JP2012530351A - System and method for operating a fuel cell system - Google Patents

Abstract

  Methods and systems for operating a molten carbonate fuel cell system are described herein. A method for operating a molten carbonate fuel cell system comprises supplying a hydrogen-containing stream containing molecular hydrogen to the anode portion of a molten carbonate fuel cell; the molecular hydrogen utilization at the anode is less than 50% Controlling the flow rate of the hydrogen-containing stream to the anode; mixing the anode exhaust containing molecular hydrogen from the molten carbonate fuel cell with the hydrocarbon stream containing hydrocarbon; Contacting at least a portion of the mixture with the catalyst to produce a steam reforming feed; separating at least a portion of the molecular hydrogen from the steam reforming feed; and at least a portion of the separated molecular hydrogen Providing a portion to the anode of the molten carbonate fuel cell.

Description

  The present invention relates to a fuel cell system and to a method of operating a fuel cell. In particular, the present invention relates to systems and methods for operating a molten carbonate fuel cell system.

  Molten carbonate fuel cells convert chemical energy into electrical energy. The molten carbonate fuel cell is useful in that it supplies high-quality and reliable power, operates without discharging pollutants, and is a relatively small power generator. These features make molten carbonate fuel cell applications attractive as power sources in urban areas, transport vessels, or remote areas where power supply is limited.

  A molten carbonate fuel cell is composed of an anode, a cathode, and an electrolyte layer sandwiched between the anode and the cathode. The electrolyte comprises an alkali carbonate, alkaline earth carbonate, molten alkali carbonate or a mixture thereof, which may be suspended in a porous, insulating, chemically inert matrix. An oxidizable fuel gas or a gas that can be reformed into an oxidizable fuel gas in a fuel cell is supplied to the anode. The oxidizable fuel gas supplied to the anode is generally a synthesis gas, ie, a mixture of oxidizable components, molecular hydrogen, carbon dioxide and carbon monoxide. An oxidant-containing gas, typically air and carbon dioxide, can be supplied to the cathode to supply chemical reactants for producing carbonate anions. During the operation of the fuel cell, carbonate anions are constantly replenished.

  Molten carbonate fuel cells are operated at high temperatures, typically 550 ° C. to 700 ° C., to react oxygen in the oxidant-containing gas with carbon dioxide to produce carbonate anions. Carbonate anions pass through the electrolyte and interact with the fuel gas hydrogen and / or carbon monoxide at the anode. Electric power is generated by the conversion of oxygen and carbon dioxide to carbonate ions at the cathode and the chemical reaction of carbonate ions with hydrogen and / or carbon monoxide at the anode. The following reaction describes the electrochemical reaction in the battery in the absence of carbon monoxide.

Cathode charge transfer: CO ₂ + 0.5O ₂ + 2e ⁻ → CO ₃ ⁼
Anode charge transfer: CO ₃ ⁼ + H ₂ → H ₂ O + CO ₂ + 2e ⁻ and total reaction: H ₂ + 0.5O ₂ → H ₂ O
When carbon monoxide is present in the fuel gas, the chemical reaction below describes the electrochemical reaction in the cell.

Cathode charge transfer: CO ₂ + O ₂ + 4e ⁻ → 2CO ₃ ⁼
Anode charge transfer: CO ₃ ⁼ + H ₂ → H ₂ O + CO ₂ + 2e ⁻ and
CO ₃ ⁼ + CO → 2CO ₂ + 2e ⁻
Total reaction: H ₂ + CO + O ₂ → H ₂ O + CO ₂
An electrical load or storage device can be connected between the anode and cathode to allow current to flow between the anode and cathode. The current supplies power to the electrical load or powers the storage device.

  Fuel gas is generally supplied to the anode by a steam reformer that reforms low molecular weight hydrocarbons and steam into hydrogen and carbon oxide. For example, methane in natural gas is a preferred low molecular weight hydrocarbon used to produce fuel gas for fuel cells. Alternatively, the anode of the fuel cell can be designed to cause a steam reforming reaction to occur internally against low molecular weight hydrocarbons such as methane and steam supplied to the anode of the fuel cell.

Steam reforming of methane yields a fuel gas containing hydrogen and carbon monoxide according to the following reaction: CH ₄ + H ₂ O⇔CO + 3H ₂ . In general, the steam reforming reaction is conducted at a temperature effective to convert substantial amounts of methane and steam to hydrogen and carbon monoxide. Further hydrogen production can occur in the steam reformer by conversion of steam and carbon monoxide to hydrogen and carbon dioxide by a water gas shift reaction of H ₂ O + CO⇔CO ₂ + H ₂ .

  However, in a conventional steam reformer that is used to supply fuel gas to a molten carbonate fuel cell, the steam reformer is energetically responsible for the production of carbon monoxide and hydrogen by the steam reforming reaction. Since it is operated at an advantageous temperature, little water is produced by the water gas shift reaction. Operation at such temperatures is disadvantageous for the production of carbon dioxide and hydrogen by the water gas shift reaction.

  Carbon monoxide can be oxidized in the fuel cell to supply electrical energy, but not carbon dioxide. Implementation is generally accepted as a preferred method of supplying fuel to a fuel cell. The fuel gas is typically supplied to the anode by external or internal steam reforming and thus includes hydrogen, carbon monoxide and a small amount of carbon dioxide, unreacted methane and water as steam.

However, fuel gases containing non-hydrogen compounds such as carbon monoxide are less efficient at generating power in molten carbonate fuel cells than the purer hydrogen fuel gas stream. At a given temperature, the power that can be generated in a molten carbonate fuel cell increases with increasing hydrogen concentration. This is due to the electrical oxidation potential of molecular hydrogen compared to other compounds. For example, Watanabe et al., "Applicability of molten carbonate fuel cells to various fuels ", Journal of Power Sources, 2006 years, pp 868-871, 1500A / ^{m 2} with 50% molecular hydrogen and 50% water supply fuel A 10 kW molten carbonate fuel cell stack operating at 90% fuel utilization and 0.49 MPa pressure at a current density of 0.192 W produces a power density of 0.12 W / cm ² at 0.792 volts, but with the same operation It states that 50% carbon monoxide and 50% water feed fuel at conditions produces a power density of only 0.11 W / cm ² at 0.763 volts. Thus, a fuel gas stream containing a significant amount of non-hydrogen compounds is not as efficient at generating power in a molten carbonate fuel cell as a fuel gas containing primarily hydrogen.

  However, molten carbonate fuel cells are commonly used in a “hydrogen lean” mode, for example, where the conditions for producing fuel gas by steam reforming are selected to limit the amount of hydrogen exiting the fuel cell in the fuel gas. Are commercially operated. This is done to balance the electrical energy potential of hydrogen in the fuel gas with potential energy (electrochemical + thermal) losses due to hydrogen leaving the cell without being converted to electrical energy.

  Certain measures have been taken to recapture the energy of the hydrogen exiting the fuel cell, but these are significantly less energy efficient than if the hydrogen reacted electrochemically in the fuel cell. For example, anode exhaust generated by electrochemically reacting fuel gas in a fuel cell is burned and drives a turbine expander to generate electricity. However, because much of the thermal energy is lost rather than converted to electrical energy by the expander, burning the anode exhaust to generate electricity captures the electrochemical potential of hydrogen in the fuel cell. Is significantly less efficient. The fuel gas exiting the fuel cell is also burned to provide thermal energy for various heat exchange applications. However, nearly 50% of the heat energy is lost in such heat exchange applications after combustion. Hydrogen is a very expensive gas to use to burn burners utilized in inefficient energy recovery systems, and therefore the amount of hydrogen normally used in molten carbonate fuel cells is The majority of the hydrogen supplied to the fuel cell is used to generate power and is adjusted to minimize the amount of hydrogen exiting the fuel cell in the fuel cell exhaust.

  Other hydrogen for generating more hydrogen from the fuel gas present in the anode exhaust by supplying fuel gas to the post-reformer and / or gas separator and / or recycling the hydrogen in the anode gas Action was taken. To recover hydrogen and / or carbon dioxide, the fuel gas present at the anode is reformed in a post-reformer to enrich the anode gas stream with hydrogen and / or subjected to a water gas shift reaction to provide hydrogen and dioxide. Generate carbon. Heat can be supplied by the anode gas stream.

  Heat for inducing the methane steam reforming reaction in the steam reformer and / or converting the liquid fuel to the steam reformer feed was also supplied by the burner. A burner that burns a fuel, typically an oxygen-containing gas containing a hydrocarbon fuel such as natural gas, can be used to supply the heat required for the steam reformer. Flameless combustion is also used to provide heat to promote the steam reforming reaction, which is a relative amount that avoids inducing flame combustion in the flameless combustion device with hydrocarbon fuel and It is also promoted by supplying an oxidizing agent. These methods of supplying the heat necessary to promote the steam reforming reaction and / or the water gas shift reaction are energetically compared because a significant amount of the thermal energy supplied by combustion is lost without being captured. Inefficient.

  Hydrogen and carbon dioxide in the reformed gas stream can be separated from the anode exhaust using, for example, a pressure swing adsorption device and / or a membrane separation device. The temperature of the anode exhaust is generally higher than that required by commercial hydrogen and / or carbon dioxide separators. The stream can be cooled, for example, by a heat exchanger, but heat energy can be lost in the cooling process.

  The separated hydrogen is supplied to the anode part of the fuel cell. By recycling hydrogen to the anode, hydrogen can be mixed into the fuel gas entering the molten carbonate fuel cell. The separated carbon dioxide is supplied to the cathode part of the fuel cell. By recycling carbon dioxide to the cathode, carbon dioxide can be enriched in the air entering the molten carbonate fuel cell.

The cell potential (V) of the molten carbonate fuel cell is indicated by the difference between the open circuit voltage (E) and the loss. For high temperature fuel cells, the activation loss is very small and the cell potential can be obtained over a practical range of current densities by considering only ohmic losses. Thus, the battery potential V = E−iR, where V and E have units of volts or millivolts, i is the current density (mA / cm ² ), R is the electrolyte, cathode and Total ohm resistance (Ωcm ² ) combined with the anode. Open circuit voltage is a major term in battery potential. The total voltage (electromotive force) of the molten carbonate fuel cell is Nernst, that is, E = E ° + (RT / 2F) ln (P _H2 PO ₂ ^.5 / P _H2O ) + (RT / 2F) ln ( P _CO2 ^c / P _CO2 ^a ), where E is the standard cell potential, R is the universal gas constant of 8.314472 JK ⁻¹ mol ⁻¹ , and T is absolute Temperature, F is a Faraday constant of 9.6483399 × 10 ⁴ Cmol ⁻¹ . As shown, the cell voltage of a molten carbonate fuel cell can be changed by changing the concentration of carbon dioxide, hydrogen and oxygen.

  Specific measures have been taken to adjust the concentration of hydrogen, oxygen and carbon dioxide supplied to the fuel cell to maximize the cell voltage. US Pat. No. 7,097,925 (the '925 patent) enriches the stream fed to the anode of a molten carbonate fuel cell while enriching the stream fed to the cathode with oxygen and carbon dioxide. The ratio of

の分母を最大にしている。富化された流れは、圧力スイング吸着装置から供給される。

Has the largest denominator. The enriched stream is supplied from a pressure swing adsorption device.

  Although the prior art is effective in supplying fuel cells with hydrogen, oxygen and carbon dioxide at various concentrations, the method is relatively inefficient in generating hydrogen, carbon dioxide and oxygen streams. . The method also cools the anode gas to remove water before entering the pressure swing adsorber, so it is relatively thermally inefficient in gas production and thermal processes. In addition, the reformer also does not convert the liquid hydrocarbon feedstock into a low molecular weight feedstock for the steam reformer, so that insufficient heat may be supplied from the fuel cell.

US Pat. No. 7,097,925

Watanabe et al., "Applicability of molten carbonate fuel cells to various fuels", Journal of Power Sources, 2006, pages 868-871.

  It would be desirable to further improve the efficiency and increase the power density of the molten carbonate fuel cell in the operation of the molten carbonate fuel cell system to generate electricity.

(Summary of the Invention)
The present invention
Supplying a hydrogen-containing stream containing molecular hydrogen to the anode of a molten carbonate fuel cell;
Controlling the flow rate of the hydrogen-containing stream to the anode such that the utilization of molecular hydrogen at the anode is less than 50%;
Mixing an anode exhaust containing molecular hydrogen from a molten carbonate fuel cell with a hydrocarbon stream containing hydrocarbons, and the anode exhaust mixed with the hydrocarbon stream has a temperature from 500 ° C to 700 ° C;
Contacting at least a portion of the anode exhaust and hydrocarbon stream mixture with the catalyst to produce a steam reforming feed fuel comprising one or more gaseous hydrocarbons, molecular hydrogen and at least one carbon oxide;
Separating at least a portion of the molecular hydrogen from the steam reforming feed fuel;
And operating a molten carbonate fuel cell comprising supplying at least a portion of the separated molecular hydrogen to the anode of the molten carbonate fuel cell as at least a portion of a hydrogen-containing stream comprising molecular hydrogen. Target method.

In another aspect, the present invention provides
A molten carbonate fuel cell configured to accept a hydrogen-containing stream comprising molecular hydrogen at a flow rate such that the hydrogen utilization at the anode is less than 50%;
At least one reformer is configured to receive the anode exhaust and hydrocarbons from the molten carbonate fuel cell, allowing the anode exhaust to mix well with the hydrocarbons to remove a portion of the hydrocarbons. At least partially reformed and configured to produce a reformed product stream, the reformed product stream operatively coupled to a molten carbonate fuel cell that includes molecular hydrogen and at least one carbon oxide. One or more reformers; and at least one part of or connected to at least one of the reformers, and operably connected to the molten carbonate fuel cell, one or more hot hydrogens A high temperature hydrogen separator including a separation membrane, configured to receive a reformate product stream and to supply a stream containing at least a portion of molecular hydrogen to a molten carbonate fuel cell; The target is a molten carbonate fuel cell system.

FIG. 1 is a schematic diagram of an embodiment of a system that includes a high temperature hydrogen separator combined with a first reformer and a second reformer for performing the methods described herein. FIG. 2 is a schematic of an embodiment of a system that includes a first reformer that includes a heat exchanger for performing the methods described herein, and a high-temperature hydrogen separator combined with a second reformer. FIG. FIG. 3 is a schematic diagram of some embodiments of the system in which the high temperature hydrogen separator is external to the second reformer. FIG. 4 is a diagram showing cell voltage (mV) versus current density (mA / cm ² ) for an embodiment of a molten carbonate fuel cell system operated at an absolute pressure of 1 bar. FIG. 5 is a diagram showing power density (W / cm ² ) versus current density for an embodiment of a molten carbonate fuel cell system operated at an absolute pressure of 1 bar. FIG. 6 is a graph showing cell voltage (mV) versus current density (mA / cm ² ) for an embodiment of a molten carbonate fuel cell system operated at an absolute pressure of 7 bar. FIG. 7 shows the power density (W / cm ² ) versus current density (mA / cm ² ) of various embodiments of a molten carbonate fuel cell system operated at an absolute pressure of 7 bar. FIG. 8 is a graph showing the percentage hydrogen utilization versus ΔP _CO2 (absolute bar) for an embodiment of operation of a molten carbonate fuel cell using various amounts of excess air at a given hydrogen utilization. FIG. 9 is a diagram showing the percentage of hydrogen utilization versus ΔP _CO2 (absolute bar) for an embodiment of operation of a molten carbonate fuel cell using methane or benzene as the feed fuel source. FIG. 10 is a diagram showing cell voltage (mV) versus current density (mA / cm ² ) for an embodiment of a molten carbonate fuel cell system using various fuel sources. FIG. 11 is a diagram showing the average excess carbon dioxide (ΔP _{CO2 (avg)} ) versus hydrogen utilization percentage for an embodiment of a molten carbonate fuel cell system using various fuel sources.

  The invention described herein provides a highly efficient method of operating a molten carbonate fuel cell to generate high power density electricity and a system for implementing such a method. First, the method described herein maximizes the power density of a fuel cell system by minimizing rather than maximizing the single pass fuel utilization of the fuel in a molten carbonate fuel cell. To do. The single pass fuel utilization is minimized to reduce the concentration of carbon dioxide and oxidation products, particularly water, over the fuel cell anode path length so that a high hydrogen concentration is maintained throughout the anode path length. High power density is provided by the fuel cell because there is an excess of hydrogen for the electrochemical reaction at the anode electrode along the entire anode path length of the fuel cell. In methods directed to achieving high one-pass fuel utilization, eg, greater than 60% fuel utilization, the concentration of oxidation products and carbon dioxide is reduced before the fuel travels into the fuel cell. Of more than 40%. The concentration of oxidation products and carbon dioxide is several times the concentration of hydrogen in the fuel cell exhaust so that the power provided along the anode path is significantly reduced as the fuel supplied to the fuel cell travels through the anode. possible.

  In the method described herein, the anode of the molten carbonate fuel cell is connected over the entire path length of the anode such that the concentration of hydrogen in the anode electrode available for electrochemical reaction is maintained at a high level over the entire anode path length. Flooded with hydrogen. Therefore, the power density of the fuel cell is maximum.

  Since hydrogen has an electrochemical potential that is significantly greater than other oxidizable compounds commonly used in molten carbonate fuel cell systems (eg, carbon monoxide), it is primarily preferably almost all hydrogen. The use of certain hydrogen rich fuels in the present method maximizes fuel cell system power density.

  The method described herein uses a fuel rich in hydrogen and melts more than systems disclosed in the art by minimizing rather than maximizing the single pass fuel utilization of the fuel cell. A high power density is produced in a carbonate fuel cell system. Minimize selected to separate and recycle captured hydrogen from fuel cell fuel exhaust, eg, anode exhaust, and minimize single pass fuel utilization with hydrogen from feed fuel and recycle stream Achieved by feeding at a rate of

  The system described herein minimizes the amount of hydrocarbons supplied to the fuel cell compared to conventional systems, while allowing a hydrogen rich stream to be supplied to the molten carbonate fuel cell. To do. The system generates a hydrogen rich stream that can be introduced directly into the anode section of a molten carbonate fuel cell.

  The system does not require a reformer connected directly to and / or located at the anode of the molten carbonate fuel cell to ensure production of sufficient hydrogen as fuel at the anode of the fuel cell. By removing or eliminating the reformer or reforming zone in the molten carbonate fuel cell, the majority of the heat from the anode exhaust is supplied to the first reformer while the molten carbonate fuel cell is hydrogenated. It becomes possible to overflow. A fuel cell that already has an internal reforming zone can be combined with the system described herein. Such fuel cells can operate more economically and efficiently than systems disclosed in the art.

  In the method described herein, the cathode of the molten carbonate fuel cell has a total cathode path length such that the concentration of carbon dioxide at the cathode electrode available for electrochemical reaction is maintained at a high level over the entire cathode path length. Overflowing with carbon dioxide. Therefore, the power density and / or cell voltage of the fuel cell is maximum.

  The method described herein utilizes a stream comprising an oxidant gas rich in carbon dioxide so that the carbon dioxide partial pressure at the majority of the cathode portion of the molten carbonate fuel cell is reduced in the molten carbonate fuel cell. The fuel cell can be operated to be higher than the partial pressure of carbon dioxide in most of the anode portion. Operating the fuel cell in this manner results in a higher power density than the systems disclosed in the art.

By using the oxidant gas rich in carbon dioxide, the voltage of the molten carbonate fuel cell increases, and the carbon dioxide deficiency of the molten carbonate fuel cell is suppressed. “Carbon deficiency” means when the partial pressure of carbon dioxide exiting the cathode (P _CO2 ^c ) is lower than the partial pressure of carbon dioxide exiting the anode (P _CO2 ^a ). By supplying excess carbon dioxide to the molten carbonate fuel cell with minimal hydrogen utilization, it is possible to obtain higher voltage and / or current density from the molten carbonate fuel cell.

  The system described herein allows a stream rich in carbon dioxide from the hydrocarbons supplied to the fuel cell to be supplied to the molten carbonate fuel cell as compared to conventional systems. Carbon dioxide generated from the system can be introduced directly into the cathode of the molten carbonate fuel cell. The system does not require an external carbon dioxide source to ensure sufficient carbon dioxide as the feed fuel at the fuel cell cathode.

  The method described herein is also highly efficient because it continuously recycles hydrogen and carbon dioxide that were not utilized to generate electricity in the fuel cell through the fuel cell system. This enables the generation of high power density related to the lowest heating value of the fuel by eliminating problems related to energy loss due to hydrogen and / or carbon dioxide leaving the battery without being converted to electrical energy. Become.

  The system includes an appropriate amount of air or molecular oxygen fuel cell cathode such that the molar ratio of carbon dioxide to molecular oxygen in the fuel supplied to the cathode minimizes concentration polarization at the fuel cell electrode. Allows simultaneous supply to The system does not require oxygen enrichment of air. The method of the present invention controls the amount of molecular oxygen so that the molar ratio of carbon dioxide to molecular oxygen in the fuel supplied to the cathode is at least 2 or at least 2.5, while at the same time simultaneously anodic with hydrogen. And simultaneous overflow of the cathode with carbon dioxide.

  By using the fuel cell system described in the present invention, a molten carbonate fuel cell can be operated at a high power density at 0.1 MPa (1 atm). Generally, molten carbonate fuel cells are operated at pressures from atmospheric pressure to about 1 MPa (10 atmospheres). Operating at pressures greater than atmospheric pressure can affect the seal life of various parts in a molten carbonate fuel cell. Operating a molten carbonate fuel cell at or near atmospheric pressure generates high current density and / or power density electricity at a given cell voltage while simultaneously sealing in a molten carbonate fuel cell. Can extend the lifespan.

  In the methods described herein, relatively little carbon dioxide is generated per unit of electricity generated by the method. By supplying the hot anode exhaust stream from the fuel cell to the first reformer, the heat generated in the fuel cell is transferred directly in the first reformer, and then the first reformer is generated. The fuel cell, the first reformer, and the second reformer are fed directly to the second reformer, and then the product of the second reformer is fed directly to the high-temperature hydrogen separator. The thermal integration of the reformer and the high temperature hydrogen separator reduces, preferably eliminates, the additional energy that needs to be supplied to facilitate the endothermic reforming reaction in one or both reformers. Such thermal integration reduces the need to supply additional energy, for example by combustion. Thus, the amount of carbon dioxide produced when supplying energy to promote the reforming reaction (s) is reduced.

  Recycling of the anode exhaust stream through the system, and separation of the carbon dioxide from the reformed gas product, and then feeding the carbon dioxide gas stream to the fuel cell by feeding the carbon dioxide containing gas stream to the fuel cell, by combustion The amount of carbon dioxide that needs to be generated is reduced. Such recycling increases the electrical efficiency of the process, thereby reducing all carbon dioxide emissions.

  In addition, recycling the anode exhaust stream through the system, and separating the hydrogen-containing gas stream from the reformed gas product, and then supplying the hydrogen-containing gas stream to the fuel cell, the molecular hydrogen-rich hydrogen content to the fuel cell. The supply of gas flow reduces the amount of hydrogen that needs to be produced by the second reformer. Such recycling of the anode exhaust increases the electrical efficiency of the process. Furthermore, the power density of the molten carbonate fuel cell is improved, so that for the same amount of power generated, power can be generated using a fuel cell that has smaller dimensions than conventional fuel cells.

  The methods described herein are more thermally and energy efficient than methods disclosed in the art. Thermal energy from the fuel cell exhaust moves directly to the first reformer. In some embodiments, some of the transferred thermal energy is then transferred from the first reformer to the second reformer. The transfer of thermal energy directly from the fuel cell anode exhaust to the first reformer is highly efficient. The reason is that the migration occurs by directly molecularly mixing the hot anode exhaust stream from the fuel cell with the hydrocarbon stream containing hydrocarbons and steam in the first reformer. The heat supply fuel is generated by the first reformer and then supplied to the second reformer. Since the transfer of thermal energy from the first reformer to the second reformer is also included in the fuel supplied from the first reformer to the second reformer, Highly efficient.

The methods described herein are also thermally more efficient than methods disclosed in the art because they use heat from the anode exhaust to produce hydrogen at lower temperatures than typical steam reforming processes. . In the method of the present invention, hydrogen can be separated from the reformed product gas using a high-temperature hydrogen separator, and the high-temperature hydrogen separator is a membrane separator. The high temperature hydrogen separator may be operably coupled to the second reformer so that hydrogen can be separated from the reformed gas when the reforming reaction occurs in the second reformer. Hydrogen separation shifts the equilibrium in the direction of hydrogen production and reduces the temperature required to produce hydrogen. Furthermore, the water gas shift reaction (H ₂ O + CO⇔CO ₂ + H ₂ ) is advantageous for the production of hydrogen at lower reforming temperatures, but it is not advantageous at normal reforming reaction temperatures, so more hydrogen Can be produced at lower reforming temperatures. Substantial amounts or all molecular hydrogen and carbon dioxide produced by the second reformer are fed to the molten carbonate fuel cell.

  The methods described herein allow liquid fuel to be utilized. The use of liquid fuel allows one fuel to be used for multiple power sources. For example, diesel fuel could be used on board to power a molten carbonate fuel cell and engine. Hydrogen is added to the first reformer by mixing the anode exhaust with the liquid feed fuel. Hydrogen recycling eliminates the need for a separate hydrogen source for the pyrolysis of liquid feed fuel. Some hydrogen is consumed, but hydrogen is generated by reforming cracked hydrocarbons. Integration of the reformer and the high temperature hydrogen separator allows the system to generate substantially all the hydrogen needed for the process.

  Since the ratio of hydrogen to carbon is lower in the case of fuels having a carbon number greater than 6 (eg diesel and naphtha) than in the case of fuels having a carbon number less than 6 (eg methane) and Hydrocracking generates more carbon dioxide per mole of hydrogen produced. By generating more carbon dioxide per mole of hydrogen produced, substantially all or all of the carbon dioxide required for the molten carbonate fuel cell can be generated from the liquid fuel. Generating carbon dioxide in this manner eliminates the need to use part of the feed fuel gas as fuel for the anode gas and / or thermally inefficient combustion burner to generate carbon dioxide or It can be reduced. In the methods described herein, excess hydrogen and carbon dioxide are generated that allow hydrogen and carbon dioxide to be recycled through the system.

The method of the present invention allows a molten carbonate fuel cell to be operated at a pressure of 0.1 MPa (1 atm) or less, a power density of at least 0.12 W / cm ² and / or a battery voltage of at least 800 mV. I will provide a. In some embodiments, the method of the present invention allows a molten carbonate fuel cell to be operated at a pressure of 0.1 MPa (1 atm) or less, a power density of at least 0.12 W / cm ² and Providing a battery voltage of at least 800 mV.

  As used herein, the term “hydrogen” means molecular hydrogen unless otherwise specified.

  As used herein, the term “hydrogen source” means a compound capable of generating free hydrogen. For example, the hydrogen source may be a hydrocarbon such as methane, or a mixture of such compounds, or a hydrocarbon-containing mixture such as natural gas.

  As used herein, when two or more elements are described as “operably connected” or “operably linked”, the elements are directly or between the elements. Defined as being directly or indirectly coupled to allow indirect fluid flow. The term “fluid flow”, as used herein, means a gas or fluid flow. As used in the definition of “operably connected” or “operably linked”, the term “indirect fluid flow” refers to the flow of fluid or gas between two defined elements. Means that one or more other elements may be guided to change one or more conditions of the fluid or gas when the fluid or gas flows between the two defined elements . Fluid or gas conditions that can be altered in indirect fluid flow are physical properties such as the temperature or pressure of the gas or fluid, and / or, for example, by separating components of the gas or fluid, or For example, the composition of the gas or fluid by condensing water from the gas stream it contains. “Indirect fluid flow”, as defined herein, refers to a gas or gas between two defined elements by chemical reaction of one or more elements of the fluid or gas, eg, oxidation or reduction. Exclude changing the composition of the fluid.

  As used herein, the term “selectively permeable to hydrogen” is permeable to molecular hydrogen or elemental hydrogen and is at most 10% of a non-hydrogen element or compound. Or impervious to other elements or compounds that can permeate those that are permeable to molecular hydrogen or elemental hydrogen, or at most 5%, or at most 1% The

  As used herein, the term “hot hydrogen separator” refers to the separation of molecular or elemental hydrogen from a gas stream at a temperature of at least 250 ° C. (eg, a temperature from 300 ° C. to 650 ° C.). It is defined as a device or instrument that is effective for.

  As used herein, “single pass hydrogen utilization”, which refers to the utilization of hydrogen in fuel in a molten carbonate fuel cell, is relative to the total amount of hydrogen in the fuel input to the fuel cell in that passage. Defined as the amount of hydrogen in the fuel utilized to generate electricity in a single pass to the molten carbonate fuel cell. Single pass hydrogen utilization measures the amount of hydrogen in the fuel supplied to the anode of the fuel cell, measures the amount of hydrogen in the anode exhaust of the fuel cell, and measures the hydrogen in the anode exhaust of the fuel cell The amount of hydrogen used in the fuel cell is determined by subtracting the amount from the measured amount of hydrogen in the fuel supplied to the fuel cell, and the calculated amount of hydrogen used in the fuel cell is calculated in the fuel supplied to the fuel cell. It can be calculated by dividing by the measured amount of hydrogen. The single pass hydrogen utilization may be expressed as a percentage by multiplying the calculated single pass hydrogen utilization by 100.

As used herein, “excess carbon dioxide” means the value of the difference between the partial pressures of carbon dioxide at the anode and cathode of the molten carbonate fuel cell (ΔP _CO2 ). “Excess carbon dioxide” (ΔP _CO2 ) measures the partial pressure of carbon dioxide in the anode exhaust and cathode exhaust at the anode and cathode outlet, respectively, and the measured carbon dioxide partial pressure value at the anode is measured at the cathode. Calculation is performed by subtracting from the carbon partial pressure value (for example, ΔP _CO2 = (P _CO2 ^c ) − (P _CO2 ^a )). For counter-current feed to the anode and cathode, “excess carbon dioxide” measures the partial pressure of carbon dioxide in the anode exhaust and cathode exhaust at the anode outlet and cathode inlet, and the measured carbon dioxide content at the anode. The pressure value is calculated by subtracting from the measured value of carbon dioxide partial pressure at the cathode (eg, ΔP _CO2 = (P _CO2 ^cinlet )-(P _CO2 ^outlet )). The average excess carbon dioxide is calculated by the following formula:

ΔP _{CO2 (avg)} = [{P _CO2 ^cinlet + P _CO2 ^outlet } − {P _CO2 ^ainlet + P _CO2 ^outlet }] / 2
“Local excess carbon dioxide” is the value of the difference in partial pressure of carbon dioxide in a molten carbonate fuel cell per percent hydrogen utilization over a standardized distance when symmetry in the y direction (width) is estimated (ΔP _{CO2 (local )} ) Means. Local excess carbon dioxide is calculated by ΔP _CO2 (x) = (P _CO2 ^c ) (x) − (P _CO2 ^a ) (x), where x is the normalized distance along the length of the anode compartment.

  1-3 shows a schematic diagram of an embodiment of the system of the present invention for carrying out the method according to the present invention for operating a molten carbonate fuel cell generating electricity. The fuel cell system 10 includes a molten carbonate fuel cell 12, a first reformer 14, a second reformer 16, a high-temperature hydrogen separator 18 and an oxidation unit 20. In a preferred embodiment, the second reformer 16, high temperature hydrogen separator 18, and oxidation unit 20 are one unit. In a preferred embodiment, the oxidation unit 20 is a catalytic partial oxidation reformer. In one embodiment, the high temperature hydrogen separator 18 is a molecular hydrogen membrane separator. In one embodiment, the second reformer 16 includes a reforming zone, a high temperature hydrogen separator 18, a catalytic partial oxidation reformer 20, and a heat exchanger 22. The thermally integrated system provides sufficient hydrogen and carbon dioxide for continuous operation of the molten carbonate fuel cell to generate electricity.

  The molten carbonate fuel cell 12 includes an anode 24, a cathode 26 and an electrolyte 28. Electrolyte 28 is placed between and in contact with anode 24 and cathode 26. The molten carbonate fuel cell 12 may be a conventional molten carbonate fuel cell and preferably has a tube or planar shape. Molten carbonate fuel cell 12 may include a plurality of individual fuel cells stacked together. The individual fuel cells are electrically connected by an interconnect and operate to allow one or more gas streams to flow through the anode of the stacked fuel cell and an oxidant-containing gas to flow through the cathode of the stacked fuel cell. It may be connected as possible. As used herein, the term “molten carbonate fuel cell” refers to a single molten carbonate fuel cell or a plurality of operably connected or stacked molten carbonate fuel cells. Defined. The anode 24 of the molten carbonate fuel cell 12 is an anode of a porous sintered nickel compound, a nickel-chromium alloy, nickel and / or nickel-copper alloy containing lithium-chromium oxide, or a molten carbonate fuel cell. It may be formed from any material suitable for use. The cathode 26 of the molten carbonate fuel cell 12 is formed from a porous sintered material such as nickel oxide, lithium-nickel-iron oxide, or any material suitable for use as the cathode of a molten carbonate fuel cell. May have been.

  In order to supply the reactants necessary to generate electricity in the fuel cell 12, a gas stream is supplied to the anode and cathode. A hydrogen-containing stream enters anode 24 and an oxidant-containing gas stream enters cathode 26. The electrolyte portion 28 prevents the hydrogen-containing gas stream (s) from entering the cathode and the oxidant-containing gas stream (s) —the oxygen and carbon dioxide streams—in the fuel cell to prevent them from entering the anode. Is placed in. The oxidant-containing gas stream (s) includes one or more streams comprising oxygen and / or carbon dioxide.

  The electrolyte portion 28 conducts carbonate ions from the cathode to the anode for electrochemical reaction with hydrogen at one or more anode electrodes and, optionally, an oxidizable compound in an anode gas stream such as carbon monoxide. The electrolyte portion 28 may be formed from a molten salt of alkali metal carbonate, alkaline earth metal carbonate, or a combination thereof. Examples of the electrolyte material include porous materials formed from lithium sodium carbonate, lithium carbonate, sodium carbonate, lithium sodium barium carbonate, lithium sodium calcium carbonate, and lithium potassium carbonate.

  The fuel cell 12 is configured to allow a hydrogen-containing gas stream or streams to flow from the anode inlet 30 through the anode 24 and out of the anode exhaust outlet 32. The hydrogen-containing gas stream contacts one or more anode electrodes that span the anode path length from the anode inlet 30 to the anode exhaust outlet 32.

  In one embodiment, a gas stream comprising molecular hydrogen, hereinafter a “hydrogen-containing stream” or hydrogen source, is supplied to the anode inlet 30 via line 34. Metering valve 36 can be used to select and control the flow rate of the hydrogen-containing stream to anode inlet 30. In a preferred embodiment, hydrogen is supplied to the anode 24 of the fuel cell 12 from a high temperature hydrogen separator 18 which is a membrane unit as will be described in detail below. In one embodiment, the hydrogen-containing gas stream is at least 0.6, or at least 0.7, or at least 0.8, or at least 0.8, or at least 0.9, or at least 0.95, or at least 0. It may contain 98 mole fraction of hydrogen.

  The gas supplied to the cathode contains an oxidant. As referred to herein, “oxidizer” means a compound capable of being reduced by interaction with molecular hydrogen. In some embodiments, the oxidant-containing gas supplied to the cathode comprises oxygen, carbon dioxide, an inert gas, or a mixture thereof. In one embodiment, the oxidant-containing gas is an oxygen-containing gas stream and a carbon dioxide-containing gas stream, or a combination of oxygen / carbon dioxide-containing streams. In a preferred embodiment, the oxidant-containing gas supplied to the cathode is air or oxygen-enriched air mixed with sufficient carbon dioxide such that the molar ratio of carbon dioxide to oxygen is at least 2 or at least 2.5. is there.

  The oxidant-containing gas may flow from the cathode inlet 38 through the cathode 26 and then out through the cathode exhaust outlet 40. The oxidant-containing gas contacts one or more cathode electrodes that span the cathode path length from the cathode inlet 38 to the cathode exhaust outlet 40. In one embodiment, the oxidant-containing gas may flow counter-currently to the hydrogen-containing gas stream that flows to the anode 24 of the fuel cell 12.

  In one embodiment, the oxidant-containing gas stream is supplied from the oxidant-containing gas source 42 via line 44 to the cathode inlet 38. Metering valve 46 can be used to select and control the rate at which the gas stream is supplied to cathode 26. In some embodiments, the oxidant-containing gas is supplied by an air compressor. The oxidant-containing gas stream may be air. In one embodiment, the oxidant-containing gas may be pure oxygen. In one embodiment, the oxidant-containing gas stream may be carbon dioxide enriched air comprising oxygen and / or at least 13 wt% oxygen and / or at least 26 wt% carbon dioxide. In preferred embodiments, the flow of air and / or carbon dioxide is controlled such that the molar ratio of carbon dioxide to molecular oxygen in the air is at least 2 or at least 2.5.

  In one embodiment, the oxidant-containing gas stream is supplied by a carbon dioxide-containing gas stream and an oxygen-containing gas stream. The carbon dioxide stream and the oxygen-containing gas stream may be provided by two separate sources. In a preferred embodiment, most or substantially all of the carbon dioxide for the molten carbonate fuel cell 12 is derived from a hydrocarbon stream comprising hydrocarbons fed to the first reformer 14. A carbon dioxide containing gas stream is supplied from a carbon dioxide source via line 44 to cathode inlet 38. The carbon dioxide-containing gas stream supplied to the fuel cell 12 may be supplied to the same cathode inlet 38 as the oxygen-containing gas stream, or may be mixed with the oxygen-containing gas stream before being supplied to the cathode inlet 38. Alternatively, the carbon dioxide containing gas stream may be supplied to the cathode 26 via a separate cathode inlet.

  In a preferred embodiment, the carbon dioxide stream is supplied from the hot hydrogen separator 18 via lines 48 and 44 to the cathode 26 of the fuel cell 12 as described herein. Oxygen is supplied to the cathode 26 of the fuel cell 12 via a conduit 44.

  The gas supplied to the cathode and / or the anode, regardless of whether it is a single flow or a plurality of flows, preferably exits from the cathode exhaust port 40 and is connected to the heat exchanger 22 via the conduit 50. By exchanging heat with the oxygen-depleted cathode exhaust stream, it can be heated in heat exchanger 22 or other heat exchanger before being supplied to cathode 26 and / or anode 24.

In the method of the present invention, the hydrogen-containing gas stream (s) is mixed with an oxidant at one or more anode electrodes of the molten carbonate fuel cell 12 to generate electricity. The oxidant is preferably carbonic acid obtained by the reaction of carbon dioxide and oxygen flowing through the cathode 26 and carried across the fuel cell electrolyte. As discussed in more detail below, the hydrogen-containing gas stream and / or oxidant are fed to the fuel cell at a selected independent rate by supplying the hydrogen-containing gas stream and / or oxidant-containing gas stream to the anode of the fuel cell 12. In one or more anode electrodes. Hydrogen-containing gas stream and the oxidizing agent is preferably mixed in one or more anode electrodes of the fuel cell, at least 0.1W absolute pressure of 1 bar / cm ^2, or at least 0.15 W / cm ^2, or at least 0, .2W / cm ^2, or at least 0.3 W / cm ^2, or to generate electricity at least 0.6 W / cm ² power density. Higher power density can be obtained at higher pressures and / or by using an enriched oxidant-containing gas stream (eg, enriched air).

  Molten carbonate fuel cell 12 is operated at a temperature effective to allow carbon dioxide to traverse electrolyte section 28 from cathode 26 to anode 24. The molten carbonate fuel cell 12 can be operated at temperatures from 550 ° C to 700 ° C, or from 600 ° C to 650 ° C. The oxidation of hydrogen by carbonic acid at one or more anode electrodes is an exothermic reaction. The heat of reaction generates heat necessary for operating the molten carbonate fuel cell 12. The temperature at which the molten carbonate fuel cell is operated can be controlled by several factors including, but not limited to, adjusting the supply temperature and flow rate of the hydrogen-containing gas and oxidant-containing gas. Since hydrogen utilization is minimized, excess hydrogen is fed to the system, and unreacted hydrogen carries excess heat to the first reformer, partially forming the molten carbonate fuel cell. Can be cooled to. Adjusting the flow rate of the carbon dioxide stream and / or the oxidant-containing stream to maintain a molar ratio of carbon dioxide to molecular oxygen of about 2 requires reacting with some of the hydrogen utilized at the anode. Sufficient oxidant-containing gas is required to achieve an excess of molecular oxygen of about 1.3-2.0 times the amount. Accordingly, excess oxygen-depleted air or oxidant-containing gas exiting the cathode exhaust can carry significant heat from the molten carbonate fuel cell. The temperature of the hydrogen-containing stream described below that is supplied from the high temperature hydrogen separator 18 to the anode 24 of the molten carbonate fuel cell 12 is heat recovered (e.g., heat Can be reduced by means of the exchanger 22). The temperature of the high pressure carbon dioxide stream described below that is supplied from the high temperature hydrogen separator 18 to the cathode 26 of the molten carbonate fuel cell 12 is heat recovered (e.g., By the heat exchanger 22). The temperature of the effluent stream generated from the catalytic partial oxidation reformer 20 can be reduced by heat recovery (eg, by heat exchanger 22) before being fed to the cathode of the molten carbonate fuel cell. Waste heat from the fuel cell can be used to heat one or more streams utilized in the system. If necessary, the temperature of the molten carbonate fuel cell can be controlled using any auxiliary system for cooling molten carbonate fuel known in the art.

  In one embodiment, the oxidant-containing gas stream (s) supplied to the cathode may be heated to a temperature of at least 150 ° C. or 150 ° C. to 350 ° C. before being supplied to the cathode 26. In one embodiment, when using an oxygen-containing gas, the temperature of the oxygen-containing gas stream is controlled to a temperature from 150 ° C to 350 ° C.

  To begin operation of the fuel cell 12, the fuel cell is heated to its operating temperature, that is, a temperature sufficient to melt the electrolyte salt to allow carbonate ion flow. As shown in FIG. 1, the molten carbonate fuel cell 12 is operated by generating a hydrogen-containing gas stream in the catalytic partial oxidation reforming apparatus 20, and the hydrogen-containing gas stream via the pipes 52 and 34. It can be started by feeding the anode 24 of the fuel cell.

  The hydrogen-containing gas stream may be a hydrocarbon stream containing hydrocarbons described below in a catalytic partial oxidation reformer 20 in the presence of a conventional partial oxidation catalyst, or a different hydrocarbon stream, for example a fuel stream rich in natural gas. And the amount of oxygen in the oxidant-containing gas supplied to the catalyst partial oxidation reforming device 20 can be generated in the catalyst partial oxidation reforming device 20 by burning the oxidant-containing gas. Less than stoichiometric with respect to the amount of hydrocarbon in the hydrocarbon stream. The flow rate of the hydrogen-containing gas stream can be controlled by the valve 60.

  As shown in FIG. 2, a hydrogen-containing gas stream is generated in the oxidation unit 20, and the hydrogen-containing gas stream is supplied to the anode 24 of the molten carbonate fuel cell via lines 96, 104, and 34, thereby providing fuel. The battery is heated to its operating temperature. The rate at which the hydrogen-containing gas stream is supplied from the oxidation unit 20 via lines 96 and 104 to the anode 24 is controlled by the three-way valve 102. A portion of the heat from the hydrogen-containing gas stream passes through heat exchanger 98 via line 96 and includes hydrocarbons including hydrocarbons that enter first reformer 14 and / or the first reformer. Heat can be supplied to the stream.

  With reference to FIGS. 1 and 2, the fuel supplied to the catalytic partial oxidation reformer 20 may be a liquid or gaseous hydrocarbon or a mixture of hydrocarbons, preferably supplied to the first reformer 14. Same as hydrocarbon stream containing hydrocarbons. The fuel can be supplied to the catalytic partial oxidation reforming apparatus 20 via the pipe line 62. In one embodiment, the fuel supplied to the catalytic partial oxidation reformer 20 is rich in natural gas and / or hydrogen from the hydrogen source 64.

  The oxidant supplied to the catalyst partial oxidation reformer 20 may be pure oxygen, air, or oxygen-enriched air (hereinafter “oxidant-containing gas”). Preferably, the oxidant-containing gas is air. The oxidant should be supplied to the catalytic partial oxidation reforming apparatus 20 such that the amount of oxygen in the oxidant is less than the stoichiometric amount relative to the hydrocarbons supplied to the catalytic partial oxidation reforming. In a preferred embodiment, the oxidant-containing gas is supplied from the oxidant source 42 to the catalytic partial oxidation reformer 20 via the pipeline 56. The valve 58 can control the rate at which the oxidant-containing gas (air) is supplied to the catalytic partial oxidation reformer 20 and / or the cathode 26 of the fuel cell 12. In one embodiment, the oxidant-containing gas entering the catalytic partial oxidation reformer 20 can be heated by exchanging heat with the oxygen-depleted cathode exhaust stream exiting the cathode exhaust 40.

  In the catalytic partial oxidation reforming apparatus 20, by burning hydrocarbons and an oxidant in the presence of a normal partial oxidation catalyst, a hydrogen-containing gas stream is generated, and the oxidant is in a stoichiometric amount with respect to the hydrocarbon. It is as follows. The hydrogen-containing gas stream produced by contacting the hydrocarbon and oxidant in the catalytic partial oxidation reformer 20 includes a compound that can be oxidized at the anode 24 of the fuel cell by contact with carbonate ions at one or more anode electrodes. . The hydrogen-containing gas stream from the catalytic partial oxidation reformer 20 is preferably free of compounds that oxidize one or more anode electrodes at the anode 24 of the fuel cell 12.

  The hydrogen-containing gas stream produced in the catalytic partial oxidation reformer 20 may be hot and have a temperature of at least 700 ° C, or from 700 ° C to 1100 ° C, from 800 ° C to 1000 ° C. Using the hot hydrogen gas stream from the catalytic partial oxidation reformer 20 to initiate the start of the molten carbonate fuel cell 12 raises the temperature of the fuel cell almost instantaneously to the operating temperature of the fuel cell. This is preferable in the method of the present invention. In one embodiment, when starting operation of the fuel cell, heat is exchanged in the heat exchanger 22 between the hot hydrogen-containing gas from the catalytic partial oxidation reforming apparatus 20 and the oxidant-containing gas supplied to the cathode 26. can do.

  Referring to FIG. 1, the hydrogen-containing gas stream is supplied into the anode 24 by opening the valve 36, and at the same time, the flow rate of the hot hydrogen-containing gas stream from the catalytic partial oxidation reforming apparatus 20 into the fuel cell 12 is controlled by the valve 60. Can be used to adjust. The flow of the hydrogen-containing gas stream from the high-temperature hydrogen separator 18 is simultaneously reduced or stopped at the flow rate of the hydrocarbon feed via the line 62 and the oxidant feed via the line 56 to the catalytic partial oxidation reformer 20. After starting, the valve 60 can be closed.

  Referring to FIG. 2, the hydrogen-containing gas flow is supplied into the anode 24 by opening the valve 36, and at the same time, into the fuel cell 12 via the pipe 96 of the hot hydrogen-containing gas flow from the catalytic partial oxidation reformer 20. Can be adjusted using the three-way metering valve 102. Reduce or stop the flow of hydrocarbon feed through line 62 and oxidant feed through line 56 to catalytic partial oxidation reformer 20 and simultaneously generate a hydrogen-containing gas stream from hot hydrogen separator 18. After that, the valve 102 can be closed. Next, continuous operation of the fuel cell can be carried out by the method of the present invention.

  The three-way metering valve 102 controls the flow rate of the effluent from the catalytic partial oxidation reformer 20 to the anode 24 or the cathode 26. At start-up, the effluent from the catalytic partial oxidation reformer 20 is rich in hydrogen, so that the effluent passes through the heat exchanger 98 via line 96 and then to the anode 24 via line 104. It is burned. If the catalytic partial oxidation reformer 20 is used to generate carbon dioxide for the cathode 26 after start-up has started, the metering valve 102 is connected to the catalytic partial oxidation reformer to the cathode 26 via line 96. Control the flow of effluent from 20.

  In another embodiment, the operation of the fuel cell is performed by a starter heater to bring the fuel cell to its operating temperature before introducing a hydrogen-containing gas stream via line 66 into the fuel cell 12, as shown in FIG. A hydrogen starting gas stream from a hydrogen source 64 that can be passed through (not shown) can be used. The hydrogen source 64 may be a storage tank that can receive hydrogen from the hot hydrogen separator 18. A hydrogen source can be operatively connected to the fuel cell to allow introduction of a hydrogen starting gas stream to the anode of the molten carbonate fuel cell. The starter heater can indirectly heat the hydrogen starter gas stream to a temperature from 750 ° C to 1000 ° C. Alternatively, the starter heater may supply hydrogen due to incomplete combustion of hydrogen from the hydrogen source 64 supplied to the heater. The starter heater may be an electric heater or a combustion heater. After reaching the operating temperature of the fuel cell, the flow of hydrogen starting gas flow into the fuel cell can be stopped by a valve, and the hydrogen generator valve to the fuel cell anode can be turned on to start the fuel cell operation. By opening it, a hydrogen-containing gas stream can be introduced into the fuel cell.

  In one embodiment, the first reformer 14 includes a catalytic partial oxidation reformer that is used to supply hydrogen to the molten carbonate fuel cell at startup. The first reformer 14 is used for autothermal reforming and then for steam reforming when the molten carbonate fuel cell reaches operating temperature. It may contain one or more catalyst beds that make it possible.

  When the fuel cell 12 starts operation, the cathode 26 and the anode 24 emit exhaust gas. The exhaust from the cathode 26 and the anode 24 is hot, and the heat from the exhaust is thermally integrated with other units to remove all the fuel (hydrogen) and oxidant (carbonate ions) necessary for fuel cell operation. Forms a thermally integrated system that yields.

  As shown in FIGS. 1 and 2, the method described herein includes a thermally integrated hydrogen separator 18, a molten carbonate fuel cell 12, a first reformer 14, and a second reformer. A system is utilized that includes the apparatus 16 as well as the catalytic partial oxidation reformer 20 in some embodiments. The high temperature hydrogen separator 18 includes one or more high temperature hydrogen separation membranes 68 and is operatively coupled to the molten carbonate fuel cell 12. The high-temperature hydrogen separator 18 supplies a hydrogen-containing gas stream containing mainly molecular hydrogen to the anode 24 of the fuel cell 12, while the exhaust from the anode of the molten carbonate fuel cell 12 is the first reformer. 14. The first reformer 14 and the second reformer 16 may be one unit or two units operably connected. The first reformer 14 and the second reformer 16 may include one or more reforming zones. In one embodiment, the first reformer 14 and the second reformer 16 are a single unit that includes a first reformer zone and a second reformer zone.

  A hydrocarbon stream containing hydrocarbons is supplied to the first reformer 14 via line 62 and the anode exhaust is mixed with the hydrocarbons. The process is thermally integrated, and heat for promoting the endothermic reforming reaction in the first reformer 14 is supplied from the anode exhaust of the exothermic molten carbonate fuel cell 12 to the first. It is fed directly into the reformer and / or with the hydrocarbons in the hydrocarbon stream fed to the first reformer. In one embodiment, a portion of the heat from the anode exhaust is mixed with the hydrocarbon in the first reformer or in a heat exchanger operatively connected thereto. As shown in FIG. 2, additional heat to the first reformer 14 can be supplied from the heat outflow from the catalytic partial oxidation reformer 20. In the first reformer 14, at least a portion of the hydrocarbons of the hydrocarbon stream is cracked and / or reformed and supplied to the second reformer 16 via line 70. Is generated.

  The second reformer 16 is operably connected to the high temperature hydrogen separator 18, which is at least a portion of the hydrogen-containing gas entering the anode 24 of the molten carbonate fuel cell 12, a large amount. Produce at least 75% or at least 90% or substantially all by volume. The high-temperature hydrogen separator can be disposed after the second reformer 16 and before the molten carbonate fuel cell 12. In a preferred embodiment, the high temperature hydrogen separator 18 is a membrane separation unit that is part of the second reformer 16. The high temperature hydrogen separator 18 separates hydrogen from the reformed product. The separated hydrogen is supplied to the anode 24 of the molten carbonate fuel cell 12.

  In one embodiment of the method, the hydrocarbon stream is liquid at 20 ° C. at atmospheric pressure (optionally oxygenated) and volatile at temperatures up to 400 ° C. at atmospheric pressure. Including any volatile hydrocarbons. Such hydrocarbons may include, but are not limited to, petroleum fractions such as naphtha, diesel, jet fuel, gas oil and kerosene having a boiling range from 50 ° C to 360 ° C. In one embodiment, the hydrocarbon stream is decane. In a preferred embodiment, the hydrocarbon stream is diesel fuel. In one embodiment, the hydrocarbon stream comprises hydrocarbons having a carbon number in the range of 5 to 25. In preferred embodiments, the hydrocarbon stream comprises at least 0.5 or at least 0.6 or at least 0.7 or at least 0.8 mole fraction comprising at least 5 or at least 6 or at least 7 carbon atoms. Contains hydrocarbons.

  The hydrocarbon stream optionally includes some hydrocarbons that are gaseous at 25 ° C., such as methane, ethane, propane, or other compounds that contain 1 to 4 carbon atoms that are gaseous at 25 ° C. May be. The hydrocarbon stream is used to remove any material that may poison the catalyst used in the first reformer for the conversion of high molecular weight hydrocarbons to low molecular weight hydrocarbons. The first reformer 14 may be supplied and / or processed before being heated in the heat exchanger 72. For example, the hydrocarbon stream may have undergone a series of treatments to remove metals, sulfur and / or nitrogen compounds.

  In one embodiment of the method, the hydrocarbon stream is mixed with natural gas comprising at least 20% by volume or at least 50% by volume or at least 80% by volume carbon dioxide. When necessary, natural gas was processed to remove hydrogen sulfide. In one embodiment, a hydrocarbon stream having at least 20% by volume carbon dioxide, at least 50% by volume carbon dioxide, or at least 70% by volume carbon dioxide can be used as a fuel source.

  In one embodiment, the hydrocarbon stream can be fed to the first reformer 14 at a temperature of at least 150 ° C., preferably from 200 ° C. to 400 ° C., and the hydrocarbon stream is heated as described below. It can be heated to the desired temperature in the exchanger. The temperature at which the hydrocarbon stream is fed to the first reformer 14 can be selected to be as high as possible to evaporate the hydrocarbons without producing coke. The temperature of the hydrocarbon stream may be in the range from 150 ° C to 400 ° C. Alternatively, although less preferred, the hydrocarbon stream may be directly fed to the first reformer 14 at a temperature below 150 ° C., for example, without heating the hydrocarbon stream, if the sulfur content of the hydrocarbon stream is low. Can be supplied.

  As shown in FIG. 1, a hydrocarbon stream can be passed through one or more heat exchangers 72 to heat the feed. The hydrocarbon stream can be heated by exchanging heat with the cathode exhaust stream separated from the cathode of the molten carbonate fuel cell 12 and fed to the heat exchanger 72 via line 74. The rate at which the cathode exhaust stream is supplied to heat exchangers 72 and 22 can be controlled by adjusting metering valves 76 and 78.

  In a preferred embodiment, the separated anode exhaust stream is fed via line 80 to one or more reforming zones of the first reformer 14. The rate at which the anode exhaust stream is supplied to the first reformer 14 can be controlled by adjusting the metering valve 82. The temperature of the anode outlet can range from about 500 ° C. to about 700 ° C., preferably about 650 ° C.

  The anode exhaust stream contains hydrogen, water vapor, and reaction products and unreacted fuel from the oxidation of the fuel supplied to the anode 24 of the fuel cell 12. In one embodiment, the anode exhaust stream comprises at least 0.5 or at least 0.6 or at least 0.7 mole fraction of hydrogen. Hydrogen in the anode exhaust stream supplied to the first reformer 14 or the reformer zone of the first reformer can help prevent coke formation in the first reformer. In one embodiment, the anode exhaust stream comprises 0.0001 to about 0.3 or 0.001 to about 0.25 or 0.01 to about 0.2 mole fraction of water (as water vapor). In addition to hydrogen, water vapor present in the anode exhaust stream supplied to the first reformer 14 or the reformer zone of the first reformer also helps to prevent coke formation in the first reformer. Can be. The anode exhaust stream may contain sufficient hydrogen to inhibit coking and sufficient water vapor to reform most of the hydrocarbons in the hydrocarbon stream to methane, hydrogen and carbon monoxide. Accordingly, less steam may be required to reform the hydrocarbons in the first reformer and / or the second reformer.

  In some cases, the steam is first reformer 14 or first reformer via line 84 for mixing with the hydrocarbon stream in the first reformer or reforming zone of the first reformer. You may supply to the reforming zone of an apparatus. The first reformer 14 is used to suppress or prevent coke formation in the first reformer and optionally in the reforming reaction that takes place in the first reformer. Alternatively, it may be supplied to the reforming zone of the first reformer. In one embodiment, the steam has a molar ratio of total steam added to the first reformer that is at least twice or at least three times the moles of carbon in the hydrocarbon stream added to the first reformer. , Supplied at a rate to the first reformer 14 or the reforming zone of the first reformer. The total water vapor added to the first reformer may include water vapor from the anode exhaust, for example, water vapor from an external source via line 84 or a mixture thereof. At least 2: 1 or at least 2.5: 1 or at least 3: 1 or at least 3.5 of steam and carbon in the hydrocarbon stream in the first reformer 14 or the reforming zone of the first reformer. Preparing a molar ratio of 1 is useful for suppressing coke formation in the first reformer. The metering valve 86 can be used to control the rate at which steam is supplied to the first reformer 14 or the reformer zone of the first reformer via line 84. Since the anode exhaust contains a significant amount of hydrogen, less coking tends to occur during reforming. Therefore, the amount of water vapor supplied to the first reformer 14 may be significantly less than the amount of water vapor used in a conventional reforming unit.

  The steam may be supplied to the first reformer 14 at a temperature of at least 125 ° C., preferably 150 ° C. to 300 ° C., and may have a pressure of 0.1 MPa to 0.5 MPa, preferably , Having a pressure that is equal to or less than the pressure of the anode exhaust stream supplied to the first reformer as described herein. Steam can be generated by heating high pressure water having a pressure of at least 1.0 MPa, preferably 1.5 MPa to 2.0 MPa by passing the high pressure water through line 88 and through heat exchanger 90. it can. The high pressure water is heated by exchanging heat with the supplied cathode exhaust after the cathode exhaust feed has passed through the heat exchanger 72 via line 74 to produce high pressure steam. Alternatively, the cathode exhaust may be fed directly to heat exchanger 90 (not shown) or to one or more heat exchangers. When heat exchanger 90 or a plurality of heat exchangers are utilized, high pressure steam can be supplied to line 84 via line 92 after exiting the final heat exchanger. The high pressure steam can be depressurized to the desired pressure by expanding the high pressure steam with an expansion device and then fed to the first reformer. Alternatively, the steam is generated for use in the first reformer 14 by supplying low pressure water to one or more heat exchangers 90 and passing the resulting steam through the first reformer. be able to.

  In some cases, high pressure steam that is not utilized in the first reformer 14 or the second reformer 16 may be other, such as a turbine, with or without any unused high pressure carbon dioxide stream. Through a power generation device (not shown). The power source may be used to generate electricity and / or in addition to the electricity generated by the fuel cell 12. The power generated by the power source and / or fuel cell can be used to power the compressor 94 and / or any other compressor used in the method of the present invention.

  The hydrocarbon stream, optionally steam and the anode exhaust stream are mixed to evaporate any hydrocarbons that are not in the form of steam in the first reformer 14 or the reforming zone of the first reformer, and remove the hydrocarbons. Contact with the reforming catalyst at a temperature effective to decompose to produce feed fuel.

  The reforming catalyst may be a conventional reforming catalyst, and may be any reforming catalyst known in the art. Common reforming catalysts that can be used include, but are not limited to, Group VIII transition metals, particularly nickel, and supports or substrates that are inert under high temperature reaction conditions. Inert compounds suitable for use as a support for the high temperature reforming / hydrocracking catalyst include, but are not limited to, α-alumina and zirconia.

  In a preferred embodiment, the hydrocarbon stream, anode exhaust, and optional steam are mixed and contacted with the catalyst at a temperature of about 500 ° C. to about 650 ° C. or about 550 ° C. to 600 ° C., as required for the reforming reaction. All heat is supplied by the anode exhaust. In one embodiment, the hydrocarbon stream, optional steam and anode exhaust stream are mixed and contacted with the catalyst at a temperature of at least 400 ° C. or 450 ° C. to 650 ° C. or 500 ° C. to 600 ° C.

  The heat supplied from the anode exhaust stream supplied from the exothermic molten carbonate fuel cell 12 to the first reformer 14 or the reforming zone of the first reformer is the endothermic in the first reformer. Promotes sexual degradation and reforming reactions. The anode exhaust stream fed from the molten carbonate fuel cell 12 to the first reformer 14 and / or the reformer zone of the first reformer is very hot and has a temperature of at least 500 ° C. It typically has a temperature from 550 ° C to 700 ° C or from 600 ° C to 650 ° C. Thermal energy from the fuel cell is included in the anode exhaust stream and the first exhaust reformer 14 or the reformer of the first reformer is reformed by direct mixing of the anode exhaust stream with the hydrocarbon stream and steam. Heat from the molten carbonate fuel cell 12 to the first reformer 14 or the reformer zone of the first reformer as it travels to a mixture of hydrocarbon stream in the zone, optionally steam and anode exhaust stream Energy transfer is extremely efficient.

  In a preferred embodiment of the method described herein, the anode exhaust stream is at least 99% or substantially all of the heat required to produce a feed fuel from a mixture of hydrocarbon stream, optional water vapor and anode exhaust stream. Supply. In a particularly preferred embodiment, no heat source other than the anode exhaust stream is supplied to the first reformer 14 to convert the hydrocarbon stream to the feed fuel.

  In one embodiment, the pressure at which the anode exhaust stream, hydrocarbon stream and optional water vapor contact the reforming catalyst in the first reformer 14 may range from 0.07 MPa to 3.0 MPa. When high pressure steam is not supplied to the first reformer 14, the anode exhaust stream, hydrocarbon stream and optional low pressure steam are generally from 0.07 MPa to 0.5 MPa or from 0.1 MPa to 0.3 MPa. The lower limit of the range may be contacted with the reforming catalyst in the first reformer. When supplying high pressure steam to the first reformer 14, the anode exhaust stream, hydrocarbon stream and steam are generally in the pressure range from 1.0 MPa to 3.0 MPa or from 1.5 MPa to 2.0 MPa. The upper limit may be contacted with the reforming catalyst.

  Referring to FIG. 2, the first reformer 14 is higher than 630 ° C. or from 650 ° C. to 900 ° C. or by exchanging heat with the effluent from the catalytic partial oxidation reformer 20 via line 96. It can be heated to temperatures from 700 ° C to 800 ° C. Line 96 is operably connected to heat exchanger 98. The heat exchanger 98 may be part of the conduit 96. A heat exchanger 98 may be present in the first reformer 14 or connected to the first reformer so that heat can be exchanged with the hydrocarbon stream entering the first reformer. It may be. The rate at which the effluent from the catalytic partial oxidation reformer 20 is supplied to the first reformer 14 can be controlled by adjusting the metering valve 100 and the three-way metering valve 102.

  Contacting the hydrocarbon stream, steam, catalyst and anode exhaust stream in the first reformer 14 at a temperature of at least 500 ° C. or 550 ° C. to 950 ° C. or 600 ° C. to 800 ° C. or 650 ° C. to 750 ° C. As a result, at least a portion of the hydrocarbons are decomposed and / or reformed to produce a feed fuel. The cracking and / or reforming of the hydrocarbon in the hydrocarbon stream reduces the number of carbon atoms in the hydrocarbon compound in the hydrocarbon stream, thereby producing a reduced molecular weight hydrocarbon compound. In one embodiment, the hydrocarbon stream is converted to a hydrocarbon that is useful as a feed fuel to the second reformer 16 comprising at most 4, or at most 3, or at most 2 carbon atoms. It may contain hydrocarbons containing 5, at least 6 or at least 7 carbon atoms. In one embodiment, the hydrocarbons in the hydrocarbon stream comprise four or more mole fractions of feed fuel produced by the first reformer of 0.1 or less, 0.05 or less, or 0.01 or less. The reaction can be performed in the first reformer 14 or the reforming zone of the first reformer so as to include the hydrocarbon having the above carbon atoms. In one embodiment, the hydrocarbon in the hydrocarbon stream is at least 0.7 or at least 0.8 or at least 0.9 or at least 0.9 of the resulting hydrocarbon in the feed fuel produced from the hydrocarbon in the hydrocarbon stream. It can be cracked and / or reformed so that the 0.95 mole fraction is methane. In one embodiment, the average carbon number of hydrocarbons in the feed fuel that is at most 1.3, at most 1.2, or at most 1.1 due to cracking and / or reforming of hydrocarbons in the hydrocarbon stream. A feed fuel is produced.

  As described above, the hydrogen and steam from the anode exhaust stream and the steam when added to the first reformer 14 are in the first reformer when hydrocarbons are decomposed to produce feed fuel. Suppresses coke generation. In a preferred embodiment, the relative rates of feeding the anode exhaust stream, hydrocarbon stream and steam to the first reformer 14 are such that the hydrogen and steam in the anode exhaust stream and line 84 are passed to the first reformer. The added steam is selected to prevent coke formation in the first reformer.

  In one embodiment, contacting the hydrocarbon stream, steam and anode exhaust with the reforming catalyst in the first reformer 14 at a temperature of at least 500 ° C. or 550 ° C. to 700 ° C. or 600 ° C. to 650 ° C. As a result, reforming of the hydrocarbons in the hydrocarbon stream and the hydrocarbons in the feed fuel produced in the first reformer 14 also occurs to produce hydrogen and carbon oxide, especially carbon monoxide. The amount of reforming can be substantial, and the feed fuel produced by both cracking and reforming in the first reformer 14 or the reforming zone of the first reformer is at least 0.05, at least 0. .1 or at least 0.15 mole fraction of carbon monoxide.

  The temperature and pressure conditions in the first reformer 14 or the reforming zone of the first reformer are such that the feed fuel produced in the first reformer is gaseous at 20 ° C., and is generally 1 -4 can be selected to include light hydrocarbons containing 4 carbon atoms. In a preferred embodiment, hydrocarbons in the feed fuel produced by the first reformer (hereinafter “steam reformed feed fuel”) is at least 0.6 or at least 0.7 or at least 0.8 or at least 0. Contains 9 mole fraction of methane. The steam reforming feed also includes hydrogen from the anode exhaust stream and from the reformed hydrocarbon if further reforming occurs in the first reformer. The steam reforming feed fuel also includes steam from the anode exhaust stream, and optionally from the reformer steam feed fuel. A supply produced by the first reformer that is supplied to the second reformer 16 when substantial reforming occurs in the first reformer 14 or the reforming zone of the first reformer. The fuel can include carbon monoxide in addition to carbon dioxide.

  In the method of the present invention, the steam reforming supply fuel is supplied from the first reformer 14 to the second reformer 16 operatively connected to the first reformer via the pipeline 70. Is done. The steam reforming feed fuel exiting the first reformer 14 may have a temperature from 500 ° C. to 650 ° C. or from 550 ° C. to 600 ° C. The temperature of the steam reforming feed fuel that exits the first reformer 14 is obtained by exchanging heat in one or more heat exchangers 90 before being supplied to the second reformer 16. Before being supplied to the reformer 16. In some cases, the steam reforming feed fuel is not cooled before entering the second reformer. In an embodiment where the first reformer 14 is heated by another heat source (eg, steam and / or heat from the catalytic partial oxidation reformer 20, as shown in FIG. 2), the first reformer 14 The feed fuel exiting the quality device may have a temperature from 650 ° C. to 950 ° C. or from 700 ° C. to 900 ° C. or from 750 ° C. to 800 ° C.

  The steam reforming feed fuel exchanges heat with water supplied to the system, cools the feed fuel, and generates steam that can be fed to the first reformer 14 as described above. Can be cooled. When using multiple heat exchangers 90, steam reforming feed fuel and water / steam are fed in series with each of the heat exchangers, preferably countercurrent to cool the feed fuel and heat the water / steam can do. The steam reforming feed fuel can be cooled to a temperature of 150 ° C. to 650 ° C. or 150 ° C. to 300 ° C. or 400 ° C. to 650 ° C. or 450 ° C. to 550 ° C.

  The cooled steam reforming feed fuel can be fed from the heat exchanger 90 to the compressor 94, or in other embodiments can be fed directly to the second reformer 16. Alternatively, although less preferred, the steam reforming feed fuel that exits the first reformer 14 or the reforming zone of the first reformer is not cooled and is compressed by the compressor 94 or the second reformer 16. Can be supplied to. The compressor 94 is a compressor that can operate at a high temperature, and is preferably a commercially available StarRotor compressor. The steam reforming feed fuel may have a pressure of at least 0.5 MPa and a temperature from 400 ° C to 800 ° C, preferably from 400 ° C to 650 ° C. The steam reformed feed fuel is at least 0.5 MPa or at least 1.0 MPa or at least 1.5 MPa or at least 2 MPa or more by the compressor 94 to maintain sufficient pressure in the reforming zone 108 of the second reformer 16. It can be compressed to a pressure of at least 2.5 MPa or at least 3 MPa. In one embodiment, the steam reforming feed fuel is compressed to a pressure of 0.5 MPa to 6.0 MPa before feeding the feed fuel stream to the second reformer.

  The optionally compressed and optionally cooled steam reforming feed fuel comprising hydrogen, light hydrocarbons, steam and optionally carbon monoxide is supplied to the second reformer 16. The steam reforming feed fuel may have a pressure of at least 0.5 MPa and a temperature from 400 ° C to 800 ° C, preferably from 400 ° C to 650 ° C. In one embodiment, the temperature of the steam reforming feed fuel produced by the first reformer 14 is determined by circulating a portion of the feed fuel via heat exchangers 90 and / or 72, if necessary. It can be raised after leaving the compressor 94.

  In some cases, when necessary to reform the feed fuel, additional steam is modified in the second reformer 16 for mixing with the steam reformed feed fuel produced by the first reformer. It can be added to the mass zone 108. In the preferred embodiment, the additional water vapor injects high pressure water from the water inlet line 88 into the compressor 94 via line 110 for mixing with the feed fuel as it is compressed in the compressor. Can be added by. In one embodiment (not shown), the high pressure water can be injected into the feed fuel by mixing the high pressure water and the feed fuel in the heat exchanger 90. In other embodiments (not shown), the high pressure water may be injected into the feed fuel in line 110 before or after passing the feed fuel through the heat exchanger 90 or before or after passing the feed fuel through the compressor 94. it can. In one embodiment, high pressure water can be injected into line 70 or into compressor 94 or into heat exchanger 90, and neither a compressor nor a heat exchanger is included in the system.

  The high pressure water is heated by mixing with the steam reforming feed fuel to form steam, and the steam reforming feed fuel is cooled by mixing with water. The cooling provided to the steam reforming feed by the injected water eliminates or reduces the need for the heat exchanger 90, and preferably uses a large number of heat exchangers to cool the steam reforming feed. Is limited to one.

  Alternatively, although less preferred, the high pressure steam is in the reforming zone 108 of the second reformer 16 or in the conduit 70 to the second reformer so that it is mixed with the steam reforming feed fuel. Can be injected. The high-pressure steam is generated by heating the high-pressure water injected into the system via the water inlet line 88 in the heat exchanger 90 by exchanging heat with the fuel supplied from the first reformer 14. It may be. The high-pressure steam can be supplied to the second reformer 16 via the pipe line 112. The metering valve 114 can be used to control the flow rate of water vapor to the second reformer. The high-pressure steam may have a pressure that is similar to the pressure of the fuel supplied to the second reformer. Alternatively, the high pressure steam can be supplied to line 70 such that the feed fuel is mixed with the feed fuel before it is fed to the compressor 94, and thus the steam and feed fuel mixture is selected at a selected pressure. Can be compressed together. The high pressure steam may have a temperature from 200 ° C to 500 ° C.

  The rate at which high pressure water or high pressure steam is fed into the system is such that the amount of steam effective to optimize the reaction in the reformer for producing the hydrogen-containing gas stream is reduced to the first reformer 14 and / or. It can be selected and controlled to be supplied to the second reformer 16. The rate at which water vapor other than water vapor in the anode exhaust stream is supplied to the first reformer 14 can be adjusted by adjusting metering valves 116 and 118 that control the rate at which water is supplied to the system, This can be controlled by adjusting the metering valves 86, 120 and 114 that control the speed supplied to the first reformer 14 and the second reformer 16. Steam can be supplied to additional components in a system such as, for example, a turbine.

  When high pressure water is injected into the second reformer 16, the metering valves 114 and 120 can be adjusted to control the rate at which water is injected into the second reformer via line 112. When high pressure steam is injected into the second reformer 16 or line 70, the metering valves 114, 116 and 118 are adjusted to control the rate at which the steam is injected into the second reformer 16 or line 70. can do. The flow rate of water vapor can be adjusted to obtain a water vapor to carbon molar ratio of at least 2: 1 or at least 2.5: 1 or at least 3: 1 or at least 3.5: 1.

  The steam reformed fuel produced by the first reformer and optional additional steam are fed into the reforming zone 108 of the second reformer 16. The reforming zone may contain, preferably contain, the reforming catalyst therein. The reforming catalyst may be a conventional steam reforming catalyst and may be known in the art. Common steam reforming catalysts that can be used include, but are not limited to, Group VIII transition metals, particularly nickel. It is often desirable to support the reforming catalyst on a refractory substrate (or support). When used, the carrier is preferably an inert compound. Inert compounds suitable for use as carriers include, for example, Group III and IV elements of the periodic table such as oxides or carbides of Al, Si, Ti, Mg, Ce and Zr.

  The steam reforming feed fuel and optional additional steam are mixed and contacted with the reforming catalyst in the reforming zone 108 at a temperature effective to produce a reformed product gas comprising hydrogen and carbon oxide. The reformed product gas can be generated by steam reforming hydrocarbons in the supplied fuel. The reformed product gas can also be generated by a water gas shift reaction of water vapor and carbon monoxide in the feed fuel and / or by steam reforming the feed fuel. In one embodiment, a substantial amount of reforming occurs in the first reformer 14 or the reforming zone of the first reformer, and the steam reforming feed fuel includes a substantial amount of carbon monoxide. In this case, the second reformer 16 can further serve as a water gas shift reactor. The reformed product gas includes hydrogen and at least one carbon oxide. In one embodiment, the reformed product gas includes gaseous hydrocarbons, hydrogen, and at least one carbon oxide. Carbon oxides that may be present in the reformed product gas include carbon monoxide and carbon dioxide.

  In one embodiment, the heat from the effluent from the catalytic partial oxidation reformer 20 is supplied to the reforming zone 108 and / or heat exchanged with the steam reforming feed fuel stream in the reforming zone 108. it can. The temperature of the effluent from the catalytic partial oxidation reformer 20 can range from 750 ° C to 1050 ° C, or from 800 ° C to 1000 ° C, or from 850 ° C to 900 ° C. The heat from the effluent may heat the reforming zone 108 of the second reformer 16 to a temperature from about 500 ° C. to about 850 ° C. or from about 550 ° C. to 700 ° C. The temperature in the reforming zone 108 of the second reformer 16 reforms substantially all or all of the fuel supplied from the first reformer 14 to include hydrogen and at least one carbon oxide. It may be sufficient to produce product gas.

  The reformed product gas may enter a hot hydrogen separator 18 that is operatively connected to the second reformer 16. As shown in FIGS. 1 and 2, the high-temperature hydrogen separator 18 is a part of the second reformer 16. As shown in FIG. 3, the high-temperature hydrogen separator 18 is separated from the second reformer 16 and is operably connected to the second reformer via a pipe line 122.

  The hot hydrogen separator 18 may include one or more hot tubular hydrogen separation membranes 68. The membrane 68 can be installed in the reforming zone 108 of the second reformer 16 and arranged so that the supplied fuel and reformed product gas can contact the membrane 68. Hydrogen may travel through the membrane wall (not shown) of membrane 68 to hydrogen conduit 124 installed in membrane 68. The membrane wall of each membrane separates the hydrogen conduit 124 from gas communication with the non-hydrogen compound of the reformed product gas, feed fuel and steam in the reforming zone 108 of the second reformer 16. The membrane wall is selectively permeable to elemental and / or molecular hydrogen so that hydrogen in the reforming zone 108 can travel through the membrane wall of the membrane 68 to the hydrogen conduit 124, Other gases in the reforming zone are prevented from moving to the hydrogen conduit by the membrane wall. The hydrogen flux through the hot hydrogen separator 18 can be increased or decreased by adjusting the pressure in the second reformer 16. The pressure in the second reformer 16 can be controlled by the rate at which the anode exhaust stream is supplied to the first reformer 14.

  Referring to FIG. 3, the fuel supplied from the second reformer 16 is supplied to the high temperature hydrogen separator 18 via the pipe line 122. The high temperature hydrogen separator 18 may include a membrane that is selectively permeable to molecular or elemental hydrogen. In a preferred embodiment, the high temperature hydrogen separator includes a membrane that is selectively permeable to hydrogen. In one embodiment, the high temperature hydrogen separator includes a tubular membrane coated with palladium or a palladium alloy that is selectively permeable to hydrogen.

  The gas stream that enters the hot hydrogen separator 18 via line 122 may include hydrogen, carbon oxide, and hydrocarbons. The gas stream can contact the tubular hydrogen separation membrane (s) 68 and the hydrogen can travel through the membrane wall to a hydrogen conduit 124 installed in the membrane 68. The membrane wall separates the hydrogen conduit 124 from gas communication with non-hydrogen compounds and is selectively permeable to elemental and / or molecular hydrogen so that the hydrogen in the incoming gas is , Through the membrane wall to the hydrogen conduit 124, but other gases are prevented from moving to the hydrogen conduit by the membrane wall.

  The hot tubular hydrogen separation membrane (s) 68 in FIGS. 1 and 2 may include a support coated with a thin layer of metal or alloy that is selectively permeable to hydrogen. The support may be formed from a ceramic or metallic material that is porous to hydrogen. Porous stainless steel or porous alumina is the preferred material for the support of the membrane 68. Hydrogen selective metals or alloys coated on the support include, in particular, Pd, Pt, Ni, Ag, Ta, V, Y, Nb, Ce, In, Ho, La, Au and Ru in the form of alloys, It can be selected from metals of group VIII that are not limited thereto. Palladium and platinum alloys are preferred. A particularly preferred membrane 68 used in the method of the present invention has a very thin membrane of palladium alloy with a high surface area coated on a porous stainless steel support. This type of membrane can be prepared using the method disclosed in US Pat. No. 6,152,987. Thin films of platinum or platinum alloys with high surface areas may also be suitable as hydrogen selective materials.

  The pressure in the reforming zone 108 of the second reformer 16 is such that the hydrogen is forced into the hydrogen conduit 124 from the reforming zone 108 of the second reformer 16 through the membrane wall. It is maintained at a level well above the pressure in the hydrogen conduit 124. In one embodiment, the hydrogen conduit 124 is maintained at or near atmospheric pressure and the reforming zone 108 is maintained at a pressure of at least 0.5 MPa or at least 1.0 MPa or at least 2 MPa or at least 3 MPa. As described above, the reforming zone 108 is such a high by compressing the feed fuel from the first reformer 14 with the compressor 94 and injecting the mixture of feed fuel into the reforming zone 108 at high pressure. Can be maintained at pressure. Alternatively, the reforming zone 108 is maintained at such a high pressure by mixing high pressure steam with the feed fuel as described above and injecting the high pressure mixture into the reforming zone 108 of the second reformer 16. Can do. Alternatively, the reforming zone 108 mixes high pressure steam and hydrocarbon streams in the first reforming device 14 or the reforming zone of the first reforming device, and the high pressure supply fuel produced in the first reforming device. Can be maintained at such high pressures directly or through one or more heat exchangers 90 into the second reformer 16. The reforming zone 108 of the second reformer 16 can be maintained at a pressure of at least 0.5 MPa or at least 1.0 MPa or at least 2.0 MPa or at least 3.0 MPa.

  The temperature at which the steam reforming feed fuel and optional additional steam are mixed in the reforming zone 108 of the second reformer 16 and contacted with the reforming catalyst is at least 400 ° C., preferably from 400 ° C. to 650 ° C. It may be in the range up to 0 ° C, most preferably in the range from 450 ° C to 550 ° C. A typical steam reformer is operated at a temperature of 750 ° C. or higher in order to obtain a sufficiently high equilibrium conversion. In the method of the present invention, the reforming reaction is performed by continuously removing hydrogen from the reforming zone 108 into the hydrogen conduit 124 of the membrane 68 in the reformer operating temperature range from 400 ° C. to 650 ° C. Removal from the reformer 16 facilitates the direction of hydrogen production. In this way, the process of the present invention is capable of obtaining almost complete conversion of the reactants to hydrogen without equilibrium limitations. An operating temperature from 400 ° C. to 650 ° C. is also advantageous for the shift reaction, which converts carbon oxides and water vapor into more hydrogen, and the hydrogen moves from the reforming zone 108 to the membrane wall (s). Then, it is removed in the hydrogen conduit 124. Since the equilibrium is never reached because hydrogen is continuously removed from the second reformer, almost complete conversion of hydrocarbons and carbon monoxide to hydrogen and carbon dioxide by reforming and water gas shift reactions is the first. It can be achieved in two reformers 16.

  In one embodiment, the steam reforming supply fuel supplied from the reforming zone of the first reformer 14 and / or the first reformer to the second reformer 16 is the second reformer. Supply heat to promote the reaction in The steam reforming supply fuel to the second reformer 16 produced from the reforming zone of the first reformer 14 and / or the first reformer promotes the reaction in the second reformer. It contains sufficient thermal energy to do and may have a temperature from 400 ° C to 950 ° C. The thermal energy of the steam reforming feed fuel produced from the first reformer 14 and / or the reforming zone of the first reformer is necessary to promote the reaction in the second reformer 16. As mentioned above, the feed fuel may be water supplied to the feed fuel in the heat exchanger 90 and / or before the feed fuel is fed to the second reformer 16. By injecting, the temperature can be lowered from 400 ° C. to less than 600 ° C. 1) the temperature in the second reformer 16 can be adjusted to favor hydrogen production in the water gas shift reaction; 2) the lifetime of the membrane (s) 68 can be extended. And 3) it may be preferable to have a feed fuel at or near the temperature required for the second reformer 16 so that the performance of the compressor 94 is improved. Since the heat energy from the first reformer is included in the supplied fuel that is closely related to the reaction in the second reformer, the first reformer 14 to the second reformer 16 The transfer of thermal energy is extremely efficient.

  The hydrogen-containing stream is heated at a high temperature by selectively transferring hydrogen into the hydrogen conduit 124 through the membrane wall of the hydrogen separation membrane (s) 68 to separate the hydrogen-containing gas stream from the reformate product gas. It is formed from the reformed product gas in the hydrogen separator 18. The hydrogen-containing gas stream may contain a very high concentration of hydrogen and may contain at least 0.9 or at least 0.95 or at least 0.98 mole fraction of hydrogen.

  The hydrogen-containing gas stream can be separated from the reformed product gas at a relatively high rate due to the high hydrogen flux through the hydrogen separation membrane (s) 68. In one embodiment, the temperature at which hydrogen is separated from the reformed product gas via hydrogen separation membrane (s) 68 is at least 300 ° C. or about 350 ° C. to about 600 ° C. or 400 ° C. to 500 ° C. is there. Since hydrogen is present in the second reformer 16 at a high partial pressure, the hydrogen passes through the hydrogen separation membrane (s) 68 at a high flow rate. The high partial pressure of hydrogen in the second reformer 16 is: 1) a significant amount of hydrogen in the anode exhaust stream is supplied to the first reformer 14 and is contained in the supplied fuel and second modified. 2) Hydrogen is produced in the first reformer and fed to the second reformer; 3) Hydrogen is reformed and shifted in the second reformer It is to be produced. Due to the high rate at which hydrogen is separated from the reformed product, a sweep gas to facilitate removal of hydrogen from the hydrogen conduit 124 and the hot hydrogen separator 18 is not required.

  As shown in FIG. 1-2, the hydrogen-containing gas stream exits the high temperature hydrogen separator 18 and enters the anode inlet 30 from the hydrogen conduit 124 via lines 126 and 34 and then enters the molten carbonate fuel cell 12. Enters the anode 24. Alternatively, the hydrogen-containing gas is supplied directly to the anode inlet 30 via line 126. The hydrogen gas stream supplies hydrogen to the anode 24 for an electrochemical reaction with the oxidant at one or more anode electrodes along the anode path length in the fuel cell 12. The molecular hydrogen partial pressure entering the second reformer 16 is higher than the molecular hydrogen partial pressure in the hydrogen-containing gas stream exiting the hot hydrogen separator 18. The difference in partial pressure between the second reformer 16 and the molecular hydrogen partial pressure in the hydrogen-containing gas stream exiting the high temperature hydrogen separator 18 can cause the reforming reaction and / or the water gas shift reaction to remove more hydrogen. Promote production. In some embodiments, a sweep gas, such as water vapor, is injected into the hydrogen conduit to sweep hydrogen from the inner portion of the membrane wall member into the hydrogen conduit, whereby the hydrogen is separated from the reforming zone by the hydrogen separation membrane. The speed that can be done can be increased.

  Before supplying the hydrogen-containing gas stream to the anode 24, supplying the hydrogen-containing gas stream or a portion thereof to the heat exchanger 72 to heat the hydrocarbon stream and cool the hydrogen gas stream through line 128. Can do. The hydrogen-containing gas stream may have a temperature from 400 ° C. to 650 ° C., generally from 450 ° C. to 550 ° C. as it exits the hot hydrogen separator 18. The pressure of the hydrogen-containing gas exiting the high temperature hydrogen separator 18 has a pressure of about 0.1 MPa or 0.01 MPa to 0.5 MPa or 0.02 MPa to 0.4 MPa or 0.3 to 0.1 MPa. It may be. In a preferred embodiment, the hydrogen-containing gas stream exiting the hot hydrogen separator 18 has a temperature of about 450 ° C. and a pressure of about 0.1 MPa. The pressure and temperature of the hydrogen-containing gas stream exiting the hot hydrogen separator 18 may be suitable to supply the hydrogen-containing gas stream directly to the anode inlet 30 of the molten carbonate fuel cell 12.

  The hydrocarbon stream can optionally be heated by exchanging heat with the hydrogen gas stream in the heat exchanger 72 and optionally exchanging heat with the carbon dioxide gas stream as described below. The hydrogen gas stream supplied to the anode 24 of the molten carbonate fuel cell 12, coupled with selecting and controlling the temperature of the oxidant-containing gas stream supplied to the cathode 26 of the molten carbonate fuel cell 12, In order to control the operating temperature of the molten carbonate fuel cell within the range from 600 ° C. to 700 ° C., the temperature is as high as 400 ° C. or as high as 300 ° C. or as high as 200 ° C. or as high as 150 ° C. or as 20 ° C. To 400 ° C or 25 ° C to 250 ° C. The hydrogen-containing gas stream or a portion thereof can generally be cooled to temperatures from 200 ° C. to 400 ° C. by exchanging heat with the hydrocarbon stream in heat exchanger 72. In some cases, the hydrogen gas stream or a portion thereof is passed through one or more additional heat exchangers (not shown) from the heat exchanger 72 through one or more additional heat exchangers (not shown). Further cooling can be achieved by exchanging additional heat with the hydrocarbon stream or water stream in each of the heat exchangers. When an additional heat exchanger is used in the system, the hydrogen gas stream or part thereof can be cooled to a temperature from 20 ° C to 200 ° C, preferably from 25 ° C to 100 ° C. In one embodiment, a portion of the hydrogen gas stream can be cooled in the heat exchanger 72 and optionally one or more additional heat exchangers, and a portion of the hydrogen gas stream can be in the heat exchanger. It can be supplied to the anode 24 of the molten carbonate fuel cell 12 without cooling, in which case the combined portion of the hydrogen gas stream is as high as 400 ° C. or as high as 300 ° C. or as high as 200 ° C. or as high as 150 It can be fed to the anode of the fuel cell at a temperature of 0 ° C. or at a temperature of 20 ° C. to 400 ° C. or a temperature of 25 ° C. to 100 ° C.

  The flow of hydrogen gas, or a portion thereof, to the heat exchangers 72, 22 and optionally one or more additional heat exchangers is determined by Can be selected and controlled to control the temperature. The flow of hydrogen gas or a portion thereof to heat exchanger 22 and optionally additional heat exchanger (s) can be selected and controlled by adjusting metering valves 36, 130 and 132. . Metering valves 36 and 130 are for controlling the flow of hydrogen gas flow or a portion thereof to the anode 24 of molten carbonate fuel cell 12 through line 126 without cooling the hydrogen gas flow or portions thereof. Can be adjusted. Metering valve 130 may also control the flow of hydrogen gas to heat exchanger 22 or a portion thereof. Metering valve 132 can be adjusted to control the flow of hydrogen gas, or a portion thereof, to heat exchanger 72 through line 128 and optionally to additional heat exchangers. Metering valves 130 and 132 can be coordinated and adjusted to provide the desired degree of cooling to the hydrogen gas stream prior to supplying the hydrogen gas stream to the anode 24 of the molten carbonate fuel cell 12. In one embodiment, metering valves 130 and 132 can be automatically coordinated and adjusted in response to feedback measurement of the temperature of the anode exhaust stream and / or cathode exhaust stream exiting fuel cell 12. The hydrogen gas stream supplies hydrogen to the anode 24 for electrochemical reaction with the oxidant at one or more anode electrodes over the anode path length in the fuel cell 12. The rate at which the hydrogen gas stream is supplied to the anode 24 of the molten carbonate fuel cell 12 can be selected by selecting the rate at which the supplied fuel is supplied to the second reformer 16, which in turn is The rate at which the hydrocarbon stream is fed to the first reformer 14 can be selected and can be controlled by adjusting the hydrocarbon inlet valve 106.

  Any portion of the hydrogen-containing gas stream supplied to heat exchanger 72 and optional additional heat exchanger (s) is routed to the anode of the molten carbonate fuel cell around the heat exchanger. It can be supplied from a heat exchanger used to cool the hydrogen-containing gas stream by any part of the gas stream, or via a final additional heat exchanger. In one embodiment, the hydrogen-containing gas stream or the combined portion of the hydrogen-containing gas stream exiting the hot hydrogen separator 18 is compressed with a compressor (not shown) to increase the pressure of the hydrogen gas stream, and then the hydrogen gas A stream can be fed to the anode. In one embodiment, the hydrogen gas stream can be compressed to a pressure of from 0.15 MPa to 0.5 MPa, or from 0.2 MPa to 0.3 MPa, or 0.7 MPa, or 1 MPa. All or part of the energy required to drive the compressor may be supplied by the expansion of high pressure steam by a high pressure carbon dioxide stream and / or one or more turbines formed as described below.

  Alternatively, the rate at which the hydrogen gas stream is supplied to the anode 24 of the molten carbonate fuel cell 12 can be selected by controlling metering valves 36 and 134 in conjunction. Metering valve 36 can be adjusted to increase or decrease the flow rate of the hydrogen gas flow into anode 24. Metering valve 134 can be adjusted to increase or decrease the flow rate of the hydrogen gas flow to hydrogen source 64. Metering valves 36 and 134 are capable of supplying a selected rate of hydrogen gas flow via line 34 to the anode 24 of molten carbonate fuel cell 12, while providing the required rate. A part of the hydrogen gas flow exceeding the amount of the hydrogen gas flow can be controlled in a linked manner so that it can be supplied to the hydrogen source 64 via the pipe 136.

  The hydrogen-depleted reformed product gas stream can be removed from the hot hydrogen separator 18 via line 48, and the hydrogen-depleted reformed product gas stream is unreacted in the feed fuel and reformed product gas. Gaseous non-hydrogen reforming products can be included. Non-hydrogen reformed products and unreacted feed fuel may include carbon dioxide, water (as steam) and small amounts of carbon monoxide and unreacted hydrocarbons. A small amount of hydrogen may also be included in the hydrogen depleted reformate product gas stream.

  In one embodiment, the hydrogen depleted reformate product gas stream leaving the hot hydrogen separator 18 is at least 0.8 or at least 0.9 or at least 0.95 or at least 0.98 mole fraction of dioxide dioxide on a dry basis. It can be a carbon dioxide gas stream containing carbon. The carbon dioxide gas stream is a high pressure gas stream having a pressure of at least 0.5 MPa or at least 1 MPa or at least 2 MPa or at least 2.5 MPa. Hereinafter, the hydrogen depleted reformate product gas stream will be referred to as the high pressure carbon dioxide gas stream. The temperature of the high pressure carbon dioxide gas stream leaving the hydrogen separator 18 is at least 400 ° C or generally from 425 ° C to 600 ° C or from 450 ° C to 550 ° C.

  The high pressure carbon dioxide gas stream may exit the hot hydrogen separator 18 and be supplied to the cathode 26 of the fuel cell 12 via lines 48 and 44. As shown, the high pressure carbon dioxide gas stream can be utilized to pass through the heat exchanger 22 and heat the oxidant gas stream. In one embodiment, a portion of the carbon dioxide stream is mixed directly with the oxidant gas stream that enters the cathode 26 via line 44.

In a preferred embodiment, the high pressure carbon dioxide gas stream is supplied to the catalytic partial oxidation reformer 20 via line 48. In the catalytic partial oxidation reformer 20, residual hydrocarbons (eg, methane, ethane and propane) in the carbon dioxide stream are combusted in the presence of oxygen or air supplied from the oxidant source 42 via line 56. Thus, a heat effluent combustion flow passing through the heat exchanger 22 via the pipe line 138 is formed and supplied to the cathode 26 via the pipe line 44. In one embodiment, the combustion stream is supplied directly to the cathode 26 via lines 138 and 44. The amount of molecular oxygen in the oxidant-containing stream fed to the catalytic partial oxidation reformer 20 is at least 0.9 times the stoichiometric amount required for complete combustion of hydrocarbons in the carbon dioxide stream. The thermal combustion stream that is 1.1 times or less can contain a substantial amount of carbon dioxide, but can also contain nitrogen gas and water. The thermal combustion stream exiting the catalytic partial oxidation reformer 20 may have a temperature that is at least in the range of 750 ° C. to 1050 ° C. or 800 ° C. to 1000 ° C. or 850 ° C. to 900 ° C. Heat from the hot combustion gas may be exchanged in the heat exchanger 22 for a hydrogen-containing gas stream and / or in the heat exchanger for an oxidant-containing gas stream. As shown in FIG. 2, at least a portion of the heat from the combustion stream leaving the catalytic partial oxidation reformer 20 can be exchanged with the first reformer 14 in a heat exchanger 98 via line 96.

  In one embodiment, the hot combustion gas can be supplied directly to the cathode exhaust inlet 38. The temperature of the oxidant-containing gas can be adjusted so that the temperature of the cathode exhaust stream exiting the fuel cell is in the range of 550 ° C to 700 ° C. The temperature of the oxidant-containing gas can be adjusted to a temperature of 150 ° C. to 450 ° C. by cooling and / or heating in the heat exchanger 22. The flow rate of the oxidant-containing gas stream from the hot hydrogen separator 18 to the heat exchanger 22 and / or the catalytic partial oxidation reformer 20 can be controlled by adjusting the metering valves 46, 58 and 140.

  The hot combustion gas stream may contain a significant amount of water as water vapor as it exits the catalytic partial oxidation reformer 20. In one embodiment, the water vapor converts the thermal combustion gas stream into the heat exchanger 22 and / or heat exchanger 72 and, if necessary, one or more additional heat exchangers (not shown) and the thermal combustion gas. By cooling with condensed water from the stream, it can be removed from the hot combustion gas stream.

  The high pressure carbon dioxide gas stream from the hot hydrogen separator 18 feeds the hydrocarbon stream to the heat exchanger 72 via the hydrocarbon stream line 62 and simultaneously the carbon dioxide containing gas stream to the heat exchanger 72 via the line 142. It can be used to heat the hydrocarbon stream by passing it through. The flow rate of the high pressure carbon dioxide stream from the hot hydrogen separator 18 to the heat exchanger 72 can be controlled by adjusting the metering valve 144. Metering valve 144 can be adjusted to control the flow rate of the carbon dioxide stream to heat exchanger 72 to heat the hydrocarbon stream to a selected temperature. The hydrocarbon stream can be heated to a temperature such that the hydrocarbon stream has a temperature of at least 150 ° C. or from 200 ° C. to 500 ° C. when the hydrocarbon stream is fed to the first reformer 14.

  Metering valves 46, 58 and 140 can be automatically adjusted by a feedback mechanism that feeds the temperature of the cathode exhaust stream exiting fuel cell 12 and / or enters first reformer 14. The temperature of the hydrocarbon stream is measured and the internal pressure in the second reformer 16 and / or the hot hydrogen separator 18 is maintained at a desired level while the cathode exhaust stream and / or the first reformer 14 is Metering valves 46, 58 and 140 can be adjusted to maintain the temperature of the incoming hydrocarbon stream within set limits.

A hydrogen gas stream and oxidant (carbonic acid) (generated by the reaction of oxygen and carbon dioxide at the cathode) are preferably mixed at one or more anode electrodes of the fuel cell 12 as described above to provide at least 0.1 W / cm ^2, more preferably generates an electric least 0.15 W / cm ^2, or at least 0.2 W / cm ^2, or at least 0.3 W / cm ² power density. Electricity is at such power density by selecting and controlling the rate at which the hydrogen gas stream is supplied to the anode 24 of the fuel cell 12 and the rate at which the oxidant-containing gas stream is supplied to the cathode 26 of the fuel cell 12. Can be generated. The flow rate of the oxidant-containing gas flow to the cathode 26 of the fuel cell 12 can be selected and controlled by adjusting the oxidant gas inlet valve 46.

  As described above, the flow rate of the hydrogen gas flow to the anode 24 of the fuel cell 12 can be controlled by selecting and controlling the rate at which the supplied fuel is supplied to the second reformer 16, which is , And in turn, can be selected and controlled by the rate at which the hydrocarbon stream is fed to the first reformer 14, which can be selected and controlled by adjusting the hydrocarbon inlet valve 106. Alternatively, as described above, the rate at which the hydrogen gas stream is supplied to the anode 24 of the fuel cell 12 can be selected and controlled by controlling the metering valves 36, 130, 132 and 134 in a coordinated manner. . In one embodiment, metering valves 36, 130, 132, and 134 can be automatically adjusted by a feedback mechanism to maintain a selected flow rate of the hydrogen gas flow to anode 24, which is the anode exhaust. It can function based on the hydrogen content in the stream or the water content in the anode exhaust stream or the ratio of water produced in the fuel cell to hydrogen in the anode exhaust stream.

  In the method of the present invention, a mixture of hydrogen gas stream and oxidant at one or more anode electrodes causes water (water vapor) to be oxidized by a portion of the hydrogen present in the hydrogen gas stream supplied to the fuel cell 12 by the oxidant. As occurs). The water generated by the oxidation of hydrogen by the oxidant is swept through the anode 24 of the fuel cell 12 by the unreacted portion of the hydrogen gas stream exiting the anode 24 as part of the anode exhaust stream.

  In one embodiment of the method of the present invention, the flow rate at which the hydrogen gas stream is supplied to the anode 24 is the amount of water produced in the fuel cell 12 per unit time and the amount of hydrogen in the anode exhaust per unit time. The ratio can be selected and controlled to be at most 1.0 or at most 0.75 or at most 0.67 or at most 0.43 or at most 0.25 or at most 0.11. In one embodiment, the amount of water produced in the fuel cell 12 and the amount of hydrogen in the anode exhaust is determined by the amount of water produced in the fuel cell per unit time and the anode per unit time in moles per unit time. Moles so that the ratio to the amount of hydrogen in the exhaust is at most 1.0 or at most 0.75 or at most 0.67 or at most 0.43 or at most 0.25 or at most 0.11 It can be measured in units. In one embodiment, the flow rate at which the hydrogen gas stream is supplied to the anode 24 is such that the single pass hydrogen utilization in the fuel cell 12 is less than 50% or more than 45% or more than 40% or more than 30% or more. It can be selected and controlled to be 20% or at most 10%.

  In other embodiments of the method of the present invention, the flow rate at which the hydrogen gas stream is fed to the anode 24 is such that the anode exhaust stream is at least 0.6 or at least 0.7 or at least 0.8 or at least 0.9 mole fraction. Can be selected and controlled to contain any hydrogen. In other embodiments, the flow rate at which the hydrogen gas stream is supplied to the anode 24 is such that the anode exhaust stream is greater than 50% or at least 60% or at least 70% or at least of the hydrogen in the hydrogen gas stream supplied to the anode 24. It can be selected and controlled to include 80% or at least 90%.

  In some embodiments, the flow rate at which carbon dioxide is supplied to the cathode 26 is such that the partial pressure of carbon dioxide at the majority of the cathode portion of the molten carbonate fuel cell is the majority of the anode portion of the molten carbonate fuel cell. It can be selected and controlled to be higher than the partial pressure of carbon dioxide at. In one embodiment, the flow rate at which carbon dioxide is supplied to the cathode 26 is such that the partial pressure of carbon dioxide in the cathode exhaust stream exiting the fuel cell is greater than the partial pressure of carbon dioxide in the anode exhaust stream exiting the fuel cell. Can be selected and controlled. The flow rate of carbon dioxide is such that the partial pressure of carbon dioxide at least 75 percent or at least 95 percent or substantially all of the cathode portion of the molten carbonate fuel cell is at least 75 percent of the anode portion of the molten carbonate fuel cell, 95 It can be selected and controlled to be higher than the partial pressure of carbon dioxide in percent or substantially all.

Lack of carbon dioxide in a molten carbonate fuel cell by operating the molten carbonate fuel cell to control ΔP _CO2 at a pressure greater than zero at any concentration of air and / or at any utilization of hydrogen Can be suppressed, and the cell potential of the molten carbonate fuel cell can be increased. The flow rate at which the carbon dioxide stream is supplied to the cathode 26 of the molten carbonate fuel cell 12 is such that the hydrogen utilization rate is at most 60%, at most 50% or at most 40%, at most 30%, at most 20% or When the flow rate of air is controlled so that it is at most 10% and / or the molar ratio of carbon dioxide to molecular oxygen is about 2, the formula: (ΔP _CO2 ) = (P _CO2 ^c ) − (P _CO2 ^a ) The carbon dioxide partial pressure delta determined by ^a ) is selected and controlled such that the absolute pressure is above about 0 bar or above 0 bar or from 0.01 to 0.2 bar or from 0.05 to 0.15 bar. it can.

(Example)
Non-limiting examples are shown below.

  A detailed process simulation of the molten carbonate fuel cell system of the present invention was constructed using the UniSim® simulation program (Honeywell) combined with battery potential calculation. Material balance and energy balance data were obtained using the UniSim program. Detailed process simulations were iteratively solved for various values of hydrogen utilization and other related system parameters. The detailed process simulation output included detailed composition data for all process streams entering and exiting the molten carbonate fuel cell.

For high temperature fuel cells, the activation loss is small and the cell potential can be obtained over a practical range of current densities by considering only ohms and electrode losses. Therefore, the cell potential (V) of the molten carbonate fuel cell is the difference between the open circuit voltage (E) and the loss (iR) as shown in equation (1).
V = E-iR (1)
Where V and E have units of volts or millivolts, i is the current density (mA / cm ² ), and R (Ωcm ² ) is the electrolyte, cathode and A combination of Ohm (R _ohm ), Cathode (η _c ), and Anode (η _a ) resistance combined with the anode.
R = R _ohm + η _c + η _a (2)
E is obtained from the following Nernst equation.
E = E ° _{^{+ (RT / 2F) ln (}} P H2 P O2 0.5 / P H2O) + (RT / 2F) ln (P CO2 c / P CO2 a) (3)

  Using the detailed process simulation described above, the cell voltage versus current density of the molten carbonate fuel cell system described herein in which the first reformer was heated by anode exhaust and no other heating. And the power density configuration was simulated. For example, the system is shown in FIG. The heat for the second reformer was heated by exchange with the heat effluent from the catalyst partial oxidation reformer. The output temperature of the effluent from the catalytic partial oxidation reformer was increased by using cathode exhaust to preheat the catalytic oxidation reformer feed air.

  Using the simulation described above, the cell voltage versus current density of the molten carbonate fuel cell system described herein, wherein the first reformer is heated by heat from the anode exhaust and catalytic partial oxidation reformer. And the power density configuration was simulated. For example, the system is shown in FIG.

For Examples 1 and 2, the molten carbonate fuel cell was operated at an absolute pressure of 1 bar (about 0.1 MPa or about 1 atmosphere) and a temperature of 650 ° C. The feed fuel flow to the cathode of the molten carbonate fuel cell was countercurrent to the feed fuel flow to the anode. Air was used as a source of oxygen. Air values were used to provide a molar ratio of carbon dioxide to molecular oxygen of 2 at various hydrogen utilization rates. Examples 1 and 2 Hydrogen utilization rate (%) of molten carbonate fuel cell for simulation, operating conditions of first and second reformers, ratio of water vapor to carbon and conversion rate of benzene to hydrogen ( %) Is shown in Table 1. R in Formula 2 is J. Obtained from Power Sources, 2002, 112, 509-518 and assumed to be equal to 0.75 Ωcm ² .

  Examples 1 and 2 The data from the simulations were used to determine the cell voltage in the state of the state of the art molten carbonate fuel cell as described in “Fuel Cell Systems Explained”, 2003, Wiley & Sons, page 199, Larmine et al. Comparison with literature values of current density and power density.

FIG. 4 shows the molten carbonate fuel cell system simulated in Examples 1 and 2 with respect to the cell voltage (mV) versus current density (mA / cm ² ) and the molten carbonate fuel cell having the reformate as the supply fuel. Indicates the value. Molten carbonate fuel cells were operated at 20% and 30% hydrogen utilization. Data line 160 shows the cell voltage (mV) versus current density (mA / cm ² ) at 20% hydrogen utilization for the molten carbonate fuel cell systems of Examples 1 and 2. Data line 162 shows battery voltage (mV) versus current density (mA / cm ² ) at 30% hydrogen utilization of Examples 1 and 2. Data line 164 is the cell voltage (mV) versus current density for the state of the art molten carbonate fuel cell system described by Larmine et al. In “Fuel Cell Systems Explained”, 2003, Wiley & Sons, p.199. (MA / cm ² ). As shown in FIG. 4, for a given current density, the cell voltage of the molten carbonate fuel cell system described herein is that of a state of the art molten carbonate fuel cell having reformate gas as the feed fuel. Higher than the battery voltage in the state.

FIG. 5 shows the power density (W / cm ² ) versus current density (mA / cm ² ) of the molten carbonate fuel cell system simulated in Examples 1 and 2 operated at 20% and 30% hydrogen utilization, and Literature values for molten carbonate fuel cells having reformate gas as the feed fuel are shown. Data line 166 shows the power density (W / cm ² ) versus current density (mA / cm ² ) at 20% hydrogen utilization of Examples 1 and 2. Data line 168 shows the power density (W / cm ² ) versus current density (mA / cm ² ) at 30% hydrogen utilization of Examples 1 and 2. The data line 170 is the power density (W / cm ² ) of the state-of-the-art molten carbonate fuel cell system described in “Fuel Cell Systems Explained”, 2003, Wiley & Sons, page 199 by Larmine et al. Current density (mA / cm ² ) is shown. As shown in FIG. 5, for a given current density, the power density of the molten carbonate fuel cell system described herein is greater than the power density of a molten carbonate fuel cell having reformate gas as the feed fuel. high.

FIG. 6 shows excess carbon dioxide (ΔP _CO2 (absolute pressure bar)) and total fuel cell potential (mV) versus hydrogen utilization of Example 1. Data line 172 shows excess carbon dioxide values (at a given hydrogen utilization and a current density of 200 mA / cm ² ). Data 174 shows the average excess carbon dioxide value at a given hydrogen utilization. Data line 176 shows the total cell potential (mV) at a given hydrogen utilization determined from the Nernst equation for the fuel cell. As shown in FIG. 6, as the hydrogen utilization increases, ΔP _CO2 decreases, the cell potential decreases, and thus molten carbonate fuel at a hydrogen utilization of less than 50% with carbon dioxide flooding. Operating the system results in an increase in the cell potential of the molten carbonate fuel cell.

FIG. 7 shows the carbon dioxide portion of the fuel cell potential (mV) of FIG. The data line 178 shows the carbon dioxide portion of the cell potential (mV) of the fuel cell (eg, the Nernst (RT / 2F) ln (P _CO2 ^c / P _CO2 ^a ) portion). As shown in FIG. 7, when the cathode of the fuel cell overflows with carbon dioxide, the cell voltage of the fuel cell is increased. For example, when the fuel cell was operated at 20% utilization of hydrogen and an excess carbon dioxide value of about 0.105, 30 mV of the total fuel cell potential was attributed to excess carbon dioxide.

As shown in FIGS. 6 and 7, the amount of carbon dioxide supplied to the fuel cell is excessive (ΔP _CO2 > 0) and the hydrogen utilization is low (eg, less than 35%, less than 30% or less than 20%). Sometimes the battery potential is maximized. Therefore, the molten carbonate fuel cell is operated at a hydrogen utilization rate of less than 50%, and the partial pressure of carbon dioxide in the majority of the cathode portion of the molten carbonate fuel cell is high in the anode portion of the molten carbonate fuel cell. By supplying excess carbon dioxide to the cathode part of the molten carbonate fuel cell so that it is higher than the partial pressure of carbon dioxide in the part, the cell potential is increased, thereby the cell voltage of the molten carbonate fuel cell. Becomes higher.

Using the simulation described above, an absolute pressure of 7 bar (about 0.7 MPa or about 7 MPa) in a molten carbonate fuel cell system (eg, the system shown in FIG. 1) including a first reformer heated by anode exhaust. The current density, cell voltage and power density of the molten carbonate fuel cell operated at atmospheric pressure) were determined. Molten carbonate fuel cells were operated at a hydrogen utilization of 20% or 30% at a pressure of 7 bar absolute and a temperature of 650 ° C. The first reformer had a steam to carbon ratio of 2.5. The temperature of the first reformer was changed. The second reformer combined with the high temperature hydrogen separator had a temperature of 500 ° C. and an absolute pressure of 15 bar. Air was used as a source of oxygen. Air values were used so that the ratio of carbon dioxide to molecular oxygen in the cathode feed fuel was stoichiometric, thereby minimizing cathode side concentration polarization. In all cases, the total carbon conversion value in systems using benzene as the feed fuel was 93% to 95%. The heat of reaction of the second reformer was supplied by heat integration in the system. R is J. Electrochem. Soc. 138, No. 12, December 1991, C.I. Y. Yuh and J.H. R. Calculated by separately calculating the individual terms in Equation 2 above by the method described by Selman. For Example 3, R is 0.57 Ω. Calculated as cm ² .

FIG. 8 shows the cell voltage (mV) versus current density (mA / cm ² ) of the molten carbonate fuel cell shown in FIG. Data line 180 shows battery voltage (mV) versus current density (mA / cm ² ) at 20% hydrogen utilization. Data line 182 shows battery voltage (mV) versus current density (mA / cm ² ) at 30% hydrogen utilization. Comparing FIG. 4 with FIG. 8, at a given current density, the molten carbonate type operated at a pressure of about 7 bar absolute compared to the cell voltage of the molten carbonate fuel cell system operated at an absolute pressure of 1 bar. Higher cell voltages have been observed in fuel cell systems.

FIG. 9 shows the power density (W / cm ² ) versus current density of the molten carbonate fuel cell system shown in FIG. 1 and the state-of-the-art molten carbonate fuel cell. Data line 184 shows power density (W / cm ² ) versus current density (mA / cm ² ) at 20% hydrogen utilization. Data line 186 shows power density (W / cm ² ) versus current density (mA / cm ² ) at 30% hydrogen utilization. Data points 188 are described in J. Journal of Power Sources, 2006, pages 852-857. R. Figure ² shows the power density (W / cm ² ) versus current density (mA / cm ² ) of a state-of-the-art molten carbonate fuel cell described by Selman. As shown in FIG. 9, at a current density of about 300 mA / cm ² , the power density of the molten carbonate fuel cell system described herein is higher than the power density of the state-of-the-art molten carbonate fuel cell.

  Using the simulations described above, the use of methane and benzene as fuel sources for a molten carbonate fuel cell system in which the first reformer was heated by anode exhaust and no other heating was compared. For example, the system is shown in FIG. The heat of reaction of the second reformer was supplied by heat integration in the system. For these simulations, the molten carbonate fuel cell was operated at an absolute pressure of 1 bar (about 0.1 MPa or about 1 atmosphere) and a temperature of 650 ° C. Air was used as a source of oxygen. Using the air value, a molar ratio of carbon dioxide to molecular oxygen of 2 at various hydrogen utilization rates was obtained. The amount of fuel supplied to the first reformer was 100 kgmol / hour for benzene and 600 kgmol / hour for methane. The hydrogen utilization of the molten carbonate fuel cell, the operating conditions of the first and second reformers, and the water vapor to carbon ratio are shown in Table 2 for benzene and Table 3 for methane.

R in Formula 2 is J. As taken from Power Sources, 2002, 112, 509-518, it was assumed to be equal to 0.75 Ωcm ² .

FIG. 10 shows cell voltage (mV) versus current density (mA / cm ² ) of a molten carbonate fuel cell system using benzene or methane as a fuel source. Data line 190 shows cell voltage (mV) versus current density (mA / cm ² ) at 20% hydrogen utilization with benzene as the fuel source. Data line 192 shows cell voltage (mV) versus current density (mA / cm ² ) at 20% hydrogen utilization with methane as the fuel source. As shown in FIG. 10, at all current densities, higher cell voltages of the molten carbonate fuel cell system are observed when benzene is used as the fuel source for the first reformer.

FIG. 11 shows the average excess carbon dioxide (ΔP _{CO2 (avg)} ) versus hydrogen utilization of a molten carbonate fuel cell system using benzene or methane as a fuel source at a current density of 200 mA / cm ² . Data line 194 shows the average excess carbon dioxide value at a given hydrogen utilization for benzene. Data line 196 shows the average excess carbon dioxide value for methane. As shown in FIG. 11, at less than 50% hydrogen utilization, benzene yields more excess carbon dioxide at a given hydrogen utilization than methane. Thus, when benzene is used as a fuel source, a greater number of moles of carbon dioxide is produced per mole of hydrogen.

  As shown in Examples 1-4, the molten carbonate fuel cell system and method described herein provides a hydrogen-containing stream containing molecular hydrogen to the anode portion of a molten carbonate fuel cell. Controlling the flow rate of the hydrogen-containing stream to the anode so that the molecular hydrogen utilization at the anode is less than 50%; carbonizing the anode exhaust containing molecular hydrogen from the molten carbonate fuel cell with hydrocarbons; Mixing with the hydrogen stream (the anode exhaust mixed with the hydrocarbon stream has a temperature from 500 ° C. to 700 ° C.); contacting at least a portion of the mixture of the anode exhaust and the hydrocarbon stream with the catalyst; Producing a steam reforming feed fuel comprising one or more gaseous hydrocarbons, molecular hydrogen and at least one carbon oxide; at least a portion of the molecular hydrogen from the steam reforming feed fuel Separating; and supplying at least a portion of the separated molecular hydrogen to the anode of the molten carbonate fuel cell as at least a portion of a hydrogen-containing stream containing molecular hydrogen, thereby providing high current density, current voltage Provides power density and suppresses fuel cell carbon deficiency.

Claims (10)

Supplying a hydrogen-containing stream containing molecular hydrogen to the anode of a molten carbonate fuel cell;
Controlling the flow rate of the hydrogen-containing stream to the anode such that the molecular hydrogen utilization at the anode is less than 50%;
Mixing an anode exhaust containing molecular hydrogen from a molten carbonate fuel cell with a hydrocarbon stream containing hydrocarbons, and the anode exhaust mixed with the hydrocarbon stream has a temperature from 500 ° C to 700 ° C;
Contacting at least a portion of a mixture of anode exhaust and hydrocarbon stream with a catalyst to produce a steam reforming feed fuel comprising one or more gaseous hydrocarbons, molecular hydrogen and at least one carbon oxide; ;
Separating at least a portion of the molecular hydrogen from the steam reforming feed fuel;
And operating a molten carbonate fuel cell comprising supplying at least a portion of the separated molecular hydrogen to the anode of the molten carbonate fuel cell as at least a portion of a hydrogen-containing stream comprising molecular hydrogen. Method.   The method of claim 1, wherein the hydrogen-containing stream comprises at least 0.6 or at least about 0.95 mole fraction of molecular hydrogen.   The method of claim 1, wherein at least a portion of the hydrocarbons of the hydrocarbon stream comprise one or more volatile hydrocarbons having at least 4 carbon atoms.   Molten carbonate fuel cell in such an amount that the partial pressure of carbon dioxide in the majority of the cathode portion of the molten carbonate fuel cell is higher than the partial pressure of carbon dioxide in the majority of the anode portion of the molten carbonate fuel cell. The method according to claim 1, further comprising supplying carbon dioxide to the cathode portion of the first electrode.   The difference between the partial pressure of carbon dioxide at the inlet or outlet of the cathode of the molten carbonate fuel cell and the partial pressure of carbon dioxide at the outlet of the anode of the molten carbonate fuel cell is at least 0.05 bar absolute 5. The method of claim 4, wherein the pressure is at least 0.1 bar absolute or at least 0.15 bar absolute.   The method according to claim 4, wherein at least part of the carbon dioxide supplied to the cathode portion of the molten carbonate fuel cell is supplied by a high-temperature hydrogen separator.   Separating at least a portion of a hydrogen-depleted gas stream comprising at least one of carbon oxides and at least one of gaseous hydrocarbons from the steam reforming feed, at least a portion of the separated hydrogen-depleted stream with an oxidant The method of claim 1, further comprising contacting to produce a heated stream and supplying at least a portion of the heat from the heated stream to an anode exhaust and / or a hydrocarbon stream comprising hydrocarbons.   Air and carbon dioxide are supplied to the cathode of the molten carbonate fuel cell, the air contains molecular oxygen, and the flow rate of air and / or carbon dioxide is such that the molar ratio of carbon dioxide to molecular oxygen is at least 2. The method of claim 1, further comprising controlling. At least a portion of the molecular hydrogen supplied to the molten carbonate anode at one or more anode electrodes in the anode of the molten carbonate fuel cell is mixed with an oxidant and at least 0.1 W from the molten carbonate fuel cell. The method of claim 1, further comprising generating electricity at a power density of / cm ² . A molten carbonate fuel cell configured to receive a hydrogen-containing stream comprising molecular hydrogen at a flow rate such that the hydrogen utilization at the anode is less than 50%;
At least one reformer is configured to receive the anode exhaust and hydrocarbons from the molten carbonate fuel cell, allowing the anode exhaust to mix well with the hydrocarbons to remove a portion of the hydrocarbons. At least partially reformed and configured to produce a reformed product stream, the reformed product stream operatively coupled to a molten carbonate fuel cell that includes molecular hydrogen and at least one carbon oxide. One or more reformers; and at least one part of or connected to at least one of the reformers, and operably connected to the molten carbonate fuel cell, one or more hot hydrogens A high temperature hydrogen separator including a separation membrane, configured to receive a reformate product stream and to supply a stream containing at least a portion of molecular hydrogen to a molten carbonate fuel cell; Molten carbonate system.

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