Patent Grant
7968236
This invention relates generally to power systems. More specifically, this invention relates to hydrogen fuel cell power systems with forced air supplies.
Small portable electrical and electronic devices have typically used batteries for power. However, conventional batteries have limited energy storage capacity. Thus, applications like professional video cameras, laptop computers, and cell phones often require longer runtimes than batteries can provide.
These conventional batteries can be replaced by a fuel cell integrated with a fuel storage container that stores hydrogen, hydrogen rich gas, or a substance from which hydrogen can be extracted on demand. Such a fuel cell includes an anode end for splitting hydrogen atoms into electrons and protons, a current bearing portion providing a pathway for the electrons, a medium such as a proton exchange membrane providing a pathway for the protons, and a cathode end for rejoining the electrons and protons into water molecules in the presence of oxygen. Such a fuel cell can thus generate electricity over a longer time period than conventional batteries can, provided that the hydrogen in the storage container is periodically refreshed.
It is therefore desirable to develop a hydrogen fuel cell electricity generation device capable of supplying electricity for a longer period of time than conventional batteries.
As conventional batteries can be designed to power small, portable devices, it is also desirable to develop a hydrogen fuel cell electricity generation device that is sufficiently small and lightweight to be of use in portable electrical and electronic devices.
A portable electricity generation device comprises a plurality of fuel cells, each fuel cell having an anode end with a catalyst facilitating the separation of hydrogen atoms into electrons and protons, a cathode end facilitating the combination of the electrons and protons into water molecules in the presence of oxygen, and a current bearing portion providing a current path for the electrons to traverse. The electricity generation device also includes a fuel storage container for storing a supply of hydrogen and delivering the supply of hydrogen to an anode end of the plurality of fuel cells so as to initiate a flow of the electrons through the current bearing portion. In addition, the portable electricity generation device includes an air moving device configured to direct atmospheric air toward a cathode end of the plurality of fuel cells, wherein the air moving device is positioned to convectively cool the plurality of fuel cells as it supplies atmospheric air to the cathode end.
A portable electricity generation device (50) that is used to store energy and replace secondary batteries consists of a fuel storage container (13) for storing a supply of hydrogen fuel, a fuel delivery apparatus (14) that connects the fuel storage container (13) to a stack or plurality of fuel cells (11) that each have an anode end (3) and a cathode end (4), an oxidant source such as atmospheric air, and an air moving device (12) such as a fan. In operation, the fuel cell power system (50) converts molecular hydrogen H2 to H2O in the presence of oxygen from the atmosphere according to the above described process, generating an electric current in the process.
In one embodiment the fuel cell power system (50) includes a stack of fuel cells (11) that is supplied with hydrogen from a fuel storage container (13), also referred to as a fuel tank, fuel canister, fuel cartridge or fuel storage system, and the entire assembly is enclosed by a cover (30), see
In this embodiment, the fuel storage container (13) stores compressed hydrogen as the fuel for the fuel cells (11). A pressure regulator (15) is used to reduce the pressure of hydrogen in the fuel storage container (13) to a level acceptable to the stack of fuel cells (11). A purge valve (24) is connected to the outlet of the stack of fuel cells (11) by conventional methods. The purge valve (24) can be a standard normally closed solenoid valve, see
The reaction of the fuel cell is dependent on the operating temperature of the stack of fuel cells (11), the availability and purity of hydrogen supplied by the fuel storage container (13), and the availability and pressure of the oxidant supplied to it by the air moving device (12). Further, as it is known in the art to use a proton exchange membrane fuel cell, the humidity of gases within the stack of fuel cells (11) can be a major factor influencing the performance of the system.
The stack of fuel cells (11) is created from individual fuel cells sandwiched between a front plate (8) and a back plate (9), see
In one embodiment the stack of fuel cells (11) is capable of utilizing the oxygen in the surrounding ambient atmosphere. When supplied with hydrogen fuel from the fuel cartridge (13), the stack of fuel cells (11) is capable of completing the abovementioned electrochemical reaction to supply electrical energy by just breathing the air within the stack of fuel cells (11).
In such a system the heat produced by the fuel cell reaction cannot be effectively removed, resulting in the temperature of the stack of fuel cells (11) rising to a point of failure. In order to prevent such a failure the stack of fuel cells (11) must be operated at a point where the heat from the reaction is rejected via natural convection, thus reducing the power capability of the system.
The stack of fuel cells can therefore be supplied with air using an air moving device (12) such as a fan or low pressure blower. While typical fuel cell systems are known to require air pumps, compressors or high pressure blowers to supply the required air to the stack of fuel cells (11), the current embodiment allows the use of a low pressure air moving device (12) like a fan or low pressure blower. Usage of the fan or low pressure blower has a number of advantages such as:
In the present embodiment the air moving device (12) is positioned such that air is blown into the stack of fuel cells (11), see
The top of the stack of fuel cells (11) can also have an attached seal plate (28) with openings for air to exhaust from the stack of fuel cells (11). By varying the area of the openings in the seal plate (28) the flow rate and the pressure of air in the stack of fuel cells (11) can be changed, see
The air moving device can also be positioned such that the stack of fuel cells (11) is on the low pressure side of the air moving device (12), see
Similarly, the air moving device (12) can also be positioned on top of the stack of fuel cells (11) by the fan or low pressure blower mounting plate (27), see
When the air moving device (12) supplies air to the fuel cell stack, the air flows through the stack of fuel cells. It then strikes the seal plate, changes direction, and returns to the top of the stack of fuel cells (11), eventually escaping out through the openings (33) in the air mount plate (27). This change of direction results in improved heat transfer characteristics for the fuel cell stack (11). In addition, the opposing streams of incoming and outgoing air from the fuel cell stack (11) result in the hot outgoing air stream transferring some of the heat and water collected from the fuel cell reaction back to the incoming air stream, thus helping to retain a moist environment resulting in consistent performance of the stack of fuel cells (11). In addition, by controlling the openings (33) of the exhaust in the air mount plate (27), the degree of backpressure in the stack of fuel cells (11) can be more precisely controlled.
The seal plate (28) can be advantageously made of a material that is a good conductor of heat and can be used to perform the function of an intermediate heat exchanger. While a flat or planar seal plate is discussed here, one of skill in the art will realize that non-planar surfaces like those seen in commercial heat sinks (that increase the surface area available for heat transfer) can also be used, allowing for improved heat transfer from the seal plate. For further improved heat transfer, a conventional fluid heat transfer methods may be employed to better control the temperature of the seal plate (28) and thus improve the efficiency of heat transfer between the air in the stack of fuel cells (11) and the seal plate (28).
A porous sponge like material that is a good conductor of heat can also be applied to the surface of the seal plate (28). The porosity of this sponge like material provides a large surface area for the air in the fuel cell system (50) to better transfer heat away from the fuel cells (11).
As illustrated in
The fuel storage container (13) can be configured as a removable and replaceable cartridge. Hydrogen required by the stack of fuel cells (11) is then stored in this cartridge (13), see
Typically, such hydrogen storage methods allow for liberation of this hydrogen under pressure. Hence, a pressure regulator (15) is used to manage the pressure to a level acceptable to the stack of fuel cells (11).
In order for the fuel cell power system to operate over a long period of time, the system should allow for the replacement of the spent fuel storage cartridge (15) with a new filled fuel storage cartridge. The fuel storage cartridge (13) can thus consist of a self sealing connector (21) and a mechanism to mate the cartridge (13) to the remainder of the fuel cell system. An interface such as a coarse screw thread (17) mates the cartridge (13) with the corresponding threads (18) located in the fuel cell system. The connector results in the opening of the self sealing connector (21) and supply of hydrogen to the fuel cell system. The interface that uses the coarse screw threads (17, 18) creates a leak tight joint between the cartridge (13) and the rest of the fuel cell system. A twist connector, bayonet mount or any other mate known to one familiar in the mechanical arts may also be used to accomplish the same goal.
When hydrogen supplies are removed from conventional fuel cells pending replacement, no hydrogen is available to the fuel cells, and as a result they typically cease to produce power. There is, however, a need in a number of applications for continuous and uninterrupted operation over a long duration of time. An embodiment of the present invention thus utilizes a tank that acts as a reservoir (16), see
The reservoir (16) can be connected between the cartridge (13) and the pressure regulator (15) on the high pressure side of the system, see
The above mentioned reservoir (16), pressure regulator (15), interface connection (18) to the storage cartridge (13), and fuel delivery to the stack of fuel cells can all be incorporated in a single component, a control block (14), see
In such a control block (14), the reservoir (16) can be a cavity built into the control block (14), see
Alternatively, the reservoir (16) can be created by an expandable bladder that expands when filled with hydrogen and collapses as the hydrogen gas is consumed by the stack of fuel cells (11). The bladder (shaded gray), see
In addition, the reservoir (16) may be a container that is filled with hydrogen separate from the control block (14). When the reservoir (16) is a separate container, the reservoir (16) can be permanently attached to the control block. In another embodiment the reservoir (16) could be attached and detached from the control block (14) by the system operator. Here, when the cartridge (13) is close to being depleted, the reservoir (16), externally filled with hydrogen, can be connected to the control block (14) to supply the required hydrogen while the cartridge (13) is removed. In this embodiment the reservoir (16) acts like the cartridge (13) in all respects. Those of skill in the art will recognize that a number of methods exist to store hydrogen in the reservoir (16) that have been already discussed in this description, all of which are contemplated in the scope of the invention.
The ability to hot-swap cartridges (13) without interrupting the supply of power is critical to a number of users. For example: in the electronic news gathering industry where recording critical events can be financially rewarding. Losing a shot because the operator is replacing the energy storage device is not acceptable to most if not all the operators.
Where a secondary metal hydride is used to store hydrogen in the cartridge (13), heat energy is required to maintain the evolution of hydrogen at constant pressure. In the absence of heat the hydride drops in temperature, resulting in the drop in pressure and eventually resulting in the cartridge (13) not being able to supply hydrogen to the fuel cells (11). In order to prevent such a situation the invention includes utilization of waste heat created by the inefficiencies in the stack of fuel cells (11) to help maintain the temperature of the hydride energy storage cartridge (13). By placing the storage cartridge (13) directly above the openings (33) in the exhaust air stream (32) from the stack of fuel cells (11), heat energy is supplied to the storage cartridge (13), see
To alleviate such an inefficiency, the hot air exiting the stack of fuel cells can be routed through features in the cover (30) in a manner where most of the air exhausts out of the system (50) only after coming in contact with the storage cartridge (13). The cover (30) has a longitudinal cavity (23) that is used to accept the storage cartridge (13). The longitudinal cavity (23) is sized such that it creates a small air gap between the storage cartridge (13) and the cover (30), shaded gray; see
The cover (30) is designed a duct, such that the exhausting air stream (32) from the stack of fuel cells (11) is routed through inside port (29A) in the cover, through outside port (29B), to the storage cartridge cavity (23), see
The cover (30) can also be designed such that the path from inside port (29A) to outside port (29B) is helical in nature. In such a configuration, the air exiting the system (50) via the cavity (23) will follow a helical path around the storage cartridge (13) increasing the time of contact with the storage cartridge (13) and creating turbulence in the exiting air stream (32), both resulting in improved heat exchange with the storage cartridge (13).
In another configuration, the gap (shaded gray in
The life of the stack of fuel cells (11) is affected by pollutants such as carbon monoxide, chlorine, sulfur dioxide, and particulate dust. The air inlet (31) to the system (50) can thus include a filter (32) which removes pollutants like chlorine, particulate dust and sulfur dioxide from the incoming air stream before it enters the stack of fuel cells (11). Such a filter (32) can be a conventional consumable filter that can be replaced easily by, for instance, removing the cover (30), see
The operation of the stack of fuel cells (11) is controlled by a conventional control circuit (25) that ensures the safe, reliable and efficient operation of the system (50). The control circuit (25) controls the air supplied to the stack of fuel cells (11) by controlling the air moving device (12) and/or the purge valve (24).
The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the invention. Thus, the foregoing descriptions of specific embodiments of the present invention are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, obviously many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.
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| Number | Date | Country | |
|---|---|---|---|
| 20100291454 A1 | Nov 2010 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60345855 | Jan 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10328709 | Dec 2002 | US |
| Child | 11827061 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11827061 | Jul 2007 | US |
| Child | 12725411 | US |
