Liquid-phase chemical looping energy generator

Abstract

A closed loop combustion system for the combustion of fuels using a molten metal oxide bed.

Claims

1. A process of repeated chemical looping combustion (CLC) for the production of energy while arranging for the efficient sequestration of carbon dioxide produced by combustion and oxidation, wherein the process comprises: a) providing at least a first reactor and a second reactor, each containing molten metal oxide and each also containing elements of a closed loop system with a heat transfer fluid therein to gather heat from each of the reactors to use in the production of energy; b) increasing the pressure of in said first reactor to a first pressure that is above ambient pressure; c) conducting a combustion step in said first reactor at said first pressure by contacting the mixture of molten metal oxide with a carbon containing fuel to thereby oxidize said fuel with the molten metal oxide and concurrently reduce the molten metal oxide to generate combustion product that is predominantly carbon dioxide along with reduced metal species within the molten metal oxide wherein the oxygen carrier to the fuel is the molten metal oxide wherein this combustion step further provides heat to the heat transfer fluid for the production of energy; d) while conducting the combustion step c) in the first reactor, conducting an oxidation step in the second reactor at a second pressure which is lower that said first pressure by directing a flow of air into the second reactor such that oxygen in the air comes into contact with reduced solids in the second reactor to thereby oxidize such solids to form and reform the solids into molten metal oxide and thereby regenerate the molten metal oxide in the second reactor in preparation for a combustion step wherein this oxidation step provides heat to the heat transfer fluid for the production of energy; e) capturing and compressing the carbon dioxide from combustion step c) within the first reactor and directing the carbon dioxide from the combustion step c) to a carbon dioxide sequestration conduit; f) directing oxygen depleted air from the second reactor to a spent oxidant conduit wherein the spent oxidant conduit and the carbon dioxide conduit are separate and apart from one another; g) stopping the flow of fuel to the first reactor thereby terminating the combustion step therein; h) stopping the flow of air to the second reactor thereby terminating the oxidation step therein; i) lowering the pressure in the first reactor down to the second pressure; j) raising the pressure in the second reactor up to the first pressure; k) initiating a flow of air to the first reactor to conduct an oxidation step in the first reactor and also produce and provide heat for the heat transfer fluid in the first reactor; l) while conducting the oxidation step in the first reactor, initiating a flow of carbon containing fuel to the second reactor to thereby conduct a combustion step within the second reactor by oxidizing the carbon containing fuel with the molten metal oxide and reducing the molten metal oxide and also produce and provide heat for the heat transfer fluid in the second reactor; m) directing oxygen depleted air from the first reactor to the spent oxidant conduit wherein the spent oxidant conduit; n) capturing and compressing the carbon dioxide from combustion step l) within the second reactor and directing the carbon dioxide from the combustion step l) to the carbon dioxide sequestration conduit; o) stopping the flow of air to the first reactor thereby terminating the oxidation step therein; p) stopping the flow of fuel to the second reactor thereby terminating the combustion step therein; q) lowering the pressure in the second reactor down to the second pressure; and r) continually repeating steps b) through q) to produce energy in each reactor during cyclically repeated combustion and oxidation steps while carbon dioxide is captured at an elevated pressure from each reactor and also kept separate from oxygen depleted air.

2. The process of claim 1, wherein said molten metal oxide (a) is selected from the group consisting of vanadium pentoxide (V.sub.2O.sub.5), manganese (III) oxide (Mn.sub.2O.sub.3), copper (I) oxide, copper (II) oxide, molybdenum trioxide (MoO.sub.3), bismuth (III) oxide (Bi.sub.2O.sub.3) or combinations thereof.

3. The process of claim 1, wherein said molten metal oxide (a) is molybdenum trioxide (MoO.sub.3).

4. The process of claim 1, wherein secondary metal oxides are also incorporated into the liquid metal oxide (a) are selected from the group consisting of iron (III) oxide (Fe.sub.2O.sub.3), cobalt (II) oxide (CoO), nickel (II) oxide (NiO), tin (II) oxide (SnO), tin (IV) oxide (SnO.sub.2), antimony (III) oxide (Sb.sub.2O.sub.3), tungsten trioxide (WO.sub.3), and lead (II) oxide (PbO).

5. The system of claim 1, wherein the molten metal oxide is contained within a melt of other molten species including glass melt, ionic melt, and combinations thereof.

6. The process of claim 1, wherein said fuel source (b) is selected from the group consisting of, diesel, kerosene, coal, bitumen, crude oil, fuel gas, crude oil distillate, light distillates, naphthas, gasoline, or combinations thereof.

7. The process of claim 1, wherein said fuel source (b) is a gas selected from the group consisting of methane, propane, volatile organic carbons, vaporized gasoline, synthesis gas, dilution gas, mixture of dilution-synthesis gas and combinations thereof.

8. The process of claim 1, wherein said fuel source is biomass, wood, cellulose, corn stover, waste paper, municipal solid waste and combinations thereof.

9. The process of claim 5 wherein the molten metal oxide is contained within a melt of other molten species including glass melt.

10. The process of claim 9 wherein the only feedstocks to the molten metal oxide are air and the fuel.

11. The process of claim 1 wherein the molten metal oxide is contacted by the fuel and air, separately.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention may best be understood by reference to the following description taken in conjunction with the accompanying figures.

(2) FIG. 1: Molten Metal Oxide CLC Operating States. This figure shows the two operating states between which a single reactor would be switched. In State 1, the reactor is initially charged with the active metal oxide, and then fuel is introduced into the reactor. The ensuing reaction results in the combustion of the fuel and the reduction of the metal oxide to the reduced species. Gases released from combustion are removed from the reactor, and the heat they contain is recovered. In State 2, the reactor initially contains some amount of reduced species, and the flow of fuel has been shut off. Air is then introduced into the reactor, which causes the reduced species to be oxidized back to metal oxide. A hot stream of depleted air exits the reactor, and the heat it contains is recovered. Once the reduced species is mostly or completely oxidized, the reactor is ready for fuel to be introduced once again.

(3) FIG. 2: Two CLC Reactors Connected for Optional Direct Production of Steam. While some or all of the heat from combustion of fuel will leave the reactor with the exhaust gases or the depleted air, this figure also shows how heat may be directly removed from the reactors by way of steam coils. Valve positions are indicated to show that when Reactor 1 is in combustion mode, no air is allowed into the reactor. Similarly, when Reactor 2 is in regeneration mode, no fuel is allowed into the reactor. Because heat may be released during both combustion and regeneration, water may be directed to the steam coils of both reactors in varying proportions during all stages of CLC.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(4) The current invention proposes an improved method for using chemical-looping combustion (CLC) of hydrocarbons as an energy source. In one aspect, the oxygen carrier is a molten metal oxide (as opposed to solid) when it is in an oxidized state, and solid when it is reduced in the presence of a fuel source. The reduced solid may or may not have significant solubility in the molten metal oxide. In a second aspect, the reduced species is not a solid, rather is another molten liquid that may or may not be soluble in the remaining unreacted liquid metal oxide. In a third aspect, the reduced solid species need not be separated from the remaining unreacted metal oxide, rather, it can remain physically mixed with, or dissolved within, the molten oxide. The reduced solid species may be directly oxidized within the mixture by stopping the flow of fuel and initiating the flow of air through the mixture. A fourth aspect is that other materials may be used in combination with the reactive species, which may not participate in any chemical reactions with the fuel or air, but which may be beneficial for controlling melting point, vapor pressure, viscosity, slagging potential, solubility or other chemical or physical properties of the melt. A fifth aspect is that no movement of the molten metal oxide or reduced solid species from one reaction chamber to another is required. A sixth aspect is that the operating state of a particular reactor vessel is controlled by controlling whether fuel or oxidant is flowing to the reactor vessel. A seventh key aspect is that, in addition to capturing heat from the gaseous species leaving the reactor, some heat released from the reactions could also be removed directly from the reactor by a closed-loop system. An eighth key aspect is that the current invention is connected to a CO.sub.2 capture system, which would be simple to construct since the product of combustion would be predominantly CO.sub.2. In order to minimize subsequent energy demands related to compressing the captured CO.sub.2 for transportation and storage, the CLC reactor may be operated at above ambient pressure during the combustion step. Another embodiment uses an array of multiple identical CLC reactors operated in a synchronized manner, wherein the process is cycled through the reactors to maintain steady state combustion and steam production. A ninth key aspect is an embodiment where the steady state steam production from an array of multiple identical CLC reactors is used for power generation, with each CLC reactor being operated in a combination of identical and different stages of the CLC cycle to provide continuous steam for power generation.

(5) An example material is MoO.sub.3. Above its melting point of about 795 C., The MoO.sub.3 remains fluid until it is reduced by the fuel, causing a phase change to MoO.sub.2 solid, the simultaneous generation of product gases, and the generation of heat in some amount equal to a fraction of the heat of combustion of the fuel itself. The use of a liquid phase MoO.sub.3 significantly improves the efficacy of the CLC process because there is no solid reaction surface to degrade during repeated looping. The interface of the fuel with the liquid MoO.sub.3 is continuously renewed during reaction, helped by the generation of product gases. The MoO.sub.2 is regenerated to MoO.sub.3 by exposure to air. Summed together, the heat released during this regeneration step in addition to the heat released during the first reduction step is typically equal to the heat of combustion of the fuel itself.

(6) As used herein, metal oxide (MeOx) includes oxides of V, Mn, Cu, Mo, Bi, other metal oxides, and mixtures thereof. For more information about metal oxides see the CRC Handbook of Chemistry and Physics, pp. 4-35 to 4-119 and 5-72 to 5-75, or other standard chemistry resource. The metal oxides for the disclosed process are selected by ensuring that each step of the CLC process is both spontaneous and results in the release of heat. That is to say, in the disclosed process, both the reduction step that generates the reduced species and regeneration of the metal oxide are net exergonic and net exothermic. Thus, as long as the reduction step for all reacting species is net exergonic, metal oxides that undergo net endothermic reduction during their reaction with fuel may be used in combination with metal oxides that undergo net exothermic reduction during their reaction with fuel to tailor a reduction step with a desired amount of exothermicity. The control of reaction energetics simplifies the reactor design, reaction process and ensures high levels of combustion. The regeneration of the reduced species back to its oxide form is exergonic and exothermic for all reactive materials in the disclosed process. In conventional CLC, the reaction with the fuel is often endothermic, which reduces process efficiency and introduces design limitations due to the quenching nature of the combustion step. Table 1 shows a non-exhaustive list of example oxide fuel reactions. While many types of fuel could be used, carbon, methane and carbon monoxide are shown for reference, along with their net combustion enthalpies and free energies of combustion.

(7) TABLE-US-00001 TABLE 1 Example Fuel Reactions H(25 C.) G(25 C.) Reactions [kJ/mol] [kJ/mol] Carbon as Fuel V.sub.2O.sub.5 + C = V.sub.2O.sub.3 + CO.sub.2 59.3 110.6 2Mn.sub.2O.sub.3 + C = 4MnO + CO.sub.2 20.6 88.0 2Cu.sub.2O + C = 4Cu + CO.sub.2 52.3 98.7 2CuO + C = 2Cu + CO.sub.2 81.9 138.2 4CuO + C = 2Cu2O + CO.sub.2 111.5 177.7 2MoO.sub.3 + C = 2MoO2 + CO.sub.2 82.9 126.4 0.667Bi.sub.2O.sub.3 + C = 1.333Bi + CO.sub.2 8.0 62.8 Methane as Fuel V.sub.2O.sub.5 + 0.5CH.sub.4 = V.sub.2O.sub.3 + 0.5CO.sub.2 + H.sub.2O 67.1 116.7 2Mn.sub.2O.sub.3 + 0.5CH.sub.4 = 4MnO + 0.5CO.sub.2 + 28.4 94.1 H.sub.2O 2Cu.sub.2O + 0.5CH.sub.4 = 4Cu + 0.5CO.sub.2 + H.sub.2O 60.1 104.8 2CuO + 0.5CH.sub.4 = 2Cu + 0.5CO.sub.2 + H.sub.2O 89.7 144.3 4CuO + 0.5CH.sub.4 = 2Cu.sub.2O + 0.5CO.sub.2 + H.sub.2O 119.3 183.9 2MoO.sub.3 + 0.5CH.sub.4 = 2MoO.sub.2 + 0.5CO.sub.2 + 90.7 132.5 H.sub.2O 0.667Bi.sub.2O.sub.3 + 0.5CH.sub.4 = 1.333Bi + 15.9 69.1 0.5CO.sub.2 + H.sub.2O Carbon Monoxide as Fuel V.sub.2O.sub.5 + 2CO = V.sub.2O.sub.3 + 2CO.sub.2 231.7 230.6 2Mn.sub.2O.sub.3 + 2CO = 4MnO + 2CO.sub.2 193.1 208.0 2Cu.sub.2O + 2CO = 4Cu + 2CO.sub.2 224.7 218.7 2CuO + 2CO = 2Cu + 2CO.sub.2 254.3 258.2 4CuO + 2CO = 2Cu.sub.2O + 2CO.sub.2 283.9 297.7 2MoO.sub.3 + 2CO = 2MoO.sub.2 + 2CO.sub.2 255.3 246.4 0.667Bi.sub.2O3 + 2CO = 1.333Bi + 2CO.sub.2 180.4 182.8 Regeneration V.sub.2O.sub.3 + O.sub.2 = V.sub.2O.sub.5 334.2 283.8 4MnO + O.sub.2 = 2Mn.sub.2O.sub.3 372.9 306.4 4Cu + O.sub.2 = 2Cu.sub.2O 341.2 295.7 2Cu + O.sub.2 = 2CuO 311.6 256.2 2Cu.sub.2O + O.sub.2 = 4CuO 282.0 216.6 2MoO.sub.2 + O.sub.2 = 2MoO.sub.3 310.6 268.0 1.333Bi + O.sub.2 = 0.667Bi.sub.2O.sub.3 385.4 331.4 Net Reactions Carbon: C + O.sub.2 = CO.sub.2 393.5 394.4 Methane: 0.5CH.sub.4 + O.sub.2 = 0.5CO.sub.2 + H.sub.2O 401.3 400.5 Carbon Monoxide 2CO + O.sub.2 = 2CO.sub.2 565.9 514.4

(8) This invention describes an improved method of CLC, in which the oxygen carrier is a molten metal oxide. The molten metal oxide is contained in a reaction vessel, and may be mixed with other materials that control the physical or chemical properties of the bulk melt. In one embodiment a molten Bi.sub.2O.sub.3 as one constituent of a molten glassy matrix is mixed with a diesel, synthesis gas, dilution gas, mixture of dilution-synthesis gas, kerosene, fuel gas, or other liquid fuel source. In another embodiment a molten molybdenum oxide is mixed with a methane, vaporized gasoline, diesel, synthesis gas, dilution gas, mixture of dilution-synthesis gas, kerosene, fuel gas, or mixtures thereof. Additionally, molten metal oxide may be mixed with a fine coal, petroleum coke or shale powder to achieve thorough oxidation of the fuel powder. By pulverizing the solid fuels and mixing with a liquid metal oxide, effective combustion may be achieved. In yet another embodiment, molten CuO or Cu.sub.2O is incorporated within a molten glassy matrix, and contacted with biomass, such as wood, cellulose, dried corn stover, waste paper, municipal solid waste, or mixtures thereof. In all the embodiments, fuel is added until a desired amount of the metal oxide is depleted, at which time, the fuel will cease to be added to the reaction vessel. Flow of air into the reaction vessel can then be initiated, which will regenerate the active metal oxides. Because impurities within the fuels may slowly degrade the metal oxides, and ash constituents of the fuel will incorporate into the melt and dilute the metal oxides, some amount of the melt may be removed and fresh metal oxide may be added either continuously or discontinuously during operation.

(9) The following examples of certain embodiments of the invention are given. Each example is provided by way of explanation of the invention, one of many embodiments of the invention, and the following examples should not be read to limit, or define, the scope of the invention.

EXAMPLE 1

Molybdenum Oxide Reaction

(10) In one embodiment a desirable metal oxide would be MoO.sub.3. MoO.sub.3 has a sufficiently low melting point of approximately 795 C. that conventional reactor materials with standard construction and care may be used to contain the reaction. Assuming the carbonaceous fuel to be pure carbon, the reaction chemistry is as follows:

(11) TABLE-US-00002 TABLE 2 Molybdenum Oxide CLC reactions Rxn. Type Rxn. Stoichiometry Std. Rxn. Enthalpy Fuel Oxidation 2 MoO.sub.3 + C = 2 MoO.sub.2 + CO.sub.2 82.9 MJ/mol carbon Oxide 2MoO.sub.2 + O.sub.2 = 2 MoO.sub.3 310.6 MJ/mol O.sub.2 Regeneration Net C + O.sub.2 = CO.sub.2 393.5 MJ/mol

(12) A reactor contains a pool of molten MoO.sub.3 in direct or indirect thermal contact with a closed-loop steam system and a heat recovery system to recover useful heat from the exiting exhaust and regeneration gas streams. In addition, the reactor would also be in contact with a CO.sub.2 capture system that captures and prepares the CO.sub.2 released from fuel combustion with MoO.sub.3 for disposal. The reactor would ideally be operated at pressure such that the CO.sub.2 evolved would require minimal additional compression for sequestration. Conventional CLC has multiple reactors, each with a specific function, and solids must be transported between the reactors. The current invention allows for multiple identical reactors to be operated in a cyclic manner, such that as few as one reactor would be sufficient for a process. For power generation, two or more liquid CLC reactors may be required, with each reactor being operated at different stages of combustion/regeneration at a given moment. In one embodiment two reactors are run in alternate with one reactor undergoing combustion while the other reactor is undergoing oxidation.

EXAMPLE 2

Blended Metal Oxides

(13) Metal oxides including molybdenum, vanadium, manganese, copper, and bismuth oxides may be blended. These metal oxides may also be blended with other oxides such as boric oxide, lime and other materials, to change the overall melt temperature, change the upper or lower temperatures of the reaction, and generally to obtain desirable properties of the bulk melt. Refractory materials for the reaction chamber are widely available and include materials such as silicon carbide, chromia, alumina, magnesia, dolomite or combinations. An extensive, but not exhaustive, list of metal oxides that are useful for the refractory, melt, or as a oxide catalyst are listed in Table 3. More strongly ionic species such as nitrate, phosphate, silicate and sulfate metallic salts, are not shown, but could also be used in varying amounts in the melt.

(14) TABLE-US-00003 TABLE 3 Metal Species Melting Melting Point Primary Metal Point [ C.] Use Oxide [ C.] Primary Use Group IA Li 186 n/a Li.sub.2O 1,570 Melt Na 98 n/a Na.sub.2O 1,132 Melt K 62 n/a K.sub.2O .sup.350 d. Melt Group IIA Mg 651 n/a MgO 2,800 Melt, Refractory Ca 810 n/a CaO 2,570 Melt, Refractory Sr 800 n/a SrO 2,430 Melt Ba 850 n/a BaO 1,923 Melt Group IIIA B 2,300 n/a B.sub.2O.sub.3 577 Melt Al 660 n/a Al.sub.2O.sub.3 2,054 Melt, Refractory Group IVA Si 1,414 n/a SiO.sub.2 1,710 Melt, Refractory Sn 232 Reactant SnO 1,080 Melt, Reactant Sn 232 Reactant SnO.sub.2 1127 Melt, Reactant Pb 328 Reactant PbO 888 Melt, Reactant Group VA P n/a n/a P.sub.2O.sub.5 340 Melt Sb 73 Reactant Sb.sub.2O.sub.3 656 Melt, Reactant Bi 271 Reactant Bi.sub.2O.sub.3 860 Melt, Reactant Group IIIB Sc 1,200 n/a Sc.sub.2O.sub.3 2,485 Refractory Y 1,490 n/a Y.sub.2O.sub.3 2,690 Refractory Group IVB Ti 1,800 n/a TiO.sub.2 1,843 Melt Zr 1,700 n/a ZrO.sub.2 2,715 Refractory Hf 2,812 n/a HfO.sub.2 2,760 Refractory Group VB V 1,710 n/a V.sub.2O.sub.3 1,970 Melt, Reactant V 1,710 n/a V.sub.2O.sub.5 800 Melt, Reactant Nb 2,750 n/a Nb.sub.2O.sub.3 1,520 Melt Group VIB Cr 1,615 n/a Cr.sub.2O.sub.3 2,432 Melt, Refractory Mo 2,620 n/a MoO.sub.3 795 Melt, Reactant W 3,370 n/a WO.sub.3 1,473 Melt, Reactant Group VIIB Mn 1,244 n/a MnO 1,650 Melt, Reactant Group VIIIB Fe 1,505 Reactant FeO 1,360 Melt, Reactant Fe 1,505 Reactant Fe.sub.2O.sub.3 1,566 Melt, Reactant Co 1,480 Reactant CoO 1,800 Melt, Reactant Ni 1,452 Reactant NiO 1,984 Melt, Reactant Group IB Cu 1,083 Reactant Cu.sub.2O 1,235 Melt, Reactant Cu 1,083 Reactant CuO 1,026 d. Melt, Reactant Group IIB Zn 420 n/a ZnO 1,975 Melt Lanthanides Ce 645 n/a CeO.sub.2 2,600 Melt

(15) Although the systems and processes described herein have been described in detail, it should be understood that various changes, substitutions, and alterations can be made without departing from the spirit and scope of the invention as defined by the following claims. Each and every claim is incorporated into the specification as an embodiment of the present invention. Thus, the claims are part of the description and should be deemed to be additional description to the preferred embodiments of the present invention.

REFERENCES

(16) All of the references cited herein are expressly incorporated by reference. The discussion of any reference is not an admission that it is prior art to the present invention, especially any reference that may have a publication data after the priority date of this application. Incorporated references are listed again here for convenience: 1. U.S. Pat. No. 5,447,024, Ishida and Hongguang, Chemical-Looping Combustion Power Generation Plant System. Tokyo Electric Power Co., Inc. (1995). 2. U.S. Pat. No. 5,827,496, Lyon, Methods And Systems For Heat Transfer By Unmixed Combustion. Energy and Environmental Research Corp. (1998). 3. U.S. Pat. No. 6,214,305, van Harderveld, Method and apparatus for the treatment of diesel exhaust gas. Technische Universiteit Delft (2001). 4. CRC Handbook of Chemistry and Physics 74.sup.th Edition, Editor Lide, D. R., CRC Press, Boca Raton, (1993). 5. Jerndal, et al., Thermal analysis of chemical-looping combustion. Trans IChemE, Part A Chem. Eng. Res. and Des. 84: 795-806 (2006). 6. McGlashan, Chemical looping combustiona thermodynamic study Proc. IMechE, Part C: J. Mech. Eng. Sci. 222: 1005-1019 (2008). 7. Ishida, M., and Jin, N. (1997). CO.sub.2 Recovery in a power plant with chemical looping combustion. Energy Cony. Mgmt. 38: S187-S192. 8. Brandvoll and Bolland, Inherent CO.sub.2 capture using chemical looping combustion in a natural gas fired cycle. Trans. ASME 126: 316-21 (2004). 9. Yan, et al., Properties of carbide-metal cermets prepared from composite powders by direct reduction and carburization process Key Engineering Materials Pt. 2, High-Performance Ceramics V 368-372:1099-1103 (2008). 10. Barthos, et al., Hydrogen production in the decomposition and steam reforming of methanol on MoZClcarbon catalysts. Journal of Catalysis (2007), 249(2), 289-299. (2008).