U.S. patent application number 12/043444 was filed with the patent office on 2009-02-19 for hydrogen generation systems.
Invention is credited to Keith A. Fennimore, Kevin W. McNamara, John Spallone.
Application Number | 20090047185 12/043444 |
Document ID | / |
Family ID | 40263857 |
Filed Date | 2009-02-19 |
United States Patent
Application |
20090047185 |
Kind Code |
A1 |
Fennimore; Keith A. ; et
al. |
February 19, 2009 |
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.
Inventors: |
Fennimore; Keith A.;
(Columbus, NJ) ; Spallone; John; (Virginia Beach,
VA) ; McNamara; Kevin W.; (Red Bank, NJ) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
40263857 |
Appl. No.: |
12/043444 |
Filed: |
March 6, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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60905035 |
Mar 6, 2007 |
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60905034 |
Mar 6, 2007 |
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Current U.S.
Class: |
422/129 ;
417/315; 422/211 |
Current CPC
Class: |
C01B 2203/1076 20130101;
Y02E 60/362 20130101; C01B 2203/1029 20130101; C01B 2203/1052
20130101; C01B 2203/107 20130101; Y10T 137/86027 20150401; C01B
2203/1011 20130101; Y10T 137/85986 20150401; C01B 2203/1058
20130101; C01B 2203/1047 20130101; C01B 2203/1064 20130101; C01B
3/065 20130101; Y10T 137/86019 20150401; C01B 2203/1023 20130101;
Y10T 137/85978 20150401; Y10T 137/86815 20150401; Y02E 60/36
20130101; C01B 2203/1041 20130101 |
Class at
Publication: |
422/129 ;
422/211; 417/315 |
International
Class: |
B01J 19/00 20060101
B01J019/00; F04B 19/00 20060101 F04B019/00 |
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; and wherein 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; and wherein 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; and flow 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; and
selecting 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.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 60/905,035 filed Mar. 6, 2007, which is
incorporated herein by reference; and is related to the United
States patent application filed concurrently herewith, which claims
priority to U.S. Provisional Patent Application No. 60/905,034
filed Mar. 6, 2007; all of these applications are commonly
assigned.
TECHNICAL FIELD
[0002] 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
[0003] 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.
[0004] 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.
[0005] 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., CO.sub.2 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.
CH.sub.3OH+H.sub.20.fwdarw.3H.sub.2+CO.sub.2 Equation 1
[0006] 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:
MBH.sub.4+2H.sub.2O.fwdarw.MBO.sub.2+4H.sub.2+300 kJ Equation 2
where MBH.sub.4 and MBO.sub.2, 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.
[0007] Sodium borohydride (NaBH.sub.4) 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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
[0014] The present invention overcomes or mitigates one or more of
the afore-mentioned limitations of known systems and methods for
generation of hydrogen.
[0015] 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.
[0016] 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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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.
[0032] 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
[0033] 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:
[0034] FIG. 1 is a schematic diagram of a conventional system for
generation of hydrogen from a fuel mixture comprising a metal
hydride solution;
[0035] 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;
[0036] 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;
[0037] 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;
[0038] 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;
[0039] 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;
[0040] 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;
[0041] 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;
[0042] 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;
[0043] 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.
[0044] 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.
[0045] In the drawings, identical or corresponding elements in the
different Figures have the same reference numeral.
DETAILED DESCRIPTION OF THE INVENTION
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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
[0074] 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
(BH.sub.4).sub.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:
NaBH.sub.4, LiBH.sub.4, KBH.sub.4, and Ca(BH.sub.4).sub.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.
[0075] 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.
[0076] 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.
[0077] 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.
[0078] 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.
[0079] 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.
[0080] 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.
[0081] 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.
[0082] 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.
[0083] 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.
[0084] 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
(H.sub.2SO.sub.4), and phosphoric acid (H.sub.3PO.sub.4), and
organic acids, such as acetic acid (CH.sub.3COOH), and water
soluble transition metal salts such as cobalt chloride
(CoCl.sub.2).
[0085] 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.
[0086] 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.
[0087] 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 NaBH.sub.4 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.
[0088] 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.
[0089] 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.
[0090] 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.
[0091] 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.
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