A hydrogen supply device which generates hydrogen from hydrogen storing material which chemically stores hydrogen by a catalyst, wherein said device comprises valves on the fuel supply port and the exhaust port, and a valve controller which controls timing to opening and close the valves Fuel supply pressure is 2 to 20 atm. Hydrogen generation pressure is 5 to 300 atm. Exhaust pressure is atmospheric pressure to 0.01 atm.
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This application claims priority from Japanese application Serial No. 2005-064764, filed on Mar. 9, 2005, the content of which is hereby incorporated by reference into this application.
1. Field of the Invention
This invention relates to a hydrogen supply device for supplying hydrogen to automobiles or distributed power supplies such as home fuel cells.
2. Related Art
From the viewpoint of preventing global warming due to the release of gases such as carbon dioxide, fossil-fuel is going to be outplaced by hydrogen which is expected as the third generation energy source. Further, to promote energy saving by using energy effectively and reducing the release of carbon dioxide, cogeneration of electric power facilities has been attracting public attention. Recently, fuel cell power generation systems which use hydrogen for power generation have been rapidly researched and developed to be used widely in various power generation fields such as power generation facilities for cars, homes, automatic vending machines, portable devices and so on. A fuel cell generates electricity and thermal energy simultaneously by reacting hydrogen and oxygen into water. These electric and thermal energies are used for hot-water supply and air-conditioning. So, a fuel cell is available as a distributed power supply for home use. Development of internal combustion engines such as micro-turbines and micro-engines besides fuel cells have also been under development.
However, hydrogen which is essential as a fuel is very hard to be handled in delivery, storage, and distribution. Hydrogen is a gas substance at ordinary temperature and harder to be handled in storage and delivery than liquid and solid materials. What is worse, hydrogen is combustible and may explode violently when it is mixed up with air at a preset ratio or higher.
To solve such problems, an organic hydride system which uses hydrocarbons such as cyclohexane and decarin has attracted a great deal of public attention as-a hydrogen storage system which excels in safety, transportability, storage ability, and cost-reduction. These hydro carbons are liquid at ordinary temperature and easy to be transported.
For example, benzene and cyclohexane are cyclic hydrocarbons of the same number of carbons. However, benzene is an unsaturated hydrocarbon having double bonds of carbons but cyclohexane is a saturated hydrocarbon having no double bond. Cyclohexane is obtained by hydrogenation of benzene and benzene is obtained by dehydrogenation of cyclohexane. In other words, hydrogenation and dehydrogenation of hydrocarbon enable storage and supply of hydrogen.
There have been disclosed some hydrogen supply devices using organic hydrides which are hydrocarbons such as cyclohexane and decarin. For example, they are a method of spraying organic hydride directly over hot catalyst and a method of inserting a hydrogen separating tube into a cylindrical reactor to reduce the partial pressure of hydrogen, and cooling the reaction temperature. (Patent Document 1 and Non-patent Document 1)
Patent Document 1: Japanese Patent Publication 2002-184436
Non-patent Document 1: Applied Catalysis A: General 233, 91-102 (2002)
However, the above technologies also have problems. It is necessary to increase the efficiency of hydrogenation and dehydrogenation of cyclic hydrocarbons such as benzene and cyclohexane to put storage and supply of hydrogen to practical use.
Practically, dehydrogenation of organic hydride such as cyclohexane and decarin is carried out at a high temperature (e.g. 250° C. or higher). Part of electric energy generated by a fuel cell must be used to heat up the organic hydride. This will reduce the efficiency of power generation. Further, a large-scale facility is required by the method disclosed by Patent Document 1 which sprays cyclohexane over a hot catalyst layer through a sprayer to dehydrogenate it and cools the products (hydrogen and benzene) to separate as air and liquid. A conventional hydrogen supply device which uses cyclohexane as a hydrogen supplier intermittently sprays cyclohexane over a catalyst which is heated to about 300° C. When cyclohexane droplets touch the surface of the catalyst layer, cyclohexane evaporates. As the result, a complex interface of air, liquid, and solid is formed on the surface of the catalyst layer and hydrogen generates. Such a hydrogen supply device requires a lot of ancillary equipment such as a sprayer, a cylinder, and a cooler and cannot be down-sized. Further, since an electric heater is used to heat the catalyst, the overall power efficiency of a power generation system connected to a fuel cell will go down.
Meanwhile, when a hydrogen separating tube is used to cool the partial hydrogen pressure, the reaction speed goes down and the equipment must be greater although a high conversion rate is obtained at a temperature as low as about 200° C. The dehydrogenation of the organic hydride is an endothermic reaction. The equilibrium position of the dehydrogenation moves to the dehydrogenation side as the partial pressures of hydrogen and produced aromatic hydrocarbon become smaller at high temperature. Therefore, it is possible to get a high conversion rate even at low temperature by separating generated hydrogen by the hydrogen separating tube and reducing the partial pressure in the reaction gas. However, the reaction rate of the catalyst becomes smaller as the temperature goes down and the quantity of the catalyst must be increased to speed up the supply of organic hydride. This will make the reaction layer greater, requires more expensive hydrogen separating tubes, and pushes up the production cost.
In view of the above problems, an object of this invention is to provide a high-efficient hydrogen supply device.
To attain the above object, a hydrogen supply device of this invention is a device for using a hydrogen storage material which chemically stores hydrogen and extracting hydrogen from the-material by a catalyst, wherein
the hydrogen supply device comprises valves for a fuel inlet and an exhaust outlet of the-device and a valve control unit for controlling timing to open and close the valves;
the pressure in the hydrogen supply device varies in the range of 0.01 to 300 atm;
the fuel supply pressure is 2 to 20 atm, the hydrogen generation pressure is 5 to 300 atm, and the exhaust pressure is normal atmosphere to 0.01 atm; and
the fuel inlet valve and the exhaust outlet valve are controlled so that the device may receive fuel with the fuel inlet valve open and the exhaust outlet valve closed and may exhaust gas with the fuel inlet valve closed and the exhaust outlet valve open.
FIG. 1 shows the most basic schematic block diagram of the hydrogen supply device in accordance with this invention.
FIG. 2 shows one of the most basic valve control diagrams of the hydrogen supply system.
FIG. 3 shows a schematic illustration of a hydrogen storage/supply system for private power generation using reusable energies.
FIG. 4 shows the functional block diagram of a hydrogen supply device of Comparative Example 1.
FIG. 5 shows a functional block diagram of one of the most basic hydrogen system devices of this invention.
FIG. 6 shows a cross sectional view of a turbine type exhaust device.
FIG. 7 shows the schematic configuration of a hydrogen supply system using a hydrogen separation tube.
FIG. 8 shows sectional views of the hydrogen separation tube of the hydrogen supply device.
FIG. 9 shows a sectional view of the micro reactor of the hydrogen supply device.
FIG. 10 shows a sectional view of the micro reactor of the hydrogen supply device combined with a hydrogen separating membrane.
FIG. 11 shows the sectional view of a reciprocation type hydrogen supply device.
FIG. 12 shows a cycle of dehydrogenation of organic hydride and reactivation at high temperature.
FIG. 13 shows a schematic external view of a power generation system comprising a solid polymer type fuel cell and a hydrogen supply device of this invention.
FIG. 14 shows an operation flow of the power generation system combined with solid polymer fuel cell.
FIG. 15 shows the configuration of a tank which stores both fuel and waste liquid separately.
FIG. 16 shows an operation flow of a turbine-combined system of this embodiment.
FIG. 17 shows a sectional view of the hydrogen supply device unified with NOx removal catalyst of Embodiment 10.
FIG. 18 shows an operation flow of the hydrogen supply device unified with NOx removal catalyst.
According to one aspect of the present invention, there is provided a hydrogen supply device of this invention, which comprises,
a hydrogen supply device having a catalyst and a heater,
a valve timing control unit to control opening/closing timing of the valves provided on a fuel supply port and an exhaust port of the hydrogen supply device,
a booster pump for fuel supply,
an exhaust pump for exhausting product gas from the hydrogen supply device,
a separator for separating hydrogen from a dehydrogenate,
a compressor for compressing generated hydrogen, and
a hydrogen tank for storing the generated hydrogen,
wherein the exhaust pump, the separator, and the compressor are built in an exhaust/separation/compression unit.
According to another aspect of the present invention, there is provided a hydrogen supply device of this invention provides a hydrogen separating membrane adjacent to a catalyst layer, separates generated hydrogen by means of the membrane, and collects hydrogen for recovery. The available catalyst is made of a metal catalyst and a carrier. The metal catalyst is at least one selected from a group of nickel, palladium, platinum, rhodium, iridium, ruthenium, molybdenum, rhenium, tungsten, vanadium, osmium, chromium, cobalt, and iron. The carrier is at least one selected from a group of alumina, zinc oxide, silica, zirconium oxide, diatomite, niobium oxide, vanadium oxide, activated carbon, zeolite, antimony oxide, titanium oxide, tungsten oxide, and iron oxide.
Another aspect of the present invention provides a hydrogen supply device of this invention provides a hydrogen separating membrane which forms a dehydrogenation catalyst a dehydrogenate catalyst on one side of the metal foil and a hydrogen channel on the other side. The hydrogen separating membrane mainly contains at least one of Zr, V, Nb, and Ta. The hydrogen storage materials available to this invention are one or more aromatic compounds selected from a group of benzene, toluene, xylene, mesitylene, naphthalene, methylnaphthalene, anthracene, biphenyl, phenancelene, and their alkyl substituents.
This invention provides a distributed power supply and an automobile comprising a hydrogen supply system and a generator selected from fuel cell, turbine and engine. The hydrogen supply device is used as a hydrogen engine which burns hydrogen since it can prevent overheating of the NOx purification catalyst by the endothermic reaction of the hydrogen supplying catalyst. The hydrogen supplying catalyst is provided on one part of a highly-thermal conductive substrate and the NOx purification catalyst is provided to the other part of the substrate. Zeolite-related catalyst is mainly used as the NOx purification catalyst.
Another aspect of the,present invention provides a hydrogen supply device of this invention produces hydrogen by power generated by reusable energy and supplies hydrogen to a distributed power supply or car to drive thereof.
This invention can provide a high-efficiency hydrogen supply device which stores hydrogen and supplies it to a distributed power supply such as car or home fuel cell.
In the following, there will be explained a hydrogen supply device and system in accordance with this invention.
FIG. 1 shows the most basic schematic block diagram of the hydrogen supply device in accordance with this invention. Hydrogen supply device 1 comprises hydrogen supply unit 2, fuel supply valve 3, exhaust valve 4, and valve controller 5. Valve controller 5 controls timing to open and close fuel supply valve 3 and exhaust valve 4. Fuel supply valve 3 and exhaust valve 4 are electrically connected to valve controller 5. Hydrogen supply unit 2 will be explained later in detail. Fuel supply valve 3 and exhaust valve 4 can be of any type as long as they can be operated steadily for a specified period under operating temperature and pressure conditions. Also available are general-purpose valves (such as pneumatic valves and solenoid valves) and valves for car fuel supply.
In the following, there will be explained the valve open/close timing of the fuel supply valve and the exhaust valve.
FIG. 2 shows one of the most basic valve control diagrams. The valve controller controls the valves on the fuel inlet port and the exhaust port as follows
Opening the fuel supply valve and closing the exhaust valve to supply a preset quantity of fuel to the hydrogen supply device; closing the fuel supply valve, waiting until the internal pressure of the hydrogen supply device increases by generated hydrogen and the reaction is complete, opening the exhaust valve when the internal pressure of the hydrogen supply device increases by generating hydrogen so that the reaction is completed, and closing the exhaust valve after hydrogen in the hydrogen supply device is exhausted. These steps are repeated. The valve controller uses sensors provided in the hydrogen supply device to control valve operations. For example, in the case of a pressure sensor, the valve controller closes the exhaust valve based on the internal pressure of the hydrogen supply device, and opens the fuel supply valve to let fuel come into the hydrogen supply device. Further, when the reaction is completed and the internal pressure is stable, the valve controller opens the exhaust valve. The valve controller can also control timing to open and control valves by monitoring temperature changes by a temperature sensor or changes in thermal conductivity of gas by a thermal conductivity detector (TCD which is used for gas chromatography). Since evaporation of fuel and dehydrogenation are endothermic reactions, temperature of the hydrogen supply device slightly drops. After the reaction is completed, the temperature rises because of no endothermic reaction. The temperature sensors monitor these temperature changes and send signals to the valve controller. A temperature controlling using the TCD uses a change in thermal conductivity due to a change in gas components. Hydrogen is lower in thermal conductivity than fuel and dehydrogenates. Therefore, when the partial pressure of hydrogen increases after the reaction is complete or when the gas pressure in the hydrogen supply device reduces by exhausting, the thermal conductivity of gases in the device reduces. Signals of changes in thermal conductivity are sent to the valve controller to control timing to open and close the valves.
The fuel supply pressure can be some atmospheric pressures to some hundred atmospheric pressures. The gas in the hydrogen supply device can be exhausted naturally (through the exhaust valve) or forcibly by an air pump, turbo pump, or vacuum pump. Usually, it is preferable that the fuel supply pressure, hydrogen generation pressure, and exhaust pressure are respectively 2 to 20 atm, 5 to 300 atm, and atmospheric pressure to 0.01 atm in this order. The internal pressure of the hydrogen supply device varies 0.01 to 300 atm depending upon the operating status (fuel supply and gas exhausting).
The interval of intermittent (or pulsating) fuel supply is not specifically limited. It is optimized depending upon reaction temperature and pressure conditions. Fuel can be injected continuously or intermittently until the conversion rate reduces to some extent.
This invention basically controls the operation timing of the fuel inlet valve and the exhaust outlet valve to open the fuel inlet valve and close the exhaust outlet valve when supplying fuel to the hydrogen supply device,
to close both the fuel inlet valve and the exhaust outlet valve when hydrogen is generated, and
to close the fuel inlet valve and open the exhaust outlet valve when exhausting gas from the hydrogen supply device. However, this invention is not limited to this.
It is also possible to adopt the following steps:
opening both the fuel inlet valve and the exhaust outlet valve until the conversion rate reduces to some extent,
advancing the continuous reaction in the circulation system,
closing both the fuel inlet valve and the exhaust outlet valve when the conversion rate reaches a preset value, and
opening the exhaust valve which is connected to a vacuum pump to evacuate the hydrogen supply device for reactivation. The valve controlling brings about a great pressure change in reactivation of the system. The system need not be reactivated in a short time and it is possible to return the system to the continuous reaction of the circulation system after reactivation. In other words, it is possible to use a controlling method which combines valve timing control and continuous reaction of the circulation system. In some cases, the reactivation requires about 10 minutes but it depends upon temperature and pressure. Usually, it is 30 seconds or less. It can be a few seconds if the continuous reaction of the circulation system is not included.
It is also possible to control the time of dehydrogenation in the hydrogen supply device after injection of fuel. It is possible to carry out exhausting and reactivation simultaneously by closing both the fuel supply valve and the exhaust valve until dehydrogenation reaction of the supplied fuel is completed and opening the exhaust valve at the end of the dehydrogenation.
There are two valve timing control methods: controlling valves by their specified timing patterns and controlling valves by feeding back sensor signals. In time controlling, the characteristics of catalysts and reaction temperature, pressures, etc are investigated to obtain a sequence program in advance, the valve controlling device is operated in accordance with the sequence program. The valve controlling method by feedback of sensor signals uses various sensors such as pressure sensor, temperature sensor, flow-rate sensor, and hydrogen sensor, receives signals from the sensors, calculates the conversion rate of the reaction, and sends signals directly to operate the valves to minimize the change in the conversion rate.
The dehydrogenation of organic hydride is thermodynamically restricted and the conversion rate of the normal reaction is the equilibrium conversion rate which is thermodynamically calculated. To increase the efficiency of extracting hydrogen from organic hydride, the dehydrogenation must be kept at a preset low temperature. However, in this case, it is difficult to increase the conversion rate because of a thermo dynamical restriction. After thorough research and study, the inventors found that the conversion rate of the dehydrogenation at a temperature of 250° C. or lower is initially very high (when fuel is intermittently injected over the catalyst) but decreases down to the equilibrium conversion rate as the shots of fuel increases.
After further consideration, the inventors found that the catalyst of the equilibrium conversion rate can be reactivated by heating it to a high temperature or degassing it in a vacuum state. In the early stage of the reaction, catalyst surfaces are very active and show a high conversion rate. However, as the reaction proceeds, aromatic hydrocarbons (which are dehydrogenates) are adsorbed to the surface of the catalyst and the dehydrogenation becomes balanced with the hydrogenation. When the reaction is balanced, the conversion rate of the reaction is equal to the equilibrium conversion rate. When heated or degassed, the catalyst separates dehydrogenates from its surface and recovers the initial high activity. Naturally, the conversion rate of the reactivated catalyst is very high.
The catalyst reactivation by heating or vacuum-degassing can be carried out under any condition as long as the dehydrogenate can be removed from catalyst surfaces. For example, the catalyst reactivating condition can be 300° C. or lower and about 0.5 atm when the catalyst material can separate dehydrogenates easily but 400° C. and about 0.1 atm when the catalyst material is hard to separate dehydrogenates.
The hydrogen supply device of this invention is a reactor and a system which continuously reactivates catalysts by heating or vacuum-degassing using the above properties and assures high conversion rates even at low temperature. As described above, the hydrogen supply device of this invention unlike conventional hydrogen supply devices enables catalyst reactivation using pressure changes or catalyst reactivation by heating. By such a catalyst reactivation, the hydrogen supply device of this invention efficiently extracts hydrogen from organic hydrides even at low temperature and supplies hydrogen to hydrogen-requiring units such as a fuel cell and an engine.
Various auxiliary units are connected to the hydrogen supply device of this invention and explained below.
Auxiliary units connected to the hydrogen supply device of this invention which contains catalyst and a heater are:
a valve timing control unit for controlling timing to open and close valves provided on a fuel supply port and an exhaust port of the hydrogen supply device,
a booster pump for fuel supply,
an exhaust pump for exhausting product gas from the hydrogen supply device,
a separator for separating hydrogen from dehydrogenate,
a compressor for compressing generated hydrogen, and
a hydrogen tank for storage of generated hydrogen.
The valve timing control unit can be any unit as long as it can process parameters such as time, temperature, pressure, and thermal conductivity. For example, such units are a valve timing control device and circuit for automobile, a device and circuit for controlling an exhaust system such as a vacuum unit, etc.
The booster pump for fuel supply can be of any type (plunger type or piston type) as long as it can pressure-deliver liquid fuel. For example, it can be a fuel supply pump for automobile or a liquid pump for liquid chromatography which is available commercially.
The exhaust pump can be of any type (piston type or turbine type) as long as it can suck gases. For example, it can be an air pump, a vacuum pump, a micro turbine, or a supercharging turbine for automobile which is available commercially. Usually these pumps are driven by electric power but can be driven by exhaust gas from a fuel cell or engine. When an engine pump is used, the pump can be driven directly by the power of the engine. When the hydrogen supply device is mounted on a car, the pump can be driven by the power of an axle of the car. The separator uses air- or water-cooling to separate hydrogen (gas) and dehydrogenate (liquid) from each other. A cooling unit combined with a compressor or an electric means using the Peltier effect can be used for gas-liquid separation by cooling. Further, it is possible to use fuel instead of the cooling water to cool the gas-liquid mixture and-pre-heat the fuel simultaneously (just like a heat exchange). This kind of separator is not required when a hydrogen separating membrane is used to directly separate hydrogen in the hydrogen supply device.
The hydrogen supply device of this invention can be of any type (straight tube type, piston type, or micro reactor type). The hydrogen supply device basically comprises a highly-thermal conductive substrate and a catalyst layer, but can contain a hydrogen separation membrane in some cases. Independently of the device type (straight tube type, piston type, or micro reactor type), the hydrogen supply device have the same materials. The materials are explained below.
The highly-thermal conductive substrate can be made of ceramics such as aluminum nitride, silicon nitride, alumina, mullite, etc., carbon materials such as graphite sheet, etc., metals such as copper, nickel, aluminum, silicon, titanium, zirconium, niobium, and vanadium) or metal alloy. The highly-thermal conductive substrate should be thinner and have a greater thermal conductivity to quickly transfer heat to the catalyst layer and heat the catalyst layer efficiently without causing a temperature drop even in the endothermic reaction.
Next will be explained the catalyst. The catalyst is made of a metal catalyst and a carrier. The metal catalyst is at least one selected from a group of Ni, Pd, Pt, Rh, Ir, Re, Ru, Mo, W, V, Os, Cr, Co, Fe, and alloy of these metals. The carrier is at least one selected from a group of activated carbon, carbon nano-tube, silica, alumina, aluminum silicate (e.g., zeolite), zinc oxide, zirconium oxide, diatomite, niobium oxide, vanadium oxide, and so on.
The catalyst material can be prepared by any method such as a coprecipitation method or thermal decomposition method. The catalyst layer can be formed by a solution process such as a sol-gel process or a dry process such as a CVD process. To use a metal such as aluminum, zirconium, niobium, or vanadium for the highly-thermal conductive substrate, it is possible to anodize the metal and form the oxide carrier directly on the surface of the metal.
The hydrogen separation membrane is made of heat-resistant polymers such as porous polyimide, etc, alumino-silicate such as zeolite, etc, oxides such as silica, zirconia, or alumina, etc, metal alloys of Pd. Nb, Zr, V, or Ta. Nb and V foils are preferable. It is possible to use alloys of Nb or V with Mo, Co, or Ni.
The hydrogen separation membrane can be produced by a film-forming method such as a solution process, a vapor deposition process, and a sputtering process. The solution process is further divided into a dipping process, a spin-coating process, and a spraying process. The hydrogen separation membrane is formed by coating by any of these processes. The coating liquid can be a liquid, which contains dispersed particles. A metallic hydrogen separation membrane can be formed by a plating method such as electroless plating or electroplating method.
The hydrogen separation membrane, when made of porous polyimide, can have a skin layer on one side of the membrane and a porous polyimide layer containing voids or sponge-like cavities on the other side.
To increase the hydrogen separating efficiency, the catalyst material and the hydrogen separation membrane should preferably be adjacent to each other and more preferably be combined in a body. Porous membranes and metal foil membranes are available for hydrogen separation membranes unified with catalyst. The metal foil membrane comprises a metallic foil for separation of hydrogen which is a metallic foil of zirconium, niobium, vanadium or alloy thereof and a catalyst carrier of anodized metal (oxide) which is formed on the metallic foil.
The porous hydrogen separation membrane can hold catalyst in voids of the porous membrane made of alumina, zeolite, or porous polyimide. The hydrogen separating membrane can be formed on one side of the porous material by sputtering or plating.
The hydrogen storage and supply devices can be fabricated by laminating the above members into a large sheet of devices and cutting the sheet into small pieces of devices.
It is possible to use a catalyst carrier unified with the hydrogen separation membrane. For example, a clad catalyst carrier comprises metal alloy cores (Ni—Zr—Nb alloy) coated with a Nb layer. The Ni—Zr—Nb alloy membrane is more resistant to hydrogen embrittlement than a single metal membrane (Zr or Nb only) and has a good hydrogen permeability. The catalyst carrier unified with the hydrogen separation membrane can be fabricated by anodizing the Nb layer on the surface of the carrier material and adding Pt to the niobium oxide layer. It is more preferable to form a palladium layer selectively on the surface of the Ni—Zr—Nb layer by electro plating after anodizing since this accelerates association and dissociation of hydrogen molecules on the surface of the hydrogen separation membrane and increases the speed of hydrogen permeability.
The inventors measured the peak area of methylcyclohexane (98) and the peak area of toluene (92) and calculate the conversion rate (from methylcyclohexane to toluene) by gas chromatography GC-mass (GC-6500 by Simadzu Corp.). Table 1 lists the results.