U.S. patent application number 12/237999 was filed with the patent office on 2010-01-07 for various methods and apparatus for solar assisted fuel production.
This patent application is currently assigned to Sundrop Fuels, Inc.. Invention is credited to Brian L. Hinman, Peter Le Lievre, John Henry Stevens.
Application Number | 20100000874 12/237999 |
Document ID | / |
Family ID | 42060057 |
Filed Date | 2010-01-07 |
United States Patent
Application |
20100000874 |
Kind Code |
A1 |
Hinman; Brian L. ; et
al. |
January 7, 2010 |
VARIOUS METHODS AND APPARATUS FOR SOLAR ASSISTED FUEL
PRODUCTION
Abstract
Products from a solar assisted reverse-water-gas-shift reaction
(RWGS) are used to create a liquid hydrocarbon fuel. Heliostats
focus solar energy to heat carbon dioxide gas. A water splitter
splits water into hydrogen molecules and oxygen molecules via the
addition of the solar energy also directed from either the same
array of heliostats via a beam splitter off a common receiving
tower redirecting a portion of the electromagnetic spectrum, a
heliostat field dedicated for the water splitter, or from its own
parabolic trough. A chemical reactor mixes heated carbon dioxide
gas with all or just a portion of the hydrogen molecules from the
water splitter in a RWGS reaction to produce resultant carbon
monoxide. A synthesis reactor uses any unconsumed hydrogen
molecules and the resultant stabilized carbon monoxide molecules
from the RWGS reaction in the hydrocarbon fuel synthesis process to
create a liquid hydrocarbon fuel.
Inventors: |
Hinman; Brian L.; (Los
Gatos, CA) ; Stevens; John Henry; (Palo Alto, CA)
; Le Lievre; Peter; (Palo Alto, CA) |
Correspondence
Address: |
Rutan & Tucker, LLP.
611 ANTON BLVD, SUITE 1400
COSTA MESA
CA
92626
US
|
Assignee: |
Sundrop Fuels, Inc.
Pojoaque
NM
|
Family ID: |
42060057 |
Appl. No.: |
12/237999 |
Filed: |
September 25, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12145383 |
Jun 24, 2008 |
|
|
|
12237999 |
|
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Current U.S.
Class: |
205/340 ;
204/274 |
Current CPC
Class: |
F24S 20/20 20180501;
Y02P 20/129 20151101; C25B 1/55 20210101; F24S 30/452 20180501;
Y02E 10/47 20130101; Y02P 20/00 20151101; Y02P 20/133 20151101;
F24S 23/74 20180501; Y02E 60/36 20130101 |
Class at
Publication: |
205/340 ;
204/274 |
International
Class: |
C25B 1/04 20060101
C25B001/04 |
Claims
1. An apparatus, comprising: a window, where a first solar receiver
focuses solar energy thru the window to a
solar-energy-to-gas-heat-exchanger to heat carbon dioxide gas via
convection heating of the carbon dioxide gas from the heated
solar-energy-to-gas-heat-exchanger; a gas supply input to receive
gases from a water splitter containing one or more electrolysis
cells to split water molecules into hydrogen molecules and oxygen
molecules via the solar energy directed at the one or more
electrolysis cells from at least one of 1) the first solar
receiver, 2) an array of heliostats separate from the first solar
receiver and 3) a parabolic trough separate from the first solar
receiver; a chemical reactor chamber to mix the heated carbon
dioxide gas with the hydrogen molecules from the water splitter in
the form of gas in a reverse-water-gas-shift reaction to produce
resultant carbon monoxide and water molecules as well as unconsumed
carbon dioxide gas and hydrogen molecules; a recuperator to
pre-heat both the carbon dioxide gas and the hydrogen molecules
from the water splitter using at least an energy of the resultant
carbon monoxide exiting the chemical reactor chamber where the
reverse-water-gas-shift reaction occurred; and a gas supply output
to supply at least the resultant carbon monoxide molecules and
unconsumed hydrogen molecules from the reverse-water-gas-shift
reaction to a hydrocarbon liquid fuel synthesis reactor to create a
liquid hydrocarbon fuel.
2. The apparatus of claim 1, wherein the water splitter further
comprises: the parabolic trough contains a set of parabolic
mirrors, where each mirror connects to a tracking actuator to
rotate that mirror in both an azimuth axis and an elevation axis,
where each parabolic mirror reflects sunlight upwards in a frame of
the parabolic trough at a focal line of the parabolic trough onto
an associated light receiver that contains tubes with a titanium
based catalyst forming the one or more photoelectrolysis cells,
wherein the light receiver and frame in the parabolic trough may be
tilted at a slight upward angle to allow disassociated gases of
hydrogen and oxygen from the water splitting process to naturally
float upward and be collected/harvest for future use.
3. The apparatus of claim 2, further comprising: a quenching unit
to immediately cool at least a portion of exit gases from the
chemical reactor chamber in which the reverse-water-gas-shift
reaction occurs, in order to stabilize at least the carbon monoxide
molecule in the exit gases, wherein the parabolic trough uses
multiple mirrors, each mirror with a frame construction having two
axis of rotation and the frame is coupled to the tracking actuator,
and an electronic controller coupled to the tracking actuator and
feedback limit switches to control positioning of each mirror to
concentrate the solar energy on the associated light receiver,
wherein the parabolic trough is composed of multiple individual
mirrors connected together to form the trough and a series of the
associated light receivers are ganged together in a frame of the
parabolic trough.
4. The apparatus of claim 2, further comprising: a front surface of
a reflective mirror portion of each mirror in the set of parabolic
mirrors is formed by a reflective metal, wherein the unconsumed
carbon dioxide gas and hydrogen molecules from the
reverse-water-gas-shift reaction are also used in the recuperator
to pre-heat both the carbon dioxide gas and the hydrogen molecules
prior to entering the chemical reactor chamber.
5. The apparatus of claim 4, further comprising: a polymer or
acrylic coating on top of the front surface of the reflective metal
mirror, which is optically transmissive in passing wavelength bands
in an electromagnetic spectrum below infra red is on top of the
front surface of the reflective mirror to maximize an amount of
solar power being concentrated into the light receivers in a
desired UV and visible light spectrum while limiting generation of
waste heat, and the hydrogen splitting with the tubes with the
titanium based catalyst in the light receiver occurs at 50-80
degrees Celsius and 30-50 sun concentration units.
6. The apparatus of claim 1, wherein the gas supply output supplies
a portion of the unconsumed carbon dioxide from the
reverse-water-gas-shift reaction to the hydrocarbon liquid fuel
synthesis reactor.
7. The apparatus of claim 1, wherein the water splitter has one or
more light receivers with tubes that use a titanium based catalyst
forming the photoelectrolysis cells that receives UV rays and
visible light from an array of heliostats splits the water into the
hydrogen and oxygen molecules via the titanium based catalyst,
where the titanium based catalyst absorbs both the UV rays and a
portion of the visible light directed from the array of heliostats,
and where the titanium based catalyst is in a shape to strain the
catalyst to 1) pull apart its atoms or 2) even compress together
its atoms in order to alter the material's electronic properties
and allow the titanium based catalyst to absorb both wavelengths in
the portion of the visible light and ultraviolet light
spectrum.
8. The apparatus of claim 7, wherein the titanium based catalyst
consists of titanium oxide nanotubes in a strained shaped ripple
pattern coated with a tungsten oxide to enhance the visible
spectrum absorption of the titanium dioxide nanotube array, as well
as their solar-spectrum induced photocurrents.
9. The apparatus of claim 7, wherein the water splitter may be a
tower mounted device that contains the one or more
photoelectrolysis cells, where each cell has a clear tube filled
with an aqueous electrolyte solution that reacts with the
titanium.
10. The apparatus of claim 1, wherein the electrolysis cells are
photoelectrolysis cells that dissociate water and produce the
hydrogen molecules in the form of gas from an aqueous solution when
exposed to the solar energy, and the photoelectrolysis cell employs
an electrode made of a titanium-based element or compound with a
stress-induced band-gap that is shifted and broadened to absorb
both wavelengths in a portion of the visible light and the
ultraviolet light spectrum.
11. The apparatus of claim 10, wherein the electrode contains a
substrate that has surface ripples with a
sub-visible-light-wavelength spatial period that causes stress in
the titanium-based element or compound on the substrate in the form
of a thin film and thereby shifts the bandgap of the titanium based
element or compound to support spontaneous photoelectrolysis of the
water in visible light.
12. The apparatus of claim 1, wherein the water splitter contains
one or more high-temperature electrolysis cells for water
electrolysis that decompose the water into the oxygen and hydrogen
molecules in the form of gas due to an electric current being
passed through the water with most of the energy causing the high
temperature above 280 degrees Celsius supplied as heat from the
solar energy from a separate array of heliostats.
13. The apparatus of claim 1, further comprising: an optical filter
to pass a portion of the electromagnetic spectrum including the
visible light and UV ray range from the heliostats into the
electrolysis cells in the water splitter at around 20-50 sun
concentration units, wherein the first solar receiver is an array
of heliostats that focuses the solar energy from their mirrors onto
a dish on a first tower portion of the water splitter which is
coated with the optical filter.
14. The apparatus of claim 10, further comprising: one or more
solar photovoltaic cells that receive solar energy and convert that
energy directly into electricity, which are coupled to the
photoelectrolysis cell as a voltage source for the
photoelectrolysis cell device.
15. A method, comprising: heating a
solar-energy-to-gas-heat-exchanger and carbon dioxide gas via the
addition of the solar power directed from a first set of solar
receivers; splitting water molecules into hydrogen gas and oxygen
gas via the addition of the solar power directed from a second set
of solar receivers; producing the hydrogen gas from an aqueous
solution in contact with an electrode made of a titanium-based
element or compound with a stress-induced band-gap that is shifted
and broadened to absorb both wavelengths in a portion of a visible
light and in an ultraviolet light spectrum, where the wavelengths
are directed from the second set of solar receivers and the band
gap of the titanium-based element or compound is shifted and
broadened to a band gap of 3.0 electron volts (eV) or lower; mixing
the heated carbon dioxide gas with all of the hydrogen gas from the
water splitting process in a reverse-water-gas-shift reaction to
produce resultant carbon monoxide and water molecules and
unconsumed hydrogen; quenching a portion of the exit gases from a
chemical reactor chamber in which the reverse-water-gas-shift
reaction occurs, to stabilize at least the carbon monoxide
molecule; and mixing the unconsumed hydrogen gas and the resultant
carbon monoxide from the reverse-water-gas-shift reaction in a
hydrocarbon fuel synthesis process to create a liquid hydrocarbon
fuel.
16. The method of claim 15, further comprising: using a dye
sensitized solar cell, which includes a chromophoric substance to
chemically create the stress induced band gap.
17. The method of claim 15, further comprising: tracking the Sun in
two axis of rotation with the second set of solar receivers; and
reflecting the solar energy from the Sun upwards in a frame of a
parabolic trough at a focal line of the parabolic trough onto a
series of associated light receivers that each contain clear tubes
coated with a titanium based element or compound catalyst.
18. A system, comprising: a first array of heliostats to focus
solar energy to a solar-energy-to-gas-heat-exchanger to heat carbon
dioxide gas via convection heating of the carbon dioxide gas from
the heated solar-energy-to-gas-heat-exchanger; a parabolic trough
having multiple mirrors, where each mirror having a rotational
frame with two axis of rotation coupled to a tracking actuator to
redirect a portion of an electromagnetic spectrum including
ultraviolet rays and visible light from the solar energy to a water
splitter to split water molecules into hydrogen molecules and
oxygen molecules, one or more photoelectrolysis cells contained in
the water splitter, which each have an electrode made of a
titanium-based element or compound with a stress-induced band-gap
that is shifted and broadened by a formation of surface ripples
with a sub-visible-light-wavelength spatial period that causes
stress in the titanium based element or compound to shift the
bandgap of the titanium based element or compound to support to an
absorption of both a portion of the visible light and the
ultraviolet rays; a Nickel alloy based chemical reactor chamber to
mix the heated carbon dioxide gas with all of or just a first
portion of the hydrogen gas from the water splitter in a
reverse-water-gas-shift reaction in order to produce resultant
carbon monoxide and water molecules; a quenching unit to cool at
least a portion of the exit gases from the chemical reactor chamber
in which the reverse-water-gas-shift reaction occurs, in order to
stabilize at least the carbon monoxide molecule in the exit gases;
and a methanol synthesis reactor to mix unconsumed hydrogen
molecules and the resultant stabilized carbon monoxide molecules
from the reverse-water-gas-shift reaction in a methanol synthesis
process to create methanol.
19. The system of claim 18, further comprising: a front surface of
a reflective mirror portion of each mirror in the parabolic trough
is formed by a reflective metal.
20. The system of claim 19, further comprising: a polymer or
acrylic coating is on top of the front surface of the reflective
metal mirror, which is optically transmissive in passing wavelength
bands in the electromagnetic spectrum below infrared.
Description
RELATED APPLICATION
[0001] This application is a continuation in part of and claims the
benefit of U.S. application Ser. No. 12/145,383, titled "Various
Methods And Apparatus For Solar Assisted Chemical And Energy
Processes", filed Jun. 24, 2008.
NOTICE OF COPYRIGHT
[0002] A portion of the disclosure of this patent document contains
material that is subject to copyright protection. The copyright
owner has no objection to the facsimile reproduction by anyone of
the software engine and its modules, as it appears in the Patent
and Trademark Office Patent file or records, but otherwise reserves
all copyright rights whatsoever.
FIELD OF THE INVENTION
[0003] Embodiments of the invention generally relate to use of
solar receivers, such as heliostats, focusing solar power on a unit
containing a chemical reactor. More particularly, an aspect of an
embodiment of the invention relates to use of solar receivers
focusing solar power on a unit containing a chemical reactor to
heat gas up to temperatures such, as 1500 degrees Celsius or lower
as an upper temperature limit, in order to form a hydrocarbon fuel,
such as methanol, and possibly drive a Brayton turbine engine.
BACKGROUND OF THE INVENTION
[0004] Carbon dioxide may be put to use in beneficial applications
such as generation of a hydrocarbon fuel including methanol and
gasoline.
SUMMARY OF THE INVENTION
[0005] In general, various methods, apparatuses, and systems are
described to use products from a solar assisted
Reverse-water-gas-shift reaction (RWGS) to create a liquid
hydrocarbon fuel. Heliostats focus solar energy to heat carbon
dioxide gas. A water splitter splits water into hydrogen molecules
and oxygen molecules via the addition of the solar energy also
directed from either the same array of heliostats via a beam
splitter off a common receiving tower redirecting a portion of the
electromagnetic spectrum, a heliostat field dedicated for the water
splitter, or from its own parabolic trough. A chemical reactor
mixes heated carbon dioxide gas with all or just a portion of the
hydrogen molecules from the water splitter in a RWGS reaction to
produce resultant carbon monoxide. A synthesis reactor uses the
hydrogen molecules from the water splitter or the RWGS reaction and
the resultant stabilized carbon monoxide molecules from the RWGS
reaction in the hydrocarbon fuel synthesis process to create a
liquid hydrocarbon fuel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] The drawings refer to embodiments of the invention in
which:
[0007] FIG. 1 illustrates an embodiment of a solar assisted process
to create a liquid fuel;
[0008] FIGS. 1a and 1b illustrate embodiments of a solar assisted
process to create a hydrocarbon liquid fuel;
[0009] FIG. 2 illustrates a view of an embodiment of the parabolic
trough;
[0010] FIG. 3 a view of an embodiment of the parabolic trough;
[0011] FIGS. 4a and 4b illustrate a flow diagram to generate
methanol from solar heated carbon dioxide; and
[0012] FIG. 5 illustrates an embodiment of an electrolysis
cell.
[0013] While the invention is subject to various modifications and
alternative forms, specific embodiments thereof have been shown by
way of example in the drawings and will herein be described in
detail. The invention should be understood to not be limited to the
particular forms disclosed, but on the contrary, the intention is
to cover all modifications, equivalents, and alternatives falling
within the spirit and scope of the invention.
DETAILED DISCUSSION
[0014] In the following description, numerous specific details are
set forth, such as examples of named components, connections, types
of catalyst, etc., in order to provide a thorough understanding of
the present invention. It will be apparent, however, to one of
ordinary skill in the art that the present invention may be
practiced without these specific details. In other instances, well
known components or methods have not been described in detail but
rather in a block diagram in order to avoid unnecessarily obscuring
the present invention. Further specific numeric references such as
first portion of gas, may be made. However, the specific numeric
reference should not be interpreted as a literal sequential order
but rather interpreted that the first portion of gas is different
than a second portion of gas. Thus, the specific details set forth
are merely exemplary. The specific details may be varied from and
still be contemplated to be within the spirit and scope of the
present invention.
[0015] In general, a method, apparatus, and system are described in
which products from a solar assisted reverse-water-gas-shift
reaction are used in a hydrocarbon fuel synthesis process to create
a liquid hydrocarbon fuel. An array of heliostats focuses solar
energy to a solar-energy-to-gas-heat-exchanger to heat the carbon
dioxide gas. A water splitter with one or more electrolysis cells
splits water molecules into hydrogen molecules and oxygen molecules
via the addition of the solar energy also directed from either 1)
the same array of heliostats via a beam splitter off a common
receiving tower redirecting a portion of the electromagnetic
spectrum, 2) a separate heliostat field dedicated for the water
splitter, or 3) from its own parabolic trough. A chemical reactor
chamber mixes the heated carbon dioxide gas with all or just a
portion of the hydrogen molecules generated from the water splitter
in a reverse-water-gas-shift reaction to produce resultant carbon
monoxide. A hydrocarbon liquid fuel synthesis reactor receives and
uses the hydrogen molecules and the resultant stabilized carbon
monoxide molecules from the reverse-water-gas-shift reaction in the
hydrocarbon fuel synthesis process to create a liquid hydrocarbon
fuel.
[0016] Essentially, two main embodiments, as well as a couple of
other embodiments, are described.
[0017] The first solar assisted embodiment has all of the moles of
hydrogen generated from the water splitter being heated up and run
through the reverse water gas shift reaction. The heated hydrogen
gas, carbon dioxide gas, and resultant carbon monoxide will then be
cooled by exchanging their energy to preheat the feed gases. The
unconsumed hydrogen from the RWGS is routed in whole to the fuel
synthesis process and during the routing is used in a recuperator
to preheat new feed gases for the RWGS reaction.
[0018] The second solar assisted embodiment merely heats up a
portion of the moles of hydrogen generated from the water splitter
and then sends the other portion of the non-superheated moles of
hydrogen to the fuel synthesis process. The unconsumed hydrogen
from the RWGS along with any unconsumed carbon dioxide may be
recycled back into the RWGS to preheat new feed gases for the RWGS
reaction. Therefore, merely the heated carbon monoxide from the
RWGS needs to be cooled enough to be sent to the fuel synthesis
process while the non-superheated moles of hydrogen may already be
close to the right temperature.
[0019] In both of these embodiments, more moles of hydrogen are
supplied to the RWGS reaction than is needed for equilibrium in
order to overdrive the reaction to maximize the carbon monoxide
production. In both of these embodiments, a variety of solar
receivers can be used to direct the solar energy and a variety of
electrolysis cells may be used to generate hydrogen. In both
embodiments, a small percentage of the carbon dioxide may be sent
along with the carbon monoxide and hydrogen to the fuel synthesis
process. The small percentage, such as between 0.1% to 3% by volume
of carbon dioxide, helps the fuel synthesis process.
[0020] Thus, the water splitting process and the
reverse-water-gas-shift reaction process produce synthesis gas (a
gas combination including carbon monoxide (CO) and hydrogen (H2))
via the addition of solar energy. The resultant synthesis gas from
the RWGS reaction may be used to create any number of hydrocarbon
liquid fuels, such as methanol, ethanol, diesel fuel, gasoline and
crude oil.
[0021] The Sun's energy may be concentrated by solar receivers, via
one or more arrays of heliostats, a parabolic trough or dish, etc.,
to provide the energy needed for the chemical transformations to
occur in the RWGS unit and be concentrated via one of the three
example methods above for the H2O splitting process. The Sun's
energy may be also coupled to a process for driving a Brayton
turbine engine or photovoltaic solar cells for generating
electricity.
Operation of the Reactor
[0022] FIG. 1 illustrates solar assisted processes of water
splitting and a RWGS reaction to supply a synthesis gas to a liquid
fuel synthesis process to create a liquid fuel. Water is supplied
to a water (H2O) splitter 02 that uses the energy of the sun to
disassociate the H2O into H2 and O2 molecules. The produced
hydrogen gas is supplied to the RWGS unit 04. The RWGS unit 04 also
receives a supply of carbon dioxide (CO2). The RWGS unit 04 heats
both the hydrogen and carbon dioxide with the energy of the Sun and
then uses the heated gases in a RWGS reaction to produce synthesis
gas. The synthesis gas from the RWGS reaction may be used in a
recuperator 05 to preheat the incoming feed gases of hydrogen and
carbon dioxide. The synthesis gas is supplied to a liquid fuel
synthesizer 08. The liquid fuel synthesizer 08 converts the
synthesis gas to liquid fuel. The liquid fuel synthesizer 08 may
produce fuel and have left over carbon dioxide, and any imbalance
of carbon monoxide or hydrogen left from the synthesis process. All
three of these gases can be recycled back to the CO2 recirculation
point back into the RWGS unit 04.
[0023] FIGS. 1a and 1b illustrate a solar assisted process to
create a hydrocarbon liquid fuel.
[0024] Referring to FIG. 1a, a water splitter 102a that uses one or
more electrolysis cells 180, including photoelectrolysis cells,
high temperature electrolysis cells, and similar cells, can be used
to supply hydrogen gas into a unit 104 that generates synthesis gas
for a fuel production unit 108 to generate a hydrocarbon liquid
fuel, such as methanol.
[0025] The RWGS unit 104 may also contain sections such as a
solar-energy-to-gas-heat-exchanger 122, a chemical reactor 106a, a
H2 gas supply line 124, which can be supplied by the water splitter
or other H2 sources, the carbon dioxide gas supply line 126, and
other gas supply lines 128, a quenching unit 130, a heat
recuperator 105a, and other similar components. This solar assisted
embodiment may have substantially all of the moles of hydrogen
generated from the water splitter 102a being heated up and run
through the RWGS reaction in the chemical reaction chamber
106a.
[0026] Referring to FIG. 1b, the unit 104 may also include a H2
recirculation loop 110, a carbon monoxide (CO) recirculation loop
112, and a carbon dioxide recirculation loop 114 and could be
either discrete loops or combined. The RWGS unit 104 may also
contain sections such as a water condenser/separator 120, and other
similar components. The Sun's energy may also be stored within the
RWGS unit 104 in a storage unit 116 for continued operations at
night, or may be stored directly in a solar receiver. The RWGS unit
104 may also have an alternative supply of energy 118 for
supplemental power or primary power in times of inadequate solar
power or maintenance. This solar assisted embodiment may merely
heat up a portion of the moles of hydrogen generated from the water
splitter 102b in the RWGS reaction and send the remaining portion
of the non-superheated moles directly to the fuel synthesis process
108.
[0027] In both of these solar assisted embodiments, more moles of
hydrogen are supplied to the RWGS reaction than needed for
equilibrium in order to overdrive the reaction to maximize the
carbon monoxide production.
[0028] The Chemical Operation may be Summed:
[0029] 1. Water (H2O) is split into Hydrogen (H2) molecules and
Oxygen (O2) molecules (2 H2O+energy.fwdarw.H2+O2) via the addition
of solar power in combination with standard H2O cleaving
techniques, water splitting with a Titanium based alloy, high
temperature electrolysis, or other similar techniques. The water
splitter 102 may be a tower mounted device that contains clear
tubes, such as quartz or borosilicate, that are filled with water
in the form of gas or liquid reacting with the titanium. Another
example form the water splitter 102 may take is a parabolic trough
system.
[0030] 2. The carbon dioxide gas is heated by the solar receivers,
such as heliostats 134, directing the rays of the Sun to the
solar-energy-to-gas-heat-exchanger 122 to a steady state
temperature between 200-1000 degrees Celsius as the gas exits the
heat exchanger area 122. Complete conversion of carbon dioxide may
occur around 900 degrees Celsius without a catalyst. The hot carbon
dioxide gas is mixed with the other gases for the
reverse-water-gas-shift reaction. However, in an embodiment, the
carbon dioxide is heated by the Sun to the steady state temperature
at the same time while the hydrogen is being heated up. A
temperature, such as 1500 degrees Celsius (C.) or lower, may be
established as an upper temperature limit for the
reverse-water-gas-shift reaction. Also, both the carbon dioxide
gas, from the CO2 supply 126 in a first outer pipe 176, and the
feed hydrogen gas, from the H2 supply 124 in a second outer pipe
175, may be additionally pre-heated using the energy of the
recycled gases and/or waste gases exiting the RWGS reactor 106 in
one or more inner pipes 170 located in the recuperator 105.
[0031] 3. Next, the solar-assisted endothermic RWGS produces the
resultant carbon monoxide molecules for the synthesis gas. The
heated carbon dioxide and hydrogen mixture may be supplied to a
Nickel alloy RWGS reactor 106, such as an Inconel 600.TM. reactor,
Ni/Al2O3 reactor, etc. In the RWGS reaction, the heated CO2, from
step 2 above, is combined with the hydrogen molecules, from step 1
above, in a ratio such as one mole of carbon dioxide per three
moles of hydrogen, in potentially the presence of a catalyst, plus
the heat from the Sun to yield in the reaction at least produced
carbon monoxide plus water plus unconsumed two moles of hydrogen.
The flow rate of each gas, hydrogen and heated carbon dioxide, may
be controlled to maximize the yield of carbon monoxide produced
based upon the supplied hydrogen.
[0032] 4. A portion of the exit gases from the RWGS reactor chamber
may then be immediately cooled/quenched by the quencher 130 to
stabilize or otherwise capture at least the carbon monoxide
molecule. The resultant carbon monoxide plus 1) the unconsumed
hydrogen molecules from the RWGS reaction or 2) the non-superheated
hydrogen supplied directly from the water splitter 102 are used in
the methanol synthesis step (5) below. Referring to FIG. 1b, 2/3rds
of the hydrogen generated is supplied directly from the water
splitter 102b to the fuel production unit 108 while the other
portion of the hydrogen, such as the remaining third, is mainly
consumed in the RWGS reaction in reactor 106b and any unconsumed
hydrogen is recycled back into the RWGS synthesis gas production of
step 3. Accordingly, the heated carbon dioxide gas and hydrogen gas
would be separated from the resultant carbon monoxide and
water.
[0033] In an embodiment, substantially all of the moles of hydrogen
molecules 1) generated from the water splitter 102a and 2) passed
through the chemical reactor chamber 106a, which are not consumed
in the reverse water gas shift reaction are sent with the resultant
carbon monoxide from the reverse water gas shift reaction and
between 0.1% to 3% by volume of carbon dioxide in the inner pipe
170 to the hydrocarbon fuel synthesis 108 process to create the
liquid hydrocarbon fuel.
[0034] 5. Thru standard chemical processes, either on-site or
off-site, hydrocarbon fuel synthesis occurs. A properly blended
form of synthesis gas that includes (at least two moles of
hydrogen, carbon monoxide, and carbon dioxide) reacts with a
catalyst to yield >CH3OH .DELTA.rH (methanol)+heat, or another
desired hydrocarbon fuel.
[0035] In an embodiment, the hydrogen splitting with Titania (TiO2)
occurs at low temperatures and low sun units (50-80 degrees
Celsius, 30-50 sun concentration, 15 pounds per square inch (PSI)
pressure), reformation to synthesis gas occurs at a higher
temperature (800-1000 degrees Celsius, 1000 sun concentration, 15
psi pressure), and the hydrocarbon fuel synthesis is an exothermic
reaction occurring at a moderate temperature (260 degrees Celsius,
no sun, 1000 psi pressure).
[0036] Referring to FIG. 1a, as discussed in step 4, there can be
three moles of hydrogen for every one mole of carbon dioxide
initially, and then one mole of hydrogen is compromised to make
carbon monoxide. However, all three moles of hydrogen may be mixed
with or heated by waste carbon dioxide gas before doing the RWGS.
The elevated temperature makes it easier to move the reaction
toward completion. Accordingly, as discussed in step 2, the
recuperator 105a plumbs pipes to the feed gases input ports 124,
126 and exhaust gases output ports from the quencher 130. The
recuperator 105a passes the exhaust gases from the chemical
reaction chamber 106a in an inner pipe 170 in order to pre-heat the
feed carbon dioxide and hydrogen gases passed through a larger
outer pipe carrying the feed carbon dioxide and hydrogen gases. The
pipes 175 and 176 for the feed carbon dioxide and hydrogen gases
may be combined or kept separate during this pre-heating
process.
[0037] The recuperator 105a pre-heats both the feed carbon dioxide
gas and hydrogen gas prior to the carbon dioxide gas and the
hydrogen molecules entering the chemical reactor chamber 106a by
transferring the energy of the exit gases (carbon dioxide gas,
unconsumed hydrogen gas, resultant carbon monoxide, and resultant
water) leaving the chemical reactor chamber 106a.
[0038] Similarly, the recuperator 105a cools the unconsumed
portions of the carbon dioxide gas and the hydrogen molecules from
the reverse water gas shift reaction and the resultant carbon
monoxide and water molecules to preheat at least the hydrogen
molecules from the water splitter and the feed carbon dioxide.
[0039] The cooled hydrogen molecules, the carbon monoxide, and a
small percentage of the carbon dioxide from the reverse water gas
shift reaction are sent to the hydrocarbon fuel synthesis process
to create a liquid hydrocarbon fuel.
[0040] Gas flow in the recuperator 105a is in the direction of the
temperature gradient of the heat-exchanging surface. This minimizes
entropy production in the process. Thus, the feed gas flow starts
flowing along the inner pipe at its relative lowest temperature
area and flows along the inner pipe 170 to the recuperator's 105a
relative highest temperature area. Filters in the recuperator 105a
remove a portion of the carbon dioxide once it has given up a
majority of its heat to the feed gases. The condenser 120 couples
to the recuperator 105a at its cooler end portion to remove the
water gases from the produced synthesis gas. Also, the filtered out
carbon dioxide can be recycled back in with new feed carbon dioxide
feed gas 126.
[0041] Thus, the reverse water gas shift reaction can be driven to
maximize production of carbon monoxide for a subsequent exothermic
reaction in the generation of methanol as the hydrocarbon fuel, by,
supplying at least fifty percent more moles of heated hydrogen
molecules relative to an amount of carbon dioxide present in the
chemical reactor chamber 106 than necessary to achieve equilibrium
in the reverse water gas shift reaction to force maximum production
of the resultant carbon monoxide.
[0042] Referring to FIG. 1b, as discussed in step 4, the chemical
reactor chamber 106b mixes the heated carbon dioxide gas with a
first portion of the hydrogen molecules from the water splitter
102b in the form of gas in the reverse water gas shift reaction in
order to produce resultant carbon monoxide and water molecules. One
or more filters 127 then separate out the heated unconsumed carbon
dioxide gas and hydrogen gas from the resultant carbon monoxide and
water produced in the reverse water gas shift reaction. One or more
recycle pipes 110, 112, 114 recycle both the separated out carbon
dioxide back to the solar-energy-to-gas-heat-exchanger area 122 and
recycle at least a portion of the separated out hydrogen gas back
to the into the hydrogen-carbon dioxide mixing area.
[0043] Thus, the reverse water gas shift reaction is driven to
maximize production of carbon monoxide for the subsequent
exothermic reaction in the generation of the hydrocarbon fuel,
including methanol, by overloading an initial amount of hydrogen
molecules relative to an amount of carbon dioxide present in the
chemical reactor chamber during the reverse water gas shift
reaction. The excess hydrogen from the initial batch (and
subsequent batches) is both continuously recycled to 1) preheat
incoming feed gases as well as 2) ensure that RWGS reaction is
overdriven with hydrogen molecules. However, in this embodiment,
the remainder of the hydrogen produced from the water splitter 102b
is sent directly to the fuel production 108 eliminating a need to
cool the hydrogen gas for the fuel synthesis process.
[0044] The quenching unit 130 immediately cools at least a portion
of exit gases from the chemical reactor chamber 106 in which the
reverse-water-gas-shift reaction occurs, in order to stabilize at
least the carbon monoxide molecule and potentially the carbon
monoxide molecules in the exit gases. In an embodiment, the
quenching unit 130 is a heat exchanger placed immediately
downstream of the chemical reactor 106 to cool the gas below
degrees 700 Celsius, where radicals involved in the back reaction
are favored, and the heat exchanger moves the resultant carbon
monoxide away from a catalyst located in the chemical reactor 106,
which then also raises an activation energy of the carbon monoxide
to revert back to carbon dioxide.
[0045] The RWGS unit 104 has a gas supply output to supply at least
the resultant stabilized carbon monoxide molecules from the
reverse-water-gas-shift reaction to a hydrocarbon liquid fuel
synthesis reactor 108. The hydrocarbon liquid fuel synthesis
reactor 108 also receives and uses a second portion of the hydrogen
molecules from the water splitter 102 and the resultant stabilized
carbon monoxide molecules from the reverse-water-gas-shift reaction
in the hydrocarbon fuel synthesis process to create the liquid
hydrocarbon fuel. For example, a methanol synthesis reactor may mix
a second portion of the hydrogen molecules from the water splitter
and the resultant stabilized carbon monoxide molecules from the
reverse-water-gas-shift reaction in a methanol synthesis process to
create methanol.
[0046] In an embodiment, the carbon dioxide in step 2 may be heated
high enough such as 900 Celsius to 2300 degrees Celsius for solar
assisted reduction of carbon dioxide to occur. The heated carbon
dioxide is reduced to carbon monoxide molecules and oxygen
molecules. The oxygen from the carbon dioxide reduction and the
water splitting may be cooled and stored as a liquid fuel or a
portion may be used as a catalyst in the RWGS discussed later. This
process will cause a lot of waste heat for use in other processes
such as the synthesis gas generation and the heated carbon dioxide
may also be used as an energy source to drive a Brayton turbine
engine 132.
[0047] As shown in figure la, there may be a first field of
heliostat arrays and a discrete second field of heliostat arrays.
The first array of heliostats 143 focuses the Sun's rays from their
mirrors onto a dish on a first tower portion of the water splitter
102 which is coated with an optical filter to pass a portion of the
electromagnetic spectrum including the UV ray range from the Sun
towards into the water splitter 102 at around 20-50 sun
concentration units. The water splitter 102 is located within the
first tower and the visible light and UV rays pass through the
optical filter. A second array of heliostats 147 focuses the Sun's
rays from their mirrors onto a dish on a second tower that contains
the solar-energy-to-gas-heat-exchanger 122. These power tower
systems use an array of large individually tracking mirrors, known
as heliostats. The heliostats use a two axis tracking of the sun to
focus light rays onto a central receiver mounted near the top of a
tower. Very high temperatures up to 1500.degree. Celsius can be
achieved at concentration ratios around 1500.times. sun
concentration units.
[0048] Alternatively, the heliostats may focus their rays on a
single dish on the single tower which is coated with an optical
beam splitter for beam splitting to direct a portion of the
electromagnetic spectrum including the UV ray range from the Sun's
rays towards the water splitter at around 20-50 sun concentration
units while directing the remaining optical spectrum to the RWGS
unit using around 800-1200 sun concentration units. The water
splitter may be located within the tower and the visible light and
UV rays pass through the beam splitter and the beam splitter
reflects the other wavelengths to the
solar-energy-to-gas-heat-exchanger.
[0049] Instead of a second field of heliostat arrays 143 there may
be another solar receiver such as a parabolic trough. As discussed
in step 1, water may be split in hydrogen molecules and oxygen
molecules in the water splitter 124 via the addition of solar power
in combination with standard water cleaving techniques, water
splitting with titanium, or other similar techniques. In an
embodiment, the water splitter 124 via the addition of solar power
from the heliostats 134 or parabolic trough may use photo catalytic
splitting of water into hydrogen and oxygen in an electrolysis
cell. For example, Titanium oxide nanotubes coated with tungsten
oxide can be prepared to harvest hydrogen and oxygen with solar
light. The tungsten trioxide coatings on the nanotubes can
significantly enhance the visible spectrum absorption of the
titanium dioxide nanotube array, as well as their solar-spectrum
induced photocurrents. The catalytic Titanium dioxide materials use
sunlight to split water on the spot, via a process known as direct
solar-hydrogen production. The solar-hydrogen systems, when photons
strike the catalytic material, they excite electrons, which then
roam about freely until they meet a water molecule at the
material's surface. The extra electrons strip the two hydrogen
atoms away from water's one oxygen atom, producing hydrogen fuel.
The oxygen atom simultaneously hooks up with another oxygen atom,
forming an oxygen molecule.
[0050] FIGS. 2a and 2b illustrate perspective views of embodiments
of a parabolic trough system used with the water splitter.
[0051] In an embodiment, the parabolic trough 243 contains a set of
parabolic mirrors 251. Each mirror 251 connects to a tracking
actuator 253 to rotate that mirror in both the azimuth and
elevation axis. Each parabolic mirror 251 reflects sunlight upwards
in a frame of the parabolic trough at a focal line of the parabolic
trough onto small areas of an associated light receiver 255 that
contains glass or similar clear tubes coated with a titanium based
element or compound catalyst in an electrolyte. The light receiver
255 and frame in the parabolic trough may be tilted at a slight
upward angle to allow disassociated gases of hydrogen and oxygen
from the water splitting process to naturally float upward and be
collected/harvest for future use.
[0052] An electronic controller 261 couples to the tracking
actuator 253 and feedback limit switches 259 to controlled
positioning of each mirror to concentrate the sun's rays on the
light receiver 255.
[0053] The mirror 251 can be held in its parabolic shape by stamped
tab ribs 257 at either end of the mirror. The ribs 257 are trimmed
just above the stamped tabs so that they cause minimal shading, and
fixed from below to receiver support brackets.
[0054] FIG. 3 illustrates a top down view of an embodiment of a
parabolic trough system used with the water splitter. The exterior
casing of the frame of the parabolic trough is cut away in this
view to reveal the light receivers 355 and tubes forming the
electrolysis cells located in each light receiver 355.
[0055] As discussed, the parabolic trough 343 can use multiple
mirrors 351. Each mirror has two axis of rotation frame
construction and couples to the tracking actuator. In this
embodiment, the long trough of the parabolic trough 343 is composed
of multiple individual mirrors connected together to form the
trough and a series of the associated light receivers 355 are
ganged together in a frame of the parabolic trough 343. Thus, all
of the TiO2 tubes can be in the same frame containing light
receivers that can be put at a slight upward incline to assist in
collection of hydrogen and oxygen gases by the bubbles of gas
traveling up the incline.
[0056] The parabolic-trough water-splitter has one or more light
receivers with tubes that use titanium based catalyst, which form
the electrolysis cells that receive UV rays and visible light from
the mirrors to split water into hydrogen and oxygen via the
titanium based catalyst that absorbs both the UV rays and a portion
of the visible light directed from the heliostats. One electrode
draws the hydrogen gas and the other electrode draws the oxygen
gas.
[0057] In an embodiment, the parabolic trough concentrator uses
two-axis tracking, and aluminum reflectors with the use of
anti-corrosive additives on the reflectors.
[0058] Referring to FIGS. 2a and 2b, the parabolic trough
concentrator's two-axis tracking system may be based on a `daisy
wheel` arrangement. The mirrors are supported by metal frames,
which in turn are mounted on a 2-axis tracking mechanical
structure. The tracking system reliably and accurately tracks the
sun. Each mirror may rotate in both the azimuth (side to side) axis
of rotation as well as the elevation (top to bottom) rotation. The
azimuth tracking is achieved by rotation on a ring mounted flush to
a ground. The second elevation axis of rotation was along the edge
of the mirror, allowing each trough to roll to the correct
elevation zenith angle. A microprocessor electronic controller
cooperating with a linear actuator positions the troughs pointing
towards the sun, even during cloudy weather. The troughs `roll`
from east to west each day and the long central support tilts the
troughs to adjust for seasonal variation. This is called `two-axis`
tracking. The microprocessor positions a linear actuator and reads
encoders for feedback in order to move the mirrors a precise
amount. The linear actuator causes rotation of the main beam
through cables and a pulley. Stepper motors can be an alternative
to the linear actuator.
[0059] Parabolic trough tracking and calibration requirements are
lower than for a heliostat array. Power output can be increased by
40% compared to fixed array, by tracking the Sun along the
north-south and the east-west axes.
[0060] Referring to FIG. 3, the front surface of the reflective
mirror portion of the parabolic trough (or tower dish) may be
formed by a reflective metal such as aluminum and chrome, which are
actually better at reflecting lower electromagnetic spectrum rays,
such as UV rays, than typical glass mirrors which absorb a greater
percentage of waves in this portion of the electromagnetic
spectrum. Further, a coating may be stretched across either the
mirror and/or the aperture of the light receiver in which the sun's
rays are being focused into in order to assist in controlling the
passing or deflecting different wavelength bands in the
electromagnetic spectrum. An essentially transparent polymer or
acrylic, such as ETFE, may also be placed across or adhered to the
surface of the mirrors, which is transparent in the electromagnetic
wavelength bands of desire, in order to protect the mirror from
environmental damage such as acid rain, chipping etc. Thus, a
polymer or acrylic coating on top of the front surface of the
reflective metal mirror, which is optically transmissive in passing
wavelength bands in the electromagnetic spectrum below infra red is
on top of the front surface of the reflective mirror to maximize
the amount of Sun being concentrated into the light receivers in
the desired UV and visible light spectrum while limiting generation
of waste heat, and the hydrogen splitting via tubes with a titanium
based catalyst in the light receiver to occur at 50-80 degrees low
temperature, 30-50 sun concentration units.
[0061] Note, electromagnetic radiation can be classified by
wavelength into radio, microwave, infrared, the visible region we
perceive as visible light, ultraviolet, X-rays and gamma rays.
[0062] The polymer or acrylic coating on top of the front surface
of the reflective metal mirror can be highly scratch resistant and
resistant to significant deterioration. Each mirror can deliver a
concentration ratio of about 20 to 1.
[0063] The temperature of the process in the light receiver can be
controlled with passive heat sinks such as aluminum fins or active
cooling flow of air/water to the receiver. In an embodiment, each
solar light receiver has an integrated passive heat sink to
maintain the cells at a moderate temperature.
[0064] Referring to FIG. 1, the water splitter generates commercial
quantities of hydrogen gas on site as a feed gas to produce both
synthesis gas in a reverse-water-gas-shift reaction and then
combined with resultant carbon monoxide from the RWGS to produce a
hydrocarbon liquid fuel. The hydrogen gas generated on site as a
feed gas is generated on site via a low/zero carbon emission
process. The water splitter can generate hydrogen gas from water
splitting with titanium or high temperature water splitting via
electrolysis and the electrical power for the water splitting is
generated via a Brayton engine or photovoltaic electrical power
generation mechanism. This also allows the hydrocarbon liquid fuel
to be generated in geographic areas not located near the public
utility grid.
[0065] Electrolysis cells 180 consisting of dye-sensitized solar
cells using a TiO2 thin film electrode may also be used to harvest
hydrogen and oxygen with solar light.
[0066] The catalytic Titanium dioxide materials use sunlight to
split water on the spot, via a process known as direct
solar-hydrogen production. The solar-hydrogen systems, when photons
strike the catalytic material, they excite electrons, which then
roam about freely until they meet a water molecule at the
material's surface. The extra electrons strip the two hydrogen
atoms away from water's one oxygen atom, producing hydrogen fuel.
The oxygen atom simultaneously hooks up with another oxygen atom,
forming an oxygen molecule.
[0067] A titanium di-silicide catalyst can also be used with
focused sunlight to split water into hydrogen and oxygen. The
heliostats supply the energy to drive the water to hydrogen and
oxygen. Titania is used to capture energy from sunlight. The
absorbed energy releases electrons, which split water to make
hydrogen. The Titania material may be strained so that its atoms
are slightly pressed together or pulled apart to alter the
material's electronic properties. In an embodiment, a coating of
Titania may be physically stretched and deposited on dome-like
nanostructures that cause the atoms to be slightly pulled apart.
The TiO2 may be physically stressed by creating a substrate with
ripples in the substrate that have a visible light wavelength
spacing and when the TiO2 thin film is stretched over the rippled
substrate, the TiO2 essentially inherits a stressed band gap to
absorb visible light. By pulling the atoms apart, less energy is
required to knock the electrons out of orbit. Thus, light with
lower energy can be used to split water, which means both visible
light and ultraviolet light can be used. Similarly, when dopants
are added in the dye sensitized solar cells, the coating of Titania
absorbs a greater spectrum of light waves than in its native
unstressed state.
[0068] Generally, electromagnetic radiation is classified by
wavelength into radio, microwave, infrared, the visible region we
perceive as light, ultraviolet, X-rays and gamma rays. EM radiation
with a wavelength between approximately 400 nm and 700 nm is
detected by the human eye and perceived as visible light.
Ultraviolet (shorter than 400 nm to about 1 nm) are also sometimes
referred to as light. Being very energetic, UV rays can break
chemical bonds, making molecules unusually reactive or ionizing
them, in general changing their mutual behavior.
[0069] Note, the strain on the atoms also affects the way that
electrons move through the material. Too much strain, and the
electrons tend to be reabsorbed by the material before they split
water. Thus, a balance between absorbing more sunlight and allowing
the electrons to move freely out of the material is attempted to be
achieved with the strain applied. Overall, the Titania (TiO2) can
be stressed to lengthen the band gap by mechanical and/or chemical
means.
[0070] FIG. 5 is a cross-sectional drawing of a photoelectrolysis
cell device for dissociation and production of hydrogen gas from an
aqueous solution when illuminated. The water splitter may contain a
photoelectrolysis cell device 580. The photoelectrolysis cell 580
employs an electrode made of a titanium-based element or compound
with a stress-induced band-gap shifted and broadened to be active
at light wavelengths more prevalent in sunlight. The
photoelectrolysis cell device may include some or all of the
following: a first working electrode that has thin layers of
adhesion and/or conductivity promoting materials and a Titania
semiconductor photocatalyst coated on top of the rippled surface of
a polycarbonate substrate(s) 585, housing, aqueous electrolyte,
separation membrane 586, second electrode 588, bias voltage source
590, tanks for collecting and storing the hydrogen gas 592 and
oxygen gas 594. An enlarged view of the rippled surface of a
polycarbonate substrate(s) 585 with the Titania semiconductor
photocatalyst coated on top is shown at the top of FIG. 5.
[0071] The rays of solar energy from the solar receivers 534
illuminate the polycarbonate substrate that also comprises one side
of the cell. The polycarbonate 585 has a distal surface that has
been embossed with ripples, and coated with Titania. Nanoscale
ripples are present in the substrate 585 such that stress is
induced in the thin film of Titania by forming local high-stress
bending radii.
[0072] A high stress-bending radius depends on the two materials
involved, specifically these materials Young's moduli, and how the
covering layer is formed relative to the ripple/wave on the other
layer. Titania in an unstressed state has a maximum band gap of
about 3.4 eV, and a more typical band gap of about 3.2 eV. The
bandgap of Titania thin film being stressed is a shifted and
broadened to a bandgap of 3.0 eV or lower. The Titania
semiconductor film 585 has a native bandgap that does not support
spontaneous photoelectrolysis of water in visible light wavelengths
present in sunlight.
[0073] The electrode contains a substrate that has surface ripples
with a sub-visible-light-wavelength spatial period that causes
stress in the titanium based element or compound semiconductor thin
film on the substrate 585 and thereby shifts the bandgap of the
titanium based element or compound to support spontaneous
photoelectrolysis of water in visible light. The shift in the band
gap increases the absorption of photons and light beyond
ultra-violet and well into the visible, abundant part of the solar
spectrum. (=the bandgap of Titania is too large to absorb in the
visible region. The substrate 585 has surface ripples with a
sub-visible-light spatial pitch and hence the thin film stretched
over the substrate inherits these ripples with a sub-visible-light
spatial pitch. The pitches among the linear irregularities or
recesses in the ripples in the thin film are not necessary uniform
but stay within the range on the substrate. The substrate 585 has
surface ripples in a waveform shape that have a spacing/pitch
between 20 nm to 350 nm. Note visible light at the low end is waves
greater than 400 nm. Thus, the substrate 585 has ripples on a
surface thereof, the ripples having a spatial period smaller than a
light wavelength in the visible spectrum. The semiconductor film
can be grown onto the rippled substrate 585. The ripples are
substantially cylindrical, hemispherical, or sinusoidal in profile
and shape (=sinusoidal). Thus, the semiconductor thin film is
stressed to shift the bandgap therein to support spontaneous
photoelectrolysis of water in visible light.
[0074] The second half of the cell is provided by membrane 586,
which may also be polycarbonate but can be other materials as well.
The second electrode 588 is aluminum, platinum, or aluminized thin
film coating on a substrate, for example. An aqueous electrolyte,
such as seawater, sulfuric acid, etc, is in contact with the
semiconductor film. A separator membrane allows the hydrogen and
oxygen gasses released in photoelectrolysis to be collected
separately. Further, this controls the amount of dissolved oxygen
that is present in the water, to make the photoelectrolysis
reaction more efficient and predictable.
[0075] Upon exposure of the semiconductor Titania film to an
aqueous solution and illumination of the semiconductor film with
sunlight, the semiconductor film will split the aqueous solution
into hydrogen and oxygen. Gaseous oxygen collects at the
semiconductor Titania electrode cathode 585 and gaseous hydrogen
collects at the conducting anode 588, with the membrane 586
preventing their recombining. The Titania electrode can also be
formed to be an anode rather than a cathode. An optional bias
voltage source 590 is shown connected to the electrodes to adjust
the electric potential for best electrolysis efficiency, but a
redox-mediating electrolyte can also be used to reduce
hole/electron recombination if necessary. Each gas displaces water
and collects at the top of the two outer tubes, where it can be
drawn off with a stopcock. Reservoirs 592 and 594 collect the
separated hydrogen and oxygen gases. The titania-coated substrates
can be stacked in layers to increase the total absorption of the UV
and visible light over a given illumination area. The shape of the
ripples can be concave or convex or a mix of both.
[0076] The stress-induced bandgap-shifted semiconductor may have
its stress is induced by some or all of the following ways:
controlling the shape of and thickness of said semiconductor thin
film; tuning the film coating parameters to optimize stress;
forming nanoscale ripples in the substrate to cause local
high-stress bending radii; controlling the pitch and depth of said
ripples; controlling the mismatch in Young's modulus between the
coating and the substrate; inducing photon stress by self-focusing
of the illumination; inducing electron stress by adding a layer
such as gold in contact with the semiconductor and in between the
semiconductor and the substrate.
[0077] The stress-induced bandgap-shifted semiconductor may include
materials such as titanium, Titania, compounds of Titania, and
doped Titania. The bandgap of the known chemically-inert
photocatalyst titania (TiO2) is shifted and broadened to be active
at wavelengths more prevalent in sunlight and artificial light by
inducing and managing sufficiently high stress in titania by vacuum
coating a thin film of titania onto a substrate, preferably of a
different Young's modulus, with bending ripples on the surface of a
spatial radius similar to the film thickness. The rippled coating
also serves to self-focus and concentrate the incident light
required for the process, increase photocatalytic surface area, and
prevent delamination of the film from the substrate. The electrical
activity so induced in the band-shifted Titania subsequently by
visible light is applied to photoelectrolysis (hydrogen production
from water and light).
[0078] When tensile stress is applied to or caused in a
semiconductor, the inter-atomic spacing increases directly. An
increased inter-atomic spacing decreases the potential seen by the
electrons in the material, which in turn reduces the size of the
energy bandgap. The same effect occurs with increased temperature,
because the amplitude of the atomic vibrations increases with the
increased thermal energy, thereby causing increased inter-atomic
spacing. The stress can be carefully controlled to achieve the
desired bandgap shift, and further managed to prevent delamination,
by introducing periodic three-dimensional nano-scale surface
features into or onto the substrate. These features act as a
template such that the film that is grown onto the template takes
on a similar shape. The Titania film grown onto the polycarbonate
template has a three dimensional sinusoid surface, much like an egg
carton, with a spatial period of 300 nanometers (nm) or 0.3
microns.
[0079] Note, the photoelectrolysis cell device for dissociation and
production of hydrogen gas from an aqueous solution when
illuminated could also could substitute chemically induced stress
via dopants and use a dye sensitive solar cell. The cell uses a
semi conductive metal oxide layer on a conductive substrate,
sensitized by at least one chromophoric substance. The
nanocrystalline semi conductive metal oxide, in particular TiO2, is
in polycrystalline form with a granulometry of the order of several
nanometers, for example 10 to 50 nanometers. A chromophoric
substance, often called photosensitizer or photosensitizing dye,
forms a substantially monomolecular layer attached to the semi
conductive metal oxide layer. The chromophoric substance may be
bound to the metal oxide layer by means of anchoring groups like
carboxylate or phosphonate or cyano groups or chelating groups with
conducting character like oxymes, dioxymes, hydroxyquinolines,
salicylates and keto-enolates. Several transition metal complexes,
in particular ruthenium complexes, but also osmium or iron
complexes, with heterocyclic ligands like bidentate, tridentate or
polydentate polypyridil compounds, have been shown to be efficient
photosensitizing dyes.
[0080] The photo-catalytic nano-crystalline thin films may even
include use of iron oxide-based materials.
[0081] Further, the photoelectrolysis cell device for dissociation
and production of hydrogen gas from an aqueous solution when
illuminated could also be a thin film semiconductor device with
multiple junctions. The semiconductor includes a substrate; a
solid-state semiconductor layer disposed on the substrate; a
photoactive semiconductor top layer further comprising a photo
electrochemical electrode junction; and an interface layer disposed
between the solid-state semiconductor layer and the photoactive
semiconductor top layer. The multiple junctions create more current
or electrons available to react with a liquid electrolyte. A
surface of the photoactive semiconductor top layer is exposed to
both a source of light such as the sun and to the liquid
electrolyte.
[0082] Another method to generate hydrogen via the addition of
solar energy is high-temperature electrolysis. The water splitter
contains a high-temperature, 280-320 degree Celsius, electrolysis
cell device for water electrolysis to decompose water (H2O) into
oxygen (O2) and hydrogen gas (H2) due to an electric current being
passed through the water with most of the energy causing the high
temperature above 280 degrees Celsius supplied as heat from the
Sun, which is cheaper than electricity, and because the
electrolysis reaction is more efficient at higher temperatures. An
electrical power source is connected to two electrodes to pass the
electricity and the oxygen gas gathers at a first electrode and the
hydrogen gas gathers at a second electrode. The electrolysis cell
device functions similar to the catalyst cell discussed above. The
hydrogen gas gathers at the cathode (the negatively charged
electrode, where electrons are pumped into the water), and the
oxygen gas gathers at the anode (the positively charged electrode).
The generated amount of hydrogen is twice the amount of oxygen, and
both are proportional to the total electrical charge that was sent
through the water. Electrolysis of water is sped up dramatically by
adding an electrolyte (such as a salt, an acid or a base).
[0083] In the water at the negatively charged cathode, a reduction
reaction takes place, with electrons (e-) from the cathode being
given to hydrogen cat ions to form hydrogen gas (the half reaction
balanced with acid):
[0084] Cathode (reduction): 2H+(aq)+2e-.fwdarw.H2(g).
[0085] At the positively charged anode, an oxidation reaction
occurs, generating oxygen gas and giving electrons to the anode to
complete the circuit:
[0086] Anode (oxidation): 2H2O(l).fwdarw.O2(g)+4H+(aq)+4e-.
[0087] The same half reactions can also be balanced with base as
listed below. Not all half reactions must be balanced with acid or
base. Many do like the oxidation or reduction of water listed here.
To add half reactions they must both be balanced with either acid
or base.
[0088] Cathode (reduction): 2H2O(l)+2e-.fwdarw.H2(g)+2OH-(aq);
[0089] Anode (oxidation): 4OH-(aq).fwdarw.O2(g)+2H2O(l)+4e-;
[0090] Combining either half reaction pair yields the same overall
decomposition of water into oxygen and hydrogen:
[0091] Overall reaction: 2H2O(l).fwdarw.2H2(g)+O2(g).
[0092] The number of electrons pushed through the water is twice
the number of generated hydrogen molecules and four times the
number of generated oxygen molecules. If a water-soluble
electrolyte is added, the conductivity of the water rises
considerably. The electrolyte disassociates into cat ions and
anions; the anions rush towards the anode and neutralize the
buildup of positively charged H+ there; similarly, the cat ions
rush towards the cathode and neutralize the buildup of negatively
charged OH- there. This allows the continued flow of
electricity.
[0093] Care should be taken in choosing an electrolyte, since an
anion from the electrolyte is in competition with the hydroxide
ions to give up an electron. An electrolyte anion with less
standard electrode potential than hydroxide will be oxidized
instead of the hydroxide, and no oxygen gas will be produced. A cat
ion with a greater standard electrode potential than a hydrogen ion
will be reduced in its stead, and no hydrogen gas will be
produced.
[0094] The following cat ions have lower electrode potential than
H+ and are therefore suitable for use as electrolyte cat ions: Li+,
Rb+, K+, Cs+, Ba2+, Sr2+, Ca2+, Na+, and Mg2+. Sodium and lithium
are frequently used, as they form inexpensive, soluble salts.
[0095] If an acid is used as the electrolyte, the cat ion is H+,
and there is no competitor for the H+ created by disassociating
water. The most commonly used anion is sulfate (SO42-), as it is
very difficult to oxidize, with the standard potential for
oxidation of this ion to the peroxydisulfate ion being -0.22
volts.
[0096] Strong acids such as sulfuric acid (H2SO4), and strong bases
such as potassium hydroxide (KOH), and sodium hydroxide (NaOH) are
frequently used as electrolytes.
[0097] Solar photovoltaic cells are used to convert solar energy
directly into electricity and may be used as the voltage source for
the Ti based and high temperature based electrolysis cell devices
discussed above. The solar cells maybe based on the photovoltaic
(PV) effect in which light falling on a two layer semi-conductor
device produces a photovoltage or potential difference between the
layers. The solar photovoltaic cells can be used as a voltage
source for the photoelectrolysis cell device that employs an
electrode made of a titanium based element or compound with a
stress-induced band-gap.
[0098] In an embodiment, the carbon dioxide in step 2 may be heated
high enough such as 900 Celsius to 2300 Celsius for solar assisted
reduction of carbon dioxide to occur and the heated carbon dioxide
is reduced to carbon monoxide molecules and oxygen molecules. The
oxygen from the carbon dioxide reduction and the water splitting
may be cooled and stored as a liquid fuel or a portion may be used
as a catalyst discussed later. This process will cause a lot of
waste heat for use in other processes such as the synthesis gas
generation and the heated carbon dioxide may be used to drive a
Brayton engine, which supplies the voltage source for the Ti based
and high temperature based electrolysis cell devices discussed
above
[0099] After the carbon dioxide is converted to carbon monoxide and
water by the reverse-water-gas-shift reaction in the RWGS reactor,
the exiting water from that chemical transformation is removed by
the condenser 120 before the methanol is synthesized. With the
elimination of water by RWGS, the purge gas volume is minimized as
the recycle gas volume decreased. Because of the minimum purge gas
loss by the pretreatment of RWGS reactor 106, the overall methanol
yield may be increased. Also, the removal of water vapor from the
reactor 106 via the condenser 120 can drive the equilibrium of the
RWGS reaction to the right to increase the yield of carbon monoxide
produced per inputted heated carbon dioxide. The condensed water
from the condenser 120 can be recycled to the water splitter 102.
The condenser 120 for water removal could either be a desiccant bed
or cooling condensing apparatus.
[0100] On cloudy days, use an alternative heat source to keep the
hydrogen feedstock coming in or large storage tanks may be used to
keep the flow of hydrogen feedstock steady to the RWGS unit. This
minimizes the transient start up and shut down operations on the
RWGS unit.
[0101] FIGS. 4a and 4b illustrate a flow diagram to generate
methanol from solar heated carbon dioxide.
[0102] In block 402, the process uses solar receivers, such as
heliostats, to focus the solar energy power of the Sun on a unit
containing a chemical reactor to heat gas to provide energy needed
for chemical transformations to occur.
[0103] In block 404, the process splits water molecules into
hydrogen molecules and oxygen molecules via 1) the addition of the
solar power directed from the solar receivers (heliostats,
parabolic trough, etc.) and 2) use of a titanium based catalyst in
the water splitting process that absorbs at least the UV rays
directed from the solar receivers or a high-temperature
electrolysis that absorbs rays directed from the solar
receivers.
[0104] In block 406, the process heats a
solar-energy-to-gas-heat-exchanger and the carbon dioxide gas via
the addition of solar power directed from the solar receivers and
potentially pre-heating the feed gases with recycled and/or waste
gas.
[0105] In block 408, the process mixes the heated carbon dioxide
gas with a first portion of the hydrogen gas from the water
splitting process in the solar-assisted endothermic
reverse-water-gas-shift-reaction to produce resultant carbon
monoxide and water molecules.
[0106] In block 410, the process drives the RWGS reaction to
maximize the production of carbon monoxide for the subsequent
exothermic reaction in the generation of a hydrocarbon fuel
including methanol. As discussed above, one of the ways would be to
remove water vapor from the chemical reactor chamber in which the
reverse water gas shift reaction occurs and overload the input of
carbon dioxide for maximum hydrogen consumption. Another method is
to overload an amount of moles of heated hydrogen molecules
relative to an amount of carbon dioxide present in the chemical
reactor chamber than necessary to achieve equilibrium in the
reverse water gas shift reaction to force maximum production of the
resultant carbon monoxide.
[0107] In block 412, the process separates the heated carbon
dioxide gas and hydrogen gas from the resultant carbon monoxide and
water molecules and recycles these back to RWGS step 408 or the
preheating step 406. Alternatively, the process uses all four of
the above chemical compounds to initially preheat feed gases and
then removes the water and some of the now cooled carbon dioxide
gas in order to create the synthesis gas sent to the Hydrocarbon
Fuel synthesis process in step 418.
[0108] Thus, the process recycles the separated out carbon dioxide
after its been used in the recuperator back to the
solar-energy-to-gas-heat-exchanger area. The process may also
recycle none of the hydrogen if it is all being sent through the
RWGS reaction and then the unconsumed hydrogen is sent onto the
fuel process. The process may recycle a portion of the unconsumed
hydrogen gas if that portion is being used to initially overload
the hydrogen concentration and then recycled to preheat feed gas
and reused in the RWGS reaction.
[0109] In block 416, the process quenches a portion of the exit
gases from a chemical reactor chamber in which the reverse water
gas shift reaction occurs, to stabilize at least the carbon
monoxide molecule.
[0110] In block 418, the process mixes the hydrogen molecules from
the water splitting process or RWGS reaction and the resultant
carbon monoxide from the reverse water gas shift reaction in
hydrocarbon fuel synthesis process to create a liquid hydrocarbon
fuel. The process may mix all of the unconsumed hydrogen molecules,
the resultant carbon monoxide and a small percentage of the
unconsumed carbon dioxide from the reverse-water-gas-shift reaction
in hydrocarbon fuel synthesis process to create a liquid
hydrocarbon fuel. The process also may mix a remaining portion of
the hydrogen molecules from the water splitting process and the
resultant carbon monoxide from the reverse-water-gas-shift reaction
in hydrocarbon fuel synthesis process to create a liquid
hydrocarbon fuel.
[0111] In block 420, the carbon dioxide may be heated high enough
such as 900 Celsius to 2100 Celsius for solar reduction of carbon
dioxide to occur and the heated carbon dioxide is reduced to carbon
monoxide and oxygen. The intense solar energy from a well-focused
heliostat array super-heats and dissociates the carbon dioxide.
Some of the carbon dioxide becomes carbon monoxide and oxygen. Then
the reaction is "quenched" by fast cooling, preserving the products
from back-reaction (recombination). Thus, the dissociation reaction
can be cooled to prevent back-reaction. The resulting mix of carbon
dioxide, carbon monoxide, and oxygen gas is separated into its
three components. The carbon dioxide is recycled back into the
process. The oxygen can be used for many valuable purposes. The
carbon monoxide, an energy-rich molecule, carries the captured
solar energy in its bonds. Waste heat from the process generates
high quality steam to potentially turn an electricity-producing
turbine.
[0112] In block 422, the small mirrors in heliostats array are used
to heat the carbon dioxide gas. A technique that allows the mirrors
to be calibrated in groups is used. The smaller mirrors require
less support structure since the wind loads are much lower. Also,
by spacing the mirrors in a regular pattern, the support structure
carrying the heliostats can be a standardized frame easily
installed in the field. The mirrored arrays use this carriage
linkage to tie them together and communally use a shared camera
tracking system and periodic calibration.
[0113] As discussed, the process allows for a high enough volume of
hot carbon dioxide gas for commercial quantities of carbon monoxide
for hydrocarbon based fuel generation, such as via methanol
synthesis, and may even allow for a higher volume of hot gas for
operation of the Brayton cycle turbine engine.
Operation of the Brayton Cycle Turbine Engine
[0114] The Brayton cycle turbine engine 132 receives a portion of
the carbon dioxide gas from the solar-energy-to-gas-heat-exchanger.
The high quality heat from the carbon dioxide gas is transferred
from the carbon dioxide gas to steam to run a turbine portion of
the turbine engine that generates electricity. The heated carbon
dioxide gas is heated to a steady state temperature between 800 and
1000 degrees Celsius. The quantity of excess heat is used to
generate power through the traditional Brayton cycle, using
microturbine-generators.
[0115] Thus, the Brayton engine 132 is driven with gas heated from
the solar energy and that same solar energy is a heat source for
the transforming carbon dioxide to carbon monoxide in the RWGS. The
Brayton engine 132 is configured with a higher throughput, lower
entropy production design, which is more advantageous for heating
at up to 900 C. The same solar energy is doing twice the work,
resulting in much more efficient power production. The Brayton
turbine engine 132 unit can produce electrical power.
[0116] In one embodiment, the software used to facilitate the
processes discussed above can be embodied onto a machine-readable
medium. A machine-readable medium includes any mechanism that
provides (e.g., stores and/or transmits) information in a form
readable by a machine (e.g., a computer). For example, a
machine-readable medium includes read only memory (ROM); random
access memory (RAM); magnetic disk storage media; optical storage
media; flash memory devices; Digital VideoDisc (DVD's), EPROMs,
EEPROMs, FLASH memory, magnetic or optical cards, or any type of
media suitable for storing electronic instructions. The software
may be written in any number of programming languages such as C,
etc.
[0117] While some specific embodiments of the invention have been
shown the invention is not to be limited to these embodiments. For
example, most functions performed by electronic hardware components
may be duplicated by software emulation. Thus, a software program
written to accomplish those same functions may emulate the
functionality of the hardware components in input-output circuitry.
The reverse-water-gas-shift-reactor and the methanol synthesis
reactor can be part of two separate units located in relatively
close proximity of each other, such as both being on the same
production facility site. The hydrogen, carbon monoxide, and carbon
dioxide recirculation loops may be combined. For example, the
hydrogen, carbon monoxide may be combined when sent to the methanol
synthesis reactor. The hydrogen and carbon dioxide may be combined
when recirculated back to the RWGS process. The system may use two
or more discrete solar-energy-to-gas-heat-exchangers. The array of
heliostats may be formed in two or more sets of heliostats. The
solar energy receiver may be heliostats or other devices such as
solar collector mirrors, parabolic troughs, or any number of other
apparatus to focus the rays of the sun. The invention is to be
understood as not limited by the specific embodiments described
herein, but only by scope of the appended claims.
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