Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2001-11-09
2004-12-21
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S010000, C429S010000, C204SDIG004
Reexamination Certificate
active
06833207
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a regenerative fuel cell system. More particularly, this invention relates to a regenerative fuel cell apparatus which combines a fuel cell unit and an electrolyzer unit, and method of use thereof.
BACKGROUND OF THE INVENTION
Fuel cells have been proposed as a clean, efficient and environmentally friendly power source that has various applications. A conventional proton exchange membrane (PEM) fuel cell is typically comprised of an anode, a cathode, and a selective electrolytic membrane disposed between the two electrodes. A fuel cell generates electricity by bringing a fuel gas (typically hydrogen) and an oxidant gas (typically oxygen) respectively to the anode and the cathode. In reaction, a fuel such as hydrogen is oxidized at the anode to form cations (protons) and electrons by the reaction H
2
=2H
+
+2e−. The proton exchange membrane facilitates the migration of protons from the anode to the cathode while preventing the electrons from passing through the membrane. As a result, the electrons are forced to flow through an external circuit thus providing an electrical current. At the cathode, oxygen reacts with electrons returned from the electrical circuit to form anions. The anions formed at the cathode react with the protons that have crossed the membrane to form liquid water as the reaction by-product following ½O
2
+2H
+
+2e−=H
2
O. On the other hand, an electrolyzer uses electricity to electrolyze water to generate oxygen from its anode and hydrogen from its cathode. Similar to a fuel cell, a typical solid polymer water electrolyzer (SPWE) or proton exchange membrane (PEM) electrolyzer is also comprised of an anode, a cathode and a proton exchange membrane disposed between the two electrodes. Water is introduced to, for example, the anode of the electrolyzer which is connected to the positive pole of a suitable direct current voltage. Oxygen is produced at the anode by the reaction H
2
O=½O
2
+2H
+
+2e−. The protons then migrate from the anode to the cathode through the membrane. On the cathode which is connected to the negative pole of the direct current voltage, the protons conducted through the membrane are reduced to hydrogen following 2H++2e−=H
2
.
It is well known in the art that one type of regenerative fuel cell system combines separated fuel cell and electrolyzer units so that during the fuel cell mode of the system, the fuel cell unit generates electricity while consuming fuel gas (typically hydrogen) and oxidant (typically oxygen or air) and during the electrolyzer mode of the system, the electrolyzer unit generates the two process gases for consumption by the fuel cell unit, i.e. oxygen and hydrogen, while consuming electricity. Individual fuel cell and electrolyzer cells are usually interconnected in a series arrangement, often called “stacks”.
U.S. Pat. No. 5,376,470 entitled “Regenerative Fuel Cell System” and No. 5,506,066 entitled “Ultra-Passive Variable Pressure Regenerative Fuel Cell System”, both issued to Rockwell International Corporation, disclose such a regenerative fuel cell system. The regenerative fuel cell system comprises a fuel cell including an anode for receiving hydrogen and a cathode for receiving oxygen, an electrolyzer for electrolyzing water to produce pure hydrogen and pure oxygen, storage tanks to respectively store hydrogen and oxygen from the electrolyzer, a water storage tank communicating with the fuel cell and the electrolyzer. The fuel cell is located above the water storage tank while the electrolyzer is located below the water storage tank. Hydrogen is supplied to the fuel cell during fuel cell mode or extracted from the cathode side of the electrolyzer during electrolyzer mode via a hydrogen line that is connected to the hydrogen storage tank and through a liquid-gas separator. Similarly, oxygen is supplied to the fuel cell via lines and through the water storage tank during fuel cell mode or extracted from the anode side of the electrolyzer via an oxygen line and through the water storage tank. The oxygen, when reaching the water storage tank, bubbles up to the fuel cell via a supply line during fuel cell mode or to the oxygen storage tank, when in the electrolyzer mode.
However, these regenerative fuel cell systems cannot meet the increasingly demanding requirement for fuel cell stacks. The systems are usually large in size and heavy in weight and require complex plumbing and ancillary equipment such as valves and controls. As is known in the art, the performance of the fuel cell unit in this system cannot be optimized unless an additional humidification device is provided to humidify the process gases and an additional heat exchanger is included to facilitate the heat dissipation, all of which results in increased system size and weight. When switching from electrolyzer mode to fuel cell mode, the fuel cell unit in the conventional regenerative fuel cell systems is cold and therefore is unable to achieve full power output until the stack is warm.
Moreover, at present there is an expanding interest in vehicular applications of fuel cell stacks, e.g. as the basic power source for cars, buses and even larger vehicles. Vehicular applications are quite different from many stationary applications. In stationary applications, fuel cell stacks are usually used as an electrical power source and are simply expected to run at a relatively constant power level for an extended period of time. In contrast, in a vehicular, particularly an automotive environment, the actual power required from the fuel cell stack can vary significantly. Moreover, the fuel cell stack is expected to respond rapidly to changes in power demand while maintaining high efficiencies. Further, for vehicular, particularly automotive applications, a fuel cell power unit is expected to operate under a disparate range of ambient temperature and humidity conditions. In addition, during regenerative braking period, the prior regenerative fuel cell systems are unable to capture the electricity to recharge the system due to their slow switchover times, making them less efficient. All these requirements are exceedingly demanding and make it difficult to incorporate a conventional regenerative fuel cell system into a vehicle and operate efficiently.
In view of the disadvantages and drawbacks associated with conventional regenerative fuel cell systems, it is desirable to provide a regenerative fuel cell system that enables improved fuel cell performance, including rapid switchover between fuel cell and electrolyzer modes, instantaneous full power operation, higher power density, less peripherals and hence higher system efficiency.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a regenerative fuel cell system is provided, comprising an electrolyzer portion and a fuel cell portion;
the electrolyzer portion has a closeable hydrogen inlet and a hydrogen outlet in communication with the cathode of the electrolyzer portion for conducting hydrogen, a gas bypass having a gas bypass inlet and a gas bypass outlet for conducting oxidant gas for fuel cell reaction to the fuel cell portion, a water inlet and an oxygen-water outlet for exhausting oxygen generated in electrolyzer operation and coolant water from the fuel cell portion out of the electrolyzer portion;
the fuel cell portion has a hydrogen inlet, a first closeable hydrogen outlet for exhausting excess hydrogen in fuel cell mode, a second closeable hydrogen outlet for exhausting hydrogen generated in the electrolyzer portion in electrolyzer mode, an oxidant gas inlet, an oxidant gas outlet, a coolant water inlet and a coolant water outlet; and
the hydrogen inlet of the fuel cell portion being in communication with the hydrogen outlet of the electrolyzer portion; the oxidant gas inlet of the fuel cell portion being in communication with the gas bypass outlet of the electrolyzer portion; and the water inlet of the electrolyzer port
Cargnelli Joseph
Frank David
Joos Nathanial Ian
Bereskin & Parr
Chaney Carol
Hydrogenics Corporation
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