Patent Application
20220380691
This disclosure relates generally to a carbon-neutral process for generating electricity and to a liquid organic hydrogen carrier (LOHC) for supplying hydrogen for generating the carbon-neutral electricity. More specifically, this disclosure relates to methods of use of regenerable carbon-neutral compositions consisting of liquid organic hydrogen carriers used in processes to supply hydrogen to generate electricity under carbon-neutral conditions using processes and apparatus operating with a net zero atmospheric emission of carbon oxides.
The present disclosure relates to the field of electricity generation. Systems employing battery storage to supply electricity are known and readily available. But systems that depend exclusively on battery electrical storage are limited in battery capacity, limited by battery weight, and limited in operating time by the extended battery recharging time required.
A great deal of effort has been expended in developing systems that convert chemical energy into electricity. Having the capability of loading a gaseous, liquid, or solid material in a system for converting resulting hydrogen gas into electricity greatly increases the flexibility for the developing electrified economy. Hydrogen has been acknowledged for many years as a potential source of electrical energy by electrochemical hydrogen conversion (oxidation) that generates electrical energy. Hydrogen may be stored as a compressed gas or as liquid hydrogen at cryogenic temperatures. However, increasing the operating flexibility of an electric powered vehicle by providing high pressure hydrogen for electrochemical conversion and generation of additional electrical energy requires the storage of high-pressure hydrogen, along with its not insignificant associated risks. Furthermore, the lack of a hydrogen delivery infrastructure in virtually all locations limits applicability of a high-pressure hydrogen solution. Hydrogen may be stored as the captured or contained gas in various carrier media such as metal hydrides, high surface area carbon materials, and metal-organic framework materials. Generally, the contained hydrogen in such carrier media can be released by raising the temperature and/or lowering the hydrogen pressure.
Hydrogen can also be stored by means of reversible catalytic hydrogenation of unsaturated, usually aromatic, organic compounds. An organic hydrogen carrier, referred to herein as a “liquid organic hydrogen carrier” (LOHC), is generally liquid at ambient conditions, and contains a significant amount of chemically bound hydrogen that may be liberated by an elevated temperature catalytic process. The release of hydrogen by dehydrogenation is an endothermic process, i.e., one which requires an input of heat, at a temperature where the dehydrogenation of the carrier can proceed with adequate reaction rates. A number of methods have been suggested for generating the heat required to maintain the dehydrogenation reaction step, including combustion of hydrogen that is generated in the process, or combustion of a supplied fuel to provide the necessary heat. Using generated hydrogen as combustion fuel has a significant impact on hydrogen availability for generating electricity. Burning a combustion fuel in the conventional method for heat generation creates greenhouse emissions, which serves to neutralize the benefit of using hydrogen as a source of system energy.
Conventional use of LOHC feedstocks as hydrogen carriers has had limited success on account of the relatively low efficiency of energy conversion, the challenges of operating a dehydrogenation reaction zone within size constraints while maintaining acceptable catalyst activity, and the requirement for generating thermal energy without using a portion of the generated hydrogen for thermal energy production and while maintaining carbon-neutral operation with hydrocarbon combustion.
Fossil fuels (e.g., coal, oil, and natural gas) have been powering economies for over 300 years, and currently supply over 80 percent of the world's energy. It is well established combustion of fossil fuels produces undesirable emissions such as greenhouse gases. Atmospheric greenhouse gases are harmful to the environment because they absorb infrared radiation (IR) which is subsequently released and reflected into the atmosphere, thereby increasing the mean planetary temperature overtime.
Rising global warming challenges due to greenhouse gas emissions necessitates a shift in the world's energy economies to alternative energy sources such as battery, solar and wind. Unfortunately, these alternative energy sources only make up only about twenty percent of the world's current total energy economy. Further, governmental regulating authorities continue to reduce the allowable greenhouse gas emissions for various fossil fuel emissions sources, including new vehicles.
Society is turning towards carbon-neutral (CN) electricity as it moves away from fossil fuels in an effort to significantly reduce Greenhouse Gas (GHG) emissions. Electric Vehicles (EVs) are beginning to make an impact in the passenger car and pickup truck market, and they are anticipated to penetrate the short and medium-haul truck market. Limitations in energy density currently limit battery use in Class 7/8 long-haul tractor-trailers, trains, shipping, and aircraft. Battery banks are used to load-balance certain utility grids for short durations, typically four hours or less, but cannot support large back-up energy needs.
Hydrogen has been acknowledged for many years as a potential large-scale source of energy (“hydrogen economy”). Hydrogen is a powerful fuel and produces on a mass basis three times the energy content of gasoline (120 vs. 44 MJ/kg (megajoules/kilogram)). Further, combustion of hydrogen does not produce environmentally harmful IR-absorbing gas emissions.
However, numerous technical challenges are inhibiting the shift to a large-scale hydrogen economy. These challenges include, among other things, the difficulty of developing large scale long-term, safe delivery and storage infrastructures for compressed hydrogen.
Carbon-neutral systems utilizing hydrogen are known and readily available but currently available systems generally require high pressure compression in the 10,000-psig region for storage and use in fuel cells. A national high pressure hydrogen distribution infrastructure does not exist and is estimated to cost hundreds of billions of dollars to install.
Systems utilizing LOHCs to transport labile hydrogen via existing fossil fuel delivery systems to remote sites where, after dehydrogenation, they provide hydrogen to power fuel cells are known, but they cannot currently operate in a carbon-neutral (CN) mode without a CN external power or heat supply.
There have been efforts to eliminate IR-absorbing gas emissions from LOHC-based hydrogen production processes. However, this method requires the generation and/or storage of a sufficient amount of electricity to ensure continued operations of the hydrogen production process. Current methods also require additional electrical storage and battery management equipment. In addition, drawing electricity for the heating element from downstream equipment (e.g., a fuel cell) reduces the amount of electricity available for the target application (e.g., powering an electrical motor in a vehicle).
Others have suggested combusting produced hydrogen to generate the heat for dehydrogenation of the LOHC. However, this method lowers the amount of hydrogen available for use by downstream equipment (e.g., a hydrogen fuel cell), thereby reducing the efficiency of the overall system.
One approach known in the art employs a combustible/evaporable fossil fuel or biofuel additive to the LOHC feed. The additive is then separated during the hydrogen production process and combusted to form heat for dehydrogenation of the LOHC. However, combustion of the additive produces IR-absorbing gas emissions, thereby increasing the total atmospheric concentration of these harmful gases, and requires separation of the additive prior to combustion, adding an additional process step. Furthermore, the additive decreases the amount of LOHC in the total feed, thereby reducing the amount of hydrogen produced as compared to a feed containing 100% LOHC.
Accordingly, there is a need for a LOHC-based process for producing electricity and hydrogen which eliminates or reduces the net increase in atmospheric GHG emissions, and which is not completely reliant on chemical or energy products (e.g., hydrogen and electricity) needed by downstream equipment such as for example fuel cells, hydrogen internal combustion engines, and the like.
The present disclosure relates to apparatus, means and methods for generating electricity in an electrochemical reaction using hydrogen as fuel. In one embodiment of the present disclosure, the hydrogen is delivered to the process in the form of a liquid hydrogen carrier, termed a liquid organic hydrogen carrier (LOHC), wherein the LOHC contains chemically bound labile hydrogen on an aromatic backbone substrate. The labile hydrogen may be separated from the substrate by reversible catalytic dehydrogenation to produce hydrogen gas, and the substrate (hydrogen depleted, unloaded or spent LOHC (“S-LOHC”) recovered from the dehydrogenation reaction may be recycled and, after conditioning, rehydrogenated to recover an amount of the recovered or recycled LOHC (“R-LOHC”), which may be reused in the processes disclosed herein, or other related processes.
In the disclosed embodiments, herein, the hydrogen produced by the dehydrogenation reaction, optionally after conditioning, is passed to a fuel cell unit. Hydrogen oxidation that occurs in a fuel cell generates electricity by reaction of the hydrogen on a fuel cell anode electrode and concurrent reaction of oxygen on a fuel cell cathode electrode. Ions generated in these reaction zones pass through an electrolyte sandwiched between the electrodes, and a resulting electric current is caused to flow through an external circuit between electrodes as useable electricity.
The present disclosure also relates to generating electricity in a thermally balanced process involving an endothermic dehydrogenation reaction and an exothermal hydrogen oxidation reaction with substantially no heat loss to the environment. In one embodiment of the disclosed processes, the amount of heat generated in the fuel cell unit is balanced with respect to the heat required for the dehydrogenation reaction. In another embodiment, the disclosed fuel cell unit(s) are the sole source of heat for the dehydrogenation reaction.
In related embodiments, the disclosed processes include operating the fuel cell unit at a temperature above the operating temperature of the dehydrogenation reactor to drive maximum efficiency. In a further embodiment, the fuel cell unit is temperature controlled using a liquid heat transfer fluid (HTF) to pass either a requisite amount or substantially all of the heat generated during the fuel cell reactions to the dehydrogenation reactor. This is in contrast to traditional operations of fuel cells that are cooled by flowing air or nitrogen. The advantages of using a liquid HTF include improved heat transfer efficiency, improved temperature control, the ability to move heat as thermal energy between various apparatus of the present disclosure, as well as to enable the reduction in the size and weight of the associated apparatus and equipment used as a means to achieve the disclosed embodiments.
In one embodiment, and in particular when the process for generating electricity produces undesirable greenhouse gas emissions, the LOHC feed may contain an additive amount of a carbon-neutral (CN) component to partially or fully offset the amount of carbon included in the greenhouse gas emissions.
In another embodiment, the disclosed processes for producing hydrogen from an LOHC and generating electricity by electrochemical hydrogen conversion are carbon-neutral (CN) processes. In a related embodiment, maintaining the disclosed CN operations involves including an additive CN component in the LOHC feed.
Further, to maintain carbon-neutral operation, any carbon that is emitted or exhausted from any of the presently disclosed processes, either as CO2 based carbon or as hydrocarbon-based carbon, is no greater, on a molar basis, than the carbon contained in the additive CN components of the LOHC feed used in the embodied processes.
In further embodiments that maintain an overall CN operation, the labile hydrogen chemically removed from the LOHC during dehydrogenation and electrochemically converted is either green or blue hydrogen, representing that no net carbon or CO2 were added or released to the atmosphere during production of the labile hydrogen.
Accordingly, in one embodiment, the LOHC feed used in the disclosed processes is a hydrogen-rich hydrocarbon containing a CN additive component comprising sufficient CN carbon to balance any carbon emissions, including CO2 emissions, resulting from the process.
The carbon in the additive component may be recovered from the air as CO2, either through photosynthesis and generation of biomass or by another CO2 extraction process from the atmosphere. The hydrogen in the CN additive may be green or blue hydrogen, also obtained with net zero atmospheric carbon emissions. While the additive component is considered CN by reason of its composition, it is expected that some of the multiple processes involved during biomass generation and conversion to the LOHC may include atmospheric carbon emissions. Any emissions in one or more steps in the sequence of forming the LOHC do not diminish the potential impact of the present process for generating electricity for an improved environment, as the emissions may be offset by additional CN component.
In another embodiment, the process includes operating a fuel cell unit with liquid heat transfer fluid (HTF) cooling means. The disclosed fuel cell units include stacked fuel cell elements, at least some of which are separated by a fluid delivery assembly for delivering HTF to the fuel cell elements. In the disclosed embodiments, an HTF delivery plate component of the assembly is configured to flow HTF in a tortuous path between fuel cell elements and stacks to maintain optimum temperatures within and for removing excess heat generated by the operating elements. In one embodiment, a hydrogen delivery plate may be included in the assembly for providing hydrogen gas to the anode side of a fuel cell element. In a further embodiment, an air delivery plate may be included for providing oxygen-enriched gas or air to the cathode side of a fuel cell element. In the embodiments disclosed hereinbelow, the addition of at least one fluid delivery assembly to a fuel cell stack provides for improved liquid cooling, rather than the air cooling means that is generally used in conventional fuel cell units with much less efficiency owing to the lower heat capacity of air compared to liquid HTFs. A further advantage of liquid HTF is the ability to efficiently pump them as well as their ability to thermally equilibrate and transfer heat from a hot surface to a cooler surface by convective means even without pumping. In further embodiments, a single auxiliary plate may be used that features a HTF port, a hydrogen gas port and an oxygen-enriched gas or air port, and combinations thereof between fuel cell elements in stack to enable the more efficient flow and transfer of gas and liquid reactants and heat control fluids between the respective fuel cell elements, fuel cell stacks and external heat and thermal control and exchange units as disclosed herein.
In another embodiments the fuel cell elements and whole stacked assemblies may be immersed in a HTF bath providing close to isothermal conditions. In related embodiments, heat flow and maintenance of a desired temperature gradient between the cathode and anode electrodes of the fuel cell components may be achieved by adjusting the excess oxygen-enriched gas or air flow rate supplied to the cathode element or respective cathode chamber of the fuel cells. In yet further related embodiments, heat flow and temperature control may be achieved by a combination of the use of controlled liquid HTF flow to the fuel cell components and air flow rates to the cathode element.
In further embodiments, one or more heat transfer loops utilizing a HTF may be employed in association with a fuel cell as disclosed herein in order to improve heat and thermal energy transfer and prevent any hot spots from developing within a fuel cell unit or fuel cell stack of multiple fuel cell units. In these embodiments, multiple heat transfer loops enable improved optimization of temperatures by heat exchange and temperature control of the various components of the disclosed apparatus, including the catalytic dehydrogenation units and fuel cells, regardless of their individual configurations, sizes, and location.
In yet further embodiments, two or more HTFs may be employed in different apparatus and modules according to the present disclosure for improved efficiency, and in some embodiments may be coupled to enable heat and thermal energy transfer between the modules more efficiently that with the use of a single HTF. A further embodiment is thus enabled by allowing the two or more different HTFs to operate modules at different optimum temperatures while enabling heat control and heat/thermal energy distribution between them to reduce the amount of any wasted heat, while enabling selection of a preferred HTF for a particular unit of the disclosed modules.
The present disclosure further includes multiple embodiments including steps, methods and processes using the disclosed apparatus and equipment detailed herein.
One embodiment includes a method for operating a power module for generating electricity by catalytically dehydrogenating a hydrogenated liquid organic hydrogen carrier (LOHC) to produce hydrogen by means of a dehydrogenation unit; generating electricity by means of a fuel cell unit employing hydrogen (gas); and then redirecting heat generated by the fuel cell by means of thermal energy transfer employing a heat transfer fluid (HTF) in thermal communication with the dehydrogenation unit and the fuel cell unit; wherein the thermal energy produced by the fuel cell is the source of heat for operating the dehydrogenation unit.
A related embodiment further includes the steps of recovering thermal energy generated during a hydrogen electrochemical conversion reaction in a fuel cell unit by means of a first heat transfer fluid (first HTF) in thermal communication with the fuel cell unit; and transferring the thermal energy to a dehydrogenation unit by means of the first HTF in thermal communication with the dehydrogenation unit; wherein the first HTF is circulated between the fuel cell and the dehydrogenation unit by means of a first HTF exchange loop; and wherein the first HTF fluid exchange loop optionally includes a heat exchanger.
Yet another embodiment includes the further steps of recovering thermal energy generated during a hydrogen electrochemical conversion reaction within a fuel cell unit by means of a first heat transfer fluid (first HTF) in thermal communication with the fuel cell unit; and then exchanging a portion of the thermal energy recovered by the first HTF with a second heat transfer fluid (second HTF) by means of a heat exchanger in fluid communication with the first HTF exchange loop and a second HTF exchange loop; wherein the second HTF is in thermal communication by means of a second HTF exchange loop with the dehydrogenation unit; wherein the first and the second HTF are in thermal communication with each other by means of the heat exchanger.
In a further embodiment, the fuel cell unit is operated at a temperature higher than the temperature of the dehydrogenation unit, for example, but not limited to conditions wherein the fuel cell unit is operated within a temperature range of between 400 to 600° C.; and wherein the dehydrogenation unit is operated within a temperature range of between 250 to 450° C.
In other embodiments, the method provides for at least 90% of the thermal energy recovered from the fuel cell unit is transferred to the dehydrogenation unit, or alternatively at least 95%, or yet alternatively at least 99%.
The embodied methods include use of a first HTF comprising a material that is a liquid within the fuel cell operating range and that maintains chemical stability at a temperature above the fuel cell unit operating temperature range; and alternatively wherein the second HTF comprises a material that is a liquid within the dehydrogenation unit operating temperature range and that maintains chemical stability at a temperature above the dehydrogenation unit operating temperature range.
In one embodiment, the disclosed methods include recovering thermal energy generated during a hydrogen electrochemical conversion reaction by means of a first HTF in thermal communication with a plurality of fuel cell elements located within the fuel cell unit; exchanging the recovered thermal energy between the first HTF and a second HTF by means of a heat exchanger; and then transferring at least a portion of the recovered thermal energy to the dehydrogenation reaction by means of the second HTF in thermal communication with a plurality of catalyst-containing vessels located within the dehydrogenation unit.
In a related embodiment, the disclosed methods further include circulating a first HTF in thermal contact with a plurality of fuel cell elements by means of a first heat exchanger and optionally a first pump located either internally or externally to the fuel cell unit; and then circulating the second HTF in thermal contact with a plurality of catalyst-containing vessels located within the dehydrogenation unit by means of a second heat exchanger and optionally a second pump located either internally or externally to the dehydrogenation unit.
In a further related embodiment, the disclosed methods include the steps wherein a portion of thermal energy contained in either of a first HTF or a second HTF is redirected by means of a feed preheater to heat or vaporize an incoming LOHC feed stream prior to injection into the dehydrogenation unit.
Another embodiment includes the method of supplying an LOHC feed to a dehydrogenation unit that is operating at a dehydrogenation temperature and generating hydrogen; conditioning the generated hydrogen to recover a purified hydrogen feed; supplying the purified hydrogen feed to a fuel cell unit for electrochemical conversion of the purified hydrogen feed to produce electricity; and then recovering a hydrogen-containing exhaust stream from a fuel cell unit; wherein the hydrogen-containing exhaust stream comprises unreacted hydrogen and hydrocarbon contaminants; then further recycling a portion of the hydrogen-containing exhaust stream by combination with a purified hydrogen feed; and then venting a portion of the hydrogen-containing exhaust stream to the atmosphere; wherein the LOHC feed to the dehydrogenation reactor comprises an amount of carbon-neutral carbon that is at least as great as the amount of carbon contained in the vented portion of the hydrogen-containing exhaust stream.
In a related embodiment, the method includes use of the labile hydrogen contained in an LOHC feed that is selected from renewable sources, carbon-neutral sources, carbon-neutral carbon sources, blue or green hydrogen sources, or combinations thereof.
In some embodiments, the method employs a fuel cell unit consisting of a plurality of fuel cell elements located adjacent to one another within a fuel cell unit; wherein the fuel cell elements are separated by means of one or more auxiliary plates selected from an air flow plate, a heat exchange plate, and a hydrogen flow plate.
In related embodiments, the method uses an air flow plate that delivers air or an oxygen-enriched gas, optionally preheated, using thermal energy supplied by a HTF; wherein the hydrogen flow plate delivers hydrogen, optionally preheated, to the anode side of the fuel cell unit; and wherein the heat exchange plate operates to recover, redistribute and remove heat generated by the fuel cell unit by means of the HTF, and alternatively includes use of an auxiliary plate that is a combination of an air flow plate, a heat exchange plate and a hydrogen flow plate.
In further related embodiments, the disclosed methods include use of a heat exchange plate or an auxiliary plate that further operate to exchange thermal energy between a HTF and a portion of outgoing HTF circulated externally to the fuel cell unit, or alternatively further operate to exchange thermal energy between an incoming portion of the HTF and a portion of the HTF internal to the fuel cell unit, or yet alternatively further operate to facilitate the exchange of thermal energy between the outgoing HTF and at least a portion of HTF circulated through a dehydrogenation unit by means of a heat transfer loop in fluid communication between the fuel cell unit and the dehydrogenation unit.
In some embodiments, the method includes the exchange of thermal energy between a fuel cell unit and a dehydrogenation unit as achieved by means of a second HTF in thermal communication with the outgoing HTF employing a heat exchange unit capable of proportioning thermal energy between the outgoing HTF and the second HTF.
As used herein, “liquid organic hydrogen carrier” or “LOHC” refers to a hydrogenated organic substrate selected from monocyclic, polycyclic, heterocyclic, and homocyclic organic compounds that can be processed to release chemically bound hydrogen via dehydrogenation and are liquid at standard temperature and pressure (STP, 0° C., 1 bar).
As used herein, the term “R-LOHC” refers to a regenerated or hydrogen-enriched, fully, or at least partially hydrogenated form of the liquid organic hydrogen carrier. The R-LOHC may be, in sequential process steps, dehydrogenated to remove at least a portion of the hydrogen atoms contained in the carrier, and rehydrogenated to replace at least a portion of the removed hydrogen atoms.
As used herein, the term “S-LOHC” refers to a spent or hydrogen-deficient, at least partially dehydrogenated form of the liquid organic hydrogen carrier, also referred to as an “unloaded hydrogen carrier.”
As used herein, the term “recycle” or “recyclable” used in conjunction with LOHC refers to LOHC material that, when at least partially used or spent, is capable of being converted to enriched or regenerated LOHC for further use or storage.
As used herein, the term “labile hydrogen” refers to the portion of chemically bound hydrogen in a hydrogenated LOHC that may be reversibly removed by dehydrogenation, and subsequently reversibly replaced by a following hydrogenation reaction.
As used herein, the term “recyclable LOHC” refers to an LOHC having the capability of being reversibly hydrogenated to form R-LOHC, and then reversibly dehydrogenated to form S-LOHC, in a multiply cyclic process.
As used herein, the related terms “CN component” refers to liquid compounds containing carbon-neutral carbon that may be added to the LOHC feed at various stages in the disclosed methods and processes in sufficient amounts to at least equal the quantity of carbon atoms being exhausted during an energy generation process. The exhausted carbon atoms may include vented hydrocarbons and/or vented carbon oxides. The carbon in these “CN components” is termed as “carbon-neutral carbon” by reason of its origin from carbon compounds that are captured from the atmosphere (including photosynthesis) or from flue gas that is being vented to the atmosphere, including carbon dioxide (CO2).
Unless otherwise indicated, the acronym “GHG” is intended to refer to a greenhouse gas found in or emitted to the earth's atmosphere that may absorb and emit radiant energy within the thermal infrared range.
Unless otherwise indicated, the term “CN” is intended to refer to “carbon-neutral” compositions, processes and apparatus employing these compositions. The process of generating hydrogen from a blended LOHC feed and of generating electricity from the generated hydrogen is termed as “carbon-neutral” by reason of the purposeful addition of the CN component containing carbon-neutral carbon to the LOHC feed in sufficient amount to at least equal the number of carbon atoms being exhausted during the electrical generation process, including vented hydrocarbons and vented carbon oxides.
Unless otherwise indicated, the term “carbon-neutral carbon” or “CNC” further includes carbon compounds that are captured from the atmosphere, including carbon oxides, and from combustion processes and from flue gas emissions that would otherwise persist or be released into the atmosphere.
As used herein, the terms “wt %” and “weight %” as used here is equivalent to “percent by weight.”
As used herein, the term “unloaded hydrogen carrier” refers to a hydrocarbon having the capacity to capture chemically bound hydrogen in a catalytic hydrogenation process. An unloaded hydrogen carrier may be a single or double ring aromatic, such as benzene, toluene or decalin. In some circumstances, the unloaded hydrogen carrier may further comprise one or more partially hydrogenated carriers such as for example, but not limited to a cyclohexene and cyclohexadiene pair, or the corresponding partially hydrogenated analogs of toluene and decalin. Suitable hydrocarbons include alkyl and aromatic compounds of between C6 to C12 content.
As used herein, the term “green hydrogen” is intended to refer to hydrogen, either as a gaseous molecule or as source of labile hydrogen, that is produced by using clean energy from renewable energy sources, such as for example, but not limited to solar or wind power, to split water into two hydrogen atoms and one oxygen atom through a process called electrolysis, and gasification of biomass and subsequent steam reforming of the bio-syngas.
A used herein, the term “blue hydrogen” is intended to refer to hydrogen, either as a gaseous molecule or as a source of labile hydrogen that is produced from, for example, steam reforming, partial oxidation or thermal pyrolysis, and the byproduct carbon compounds are captured and stored underground through an industrial carbon capture and storage (CSS) process. “Blue hydrogen” is sometimes referred to as carbon-neutral (CN) as the emissions are not dispersed in the atmosphere.
As used herein, the term “power module” refers to at least the combined elements of an R-LOHC supply, a dehydrogenation reaction unit for generating gaseous hydrogen from the supplied R-LOHC, and an electrochemical conversion unit for converting at least a portion of the generated hydrogen to electricity.
Described below are apparatus, methods, processes, and systems that provide carbon-neutral electricity. Reference will be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure and the embodiments described herein. However, embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures, components, and mechanical apparatuses have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.
The embodiments of apparatus and processes described herein generate electricity from a hydrogen based LOHC feed using a fuel cell unit. The disclosed processes provide net zero greenhouse gas emissions by redirecting and balancing the heat flows in the process. In one embodiment, the fuel cell unit is the sole heat source for the process, eliminating the need for a separate heat source for operating the dehydrogenation reactor. In further embodiments, the fuel cell unit may be operated at conditions that substantially reduce or eliminate any heat emissions from the process. The LOHC feed may include an additive amount of a CN component in some embodiments to balance fugitive hydrocarbon and CO2 emissions from the process so that the overall process is carbon neutral with respect to the environment.
Suitable hydrogen carriers include hydrocarbons comprising an aromatic backbone structure with chemically bonded “labile” hydrogen atoms that may be removed from the backbone structure by dehydrogenation. Following dehydrogenation of the hydrogen carrier and generation of gaseous hydrogen, the remaining aromatic, having the backbone structure of the feed, may be recycled by rehydrogenation for reuse as a hydrogen carrier. Use of the term “labile” hydrogen is meant to encompass chemically bound hydrogen that may be removed by catalytic dehydrogenation without substantially decomposing the underlying aromatic substrate from which the hydrogen is abstracted.
The LOHC is a recyclable organic carrier. The term “recyclable” as used herein means that the LOHC may be dehydrogenated to remove chemically bound hydrogen, and the resulting hydrogen deprived carrier recovered and rehydrogenated by a hydrogenation reaction to form additional LOHC. Any LOHC molecules that are further reacted during dehydrogenation into forms that are not able to be hydrogenated, and therefore cannot be recycled to produce additional LOHC, is considered to be decomposed. The dehydrogenation reaction is operated using a catalyst at dehydrogenation process conditions without substantial decomposition of the LOHC. The term “without substantial decomposition,” as used herein, means LOHC decomposition products are completely absent from system or are present in quantities that have less than a measurable effect on, or confer less than a material disadvantage to, the LOHC process described herein.
Known LOHC systems include mono- and poly-heterocyclic and homocyclic organic compounds, including N-heterocyclic compounds, which are capable of undergoing hydrogenation and dehydrogenation without substantial decomposition. LOHCs may exist as liquids or low melting point solids under ambient storage conditions.
The LOHC comprises random isomeric mixtures of substantially hydrogenated aromatic substrates having a hydrogen storage capacity of at least about 5 wt % labile hydrogen, and in some cases at least about 6 wt % labile hydrogen. Suitable LOHC compositions include, for example, substantially hydrogenated analogues of a mixture of isomers of one or more of toluene, xylene, or decalin. By substantially hydrogenated is meant to encompass hydrogenated forms of the aromatic substrate having a hydrogen storage capacity of at least about 5 wt % labile hydrogen, and in some cases at least about 6 wt % labile hydrogen. By “substantially hydrogenated” is intended to include aromatic substrates that contain less than the theoretical maximum amount of chemically bound hydrogen, e.g., in a range from 85 to 99 mole % of the fully hydrogenated maximum amount. In suitable embodiments, the LOHC feed composition supplied for catalytic dehydrogenation contains greater than 90 wt %, or greater than 95 wt %, or even greater than 99 wt % methylcyclohexane.
Other suitable LOHC compositions may include, for example, a mixture of isomers of benzyl toluene, a mixture of isomers of dibenzyl toluene, a mixture of isomers of terphenyl, a mixture of isomers of carbazole, a mixture of isomers of methyl carbazole, and a mixture of isomers of ethyl carbazole. Suitable isomeric mixtures of benzyl toluene and dibenzyl toluene are described in U.S. Patent Application Number 2015/0266731, which is hereby incorporated herein in its entirety by reference. Terphenyls are a group of aromatic compounds consisting of a central aromatic ring substituted by two phenyl groups. Carbazole is an aromatic heterocyclic organic compound having a tricyclic structure consisting of two six-membered benzene rings fused on either side of a five-membered nitrogen-containing ring.
In one embodiment, the LOHC feed composition is a blend of two or more components. Each of the components are derived from a different source, and all of the components may have the same, or different, chemical compositions. The LOHC feed may comprise a blend of a recycle component and a carbon-neutral additive component, the additive component being added to the LOHC in an amount sufficient to balance any carbon emissions that may result from the process of generating electricity using the LOHC.
The recycle component of the LOHC may be an at least partially dehydrogenated analog of the LOHC. At least a portion of the recycle component may be recovered from a hydrogen-to-electricity generation process, in which the labile hydrogen included therein is delivered as chemically bound hydrogen, liberated by dehydrogenation, and a substantially dehydrogenated byproduct from dehydrogenation recovered, at least a portion of which is recycled. At least 10 wt % and up to virtually 100 wt % of the recycle component may be recovered from a hydrogen-to-electricity generation process.
Recycling the recycle component may include one or more of a conditioning process for purifying the component prior to rehydrogenating the component for inclusion in the LOHC. The conditioning process may include one or more of, for example, filtration and distillation of the recycle component prior to hydrogenation.
In some embodiments of the disclosure, a carbon-neutral component may be included as an additive in the LOHC for maintaining carbon-neutral operation of the power module. The carbon-neutral component is produced from molecular precursors either that are produced with no CO2 generation, which are produced with recycled atmospheric CO2, including, for example, by photosynthesis, or that are produced with CO2 capture and ultimate storage generated during their production, any of which do not result in a net increase in atmospheric CO2.
In one embodiment, the carbon-neutral component is produced from biomass. Biomass from plant or animal sources can be purposely grown energy crops, wood or forest residues, waste from food crops, horticultural waste, or food processing residues. Production of carbon-neutral carrier from biomass generally involves one or more biomass conversion steps, such as pyrolysis, gasification, anaerobic digestion, or fermentation. Typical reaction products from these processing methods include one or more of methanol, ethanol, methane, acetic acid, lactic acid, and syngas. One or more of these biomass conversion products may be used to generate an aromatic precursor of the carbon-neutral carrier.
In one embodiment, the carbon-neutral component is synthesized from CO2 that has been removed from the atmosphere by an atmospheric CO2 capture process.
As carbon contained in the carbon-neutral component is itself carbon neutral, the carbon-neutral component is classified as a renewable energy source, and therefore available as an emission source for the process. Therefore, for purposes of this disclosure, any hydrocarbons that are emitted to the atmosphere or are burned for thermal input and temperature control of the process are balanced by carbon-neutral hydrocarbons in the LOHC feed, and therefore do not contribute to a net increase in atmospheric hydrocarbon emissions. Likewise, the process of using the LOHC for generating electricity is carbon neutral.
The carbon-neutral LOHC component may have the same, or a different, chemical structure as the recycle component. Because the process may be operated without separation of the recycle and CN components during at least some periods, the recycle and CN components may preferably have the same chemical structure. Thus, the process of electricity generation may include use of an at least partially hydrogenated analog of toluene as the recycle component, and an at least partially hydrogenated analog of CN toluene made from net zero emission processes for both the carbon and the hydrogen in the CN toluene.
The LOHC may contain a carbon-neutral component; in some instances, at least 0.1 wt % carbon-neutral component; in some instances, in a range from 0.1 to 25 wt % carbon-neutral component; in some instances, in a range from 0.1 to 15 wt % carbon-neutral component; in some instances, in a range from 0.1 to 5 wt % carbon-neutral component. For at least portions of the operating cycle of the power module, the thermal energy is balanced between the operating fuel cell unit and the dehydrogenation reactor, such that additional combustion heat is not required to operate the module. Under these operating conditions, an amount of carbon-neutral component in the range of 0.1 to 1 wt % of the LOHC feed may be sufficient to operate the power module in carbon-neutral mode. Accordingly, in some embodiments, the LOHC fuel used is a blended feed consisting of R-LOHC and CN R-LOHC.
The LOHC is generally available to the power module at a temperature at or approaching ambient temperature. The dehydrogenation process may involve one or more of preheating the LOHC to at least reaction temperature, supplying heat to maintain the dehydrogenation catalyst at reaction temperature, and supplying heat to compensate for heat loss through the endothermic reaction mechanism of dehydrogenation. In the various embodiments of the processes disclosed herein, the electrochemical conversion device is the sole heat source for the dehydrogenation reaction, including feed preheating, during operation of the power module to generate electricity. During normal operation, no combustion beyond the oxidative electrochemical conversion of hydrogen is required, i.e., hydrogen conversion acts as the sole source of heat without any external combustion or heat source. In some embodiments, excess thermal energy generated by hydrogen conversion is fully utilized within the power module, with only incidental losses that are normally encountered when operating above ambient temperature. In alternative embodiments during standby periods in which the power module is not generating electricity, LOHC feed lines may be electrically heat traced for enhanced start-up. Overall CN operation in the latter embodiment may than be achieved by using stored excess electricity generated by means of the present disclosure or other source of CN electricity.
Generating hydrogen by LOHC dehydrogenation is endothermic, requiring heat input for at least one of the following steps including heating the LOHC feed to dehydrogenation temperature, vaporizing the feed prior to introducing the feed to the catalyst-containing vessels in the reactor, maintaining the dehydrogenation catalyst at reaction temperature, and supplying heat to overcome the endotherm of the reacting LOHC.
The general structure of the dehydrogenation reactor provides for contacting the heated LOHC feed with catalytically active materials. The reacting LOHC may be in a liquid or a gaseous phase, or a combination. For the hydrogenated analogs of aromatics having a normal boiling point below the dehydrogenation reaction temperature, including hydrogenated analogs of benzene, toluene and naphthalene, the dehydrogenation reaction is generally conducted as a gas phase reaction.
The dehydrogenation reactor may comprise a plurality of reaction tubes filled with particulate dehydrogenation catalyst and contained within the reactor. Heat transfer fluid within the reactor and external to the reaction tubes supply the heat for maintaining the dehydrogenation reaction temperature. The reactor tubes may be configured for parallel flow, with each reactor tube configured to receive a portion of the reactor feed. Bundles of parallel flow reactor tubes may further be configured as staged reactor bundles, each stage after the first receiving partially converted products from the preceding stage of reactor tubes with respect to reactant flow, and subsequently passing additionally converted products to any subsequent stage. The LOHC may be supplied to the reactor as a single preheated, liquid or vapor phase stream, or as multiple streams, each of which may be supplied at the same, or in some cases differing, temperatures. Alternatively, the dehydrogenation reactor may be a single catalyst-containing vessel through which the LOHC is passed for conversion to hydrogen and an at least partially dehydrogenated aromatic substrate.
The dehydrogenation catalyst may comprise an active metal on an oxide support. Suitable active metals include, for example, nickel, platinum, palladium, rhodium, iridium, and ruthenium. The oxide support may be a highly porous gamma alumina, silica, magnesia, or silica-alumina support. In another embodiment, the active catalytic material may be coated on the inside surface of the reactor tubes through which the reacting fluid flows. One common issue with dehydrogenation reactors is ageing, coking, and fouling of the catalyst. Various embodiments of the disclosure contemplate approaches to minimize this issue, including (a) active control of the temperature that the feed encounters, in order to minimize catalyst deactivation; (b) venting a minimum amount of excess heat during hydrogen conversion; and (c) minimizing the number of heat exchange stages between hydrogen production and conversion.
Dehydrogenation reaction conditions may include an average catalyst temperature in the range of 250 to 600° C., or alternatively in a range of 250 to 450° C. and a total pressure in the range of 1-5 Barg (gauge pressure in bars). In one embodiment, the LOHC is preheated prior to entry into the catalytic reactor at a temperature in the range of 250° C. and 450° C. In another embodiment, the LOHC is preheated to a temperature above the catalyst temperature, to compensate for the endothermal cooling effect of the dehydrogenation reaction, while minimizing coke formation at the catalytic zone feed inlet. In this regard, an inlet temperature of up to 600° C. may be employed. Preheated hydrogen may also be supplied as feed to the dehydrogenation reactor to control and reduce catalyst fouling reactions at the feed inlet to the reactor.
In related embodiments, hydrogen conditioning may take place in a hydrogen conditioning unit. Reaction product effluent from dehydrogenation is preconditioned by separation into a first hydrogen-rich gaseous stream containing some amount of vapor phase hydrocarbons, and a liquid phase hydrocarbon. Conditioning the first hydrogen-rich gaseous stream may involve one or more of purification, temperature adjustment, pressure adjustment or additive addition prior to electrochemical conversion.
During conditioning, the first hydrogen-rich gaseous stream separated from the reaction effluent may be cooled to a temperature suitable for condensing at least a portion of the hydrocarbon contaminants, with the condensate being removed from the gaseous hydrogen using one or more vapor/liquid separation methods. Conditioning may include refrigeration of the contaminated hydrogen to a temperature below about 0° C., and in some cases below about −20° C. to condense and remove additional contaminants from the gaseous hydrogen. Conditioning may include demisting and filtering, using, as a nonlimiting example, carbon and/or molecular sieve filtration. A conditioned and purified second hydrogen-rich gaseous stream, having a purity as high as 99% or higher, or as 99.5% or higher, or even as 99.7% or higher and having been temperature and pressure adjusted as needed, is available for electrochemical conversion in the hydrogen conversion means. In embodiments, the conditioning step may include heating the purified hydrogen prior to electrochemical conversion.
The electrochemical conversion device generates electricity through the electrochemical oxidation of hydrogen or a hydrogen-containing fuel gas. In one embodiment, an exemplary electrochemical conversion device comprises stacked fuel cell elements. The fuel cell elements are configured and temperature controlled to operate at a temperature higher than the dehydrogenation reactor operating temperature, or in a temperature range of between 25 to 250° C. higher than the dehydrogenation catalyst temperature while generating electricity, or at a temperature of greater than 400° C., or at a temperature in a range of 400 to 600° C.
The electrochemical conversion of hydrogen occurs in a fuel cell suitable for the process, such as, for example, a Solid Oxide Fuel Cell (SOFC), a Molten Carbonate Fuel Cell (MCFC), a Phosphoric Acid Fuel Cell (PAFC), a Proton-Exchange Membrane Fuel Cell (PEMFC), or an alkaline fuel cell. An SOFC typically operates in an oxidant environment on a cathode side of the fuel cell, a reducing environment on an anode side of the fuel cell, and with an oxygen-ion conducting solid phase metal-oxide derived ceramic as its electrolyte.
In one embodiment, a metal supported Solid Oxide Fuel Cell comprises a thin ferritic stainless-steel plate with a screen-printed gadolinium-oxide doped ceria (GDC) electrolyte separating the anode and cathode. Hydrogen passes through the anode chamber. Oxygen (air) passes through the cathode chamber. An electrical circuit is made between the cathode and the anode. At 580° C. the electrolyte becomes activated and oxygen ions pass from the cathode to the anode through the electrolyte to oxidize hydrogen to form water in the anode. An electric current is concurrently conducted through an external circuit from the anode to the cathode to do useful work (i.e., drive motors, charge batteries, etc.) SOFCs operate at high temperatures over long periods of time in the presence of oxygen and other reactive fluids.
Ionic heat is generated by the passage of the oxygen ions from the cathode to the anode. In the process, the heat generated in the fuel cell elements may be removed using a liquid phase HTF. In one embodiment, the ionic heat is removed from the anode interface using a flat auxiliary plate or flat heat exchange plate sandwiched between fuel cell elements (see
In another embodiment, the fuel cell unit may be configured and temperature controlled such that the temperature of the heated HTF within the fuel cell unit may be greater than the dehydrogenation reactor operating temperature. Alternatively, the fuel cell unit may be configured and temperature controlled such that the temperature of the heated HTF within the fuel cell unit may be less than 600° C., or in a range from 400 to 600° C.
In another embodiment, the fuel cell unit may be configured and temperature controlled such that the temperature of the heated HTF is passed to the dehydrogenation reactor at a temperature greater than the dehydrogenation reactor operating temperature. Alternatively, the fuel cell unit may be configured and temperature controlled such that the temperature of the heated HTF is passed to the dehydrogenation reactor at a temperature of less than 600° C., or in a range from 400 to 600° C.
In one embodiment, the fuel cell unit is configured and operated to be the sole source of heat for the dehydrogenation process. In one embodiment, the heat generated by the fuel cell unit is substantially consumed within the power module. In one embodiment, the heat generated by the fuel cell unit is substantially consumed by the dehydrogenation reactor. As used herein, the term “substantially consumed” means that the only heat lost to the atmosphere is the result of unavoidable heat loss that occurs with heat transfer from one unit to another.
The fuel cell elements useful in the disclosed processes are configured to operate in a temperature range above the operating temperature of the dehydrogenation reactor. In another embodiment, the fuel cell elements are configured and temperature controlled to operate at a temperature to provide heat to and be the sole source of heat for the dehydrogenation reactor. In another embodiment, fuel cell unit comprising fuel cell elements and the dehydrogenation reactor are energy balanced, such that essentially all of the heat generated in the fuel cell elements is utilized within the power module. In this operating mode, the heat generated by the fuel cell elements is balanced by the heat requirements for LOHC feed preheating, vaporization, and dehydrogenation; the only heat loss to the atmosphere being the incidental heat losses that naturally occur when operating at a temperature above ambient. In another embodiment, the fuel cell elements are temperature controlled such that heat generated in the fuel cell unit may be exchanged with the LOHC in the dehydrogenation reactor while minimizing the coking tendency of the LOHC during preheating and reaction. In another embodiment, the fuel cell unit is configured and operated at a temperature that permits using a liquid HTF to exchange heat between the fuel cell unit and the dehydrogenation reactor.
Since external combustion is not needed when processing LOHC into hydrogen, further embodiments need only account for small hydrocarbon losses during operation, estimated to be at most about 0.5 wt % of the CN R-LOHC used, the losses due primarily to a bleed stream and venting step included wherein the bleed stream operates to exhaust a small amount of hydrogen recycled around the fuel cell in order to manage the hydrocarbon content of the recycle stream, when needed.
Operating fuel cell elements generate heat that is removed by exchange with a stationary or flowing fluid in contact with the elements. The heat transfer fluid for removing the heat may be gaseous or liquid. If liquid, the HTF remains a thermally stable liquid at the maximum operating temperature of the fuel cell elements. In embodiments, the HTF in contact with the fuel cell elements remains a thermally stable liquid at a temperature of at least 600° C.
Maintaining thermal balance during power module operation includes operating the fuel cell unit at an operating temperature higher than the temperature of the dehydrogenation unit, using a liquid HTF to supply the excess heat generated in the fuel cell unit for dehydrogenation, feed preheating and vaporization, and product hydrogen conditioning. To facilitate the efficient transfer of heat, a fluid delivery unit is provided for installation in the fuel cell unit. As described, the fuel cell unit comprises stacked fuel cell elements, each element having an anode and a cathode separated by an electrolyte. At least one fuel cell element in the stack is separated from an adjacent fuel cell element by a fluid delivery unit comprising a HTF flow plate for flowing a HTF between the adjacent elements for removing heat generated by the elements during operation of the fuel cell unit. The flow plate forms a top section and a bottom section, with a volume between provided for HTF flow. HTF flowing through the flow plate is in thermal communication with the operating fuel cell element, for removing excess heat above that required to maintain the fuel cell element temperature. The flowing HTF leaves the flow plate and is provided for heat exchange with other components of the power module. The flow plate may include baffles to create a tortuous pathway for HTF flow, thereby increasing heat transfer. The interior surface of the flow plate contacting the flowing HTF may be plated with a material, such as a ceramic, which does not add charged ions to the flowing HTF. In another embodiment, the flow plate may be of a nonconductive material to prevent any electrical shorting during operation.
In one embodiment, the fluid delivery unit may further include a hydrogen flow plate for flowing hydrogen to an anode of at least one of the adjacent fuel cells. In yet another embodiment, the fluid delivery unit further comprises an air flow plate for flowing air to a cathode of at least one of the adjacent fuel cells.
In a first embodiment, heat generated in the operating fuel cell elements may be passed via a liquid phase HTF to the dehydrogenation reactor as the sole source of heat for maintaining the reaction temperature and for preheating and vaporizing the dehydrogenation reactor LOHC feed. In a second embodiment, a first HTF that is heated by contact with operating fuel cell elements is heat exchanged with a second HTF. The second HTF is passed to the dehydrogenation reactor, for maintaining the dehydrogenation reaction temperature and for preheating and vaporizing the dehydrogenation reactor LOHC feed. The heat exchanger may be a unit separate from the dehydrogenation reactor and from the fuel cell unit, or alternatively the heat exchanger may be immersed in a bulk first HTF liquid phase contained within the fuel cell unit, or alternatively the heat exchanger may be immersed in a bulk second HTF liquid phase contained within the reactor vessel. The first HTF that is heated in the fuel cell unit is passed to a heat exchanger in the dehydrogenation reactor, for exchanging heat with a second HTF in the reactor. The heated second HTF is circulated through the reactor and optionally to a feed preheater for maintaining the dehydrogenation reaction temperature. If the process includes a second HTF, the second HTF should remain a thermally stable liquid at the operating temperature of the first HTF or at a temperature up to 400° C., or at the operating temperature of the dehydrogenation reactor.
The first liquid HTF and the second liquid HTF may have the same composition, or different compositions. Example materials for use as a first liquid HTF or a second liquid HTF include molten salts, specially formulated alkylated aromatics, a diphenyl ether-biphenyl HTF mixture or a specially formulated silicone compound.
In related embodiments, the first and second HTFs may be circulated in external heat exchange loops that enable heat and thermal energy transfer between the various units and modules according to the present disclosure.
In embodiments employing a single heat exchange loop, the HTF flows between fuel cell elements in the fuel cell unit, and then around catalyst containing reaction vessels in the hydrogen production unit, exchanging excess heat from the fuel cells to the endothermic dehydrogenation reaction, feed preheat and product conditioning units as disclosed.
In embodiments employing at least two or more exchange loops, a first HTF flows from the hydrogen generation (dehydrogenation) unit to a first heat exchanger, while a second HTF flows from the heat exchanger to the hydrogen production unit. In related embodiments, the fuel cell elements are bathed in a first liquid HTF that is circulated within the unit from a “sump” within the lower regions of the unit and likewise, the catalyst reactor vessels are bathed in a second liquid HTF that is circulated from the sump of that unit. In further embodiments, an intermediate heat exchanger may be located within the bulk second HTF contained within the hydrogen production unit; or alternatively located within the bulk first HTF contained within the dehydrogenation unit, or yet alternatively located external to both units.
In one embodiment an electric heater is submerged in dehydrogenation reactor shell, for supplying supplemental heat during startup and for reactor temperature control. Specific non-limiting embodiments of the process are illustrated by the appended figures and the following descriptions.
In the embodiment illustrated in
Preheated LOHC feed 114 is passed at a temperature in a range of 250 to 450° C. to catalyst-containing vessels 116 within the dehydrogenation reactor vessel 104 for liberating the labile hydrogen contained in the LOHC feed. The dehydrogenation reaction process is operated at a temperature between about 250 to 450° C. to liberate at least a portion of the labile hydrogen present in the LOHC feed and to produce gaseous hydrogen and an aromatic substrate byproduct, while minimizing decomposition of the carbonaceous backbone substrate structure. At least 80 wt %, and in another embodiment at least 90 wt %, and in another embodiment at least 95 wt % of the labile hydrogen contained in the LOHC may be recovered as gaseous hydrogen from the catalytic dehydrogenation process.
The one or more catalyst-containing vessels 116 within the dehydrogenation reactor vessel 104 may be maintained at a dehydrogenation reaction temperature by heat sourced solely from the fuel cell unit 102. In the embodiment illustrated in
Heated second liquid HTF 170 may be recirculated to dehydrogenation reactor vessel 104 to flow over the catalyst-containing vessels 116 in bulk flow or in film flow along the exterior vessel surfaces. Flow of HTF past the vessels may be upflow or downflow, depending on reactor design. Alternatively, the catalyst-containing vessels 116 may contain conduit channels through which the heated HTF is caused to flow. A portion 172 of the circulated second liquid HTF may be routed via temperature control unit 164 through feed preheater 162 to at least partially heat the LOHC feed 114, prior to final heating in feed effluent heat exchange unit 112 to bring the preheated LOHC feed 114 to the desired operating reaction temperature.
Following heat exchange in the second heat exchange unit 120, the relatively cooled diverted liquid HTF 124 may be routed via return line 126 through an optional heat dissipation unit 168. In alternative embodiments, unit 168 may be a third heat exchange unit with one or more heat exchange elements useful for controlling the temperature of the circulating first HTF, and in turn controlling the operating fuel cell elements temperature. For example, electrical heating may be employed for heating, and air or water cooling may be employed for cooling, both for temperature control of the fuel cell unit and of the power module. Likewise, trim heater 166 may be included in the hydrogen production unit for use during startup and for temperature control of the hydrogen production unit. In yet another embodiment, a second HTF loop and associated second HTF may be heated and the resulting stored heat/thermal energy used for improved temperature control through heat exchange with a first HTF loop and first HTF, or alternatively used to preheat one or more of the disclosed units after a shutdown and restarting operation for improved efficiency of the overall operation and faster start-up. In related embodiments employing electrical heating to assist startup, a small onboard battery or other source of CN electricity may be employed to bring the various units and modules as disclosed up to or near to their optimum operating temperatures for improved efficiency. In yet another embodiment, heat may be provided by the oxidation or catalytic combustion of LOHC feed using for example, but not limited to, a platinum catalyst that can provide small amounts of heat for use in any one of the disclosed units or modules.
The dehydrogenated product stream 130 leaving the dehydrogenation reactor vessel 104 and following cooling in the feed/effluent heat exchange unit 112, is separated in the vapor/liquid separation unit 132 into gaseous hydrogen 134 and a hydrogen depleted liquid product 136. The gaseous hydrogen 134 recovered from the product stream may be contaminated with normally liquid and/or normally gaseous contaminants from the dehydrogenation process. At least a portion of these contaminants are removed in conditioning unit 138, and the purified hydrogen 140 passed to an electrochemical conversion device, here an energy integrated fuel cell unit 102 for generating electricity by oxidative conversion of the hydrogen.
Conditioning the product hydrogen generally involves purifying the hydrogen by removing contaminants. One or more individual conditioning process steps may be employed. For example, the gaseous hydrogen may be cooled to condense at least a portion of the contaminants, with the condensate being removed from the gaseous hydrogen using one or more vapor/liquid separation methods. One step in the hydrogen conditioning process may include refrigeration of the contaminated hydrogen to a temperature below about 0° C., and in some cases below about −20° C. to condense and remove additional contaminants from the gaseous hydrogen. Contaminants separated out during conditioning may be returned to vapor/liquid separation unit 132 through liquid product return loop 142. Purified hydrogen 140 leaving the conditioning unit may have a purity as high as 99.7% or higher. In embodiments, the conditioning step may include heating the purified hydrogen prior to reaction in the fuel cell unit, in a temperature range, for example, of 450 to 600° C. The hydrogen depleted liquid product 136 recovered from vapor/liquid separation unit 132 is routed to the spent fuel vessel 144, optionally for recycle and rehydrogenation using green/blue hydrogen into fresh LOHC for recycle and reuse.
Purified hydrogen 140 is supplied to the anode(s) 204 (shown in
The hydrogen effluent stream 214 leaving the anode of each fuel cell element may be recycled via hydrogen recycle loop 148 to fresh hydrogen feed, optionally through an intermediate hydrogen conditioning step using conditioning unit 138 to purify the recycled hydrogen. In order to prevent the buildup of hydrocarbon contaminants in the recycle hydrogen, a small portion may be released as vented gas via hydrogen vent 150 under the control of control valve unit 152. Any hydrocarbon contaminants in the vented hydrogen may also be vented to the atmosphere. In order to maintain carbon-neutral operation of the power module, the LOHC feed 110 contains carbon-neutral carbon as part of any co-vented hydrocarbon. In one embodiment, the LOHC may contain in a range from 0.1 to 5 wt % carbon-neutral component, in another embodiment, in a range from 0.1 to 1 wt % carbon-neutral component.
A non-limiting example of a particular SOFC fuel cell element 146 is illustrated in
The fuel cell unit 102 illustrated in
Heat generated during the fuel cell electroconversion reaction is absorbed and removed by a second liquid HTF 122 contained within the fuel cell unit 102. The fuel cell elements may be immersed in bulk HTF surrounding the elements, or the HTF within the fuel cell unit may be circulated around and between the fuel cell elements in the unit. The fuel cell elements may be built into a fuel cell stack with channels or gaps separating each element, through which HTF may be caused to flow for removing heat from adjacent elements.
Traditional fuel cells are not optimized for the simultaneous exchange of heat transfer liquids and the injection/exhaust of gaseous materials, particularly when stacks of multiple fuel cell elements are stacked or closely spaced to produce a fuel cell stack or fuel cell unit.
A heat exchange plate 304 may be included in the fuel delivery assembly to provide a HTF for cooling adjacent fuel cell elements. The HTF is caused to flow from an HTF inlet port 312, through a circuitous flow pathway around baffles 314 located on the plate, where the flowing HTF absorbs heat generated in the adjacent fuel cell elements, exiting through a HTF outlet port 316. The HTF flow through the heat exchange plate 304 may be facilitated by convection flow, by a pumping means, or a combination of these means. The heat exchange plate 304 is configured to operate using either a liquid or gaseous HTF.
An air flow plate 302 provides gas, oxygen, or an oxygen-containing gas such as air via air inlet 318, at least some of which is caused to flow through a plurality of perforations 320 to a cathode layer of an adjacent fuel cell element. Air flow to the cathode may be sufficient only to react with the hydrogen supplied to the element. Oxygen depleted gas or air exhaust 216 (see
A hydrogen flow plate 306 may also be included for providing hydrogen to an anode layer of an adjacent fuel cell element. Coincident with the air flow through the air flow plate 302, purified hydrogen is passed through the hydrogen inlet port 324 into hydrogen flow plate 306. A substantial fraction of the hydrogen passes through a perforated section of the 306 having a plurality of perforations 326 of the hydrogen flow plate, for reaction on the anode with oxygen ions that have diffused from the cathode and through the electrolyte layer of the fuel cell. Unreacted hydrogen passes from the hydrogen flow plate through the hydrogen exhaust port 328.
An edge view 308 of the air flow plate 302 shows air or oxygen passing through perforations in the plate in the direction as illustrated by arrows to an adjacent anode of a fuel cell element (not shown). An edge view 310 of the hydrogen flow plate 306 shows hydrogen passing through perforations in the plate in the direction as illustrated by a second set of arrows to an adjacent anode of a fuel cell element (not shown).
During operation of the fuel cell stack, as illustrated in the disclosed embodiment being a combination of 146A, 146B and 402, hydrogen 410 supplied by means of the hydrogen flow plate 406 passes to anode 204A, the support substrate 208 being readily permeable to all gases and liquids. Simultaneously, at least some of the oxygen contained in the supplied air 408 delivered through the air flow plate 404 passes to cathode 202B, where the oxygen is ionized, and the resulting ionized oxygen caused to flow through the electrolyte layer 206B for reaction with the hydrogen gas at anode 204B. Each operating fuel cell stack produces an oxygen depleted gas exhaust stream 416 from the cathodes, a water exhaust stream 414 from the anodes and heated HTF 418 from contact with the central heat exchange plate 420 that acts to thermally couple the respective fuel cell elements 146A and 146B in the fuel cell stack arranged in parallel configuration as shown in
In further related embodiments, the disclosed fluid delivery assembly (not shown) consisting of at least one hydrogen flow plate 406 and a heat exchange plate 420 may be positioned between the respective anode layers (204A, 204B) of adjacent fuel cell elements (146A, 146B) to enable the supply of hydrogen (410) to the anode layers and to remove excess heat generated in the fuel cell elements by means of the flow of incoming HTF 412 and outgoing HTF 418 facilitated by the hydrogen flow plate 406. In one embodiment, the hydrogen flow plate also operates to recover heat from unreacted hydrogen recovered from the fuel cell(s).
In related embodiments, the air, hydrogen and heat exchange plates may be substituted with a single auxiliary plate bearing one or more of the plurality of features of each of the air, hydrogen and heat exchange plates so as to function identically to the combination of plates in regards to providing a path for the movement of air, hydrogen and HTF between and amongst the individual fuel cell elements within a fuel cell unit.
In yet other embodiments, the disclosed fuel cell elements described herein may be modified in shape, size, and configuration to achieve the same purpose. For example, the fuel cell elements may be configured as flat plates as shown herein, and positioned in stacks to increase operational density, wherein the stacks are arranged in parallel or anti-parallel configurations with respect to one another, or in alternating combinations thereof.
In yet alternative embodiments (not shown) the fuel cell elements described herein may be configured as concentric cylinders or concentric layers about a center fluid delivery assembly positioned along a common center axis.
In further embodiments the fluid delivery assembly may be configured as a central plate between flat or plate style fuel cell elements, or configured as a center cylindrical fluid delivery assembly having all the features of the flat plate style disclosed herein, including a hydrogen flow means, oxygen-enriched gas or air flow means and center HTF flow channel configured in a cylindrical manner along a common center axis.
Suitable fuel cells for use herein include any suitable electrochemical device for converting generated hydrogen gas to electrical power, i.e., a hydrogen electrochemical fuel cell capable of performing a hydrogen electrochemical conversion reaction. The fuel cell device generates electricity by conversion of chemical energy of the hydrogen fuel and air into electricity through a pair of redox reactions. Suitable fuel cells may be selected from an alkaline fuel cell (AFC), a proton-exchange membrane fuel cell (PEMFC), a phosphoric acid fuel cell (PAFC), a molten carbonate fuel cell (MCFC), an oxide ceramic or solid oxide fuel cell (SOFC), or the like. All may be operated according to one or more of the embodied process steps disclosed herein using atmospheric oxygen obtained from the environment as an oxidizer gas, with the result that no storage of oxygen gas is required. In further embodiments, the fuel cell device may comprise one or more individual fuel cell units, operated either in serial or parallel mode as needed. The electrochemical conversion devices suitable for use herein for converting carbon-neutral hydrogen to electrical power may include a solid oxide fuel cell (SOFC) device operating in a temperature range 400-650° C. Approximately 30-35% of the energy generated in the SOFC is thermal energy that is suitable for at least partially maintaining the dehydrogenation reaction zone temperature. Gases exhausted from the anode side of the SOFC system may include unreacted hydrogen and a small amount of S-LOHC that was carried along with hydrogen feed to the SOFC from a dehydrogenation zone. In another embodiment, gases exhausted from the cathode side of the SOFC system, including oxygen depleted air and water vapor, may be combined with the anode exhaust stream in a catalytic conversion unit, which produces water, oxygen depleted air and CO2 from aromatic liquid oxidation. An R-LOHC feed blend for use with the SOFC device may be contain in a range of 0.1-10 wt % of a secondary R-LOHC component in order to maintain the overall carbon-neutral process.
Additional suitable electrochemical conversion devices for converting carbon-neutral hydrogen to electrical power may include a proton-exchange membrane fuel cell (PEMFC) operating in a temperature range 50 to 100° C. Only a small portion, if any, of the heat generated by a PEMFC may be available for use with the dehydrogenation reaction zone. The remaining heat for dehydrogenation when employing a PEMFC fuel cell device may in one embodiment be provided by combustion of a portion of the combustion liquid. In this case, an R-LOHC feed blend for use with the PEMFC unit may contain in a range of 0.1 to 25 wt %, or alternatively 0.5 to 15 wt %, or alternatively 1 to 10 wt % of a secondary CN R-LOHC feed component in order to maintain the overall carbon-neutral process.
In alternative embodiments when the electricity demand has been achieved, excess electricity generated in the fuel cell electrochemical device may be used internally for heat or propulsion or exported to the electrical grid. Export electricity is important for compensating for reduced generation rates from renewable energy that supplies the electrical grid.
A solid oxide electrolyzer cell (SOEC) is a solid oxide fuel cell that runs in regenerative mode to achieve the electrolysis of water by using for example, but not limited to a solid oxide, or ceramic electrolyte. The electrolysis reaction proceeds with the oxidation of water occurring at the anode and reduction of water occurring at the cathode to produce hydrogen gas and oxygen. Solid oxide electrolyzer cells typically operate at temperatures between 400 and 850° C. Suitable SOEC electrolysis systems are well known in the art and are readily adaptable for use herein as disclosed
Suitable heat transfer fluids (HTFs) suitable for use with the disclosed embodiments herein include those that are liquids at the desired operating temperatures disclosed herein. Also suitable are HTFs that have high flash points and vapor transition temperatures greater than the highest desired operating temperatures employed herein, so that they remain as liquids within the disclosed apparatus and systems. Also suitable are HTFs that are solids or semi-solids at room temperature conditions, but which are readily liquified by application of heat and are readily maintained as flowable and pumpable liquids over the disclosed operating temperatures employed herein. Also suitable are HTFs that remain liquids even below operating temperatures, so as to negate the need to preheat and melt the materials prior to pumping, and which can be suitable employed in lower temperature environments, yet possess stability and liquidity over the desired operating temperatures disclosed herein.
In various embodiments, one or more HTFs may be employed, using one suitable for use with the dehydrogenation reactors (cooler side) and another suitable for use with the fuel cells (hotter side) of a heat exchanger.
Some non-limiting examples of HTFs suitable for use herein include those available from Global Heat Transfer Ltd., Cold Meece Estate, Cold Meece, Stone, Staffordshire, ST15 0SP, United Kingdom such as Globaltherm Omnitech (15-400° C.), Globaltherm Omnistore MS-600 149-600° C.) and Globaltherm RP (−20-350° C.).
Other non-limiting examples include the Therminol brand of HTFs available from Eastman Chemical Company, 200 S. Wilcox Dr., Kingsport, Tenn. 37660 U.S.A, particularly Therminol 63, Therminol 66, Therminol 68, Therminol 72, Therminol 73, Therminol 74, Therminol 75 and Therminol VP-1, with various stabilities up to temperatures of 300 to 350° C., and thus suitable for use with the dehydrogenation reactor.
In general, suitable HTFs include those exhibiting a liquid phase fluid up to and including the operating temperature of either the dehydrogenation reactor, the fuel cell elements, or both, regardless of the specific chemical compositions and including mixtures and combinations thereof. Examples include mixtures of synthetic aromatics, such as Therminol 72, mixtures of terphenyl and quat-terphenyl, such as Therminol 75, and mixtures of diphenyl oxide (DPO) and biphenyl, such as Therminol VP-1, as cited hereinabove for use with the dehydrogenation reactor.
Other examples include one or a mixture of ionic liquids, such as 1-butyl-3-methylimidazolium tetrafluoroborate (C4mimBF4), available from IOLITE GmbH, Im Zukunftspark 9, 74076 Heilbronn, Germany and 1-butyl-3-methylimidazolium bistrifluoromethane sulflonimide (C4mimTf2N), available from Tokyo Chemical Industry Co., Ltd. (TCI), having offices at 9211 North Harborgate Street, Portland, Oreg., 97203 U.S.A.
Other examples include molten salts, such as mixtures of potassium nitrate and sodium nitrate and optionally sodium nitrite, and other known salt mixtures that are liquifiable and form a flowable liquid phase over the desired operating temperatures as disclosed herein. One non-limiting example is HITEC, available from Coastal Chemical Co., LLC, 1500 Post Oak Blvd., Suite 1300, Houston, Tex. 77056 U.S.A, which is a eutectic mixture of water-soluble, inorganic salts of potassium nitrate, sodium nitrite and sodium nitrate suitable as an HTF herein as it is fluid between about 150-600° C.).
Yet further examples include newer heat transfer materials referred to as High Operating Temperature (HOT) fluids, such as those being developed by the University of California, Los Angeles (UCLA), along with partners at the University of California, Berkeley, and Yale University, under the “2012 Multidisciplinary University Research Initiative (MURI): High Operating Temperature (HOT) Fluids” funding opportunity, being either metal alloys, or halide and oxy-halide eutectic systems being developed by University of Arizona along with partners at Arizona State University and Georgia Institute of Technology, both systems being liquifiable within the temperature ranges disclosed as suitable for use herein, and suitable for operating at temperatures in excess of 800° C., and so compatible for use with the fuel cells as disclosed.
While specific embodiments of the invention have been shown, described, and disclosed here in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/052553 | Sep 2021 | US | national |
| PCT/US2021/054323 | Oct 2021 | US | national |
| PCT/US2022/018362 | Mar 2022 | US | national |
This application claims the benefit of the priority of U.S. provisional patent application Ser. No. 63/233,330, entitled “Energy Balanced Process for Producing Carbon-Neutral Electricity”, filed on Aug. 16, 2021; the benefit of the priority of U.S. utility patent application Ser. No. 17/733,667, entitled “Method For Making An Improved LOHC From Refinery Streams”, filed on Apr. 29, 2022; the benefit of the priority of U.S. provisional patent application Ser. No. 63/181,969, entitled “Method For Making An Improved LOHC From Refinery Streams”, filed on Apr. 30, 2021; the benefit of the priority of U.S. utility patent application Ser. No. 17/733,549, entitled “Fueling Station For Supply Of Liquid Organic Hydrogen Carriers And Method of Operation”, filed on Mar. 29, 2022; the benefit of the priority of U.S. provisional patent application Ser. No. 63/181,968, entitled “Fueling Station For Supply Of Liquid Organic Hydrogen Carriers And Method of Operation”, filed on Mar. 30, 2021; the benefit of the priority of International utility patent application Serial No. PCT/US2022/018362, entitled “Liquid Carbon-Neutral Energy Facility System”, filed on Mar. 1, 2022; the benefit of the priority of U.S. utility patent application Ser. No. 17/684,118, entitled “Liquid Carbon-Neutral Energy Facility System”, filed on Mar. 1, 2022; the benefit of the priority of U.S. provisional patent application Ser. No. 63/155,741, entitled “A Carbon-Neutral Energy Facility (CNEF) Business Method”, filed on Mar. 2, 2021; the benefit of the priority of International utility patent application Serial No. PCT/US2021/0543233, entitled “Carbon-Neutral Process for Generating Electricity”, filed on Oct. 9, 2021; the benefit of the priority of U.S. utility patent application Ser. No. 17/497,903, entitled “Carbon-Neutral Process for Generating Electricity”, filed on Oct. 9, 2021; the benefit of the priority of U.S. provisional patent application Ser. No. 63/091,425, entitled “Carbon-Neutral Process for Generating Electricity”, filed on Oct. 14, 2020; the benefit of the priority of International utility patent application Serial No. PCT/US2021/052553, entitled “Carbon-Neutral Process for Generating Electricity”, filed on Sep. 29, 2021; the benefit of the priority of U.S. utility patent application Ser. No. 17/488,867, entitled “Carbon-Neutral Process for Generating Electricity”, filed on Sep. 29, 2021; and the benefit of the priority of U.S. provisional patent application Ser. No. 63/088,024, entitled “Carbon-Neutral Process for Generating Electricity”, filed on Oct. 6, 2020; all of which are hereby incorporated in their entirety by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 63233330 | Aug 2021 | US | |
| 63181969 | Apr 2021 | US | |
| 63181968 | Apr 2021 | US | |
| 63155741 | Mar 2021 | US | |
| 63091425 | Oct 2020 | US | |
| 63088024 | Oct 2020 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17733667 | Apr 2022 | US |
| Child | 17876894 | US | |
| Parent | 17733549 | Apr 2022 | US |
| Child | 17733667 | US | |
| Parent | 17684118 | Mar 2022 | US |
| Child | 17733549 | US | |
| Parent | 17497903 | Oct 2021 | US |
| Child | 17684118 | US | |
| Parent | 17488867 | Sep 2021 | US |
| Child | 17497903 | US |
