplying hydrogen to a polymer membrane fuel cell

A hydrogen storage system and method having a main hydrogen storage site that contains a sufficient amount of hydrogen for a fuel cell employing a polymer membrane to generate power in accordance with a predetermined electrical power requirement. A main storage site is provided to store and supply hydrogen to meet the electrical power requirement for the fuel cell. An auxiliary hydrogen storage site contains a sufficient amount of hydrogen to allow the fuel cell to operate on a scheduled basis that is required to maintain the polymer membrane hydrated. A manifold connects the main and auxiliary hydrogen storage sites and has an outlet to deliver hydrogen to the fuel cell. The manifold allows the auxiliary hydrogen storage site to be renewed independently of the main storage site and has a flow control network to allow the fuel cell to draw hydrogen from the auxiliary hydrogen storage site for maintenance purposes without utilization of the hydrogen from the main hydrogen storage site.

FIELD OF THE INVENTION

The present invention relates to a system and method for supplying hydrogen to a polymer membrane fuel cell to power a load and that is operated on a scheduled basis to maintain the polymer membrane in a hydrated condition. More particularly, the present invention relates to such a system and method in which the hydrogen used for maintenance purposes is stored in and supplied from an auxiliary gas cylinder.

BACKGROUND OF THE INVENTION

Fuel cells provide an environmental friendly method for generating electricity for a variety of purposes. One major purpose is to provide a back-up supply of electricity in case of power outages. As can be appreciated, if hydrogen is used as a fuel, there are less pollutants produced than in the case of back-up electrical generation that involve the use of internal combustion engines.

Where fuel cells are used to supply back-up power and for other uses, a sufficient amount of hydrogen must be stored to allow the fuel cell to supply a specific amount of electrical energy for the particular load involved. For instance, the specification might be to supply 5 kilowatts of power for 8 hours. Storage of hydrogen for fuel cells that utilize polymer membranes is complicated by the fact that such a fuel cell must be powered up in accordance with a schedule, for instance, every month for 15 minutes, in order to ensure that the membrane remains properly hydrated. The problem with this is that the scheduled maintenance operation of the fuel cell will consume hydrogen that otherwise must be on hand to ensure that the fuel cell will be able to meet its intended power requirements.

As may be appreciated, the continuing requirement to recharge a bulk hydrogen supply is a logistically complex if not expensive proposition. For instance, in order to recharge a bulk hydrogen supply, a tube trailer or other heavy equipment is required. Further expense may be produced where the fuel cell is situated in a geographically remote location. The present invention overcomes this problem by providing a hydrogen supply system and method for a fuel cell employing a polymer membrane that does not require the use of heavy equipment and the like to insure that there is sufficient hydrogen banked for later use by the fuel cell.

SUMMARY OF THE INVENTION

The present invention provides a hydrogen storage system for supplying hydrogen to a fuel cell employing a polymer membrane to power a load in accordance with a predetermined electrical power requirement and to maintain the polymer membrane in a hydrated condition.

In accordance with the present invention, a main hydrogen storage site is provided. The main hydrogen storage site is sized to contain at least a sufficient amount of hydrogen for the fuel cell to generate the predetermined electrical power requirement. An auxiliary hydrogen storage site is sized to contain an amount of hydrogen that is at least sufficient to allow the fuel cell to operate on a scheduled basis to maintain the polymer membrane in a hydrated condition. A manifold connects the main hydrogen storage site and the auxiliary hydrogen storage site and has an outlet to deliver the hydrogen to the fuel cell. The manifold is configured to allow the auxiliary hydrogen storage site to be renewed independently of the main hydrogen storage site. The manifold has a flow control network to allow the fuel cell to draw the hydrogen from the auxiliary hydrogen storage site to maintain the polymer membrane in the hydrated condition, without utilization of the hydrogen from the main storage site.

The flow control network can have pressure regulators configured such that the hydrogen from the auxiliary hydrogen storage site is delivered to the outlet before the hydrogen stored in the main hydrogen storage site. Check valves are provided to prevent the flow of hydrogen between the main and auxiliary hydrogen storage site. Thus, for membrane maintenance purposes, hydrogen is drawn from the auxiliary hydrogen storage site. When the fuel cell is required to power the load, for instance, as power back-up, any remaining hydrogen is drawn from the auxiliary hydrogen storage site and then from the main hydrogen storage site. Since the amount of hydrogen stored in the auxiliary site is sufficient for the maintenance operation, there will always be a sufficient amount of hydrogen in the main storage site to allow the fuel cell to meet its power requirements.

The main hydrogen storage site can consist of two banks of compressed gas cylinders and the auxiliary hydrogen storage site can be a single compressed gas cylinder. In such case, the pressure regulators can be first, second and third pressure regulators associated with a single compressed cylinder and one and the other of the two banks of the compressed gas cylinders, respectively. An outlet pressure regulator is provided to adjust the outlet pressure of the hydrogen at the outlet of the manifold. The first pressure regulator is set at a higher pressure than the second pressure regulator which is in turn set at a higher pressure than the third pressure regulator. As a result, the hydrogen is first drawn from the single compressed gas cylinder and then the one of the two banks of the compressed gas cylinders. After the pressure has sufficiently dropped in the one bank of compressed gas cylinders, then the other of the two banks of compressed gas cylinders is used to deliver the hydrogen. This all occurs automatically without the use of any electronic controls or expensive remotely operated valves.

The two banks of cylinders can be connected to the manifold to commonly feed the manifold with hydrogen. In such case, the pressure regulators are first and second pressure regulators associated with the single compressed gas cylinder and the two banks of compressed gas cylinders, respectively. The first pressure regulator is set to a higher pressure than the second pressure regulator such that the hydrogen is first drawn from the single compressed gas cylinder to the outlet.

In another embodiment, the main hydrogen storage site can be a composite, carbon-fiber wrapped compressed gas cylinder. The auxiliary storage site is a single compressed gas cylinder. The pressure regulators are a first pressure regulator associated with a single compressed gas cylinder and second and third pressure regulators associated with the composite, fiber-wrapped compressed gas cylinder. An outlet pressure regulator is provided to the outlet pressure of the hydrogen at the outlet of the manifold. The second and third pressure regulators are situated in an in-line relationship to regulate pressure of the hydrogen supplied from the composite, carbon-fiber wrapped compressed gas cylinder to level below that regulated by the first pressure regulator. As a result, hydrogen is first drawn from the single compressed gas cylinder to the outlet. As can be appreciated, two pressure regulators are required in case of a composite, carbon-fiber wrapped compressed gas cylinder which can be designed to obtain the hydrogen at over 5,000 lbs.

In another aspect, the present invention provides a method for supplying a hydrogen to a fuel cell employing a polymer membrane to power a load in accordance with a predetermined electrical power requirement and to maintain the polymer membrane in a hydrated condition. Hydrogen is supplied to the fuel cell to generate electricity to power the load from a main hydrogen storage site charged with at least a sufficient amount of hydrogen for the fuel cell to generate the predetermined electrical power requirement. Hydrogen is also supplied to the fuel cell on a scheduled basis from an auxiliary hydrogen storage site charged with an amount of hydrogen that is at least sufficient to maintain the polymer membrane hydrated. The auxiliary hydrogen storage site is periodically renewed so that it remains charged with the amount of hydrogen to allow the fuel cell to operate on the scheduled basis without drawing hydrogen from the main hydrogen storage site.

The hydrogen can be delivered from both the main hydrogen storage site and the auxiliary hydrogen storage site to a manifold having an outlet to the fuel cell. The manifold can have check valves to present the flow of hydrogen from the auxiliary hydrogen storage site to the main hydrogen storage site and vice-versa. The hydrogen from the auxiliary hydrogen storage site is delivered to the manifold at a higher pressure than that of the main hydrogen storage site so that the hydrogen will be first drawn from the auxiliary hydrogen storage site.

The auxiliary hydrogen storage site can be a single compressed gas cylinder and the auxiliary hydrogen storage site can be renewed by periodically replacing the single compressed gas cylinder. Where a manifold is employed, the auxiliary hydrogen storage site can be renewed by periodically disconnecting the single compressed gas cylinder from the manifold and replacing the single compressed gas cylinder.

DETAILED DESCRIPTION

With reference toFIG. 1, a hydrogen storage system1is illustrated for supplying hydrogen to a polymer membrane fuel cell (not illustrated). The polymer membrane fuel cell is employed to generate electricity to power a load in accordance with the predetermined electrical power requirement, for instance, as back-up power. The polymer membrane fuel cell also operates on a scheduled predetermined basis to maintain the polymer membrane in a hydrated condition. The fuel cell itself is activated for the foregoing purposes by known automated means that activate the fuel cell upon the occurrence of, for instance, a power upset or on the scheduled basis to maintain the polymer membrane.

Hydrogen storage system1is provided with first and second banks10and12of compressed gas cylinders14that are connected to one another. The resultant main hydrogen storage site is sized to contain at least a sufficient amount of hydrogen for the fuel cell to generate the predetermined electrical power requirement. As may be appreciated, more hydrogen can be stored to provide a factor of safety. An auxiliary hydrogen storage site is formed by a single compressed gas cylinder16that is sized to contain an amount of hydrogen that is at least sufficient to allow the fuel cell to operate on the scheduled basis. Again, more hydrogen could be stored in compressed gas cylinder16to provide a factor of safety.

First and second banks of hydrogen cylinders10and12and auxiliary compressed gas cylinder16are connected to a manifold18having an outlet20to the fuel cell. Manifold18has inlet lines22,24and27that are connected to compressed gas cylinder16and first and second storage bank of hydrogen cylinders10and12, respectively. Lines22,24and27are provided with line purge valves26,28and30to allow inlet lines22,24and27to be purged upon removal of compressed gas cylinder16or first and second hydrogen storage banks10and12. Additionally shutoff valves32,34and36are provided for such purposes. For instance, if compressed gas cylinder16is to be removed, valve32is closed and line purge valve26is open. Thereafter, compressed gas cylinder16is removed from manifold18by simply uncoupling any one of a number of known pressure fittings that can be utilized for such purpose.

Manifold18is also provided with first, second and third pressure regulators38,40and42which are interposed between a junction44and an outlet pressure regulator46. First pressure regulator38is set at the highest pressure, for instance 90 psi so that hydrogen will first be drawn from compressed gas cylinder16. Second pressure regulator40which is associated with hydrogen storage bank10is set at a pressure of for instance 75 psi so that hydrogen will next be drawn from first hydrogen storage bank10. Third pressure regulator42is set at the lowest pressure, for instance, 60 psi so that hydrogen will next be drawn from second hydrogen storage bank12. First, second and third check valves48,50and56are provided to prevent flow between compressed gas cylinder16, first hydrogen storage bank10and second hydrogen storage bank12.

Assuming that there is no requirement for hydrogen from the main storage site provided by first and second hydrogen storage banks10and12, the scheduled operation of the fuel cell will cause a solenoid valve within the fuel cell (not illustrated) to open and the fuel cell will first draw hydrogen from the compressed gas cylinder16. Since pressure regulator38is set at the highest pressure, second and third check valves50and56will shut off the flow within the legs of the manifold associated with first hydrogen storage bank10and second hydrogen storage bank12. Outlet pressure regulator46will regulate the pressure down to the supply of pressure required by the fuel cell, for instance 50 psi. Since the amount of hydrogen that will be consumed for purposes of maintaining the polymer membrane in an operation condition, periodically, compressed gas cylinder16can be removed in the manner described above and renewed by replacement with a fresh gas cylinder.

Although not a preferred mode of operation, manifold18could be designed to allow hydrogen storage to compressed gas cylinder16to simply be refilled in place by an appropriate fitting installed on inlet line22.

Assuming that a requirement exists for the fuel cell to power the load and that the pressure within compressed gas cylinder16has not first fallen to the pressure set in second pressure regulator40, hydrogen will be drawn from compressed gas cylinder16until the pressure drops to below the pressure set point of second pressure regulator40. At such point, pressure from first hydrogen storage bank10will cause first check valve48to close and allow second check valve50to open. When first hydrogen storage bank10drops below the pressure set for third pressure regulator42, second check valve50will close and hydrogen will be drawn from second hydrogen storage bank12. First and second hydrogen banks10and12are refilled or replaced along with compressed gas cylinder16after the depletion thereof.

As may be appreciated, a mode of operation of the present invention could be conducted without pressure regulators38,40and42. In such case, hydrogen could be stored at the highest pressure and compressed gas cylinder16at a lower pressure in first hydrogen storage bank10and yet at a lower pressure in second hydrogen storage bank12. This would not be preferred due to the complexity that would be introduced into filling operations and further if the hydrogen were not pressure regulated, a greater amount of hydrogen would have to be stored. Also possible is the use of pressure sensors and remotely activated valves to accomplish such switch over on the depletion of compressed gas cylinder16and then first and second hydrogen storage banks10and12.

With reference toFIG. 2an alternative hydrogen supply system1′ is illustrated. A manifold18′ is provided that has first and second inlet lines57and58that join at a junction59. As in the previous embodiment line purge valves60and61are provided along with shut off valves62and63. Flow control is provided by first and second pressure regulators64and65. First pressure regulator64is set at a higher pressure, for instance, at 80 psi and second pressure regulator65is set at a lower pressure, for instance, 60 psi, so that hydrogen will initially be drawn from compressed gas cylinder16. Check valves66and68are provided to prevent flow between compressed gas cylinder16and first and second hydrogen storage banks70and72, respectively. First and second hydrogen storage banks70and72of compressed gas cylinders74are connected to a subsidiary manifold76that joins into inlet line58at junction77. Hydrogen is supplied through an outlet line78after having been first reduced in pressure by an outlet pressure regulator79. As in the prior embodiment, the higher pressure set point of first pressure regulator64over that of second pressure regulator65will cause hydrogen to be first drawn from compressed gas cylinder16which can be replaced for renewal purposes.

With reference toFIG. 3a further hydrogen supply system1″ is illustrated. In this embodiment, the auxiliary storage site is compressed gas cylinder16in which hydrogen stored with a pressure at about 2200 psig. The main hydrogen storage site is provided by a composite carbon-fiber wrapped composite cylinder80that stores hydrogen at about 6000 psig. A manifold18″ is provided having an inlet line82for hydrogen from compressed gas cylinder16and an inlet line84for composite cylinder80. As in previous examples, lines82and84are provided with line purge valves86and88and shutoff valves90and92. A first pressure regulator94is provided to preferentially to draw hydrogen from compressed gas cylinder16. It can have a higher pressure setting of about 75 psi. Second and third pressure regulators96and98are provided for composite cylinder80. Since the pressure within composite cylinder80is about 6000 psig, third pressure regulator98is used to reduce the pressure to 2000 psi and second pressure regulator96is used to further reduce the pressure below the level of that of first pressure regulator94, for instance 60 psi. The hydrogen flows to a junction100. Pressure is then further reduced by an outlet pressure regulator102and hydrogen flows from an outlet104.

While the present invention has been described with reference to preferred embodiments, as will occur to those skilled in the art, numerous changes, additions and omissions may be made without departing from the spirit and scope of the present invention. The present invention is set forth in the claims.