Abstract:
A method and apparatus are disclosed for sequestering carbon dioxide. Carbon dioxide and a reductant are fed into a combustion chamber and burned. The reductant forms an oxide with oxygen from the carbon dioxide, generating an oxidized reductant and carbon which are exhausted from the combustion chamber and separated. The oxidize reductant is then itself reduced to form reclaimed reductant, which is used to provide the reductant for reducing the carbon dioxide. The oxidized reductant is reduced by disposing the oxidized reductant in an inert environment and exposing the oxidized reductant to electromagnetic radiation of a wavelength for freeing oxygen from the oxidized reductant. The electromagnetic radiation is preferably provided by light having a wavelength which is readily absorbed by oxygen, such as light emitted by a YAG laser. Preferably the reductant is provided by a metal, such as magnesium.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates in general to carbon dioxide sequestration, and in particular to a net energy-producing process for sequestering elemental carbon from carbon dioxide. 
     BACKGROUND OF THE INVENTION 
     Sequestering carbon dioxide, a goal of international agreements and the U.S. Environmental Protection Agency, is a new field generally involving geological or other mass depositions. An even newer field is to develop useful products from captured carbon dioxide. To date, most attention has been focused on sequestering carbon dioxide (CO2) in organisms such as algae. The organisms are usually then processed into fuels and combusted. One major shortfall of this is that it is, at best, carbon neutral. Another major shortfall is that, given known efficiencies of photosynthesis and carbohydrate synthesis, no organism can produce cost-competitive fuels with current methods and fuel prices. A more viable method of carbon dioxide sequestration is creating carbonates, such as calcium or magnesium carbonate for cement, but this is limited to where it is economical to pump large amounts of seawater, and/or CO2, and requires energy. Presently, no current system can sequester CO2 on-site, within the extant confines of a normal CO2 emitting facility. No current system produces by-products of direct use to the power plant. 
     SUMMARY OF THE INVENTION 
     A novel method and apparatus for carbon dioxide sequestration is disclosed. Carbon dioxide is reduced to elemental carbon by combustion of carbon dioxide and a reductant, separation of combustion products, and recycling of the oxidized reductant. The process preferably utilizes a high purity of carbon dioxide, a reductant of sufficient strength to reduce the carbon dioxide, and centripetal separation of combustion products or an organic, aqueous phase separation of combustion products. Reduction of oxidized reductant for re-use is preferably accomplished by use of focused electromagnetic radiation. Improved reduction yields are preferably accomplished by utilizing a series of conical, centripetal separation vessels as the location of solar-driven reduction chemistry. Combustion is regulated by by means of a pump to create a steady CO2-gas fluidized-bed of metallic reductant. Preferably, heat generated during heat-producing stages of the present invention is used to heat a working fluid to make use of the generated heat. 
     Metals (“M”) are often strong reductants. Strong reductants of CO2 include the metals Lithium, Magnesium, Aluminum, and Boron. Metals are intentionally oxidized for rocket propulsion, but otherwise are not favored fuel sources, as they are costly and their combustion is difficult to control. Carbon dioxide (CO2) is not generally used for oxidizing metals, as oxygen is normally available. However, the National Aeronautics and Space Administration (NASA) has recently taken an interest in CO2 for Mars missions, as the Martian atmosphere is 95% CO2, and since the 1960s NASA has reliably controlled metal combustion by injecting metal powder with a Positive Displacement Fluidized Bed (PDFB) feeder. However, the fuel is simply blown out of the rocket engine, therefore in CO2 sequestration there is a need for a method of collecting and separating components of the exhaust: Carbon (C), CO2, CO and oxidized metal (“MOx”). 
     Ranque-Hilsch counterflowing vortex tubes are known for temperature and chemical mixture separation. Their capacity to separate out pressurized flows has been well documented, and designs have been made to improve on this function. Adiabatic expansion by lighter molecules or atoms towards a vortex in the center of the tube, plus mixing of this inner vortex with the dense layer at the walls of the tube, results in separation of lighter and heavier elements. A variation on this principle is found in “cyclone” separators, used to filter air in workshops and isolate powders in dairy and other industries. Carbon, CO2, and CO are significantly less-dense than MOx, therefore vortex tubes provide one method for their separation. 
     Oxidized metals are hygroscopic, meaning they have affinity for water, whereas carbon under moderate conditions is hydrophobic, meaning it repels water. Another possible method for separation of MOx from C is to add the mixture to water. For example, the reaction of magnesium oxide (MgO) with H2O forms Mg(OH)2, known commonly as “milk of magnesia,” which can be converted back to MgO by dehydration. Depending on the size and configuration of carbon molecules, carbon either floats above water—as with hydrocarbons—or sinks out. In a mixture with a saturated, dense solution of aqueous Mg(OH)2, carbon floats. In chemistry, this is known as a “phase-separation.” 
     Once MOx and C are separated out, MOx needs to be recycled to M. Oxygen absorbs electromagnetic radiation strongly at wavelengths of 577, 630, 1064 nanometers, as well as at other frequencies. Dichroic mirrors separate light into bandwidth ranges, and could be used to isolate those narrowed bandwidths that contain oxygen absorption peaks. Yttrium aluminum garnet (“YAG”) lasers emit light at 1064 nm, and thus can be used to focus intensified electromagnetic radiation in the form of light on the oxygen in MOx. Sufficient light absorption rapidly excites oxygen until the bond with the metal is broken. Provided oxygen is rapidly cooled in an inert environment, that is, in the presence of an inert gas, M and oxygen can remain separate. 
     One way of gaining the energy to radiate oxygen at its 1064 nm absorption peak is by solar-“pumping” a YAG laser. A “solar tower” is a system that uses a field of heliostats to focus light onto a mirror atop a tower that reflects the light down to a boiler, or focuses light through an annular space into a light-trapping and absorbing heat exchanger, or into a compound parabolic collector(s). Some solar tower systems separate the focused light out for different purposes. For example, one proposed array would have a field of heliostats focused onto a hyperboloid mirror which, in one arrangement, was dichroic, with a bandwidth passing through onto photovoltaics in the tower head, and a bandwidth reflected down to a compound parabolic concentrator at the base. In another, the hyperboloid mirror bounces light down to a dichroic mirror, which passes a bandwidth of the light onto compound parabolic concentrators at the base, and reflected a bandwidth of the light onto photovoltaics. For the end of pumping a YAG laser, any similar configuration could be used, provided the YAG absorption bandwidth reached the laser. 
     A pure stream of CO2, desirable for most forms of carbon dioxide sequestration, may come from ammonium or other solvents used to “scrub” CO2 from smokestacks. Preferable, however, is CO2 from chemical looping combustion, which also has the potential advantage—within the proposed process—of synergistically sharing its metal fuel with a solar reducing system, and allows for on-site management of reductant. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which  FIGS. 1 through 7  show various aspects for a method and apparatus for carbon dioxide sequestration made according to the present invention, as set forth below: 
         FIG. 1  illustrates a schematic flow diagram of an apparatus in which an overall process for carbon dioxide sequestration in accordance with the present invention is employed with a counter-flowing vortex tubes for combustion product separation; 
         FIG. 2  illustrates a schematic flow diagram of an apparatus employing a process in accordance with the present invention in which combustion products are separated by solvation and gravity separation followed by dehydration; 
         FIG. 3  illustrates a schematic flow diagram of an apparatus of one embodiment of the present invention, employing a process utilizing four or more counter-flowing vortex tube separators in succession; 
         FIG. 4  illustrates a schematic flow diagram of an apparatus according to one embodiment of the present invention, employing a process in which sunlight is used to pump a laser and the apparatus also including counter-flowing vortex separators; 
         FIG. 5  illustrates a schematic flow diagram of an apparatus utilizing according to one embodiment of the present invention, employing sunlight that is split by a dichroic mirror to both pump a laser and power a boiler or photovoltaic, and counter-flowing vortex separators; 
         FIG. 6  illustrates a schematic flow diagram of an apparatus according to one embodiment of the present invention employing sunlight that is split by a dichroic mirror to both pump a laser and be directed into the counter-flowing vortex separators; and 
         FIG. 7  illustrates a flow chart of a process for sequestering carbon dioxide in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the Figures,  FIG. 1  is a schematic diagram of an apparatus  100  for sequestering carbon dioxide in accordance with the present invention, using counter-flowing vortex tubes for combustion product separation and reclamation for re-use in the combustion process. A flow of carbon dioxide from an external source travels along a flow line  101  and is combined with carbon dioxide and carbon monoxide from a flow line  102 . The flow line  102  passes carbon dioxide and carbon monoxide which has not been reduced in the apparatus  100 , and thus is being looped back through the apparatus  100 . A pump  103 , or a compressor, pressurizes the carbon dioxide and carbon monoxide for passing into a combustion chamber  105 . A flow line  104  passes a reductant, or reducing agent, into the combustion chamber  105  for mixing and combusting with the carbon dioxide and carbon monoxide feed from the pump, or compresson,  103 . The reductant may be fed into the combustion chamber as a pressurized liquid or as a solid powder, and preferably is a metal such as magnesium which will combust and form an oxide with the oxygen from the carbon monoxide and carbon dioxide feed from the pump  103 . Exhaust from the combustion chamber  105  preferably passes through a flow line  106  and into a vortex tube separator  107 . 
     The vortex tube separator  107  is preferably of a counter-flowing type for receiving the exhaust gases from the combustion chamber  105  and using centripital force to separate materials of different densities and weights, such as oxidized reductant, elemental carbon, carbon monoxide and carbon dioxide. Elemental carbon exits from the fine end of the separator through the flow line  111 . The elemental carbon is freed by reduction of the carbon dioxide and the carbon monoxide. The portion of the carbon dioxide and the carbon monoxide which are not reduced in the combustion chamber  105  will pass through the flow line  106  and into the separator  107 , and then from separator  107  through the flow lines  109  and  110 . The flow lines  109  and  110  pass the non-reduced carbon monoxide and carbon dioxide through a heat exchanger  112  and into the flow line  102 . The heat exchanger  112  preferably removes heat from the flow line  102 . The carbon monoxide and carbon dioxide from the separator  107  will then mix with the carbon dioxide passing through the flow line  101  and into the apparatus  100 , for again mixing with the reductant feed from the flow line  104  and burning in the combustion chamber  105 . Oxidized reductant will pass from the course end of the separator  107 , through the flow line  108  and into a counter-flowing vortex separator  113 . 
     The vortex separator  113  is provided for reclaiming the oxidized reductant burned in the combustion chamber  105 . In the vortex separator  113  the oxidized reductant is itself reduced after sufficient exposure to electromagnetic radiation  119 . The vortex separator  113  receives the oxidized reductant from the flow line  108  connecting between the separator  107  and the separator  113 . An inert gas passes from a flow line  117  and into the separator  113  and provides an inert atmosphere around the oxidized reductant within the separator  113 . Electromagnetic radiation  119  is passed into the separator  113  for reducing the oxidized reductant in the vortex separator  113 . A discharge stream of oxygen and inert gas passes from the vortex, or fine particle end, of the separator  113  and through the flow line  115  into a gas separator  116 . A fraction of the oxygen and inert gas pass from the course end of the separator  113 , through the flow line  114  and into the gas separator  116 . Reductant is reclaimed in the vortex separator  113  and will pass from the course end of the separator  113 , through the flow line  104  and back into the combustion chamber  105  to reduce carbon dioxide and any remaining carbon monoxide. In some embodiments, more than one vortex separator  113  may used rather than a single separator  113 , such as successive centripetal counterflowing vortex reduction/separation vessel(s) (depicted in  FIGS. 4 ,  5  and  6 ). The recycled inert gas passes through the flow line  117 . The reductant may be in the form of a pressurized liquid or as a solid powder. Preferably, magnesium metal is used for the reductant. 
     The gas separator  116  is provided for receiving a mixture of the inert gas and oxygen from the flow lines  114  and  115 , and separating out purified inert gas for passing through the flow line  117  for re-use in the vortex separator  113 , and oxygen for passing through the flow line  118  as a product of the apparatus  100 . The gas separator  116  may be provided by a pressure-swing adsorption type separator, or a cryogenic distillation unit, as are well known to those skilled in the related art. 
       FIG. 2  is a schematic diagram of an apparatus  200  for sequestering carbon dioxide in accordance with the present invention, and reclaiming combustion products for re-use in the combustion process using solvation and gravity separation followed by dehydration. Similar to  FIG. 1 , carbon dioxide passes into the apparatus  200  along the flow line  101 , and is mixed with a mixture of carbon dioxide and carbon monoxide which is passed along the flow line  206 . A pump  103 , or compressor, passes the mixture into the combustion chamber  105 . Reductant passes along a flow line  104  for mixing with the carbon dioxide and carbon monoxide in the combustion chamber  105 . Combustion products from the combustion chamber  105  pass through a heat exchanger  201 , and then through the flow line  202  and into a separation tank  204 . Heat is removed from the combustion products in the heat exchanger  201 . 
     The combustion products are mixed with water in the separation tank  204 . In the separation tank  204 , unreduced carbon dioxide and partially reduced carbon monoxide gases will separate from solids and liquids, and then will be removed along the flow line  206  for mixing with carbon dioxide passing through flow line  101  and into the pump  103 . Elemental carbon from the reduced carbon dioxide and carbon monoxide will settle in a region  203  and is removed from an upper surface of a liquid phase region  205 . The oxidized reductant is solvated in liquid, preferably water, and being of greater density than the elemental carbon, will form an aqueous phase in the liquid region  205  with the lower-density elemental carbon floating above in the region  203 . Preferably, the aqueous phase is drained from the region  205  and passes along a flow line  207  to a separation tank  208 . In some embodiments, more than one separation tank  204  may be used. Separation may proceed as a batch process to drain the aqueous phase from the region  205 , followed by removal of the solid  203 , or as a continuous process with the aqueous phase slowly drained from the region  205  and the solid phase skimmed from the region  203  located above the region  205 . Gas collects in the ullage  212  above the region  205 , and passes through the flow line  206  and back into the combustion chamber  105 . 
     The aqueous phase of pure, solvated oxidized reductant passes from the region  205  of the separation tank  204 , along a flow line  207  and to the dehydrator  208 . The solvated, oxidized reductant is dehydrated in the dehydrator  208 , with the liquid phase  209  sitting atop the solid phase  210 . The oxidized reductant is preferably both dried and heated in the dehydrator  208 . Whether dehydrated by batch or continuous process, the solid oxidized reductant  210  after dehydrating is passed along a flow line  108  into a single or several successive centripetal, counter-flowing vortex reduction separators  113 . More than one vortex separator  113  may be used in succession, as shown in  FIGS. 4 ,  5  and  6 . Preferably, an inert gas is passed along a flow line  117  and into the separator  113  to provide an inert environment in which the dried oxidized reductant is exposed to eloctromagnetic radiation  119 . The oxidized reductant is reduced after sufficient exposure to electromagnetic radiation  119 . Oxygen and the inert gas are exhausted through the vortex or fine-particle end of the vortex separator  113 , and pass through the flow line  115  and to the gas separator  116 . A fraction of the gasses are passed from the dense end of the vortex separator  113 , through a flow line  114  and to the gas separator  116 . The reductant passes out the dense end of the vortex separator  113  and through the flow line  104  for use again in the combustion chamber  105 . The gas separator  116  separates out purified inert gas which exits through the flow line  117  for re-use in the vortex separator  113 , and oxygen which exits through the flow line  118  as a product of the system. 
       FIG. 3  is a schematic diagram an apparatus of one embodiment of the present invention employing four or more counter-flowing vortex tube separators in succession, such as may be used with apparatus  100  of  FIG. 1  and apparatus  200  of  FIG. 2 . Several counter-flowing vortex tube mixture separators  305 - 308  successively purify the exhaust of the combustion chamber  105  (shown in  FIGS. 1 and 2 ) passing from a flow line  106 . The combustion chamber exhaust from flow line  106  is introduced tangentially into the first separator  305 . The carbon dioxide from the flow line  101  is introduced in parallel into each of the vortex separators  305 - 307  for providing selected pressures in the separators  305 - 307 . Partially purified carbon monoxide gas, carbon dioxide gas, and elemental carbon powders exit the ends  309  of the vortex separators  305 ,  306  and  307 , and pass along the flow line  303  into the secondary fine-exhaust separator  308 . The course exhaust from the vortex separator  308  passes through the flow line  304  and back into the first vortex separator  305 . Once purified, carbon powder and gases leave the system through the flow line  111 . The more dense oxidized reductant exits the lower end  310  of the separator  308  and passes through a flow line  304  and is reintroduced to the separator  305 . The denser, partially purified oxidized reductant provides a coarse-exhaust which exits the bottoms  310  of the vortex separators  305  and  306 , and passes along the flow lines  301  and  302 . The flow line  302  passed into a final vortex separator  307 . At the coarse-exhaust  310  of the final separator  307 , the dense oxidized reductant passes through a flow line  108  for reduction in the separator  113  of  FIGS. 1 and 2 . Carbon dioxide gas is pumped down line  101  into each separator  107  to maintain a pressure gradient from injection to final purified outflows in lines  108  and  111 . In accordance with the present invention, there may be fewer or more than three coarse-exhaust separators and one or more fine-exhaust purification stages. 
       FIG. 4  is a schematic diagram of a process and apparatus of another embodiment of the present invention employing sunlight to pump a laser for use to provide electromagnetic radiation  119  for the counter-flowing vortex separators  113 ,  407  and  408 . Mirrors  401  and  402  direct light  413  into a compound parabolic collector  403 , which focuses the directed light onto a laser medium  404 , pumping the laser medium  404  to provide a coherent light  414 , or laser beam  414 . Preferably, the angle and geometry of the laser beam  414  are variable. The laser beam provides coherent light  414  which is directed to a beam splitter  405 . Split light is directed by mirrors  406  through optical ports  411  and into one or several centripetal vortex separators  113  and  408 . A mixture of inert-gas and fluidized oxidized reductant  409  are inserted tangentially along a path  410  into the centripetal vortex separator  113 , where the oxidized reductant crosses the path of coherent light  414  at which point a certain portion is reduced by the light into reductant and oxygen gas. The mixture  115  of inert gas and oxygen gas mostly exit through port  412 , from which they are sent to the gas mixture separator  116  of  FIGS. 1 and 2 . The oxidized and reduced reductant moves successively down the chain of one, three, or more vortex separators  113  and  408  until the oxidized reductant is completely reduced by light, and the reductant exits along with a fraction of the gasses along a flow path  104 . The centripetal separator  407  provides further separation for oxidized reductant flowing from the separator  113  with freed oxygen. 
       FIG. 5  illustrates a schematic diagram of an apparatus according to one embodiment of the present invention for use with the apparatus  100  and the apparatus  200  of  FIGS. 1 and 2 , employing sunlight that is split by a dichroic mirror  501  to both pump a laser  404  and power a boiler or photovoltaic  502 . In this particular embodiment, and counter-flowing vortex separators  407 ,  113  and  408  are used for separating a combustion products. Mirrors  401  and  402  direct light  413  to a dichroic mirror  501 , where a bandwidth is reflected along a path  503  to a photovoltaic and/or boiler  502 , and another bandwidth is passed along a path  504  to a compound parabolic collector  403 . The parabolic collector  403  focuses the light to pump the enclosed laser medium  404 . Light from the medium  404  is directed coherent light  414  which passes to the beam splitter  405 . From the beam splitter  405 , light is directed to mirrors  406 , and then by mirrors  406  through optical ports  411  and into one or several centripetal vortex separators  113  and  408 . The inert-gas and fluidized oxidized reductant  409  are inserted tangentially  410  into a centripetal vortex separator  113 , where the oxidized reductant crosses the path of coherent light  414 , at which point a certain portion is reduced by the light into reductant and oxygen gas. A mixture  115  of inert gas and oxygen gas mostly exit through port  412 , from which they are sent to the gas mixture separator  116  of  FIGS. 1 and 2 . The oxidized and reduced reductant moves successively down the chain of one, three, or more vortex separators  113  and  408  until the oxidized reductant is completely reduced by light  414 , and the reductant exits along with a fraction of the gasses along the flow path  104  for reuse in the combustion chamber  105  of  FIGS. 1 and 2 . The centripetal separator  407  provides further separation for oxidized reductant flowing from the separator  113  with freed oxygen. 
       FIG. 6  is a schematic diagram of an apparatus according to one embodiment of the present invention for use with the apparatus  100  and the apparatus  200  of  FIGS. 1 and 2 , employing sunlight which is split by a dichroic mirror  601  to both pump a laser  404  and to be directed into the counter-flowing vortex separator  407 . The mirrors  401  and  402  direct sun light  413  to the dichroic mirror  601 , where a bandwidth  604  is reflected to a mirror  602  that passes light through an optical port  603  and into the vortex separator  407 . Another bandwidth of the light is passed along the path  605  to a compound parabolic collector  403  which pumps an enclosed laser medium  404 . The resulting coherent light  414  is directed to a beam splitter  405 , which directs the light to the mirros  406 . The light is directed by mirrors  406  through optical ports  411  and into the centripetal vortex separators  113  and  408 . The inert-gas and fluidized oxidized reductant  409  are inserted tangentially  410  into the centripetal vortex separator  113 , where the oxidized reductant crosses the path of coherent light  414 , at which point a certain portion is reduced by the light into reductant and oxygen gas. A mixture  115  of inert gas and oxygen gas mostly exits through port  412 , from which they are sent to the gas mixture separator  116  of  FIGS. 1 and 2 . The oxidized and reduced reductant moves successively down the chain of one, three, or more vortex separators  407 ,  113  and  408 , until the oxidized reductant is completely reduced by light, and the reductant exits along with a fraction of the gasses along flow path  104 . 
     Preferably, the centripetal vortex separators of  FIGS. 1 through 6  have reflective interior surfaces, similar to a conventional compound parabolic collector, to bounce light downwards. This could involve a glass or coated surface and mirrored material beneath to keep the mirror from becoming scratched by fast-moving powder, or a strong and polished surface with no coating. The entirety of the separators may be water-jacketed as a heat sink, with inlets for input/output. 
     The preferred laser medium  404  of  FIGS. 4 ,  5  and  6  is a Yttrium-Aluminum garnet laser, doped with Neodymium 3+ cation and Chromium 3+ cation (Nd3+:Cr3+:YAG ceramic laser). The enclosure may include one or several ceramic laser mediums, arranged, pumped and cooled according to angles, proportions and means known to those skilled in the art. The laser  404  is preferably water-cooled. Preferably, both the remaining light and the heated reductant and gas are used to provide heat for a heat exchanger or any light is passed light absorber. Steam is used to drive a turbine, or heat is used to drive a Sterling engine. 
       FIG. 7  is a flow chart depicting a process for sequestering carbon dioxide in accordance with the present invention. In step  10  carbon dioxide and a reductant are combined and then combusted, and oxygen from the carbon dioxode combines with the reductant according to the following equation:
 
CO2+R→C+ROx  [Equation I]
 
The reductant is preferably a metal, such as Magnesium, Aluminum, Lithium and Boron, and during combustion metal oxides (“MOx” or MgOx) are formed, represented by ROx in Equation I.
 
     In step  12  the produced carbon is separated from the oxidized reductant (ROx). It should also be noted that not all carbon dioxide will generally be fully reduced in the first pass, such that some carbon dioxide and carbon monoxide will remain. The carbon dioxide and carbon monoxide are separated from the produced carbon and oxidized reductant, and then will again be passed through, or looped back through, a combustion chamber for again combusting with the reductant to further reduce any remaining carbon dioxide and carbon monoxide. 
     In step  14  the oxidized reductant is placed in an inert environment, preferably by mixing with an inert gas. While in the inert environment, electromagnetic radiation is applied to the oxidized reductant to reduce the oxidized reductant according to the equation:
 
ROx+Energy→R+xO  [Equation II]
 
The electromagnetic radiation is preferably light of a frequency, or wavelength, strongly absorbed by oxygen, such that the oxygen will absorb the electromagnetic radiation and become free from the reductant, and remain free if rapidly cooled in the inert environment. Wavelengths of light strongly absorbed by oxygen include 577 nanometers, 630 nanometers and 1064 nanometers, as well as other frequencies. A Yttrium aluminum garnet (“YAG”) laser emits light at 1064 nm, and is preferably used to focus intensified electromagnetic radiation in the form of light on the oxygen in the ROx, which preferably an oxidized metal (“MOx”), such as magnesium oxide (“MgO”).
 
     In step  16  the freed reductant is separated from the inert gas and the oxygen (O 2 ). In step  18  the reclaimed reductant is re-used, in step  10  for combusting with carbon dioxide. 
     The present invention provides advantages of a method and apparatus for sequestering carbon dioxide, using a reductant which is oxidized by the oxygen in the carbon dioxide. Oxidizing the reductant frees carbon from the carbon dioxide to allow the carbon to be separated from the oxidized reductant by mechanical means. After separation from the carbon, the oxidized reductant is itself reduced, preferably by exposure to electromagnetic energy in an inert environment. Metal is preferably used as a reductant, with magnesium being the preferred metal. The electromagnetic energy is preferably light provided by a YAG laser at a wavelength of 1064 nm, and is generated using solar energy. 
     Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.