US20100000874A1

US20100000874A1 - Various methods and apparatus for solar assisted fuel production

Info

Publication number: US20100000874A1
Application number: US12/237,999
Authority: US
Inventors: Brian L. Hinman; John Henry Stevens; Peter Le Lievre
Original assignee: Sundrop Fuels Inc
Current assignee: Sundrop Fuels Inc
Priority date: 2008-06-24
Filing date: 2008-09-25
Publication date: 2010-01-07
Also published as: WO2010036662A1

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.

Description

RELATED APPLICATION

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

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

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

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

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

The drawings refer to embodiments of the invention in which:

FIG. 1 illustrates an embodiment of a solar assisted process to create a liquid fuel;

FIGS. 1 a and 1 b illustrate embodiments of a solar assisted process to create a hydrocarbon liquid fuel;

FIG. 2 illustrates a view of an embodiment of the parabolic trough;

FIG. 3 a view of an embodiment of the parabolic trough;

FIGS. 4 a and 4 b illustrate a flow diagram to generate methanol from solar heated carbon dioxide; and

FIG. 5 illustrates an embodiment of an electrolysis cell.

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

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.
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.
Essentially, two main embodiments, as well as a couple of other embodiments, are described.
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.
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.
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.
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.
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

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.
FIGS. 1 a and 1 b illustrate a solar assisted process to create a hydrocarbon liquid fuel.
Referring to FIG. 1 a, a water splitter 102 a 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.
The RWGS unit 104 may also contain sections such as a solar-energy-to-gas-heat-exchanger 122, a chemical reactor 106 a, 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 105 a, and other similar components. This solar assisted embodiment may have substantially all of the moles of hydrogen generated from the water splitter 102 a being heated up and run through the RWGS reaction in the chemical reaction chamber 106 a.
Referring to FIG. 1 b, 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 102 b in the RWGS reaction and send the remaining portion of the non-superheated moles directly to the fuel synthesis process 108.
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.
The Chemical Operation may be Summed:
1. Water (H2O) is split into Hydrogen (H2) molecules and Oxygen (O2) molecules (2 H2O+energy→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.
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.
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™ 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.
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. 1 b, ⅔rds of the hydrogen generated is supplied directly from the water splitter 102 b 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 106 b 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.
In an embodiment, substantially all of the moles of hydrogen molecules 1) generated from the water splitter 102 a and 2) passed through the chemical reactor chamber 106 a, 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.
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 ΔrH (methanol)+heat, or another desired hydrocarbon fuel.
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).
Referring to FIG. 1 a, 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 105 a plumbs pipes to the feed gases input ports 124, 126 and exhaust gases output ports from the quencher 130. The recuperator 105 a passes the exhaust gases from the chemical reaction chamber 106 a 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.
The recuperator 105 a 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 106 a 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 106 a.
Similarly, the recuperator 105 a 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.
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.
Gas flow in the recuperator 105 a 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 105 a relative highest temperature area. Filters in the recuperator 105 a 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 105 a 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.
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.
Referring to FIG. 1 b, as discussed in step 4, the chemical reactor chamber 106 b mixes the heated carbon dioxide gas with a first portion of the hydrogen molecules from the water splitter 102 b 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.
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 102 b is sent directly to the fuel production 108 eliminating a need to cool the hydrogen gas for the fuel synthesis process.
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.
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.
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.
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° Celsius can be achieved at concentration ratios around 1500× sun concentration units.
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.
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.
FIGS. 2 a and 2 b illustrate perspective views of embodiments of a parabolic trough system used with the water splitter.
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.
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.
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.
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.
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.
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.
In an embodiment, the parabolic trough concentrator uses two-axis tracking, and aluminum reflectors with the use of anti-corrosive additives on the reflectors.
Referring to FIGS. 2 a and 2 b, 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
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.
The photo-catalytic nano-crystalline thin films may even include use of iron oxide-based materials.
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.
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).
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):
Cathode (reduction): 2H+(aq)+2e−→H2(g).
At the positively charged anode, an oxidation reaction occurs, generating oxygen gas and giving electrons to the anode to complete the circuit:
Anode (oxidation): 2H2O(l)→O2(g)+4H+(aq)+4e−.
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.
Cathode (reduction): 2H2O(l)+2e−→H2(g)+2OH−(aq);
Anode (oxidation): 4OH−(aq)→O2(g)+2H2O(l)+4e−;
Combining either half reaction pair yields the same overall decomposition of water into oxygen and hydrogen:
Overall reaction: 2H2O(l)→2H2(g)+O2(g).
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.
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.
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.
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.
Strong acids such as sulfuric acid (H2SO4), and strong bases such as potassium hydroxide (KOH), and sodium hydroxide (NaOH) are frequently used as electrolytes.
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.
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
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.
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.
FIGS. 4 a and 4 b illustrate a flow diagram to generate methanol from solar heated carbon dioxide.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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

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.
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.
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.
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.

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.