The present invention relates generally to fuel and exhaust containment for energy conversion systems, and more particularly, to fuel containers and recycling systems for metal-air fuel cells.
Fuel cells, and in particular metal-air battery systems, have long been considered a desirable power source in view of their inherent high energy density. A fuel-cell battery includes a cathode, an ionic medium and an anode. A metal-air cell employs an anode comprised of metal particles that is fed into the cell and oxidized as the cell discharges. The cathode is generally comprised of a semipermeable membrane, a mesh of inert conductor, and a catalyzed layer for reducing oxygen that diffuses through the membrane from outside the cell. Since oxygen is readily available in the air, it is usually unnecessary to utilize a dedicated oxygen storage vessel for the fuel-cell battery (except in certain configurations where there the oxygen supply is limited due to design considerations). This makes metal-air cells very efficient on both a volumetric energy density and cost basis. The cathode and anode are separated by an insulative medium that is permeable to the electrolyte. A zinc-air refuelable battery consumes zinc particles and oxygen as zinc is oxidized by the reaction with ions passing through the electrolyte while liberating electrons to produce electricity. The reaction products are generally comprised of dissolved zincate and particles of zinc oxide suspended in the spent electrolyte.
Prior art metal-air systems have been demonstrated with sufficient energy capacity to power electric vehicles. Such metal-air batteries having recirculating metal slurry anodes were built for demonstration purposes in the 1970s by Sony, Sanyo, the Bulgarian Academy of Sciences, and the Compagnie General d""Electricitie. These systems never achieved any commercial success because they all had relatively low power output (acceptable drain rates and overall capacities). Until now, this has been the major obstacle to providing a commercially viable system. For example, Sony could only provide 24 W/kg, and Compagnie General d""Electricitie was limited to 82 W/kg or 84 Wh/kg. The theoretical capacity, however, is well in excess of five times these values depending upon the type of fuel utilized. One type of recent metal-air cell has realized an improvement in capacity by utilizing a packed bed of stationary anode particles and an electrolyte which moves through the bed without the use of an external electrolyte pump. Although this system has increased the cell capacity to about 200 W/kg with an energy density of about 150 Wh/kg, further improvements are necessary before commercial success will be realized.
Metal-air refuelable batteries can be refueled in a short amount of time (i.e., minutes), compared to the several hours typically required to recharge conventional batteries. This characteristic makes them very well suited to mobile applications such as electric vehicles, portable power sources and the like. During the refueling operation, fresh anode metal and electrolyte are added to the cell, and the reaction products and spent electrolyte are removed. The reaction products must be either transported to an industrial facility for recycling or used, as is, for another purpose. Several methods have been proposed for refueling metal-air cells. One known system employs two reservoirs, one to store fresh anode fuel and one to accommodate reaction materials from the cell.
U.S. Pat. No. 4,172,924 discloses a metal-air cell that utilizes a fluid metal fuel comprised of a mixture of metal particles and liquid electrolyte in a paste form. The paste moves from a first reservoir through the electrochemical battery where it is oxidized at a corresponding metal oxide paste cathode. The reaction products (primarily metal oxide) are communicated to a second reservoir. While this arrangement increases the drain rate by removing the reaction materials, the multiple reservoir design wastes space, adds complexity, and increases cost.
Recently issued U.S. Pat. No. 5,952,117 discloses a fuel cell battery designed to overcome the disadvantages associated with the dual reservoir configuration described above. The ""117 patent discloses a transportable container for supplying anode material and electrolyte to the fuel cell battery, circulating electrolyte in a closed system, and collecting spent anode reaction product. In accordance with the teachings of this patent, the container is first filled with zinc fuel particles and fresh electrolyte. Next, the container is transported to the fuel cell battery and connected to the battery such that it becomes part of the electrolyte flow circuit. After the zinc fuel and electrolyte are used for a period of time during battery discharge, the container, now containing at least partially spent electrolyte and reaction products, is removed from the battery and transported back to the refilling apparatus. The contents of the container are subsequently emptied into the refilling apparatus and the process is repeated. The spent electrolyte and reaction products are regenerated at a zinc regeneration apparatus and then returned to the refilling apparatus. Although this arrangement obviates the need for two separate containers, the collection of reaction products can be made effectively only after the fuel supply has been exhausted and the container has been emptied into the refilling apparatus.
Another shortcoming of this system concerns the structure for preventing stray short circuit currents between a plurality of cells that are fed fuel in parallel. In that configuration, the cells are not electrically isolated from each other through the conductive fuel feed. To prevent short-circuiting, the ""117 patent discloses a filter for blocking large particles of anode material from passing through the conduits between the fuel compartments. Although effective for the pellet-type fuel particles disclosed in the patent, this expedient cannot block the passage of the small anode particles that are found in a paste-like fuel substance.
In view of the above, it is an object of the present invention to provide a convenient, economical and environmentally safe fuel supply and waste material retrieval system for use with an energy conversion device.
It is another object of the present invention to provide a single reservoir container for concurrently supplying fuel to an energy conversion device and collecting exhaust from the energy conversion device.
It a further object of the present invention to provide a single reservoir container for supplying fuel and collecting reaction products, respectively, to and from fuel cells, and in particular, metal-air fuel cells using zinc, aluminum, lithium, magnesium, silver, iron and the like.
It is another object of the present invention to provide a metal-air fuel cell system that can be used for varied applications in terms of power requirements (i.e., in the watt to megawatt range). Such applications include, but are not limited to, providing energy for powering motor vehicles, portable and consumer electronics, homes and industry.
It is yet another object of the present invention to eliminate short-circuiting between a plurality of electrochemical cells having a single fuel feed.
In view of the above objects and additional objects that will become apparent hereinafter, the present invention generally provides a method and system for providing fuel to an energy conversion device from a single reservoir container and concurrently receiving exhaust from the energy conversion device in the container.
In particular, the present invention provides a fuel cell system that includes a reservoir container, which is connectable to the cell to supply fuel and concurrently collect waste or reaction materials that are generated as the cell discharges. The invention is adapted for use with hybrid rechargeable fuel cells, and in particular, metal-air fuel cell batteries having metal anode material in fluid form. The word xe2x80x9cfluidxe2x80x9d is defined herein as a paste-like substance such as for example small particles of metal suspended in a fluid electrolyte, i:e., a KOH solution and varying additives. Metal-air fuel cells operate as oxygen or air (fuel) oxidizes the metal anode as part of the electrochemical cell reaction.
In the present invention, the fluid anode, particularly zinc-metal fuel, is supplied from a single reservoir to multiple cells in a battery system. During operation, as the cells discharge the resulting reaction products are continuously removed from the cells to the reservoir container and the cells are replenished with fresh anode fuel from the container.
In accordance with a general aspect of the invention, there is provided a reservoir container for storing a quantity of fuel and a quantity of exhaust in an energy conversion system having at least one energy conversion device. The reservoir container comprises a container body connectable to the at least one energy conversion device and includes at least two chambers of inversely variable volume disposed within the container for respectively storing a quantity of fuel and receiving a quantity of exhaust. A structure is provided for decreasing the volume of the first chamber while concurrently increasing the volume of the second chamber. During operation of the energy conversion device, fuel is supplied from the first of the chambers while exhaust is concurrently received in the second of the chambers. When the fuel supply is exhausted, the reservoir container may be removed and transported to another location to enable regeneration of the exhaust into fresh fuel. The reservoir container is subsequently reconnected to the energy conversion device and fresh fuel is fed from what was previously the xe2x80x9cexhaustxe2x80x9d chamber while exhaust is received in the original fuel supply chamber.
In accordance with a particular implementation of the invention for a fuel cell battery system, a single reservoir container is provided for storing a quantity of electrochemical anode material and a quantity of reaction products. The reservoir container includes at least two isolated chambers of inversely variable volume, and at least one cell element having a cathode and defining a volume for holding the anode material (metal and electrolyte) to form an electrochemical cell with the cathode. A fluid delivery circuit communicates anode material between the at least one cell element and a first of the chambers in the reservoir container. Either the same or an independent fluid delivery circuit communicates reaction products between the cell(s) and a second of the chambers in the reservoir container. In a preferred embodiment, the delivery circuit respectively comprises branch ducts or conduits disposed between the cell(s) and the reservoir container. Each conduit includes an electrically insulating valve to selectively transfer fresh anode material and reaction products to and from a single cell in a group of cells which are electrically interconnected.
In accordance with another aspect of the invention, the fuel cell power system further comprises a subsystem for regenerating the reaction products into fresh electrochemical anode material after the reaction products are removed to the reservoir container from the cell(s); and a structure for varying the respective volumes of the first and second chambers as fresh anode material is delivered to the cell and reaction products are delivered to the reservoir. The subsystem for regenerating the reaction products may be disposed proximal to the cells, or it can be situated at a remote location and the reservoir container transported thereto after all the fuel as been dispensed.
In another embodiment, the first chamber of the reservoir container comprises a first subchamber for holding fresh anode material and a second subchamber for holding electrolyte. These components are delivered to a mixer from the respective first and second subchambers prior to communication to the cell(s). Likewise, the reservoir may be configured with a first subchamber for holding anode reaction material and a second subchamber for holding used electrolyte. These components are separated from each other before they are delivered to the reservoir from the cell(s).
The invention further provides a method for supplying fuel to, and collecting exhaust from, an energy conversion device. The method comprises the steps of:
connecting to the energy conversion device a reservoir container having at least two chambers for respectively supplying a quantity of fuel to and receiving exhaust from the energy conversion device;
inversely varying the volume of the first and second of the chambers in the reservoir to supply fuel to the energy conversion device and receive exhaust from the energy conversion device;
disconnecting said container from said energy conversion device;
converting the exhaust into fuel within the container; and
reconnecting said container to the energy conversion device to supply fresh fuel thereto from the second of the chambers and to receive exhaust in the first of the chambers.
In a specific application of the above, the present invention provides a method for supplying fuel to, and collecting reaction products from, at least one fuel cell element, comprising the steps of:
connecting to the fuel cell a reservoir container having at least two chambers for respectively supplying anode fluid to and receiving reaction products from the fuel cell element;
inversely varying the volume of the first and second of the chambers in said reservoir to supply anode fluid to the fuel cell and to receive reaction products from the fuel cell element;
disconnecting said container from the fuel cell;
converting the reaction products in the second of the chambers into fuel; and
reconnecting the container to said fuel cell to supply fresh anode fluid thereto from the second of the chambers and to receive reaction products in the first of the chambers.
The present invention will now be described with particular reference to the accompanying drawings.