WO2011020560A1

WO2011020560A1 - Method and device for generating electric energy

Info

Publication number: WO2011020560A1
Application number: PCT/EP2010/004755
Authority: WO
Inventors: Hans-Jürgen MAASS; Volker Göke; Andreas Opfermann; Otto Machhammer; Sigmar BRÄUNINGER; Laszlo Szarvas; Günther Huber; Dirk Gerhard
Original assignee: Linde Aktiengesellschaft
Priority date: 2009-08-18
Filing date: 2010-08-03
Publication date: 2011-02-24
Also published as: DE102009037883A1

Abstract

The invention relates to a method and a device for generating electric energy, wherein in a fuel source, a product is derived in an endothermic process from a charge material containing carbon and hydrogen, and subsequently, is directly or indirectly conveyed as fuel to the anode side of a fuel cell. The heat generated in the fuel cell is conveyed to the fuel source for maintaining the endothermic process.

Description

description

Method and device for generating electrical energy

The invention relates to a method for generating electrical energy, wherein obtained in a fuel source from a carbon and hydrogen-containing insert in an endothermic process, a product and then anodenseitjg fuel directly or indirectly fed to a fuel cell.

Furthermore, the invention relates to a device for carrying out the

inventive method.

For decades, significant efforts have been made by the industry to develop fuel cell technology to the extent that it is commercially viable to drive vehicles, particularly passenger cars. In a variety of prototypes, the functionality of the

Although fuel cell drives are demonstrated, the high costs and the lack of everyday practicality currently still prevent a wide market introduction.

The suitability for everyday use is particularly limited by the fact that most fuel cell types require pure hydrogen as fuel, which is a problem in two respects. On the one hand, it is difficult to store pure hydrogen in an amount on board a vehicle, as required for a range that is familiar to motorists. More importantly, there is currently no petrol station network anywhere in the world that is sufficiently leak tight to supply a fuel cell vehicle at any time, anywhere

To supply hydrogen.

In order to make easier-to-handle energy sources, such as. Methanol, for the

To be able to use refueling of fuel cell vehicles, the vehicles are equipped with reformers, in which hydrogen can be obtained from the energy source in an endothermic process. According to the prior art, the energy required for this purpose is removed from the energy carrier, whereby the electrical efficiency of the overall process is considerably reduced. With the direct methanol fuel cell (DMFC, Direct Methanol Fue Cell) is in principle a fuel cell type available, which can process a methanol-water mixture as fuel instead of Wasserst off gas. A DMFC operating at low temperatures of less than 100 ° C thus directly converts the chemical energy of methanol into electrical energy without the detour via a reformer, but has a comparatively low electrical efficiency. The practical implementation of the DMFC principle is still in progress

Development stage, because several problems could not be solved yet. Thus, the so-called. Permeation, d. H. the migration of methanol molecules through the electrolyte, can not be completely suppressed. This leads to fuel losses and contamination of the cathode of the fuel cell, resulting in a reduction of the recoverable voltage. Another problem is the formation of toxic carbon monoxide at the anode, which attacks the catalysts used and reduces the kinetics of methanol oxidation.

Object of the present invention is to provide a method of the type mentioned above and a device for its implementation, which allow to produce the electrical energy with a higher efficiency than is possible in the prior art.

According to the invention, the stated object is achieved by the fact that heat arising in the fuel cell is supplied to the fuel source for the purpose of maintaining the endothermic process.

By the method according to the invention, a large part of the heat accumulating in the fuel cell, which previously had to be disposed of as waste heat, to

Fuel production can be used. For operation of the fuel source therefore less or no external energy must be used, whereby the electrical efficiency of the fuel source and the fuel cell

comprehensive reactor system is increased. In order to be able to supply as much of the heat as possible from the fuel source in the fuel cell at the highest possible temperature level, a preferred embodiment of the method according to the invention for the thermal coupling of the two units provides for the use of a heat pipe.

Heat pipes have been state of the art and known to the person skilled in the art for many years. They contain in a hermetically encapsulated volume a heat transfer medium, which is present partly as a liquid, partly in gaseous form. Energy can be transferred to the liquid heat transfer medium via an evaporator connected to a heat source. The resulting vapor (vapors) flows to a condenser located elsewhere in the heat pipe and connected to a heat sink, where it condenses. During condensation, the energy absorbed via the evaporator is released to a large extent again and transferred to the heat sink. The now again liquid heat transfer medium is then conveyed back to the evaporator by the action of gravity, capillary force or by means of a pump.

Since the liquid and gas phase of the heat transfer medium are in the same room, a heat pipe operates in the wet steam area, in which the two phases also have the same temperature at the same pressure. Usually they are

Pressure differences in a heat pipe very low, which is why the

Temperature difference between evaporator and condenser is low. Because of the nearly isothermal nature of heat transfer, a heat pipe has an internal thermal resistance that is less than that of classic, purely metallic heat exchangers.

In vehicles, steam reformers are commonly used as fuel sources in which a carbonaceous feed is converted to a hydrogen product by the addition of water and oxygen by steam reforming. For example, when used with methanol, steam reforming starts

Temperatures of more than 400 ° C from. However, apart from the molten carbonate and solid oxide fuel cells, both of which are more suitable for stationary rather than mobile use, fuel cells operate at temperatures well below 400 ° C, which is why it is not possible to obtain the heat generated during their operation directly to the steam reformer. In the event that the heat is obtained in the fuel cell at a lower level than is needed in the fuel source, provides a further embodiment of the method according to the invention that the temperature of the vaporized in the fuel cell heat transfer medium is raised by vapor compression to the required value before it is sent to the fuel source, where it condenses, giving off much of the entrained energy.

Another preferred embodiment of the method according to the invention provides that a liquid phase reformer, such as. Example, a HTK reactor is used, in which the use of carbon and hydrogen at temperatures of less than 250 ° C and pressures between 1 and 1000 bar is implemented by liquid phase reforming. This makes it possible to use the waste heat of most - fuel cell types at the same temperature level at which it is obtained. Measures to increase the temperature, such as a vapor recompression, can therefore be dispensed with.

A HTK reactor is to be understood as meaning a device for implementing an application by hydrothermal catalysis (HTK), as described in a patent application filed under the reference 102008045484.2 at the German Trademark and Patent Office, and the disclosure of which is fully cited is incorporated in the present patent application.

If a HTK reactor is used to carry out the process according to the invention, any substance listed in the abovementioned patent applications can be used as the insert. Preferably, however, an insert is selected which comprises at least one member of the group formed of on and off

polyhydric alcohols and carbohydrates. However, the use particularly preferably comprises methanol and / or ethanol and / or glycerol and / or sorbitol and / or xylitol and / or glucose and / or xylose and / or cellulose and / or hemicellulose.

As has been shown in experiments, the hydrogen yield at a

Liquid phase reforming may be increased by the fact that the reforming is carried out in the presence of water. It we therefore suggested that the Carbon and hydrogen containing insert is reacted in the presence of water.

From the use of carbon and hydrogen arises in the

A fuel source is usually a hydrogen-rich product, which in addition to hydrogen also contains by-products that are undesirable in a fuel cell, and therefore must be separated before the product as fuel in the

Fuel cell may be initiated. ^"A further preferred embodiment of the method according to the invention therefore provides that a signal generated in the fuel source product gas is cooled down in a condenser to condense at least a portion of the undesired by-products.

If the substances separated off from the product produced in the fuel source are flammable, they are expediently conducted into a tank and temporarily stored there. In the cold start phase, the combustible materials can be removed from the tank and burned, with the heat generated thereby for heating the fuel source and the fuel cell comprising

Reactor system is used. Excess combustible substances are

preferably burned during operation of the reactor system in an exhaust gas burner.

The method according to the invention is suitable for generating electrical energy both by means of stationary and mobile devices. With particular advantage, however, it is used for generating at least part of the energy required for the operation of a vehicle, in particular a passenger car, wherein the reaction system comprising the fuel source and the fuel cell is arranged on board the vehicle.

Furthermore, the invention relates to a reactor system for generating electrical energy, comprising a fuel cell and a fuel source connected thereto, in the use of a carbon and containing hydrogen in one

endothermic process, a product flow can be generated, which can be supplied on the anode side directly or indirectly as fuel of the fuel cell. The stated object is achieved on the part of the reactor system according to the invention in that the fuel cell and fuel source are thermally coupled, so that resulting in the fuel cell heat of the fuel source for maintaining the running there endothermic process can be fed.

A heat pipe is a device with which a heat source and a heat sink can be thermally coupled very effectively. In addition, it also has a comparatively low power to weight, which makes them particularly suitable for use in vehicles. A preferred embodiment of the invention therefore provides that the fuel cell and the fuel source are thermally coupled via a heat pipe.

As a fuel source, the reactor system according to the invention can be any kind of

Device (eg., A steam reformer), in which from a carbon and hydrogen-containing insert, a product can be generated, which is fed directly or indirectly to a fuel cell as fuel. Preferably, however, the fuel source is a liquid phase reformer, and more preferably a reactor designed to carry out a hydrothermal catalysis (HTK reactor).

Frequently, a product is produced in a fuel source which, in addition to substances which can be used as fuel in a fuel cell, also contains substances which are harmful in the fuel cell and which must be separated from the product before it is passed on. If the product is a product gas, an embodiment of the reactor system according to the invention provides a condenser in which harmful substance passes through the fuel cell

Condensation can be separated from the product gas generated in the fuel source.

In a further embodiment, the reactor system according to the invention comprises a tank in which substances separated off from the product produced in the fuel source can be intermediately stored. It is expedient if necessary (for example during a cold start of the device) to remove at least some of the temporarily stored substances and to burn them in a burner while generating heat required in the reaction system. For this purpose, the reactor system comprises means for detecting the sensible heat generated in the burner of one or more components of the

Reactor system can be fed to heat them. Appropriately, the Burner also be used to burn in the fuel cell resulting, still flammable substances containing exhaust gas.

Further developing the reactor system according to the invention, it is proposed that it comprises an accumulator in which the electrical energy generated in the fuel cell can be temporarily stored. The capacity of the accumulator is chosen so that it can supply the required by the fuel cell electrical line alone in the cold start phase and on the other hand can provide peak power occurring during operation (for example, for acceleration operations of a powered by the reactor system vehicle).

The reactor system according to the invention can be erected both stationary and installed on board a vehicle. Preferably, however, it is installed on board a vehicle to provide drive power to the vehicle.

In the following, the invention will be explained in more detail with reference to an exemplary embodiment shown schematically in FIG.

The exemplary embodiment is a methanol-operated one

Reactor system, as it can be used for example to drive a passenger car.

In tank T1, a mixture of water and methanol is stored, which is conveyed via line 1 by means of the pump P1 in the HTK reactor H. In the HTK reactor H, the methanol is reacted in the presence of a catalyst at a temperature of about 180 ° C and a pressure corresponding to the vapor pressure equilibrium in a liquid phase reaction, wherein a product gas is formed, which is withdrawn via line 2. The product gas 2 consists for the most part of hydrogen, but also contains flammable by-products, which are condensed in the heat exchanger E1 at a temperature of about 30 ° C and passed through line 3 for intermediate storage in the condensate tank T2. With a pressure which is only slightly higher than the ambient pressure, the purified product gas exits the heat exchanger E1 and is supplied as fuel 4 to the anode A of the fuel cell BZ. The still containing hydrogen

Anodenrestgas is withdrawn via line 5 from the fuel cell BZ and in Exhaust gas burner B disposed of, largely pollutant-free exhaust gas 15 is formed. In a cold start of the reactor system, the exhaust gas burner B is used to provide necessary for the operation of heat, via line 6 condensate can be supplied from the condensate tank T2 and burned. Via line 7 and the fan V of the cathode K of the fuel cell BZ air is supplied. With an oxygen content of cä. 10%, the cathode residual gas is withdrawn via line 8 and forwarded as oxidant to the exhaust gas burner B. To dissipate the waste heat generated in the fuel cell BZ liquid water is evaporated in the heat exchanger E2. A partial amount 10 of the resulting vapor 1 1 is condensed again in the heat exchanger E3 and gives off a large part of the energy absorbed in the fuel cell BZ to the HTK reactor H, where it serves to maintain the endothermic reaction taking place there. The remaining, not required in the HTK reactor steam 12 is also condensed in the heat exchanger E4, wherein the heat of condensation is released to the ambient air. With the help of the pump P2, the condensate flows 13 and 14 formed in the two heat exchangers E3 and E4 are finally conveyed back to the fuel cell BZ. The characteristic of a fuel cell does not allow the electric power supplied by it to vary widely and rapidly

Adjust the performance requirements of a passenger car. For this reason, the electric power generated in the fuel cell BZ is temporarily stored in the accumulator A before being supplied to the electric motor M serving to drive the passenger car.

Claims

claims

A method for generating electrical energy, wherein in a fuel source from a carbon and hydrogen-containing insert in an endothermic process, a product is obtained and then directly or indirectly fed to a fuel cell on the anode side as fuel, characterized

characterized in that resulting in the fuel cell heat the

Fuel source is supplied to maintain the endothermic process.

A method according to claim 1, characterized in that in the fuel cell resulting heat of the fuel source is supplied via a heat pipe.

Method according to one of claims 1 or 2, characterized in that the carbon and hydrogen-containing insert at temperatures of less than 200 ° C and pressures between 1 and 1000 bar by

Liquid phase reforming, preferably by hydrothermal catalysis, is implemented.

Method according to one of claims 1 to 3, characterized in that the insert contains oxygen, preferably methanol and / or ethanol and / or glycerol and / or sorbitol and / or xylitol and / or glucose and / or xylose and / or cellulose and / or hemicellulose.

Method according to one of claims 1 to 4, characterized in that the carbon and hydrogen-containing insert is reacted in the presence of water.

Method according to one of claims 1 to 5, characterized in that the electrical energy generated in the fuel cell is used for operating a vehicle.

Reactor system for generating electrical energy, comprising

Fuel cell and a fuel source connected to this, in which from a carbon and hydrogen-containing insert in an endothermic process, a product flow can be generated, which can be supplied on the anode side directly or indirectly as fuel of the fuel cell, characterized the fuel cell and the fuel source are thermally coupled, so that heat arising in the fuel cell can be supplied to the fuel source in order to maintain the endothermic process taking place there.

8. Reactor system according to claim 7, characterized in that the fuel cell and fuel source are thermally coupled via a heat pipe.

9. Reactor system according to one of claims 7 or 8, characterized in that the fuel source as a reactor for carrying out a

Liquid phase reforming, preferably a hydrothermal catalysis is executed.

10. Reactor system according to one of claims 7 to 9, characterized in that it comprises a device in which harmful substances for the fuel cell can be separated by condensation of the product gas generated in the fuel source.

11. Reactor system according to one of claims 7 to 10, characterized in that it comprises a tank, in which from the product produced in the fuel source separated substances can be cached.

12. Reactor system according to one of claims 7 to 11, characterized in that it comprises a burner, in which the exhaust gas of the fuel cell and / or from the product produced in the fuel source separated substances can be burned.

13. Reactor system according to claim 12, characterized in that it has a

Means comprises, via the sensible heat generated in the burner of one or morei components of the reactor system can be supplied to heat them.

14. Reactor system according to one of claims 7 to 13, characterized in that it is installed on board a vehicle to drive power for the

Vehicle to deliver.