Unitized electrolyzer apparatus
A unitized electrolyzer apparatus for generating hydrogen gas at high pressure. According to one embodiment, the apparatus includes a pressure-containment vessel, a water electrolyzer stack, and a water supply. The water electrolyzer stack is mounted on or in the vessel and is used to generate hydrogen gas for containment in the vessel at high pressure. The water supply is contained within the vessel, the water supply being fluidly coupled to the water electrolyzer stack to provide a cathode feeding of water to the water electrolyzer stack.
The present application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Patent Application No. 61/341,936, filed Apr. 7, 2010, the disclosure of which is incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTThe U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Grant No. DE-SC0001486 awarded by the Department of Energy.
BACKGROUND OF THE INVENTIONThe present invention relates generally to electrolyzer apparatuses used, for example, for hydrogen generation and relates more particularly to a novel such electrolyzer apparatus.
U.S. automakers have invested significant resources in the research and development of hydrogen fuel cell vehicles. However, to enable the widespread use of fuel cell vehicles, an additional major investment will be required to achieve an infrastructure for hydrogen production and delivery to fueling stations. Previous hydrogen refueling research has focused on forecourt fueling stations (1,500 kg H2/day production) and central hydrogen production facilities (>50,000 kg H2/day)—with promising results. It is apparent that, by the time that 20% of all light-duty vehicles are hydrogen-fueled, a hydrogen pipeline infrastructure will become cost-effective. However, a transition period of several years will likely be needed before such an expensive undertaking will be completed. In order to facilitate this transition, it has been recommended that high-pressure hydrogen, generated at 5,000 psi for home refueling of fuel cell vehicles, be implemented as an intermediary approach.
Some of the proposed approaches to generating hydrogen at pressures as high as the 5,000-psi pressure discussed above require the use of a mechanical hydrogen compressor. However, the present assignee has identified has certain disadvantages resulting from the use of such compressors. For example, mechanical compressors have a high capital cost, high maintenance costs, poor reliability, and are noisy. In addition, the compressed hydrogen produced by a mechanical compressor often contains small amounts of pump oil. This oil will degrade performance of fuel cells receiving the hydrogen. Most importantly, the cost of a failure in a single hydrogen compressor oil filtering system will be very high, as considerable consequential damages will be incurred in the on-board vehicle gas storage and fuel-cell systems.
One alternative to using a mechanical compressor to generate high-pressure hydrogen involves using a high-pressure proton-exchange membrane (PEM) electrolyzer, examples of which are disclosed in the following patents and published patent applications, all of which are incorporated herein by reference: U.S. Pat. No. 6,500,319, inventors LaConti et al., issued Dec. 31, 2002; U.S. Pat. No. 7,229,534, inventors LaConti et al., issued Jun. 12, 2007; U.S. Pat. No. 7,261,967, inventors LaConti et al., issued Aug. 28, 2007; U.S. Pat. No. 7,438,985, inventors LaConti et al., issued Oct. 21, 2008; U.S. Pat. No. 7,704,627, inventors LaConti et al., issued Apr. 27, 2010; and U.S. Patent Application Publication No. US 2010/0288629 A1, inventors LaConti et al., published Nov. 18, 2010. According to this approach, low-pressure, high-purity water is introduced to the anode side of an electrolytic cell. The cell then utilizes direct current to electrochemically decompose the water to produce oxygen gas, hydrogen ions, and electrons. The hydrogen ions move through the PEM to the cathode, where hydrogen gas is produced, while the electrons move through the external circuit. An excess of water is supplied to the oxygen side of the cell and is re-circulated to remove waste heat. A portion of the excess water is electro-osmotically transported across the PEM with the hydrogen ions. The oxygen and hydrogen gases are generated at the required pressure of the system. Provisions are required to separate and to recover the electrochemically transported water on the cathode via a hydrogen/water phase-separator.
One shortcoming with high-pressure PEM electrolyzers of the type described above is that it is necessary to provide reinforcement to the electrolyzer stack to enable the stack to handle the high pressures that are experienced, such reinforcements often proving to be costly.
SUMMARY OF THE INVENTIONIt is an object of the present invention to provide a novel electrolyzer apparatus.
It is another object of the present invention to provide an electrolyzer apparatus as described above that addresses at least some of the shortcomings associated with the above-described approaches to generating high-pressure hydrogen gas.
It is still another object of the present invention to provide an electrolyzer apparatus as described above that has a minimal number of components and that can be manufactured relatively inexpensively.
According to one aspect of the invention, there is provided an electrolyzer apparatus comprising (a) a pressure-containment vessel; (b) a water electrolyzer stack, said water electrolyzer stack being mounted on or in said vessel, said water electrolyzer stack generating hydrogen gas for containment in said pressure-containment vessel at high pressure; and (c) a water supply, said water supply being disposed within said pressure-containment vessel, said water supply being fluidly coupled to said water electrolyzer stack in such a way as to provide said water electrolyzer stack with water to be electrolyzed.
Additional objects, as well as aspects, features and advantages, of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention. In the description, reference is made to the accompanying drawings which form a part thereof and in which is shown by way of illustration various embodiments for practicing the invention. The embodiments will be described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural changes may be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is best defined by the appended claims.
The accompanying drawings, which are hereby incorporated into and constitute a part of this specification, illustrate various embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings wherein like reference numerals represent like parts:
The present invention is directed at a PEM-based water electrolyzer apparatus that can deliver hydrogen gas at a high pressure, such as at 5,000 psi. As a result, the present electrolyzer apparatus is well-suited for use in, for example, the home refueling of fuel cell vehicles. The electrolyzer apparatus disclosed herein provides a stationary, cost-effective approach to the generation of high-pressure hydrogen by “unitizing” a PEM-based electrolyzer stack and one or more ancillary components. This combination of components eliminates the need for bulky and costly stack parts and facilitates producing an electrolyzer apparatus that can safely operate at a balanced hydrogen pressure of 5,000 psi. In addition, the electrolyzer apparatus of the present invention also enables a realization in the reduction of major system components and in the reduction of system cost.
Referring now to
Apparatus 11 may comprise an electrolyzer stack 13. Electrolyzer stack 13, in turn, may comprise a plurality of identical PEM electrolysis cells arranged in series in a bipolar configuration.
Referring now to
Cell 15 may also comprise a pair of multi-layer metal distributor screens 29 and 31. Screen 29 may be placed in contact with the outer face of cathode 21 and may be used to define a fluid cavity through which water (serving as a reactant and as a coolant) may be fed to cathode 21 and in which hydrogen gas generated at cathode 21 may be collected. Screen 31 may be placed in contact with the outer face of anode 19 and may be used to define a fluid cavity in which molecular oxygen generated at anode 19 may be collected.
It is to be understood that screen 29 and/or screen 31 may be replaced with an electrically-conductive, resiliently-compressible, porous pad of the type disclosed in one or more of U.S. Pat. No. 6,500,319, 7,229,534, 7,261,967, 7,438,985, or 7,704,627, or in U.S. Patent Application Publication No. US 2010/0288629 A1.
Cell 15 may further comprise a pair of separators 33 and 35. Separators 33 and 35 may be made of a metal foil, such as titanium foil having a thickness of about 0.005 inch. Separator 33 may be positioned against the outer face of screen 29, and separator 35 may be positioned against the outer face of screen 31. Separators 33 and 35 may serve to axially contain the fluids within screens 29 and 31. In addition, separators 33 and 35 may serve to electrically couple cell 15 to its neighboring cells.
Referring back now to
Apparatus 11 may further comprise an electrical feed 45 connected to electrolyzer stack 13. (As seen in
Apparatus 11 may further comprise a combination water storage tank and H2/H20 separator 51. Tank/separator 51 may be mounted within vessel 41, preferably at a height above electrolyzer stack 13. A fluid conduit 53 may be disposed within vessel 41 and may be connected at one end to a cathode feed port 54 on stack 13 and may be connected at the opposite end to the bottom of tank/separator 51 to conduct liquid water, by gravity, from tank/separator 51 to stack 13. A fluid conduit 55 may be disposed within vessel 41 and may be connected at one end to a cathode output 56 on stack 13 and may be connected at the opposite end to tank/separator 51 to conduct hydrogen gas, liquid water and water vapor from stack 13 to tank/separator 51.
Apparatus 11 may further comprise a cooling coil 61. Cooling coil 61 may be disposed within vessel 41, for example, along the interior wall of vessel 41, preferably at a height above tank/separator 51. A fluid conduit 63 may be disposed within vessel 41 and may be connected at one end to the top of tank/separator 51 and may be connected at the opposite end to an inlet end of coil 61 to conduct hydrogen gas and water vapor from tank/separator 51 to cooling coil 61. As these gases circulate through coil 61, at least some of the water vapor contained therein may be condensed to liquid water.
Apparatus 11 may further comprise a second separator 65. Separator 65 may be disposed within vessel 41, preferably at a height below cooling coil 61 and above tank/separator 51. A fluid conduit 66 may be disposed within vessel 41 and may be connected at one end to the outlet end of coil 61 and may be connected at the opposite end at or near the top of second separator 65 to conduct the cooled fluids from cooling coil 61 to separator 65. In separator 65, any condensed water present in the cooled fluids may be separated, by gravity, from the hydrogen gas and remaining water vapor. The thus-separated water in separator 65 may then be conducted from second separator 65 to tank/separator 51 through gravity using a fluid conduit 67, which may be connected at one end to the bottom of second separator 65 and which may be connected at the opposite end to the top of tank/separator 51.
Apparatus 11 may further comprise a desiccant dryer 71 disposed within vessel 41. A fluid conduit 73 may be disposed within vessel 41 and may be connected at one end to the top of separator 65 and at the opposite end to top of dryer 71. Dryer 71 may be used to further remove water from the hydrogen gas.
Apparatus 11 may further comprise a hydrogen back pressure valve 81 mounted in an outlet 83 in vessel 41. A fluid conduit 85 may be disposed within vessel 41 and may be connected at one end to the bottom of dryer 71 and at the opposite end to valve 81. Valve 81 may be used to maintain a hydrogen gas pressure of 5,000 psi.
Apparatus 11 may further comprise an oxygen back pressure valve 87 mounted in an outlet 89 in vessel 41. A fluid conduit 90 may be disposed within vessel 41 and may be connected at one end to the oxygen outlet port 90-1 of electrolyzer stack 13 and at the opposite end to valve 87.
Apparatus 11 may further comprise a water feed 91, which may be, for example, a residential water supply. Apparatus 11 may further comprise a water deionization treatment device 93, which may be fluidly connected to the output of water feed 91 using a fluid conduit 95. The output of water deionization treatment device 93 may be fluidly connected to tank/separator 51 using a fluid conduit 97, which may be inserted through a water inlet 99 provided in vessel 41.
Although not shown, the unoccupied space in vessel 41 may be filled with an inert liquid, such as water, silicone oil, or a fluorochemical liquid, or an inert gas, such as nitrogen gas. The use of such an inert fluid would minimize the risks associated with a leak of gas from the electrolyzer stack into the vessel, as it minimizes the risk of producing a flammable or explosive gas mixture. The inert gas could be derived from a compressed gas cylinder, an associated inert-gas generator, such as pressure swing adsorption, an electrochemical oxygen depletion system, or other suitable system. Means could be provided (through a bladder of other means) to control the pressure of the inert liquid to closely follow the pressure internal to the electrolyzer stack, as the stack internal pressure varied from its startup conditions, through full operation at 5,000 psi, through venting and reaching a full-off, shutdown condition.
Also, although not shown, electrolyzer stack 13 may be fitted with cooling fins (integral extensions of the cell separators). Through this means, the waste heat byproduct of the electrochemical reaction may be dissipated from the stack, through the cooling fins, and to the liquid within vessel 41.
In use, water from tank/separator 51 is fed to the cathode side of electrolyzer stack 13, and a current is applied to electrolyzer stack 13. Through electrolysis, hydrogen gas is generated at the cathode side of electrolyzer stack 13, and oxygen gas is generated at the anode side of electrolyzer stack 13. Hydrogen gas and excess water leave electrolyzer stack 13 and are conducted to tank/separator 51, where the various liquids and gases present are separated by gravity. The thus-separated gases are then conducted from tank/separator 51 to cooling coil 61. As the gases pass through cooling coil 61, they are cooled, and some of the water vapor condenses to liquid water. The fluids emerging from cooling coil 61 are then conducted to separator 65, where the various liquid and gases present are separated by gravity. The liquid water in separator 65 is returned to the tank/separator 51, and the gases in separator 65 are conducted to the desiccant dryer 71. As the gases pass through dryer 71, water vapor is removed therefrom, and the hydrogen gas emerging from dryer 71 has a very low dewpoint. The hydrogen gas is then conducted to outlet 83, where back-pressure valve 81 ensures that the hydrogen gas is maintained at the desired pressure.
As can be appreciated, one benefit of the above arrangement is that there is no need for a high-pressure mechanical hydrogen compressor, along with its ancillary equipment (oil cooling system, oil mist eliminator, oil vapor filtering system, interstage cooling system, etc.) It should also be noted that an oxygen/water phase-separator is not needed in this cathode-fed design as product oxygen can be reduced from its high generation pressure and safely vented from the system.
The above-described electrolyzer apparatus may be a complete factory-packaged unit, so that only minimal site preparation and installation work (water and electricity service, cement foundation pad) will be required. As no large, noisy compressor subsystem is used, these commercial high-pressure electrolyzer systems possess significantly lower environmental impact on their surroundings. Operation is completely automatic, with a computerized control system providing load-following capability, safety interlocks, as well as remote control and monitoring. User maintenance involves periodic replacement of the deionizer bed material and filter, with limited major maintenance expected for the 10-year life of the electrolyzer system.
Referring now to
Electrolyzer apparatus 101 may comprise a vessel 103. Vessel 103, which may be made of a highly pressure-resistant, chemically-inert material, such as carbon steel or the like, is shaped to include a generally cylindrical wall 103-1, a substantially closed bottom end 103-2, and an open top end 103-3.
Electrolyzer apparatus 101 may also comprise an electrolyzer stack 105, which may be identical in size, shape and structure to stack 13 of apparatus 11. Vessel 103 may be appropriately dimensioned so that electrolyzer stack 105 may be partially inserted into the interior of vessel 103, with the top portion of stack 105 securely seated on and closing off open top end 103-3 of vessel 103. As can be seen, because the lower portion of stack 105 has an outer diameter that is less than the inner diameter of vessel 103, a space 107 is provided therebetween.
Electrolyzer apparatus 101 may further comprise a drain port 111 located at bottom end 103-2 of vessel 103. Drain port 111 may be fluidly connected to the cathode input port 113 of electrolyzer stack 105 through a fluid conduit 115. A fluid pump 117, the operation of which may be controlled by a control unit 119, may be used to pump supply water from the bottom interior of vessel 103 to cathode input port 113.
Electrolyzer apparatus 101 may further comprise a plurality of water level sensors 121, 123 and 125, each of which may be mounted in cylindrical wall 103-1 of vessel 103 and each of which may be electrically coupled to a control unit 119. Water level sensor 121 may be positioned a short distance below the output end of cathode output port 129 of electrolyzer stack 105 and may be used to signal control unit 119 to discontinue inputting water into vessel 103, for example, through inlet 130 from an external water feed 131. Water level sensor 123 may be positioned a short distance below sensor 121 and may be used to signal control unit 119 to input water into vessel 103 through inlet 130 when the water level has dropped too low. Water level sensor 125 may be positioned a short distance below sensor 123 and may be used to signal control unit 119 to shut down further electrolysis of electrolyzer stack 105 as the water level has dropped below a desired minimal level. Although not shown in this embodiment, an ultrasonic level sensor may be used instead of the above-described mechanical sensors.
Electrolyzer apparatus 101 may further comprise a hydrogen outlet port 141, which may be mounted in wall 103-1 of vessel 103, the interior end of port 141 being positioned within space 107. A back-pressure valve 145 may be coupled to the exterior end of port 141 to maintain a desired hydrogen gas pressure within vessel 103. A gas dryer 147 for drying the hydrogen gas may be fluidly coupled to the output end of valve 145.
Electrolyzer apparatus 101 may further comprise a back-pressure valve 151 coupled to the outlet end of anode output port 152 of electrolyzer stack 105, valve 151 being used to maintain the generated oxygen gas at a desired pressure. Control unit 119 may be coupled to back-pressure valves 145 and 151.
In use, a quantity of water is inputted into vessel 103 through inlet 130 using water feed 131 until the water level rises to sensor 121. This water level is then maintained as water is pumped, using pump 117, from port 111 to cathode input port 113 of electrolyzer stack 105. As electrolysis of this water is performed by stack 105, hydrogen gas and water are emitted from cathode output port 129, and oxygen gas is emitted from anode output port 152. The liquid water emitted from cathode output port 129 falls to the bottom of vessel 103 with the remaining stored water supply, and the gases emitted from cathode output port 129 rise to space 107, where they exit through port 141. Valve 145 serves to maintain a desired hydrogen gas pressure, and valve 151 serves to maintain a desired oxygen gas pressure. When the hydrogen pressure exceeds the threshold maintained by valve 151, hydrogen gas passes through valve 145 to dryer 147.
The electrolyzer apparatus of the present invention may be designed for on-demand operation. A small 2- or 3-kW, electrolyzer stack will be the criterion for the system design, providing a fill rate of 0.5 kg of hydrogen over a 5- to 12-hour period (the refueling rate will depend on the stack operating current density). This will provide 30 miles of driving range based on current fuel cell vehicle fuel economy estimates of 60 miles/kg-H2. In addition, the refueling appliance can be designed with a modular compartment in which larger, as well as additional electrolyzer stacks, may be added to increase the rate of production, thus providing the ability to increase the refueling rate or the ability to supply hydrogen in a multi-car dwelling.
A system efficiency rating, defined as system electrical input per unit of hydrogen gas output (kWhe/kg-H2) will be estimated based on the proposed design concept. State-of-the-art PEM electrolyzers use NAFION 117 or 115 membranes and typically operate at 60° C., with an input rating of 49.8 kWh/kg-H2 (HHV efficiency of 79%). Current membrane technology of the present assignee has shown 43.5 kWhe/kg (HHV efficiency of 91%). In addition, the overall system efficiency will also be increased through design of higher efficiency electronics and careful selection of process components for efficiency over the required operating life.
A number of benefits, advantages and features of the present invention are discussed above. Additional such benefits, advantages and features are identified below.
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- Pressure dome enclosing electrolyzer—enables use of low-cost low-pressure stack design
- Primarily liquid-filled pressure dome—a non-flammable, incompressible material (water) provides isolation between high-pressure hydrogen and high-pressure oxygen
- No water pump—city water pressure provides direct feed during periods of non-electrolysis
- No electrolyzer reactant water circulation pump—simple thermosiphon design, with no moving parts
- No radiator loop, eliminating a pump, cooling fan, piping, etc.—direct liquid-cooled stack design with integral cooling fins
- Passive cooling used throughout—for removing heat from the finned electrolyzer stack to the fluid in the pressure dome, for removing heat from the fluid in the pressure dome to the ambient environment, and for removing heat from the moist hydrogen exiting the primary hydrogen/water phase separator to the ambient environment.
- No electrolyzer system hydrogen storage tank—overnight direct fill of homeowners' vehicle tank
- Only uses a single desiccant dryer column—off-line regeneration during periods of non-electrolysis
- No supplemental desiccant dryer column regeneration gas supply needed—uses less than 0.3% of the design daily hydrogen production.
The embodiments of the present invention described above are intended to be merely exemplary and those skilled in the art shall be able to make numerous variations and modifications to it without departing from the spirit of the present invention. All such variations and modifications are intended to be within the scope of the present invention as defined in the appended claims.
Claims
1. An electrolyzer apparatus comprising:
- (a) a pressure-containment vessel;
- (b) a water electrolyzer stack, said water electrolyzer stack being mounted on or in said vessel, said water electrolyzer stack generating hydrogen gas for containment in said pressure-containment vessel at high pressure; and
- (c) a water supply, said water supply being disposed within said pressure-containment vessel, said water supply being fluidly coupled to said water electrolyzer stack in such a way as to provide said water electrolyzer stack with water to be electrolyzed.
2. The electrolyzer apparatus as claimed in claim 1 wherein said water electrolyzer stack comprises a plurality of proton exchange membrane electrolysis cells arranged in series in a bipolar configuration.
3. The electrolyzer apparatus as claimed in claim 2 wherein each of the proton exchange membrane electrolysis cells has an anode side and a cathode side and wherein said water supply is fluidly coupled to said water electrolyzer to feed water to the cathode side of the electrolysis cells.
4. The electrolyzer apparatus as claimed in claim 1 wherein the water supply comprises a combination separator/water tank disposed within said pressure-containment vessel, said combination separator/water tank holding a quantity of water for supply to the water electrolyzer stack.
5. The electrolyzer apparatus as claimed in claim 4 wherein the water electrolyzer comprises a cathode output port and wherein said combination separator/water tank is fluidly coupled to the cathode output port of the water electrolyzer stack.
6. The electrolyzer apparatus as claimed in claim 5 further comprising a cooling coil disposed within the pressure-containment vessel, the cooling coil having an input end fluidly coupled to the combination separator/water tank so as to receive gas disposed within the combination separator/water tank.
7. The electrolyzer apparatus as claimed in claim 5 further comprising a second separator disposed within the pressure-containment vessel, said second separator being fluidly coupled to an outlet end of the cooling coil to separate fluids received from said cooling coil.
8. The electrolyzer apparatus as claimed in claim 7 further comprising a desiccant dryer disposed within the pressure-containment vessel, the desiccant dryer being fluidly coupled to the second separator to receive gas disposed within said second separator.
9. The electrolyzer apparatus as claimed in claim 1 wherein the water supply comprises a quantity of water in direct contact with the pressure-containment vessel.
10. The electrolyzer apparatus as claimed in claim 9 further comprising means fluidly interconnecting said water supply and said water electrolyzer stack.
11. The electrolyzer apparatus as claimed in claim 10 wherein said fluidly interconnecting means comprise a pump.
12. The electrolyzer apparatus as claimed in claim 11 further comprising at least one water level sensor for sensing the water level within the pressure-containment vessel.
Type: Application
Filed: Apr 7, 2011
Publication Date: Nov 3, 2011
Inventors: Timothy J. Norman (Acton, MA), Monjid Hamdan (Worcester, MA), Keith D. Patch (Lexington, MA)
Application Number: 13/066,246
International Classification: C25B 1/10 (20060101); C25B 9/18 (20060101); C25B 9/08 (20060101);
