Patent Application
20080296167
Under 35 U.S.C. 119, the present application claims the benefit of the earlier filing date and the right of priority to Canadian Patent Application Serial No. 2,590,493, filed May 30, 2007, the disclosure of which is hereby incorporated by reference for any and all purposes.
The present invention relates generally to electrolysis systems and, more particularly, to a high efficiency electrolysis system and methods of using same.
Fossil fuels, in particular oil, coal and natural gas, represent the primary sources of energy in today's world. Unfortunately in a world of rapidly increasing energy needs, dependence on any energy source of finite size and limited regional availability has dire consequences for the world's economy. In particular, as a country's need for energy increases, so does its vulnerability to disruption in the supply of that energy. Additionally, as fossil fuels are the largest single source of carbon dioxide emissions, a greenhouse gas, continued reliance on such fuels can be expected to lead to continued global warming. Accordingly it is imperative that alternative, clean and renewable energy sources be developed that can replace fossil fuels.
Hydrogen-based fuel is currently one of the leading contenders to replace fossil fuel. However in order to successfully transition from oil-based and coal-based fuels to a hydrogen-based fuel, significant improvements must be made in terms of hydrogen production, hydrogen storage and distribution, and hydrogen engines. Clearly the state of the art in each of these developmental areas impacts the other areas. For example, if a method of inexpensively producing hydrogen in small production plants can be developed, production plants can be situated close to the end user, thus avoiding the need for extremely complex and costly distribution systems.
Although a number of techniques can be used to produce hydrogen, the primary technique is by steam reforming natural gas. In this process thermal energy is used to react natural gas with steam, creating hydrogen and carbon dioxide. Although this process is well developed, due to its reliance on fossil fuels and the release of carbon dioxide during production, it does not alleviate the need for fossil fuels nor does it lower the environmental impact of its use over that of traditional fossil fuels. Other, less developed hydrogen producing techniques include (i) biomass fermentation in which methane fermentation of high moisture content biomass creates fuel gas, a small portion of which is hydrogen; (ii) biological water splitting in which certain photosynthetic microbes produce hydrogen from water during their metabolic activities; (iii) photoelectrochemical processes using either soluble metal complexes as a catalyst or semiconducting electrodes in a photochemical cell; (iv) thermochemical water splitting using chemicals such as bromine or iodine, assisted by heat, to split water molecules; (v) thermolysis in which concentrated solar energy is used to generate temperatures high enough to split methane into hydrogen and carbon; and (vi) electrolysis.
Electrolysis as a means of producing hydrogen has been known and used for over 80 years. In general, electrolysis of water uses two electrodes separated by an ion conducting electrolyte. During the process hydrogen is produced at the cathode and oxygen is produced at the anode, the two reaction areas separated by an ion conducting diaphragm. Electricity is required to drive the process. An alternative to conventional electrolysis is high temperature electrolysis, also known as steam electrolysis. This process uses heat, for example produced by a solar concentrator, as a portion of the energy required to cause the needed reaction. Although lowering the electrical consumption of the process is desirable, this process has proven difficult to implement due to the tendency of the hydrogen and oxygen to recombine at the technique's high operating temperatures.
Although a variety of improvements have been devised to improve upon the efficiency of the electrolytic hydrogen production system, to date none of them have been able to make the process efficient enough to make hydrogen-based fuel a viable alternative to fossil fuels. Accordingly, what is needed in the art is a means for efficiently producing hydrogen, the means preferably being small enough to minimize the need for an overly complex distribution system. The present invention provides such a system and method of use.
The present invention provides a method and apparatus for achieving high output efficiency from an electrolysis system using a plurality of electrolysis cells all located within a single electrolysis tank. Each individual electrolysis cell includes a membrane which separates the portion of the electrolysis tank containing that electrolysis cell into two regions. In at least one embodiment, the system is further comprised of at least one pair of high voltage electrodes including at least one high voltage anode and at least one high voltage cathode and positioned within the electrolysis tank such that all of the individual electrolysis cells are interposed between the at least one high voltage anode and the at least one high voltage cathode, wherein each electrolysis cell is further comprised of at least one pair of low voltage electrodes of a first type and at least one pair of low voltage electrodes of a second type. In at least one other embodiment, the system is further comprised of at least one pair of high voltage electrodes including at least one high voltage anode and at least one high voltage cathode and positioned within the electrolysis tank such that all of the individual electrolysis cells are interposed between the at least one high voltage anode and the at least one high voltage cathode, wherein each electrolysis cell is further comprised of at least one pair of low voltage electrodes. In at least one other embodiment, each electrolysis cell is further comprised of at least one pair of low voltage electrodes of a first type, at least one pair of low voltage electrodes of a second type and at least one pair of high voltage electrodes. In at least one other embodiment, each electrolysis cell is further comprised of at least one pair of low voltage electrodes and at least one pair of high voltage electrodes.
The high voltage electrodes are connected to a high voltage source while the low voltage electrodes are connected to either a single low voltage source or to multiple low voltage sources. In at least one embodiment, the low voltage electrodes of each electrolysis cell are connected to a different low voltage source. In at least one embodiment in which each electrolysis cell includes two types of low voltage electrodes, one low voltage source is connected to one of the types of low voltage electrodes while a second low voltage source is connected to the other type of low voltage electrodes.
The power supplied by both the low and high voltage sources is simultaneously pulsed, preferably at a frequency between 50 Hz and 1 MHz, and more preferably at a frequency of between 100 Hz and 10 kHz. The pulse duration is preferably between 0.01 and 75 percent of the time period defined by the frequency, and more preferably between 1 and 50 percent of the time period defined by the frequency. Preferably the ratio of the high voltage to the low voltage is at least 5:1, more preferably within the range of 5:1 to 100:1, still more preferably within the range of 5:1 to 33:1, and still more preferably within the range of 5:1 to 20:1. Preferably the low voltage is between 3 and 1500 volts, more preferably between 12 and 750 volts. Preferably the high voltage is between 50 volts and 50 kilovolts, more preferably between 100 volts and 5 kilovolts.
Preferably the liquid within the tank is comprised of one or more of; water, deuterated water, tritiated water, semiheavy water, heavy oxygen water, and/or any other water containing an isotope of either hydrogen or oxygen. Preferably the liquid within the electrolysis tank includes an electrolyte with a concentration in the range of 0.05 to 10 percent by weight, more preferably in the range of 0.05 to 2.0 percent by weight, and still more preferably in the range of 0.1 to 0.5 percent by weight.
The electrodes can be fabricated from a variety of materials, although preferably the material for each electrode is selected from the group consisting of steel, nickel, copper, iron, stainless steel, cobalt, manganese, zinc, titanium, platinum, palladium, aluminum, lithium, magnesium, boron, carbon, graphite, carbon-graphite, metal hydrides and alloys thereof. If the electrolysis cells include two types of low voltage electrodes, preferably the two types are comprised of different materials.
In at least one embodiment, the electrolysis system is cooled. Cooling is preferably achieved by thermally coupling at least a portion of the electrolysis system to a portion of a conduit containing a heat transfer medium. The conduit can surround the electrolysis tank, be integrated within the walls of the electrolysis tank, or be contained within the electrolysis tank.
In at least one embodiment, the electrolysis system also contains a system controller. The system controller can be used to perform system optimization, either during an initial optimization period or repeatedly throughout system operation.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.
A typical electrolysis system used to decompose water into hydrogen and oxygen gases utilizes relatively high concentrations of electrolyte. The present invention, however, has been found to work best with relatively low electrolyte concentrations, thereby maintaining a relatively high initial water resistivity. Preferably the water resistivity prior to the addition of an electrolyte is on the order of 1 to 28 megohms. Preferably the concentration of electrolyte is in the range of 0.05 percent to 10 percent by weight, more preferably the concentration of electrolyte is in the range of 0.05 percent to 2.0 percent by weight, and still more preferably the concentration of electrolyte is in the range of 0.1 percent to 0.5 percent by weight.
Tank 101 includes multiple electrolysis cells, an electrolysis cell defined herein as having at least one pair of low voltage electrodes of different polarities separated by a membrane. Accordingly the embodiment illustrated in
Membranes 105A-105C permit ion/electron exchange between the two regions of each cell while keeping separate the oxygen and hydrogen bubbles produced during electrolysis. Maintaining separate hydrogen and oxygen gas regions is important not only as a means of allowing the collection of pure hydrogen gas and pure oxygen gas, but also as a means of minimizing the risk of explosions due to the inadvertent recombination of the two gases. Accordingly similar polarity electrodes are grouped together with the membranes keeping groups separate. Thus in the exemplary embodiment shown in
As noted herein, the present system is capable of generating considerable heat. Accordingly, system components such as the electrolysis tank (e.g., tank 101) and the membranes (e.g., membranes 105A-105C) that are expected to be subjected to the heat generated by the system must be fabricated from suitable materials and designed to indefinitely accommodate the intended operating temperatures as well as the internal tank pressure. For example, in at least one preferred embodiment the system is designed to operate at a temperature of approximately 90° C. at standard pressure. In an alternate exemplary embodiment, the system is designed to operate at elevated temperatures (e.g., 100° C. to 150° C.) and at sufficient pressure to prevent boiling of liquid 103. In yet another alternate exemplary embodiment, the system is designed to operate at even higher temperatures (e.g., 200° C. to 350° C.) and higher pressures (e.g., sufficient to prevent boiling). Accordingly, it will be understood that the choice of materials (e.g., for tank 101 and membranes 105A-105C) and the design of the system (e.g., tank wall thicknesses, fittings, etc.) will vary, depending upon the intended system operational parameters, primarily temperature and pressure.
Other standard features of the electrolysis tank are gas outlets for the hydrogen and oxygen gases. In the exemplary embodiment shown in
It is understood that a system utilizing electrolysis system 100 to produce hydrogen will also include means for either storing the produced gases, e.g., hydrogen storage tanks, or means for delivering the produced gas to the point of consumption, e.g., pipes and valves, as well as flow gauges, pressure gauges, gas compressors, gas driers, gas purifiers, water purifiers, water pumps, etc.
In at least one preferred embodiment of the electrolysis system of the invention, and as illustrated in the exemplary embodiment of
In the embodiment illustrated in
In
Preferably and as shown, the faces of the individual electrodes of each pair of electrodes are parallel to one another; i.e., the face of electrode 115A is parallel to the face of electrode 116A, the face of electrode 117A is parallel to the face of electrode 118A, the face of electrode 119A is parallel to the face of electrode 120A, etc. Additionally, and as shown, in at least one preferred embodiment the anodes and cathodes of each pair of low voltage electrodes of the first type, and of each pair of low voltage electrodes of the second type, are not positioned directly across from one another. Thus low voltage anode 115A of the first type is opposite low voltage cathode 118A of the second type, low voltage anode 117A of the second type is opposite low voltage cathode 116A of the first type, etc. Although not shown, it should be understood that the invention can also operate with electrodes of the same type being opposite one another, e.g., electrode 115A being opposite 116A, etc.
Although electrode pairs 115A-C/116A-C and 117A-C/118A-C are both low voltage electrodes and are preferably coupled to the same voltage supply, these electrode pairs are quite different in terms of composition and in some embodiments, also in terms of size. In one preferred embodiment, electrodes 115A-C/116A-C are comprised of titanium while electrodes 117A-C/118A-C are comprised of steel. It should be appreciated, however, that other materials can be used as long as electrodes 115A-C/116A-C are made up of a different material from electrodes 117A-C/118A-C. In addition to titanium and steel, other exemplary materials that can be used for electrodes 115A-C, 116A-C, 117A-C, and 118A-C include, but are not limited to, copper, iron, stainless steel, cobalt, manganese, zinc, nickel, platinum, palladium, aluminum, lithium, magnesium, boron, carbon, graphite, carbon-graphite, metal hydrides and alloys of these materials. As used in the present specification, a metal hydride refers to any compound of a metal and hydrogen or an isotope of hydrogen (e.g., deuterium, tritium).
Preferably the faces of electrodes 115A and 117A are coplanar as are the faces of electrodes 116A and 118A, electrodes 115B and 117B, electrodes 116B and 118B, electrodes 115C and 117C, and electrodes 116C and 118C. Also preferably, the combined area made up by the faces of the two side-by-side electrodes of different types (e.g., 115A and 117A, 116A and 118A, 115B and 117B, etc.) cover a large percentage of the cross-sectional area of tank 101. In an exemplary embodiment, the combined area of the faces of each pair of side-by-side electrodes of different type cover between 70 percent and 90 percent of the cross-sectional area of the electrolysis tank. Although not required, typically the electrodes of the second type, e.g., electrodes 117A-117C and 118A-118C, have a much smaller surface area than that of the electrodes of the first type, e.g., electrodes 115A-115C and 116A-116C, for example on the order of a sixth of the area. Also preferably, the height of electrodes 115A-C, 116A-C, 117A-C, and 118A-C are close to the liquid level of liquid 103 within tank 101. Although the separation distance between electrode pairs is dependent upon a variety of factors (e.g., tank size, voltage/current, etc.), in at least one preferred embodiment the separation of the plane containing electrodes 115A and 117A and the plane containing electrodes 116A and 118A (and similarly, the plane containing 115B and 117B and the plane containing electrodes 116B and 118B; the plane containing 115C and 117C and the plane containing electrodes 116C and 118C) is between 0.2 millimeters and 15 centimeters.
In the embodiment illustrated in
Preferably the ratio of the high voltage to the low voltage applied to the high voltage and low voltage electrodes, respectively, is at least 5:1, more preferably the ratio is between 5:1 and 100:1, still more preferably the ratio is between 5:1 and 33:1, and even still more preferably the ratio is between 5:1 and 20:1. Preferably the high voltage generated by source 123 is within the range of 50 volts to 50 kilovolts, and more preferably within the range of 100 volts to 5 kilovolts. Preferably the low voltage generated by source 121 is within the range of 3 volts to 1500 volts, and more preferably within the range of 12 volts to 750 volts.
Rather than continually apply voltage to the electrodes, sources 121 and 123 are pulsed, preferably at a frequency between 50 Hz and 1 MHz, and more preferably at a frequency of between 100 Hz and 10 kHz. The pulse width (i.e., pulse duration) is preferably between 0.01 and 75 percent of the time period defined by the frequency, and more preferably between 1 and 50 percent of the time period defined by the frequency. Thus, for example, for a frequency of 150 Hz, the pulse duration is preferably in the range of 0.67 microseconds to 5 milliseconds, and more preferably in the range of 66.7 microseconds to 3.3 milliseconds. Alternately, for example, for a frequency of 1 kHz, the pulse duration is preferably in the range of 0.1 microseconds to 0.75 milliseconds, and more preferably in the range of 10 microseconds to 0.5 milliseconds. Additionally, the voltage pulses are applied simultaneously to the high voltage and low voltage electrodes via sources 123 and 121, respectively. In other words, the voltage pulses applied to high voltage electrodes 119A-C/120A-C coincide with the pulses applied to low voltage electrodes 115A-C/116A-C/117A-C/118A-C. Although voltage sources 121 and 123 can include internal means for pulsing the respective outputs from each source, preferably an external pulse generator 125 controls a pair of switches, i.e., low voltage switch 127 and high voltage switch 129 which, in turn, control the output of voltage sources 121 and 123 as shown, and as described above.
As previously noted, the electrolysis process of the invention generates considerable heat. It will be appreciated that if the system is allowed to become too hot for a given pressure, the liquid within the tank will begin to boil. Additionally, various system components may be susceptible to heat damage. Although the system can be turned off and allowed to cool when the temperature exceeds a preset value, this is not a preferred approach due to the inherent inefficiency of stopping the process, allowing the system to cool, and then restarting the system. Accordingly in the preferred embodiments of the invention the system includes means to actively cool the system to within an acceptable temperature range. For example, in at least one preferred embodiment the cooling system does not allow the temperature to exceed 90° C. Although it will be appreciated that the invention is not limited to a specific type of cooling system or a specific implementation of the cooling system, in at least one embodiment the electrolysis tank is surrounded by a coolant conduit 131, portions of which are shown in
As will be appreciated by those of skill in the art, there are numerous minor variations of the system described above that will function in accordance with the invention. For example, system 200 shown in
In addition to a variety of cell configurations, as previously noted the invention can utilize differently sized/shaped tanks, various water/electrolyte solutions, a range of high and low voltages, a range of pulse frequencies and a variety of different pulse widths.
Although the use of two different types of low voltage electrodes as previously described is preferred, the multi-cell configuration of the invention can also be used to improve the performance of electrolysis systems that use a single type of low voltage electrode. For example,
It will be appreciated that as most of the requirements placed on the electrolysis system are the same regardless of whether the system uses one type of low voltage electrode or two, a multi-cell system can be designed which can easily be reconfigured from one type of low voltage electrode to two types, or vice versa. In particular, both electrolysis system configurations have the same requirements regarding electrode size and positioning, applied high voltage, applied low voltage, frequency, pulse duration, electrolysis liquid, electrolyte, membrane composition, and the use of an active cooling system (e.g., coolant conduits 131).
It will be appreciated that the supply electronics (i.e., low/high voltage supplies, low/high voltage switches, pulse generator) shown in
It should be understood that the electrolysis system of the present invention can be operated in a number of modes, the primary differences between modes being the degree of process optimization used during operation. For example,
Once set-up is complete, electrolysis is initiated (step 1109). During the electrolysis process (step 1111), and as previously noted, the water is heated by the process itself. Eventually, when operation is no longer desirable, for example when the rate of hydrogen production drops below a user preset level, the electrolysis process is suspended (step 1113). Typically prior to further operation the water is removed from the tank (step 1115) and the tank is refilled (step 1117). Prior to refilling the tank, a series of optional steps can be performed. For example, the tank can be washed out (optional step 1119) and the electrodes can be cleaned, for example to remove oxides, by washing the electrodes with diluted acids (optional step 1121). Spent, or used up, electrodes can also be replaced prior to refilling (optional step 1123). After cleaning the system and/or replacing electrodes as deemed necessary, and refilling the system, the system is ready to reinitiate the electrolysis process.
The above sequence of processing steps works best once the operational parameters have been optimized for a specific system configuration since the system configuration will impact the efficiency of the process (e.g., rate of hydrogen output). Exemplary system configuration parameters that affect the optimal electrolysis settings include tank size, quantity of water, type and/or quality of water, electrolyte composition, electrolyte concentration, electrode size, electrode composition, electrode shape, electrode configuration, electrode separation, cell number, cell separation, initial water temperature, low voltage setting, high voltage setting, pulse frequency and pulse duration.
After the initial set-up is completed, electrolysis is initiated (step 1211) and system output is monitored (step 1213), for example hydrogen output flow rate. Although system optimization can begin immediately, preferably the system is allowed to run for an initial period of time (step 1215) prior to optimization. The initial period of operation can be based on achieving a predetermined output, for example a specific level of hydrogen flow, or achieving a steady state output (e.g., steady state hydrogen flow rate). Alternately the initial period of time can simply be a predetermined time period, for example 6 hours.
After the initial time period is exceeded, the system output (e.g., hydrogen flow rate) is monitored (step 1217) while optimizing one or more of the operational parameters. Although the order of parameter optimization is not critical, in at least one preferred embodiment the first parameter to be optimized is pulse duration (step 1219). Then the pulse frequency is optimized (step 1220), followed by optimization of the low voltage (step 1221) and the high voltage (step 1222). In this embodiment after optimization is complete the electrolysis process is allowed to continue (step 1223) without further optimization until the process is halted, step 1225, for example due to the rate of hydrogen production dropping below a user preset level. In another, and preferred, alternative approach illustrated in
Note that the optimization processes described relative to
The optimization process described relative to
As will be understood by those familiar with the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention which is set forth in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2,590,493 | May 2007 | CA | national |
