Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
2000-05-30
2002-04-23
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000, C429S006000
Reexamination Certificate
active
06376114
ABSTRACT:
TECHNICAL FIELD
The present invention relates to fuel cells that are suited for usage in transportation vehicles, portable power plants, or as stationary power plants, and the invention especially relates to a fuel cell power plant that utilizes fuel processing components to produce a hydrogen enriched reformate fuel from a hydrocarbon fuel.
BACKGROUND OF THE INVENTION
Fuel cell power plants are well-known and are commonly used to produce electrical energy from reducing and oxidizing fluids to power electrical apparatus such as apparatus on-board space vehicles. In such power plants, a plurality of planar fuel cells are typically arranged in a stack surrounded by an electrically insulating frame structure that defines manifolds for directing flow of reducing, oxidant, coolant and product fluids. Each individual cell generally includes an anode electrode and a cathode electrode separated by an electrolyte. A reactant or reducing fluid such as hydrogen is supplied to the anode electrode, and an oxidant such as oxygen or air is supplied to the cathode electrode. In a cell utilizing a proton exchange membrane (“PEM”) as the electrolyte, the hydrogen electrochemically reacts at a surface of the anode electrode to produce hydrogen ions and electrons. The electrons are conducted to an external load circuit and then returned to the cathode electrode, while the hydrogen ions transfer through the electrolyte to the cathode electrode, where they react with the oxidant and electrons to produce water and release thermal energy.
The anode and cathode electrodes of such fuel cells are separated by different types of electrolytes depending on operating requirements and limitations of the working environment of the fuel cell. One such electrolyte is the aforesaid proton exchange membrane (“PEM”) electrolyte, which consists of a solid polymer well-known in the art. Other common electrolytes used in fuel cells include phosphoric acid or potassium hydroxide held within a porous, non-conductive matrix between the anode and cathode electrodes. It has been found that PEM cells have substantial advantages over cells with liquid acid or alkaline electrolytes in satisfying specific operating parameters because the membrane of the PEM provides a barrier between the reducing fluid and oxidant that is more tolerant to pressure differentials than a liquid electrolyte held by capillary forces within a porous matrix. Additionally, the PEM electrolyte is fixed, and cannot be leached from the cell, and the membrane has a relatively stable capacity for water retention.
Manufacture of fuel cells utilizing PEM electrolytes typically involves securing an appropriate first catalyst layer, such as a platinum alloy, between a first surface of the PEM and a first or anode porous substrate or support layer to form an anode electrode adjacent the first surface of the PEM, and securing a second catalyst layer between a second surface of the PEM opposed to the first surface and a second or cathode porous substrate or support layer to form a cathode electrode on the opposed second surface of the PEM. The anode catalyst, PEM, and cathode catalyst secured in such a manner are well-known in the art, and are frequently referred to as a “membrane electrode assembly”, or “M.E.A.”, and will be referred to herein as a membrane electrode assembly. In operation of PEM fuel cells, the membrane is saturated with water, and the anode electrode adjacent the membrane must remain wet. As hydrogen ions produced at the anode electrode transfer through the electrolyte, they drag water molecules in the form of hydronium ions with them from the anode to the cathode electrode or catalyst. Water also transfers back to the anode from the cathode by osmosis. Product water formed at the cathode electrode is removed from the cell by evaporation or entrainment into a gaseous stream of either the process oxidant or reducing fluid.
A fuel cell power plant includes a fuel cell or fuel cell stack to generate electricity and a variety of systems to support the fuel cell stack. For example, if the plant is to be utilized to power a transportation vehicle, it is necessary that the power plant be self-sufficient in water to be viable. Self-sufficiency in water means that enough water must be retained within the plant to offset losses from reactant fluids exiting the plant in order to efficiently operate the plant. Any water exiting the plant through a plant process exhaust stream consisting of a cathode exhaust stream of gaseous oxidant and/or an anode exhaust stream of fluid exiting the anode side of the fuel cell must be balanced by water produced electrochemically at the cathode electrode and water retained within the plant. To maintain water self-sufficiency, it is common that the plant include a water recovery device, controls, and piping to recover and direct water into the fuel cell stack to maintain proper wetting of the PEM electrolytes, and humidity of the reactant streams, etc. An additional known component that assists in maintaining water balance is a water transport cooler plate secured in fluid communication with the cathode electrode or catalyst so that product water generated electrochemically at the cathode catalyst may move into the cooler plate to mix with a cooling fluid passing through the plate and then be directed to other plant systems.
Additionally, it is known that some fuel cell power plants operate on pure hydrogen gas, while others utilize a reformate fuel wherein a hydrogen enriched reducing fluid is formed from any of a variety of hydrocarbon fuels by fuel processing components including for example use of known autothermal, steam or partial oxidation reformers. Unfortunately, such reformation of hydrocarbon fuels generates ammonia that moves with the reformate fuel gas reactant stream into the fuel cell where the ammonia dissolves in the water in the electrolyte to become ammonium ions. The ammonia is formed in the reformer by a reaction between hydrogen and nitrogen present in the air that is used in the reforming process or nitrogen added to a peak shaved natural gas. The ammonium ions are then adsorbed by the PEM electrolyte to displace protons within the PEM, thereby decreasing conductivity of the PEM, and hence having a significant negative effect on performance of the fuel cell. Depending upon the temperature of the reformer, composition of any catalyst in the reformer, and nitrogen concentration within the reformer, ammonia formed in the reforming process may range from 1-100 parts per million (“ppm”). To efficiently operate a fuel cell power plant on such reformate fuel, the ammonia must be effectively removed from the fuel prior to entry of the fuel into the fuel cells of the plant.
Accordingly, there is a need to develop a fuel cell power plant that includes a reformate fuel treatment system for producing a reformate fuel with ammonia contamination less than 1.0 ppm.
DISCLOSURE OF THE INVENTION
The invention is a reformate fuel treatment system for a fuel cell power plant that includes at least one fuel cell for generating electricity from process oxidant and reducing fluid reactant streams; fuel processing components including a steam supply, a reformer and a water shift reactor of converter for producing a hydrogen enriched reformate fuel for the fuel cell from a hydrocarbon fuel; and, an ammonia removal apparatus that treats the reformate fuel to make it appropriate for supplying hydrogen to an anode electrode of the fuel cell. I n one embodiment of the reformate fuel treatment system, the ammonia removal apparatus is a disposable ammonia scrubber including a bed of carbon pellets saturated with phosphoric acid, a molecular sieve such as alumina or zeolites, or a cation exchange resin. Additionally, the reformer that directs the reformate fuel to the disposable ammonia removal scrubber may receive steam from a burner and steam generator in fluid communication with the fuel cell, wherein the burner receives and combusts an anode exhaust stream exiting the fuel cell, and the steam generator receives water from a w
Bonville, Jr. Leonard J.
Cipollini Ned E.
Garow Jay
Lesieur Roger R.
Szydlowski Donald F.
Chisholm, Jr. Malcolm J.
Kalafut Stephen
UTC Fuel Cells LLC
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