Increased natural gas availability in the United States has presented an opportunity to decrease dependence on foreign oil (which constitutes 27% of the total consumption1), and diversify the supply for energy consumption needs. Turbulence in the oil market is seen as a driving force for the advancement of Gas to Liquids (GTL) technology. Liquid fuels are projected to continue to be a necessary component in supplying human energy needs.2 Technological advances in drilling have driven the shale-gas production boom, leading to an increase in natural gas contribution to the energy demand. Another driving force for the development of highly efficient GTL facilities is the percentage of stranded natural gas that is flared because transportation costs of gaseous fuels are too high to make transporting them economical. In 2011, 5.3×1012 cubic feet of associated petroleum gas was flared; the equivalent of about 25% of annual gas consumption in the United States.3 At current market price ($2/MMBtu)4 for natural gas, the nominal market value of the flared gas was $13.8 billion. GTL is an effective way to monetize the stranded natural gas. However, widespread applications of GTL processes have been hindered due to high risk of cost escalation associated with GTL based projects. The syngas production unit accounts for 30-50% of the total capital cost investment.5
The carbon efficiency is defined here as the percentage of carbon in the natural gas feed that is converted to CO and in-turn to liquid fuels. This number increases as the net conversion to CO2 decreases. The carbon efficiency is qualitatively measured by a reduction in the total natural gas consumption over that used in the conventional method of syngas production, which uses an auto-thermal reforming based system. The benefits of this disclosure are demonstrated by considering a case study for a 50,000 bpd GTL plant. The design H2/CO ratio for this GTL plant is 2.19, and it is achieved using a (H2—CO2)/(CO+CO2) ratio of 1.58.
Carbon Capture Utilization and Sequestration (CCUS) is also a grand challenge for modern chemical engineers. Many new technologies strive to implement either CO2 capture or CO2 utilization, but the two processes are rarely thought of as mutually inclusive. In order to have a meaningful impact on the mitigation of CO2 emissions it is paramount that CO2 capture and utilization or sequestration technologies are developed in conjunction with each other.
This disclosure relates to reactors and methods that may significantly reduce the costs associated with syngas production from natural gas using chemical looping technology and applying a novel concept of reacting the CO2 to near extinction, or consuming more CO2 than is produced. The disclosure includes a reactors and processes that allow for both the capture and the utilization of CO2 in a single process while utilizing fossil fuels. On a commercial scale, a fossil fuel process involving unprecedented simultaneous capture and utilization of CO2 can be transformational and disruptive in conventional CO2 utilization and carbon capture markets.
The methods and system configurations disclosed herein use a chemical looping system characterized by a co-current downward contacting reactive flow of oxygen carriers and carbonaceous flow which are accompanied by CO2 recycle and steam which may be introduced at variable flow rates and positions along the reducer in order to generate the desired quantity and quality of syngas for liquid fuel production. 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.
This disclosure describes specific reactors and conditions that enable the disclosed novel chemical looping process to function as a carbon negative or a carbon neutral fossil fuel process. In cases where the CO2 consumed is more than CO2 produced (CO2 negative system), the disclosed chemical looping system can function as an effective CO2 utilization system.
In one aspect, disclosed herein is 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, CO2 and steam are added to the first reactor in a co-current flow pattern relative to the metal oxide particles, wherein the first 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 H2, CO, CO2 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, CO2 and steam are added to the second reactor in a co-current flow pattern relative to the metal oxide particles, wherein the second 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 H2, CO, CO2 and steam; a separation unit, in communication with the first reactor and the second reactor, and configured to remove the CO2 from the first syngas stream and the second syngas stream, wherein the H2/CO ratios of the first and second syngas streams are controlled by recycling substantially all of the CO2 from the separation unit to the first reactor and the second reactor; and a third co-current fluidized bed reactor in communication with the first reactor and the second 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 composite metal oxide to the first reactor and the second reactor for subsequent reduction reactions.
In some embodiments, the primary component is Fe2O3. In some embodiments, 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. In some embodiments, the secondary component is titanium oxide. In some embodiments, the fuel is methane. In some embodiments, the H2/CO ratio of the first syngas stream is about 2.9 to about 3.1. In some embodiments, the H2/CO ratio of the second syngas stream is about 1.0 to about 1.5. In some embodiments, the combination of the syngas from each reducer results in a total syngas H2/CO ratio of about 1 to about 3. In some embodiments, the first reduced metal oxides and the second reduced metal oxides are oxidized by introducing steam into the third reactor. In some embodiments, the system consumes more CO2 than it produces.
In a second aspect, disclosed herein is a system for converting a fuel, the system comprising: a plurality of moving bed reactors operating in parallel, each comprising a plurality of metal oxide particles having a primary component and a secondary component, wherein the plurality of moving bed reactors are configured to reduce at least a portion of the metal oxide particles with fuel to produce reduced metal or reduced metal oxide particles, and are further configured to produce syngas streams comprising H2, CO, CO2, and steam; a separation unit, in communication with the plurality of moving bed reactors, and configured to remove the CO2 from the syngas streams, wherein the H2/CO ratios of the first and second syngas streams are controlled by recycling substantially all of the CO2 from the separation unit to the plurality of moving bed reactors; and an oxidation reactor in communication with the plurality of moving bead reactors, and configured to oxidize the reduced metal or metal oxide particles to produce oxidized metals or metal oxide particles and recycle the oxidized metals or metal oxide particles to the plurality of moving bed reactors for subsequent reduction reactions.
In some embodiments, the combination of the syngas streams results in a total syngas H2/CO ratio of about 1 to about 3.
In another aspect, disclosed herein is a method for converting fuel, the method comprising: feeding the fuel and metal oxide particles into a first moving bed reactor, operating in parallel with a second moving bed reactor, in a co-current flow pattern relative to one another, wherein the metal oxide particles comprise a primary component and a secondary component and reducing at least a portion of the metal oxide particles in the first moving bed reactor to produce a first reduced metal oxide and a first syngas stream comprising H2, CO, CO2 steam or combinations thereof; feeding the fuel and metal oxide particles into a second moving bed reactor in a co-current flow pattern relative to one another, and reducing at least a portion of the metal oxide particles in the second moving bed reactor to produce a second reduced metal oxide and a first syngas stream comprising H2, CO, CO2 steam or combinations thereof; transporting the first reduced metal oxide particles and the second reduced metal oxide particles to a third reactor to oxidize the first reduced metal oxide particles and the second reduced metal oxide particles to produce oxidized metal oxide particles and recycling the oxidized metal oxide particles to the first and second reactors for subsequent reduction reactions; and removing the CO2 from the first and second syngas streams in a separation unit and controlling the H2/CO ratio by recycling substantially all of the CO2 from separation unit to the first moving bed reactor and second moving bed reactor, wherein the combination of the first and second syngas streams result in a total syngas H2/CO of about 2.
In some embodiments, CO2 and steam are fed into the first moving bed reactor and the second moving bed reactor. In some embodiments, the first and second moving bed reactors operate at a temperature of about 800° C. to about 1190° C. In some embodiments, the first and second moving bed reactors operate at a pressure of about 1 atm to about 10 atm. In some embodiments, the fuel is methane. In some embodiments, the primary component is Fe2O3. In some embodiments, the first and second moving bed reactors have an effective Fe2O3/CH4 ratio of about 0.5 to about 1. In some embodiments, the first reduced metal oxides and the second reduced metal oxides are oxidized by introducing steam into the third reactor.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
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.
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 CO2 consumed is more than CO2 produced (CO2 negative system), the disclosed chemical looping system can function as an effective CO2 utilization system.
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.
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.
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.
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.
“Carbon neutral,” as used herein, refers to a system or process in which about 100% of the CO2 produced by a system is recycled.
“Carbon negative,” as used herein, refers to a system or process in which more CO2 is consumed than the system or process produces.
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 H2:CO requirements when linearly combined while using less fossil fuel feedstock when compared to a single reducer reactor.
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 H2:CO ratio requirements for downstream processes. A novel combination of these conditions can yield a CO2 negative scheme, in which the molar amount of CO2 entering the reactor divided by the molar amount of CO2 exiting the reactor (CRP or CO2 reaction parameter) is greater than 1.
A specific set of operating conditions is given in Table 1 (below). Group (1) refers to the reaction of CH4 with the metal oxide; Group (2) refers to the reactions of CH4 with CO2 and the metal oxide; Group (3) refers to the reactions of CH4 with H2O and the metal oxide; Group (4) refers to the reactions of CH4 with CO2, H2O 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.
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.
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 (H2/CO ratio of 2) needed for Fischer-Tropsch synthesis.
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 Fe2O3. 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.
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 TiO2:Fe2O3 molar ratio of greater than 2 will yield a reduced form, FeTiO3. On the other hand, a TiO2:Fe2O3 molar ratio of less than 2 will favor formation of FeO—Fe2TiO4 in addition to FeTiO3 in the composite's reduced form, and the chemistry must be adjusted accordingly.
The usage of ITCMO eliminates the need for molecular O2, lowers operating temperatures, and allows greater flexibility in steam usage, CO2 usage and the H2: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 O2 or Fe2O3 alone due to interactions between iron and titanium oxides. The oxygen necessary to convert CH4 to H2 and CO comes from a combination of H2O, CO2 and ITCMO.
In certain embodiments, a combination of fuel, CO2 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 H2, CO, CO2 and steam. Similarly, a combination of fuel, CO2 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 H2, CO, CO2 and steam. In another embodiment, multiple moving bed reactors, operating in parallel, receive the fuel, CO2 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 H2, CO, CO2 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 H2/CO ratio of about 2.9 to about 3.1 and the second syngas stream from the second reducer reactor has a H2/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 H2/CO of about 1 to about 3, preferably 2.
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 H2/CO ratio. In certain embodiments, the first and second moving bed reducer reactors have an effective Fe2O3/CH4 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 H2, by donating its oxygen to the metal-oxide lattice. In conjunction with the above stated variables, a CO2 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.
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 CO2 from each of the syngas streams and controls the H2/CO ratio by recycling the CO2 from the separation unit to the multiple reducer reactors. Substantially all of the CO2 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 CO2 from the first and second syngas streams and sends the CO2-depleted syngas streams downstream for further processing. Substantially all of the separated CO2 is recycled back into the first and second reactors. In certain embodiments, the system is carbon neutral which means that the CO2 input to the reducer reactors equals the CO2 output in syngas from the reducer reactors (CRP=1). In other embodiments, the system is carbon negative which means that the CO2 input to the reducer reactors is greater than the CO2 output in syngas from the reducer reactors (CRP>1).
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.
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 H2 using a co-current solids stream of ITCMO. The ITCMO, in the form of Fe2TiO5, provides oxygen necessary to partially oxidize CH4 to a mixture of CO and H2. In the reducer, the ITCMO is reduced to a mixture of Fe, FeTiO3, and Fe3O4 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 CH4 and the oxidized and reduced ITCMO solids are represented by FeTiyOx and FeTiyOx-1 respectively, the target reactions in the reducer reactor can be represented by Equation (1):
FeTiyOx+CH4→FeTiyOx-1+CO+2H2 Where ΔHreducer≥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):
FeTiyO1-x+0.5O2→FeTiyOx Where ΔHreducer≤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.
The proposed modifications eliminate direct sources of CO2 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.
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.
The modularization strategy used in this example is explained using
A modularization strategy similar to Fe2O3 can be applied to ITCMO particles. The motivation for ITCMO modularity can be explained using
The design approach for the pure Fe2O3 and the ITCMO cases discussed in example 1 and example 2 show a modularization strategy which operates the two reducer modules at the same Fe2O3:CH4 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 Fe2O3:CH4 ratios.
This application claims priority to U.S. Provisional Application No. 62/321,607, filed Apr. 12, 2016, the entire contents of which are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/US2017/027241 | 4/12/2017 | WO | 00 |
Number | Date | Country | |
---|---|---|---|
62321607 | Apr 2016 | US |