HYDROGEN GENERATION SYSTEMS

Abstract

Systems and methods are provided for hydrogen generation utilizing two or more liquid fuel components, using a fuel delivery system comprising a single pump. Advantageously, a single reversible cycle pump is used to deliver two or more fuel components of a fuel mixture in desired proportions to a mixing zone, reaction zone, or reaction chamber of a hydrogen generation system, while reducing the number of active elements required for fuel delivery and flow control of multiple fuel components. Alternatively, a unidirectional single or duel feed pump co-operable with flow control means comprising a valve provides for delivering first and second fuel components in desired proportions. Control of the pump speed, and duty cycle of the pump in continuous or pulsed modes, provides for delivery of first and second fuel components in desired proportions, to control hydrogen generation, and to provide for dilution, mixing, and flush cycles, using a single pump. A control system provides for control of the pump and/or valve, responsive to external or system conditions.

Description

TECHNICAL FIELD

This invention relates to systems and methods for generating hydrogen gas from borohydride compounds and reformable fuels. More particularly, this invention relates to systems and methods for hydrogen generation utilizing two or more liquid fuel components.

BACKGROUND OF THE INVENTION

Fuel cell power systems have an advantage over batteries in that they can be readily refuelable, and therefore a combination of a “replaceable” fuel cartridge and a “permanent” module can allow extended runtime operations without the need for grid electricity for recharging.

Although hydrogen is the fuel of choice for fuel cells, widespread use is complicated by the difficulties in storing the gaseous hydrogen. Many hydrogen carriers, including hydrocarbons, metal hydrides, and chemical hydrides are being considered as hydrogen storage and supply systems for generation of hydrogen on demand, e.g., by reformation from hydrocarbons, desorption from metal hydrides, or catalyzed hydrolysis from metal hydrides and water. Preferably the fuel mixture has a high gravimetric energy density, and controllable hydrogen generation rate, i.e., flow rate and pressure may be controlled to meet demands of a fuel cell.

Reformable fuels, which are typically defined as any substantially liquid or flowable fuel material that can be converted to hydrogen via a chemical reaction known as reformation, including for example hydrocarbons, and chemical hydrides, produce hydrogen and other gaseous and non-gaseous products. For hydrocarbons, the non-hydrogen by-products comprise carbon oxides, e.g., CO₂ and CO, and potentially other gaseous products. The resulting hydrogen rich gaseous product stream is typically sent through a purification stream before being sent to, e.g., a fuel cell unit. Hydrocarbon fuels useful for fuel cartridge systems include, for example, methanol, ethanol, methane, propane, butane, gasoline, and diesel fuel. As an example, methanol is a preferred fuel which reacts with water to form hydrogen and carbon dioxide.

CH₃OH+H₂0→3H₂+CO₂  Equation 1

One of the more promising systems for hydrogen storage and generation utilizes borohydride compounds as hydrogen storage media. Such compounds react with water to produce hydrogen gas and a borate in accordance with the following simplified:

MBH₄+2H₂O→MBO₂+4H₂+300 kJ  Equation 2

where MBH₄ and MBO₂, respectively, represent a metal borohydride and a metal metaborate. In practice, the borate is actually in one or more hydrated states, e.g., tetrahydrate, dehydrate, or hemihydrate. The rate of decomposition of the metal borohydride into hydrogen gas and a metal metaborate is pH dependent, with higher pH values hindering the hydrolysis. Accordingly, a stabilizer, such as an alkali metal hydroxide is typically added to solutions of a complex metal hydride in water to be used as the fuel from which the hydrogen gas is generated. Heat or a catalyst, e.g. acids or a variety of transition metals, can be used to accelerate the hydrolysis reaction.

Sodium borohydride (NaBH₄) is of particular interest because it can be dissolved in alkaline water solutions with virtually no reaction; in this case, the stabilized alkaline solution of sodium borohydride is referred to as fuel. Furthermore, the aqueous borohydride fuel solutions are non-volatile and will not burn. This imparts handling and transport ease both in the bulk sense and within the hydrogen generator itself.

Various hydrogen generation systems have been developed for the production of hydrogen gas from aqueous sodium borohydride fuel solutions. The advantage of such borohydride hydrogen generation systems is that they can be scaled to feed fuel cells of power ranges from less than 10 watts to greater than 50 kilowatts. In most cases, it is preferred that hydrogen generation systems be efficient and compact, have a high gravimetric hydrogen storage density, and are readily controllable to match hydrogen flow rate and pressure to the operating demands of the fuel cell. The challenge in designing such systems is to maximize energy density by minimizing the associated balance of plant components to reduce volume, weight, parasitic load and general system complexity.

A simple conventional system (FIG. 1) for generating hydrogen on demand comprises a fuel reservoir, fuel lines and a pump for delivering fuel to a reaction zone, or reaction chamber, which may contain a catalyst, and outlets for separation of gaseous hydrogen and other reaction products. However, when there is a requirement for additional fuel components, such as when mixing two or more fuel components of a mixture, or diluting a concentrated fuel mixture, a more complex system is required with additional pumps and flow controllers or fuel regulators.

For example, a system for generating hydrogen from solid and liquid fuel components has been described in U.S. patent application Ser. No. 10/115,269, filed Apr. 2, 2002, now U.S. Pat. No. 7,282,073 entitled “Method and System for Generating Hydrogen by Dispensing Solid and Liquid Fuel Components,” which is commonly assigned. Such systems utilize separate dispensing and delivery mechanisms for each fuel component.

Hydrogen generation systems may recycle or recover reaction products to control the reaction or to increase efficiency of conversion. For example, the reactant may be withdrawn from the reaction chamber to stop the reaction as described in described in U.S. Pat. No. 6,534,033 entitled “System for Hydrogen Generation,” which is commonly assigned, where, in a process for generating hydrogen from a stabilized metal hydride solution, a reversible fuel pump is in fluid communication with a fuel solution reservoir and a reaction chamber containing a hydrogen generation catalyst. The pump can run in a forward direction to deliver fuel to the reaction chamber and then in a reverse direction to drain the reaction chamber to stop hydrogen generation.

Clogging by precipitation of solid reactants from reactant solutions or precipitations of reactants or reaction products in pumps and valves may be a significant issue. Various approaches are known to allow for controlling the reaction chemistry, or flushing of the system with water or other diluent to reduce clogging. Some systems recycle fuel to increase the efficiency of hydrogen generation. It is preferable in other systems that solid by-products, and fluid reaction products which may precipitate out, are not recycled back to the reaction chamber or the fuel reservoir, to avoid clogging. However, since water is generated in significant quantities as a reaction product in hydrogen fuel cells, it may be recycled into the fuel mixture as a diluent, or used for flushing the system. Such a system which provides for water to be recovered from the exhaust of a fuel cell or condensed from a hydrogen gas stream is described for example in U.S. patent application Ser. No. 10/223,871, now U.S. Pat. No. 7,803,657, entitled “System for hydrogen generation,” which is commonly assigned.

Since gravimetric energy density is one of the key factors affecting the cost of hydrogen generation technology, it is desirable to provide a more concentrated fuel solution and a diluent, or multi-component fuel mixtures, which may be stored in concentrated form and mixed or diluted on demand (e.g., hydride and water or other aqueous reactant). Nevertheless, additional pumps required for additional components are a significant cost in dollars and energy density. Pumps are the active mechanical component that are most likely to break down, particularly if clogging is an issue, thus affecting reliability. Thus, current systems have limitations and alternative systems and methods with improved energy density, cost and reliability are required for systems for hydrogen generation on large and small scale when using multi-component fuel mixtures, or for mixing recycled or recovered fluid reaction products with fuel components.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes or mitigates one or more of the afore-mentioned limitations of known systems and methods for generation of hydrogen.

Systems and methods are provided for hydrogen generation utilizing two or more liquid fuel components, using a fuel delivery system comprising a single pump. Advantageously, a single reversible cycle pump is used to deliver two or more fuel components of a fuel mixture in desired proportions to a mixing zone, reaction zone, or reaction chamber of a hydrogen generation system, while reducing the number of active elements required for fuel delivery and flow control of multiple fuel components. Alternatively, a unidirectional single or duel feed pump co-operable with flow control means comprising a valve, provides for delivering first and second fuel components in desired proportions. Control of the pump speed, and duty cycle of the pump in continuous or pulsed modes, provides for delivery of first and second fuel components in desired proportions, to control hydrogen generation, and to provide for dilution, mixing, and flush cycles using a single pump.

One aspect of the invention provides a hydrogen generation system utilizing a fuel mixture capable of generating hydrogen and comprising at least two fuel components supplied from first and second fuel supply reservoirs. The system comprises a single fuel delivery pump and flow control means for selectively delivering first and second fuel components to a reaction zone in desired proportions; the pump and flow control means being co-operable in a first operating mode to deliver to the reaction chamber one of the first and second fuel components, and in a second operating mode to deliver to the reaction chamber a mixture of the first and second fuel components in desired proportions.

The system may further comprise a control means for controlling the pump speed, pump direction, duty cycle and other parameters of the system, and where active valves are incorporated, for controlling modulation or action of the valves. Preferably a programmable pump controller provides for automatic control of the pump and/or valves in response to signals indicative of system conditions.

Advantageously, the control means may be responsive to changes in external or system conditions, such as temperature or pressure, or a control signal from a fuel cell, to control the pump or valve to alter the fuel mix, fuel flow rate, or other parameters.

A second aspect of the invention provides a system for hydrogen generation utilizing a fuel mixture comprising two or more liquid fuel components of a fuel mixture capable of generating hydrogen, comprising a first fuel supply reservoir for a first fuel component and a second fuel supply reservoirs for a second fuel component, a reaction zone, fuel supply conduits extending between the reservoirs and the reaction zone, a single pump and flow control means for delivering first and second fuel components from the first and second supply reservoir to the reaction zone in desired proportions; wherein the flow control means are operable to deliver selectively to the reaction zone at least one of the first fuel component and the second fuel component, and mixtures of the first and second fuel components in desired proportions.

Beneficially, the pump may comprise a dual head reversible drive pump, operable in a forward direction to pump the first fuel component and in a reverse direction to pump the second fuel component, and the flow control means is operable for selecting a pump speed, direction, and duty cycle to deliver selectively a first fuel component, a second fuel component, and mixtures thereof in desired proportions.

Alternatively, a single feed unidirectional pump or a dual feed unidirectional pump may be used with flow control means comprising one of a three way valve or other valve configurations to selectively deliver one of the first and second fuel components or a mixture thereof in desired proportions to a reaction zone or reaction chamber, or to a mixing zone upstream of the reaction zone.

For example, when the first fuel component comprises a concentrated fuel mixture and the second fuel component comprises a diluent, the pump and the flow control means are operable in a dilution cycle to provide a fuel mixture of a desired concentration for hydrogen generation and in a flush cycle to flush the system with diluent.

When the first fuel component comprises a first reactant and the second fuel component comprises one of a second reactant and a catalyst solution, the pump and flow control means are operable in a mixing cycle to provide a fuel mixture at a desired concentration for hydrogen generation.

Advantageously, the system may further comprise control means for selecting at least one of a pump speed, and a duty cycle of the reversible pump for controlling delivery of the first and second fuel components to the reaction zone in desired proportions.

When the reaction mixture requires a catalyst, the reaction zone may comprise a reaction chamber containing an appropriate supported or unsupported catalyst, and may comprise a mixing zone upstream of the reaction zone.

If a third fuel component is required, a configuration using one additional three-way valve provides for connection to a third reservoir to enable delivery of more than two components of a fuel mixture with a single pump.

Other aspects of the invention provide for a pump module comprising a single pump and flow control means which may comprise a single valve co-operable with the pump in a first operating mode to deliver to an outlet of the pump module one of the first and second fuel components, and in a second operating mode to deliver to an outlet of the pump module a mixture of the first and second fuel components in desired proportions. Preferably, the flow control means is operable for selecting the pump speed and duty cycle to deliver the first and second fuel components in desired proportions to an outlet of the pump module.

Yet another aspect of the invention provides a method of providing a fuel mixture capable of generating hydrogen to a hydrogen generation system utilizing a mixture of at least two liquid fuel components supplied from first and second fuel supply reservoirs using a single pump and flow control means, the pump being co-operable with the flow control means in a first mode to pump at least one of the first and second fuel components and operable in second mode to pump a mixture thereof in desired proportions, wherein the method comprises selecting the duty cycle of the pump to deliver first and second fuel components in desired proportions to a mixing zone of a hydrogen generation system.

Thus, with a reversible drive pump, the pump can be operable in a first (e.g., forward) direction to pump a first fuel component and operable in a reverse direction to pump a second fuel component. The duty cycle of the pump can be selected in forward and reverse directions, to selectively deliver first and second fuel components sequentially in desired proportions to a mixing zone of a hydrogen generation system. For unidirectional pumps, the method may comprise for example, controlling the duty cycle of the pump and modulation of a three-way valve to deliver desired proportions of first and second fuel components to the reaction chamber to provide one of a mixing cycle, a dilution cycle, and a flush cycle.

Systems and methods of the present invention can be used for hydrogen generation from fuel mixtures requiring mixing of two or more components of a fuel mixture, for example, to dilute a concentrated fuel component with water or an aqueous reagent, or to mix two components of a fuel mixture (e.g., fuel solution and catalyst solution). Alternatively, where one fuel reservoir contains a fuel mixture, and the second reservoir contains water or another diluent, the pump may be operable to pump a fuel mixture at a desired dilution, or to flush the system with water or diluent, to control the reaction or to reduce clogging.

Two or more liquid fuel components may be mixed in variable proportions in a system where the fuel delivery system comprises a single reversible pump and valve means. Preferably, the pump provides for controllably selecting the pump speed, pumping direction and duty cycle of the reversible pump for controlling delivery of the first and second fuel components to the reaction chamber in the desired proportion. Beneficially, the operation of the pump is programmably controllable. Thus it is possible to deliver sequentially first and second fuel components in desired proportions to a mixing zone, a reaction zone, or reaction chamber to conveniently provide for dilution, mixing, or flush cycles.

Thus systems and methods of the present invention provide hydrogen generation utilizing a mixture of two or more fuel components using a single reversible pump, and a reduced number of other active elements such as valves.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features, objects and advantages of the invention will become apparent from the following description of preferred embodiments of the invention which are described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a conventional system for generation of hydrogen from a fuel mixture comprising a metal hydride solution;

FIG. 2 is a schematic diagram of a system for hydrogen generation according to a first embodiment of the invention comprising a dual feed pump with a single valve on a fuel line;

FIG. 3 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a dual feed pump with a single valve on a diluent line;

FIG. 4 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a fuel pump with a single valve on a fuel line;

FIG. 5 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a single feed pump with a single valve on a diluent line;

FIG. 6 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a unidirectional pump and a three-way valve;

FIG. 7 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a dual feed pump and a valve;

FIG. 8 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a dual feed pump and two valves;

FIG. 9 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a dual feed pump and two valves;

FIG. 10 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a double headed feed pump with no valves.

FIG. 11 is a schematic diagram of a system for hydrogen generation according to another embodiment of the invention comprising a double headed feed pump with no valves.

In the drawings, identical or corresponding elements in the different Figures have the same reference numeral.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a simple example of a conventional prior art system for hydrogen generation form an aqueous metal hydride solution. Aqueous metal hydride is withdrawn from a reservoir 100 through a conduit line 102, by a fuel pump 110 into a reaction chamber 108 which may contain a catalyst, where the fuel undergoes a chemical reaction to form a fluid product stream comprising hydrogen, a salt of the metal and water. The product stream is withdrawn through conduit line 118 into a gas liquid separator 120 where the by-product salt is withdrawn as a solution through conduit line 122, and the gaseous hydrogen product mixture comprising hydrogen is withdrawn through conduit line 124. This type of system is typically used for a single fuel mixture supplied from the reservoir. In known prior art systems, when delivery of additional fuel components or recovered products, dilution or mixing of components, or flushing of the system with water or diluent is required, additional pumps and valves must typically added to the system for each additional fuel or reactant component.

Systems and methods according to embodiments of the invention described herein are suitable for generation of hydrogen from reformable fuels, i.e., substantially liquid or flowable fuel materials that can be converted to produce hydrogen via a chemical reaction in a reactor. The fuel may also contain a catalyst, and includes hydrocarbons, e.g., methanol, and hydrides, particularly boron hydrides as described in U.S. Provisional Patent Application Ser. No. 60/905,035, incorporated herein by reference, and as described in examples set out below.

A hydrogen generation system according to one embodiment of the present invention is shown schematically in FIG. 2. The system comprises a first supply reservoir 100 and second supply reservoir 200 for first and second components 1, 2 of a fuel mixture for generating hydrogen; a reaction zone comprising a reaction chamber 108 which may include a supported or unsupported catalyst (not shown); and first and second conduits or supply lines 102, 202, for delivering the first and second fuel components to the reaction chamber 108. Flow control means comprising a pump and a valve system for controlling flow of fuel components and controlling delivery of a fuel mixture to the reaction chamber are disposed between the reservoirs 100 and 200 and the reaction chamber 108 and comprise a dual feed pump 210 accommodating feeds from first and second conduits (fuel lines) 102 and 202. The pump is for example a peristaltic pump, and a valve 216 is located between the first reservoir 100 and the pump 210 and the reaction chamber 108 to control flow of the first fuel component.

Thus, during pump operation, a first fuel component 1 is withdrawn from the first supply chamber 100, through the valve 216, and is delivered to the reaction chamber 108, and the second fuel component or diluent 2 is withdrawn from the second fuel supply reservoir 200 and delivered to the reaction chamber 108. As shown in FIG. 2, the first and second conduits converge in a mixing zone 106 upstream of the reaction chamber 108. This arrangement is particularly suitable for dilution of a concentrated fuel solution held in the first supply reservoir 100 with a diluent, held in the second supply reservoir 200. During operation of the pump in a first mode, the second fuel component, i.e. the diluent, is pumped continuously, so this arrangement also provides for flushing of the reaction chamber with diluent, which may be water, when valve 216 is closed. In a second mode, with the throttle valve 216 in an open or partially open position, operation of the pump delivers a mixture of fuel and diluent to the reaction chamber. For hydrogen generation, flow of the fuel mixture from the first supply reservoir 100 is controlled by throttle valve 216 to deliver a fuel mixture of a desired concentration to the reaction chamber.

In the configuration shown in FIG. 2 the reaction zone is provided within a reaction chamber 108, which contains a supported or unsupported catalyst. In alternative embodiments, the reaction zone may simply be a region in the conduit lines where fuel components react to generate hydrogen. This alternative arrangement is suitable for use with reformable fuels, which produce hydrogen without the use of a catalyst, for example reaction of ionic hydrides with an aqueous reagent and the reaction of ionic hydrides and boron hydrides with an aqueous reagent with a pH less than 7 in the presence of water.

The system shown in FIG. 2 comprises a mixing zone 106 upstream of the reaction chamber 108, where the first and second conduits 102, 202 converge, but alternatively it will be appreciated that the first and second conduits 102 and 202 may feed into the reaction chamber 108 so that mixing takes place within a region of the reaction chamber.

A system according to a second embodiment of the invention is shown in FIG. 3, in which all parts are similar to those shown in FIG. 2, and indicated by like numerals, except that a valve 218 is provided on the second fuel supply reservoir. In this arrangement, when the first supply reservoir 100 contains a concentrated reformable fuel, and the second supply reservoir 200 contains a diluent, the supply lines 102 and 202 are sized such that when valve 218 is fully opened, the ratio of the flow rates of diluent to concentrated fuel component is high enough to achieve proper flushing of the reaction chamber.

As an example, when the valve 218 is partially closed, a fuel mixture with a desired mixture of concentrated fuel component and diluent is delivered to the mixing zone 106. As an example of fuel dilution according to this embodiment, when the first reservoir contains 30 wt-% sodium borohydride solution flowing at 1 ml/min, and valve 218 is throttled to deliver a diluent at 0.5 ml/min, the theoretical effective concentration delivered to the reactor 108 is 20 wt-% sodium borohydride at a flow rate of 1.5 ml/min.

The configuration shown in FIG. 8 is similar except that it provides two valves, i.e. valve 216 and valve 218 located upstream of the pump, for independently controlling flows of first and second fuel components. However, where it is desired to reduce the number of valves, it will be appreciated that the single dual feed pump, single valve configurations shown in FIGS. 2 and 3 can provide conveniently for mixing, dilution, and flushing cycles with a reduced number of active components.

In a system according to another embodiment, as shown in FIG. 4, all elements are similar to those in FIGS. 2 and 3, except that the pump is a single feed, unidirectional pump 310. To accommodate delivery of two fuel components from first and second fuel supply reservoirs 100 and 200, first and second conduits 102, 202 converge at mixing zone 106 upstream of the pump. Flow of the first fuel component from the first reservoir 100 is controlled by throttle valve 216. The system according to another embodiment shown in FIG. 5 is identical except that a throttle valve 218 is provided on the conduit from the second fuel supply chamber 200. Thus in both these embodiments the two fuel components are mixed upstream of the pump, and flow of one component is controllable with throttle valve 216 or 218. That is, in a first mode, during operation of the pump with the throttle valve closed, only one fuel component is delivered to the reaction zone, while in a second mode, with the throttle valve open or partially open, a mixture of the two fuel components is delivered. While this enables use of a single feed pump, this arrangement is particularly suitable for mixing of a concentrated fuel mixture with diluent, where reaction is catalyzed in the reaction chamber 108.

The configuration shown in FIG. 9 is similar to those in FIGS. 4 and 5, except that it provides two valves, i.e., valve 216 and valve 218 located downstream of the pump, for independently controlling flows of first and second fuel components. However, where it is desired to reduce the number of valves, it will be appreciated that the single pump, single valve configurations shown in FIGS. 4 and 5 can provide conveniently for mixing, dilution, and flushing cycles with a reduced number of active components.

A system according to another embodiment is shown in FIG. 6, and comprises components similar to those shown in FIGS. 4 and 5, employing a unidirectional single feed pump 310, but differs in that instead of providing throttle valves 216 or 218 on conduit lines 102, 202 from the first and second supply reservoirs 100, 202, a single three way valve 222 is provided where first and second conduit lines 102 and 202 converge upstream of the pump 310. Thus, during operation of the pump 310, in one position of the three way valve, a first component of the fuel mixture may be withdrawn from the first fuel reservoir 100 via conduit line 102, through the three way valve 222, through the pump 310 and delivered to the reaction chamber 108, and by toggling the three way valve to a second position, a second component may be withdrawn from second fuel reservoir 200, through the three way valve 222 through the pump and delivered to the reaction chamber 108. The position of the three-way valve 222 may be modulated to alternate delivery of the first and second components to the reaction chamber 108. The flow cycles may be of the same duration or different durations to deliver the two fuel components in the desired proportions to the reaction chamber 108 using only one unidirectional single head pump, 310. The system according to this embodiment is suitable, for example, for dilution of a concentrated fuel component with a second fuel component, which may be a diluent, or water, and delivering diluted fuel mixture to the reaction chamber. Flushing of the system is readily achieved by holding the valve 222 in the second position to allow continuous flow of diluent from the second supply reservoir 200.

For example, the first fuel reservoir 100 may hold fuel at a desired concentration and the second fuel reservoir 200 may hold diluent or water for flushing the system. During operation of the pump, the valve is opened in the first position to allow flow of fuel mixture towards the reaction chamber 108 for hydrogen generation, and opened in the second position for flushing of the reaction system. Since components may mix in the zone 106 comprising part of the conduit line between the three way valve and the pump, this arrangement is particularly suitable to deliver, for example, a fuel mixture which forms hydrogen in the presence of catalyst in the reaction chamber. The fuel mixture may be mixed in a desired concentration on demand to control hydrogen generation by controlling or by modulation of the opening of the three-way valve.

Alternatively when mixing downstream of the pump in a reaction zone or close to the reaction chamber is desirable, for example, mixing two fuel components which react in the absence of catalyst to provide hydrogen, the embodiment shown in FIG. 7 may be preferred. The system according to the embodiment shown in FIG. 7 is similar to that shown in FIG. 6, except that the three way valve 220 is located downstream of the pump, and may therefore be required to be capable of high pressure operation, but otherwise operates similarly to valve 222 as described with reference to FIG. 6.

The embodiment shown in FIG. 8 is similar to that shown in FIGS. 2 and 3, except that it provides two valves to control flow from each supply reservoir, i.e., one valve 216 on conduit 102 from the first fuel reservoir 100 and a second valve 218 on the second conduit 202 from the second fuel reservoir 200, allowing independent flow control of both fuel components. The first and second conduits are shown converging at a mixing zone 106 downstream of the pump 210. The configuration shown in FIG. 8 is similar except that valve 216 and valve 218 are located upstream of the pump. In these embodiments, the flow rates of the first and second fuel components from the first and second fuel supply reservoirs 100 and 200 may be controlled independently by the use of valves 216 and 218. Typically valves located before the pump would not be subject to high-pressure conditions. Valves downstream of the pump would be operable under high-pressure conditions. While these two embodiments require two valves, they provide for independent flow control of two fuel components.

A system according to a further embodiment is shown in FIG. 10 and comprises elements similar to those shown previously except that the pump 410 comprises a double-headed reversible cycle pump. A first component of the fuel mixture is withdrawn from the first fuel reservoir 100 via conduit line 102 through the first head of pump 410, and a second component of the fuel mixture is withdrawn from the second fuel reservoir 200 via conduit line 202, through the second head of the pump 410. The double-headed pump 410 may be provided by two heads mounted on overrunning clutch bearings. When the pump motor is rotated in a clockwise direction the pumping mechanism pumps a first fuel component. When the pump motor is rotated in the opposite direction a second fuel component is pumped. The flow rates of each component can be controlled by the rotation speed. The relative proportions of each component delivered to the reaction chamber 108 can be controlled by the duty cycle of the pump, i.e. by controlling the pump speed and pumping time in each direction. By pulsing the pump motor forward and backward, batches of first and second fuel components respectively may be sent from each reservoir to the reaction chamber 108. The flow rates may be controlled by adjusting the rotation speed or by causing the pump to pause between pulses.

For example, in one mode, the system may operate to deliver one of the two fuel components continuously or in pulses; in another mode, the system may operate to sequentially deliver alternating flows or pulses of first and second fuel components in desired proportions to generate a required mixture.

Thus the system of this embodiment may be used conveniently for dilution of a concentrated fuel solution held in the first reservoir 100 when a diluent or water is held in the second fuel reservoir 200 and can provide a fuel mixture with a desired proportion of the two components by appropriate control of pump speed and duty cycle.

When components react to form hydrogen in the presence of a catalyst, mixing of components may take place in the mixing zone 106 (as shown in FIG. 10) upstream of a reaction chamber 108 containing the catalyst. Alternatively, first and second conduit lines may feed directly into a reaction zone or reaction chamber, which would be a preferred arrangement for mixing of two reactants for reactions generating hydrogen when a catalyst is not required.

Where fuel is supplied to the reaction chamber from the first supply reservoir at a desired concentration and dilution is unnecessary, the pump may be operated continuously in the forward direction during hydrogen generation; the second supply reservoir may contain diluent, catalyst solution, or water for flushing or controlling the reaction as needed by operation of the pump in the reverse direction.

The system is particularly advantageous for dilution of a concentrated fuel solution, when the fuel solution may be stored in a greater concentration than is typically fed to the catalyst in the reaction chamber, and even as a slurry or suspension, and mixed with water or other diluent on demand, thus improving efficiency in storage and gravimetric hydrogen storage density or energy density.

A system according to the embodiment shown in FIG. 10 therefore provides for controllable dilution, mixing or flushing cycles using only one motor without requiring any additional valves.

It will also be appreciated that this single pump configuration may also be combined with a three way valve, similar to those described with respect to the embodiments above, if it is desired to mix more than two fuel components and/or diluents, as shown in FIG. 11. This embodiment shows fuel components 1a and 1b held in supply reservoirs 100a and 110b, and fuel component 2 comprising a diluent held in supply reservoir 200. Mixing of fuel components 1a and 1b may be accomplished using three way valve 222 as described above, modulating operation to provide the two components in a desired proportion. In this and other embodiments, where the diluent is water, water may be recovered from the product flow from the reactor 108 or from a fuel cell (not shown) and fed back to supply reservoir 200 via conduit 212. Although an initial supply of diluent or water may be required at start up, i.e. to initiate the reaction, because a significant amount of water is generated in the reaction, recovered water may be use to dilute a concentrated fuel mix.

Also shown in FIG. 11 is a controller 214 for controlling the pump speed and duty cycle of pump 410 and modulation of the three way valve 222 to deliver fuel components 1a, 1b and diluent 2 to the reaction chamber in desired proportions to provide for dilution, mixing or flushing cycles as required. Preferably the controller is programmable to provide desired pumping cycles of the pump, and/or three way valve modulation to provide dilution, mixing and flushing functions as required for two or more fuel components, or a fuel component and diluent. Thus the system provides for two or three fuel components to be controllably delivered with a single pump and a reduced number of active elements such as valves.

Such an arrangement is particularly suitable when using concentrated borohydride fuel mixtures to improve energy density, while reducing active components and reducing the likelihood of clogging.

It will also be appreciated that addition of another three-way valve would provide a convenient way of providing another fuel component to the other embodiments described above and various combinations of the pump configurations and valve configurations described above are contemplated as alternatives. Nevertheless, an objective of the preferred embodiments is to provide a system for hydrogen generation using reformable fuels, and in particular from boron hydrides, when utilizing two or more liquid fuel components. Systems and methods as described above conveniently provide for mixing of two or more fuel components in desired proportions, and for control of reactant flow, dilution, mixing and flushing cycles with a single pump and a reduced number of valves.

The embodiments described above with respect to sodium borohydride solution and a diluent for generating hydrogen are given by way of example only. It will be apparent that the preferred embodiments described above and other embodiments may be used for generation of hydrogen from many other fuel mixtures comprising two or more fuel components.

Other suitable fuel mixtures for generation of hydrogen are more fully described in detail in U.S. Provisional Application Ser. No. 60/905,034, which is incorporated herein by reference.

EXAMPLE

In operation of the system to provide a means of generating hydrogen according to one embodiment, the fuel comprises a metal hydride fuel component that is a complex metal hydride that is water soluble and stable in aqueous solution. Examples of suitable metal hydrides are those borohydrides having the general formula M (BH₄)_n, where M is an alkali or alkaline earth metal selected from Group 1 (n=1) or Group 2 (n=2) of the periodic table, such as sodium, lithium, potassium, magnesium and calcium. Examples of such compounds include without intended limitation are: NaBH₄, LiBH₄, KBH₄, and Ca(BH₄)₂. These metal hydrides may be utilized in mixtures, but are preferably utilized individually. Sodium borohydride is preferred in the present invention due to its comparatively high solubility in water, about 35% by weight as compared to about 19% by weight for potassium borohydride. Typically, the fuel solution is comprised of from about 10% to 35% by wt. sodium borohydride and from about 0.01 to 5% by weight sodium hydroxide as a stabilizer.

Since some water is consumed in the hydrogen generation process shown in Equation 2 and additional water is lost as steam, the product stream containing the borate salt is more concentrated than the initial borohydride fuel mixture. Precipitation of the product salt from a concentrated solution in the reaction chamber itself or in any of the associated downstream apparatus will render the system ineffective until disassembled and cleaned. To prevent such precipitation, a water flush cycle is typically used to ensure that any precipitates or saturated borate solution are washed out of the system. In typical known hydrogen generation systems such as that illustrated in FIG. 1, an additional separate water tank with its own pump and plumbing (not shown) would need to be incorporated into the system to provide the desired flushing cycle.

In preferred embodiments of the present invention, one fuel pump is used to deliver both the active fuel component and water, and facilitates mixing and dilution cycles as well as flushing cycles, with a single pump. The following examples of methods of generating hydrogen will be described with reference to the system shown in FIGS. 10 and 11 using a dual head reversible cycle pump.

In operation of the system to provide a method of generating hydrogen according to one embodiment, the first fuel component 1 comprises an aqueous metal borohydride solution and the second fuel component 2 comprises water. The water component may contain other additives in solution, for example, common anti-freeze agents such as ethylene glycol.

A first fuel component, e.g. an aqueous metal hydride solution, is held in reservoir 100, and water is held in reservoir 200. When pump 410 is operated in the forward direction (i.e., clockwise as shown in FIG. 10), the metal hydride solution 1 is pumped from reservoir 100 through conduit 102 and delivered to reaction chamber 108 where it undergoes reaction to form a fluid product stream comprising hydrogen, and a salt of the metal and water. The product stream is fed to a gas liquid separator (not shown) and other components to separate and collect the byproduct salt and hydrogen. Upon completion of a hydrogen generation cycle such as when the system is to be turned off, pump 410 is operated in the reverse direction, and water is withdrawn from reservoir 200 via conduit 202 to deliver water to the reaction chamber 108, thereby flushing the system and rinsing residues from within the hydrogen generation system. This system therefore allows for a simple, low-parasitic load method for flushing system components with water.

The reaction chamber 108 preferably includes a catalyst bed comprising a catalyst metal supported on a substrate. The preparation of such supported catalysts is taught, for example, in U.S. Pat. No. 6,534,033 entitled “System for Hydrogen Generation,” the disclosure of which is incorporated herein by reference. Suitable transition metal catalysts for the generation of hydrogen from a metal hydride solution are known in the art and include metals from Group IB to Group VIIIB of the Periodic Table, either utilized individually or in mixtures, or as compounds of these metals. Representative examples of these metals include, without intended limitation, transition metals represented by the copper group, zinc group, scandium group, titanium group, vanadium group, chromium group, manganese group, iron group, cobalt group and nickel group. Specific examples of useful catalyst metals include, without intended limitation, ruthenium, iron, cobalt, nickel, copper, manganese, rhodium, rhenium, platinum, palladium, and chromium. As is known, the catalyst may also be in forms of beads, rings, pellets or chips. It is preferred that structured catalyst supports such as honeycomb monoliths or metal foams be used in order to obtain the ideal plug flow pattern and mass transfer of the fuel to the catalyst surface.

As an alternative approach to a water flush cycle, precipitation problems and clogging can be reduced or avoided by utilizing a dilute fuel feed to reduce the possibility of the system becoming clogged as a result of insufficient water in the product stream to maintain the borate product salt in solution. The advantages of such dilution are set forth in U.S. patent application Ser. No. 10/223,871, filed Oct. 20, 2002, entitled “System for Hydrogen Generation,” which is commonly assigned, the disclosure of which is incorporated herein by reference. The system described herein may advantageously be used to dilute a fuel solution held in the first reservoir with water held in the second reservoir.

Thus, in operation of the system to provide a method according to one embodiment, a concentrated borohydride solution is held in the first reservoir 100, and water is held in the second reservoir 200. The pump is operated in cycles as illustrated FIG. 10, and by cycling the pump 410 in “forward” and “reverse” cycles in rapid succession, water is periodically added to the aqueous borohydride stream, effectively diluting the fuel to a lower concentration. That is, predetermined amounts of borohydride solution and water are sequentially delivered to the reaction chamber in desired proportions to provide a fuel mixture of suitable concentration for hydrogen generation.

As mentioned above, when the first fuel component comprises, e.g., a 20 wt-% sodium borohydride solution, when pump 210 is cyclically driven “forward” at a constant rate for 2 seconds to deliver the borohydride fuel component, and then in reverse at the same rate for 0.5 seconds to deliver water, the theoretical effective concentration delivered to reactor 108 is a 16 wt-% sodium borohydride solution. Advantageously, as shown in FIG. 11, the system comprises control means 214, e.g., to provide control signals to the pump for selecting the pump parameters such as the pump speed, pump direction, and duty cycle to allow sequential delivery of the two fuel components to the reaction chamber 108 and/or mixing zone 106 upstream of the reaction zone, in a desired proportion. Optionally, where the diluent is water, a conduit 212 for water recovered from a product stream from the reaction chamber 108 or from a fuel cell (not shown) may be provided to supply recovered water to replenish the second reservoir 200. The pump cycle may be selected to provide both a dilution cycle for generation of hydrogen, and a flush cycle as needed, or to alternate cycles to control the rate of hydrogen generation.

This arrangement allows for fuel components to be stored at a greater concentration than is typically fed through the catalyst bed, improving gravimetric hydrogen storage density. In addition, such a dilution scheme would allow the storage of a slurry or a suspension of an aqueous borohydride mixture where the concentration of the metal hydride in the fuel system exceeds the maximum solubility of the particular salt utilized. Hot water recovered from the product stream from hydrogen generation or from the fuel cell may usefully be used for dilution of the concentrated mixture.

In operation of the system to provide a method of generating hydrogen according to another embodiment, the first fuel component comprises an aqueous metal borohydride solution and the second fuel component comprises a catalyst solution. Suitable catalyst solutions include acidic catalysts, i.e., catalysts having a pH less than 7, and include inorganic acids, including the so-called “mineral acids,” such as hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and phosphoric acid (H₃PO₄), and organic acids, such as acetic acid (CH₃COOH), and water soluble transition metal salts such as cobalt chloride (CoCl₂).

When pump 410 is operated in the forward direction, an aqueous metal borohydride solution is pumped from reservoir 100 via conduit line 102 and delivered to reaction chamber 108. The catalyst solution is delivered to the reaction chamber by operation of pump 410 in the reverse direction. The combination of the two fuel components in the reaction chamber produces hydrogen and a salt of the metal in accordance with Equation 2. Beneficially, the system comprises control means 214 for controlling the pump cycle to deliver the appropriate mixing cycle. For example, the pump cycle may be programmably controlled to deliver a continuous flow of a large flow of fuel components in desired proportions so that a steady stream of hydrogen is generated continuously over a period of time or alternatively small sequential portions or pulses of each component so that hydrogen is produced in short bursts, to generate hydrogen at an appropriate rate to meet demand, e.g. for a fuel cell.

Advantageously, the control means 214 is responsive to a change in external or system conditions, such as temperature or pressure, or, e.g., a control signal from a fuel cell, to control the pump and/or valve means to alter the fuel mix, fuel flow rate or other parameters as required.

For example, the control means 214 may also be responsive to one or more external or system conditions, e.g. a change in temperature, pressure or other parameter. As one example, the solubility of NaBH₄ and its borate hydrolysis reaction products increases with temperature. Thus, the control means may be utilized to change the pump speed or duty cycle to change the fuel mix dependent on temperature, i.e., increase the relative concentration of the fuel in diluent/fuel mixture as a system temperature is increased. As the temperature increases, the reaction by-products would tend to remain in liquid form even at higher concentrations. Similarly, to prevent precipitation of products as temperature decreases, the fuel to diluent ratio may be decreased.

The embodiments described in this Example above use a reversible cycle pump and additional valves are not required. In use of systems comprising dual feed or single feed unidirectional pumps and one or more valves, arrangements with three-way valves (see FIGS. 6 and 7) also provide for convenient control for mixing, dilution, and flushing cycles. Three way valves are sufficiently resistant to clogging in use with sodium borohydride systems.

Modulation of a three-way valve while controlling the pump speed and duty cycle also provides conveniently for control of fuel delivery of two or more fuel components. While the controller 214 is not shown in FIGS. 6 and 7, pump 210 or 310 may similarly provide for connection to a controller 214 of the hydrogen generation system which may also control modulation of the operation of three way valves 220 or 222, together with controlling the pump speed and duty cycle of the pump 210 or 310. Preferably, the pump and valve may be programmably controllable, to provide for delivery of fuel components in one or more of mixing, dilution and flush cycles, and for controlling the rate of hydrogen generation, in a similar manner as described above with respect to a system using a reversible cycle pump.

The embodiments of the system described above provide for hydrogen generation in systems utilizing two or more fuel components where delivery and regulation of fuel components is accomplished with a single pump unit for fuel regulation, i.e., one pump co-operable with flow control means comprising a configuration of valves and conduits, instead of requiring an additional pump for regulation and delivery of more than two fuel components. Therefore, although the use of single feed or dual feed pumps, and double headed single drive pumps is contemplated as described above, for preferred systems described herein, a single pump system having flow control means co-operable with the single pump do not encompass a second or additional pump unit for regulation of flow and delivery of two or more fuel components from fuel reservoirs to a reaction zone.

Although preferred embodiments of the invention have been described and illustrated in detail, it is to be clearly understood that these are by way of illustration and example only and not to be taken by way of the limitation, the scope of the present invention being limited only by the appended claims.

Claims

1. A hydrogen generation system utilizing a fuel mixture capable of generating hydrogen using at least two fuel components supplied from first and second fuel supply reservoirs, the system comprising: a single fuel delivery pump;flow control means for selectively delivering first and second fuel components to a reaction zone in desired proportions; andwherein the pump and flow control means are co-operable in a first operating mode to deliver to the reaction zone one of the first and second fuel components, and in a second operating mode to deliver to the reaction zone a mixture of the first and second fuel components in desired proportions.

2. A system according to claim 1 wherein the pump is a dual head reversible drive pump operable in a first direction to pump the first fuel component and in a reverse direction to pump the second fuel component, and the flow control means is operable for selecting a pump speed, direction, and duty cycle to deliver selectively a first fuel component, a second fuel component, and mixtures thereof in desired proportions.

3. A system according to claim 1 wherein the pump is a single feed unidirectional pump and the flow control means comprises a three way valve co-operable with the pump and disposed upstream of the pump, and wherein the flow control means is operable for selecting a duty cycle of the pump and modulating the three way valve to deliver selectively a first fuel component, a second fuel component, and mixtures thereof in desired proportions.

4. A system according to claim 1 wherein the pump is a dual feed unidirectional pump and the flow control means comprises a three way valve co-operable with the pump and disposed downstream of the pump, and wherein the flow control means is operable for selecting a duty cycle of the pump and modulating the three way valve to deliver selectively a first fuel component, a second fuel component and mixtures thereof in desired proportions.

5. A system according to claim 1 wherein the pump is a dual feed unidirectional pump and the flow control means comprises a valve co-operable with the pump for controlling flow of one fuel component, and wherein the flow control means is operable for selecting a duty cycle of the pump and controlling valve operation in a first mode to deliver one fuel component only, and in a second mode to deliver mixtures of the first and second fuel components in desired proportions.

6. A system according to claim 1 wherein the pump is a single feed unidirectional pump and the flow control means comprises a valve co-operable with the pump for controlling flow of one fuel component, and the flow control means is operable for selecting a duty cycle of the pump and controlling valve operation in a first mode to deliver one fuel component only, and in a second mode to deliver mixtures of the first and second fuel components in desired proportions.

7. A system for hydrogen generation utilizing a fuel mixture comprising two or more liquid fuel components of a fuel mixture capable of generating hydrogen, comprising: a first fuel supply reservoir for a first fuel component and a second fuel supply reservoir for a second fuel component;a reaction zone;fuel supply conduits extending between the reservoirs and the reaction zone;a single pump;flow control means for delivering first and second fuel components from the first and second supply reservoir to the reaction zone in desired proportions; andwherein the flow control means are operable to deliver selectively to the reaction zone at least one of the first fuel component, the second fuel component, and mixtures of the first and second fuel components in desired proportions.

8. A system according to claim 7 wherein the reaction zone is within a reaction chamber containing a catalyst, and further comprising a mixing zone upstream of the reaction zone.

9. A system according to claim 7 wherein the first fuel component comprises a concentrated fuel mixture and the second fuel component comprises a diluent, and wherein the flow control means are operable in a dilution cycle to provide a fuel mixture of a desired concentration for hydrogen generation and in a flush cycle to flush the system with diluent.

10. A system according to claim 7 wherein the first fuel component comprises a first reactant and the second fuel component comprises one of a second reactant and a catalyst solution, and wherein the flow control means are operable in a mixing cycle to provide a fuel mixture at a desired concentration for hydrogen generation.

11. A system according to claim 7 wherein the single pump flow control means comprises a dual head reversible drive pump, the pump being operable in a forward direction to deliver a first component to a mixing zone, and being operable in a reverse direction to deliver a second component to the mixing zone; and wherein the flow control means are operable for selecting the pump speed and duty cycle of the pump in forward and reverse directions to deliver the first and second fuel components to the mixing zone in desired proportions.

12. A system according to claim 11 wherein the flow control means provide for selectively operating the system in at least one of a mixing cycle, a dilution cycle and a flush cycle.

13. A system according to claim 7 wherein the pump comprises a dual feed, unidirectional pump, and the flow control means comprise a single valve.

14. A system according to claim 13 comprising a first fuel conduit extending between the first fuel supply reservoir and through a first feed of the pump, and a second fuel conduit extending between the second fuel supply reservoir and through a second feed of the pump, the first and second fuel conduits converging at a mixing zone downstream of the pump, and a valve being disposed in one of the first and second fuel conduits.

15. A system according to claim 7 wherein the pump comprises a single feed unidirectional pump and the flow control means comprise a single valve.

16. A system according to claim 15 comprising a first fuel conduit extending from the first fuel supply reservoir and a second fuel conduit extending from the second fuel supply, the first and second fuel conduits converging at a mixing zone upstream of the pump for delivering fuel components to the reaction zone, and a valve disposed in one of the first and second fuel conduits upstream of the pump.

17. A system according to claim 5 wherein the valve comprises a three-way valve and wherein a first fuel conduit extends from the first fuel supply reservoir to a first port of the three-way valve, and a second fuel conduit extends from the second fuel supply reservoir to a second port of the three-way valve, and a third conduit extends from the third port of the three way valve through the pump to the reaction zone.

18. A system according to claim 6 wherein the valve comprises a three-way valve and a first fuel conduit extends from the first fuel supply reservoir through one feed of the pump to a first port of a three-way valve, a second fuel conduit extends from the second fuel supply reservoir through the second feed of the pump to a second port of the three-way valve, and a third conduit extends from the third port of the three-way valve to the reaction zone.

19. A system according to claim 5 wherein a second valve is provided such that a valve is disposed in each of the first and second conduits.

20. A system according to claim 6 wherein a second valve is provided such that a valve is disposed in each of the first and second conduits.

21. A pump module for a hydrogen generation system utilizing a fuel mixture capable of generating hydrogen using at least two fuel components supplied from first and second fuel supply reservoirs, the pump module comprising: a first inlet for receiving a first fuel component;a second inlet for receiving a second fuel component;a single pump; andflow control means;wherein the pump and flow control means are co-operable in a first operating mode to deliver to an outlet of the pump module one of the first and second fuel components, and in a second operating mode to deliver to an outlet of the pump module a mixture of the first and second fuel components in desired proportions.

22. A pump module according to claim 21 wherein the single pump comprises a double head, reversible drive pump and the pump is operable in a first direction to selectively pump the first fuel component, and in a reverse direction to selectively pump the second fuel component, and wherein the flow control means is operable for selecting the pump speed and duty cycle to deliver the first and second fuel components in desired proportions to the outlet.

23. A pump module according to claim 21 wherein the module further comprises a mixing zone upstream of the outlet.

24. A pump module according to claim 21 wherein the single pump comprises a dual feed, unidirectional pump and the flow control means further comprises a valve, wherein the first and second inlets are coupled by first and second conduits to first and second feeds of the pump for pumping first and second fuel components, and the valve is disposed in one of the first and second fuel conduits to control the flow therethrough, the pump being operable to continuously pump one fuel component, the valve being co-operable with the pump to control flow of the other fuel component.

25. A pump module according to claim 21 wherein the pump is a single feed, unidirectional pump, and further comprising a three-way valve upstream of the pump, the first and second inlets being coupled to first and second ports of the three-way valve, and the pump being coupled to a third port of the three-way value, the three-way valve being co-operable with the pump for selectively pumping one of the first fuel component, the second fuel component, or mixtures thereof in desired proportions dependent on modulation of the three-way valve.

26. A pump module according to claim 21 wherein the pump is a single feed, unidirectional pump, the first and second inlets being coupled through first and second conduits to a mixing zone upstream of the pump, and comprising a valve in one of the first and second conduits, the pump being operable to continuously pump one fuel component and co-operable with the valve for controlling flow of the other fuel component to deliver one fuel component or mixtures of the first and second fuel components in desired proportions.

27. A pump module according to claim 21 wherein the pump comprises a dual feed, unidirectional pump, and first and second inlets are coupled through first and second conduits to first and second feeds of the pump, and further comprising a three way valve, wherein first and second ports of the three-way valve are coupled to first and second feeds from the pump and a third port of the three way valve is coupled to the outlet of the pump module.

28. A pump module according to claim 21 wherein the pump is a single feed, unidirectional pump and further comprising a three-way valve upstream of the pump and co-operable with the pump for selectively pumping one of the first fuel component, the second fuel component, or mixtures thereof in desired proportions dependent on modulation of the three-way valve.

29. A method of providing a fuel mixture capable of generating hydrogen to a hydrogen generation system utilizing a mixture of at least two liquid fuel components supplied from first and second fuel supply reservoirs comprising: providing a hydrogen generation system having a single fuel delivery pump, and flow control means, the pump being co-operable with the flow control means in a first mode to pump at least one of the first and second fuel components and operable in second mode to pump a mixture thereof in desired proportions to a mixing zone of a hydrogen generation system; andselecting the duty cycle of the pump to deliver first and second fuel components in desired proportions to the mixing zone.

30. A method according to 29 wherein the pump is a single reversible drive pump, the pump being operable in a first direction to pump the first fuel component and operable in a reverse direction to pump the second fuel component; and selecting the duty cycle of the pump in forward and reverse directions, to selectively deliver first and second fuel components sequentially in desired proportions to the mixing zone.

31. A method according to 29 wherein the flow control means comprises a three-way valve co-operable with the pump, and further comprises selectively controlling the duty cycle of the pump and modulation of the three way valve to deliver desired proportions of the first and second fuel components to the mixing zone to provide one of a mixing cycle, a dilution cycle and a flush cycle.

32. The system according to claim 1 further comprising a control means for controlling at least one of a pump speed, pump direction, and duty cycle, and where the flow control means comprises active valves.

33. A system according to claim 32 wherein the control means is responsive to a change of at least one of external conditions and system conditions for controlling at least one of the pump and valves for changing at least one of a fuel mixture, and a fuel flow.

34. A system according to claim 33 wherein the control means is responsive to a change of temperature or pressure.