The invention relates generally to direct methanol fuel cells. More particularly the invention relates to an integrated process housing for direct methanol fuel cells.
Direct-methanol fuel cells or DMFCs are a subcategory of proton-exchange fuel cells where, the fuel, methanol (CH3OH) is fed directly to the fuel cell. This eliminates the need for complicated catalytic reforming. Storage of methanol is much easier than that of hydrogen because it does not need to be done at high pressures or low temperatures, as methanol is a liquid over a fairly broad temperature range. Further, the energy density of methanol is several times greater than even highly compressed hydrogen.
DMFC's do not have moving parts and work by creating a thermodynamic potential out of the chemical reaction between methanol and air. A thermodynamic potential is created through the use of a polymer electrolyte membrane, also known as a proton exchange membrane (PEM), which allows only certain chemical species to pass through it. The most common PEM used in DMFCs today is Nafion™, produced by Dupont. The most common catalysts used are PtRu alloy for the anode and Pt for the cathode. On one side of this membrane, a methanol and water mixture is fed to an anode catalyst that separates the methanol molecule into hydrogen atoms and carbon dioxide molecules. The separated hydrogen atoms are then typically stripped of their electron to create a proton and an electron. The proton is then passed through the membrane to the cathode side of the cell. The protons at a cathode catalyst react with the oxygen in air to form water absent the electron. A conductive wire is connected from the anode side to the cathode side, where the electrons are stripped from the hydrogen atoms on the anode side and travel to the cathode side and combine with the electron deficient species. The reaction of the methanol and O2 into carbon dioxide and water derives from a difference in energy across the membrane, where the system is in a state of non-equilibrium. Once equilibrium is reached, the components stop reacting, and no additional useful energy is produced.
Useful energy is produced by lowering the voltage across the membrane to a level below the equilibrium value. Lowering the voltage occurs when a load, or resistance, is placed on the wire connecting the anode side to the cathode side, where the load is weak enough such that current can flow through it. The smaller the voltage difference that is imposed on the fuel cell in this manner, the more current is produced until a proton transport rate limit is reached, after which no additional energy is produced.
On key advantage of a DMFC is that it can simply be refilled with more fuel when it runs out, unlike a battery, for example. Portable fuel cell system users want a fuel cell that is small, light, quiet, long running, durable and low cost. High water flux increases the amount of water that must be managed by the fuel cell, increasing system size, weight, cost and complexity. High methanol crossover results in lower fuel efficiency and shorter runtimes for a given amount of fuel. Size, weight, cost and complexity of the system also increase in order to handle the excess heat and water that is produced as the methanol is oxidized on the air-side of the fuel cell.
DMFC's can be used to power a wide range of portable and mobile electronics. However, a new application is emerging that includes the material handling vehicle market, such as forklifts, tuggers, and automated guided vehicles. In the past, the forklift business has been using compressed natural gas, and plug-in electric model vehicles. A major drawback for electric vehicles is the long recharge cycles, where the batteries for these forklifts can weigh 2,000 pounds. This requires the use of cranes to carry them out of the units and putting in another 2,000 pound battery, a couple of times a shift. It is now known that large DMFC's can keep the vehicles in operation for a lot longer than plug-in electric systems. For example a forklift fuel cell, can operate from a five-gallon methanol fuel tank that is simply refilled as needed. This new class of large DMFC's can act as an on-board charger, and can be refueled just like a car, with a hose and nozzle from a compact methanol refueling cabinet.
A need exists for a direct methanol fuel cell with an integrated water and fuel management container that is compact, provides sufficient power to operate heavy equipment, and able to sustain harsh the environment of material handling.
To address the limitations found in the art, a direct methanol fuel cell integrated process assembly is provided. The assembly includes a housing, a fuel mixing and surge tank integrated to the housing, with an air and liquid separator also integrated to the housing. A vent of the mixer and surge tank is at least proximal to a vent of the separator. The housing further includes at least one condensation pathway integrated along the housing, where the pathway enables exhaust condensates to return to the assembly. At least one exhaust port is integrated to the housing, which vents directly to a cooling airstream to facilitate exhaust removal. A manifold is also integrated to the housing, with the fuel valve, a water valve, a fuel pump and a water pump integrated with the housing, where the integrated process assembly reduces an amount of plumbing between the a liquid volume in the mixer and the separator. Further, a water volume of the process assembly is reduced and a form factor of the process assembly cell is also reduced.
In one aspect of the invention, the housing is made from any plastic material that does not degrade from methanol.
According to another aspect, the fuel mixing and surge tank is integrated to a base of the housing, where the fuel mixing and surge tank is a generally rectangular-prism shaped container, and has an inlet. In this aspect, the inlet further has a baffle element that prevents entrained gasses from moving directly to an outlet port. Here, the outlet port is connected directly to a negative pressure end of a solution pump. Additionally, the surge tank further has at least one vent in a roof of the surge tank, where any gas and vapor in the surge tank passes through the vents at a low velocity. Here, the surge tank further has a vertical chamber, where the low velocity gas and vapor vents to the vertical chamber to condense on the vertical chamber and the condensed vapor returns to the fuel mixing and surge tank. Further, the vertical chamber includes convolutions, where the convolutions and a height of the vertical chamber reduce splash sensitivity. Further, the vertical chamber further includes a vertical chamber vent that opens to a region of high airflow outside the housing, whereas a removal of all exhaust products from the housing are supported. In one aspect, a fan provides the high airflow.
In another aspect of the invention, the air and liquid separator is integrated to a generally center and upper portion of the fuel mixing and surge tank. The air and liquid separator further has a single inlet port that is connected to dual air-liquid separator volumes. The air-liquid separator volumes have a generally cyclonic separator shape that has a center exhaust tube, which protrudes into a volume of the air and liquid separator. The center exhaust tube inhibits splashed water from exiting the housing. According to one aspect, the center exhaust tubes have a generally large volume, where the center exhaust tubes are disposed to promote a low gas velocity relative to the inlet port. The exhaust tubes have an opening to a plenum volume that is disposed above the air and liquid separator. Here the exhaust from the tubes condenses in the plenum volume and the plenum volume is vented to a high airflow region outside the housing, where a fan provides the high airflow. The condensate and separated liquid are collected in a water storage volume.
In another aspect of the invention, the manifold is proximal to a lower portion of the housing.
In a yet another aspect, the manifold further includes a fuel inlet, a water transfer port, an outlet port, a mixing pump, and a water outlet, where the fuel valve, the water valve, the mixing pump and the waste water pump mount directly to the manifold.
In another aspect of the invention, the condensation pathway is along a side of the housing.
In a further aspect of the invention, the exhaust ports are disposed proximal to a top end of the housing, where the exhaust ports exit directly into a high airflow region, such that exhaust removal is facilitated. Here, a fan creates the high airflow region.
In a further aspect, the fuel valve is a solenoid valve.
In another aspect, the water valve is a solenoid valve.
In yet another aspect, the fuel pump is disposed to move methanol fuel.
In a further aspect, the water pump is a waste-water pump.
The objectives and advantages of the present invention will be understood by reading the following detailed description in conjunction with the drawing, in which:
a)-(b) show perspective views of the direct methanol fuel cell tower according to the present invention.
a)-(d) show perspective views of a manifold assembly and mixer manifold plate according to the present invention.
a)-(b) show perspective views of a mixer base having a mixer manifold plate and a mixer I/O end, respectively, according to the present invention.
a)-(b) show perspective views of a mixer base with an air/liquid separator connected on top according to the present invention.
a)-(d) show perspective views of an air/liquid separator according to the present invention.
a)-(b) shows perspective views of a direct fuel cell tower housing according to the present invention.
a)-(b) show perspective vertical cutaway views of a housing according to the present invention.
Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will readily appreciate that many variations and alterations to the following exemplary details are within the scope of the invention. Accordingly, the following preferred embodiment of the invention is set forth without any loss of generality to, and without imposing limitations upon, the claimed invention.
The present invention is a direct methanol fuel cell tower having an integration of functions of several fuel cell components and its associated plumbing into one unit. A mixer/fuel surge tank is integrated into a base with an air/liquid separator in the center. Along the sides and center are pathways to allow condensate from the exhaust to return to the unit. At the top are exhaust ports that exit directly into the cooling air-stream to facilitate exhaust removal. A manifold assembly, to facilitate fuel mixing, is integrated into the lower part, incorporating fuel and water mixing valves (or solenoid valves) as well as fuel and waste-water pumps. This assembly eliminates much of the typical plumbing associated with a mixer and air/liquid separator, as well as reduces the liquid volume requirement and the overall size of the unit.
Referring now to the figures,
a)-(d) show perspective views of a manifold assembly 102 and mixer manifold plate 200 (see
a)-(b) show perspective views of a mixer base 104 having a mixer manifold plate 200 and a mixer I/O end 300. At least one vent 304 is disposed in the mixer base roof 302 of this volume, where the vent 304 allows any gas in the mixer 104 to be vented at low velocity into a vertical chamber (see
a)-(b) show perspective views of a mixer base 104 with an air/liquid separator box 106 connected on the mixer base roof 302 according to the present invention. According to one embodiment, the air/liquid separator box 106 includes a horizontal buffer plate 400, where the buffer plate restricts any negative effects that occur from splashing caused by movement of the fuel cell when in use. Further shown is a channel cavity 402 formed by the walls of the air/liquid separator box 106, and disposed along a portion of the vent 304 of the mixer base 104.
a)-(d) show the air/liquid separator plate 700 is in the form of a cyclonic separator with a center exhaust tube 702 that protrudes into the air/liquid separator box 110 and the exhaust tubes 702 vent through a cathode exhaust 704 disposed above a cathode return port 600. The center tubes inhibit splashed water from exiting the system. The center exhausts 702 have a larger area, thus lower velocity, than the inlet port 306 and associated plumbing. These center exhausts 702 open into a plenum area (see
a)-(b) show perspective views of a direct fuel cell tower housing 800 according to the present invention. As shown in
a)-(b) show perspective vertical cutaway views of a housing 800 according to the present invention. Shown in
In operation, when fuel is needed, the fuel solenoid 204 opens, and the mixing pump 208 draws fuel in from the bladder/fuel tank (not shown) through the solenoid 204. The fuel is discharged into the mixer base 104. The position of the solenoid 204 and pump 208 can be altered while retaining their function, or the solenoid 204 eliminated.
When water is needed, the water solenoid 206 opens, and the water mixing pump 208 draws water in from the air/liquid separator 106 through the water solenoid 206. The water is discharged into the mixer base 104. The position of the solenoid 206 and pump 208 can be altered while retaining their function, or the solenoid 206 eliminated. In an alternate embodiment, a dedicated pump for pumping water can be implemented in addition to the mixing pump 208.
A particulate and/or ionic filter (not shown) may be incorporated to the housing stack 800 on the anode outlet port 116 to clean the solution on its path.
Alternate forms have included an ionic filter (not shown) in the return path as well as gas/liquid phase separation devices (not shown) and varying entry points into the mixer 104.
The exhaust products travel through the vertical column 108. Any condensation products on the walls of this column 108 are able to flow back into the mixer 104. The gas can otherwise travel to the horizontal vent 110 opening at low speed, and be picked up by the cooling air flow, and be drawn out of the fuel cell tower 100. Alternate forms have exhaust ports 110 in vertical and angular configurations as well as forms venting outside of the unit so as to separate the process exhaust from the cooling air stream.
In other aspects of operation, the cooled liquid/gas mixture from the cathode side is fed from a single port 600 into at least one chamber 602 where the fluid's inertia is translated into rotation in the cylindrical chambers 602 of the air/liquid separator plate 110. Liquid is allowed to coalesce in this volume. The liquid water is retained for further use in the air/liquid separator 106 as needed. The gas travels through the center tubes 702 into a larger plenum 1200. Any condensation products in this plenum 1200 are able to flow back into the air/liquid separator 106. The gas can otherwise travel to the horizontal vent 704 opening at low speed, and be picked up by the cooling air-flow, and be drawn out of the fuel cell tower 800. Alternate versions may include returning the liquid from cathode and anode directly into a common volume.
When the unit 100 is determined to have an excess of water in the air/liquid separator 110, the waste-water pump 212 is turned on, pulling water from the integral air/liquid separator sump 306 (see
The present invention has now been described in accordance with several exemplary embodiments, which are intended to be illustrative in all aspects, rather than restrictive. Thus, the present invention is capable of many variations in detailed implementation, which may be derived from the description contained herein by a person of ordinary skill in the art. For example the direct methanol fuel cell tower 100 may be arranged to provide different form factors, for example it can be provided in a modular form where the mixer base 104 and air/fuel mixer box 106 are separated and placed in an adjacent manner, where the fuel and water are communicated there between using tubing or plumbing. Further, the current invention may include sensors for monitoring fluid levels in the mixer base 104 and air/fuel separator box 106, as well a sensor for determining the methanol content in the liquid mixture.
All such variations are considered to be within the scope and spirit of the present invention as defined by the following claims and their legal equivalents.
This application is cross-referenced to and claims the benefit from U.S. Provisional Patent Application 60/930556 filed May 16, 2007, which is hereby incorporated by reference.
Number | Date | Country | |
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60930556 | May 2007 | US |