Chemical looping syngas production from carbonaceous fuels

Abstract

A reactor configuration is proposed for selectively converting gaseous, liquid or solid fuels to a syngas specification which is flexible in terms of H.sub.2/CO ratio. This reactor and system configuration can be used with a specific oxygen carrier to hydro-carbon fuel molar ratio, a specific range of operating temperatures and pressures, and a co-current downward moving bed system. The concept of a CO.sub.2 stream injected in-conjunction with the specified operating parameters for a moving bed reducer is claimed, wherein the injection location in the reactor system is flexible for both steam and CO.sub.2 such that, carbon efficiency of the system is maximized.

Claims

1. A system for converting a fuel, the system comprising: a first moving bed reactor comprising a metal oxide particles having a primary component and a secondary component, wherein fuel, CO.sub.2 and steam are added to the first moving bed reactor in a co-current flow pattern relative to the metal oxide particles, wherein the first moving bed reactor is configured to reduce at least a portion of the metal oxide particles with the fuel to produce a first reduced metal oxide, and is further configured to produce a first syngas stream comprising H.sub.2, CO, CO.sub.2 and steam; a second moving bed reactor, operating in parallel with the first moving bed reactor and comprising metal oxide particles having a primary component and a secondary component, wherein fuel, CO.sub.2 and steam are added to the second moving bed reactor in a co-current flow pattern relative to the metal oxide particles, wherein the second moving bed reactor is configured to reduce at least a portion of the metal oxide particles with the fuel to produce a second reduced metal oxide, and is further configured to produce a second syngas stream comprising H.sub.2, CO, CO.sub.2 and steam; a separation unit, in communication with the first moving bed reactor and the second moving bed reactor, and configured to remove the CO.sub.2 from the first syngas stream and the second syngas stream, wherein the H.sub.2/CO ratios of the first and second syngas streams are controlled by recycling substantially all of the CO.sub.2 from the separation unit to the first moving bed reactor and the second moving bed reactor; and a third co-current fluidized bed reactor in communication with the first moving bed reactor and the second moving bed reactor and configured to oxidize the first reduced metal oxide and the second reduced metal oxide with an oxidizing agent to produce oxidized metal oxide particles and recycle the oxidized metal oxide particles to the first moving bed reactor and the second moving bed reactor for subsequent reduction reactions.

2. The system of claim 1, wherein the primary component is Fe.sub.2O.sub.3.

3. The system of claim 1, wherein the secondary component comprises a metal-oxide selected from the group consisting of oxides of Ti, Al, Co, Cu, Mg, Mn, Zn, and combinations thereof.

4. The system of claim 1, wherein the secondary component is titanium oxide.

5. The system of claim 1, wherein the fuel is methane.

6. The system of claim 1, wherein the H.sub.2/CO ratio of the first syngas stream is about 2.9 to about 3.1.

7. The system of claim 1, wherein the H.sub.2/CO ratio of the second syngas stream is about 1.0 to about 1.5.

8. The system of claim 1, wherein a combination of the syngas from the first moving bed reactor and the second moving bed reactor results in a total syngas H.sub.2/CO ratio of about 1 to about 3.

9. The system of claim 1, wherein the first reduced metal oxides and the second reduced metal oxides are oxidized by introducing steam into the third co-current fluidized bed reactor.

10. The system of claim 1, wherein the system consumes more CO.sub.2 than it produces.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Conceptual schematic for a carbon negative or carbon neutral iron based chemical looping system that uses CO.sub.2 recycle and an external CO.sub.2 source in the high efficiency conversion of fossil fuels.

(2) FIG. 2a: Syngas generation surface for iron-titanium composite metal oxide (ITCMO) at an Fe.sub.2O.sub.3:CH.sub.4 ratio of 0.33.

(3) FIG. 2b: Syngas purity surface for ITCMO at an Fe.sub.2O.sub.3:CH.sub.4 ratio of 0.333.

(4) FIG. 3: Conceptual schematic for a carbon negative or carbon neutral iron based chemical looping system that uses CO.sub.2 recycle and an external CO.sub.2 source in the high efficiency conversion of natural gas to syngas suitable for Fischer-Tropsch synthesis and the production of liquid fuels.

(5) FIG. 4: Comparison of obtainable H.sub.2/CO ratios with corresponding percentages of CO.sub.2 recycle at various H.sub.2O/CH.sub.4 ratios.

(6) FIG. 5: H.sub.2/CO ratio as a function of H.sub.2O/CH.sub.4 and CO.sub.2/CH.sub.4 ratios, at 900° C., 1 atm, for a co-current moving bed reactor and at an effective Fe.sub.2O.sub.3/CH.sub.4 ratio of 0.8.

(7) FIG. 6: H.sub.2 flowrate as a function of H.sub.2O/CH.sub.4 and CO.sub.2/CH.sub.4 ratios, at 900° C., 1 atm, for a co-current moving bed reactor and at an effective Fe.sub.2O.sub.3/CH.sub.4 ratio of 0.8.

(8) FIG. 7: Conceptual schematic of multiple reducers operating in parallel with a single combustor reactor.

(9) FIG. 8: Conceptual schematic of multiple reactor modules, containing multiple reducers and combustors.

(10) FIG. 9: Conceptual schematic of chemical looping CO.sub.2 recycle concept with two reducers operating in parallel with a single combustor reactor.

(11) FIG. 10: Conceptual schematic of chemical looping CO.sub.2 recycle concept with two modules, containing both a reducer and combustor, operating in parallel.

(12) FIG. 11: Conceptual schematic of chemical looping CO.sub.2 recycle concept with three reducers operating in parallel with a single combustor reactor.

(13) FIG. 12: Conceptual schematic of chemical looping CO.sub.2 recycle concept with three modules, containing both a reducer and combustor, operating in parallel.

(14) FIG. 13: H.sub.2/CO ratio as a function of H.sub.2O/CH.sub.4 and CO.sub.2/CH.sub.4 ratios, at 900° C., 1 atm, for a co-current moving bed reactor and at an effective Fe.sub.2O.sub.3/CH.sub.4 ratio of 0.8.

(15) FIG. 14: H.sub.2 flowrate as a function of H.sub.2O/CH.sub.4 and CO.sub.2/CH.sub.4 ratios, at 900° C., 1 atm, for a co-current moving bed reactor and at an effective Fe.sub.2O.sub.3/CH.sub.4 ratio of 0.8.

(16) FIG. 15: Schematic representation of an embodiment of the chemical looping CO.sub.2 recycle system with two reducers operating in parallel with a single combustor reactor and a CO.sub.2 separation unit.

(17) FIG. 16a: Syngas generation surface for pure Fe.sub.2O.sub.3 at an Fe.sub.2O.sub.3:CH.sub.4 ratio of 0.33.

(18) FIG. 16b: Geometric representation of the modularization strategy for the syngas generation performance.

(19) FIG. 17: Syngas generation surface for ITCMO at an Fe.sub.2O.sub.3:CH.sub.4 ratio of 0.333.

(20) FIG. 18a: Syngas yield at an Fe.sub.2O.sub.3:CH.sub.4 ratio of 0.34, 900° C., 1 atm.

(21) FIG. 18b: Syngas yield at an Fe.sub.2O.sub.3:CH.sub.4 ratio of 1.2, 900° C., 1 atm.

(22) FIG. 18c: Syngas yield at an Fe.sub.2O.sub.3:CH.sub.4 ratio of 9.8, 900° C., 1 atm.

(23) FIG. 18d: Operating points of the ITCMO-based modular system at 900° C., 1 atm for varying H.sub.2O and CO.sub.2 injection.

(24) FIG. 19: Co-planar view of FIG. 18d showing the operating points of the ITCMO-based modular system at 900° C., 1 atm for varying [O]/CH.sub.4.

DETAILED DESCRIPTION

(25) Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

(26) This disclosure describes specific reactors and conditions that allow the disclosed novel chemical looping process to function as a carbon negative or a carbon neutral fossil fuel process. In cases where the CO.sub.2 consumed is more than CO.sub.2 produced (CO.sub.2 negative system), the disclosed chemical looping system can function as an effective CO.sub.2 utilization system.

1. Definitions

(27) Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present invention. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

(28) The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of” and “consisting essentially of” the embodiments or elements presented herein, whether explicitly set forth or not.

(29) The conjunctive term “or” includes any and all combinations of one or more listed elements associated by the conjunctive term. For example, the phrase “an apparatus comprising A or B” may refer to an apparatus including A where B is not present, an apparatus including B where A is not present, or an apparatus where both A and B are present. The phrases “at least one of A, B, . . . and N” or “at least one of A, B, . . . N, or combinations thereof” are defined in the broadest sense to mean one or more elements selected from the group comprising A, B, . . . and N, that is to say, any combination of one or more of the elements A, B, . . . or N including any one element alone or in combination with one or more of the other elements which may also include, in combination, additional elements not listed.

(30) For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

(31) “Carbon neutral,” as used herein, refers to a system or process in which about 100% of the CO.sub.2 produced by a system is recycled.

(32) “Carbon negative,” as used herein, refers to a system or process in which more CO.sub.2 is consumed than the system or process produces.

2. Syngas Production Systems

(33) To maximize the amount of syngas produced per mole of a fossil fuel feedstock, a novel modularization strategy can be employed in which multiple reducer reactors operate in parallel. This concept allows for each reducer reactor to operate under different operating conditions and produce different qualities of syngas. The operating conditions yield the desired overall syngas purity and H.sub.2:CO requirements when linearly combined while using less fossil fuel feedstock when compared to a single reducer reactor.

(34) FIG. 1 shows a scheme for a carbon negative chemical looping process that converts fossil fuels to value added products. The process comprises co-feeding fossil fuels, CO.sub.2 and steam into multiple moving bed reducer reactors to produce syngas. The fossil fuels may include but are not limited to gaseous fossil fuels (natural gas, shale gas, coal bed methane, etc.), solid fossil fuels (coal, biomass, petcoke, etc.), or liquid fossil fuels (kerosene, petroleum, etc.).

(35) Operating conditions for a syngas producing reducer reactor are chosen to maximize the moles of syngas produced per mole fossil fuel feedstock, to maximize syngas purity, and to meet the H.sub.2:CO ratio requirements for downstream processes. A novel combination of these conditions can yield a CO.sub.2 negative scheme, in which the molar amount of CO.sub.2 entering the reactor divided by the molar amount of CO.sub.2 exiting the reactor (CRP or CO.sub.2 reaction parameter) is greater than 1.

(36) A specific set of operating conditions is given in Table 1 (below). Group (1) refers to the reaction of CH.sub.4 with the metal oxide; Group (2) refers to the reactions of CH.sub.4 with CO.sub.2 and the metal oxide; Group (3) refers to the reactions of CH.sub.4 with H.sub.2O and the metal oxide; Group (4) refers to the reactions of CH.sub.4 with CO.sub.2, H.sub.2O and the metal oxide. For a Group (4) operation, it can be seen that a CRP>1 operating condition that reasonably satisfies the previously given criteria has been determined thermodynamically and verified with experiments.

(37) TABLE-US-00001 TABLE 1 Experimental data for various reaction conditions involving CH.sub.4, Fe.sub.2O.sub.3 and/or CO.sub.2 and/or H.sub.2O in a single co-current moving bed reactor Group (1) Group (2) Group (3) Group (4) Input Conditions CH.sub.4 flow rate (SLPM) 1.0 1.3 1.1 1.1 0.9 0.9 0.9 0.7 H.sub.2O flow rate (mL/min) 0 0 0 0 0.15 0.2 0.2 0.15 H.sub.2O/CH.sub.4 molar ratio 0 0 0 0 0.61 0.79 0.79 0.78 CO.sub.2 flow rate (SLPM) 0 0 0.22 0.33 0 0 0.14 0.11 CO.sub.2/CH.sub.4 molar ratio 0 0 0.2 0.3 0 0 0.15 0.15 Fe.sub.2O.sub.3:CH.sub.4 molar ratio 1.03 0.75 0.83 0.77 0.68 0.68 0.65 0.81 Reactor temperature (° C.) 1037 1039 1039 1038 1032 1031 1037 1034 Experimental results % CH.sub.4 conversion 95.7 93.3 94.5 94.1 93.3 96.5 94.3 93.2 H.sub.2:CO molar ratio 1.83 1.84 1.53 1.41 2.14 2.15 1.95 1.90 CO/CO.sub.2 molar ratio 8.11 9.52 13.5 13.7 13.1 12.9 13.6 13.7 CRP 0 0 1.93 2.50 0 0 1.51 1.66 % Syngas Purity on dry basis 94.2 93.9 95.2 95.1 95.3 96.4 95.8 95.4 Thermodynamic results % CH.sub.4 conversion 100 100 100 100 100 100 100 100 H.sub.2:CO molar ratio 1.88 1.88 1.57 1.45 2.46 2.61 2.23 2.18 CO/CO.sub.2 molar ratio 12.8 12.8 12.8 12.9 12.9 11.3 9.09 6.89 CRP 0 0 2.31 3.20 0 0 1.32 1.03 % Syngas Purity on dry basis 97.4 97.4 97.1 96.9 97.8 97.6 96.7 95.6

(38) In certain embodiments of the carbon negative chemical looping system, the conditions necessary for a CRP greater than 1 are fixed using thermodynamic Gibbs free energy minimization simulations. FIG. 2a depicts syngas production per mole CH.sub.4 feedstock as a function of CO.sub.2 and H.sub.2O input to the reactor. It is noted that the largest amount of syngas is produced per mole CH.sub.4 at high H.sub.2O and CO.sub.2 inputs. FIG. 2b, however, shows that the syngas purity (moles (H.sub.2+CO)/(total moles syngas)) is relatively low (75%) under these operating conditions due to a fraction of the H.sub.2O and CO.sub.2 feedstocks flowing through the reactor unreacted. Typically, a high syngas purity (greater than 95%) is desirable for efficient downstream processing.

(39) FIG. 3 shows one embodiment of the design of the carbon negative chemical looping system. In this embodiment, natural gas is converted to syngas which is suitable for Fischer-Tropsch synthesis and the production of liquid fuels.

(40) FIG. 4 shows an analysis of the viable operating points for the carbon negative system shown in FIG. 3. The graph includes H.sub.2/CO ratios and corresponding ratios for the amount of CO.sub.2 in syngas to the amount of CO.sub.2 being recycled at various steam to natural gas ratios. From this graph it is possible to determine if a set of conditions yield a syngas stream at the correct H.sub.2/CO ratio and what CO.sub.2 recycle percentage this point corresponds to. One example is shown by the connection of points A and B. This example corresponds to a H.sub.2O/CH.sub.4 ratio of 0.5, a H.sub.2/CO ratio of 2.0, and a CO.sub.2 recycle rate of nearly 140%.

(41) FIG. 5 shows H.sub.2/CO ratio as a function of steam input and CO.sub.2 per mol of CH.sub.4 for a co-current moving bed reactor, operating at 900° C., 1 atm and effective Fe.sub.2O.sub.3/CH.sub.4 ratio of 0.8.

(42) FIG. 6 shows the variation of H.sub.2 flowrate, in syngas, for the H.sub.2/CO ratio shown in FIG. 4. It should be noticed that the nonlinearity between the H.sub.2/CO ratio when steam and CO.sub.2 is variably input is an unique characteristic of CO.sub.2 recycle in chemical looping systems. This nonlinearity may be leveraged to develop a multiple reducer system. Each of these reducer reactors may be exclusively optimized to maximize the overall benefits in terms of carbon efficiency and cost, obtained from minimizing the overall natural gas consumption. A multiple reducer system can be feasibly conceived on a commercial scale as a single circulating solids loop with multiple reducers and a single combustor, as shown in FIG. 7. Another commercial scale operation of the multiple reducer system can be designed with multiple modules, each containing multiple reducers and combustors, as shown in FIG. 8.

(43) In certain embodiments, the chemical looping recycle system comprises a multiple reducer design having a two reducer and a three reducer system, which may generate a syngas composition (H.sub.2/CO ratio of 2) needed for Fischer-Tropsch synthesis. FIG. 9 and FIG. 10 show a two reducer CO.sub.2 recycle chemical looping system, where operating conditions for each reducer are represented by Point A and Point B in FIG. 5 and FIG. 6. Each reducer operation, is optimized such that the net syngas has an effective H.sub.2/CO ratio of about 1 to about 3. In certain embodiments, the net syngas has an effective H.sub.2/CO ratio of about 2. In certain embodiments, the reducer operation corresponding to Point A, maximizes the H.sub.2 production, operating at a H.sub.2O/CH.sub.4 ratio of 2, CO.sub.2/CH.sub.4 ratio of 0.20, yielding a syngas H.sub.2/CO ratio of about 2.9 to about 3.1, preferably 3.02. The reducer corresponding to Point B, optimized for CO production, operates at a H.sub.2O/CH.sub.4 ratio of 0.20, CO.sub.2/CH.sub.4 ratio of 0.57, yielding a syngas ratio of about 1.0 to about 1.5, preferably 1.27. The combination of the syngas from each reducer results in a total syngas H.sub.2/CO ratio of ‘2.’ Another application of multiple reducer concepts is demonstrated using three reducer modules, as shown in FIG. 11 and FIG. 12 with the specific operating conditions represented by Points A, B, and C in FIGS. 13 and 14. FIGS. 13 and 14 show the H.sub.2/CO ratios and H.sub.2 flowrates similar to those shown in FIGS. 5 and 6. A three reducer combination could be useful for operating one reducer optimized at an extreme to produce H.sub.2 (Point A in FIG. 13), a second reducer optimized at an extreme to produce CO (Point C in FIG. 13), and a third reducer to mitigate the H.sub.2/CO ratio (Point B in FIG. 13). The first reducer could operate at Point A (H.sub.2O/CH.sub.4 ratio of 2, CO.sub.2/CH.sub.4 ratio of 0.20, outputting a H.sub.2/CO ratio of 3.0), the second reducer could operate at Point B (H.sub.2O/CH.sub.4 ratio of 1.8, CO.sub.2/CH.sub.4 ratio of 0.20, outputting a H.sub.2/CO ratio of 2.90), and the third reducer could operate at Point C (H.sub.2O/CH.sub.4 ratio of 0.4, CO.sub.2/CH.sub.4 ratio of 1.12, outputting a H.sub.z/CO ratio of 1.03). The net H.sub.z/CO ratio of these three reducers is ‘2.’ It should be noted that like the two and three reducer cases, the concept can be expanded to ‘n’ reducers or modules. Each of these ‘n’ reducer reactors may be selectively optimized for specific functions, which may include, but are not limited to, operating temperatures, operating pressures, syngas H.sub.2/CO ratios, effective Fe.sub.2O.sub.3/CH.sub.4 ratios, support weight percentages, etc. Such specialized operation may be used to reduce overall cost and maximize the efficiency, based on a given set of operating conditions.

(44) FIG. 15 schematically illustrates a chemical looping modular process for producing syngas from fossil fuel. The systems comprises three main reactor sections including the reducer reactor section, a combustor reactor and a separation unit. The reducer reactor section is a modular system in which two or more co-current moving bed reactors convert fossil fuel to a syngas stream comprising H.sub.2, CO, CO.sub.2 and steam. The modular configuration of the reducer reactors allows for maximizing the H.sub.2+CO production, beyond the configuration of a single reducer reactor. Each reactor in the modular system can be optimized based on the oxygen carrier to fuel ratio, temperature, and pressure of the reactor. One advantage of the co-current moving bed reactors is that it ensures that thermodynamic design conditions for a high syngas conversion can be obtained by controlling the reaction stoichiometric and that sufficient residence times are available for complete reactant conversion.

(45) In certain embodiments of the system, the reducer reactor section comprises two co-current moving bed reactors, operating in parallel. In another embodiment, the reducer reactor system comprises two or more co-current moving bed reactors, operating in parallel with respect to one another. The reducer reactors comprise metal oxide particles. The metal-oxide composition consists of two components, namely primary and secondary. In certain embodiments, the primary metal-oxide is being chosen to be Fe.sub.2O.sub.3. The primary metal-oxide should be able to donate oxygen to the fuel mixture. The secondary metal-oxide can be an oxide of any combination of Ti, Al, Co, Cu, Mg, Mn, Zn, etc. The secondary metal-oxide serves to strengthen the primary metal-oxide and can enhance reactivity by forming complexes which have a better thermodynamic selectivity than iron-oxide alone. The oxygen-carrier metal-oxide may contain a combination of primary and secondary metal-oxides in varying weight percentages. The metal-oxide can be prepared by methods including but not limited to extrusion, pelletizing, co-precipitation, wet-impregnation, and mechanical compression. Techniques like sintering the synthesized metal-oxide or adding a binder with sol-gel combustion can be used to increase the strength of the metal-oxide.

(46) In certain embodiments, the specific metal-oxide composition consists of an iron-titanium composite metal oxide (ITCMO) or an iron-aluminum complex. This complex can be titanium-rich, or iron-rich depending on the relative molar ratios. The overall reduced form for the specific chemistry simulated is dependent on the relative molar ratio composition of the metal-oxide. For example, a titanium-rich iron based composite metal-oxide particle contains a TiO.sub.2:Fe.sub.2O.sub.3 molar ratio of greater than 2 will yield a reduced form, FeTiO3. On the other hand, a TiO.sub.2:Fe.sub.2O.sub.3 molar ratio of less than 2 will favor formation of FeO—Fe.sub.2TiO.sub.4 in addition to FeTiO.sub.3 in the composite's reduced form, and the chemistry must be adjusted accordingly.

(47) The usage of ITCMO eliminates the need for molecular O.sub.2, lowers operating temperatures, and allows greater flexibility in steam usage, CO.sub.2 usage and the H.sub.2:CO molar ratio in syngas production. ITCMO particles are designed around lattice oxygen based on higher syngas selectivity and theoretically achieve much greater syngas yield over a wider operational range than molecular O.sub.2 or Fe.sub.2O.sub.3 alone due to interactions between iron and titanium oxides. The oxygen necessary to convert CH.sub.4 to H.sub.2 and CO comes from a combination of H.sub.2O, CO.sub.2 and ITCMO.

(48) In certain embodiments, a combination of fuel, CO.sub.2 and steam are added to a first moving bed reactor in a co-current flow pattern relative to the metal oxide particles. The first reactor reduces at least a portion of its the metal oxide particles and oxidizes the fuel to produce a first syngas stream comprising H.sub.2, CO, CO.sub.2 and steam. Similarly, a combination of fuel, CO.sub.2 and steam are added to a second moving bed reactor, operating in parallel with the first moving bed reactor, in a co-current flow pattern. The second reactor reduces at least a portion of its metal oxide particles and oxidizes the fuel to produce a second syngas stream comprising H.sub.2, CO, CO.sub.2 and steam. In another embodiment, multiple moving bed reactors, operating in parallel, receive the fuel, CO.sub.2 and steam in a co-current flow pattern relative to the metal oxide particles. Each reactor reduces at least a portion of its metal oxide particles to produce reduced metal or reduced metal oxide particles and syngas streams comprising H.sub.2, CO, CO.sub.2 and steam. The typical operating temperature range of the reducer reactors is between 800° C. and 1190° C. with the pressure range of 1 atm to 10 atm. In certain embodiments, the first syngas stream from the first reducer reaction has a H.sub.2/CO ratio of about 2.9 to about 3.1 and the second syngas stream from the second reducer reactor has a H.sub.2/CO ratio of about 1.0 to about 1.5. In other embodiments, the combination of the syngas streams from each reducer results in a total syngas H.sub.2/CO of about 1 to about 3, preferably 2.

(49) The fuel for this system can be any gaseous hydrocarbon based fuel including but not limited to natural gas, shale gas, and coal-bed methane. In certain embodiments, the fuel is methane. In addition to the specified molar ratio, a steam to hydrocarbon carbon molar ratio between 0.01 and 0.90 is implemented for adjusting the H.sub.2/CO ratio. In certain embodiments, the first and second moving bed reducer reactors have an effective Fe.sub.2O.sub.3/CH.sub.4 ratio of about 0.5 to about 1. It should be noted that operating under the specified conditions leads to a unique combination which will maximize the steam conversion to H.sub.2, by donating its oxygen to the metal-oxide lattice. In conjunction with the above stated variables, a CO.sub.2 to hydrocarbon carbon molar ratio is applied. This uniquely helps the overall syngas quality in terms of limiting the water-gas shift type effects and helps the carbon efficiency improvement significantly. It should also be noted that the above stated conditions create a unique combination and are necessary for the desired hydrocarbon to syngas conversion efficiency. These specific operating conditions along with a unique oxygen carrier and support composition, and heat transfer management yield a system with highly controlled oxygen transfer that ensures the highly efficient generation of the desired syngas quality. All of the gaseous reactants are injected into the top of the co-current moving bed reducer reactor and flow downward along with the metal oxide particles. The design condition for the injection port of these gases is based on giving them enough residence time to obtain a steady state conversion.

(50) A separation unit is connected to each of the multiple reducer reactors and configured to receive the syngas stream from each of the reducer reactors. The separation unit removes the CO.sub.2 from each of the syngas streams and controls the H.sub.2/CO ratio by recycling the CO.sub.2 from the separation unit to the multiple reducer reactors. Substantially all of the CO.sub.2 extracted from the syngas streams is recycled back into the reducer reactors. In certain embodiments having two reducer rectors, the separation unit receives a first syngas stream and a second syngas stream from the first and second reducer reactors. The separation unit extracts CO.sub.2 from the first and second syngas streams and sends the CO.sub.2-depleted syngas streams downstream for further processing. Substantially all of the separated CO.sub.2 is recycled back into the first and second reactors. In certain embodiments, the system is carbon neutral which means that the CO.sub.2 input to the reducer reactors equals the CO.sub.2 output in syngas from the reducer reactors (CRP=1). In other embodiments, the system is carbon negative which means that the CO.sub.2 input to the reducer reactors is greater than the CO.sub.2 output in syngas from the reducer reactors (CRP>1).

(51) A combustor reactor, in communication with the multiple reducer reactors, receives the reduced metal oxide particles from the reducer reactors. The combustor reactor regenerates the metal oxide particles by oxidizing the reduced metal oxide particles from the reducer reactors, in the presence of a reducing agent. This reaction is exothermic and is capable of offsetting the endothermic heat requirements in the reducer reactors. The product of the oxidation reaction is oxidized composite metal oxide particles that comprise oxidized metal oxide particles from each of the multiple reducer reactors. The oxidized composite metal oxide particles are recycled back to the multiple reducer reactors to produce additional syngas. The combustor reactor may be a bubbling fluidized reactor. In certain embodiments, the reducing agent is air.

(52) In certain embodiments, the reducer reactor is a moving bed reactor that takes in natural gas and partially oxidizes it to a mixture of CO and H.sub.2 using a co-current solids stream of ITCMO. The ITCMO, in the form of Fe.sub.2TiO.sub.5, provides oxygen necessary to partially oxidize CH.sub.4 to a mixture of CO and H.sub.2. In the reducer, the ITCMO is reduced to a mixture of Fe, FeTiO.sub.3, and Fe.sub.3O.sub.4 depending on the reactor design and contact mode. A co-current moving bed system ensures that, thermodynamic design conditions for a high syngas conversion can be obtained by controlling the reaction stoichiometric and ensuring that sufficient residence time are available for complete reactant conversion. If natural gas is represented by CH.sub.4 and the oxidized and reduced ITCMO solids are represented by FeTi.sub.yO.sub.x and FeTi.sub.yO.sub.x-1 respectively, the target reactions in the reducer reactor can be represented by Equation (1):
FeTiyOx+CH.sub.4.fwdarw.FeTi.sub.yO.sub.x-1+CO+2H.sub.2 Where ΔH.sub.reducer≥0  (1)
The design of the reducer reactor is based on an optimal oxygen carrier to fuel ratio, temperature and pressure of the reactor, and the weight ratio of active oxygen carrier to support material. The combustor reactor is a bubbling fluidized bed reactor which reoxidizes the reduced ITCMO particles from the reducer with air. The target reactions in the combustor reactor can be represented by Equation (2):
FeTiyO.sub.1-x+0.5O.sub.2.fwdarw.FeTi.sub.yO.sub.x Where ΔH.sub.reducer≤0  (2)
The combustor reaction is exothermic and the heat can be transferred to the reducer reactor using the oxygen carrier to offset the energy requirements for the endothermic heat requirements of the reducer reactor.

(53) The proposed modifications eliminate direct sources of CO.sub.2 emissions in the syngas production process. The carbon emission reduction enabled by this process results in a lower environmental impact compared to conventional fossil fuel conversion processes. Carbon efficiency is drastically increased, and what was once a waste stream of the process is now recycled to extinction and also acts as a supplemental feedstock.

3. Examples

(54) The foregoing may be better understood by reference to the following examples, which are presented for purposes of illustration and are not intended to limit the scope of the invention.

Example 1: Modularization Design for Syngas Production from 1 Kmol/Hr CH.SUB.4 .Using Fe.SUB.2.O.SUB.3., CO.SUB.2 .and H.SUB.2.O for a Constant Fe.SUB.2.O.SUB.3.:CH.SUB.4 .Ratio

(55) The modularization strategy used in this example is explained using FIG. 16b, which is a co-planar view of FIG. 16a. A ‘Point A’ is chosen such that it serves as the optimal design conditions for a single reducer syngas-production unit. This point is decomposed into two reducer operating conditions represented by Point B and Point C. The composite syngas generation performance for the points B and C lies along a straight line connecting the two points. Point D represents a composite syngas generation performance for the modular system utilizing the same H.sub.2O, CO.sub.2 and methane flow rates as that for Point A, but an improvement in syngas yield by ‘Δ’. The relative splits of natural gas and steam are determined by the ratio of differences in coordinates between Point B and Point C. It should be noted that the line connecting Point B and Point C may have components in all the three dimensions it is plotted on. A specific example for the modular syngas production system is shown in Table 2 (below). The composite Point D for the two reducer modular system shows an 11.8% increase (% Δ) in syngas yield for the same input flows as that for the one reducer system.

(56) TABLE-US-00002 TABLE 2 Specific example for the modularization strategy in syngas generation for a constant Fe.sub.2O.sub.3:CH.sub.4 ratio of 0.333 using Fe.sub.2O.sub.3 CH.sub.4 CO.sub.2 H.sub.2O Fe.sub.2O.sub.3 CO H.sub.2 CO + H.sub.2 H.sub.2:CO One Reducer System 1.000 0.418 1.100 0.333 1.000 1.999 2.999 2.00 (Point A) Reactor 1 (Point B) 0.525 0.343 1.086 0.175 0.597 1.338 1.935 2.24 Reactor 2 (Point C) 0.475 0.075 0.014 0.158 0.521 0.897 1.418 1.72 Total of Reactor 1 & 1.000 0.418 1.100 0.333 1.118 2.235 3.353 2.00 Reactor 2 (Point D) % increase in syngas production 11.8%

Example 2: Modularization Design for Syngas Production from 1 Kmol/Hr CH.SUB.4 .Using ITCMO, CO.SUB.2 .and H.SUB.2.O for a Constant Fe.SUB.2.O.SUB.3.:CH.SUB.4 .Ratio

(57) A modularization strategy similar to Fe.sub.2O.sub.3 can be applied to ITCMO particles. The motivation for ITCMO modularity can be explained using FIG. 17. A specific example for the modular syngas production system using ITCMO particles is given in Table 3 (below). The single reducer reactor performance (Point A*) is specified by a CH.sub.4 input of 1 kmol/hr. Point B* and Point C* represent the operating conditions for the modular reactors with ITCMO. Point D*, the composite of the modular Point B* and Point C*, shows a 2.2% increase (% Δ*) in syngas production with matching inputs as the one reducer system shown in Point A*.

(58) TABLE-US-00003 TABLE 3 Specific example for the modularization strategy in syngas generation for a constant Fe.sub.2O.sub.3:CH.sub.4 ratio of 0.333 using ITCMO CH.sub.4 CO.sub.2 H.sub.2O Fe.sub.2O.sub.3 CO H.sub.2 CO + H.sub.2 H.sub.2:CO One Reducer System 1.00 0.080 0.410 0.333 1.01 2.20 3.210 2.19 (Point A*) Reactor 1 (Point B*) 0.47 0.064 0.400 0.158 0.50 1.23 1.732 2.45 Reactor 2 (Point C*) 0.52 0.016 0.010 0.175 0.52 1.03 1.548 1.95 Total of Reactor 1 & 1.00 0.080 0.410 0.333 1.02 2.25 3.280 2.19 Reactor 2 (Point D*) % increase in syngas production 2.2%

Example 3: Modularization Design for Syngas Production from 1 Kmol/Hr CH.SUB.4 .Using ITCMO, H.SUB.2.O and CO.SUB.2 .for Various Fe.SUB.2.O.SUB.3.:CH.SUB.4 .Ratios

(59) The design approach for the pure Fe.sub.2O.sub.3 and the ITCMO cases discussed in example 1 and example 2 show a modularization strategy which operates the two reducer modules at the same Fe.sub.2O.sub.3:CH.sub.4 molar ratios. This section investigates an example in which a single reducer performance is compared to a modular two-reducer performance, wherein the two reducers operate at different Fe.sub.2O.sub.3:CH.sub.4 ratios. FIGS. 18a-d show the syngas production performance when the Fe.sub.2O.sub.3:CH.sub.4 ratio in each reducer reactor is ‘0.34’, ‘1.2’ and ‘9.8’, respectively. The modularization strategy may be applied to this system and is demonstrated by maintaining the same overall inputs as a single reducer system at the operating condition shown in FIG. 18d, Point A**. The two reducers are chosen such that one reducer operates at a lower Fe.sub.2O.sub.3:CH.sub.4 and produces a high syngas yield per mole of methane, Point B**, while the second reducer operates at a higher Fe.sub.2O.sub.3:CH.sub.4 and produces little syngas, Point C**. Syngas generation performance is higher at lower Fe.sub.2O.sub.3:CH.sub.4 molar ratios but comes at a cost of a higher net endothermic reaction as the lattice oxygen content in the system is lower. Thus, Point C** maintains the overall heat balance consideration similar to the single reducer case, while Point B** produces the majority of the syngas. The comparison between the single reducer and the two reducer modular system are shown in Table 4 (below). The benefits of a modular system are illustrated by the comparison between examples provided in Point A** and the modular sum, Point D**. The two reducer modular system produces a 19% increase (% Δ**) in total syngas yield over the single reducer system for comparable CH.sub.4 input, geometrically shown in FIG. 19.

(60) TABLE-US-00004 TABLE 4 Specific example for the modularization strategy in syngas generation for a constant Fe.sub.2O.sub.3:CH.sub.4 ratio of 0.333 using ITCMO Single Reactor Reactor 1 Reactor 2 Modular Sum (Point A**) (Point B**) (Point C**) (Point D**) Input Conditions: Fe.sub.2O.sub.3 1.2 0.32 0.88 1.20 TiO.sub.2 3.6 0.95 2.65 3.60 CH.sub.4 1 0.91 0.09 1.00 H.sub.2O 1.05 0.82 0.23 1.05 CO.sub.2 0.265 0.25 0.01 0.27 Output Conditions: CH.sub.4 2.1*10.sup.−4 0.00 0.00 0.00 H.sub.2O 1.12 0.36 0.41 0.77 CO 0.87 1.04 0.00 1.04 CO.sub.2 0.39 0.12 0.10 0.23 H.sub.2 1.92 2.28 0.00 2.28 H.sub.2 + CO 2.79 3.32 0.0 3.32 H.sub.2:CO 2.19 2.20 0.0 2.20 % increase in syngas production = 19% (% Δ**)

REFERENCES

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