WO2007021172A1

WO2007021172A1 - System and method for integration of renewable energy and fuel cell for the production of electricity and hydrogen

Info

Publication number: WO2007021172A1
Application number: PCT/NL2006/000398
Authority: WO
Inventors: Klaas Hemmes
Original assignee: Technische Universiteit Delft
Priority date: 2005-08-17
Filing date: 2006-08-04
Publication date: 2007-02-22
Also published as: NL1029758C2

Abstract

The invention relates to a system and method for integrating renewable energy and a fuel cell for the production of electricity and hydrogen, wherein this comprises the use of renewable energy as fluctuating energy source for the production of electricity and also comprises the use of at least one fuel cell, and wherein a control unit controls the operation of the at least one fuel cell such that the total production of electricity lies within chosen limits.

Description

SYSTEM AND METHOD FOR INTEGRATION OF RENEWABLE ENERGY AND FUEL CELL FOR THE PRODUCTION OF ELECTRICITY AND HYDROGEN

The present invention relates to a system for the integration of renewable energy and a fuel cell for the production of electricity and hydrogen.

The production of electricity with the aid of fluc- 5 tuating energy sources, for example, but not exclusively, renewable energy sources such as a heat-controlled total energy plant, and a renewable energy source chosen from wind energy, solar energy, biomass energy, hydro-energy and geo-energy, is generally known in the art. A known example of such a system

10 uses wind turbines. Wind turbines are, often in large numbers, placed together where they can make a contribution to the electricity grid.

Obviously, the amount of electricity produced depends very much on the amount of wind. At moments of little

15 or no wind it will not be possible to contribute to the electricity grid. At moments of strong wind on the other hand, it is even possible that the amount of energy cannot be transferred to the electricity grid because the electricity grid has a limited capacity of acceptance.

20 On occasions of substantial electricity production by means of wind turbines, the surplus of electricity is sometimes used for the production of hydrogen. In that case the electricity is used for the electrolysis of water. During that process oxygen is released, which is often vented into

25 the air. The hydrogen produced is stored in tanks, to be offered for retailing, or to be converted in a fuel cell into electricity in times of little wind.

This known system has disadvantages. The total costs that have to be incurred for the production of the hydrogen

30 are very high. In practice there will actually only infrequently be so much wind that a surplus of electricity has to be used for the production of hydrogen. Nevertheless, the technical equipment for doing this ought to be on hand. Another drawback exists in the fact that these known systems are not embodied in such a way as to allow the maximum amount of electricity produced in the system to be supplied to the electricity grid. Renewable electricity generated with the aid of photovoltaic cells also suffers the above-mentioned drawback as, characteristically, it is not produced continuously.

It is therefore the object of the invention to provide an improved system. A particular object of the invention is to provide a system wherein substantially independently of the electricity supplied by the fluctuating energy source, for example, irrespective of the amount of wind or sun, a constant or easily controllable production of electricity is possible, so as to meet the demand for electricity.

The object of the invention is especially to provide a system with which it is at all times possible to control the amount of electricity supplied to the electricity grid.

It is also an object of the invention to provide a system wherein electricity can be produced even when it is calm, or at night.

In order to achieve at least one of the above- mentioned objectives, the invention provides a system of the kind mentioned in the preamble, which is characterised by the measures of claim 1.

By means of this system according to the invention, it is at all times possible to produce a previously to be determined amount of electricity.

Other advantages of the invention will become appar- ent after reading the following description of the system according to the invention as well as through various exemplary embodiments .

According to a preferred embodiment of the invention, the fuel cell produces in addition to electricity also hydrogen. To this end the fuel cell may advantageously comprise a hydrogen product outlet, which may or may not be in direct communication with a gas pipe for supplying the hydrogen produced to a fuel gas pipe, preferably a natural gas pipe. Due to the combined production of electricity and hydrogen, electricity is thus supplied to the electricity grid on the one hand while, on the other hand, hydrogen can be supplied to a gas pipe. This is in particular very convenient when the fuel used for the fuel cell is gas, for example natural gas. The hydrogen produced in the fuel cell can then be returned to the natural gas pipe. This greatly improves the overall performance of the system.

The phrase "may or may not be in direct communica- tion" refers to the fact that the produced hydrogen may be conducted directly from the fuel cell to the fuel gas pipe, or that this gas is subjected to an optional pre-treatment . Such a pre-treatment is the removal of residual gasses that are not allowed to be fed into a fuel gas pipe. If the oxygen supply to the fuel cell is air, the oxygen will be used principally for the combustion of the fuel in the fuel cell. The residual gas, mainly nitrogen, may optionally be fed to the gas pipe in order to adjust the energy content of the gas to a desired value. Alternatively, this gas stream consisting mainly of nitrogen may optionally be treated in order to make it suitable for supply to a fuel gas pipe, for example, a natural gas pipe. Such a treatment may, for example, consist of the removal of oxygen. As mentioned earlier, it is especially preferred for an organic gas, for example and preferably CEU (methane, natural gas) to be used as fuel for the fuel cell. The reason is that methane can simply be converted by an internal reforming fuel cell into, among other things, hydrogen. Other product gasses are mainly CO2 and CO. According to known techniques, CO can be converted into hydrogen and CO₂ by means of a so-called shift reaction with steam (H₂O) . This further increases the total production of hydrogen.

It is further preferred for the system according to the invention to comprise the supply of heat from the fuel cell to a heat-requiring system. The heat produced in the fuel cell can then be removed from the fuel cell and supplied to the heat-requiring system. Such a heat-requiring system may, for example, be the surroundings. However, it is also possible to apply the heat produced in the fuel cell with purpose, for example, when the fuel cell is positioned near a natural gas mixing station. The pressure of the extracted natural gas is usually very much higher than the pressure in a natural gas pipeline. Since during the expansion of the extracted natural gas to the pressure prevailing in the natural gas pipeline said natural gas cools down considerably, it is advantageous to use the heat produced in the fuel cell for heating the natural gas to be expanded. This greatly improves the total energy utilisation of the system. It is especially preferred for the nitrogen stream produced in the fuel cell to be supplied to the natural gas stream to be expanded, which allows both the calorific value and the temperature of the natural gas stream to be adjusted as desired. Although in the above the application of the s.ystem refers mainly to the use of wind energy, the system is equally suitable to be used with solar energy, hydro-energy, such as wave energy, biomass energy, geo-energy and other fluctuating energy sources. The invention also relates to a method for the production of electricity, wherein a renewable energy source is used. To this end the method comprises the measures mentioned in claim 10.

The application of this method allows the objectives to be achieved as described above and with reference to the system according to the invention.

It is especially preferred for the total production from the renewable energy source and the fuel cell to be substantially equivalent to the predetermined value. This makes a very accurate electricity production possible, which is geared to electricity demand and/or is economically optimised.

It is especially preferred for the system according to the invention to be used with the method described above. This provides the combined advantages of the two aspects of the invention.

Within the scope of the invention it is preferred for the predetermined value to be variable. When the elec- tricity demand is high, for example, it is then possible to set the predetermined value at a higher value than when the electricity demand is low. However, when there is a constant electricity demand, the electricity demand can also be met in calm weather. Depending on the number of fuel cells that are used and on the operational nature of the fuel cells, it is possible to have the fuel cells produce all of the electricity, or a further to be determined maximum or minimum part thereof. The operation of a fuel cell provides, for example, the possibility to choose between an operation yielding a high electricity production and a low hydrogen production, or an operation providing little electricity and producing much hydrogen. A combination of these is also possible. A person skilled in the art is able to adapt a fuel cell such that one of these types of operations is obtained or a combination thereof.

Although in the above reference is mainly made to the use of one wind turbine and one fuel cell, the invention is not limited to the number of wind turbines or the number of fuel cells. In principle, the number of wind turbines and the number of fuel cells may be chosen arbitrarily. However, the number of fuel cells is chosen such that the maximum electricity production they are capable of is approximately the same as the maximum electricity production by wind tur- bines. This makes it possible, in calm weather, to deliver the maximum electricity production. Since a fuel cell can be easily adjusted with respect to electricity production and/or hydrogen production, a fluctuating electricity production by wind energy can be levelled out by a suitable operation of the fuel cells. Alternatively, the maximum capacity of the fuel cell and the fluctuating energy source may be chosen to equal the maximum amount of electricity that can be accepted by the electricity grid.

According to the invention it is particularly advan- tageous to use an internal reforming fuel cell in the system and the method according to the invention. It is in particular preferred for a fuel cell to be combined with devices for the generation of electricity from different sources of re- newable energy. The fuel cell may, for example, be combined with one or several wind turbines, as well as with one or several solar cells. Combinations of other renewable energy sources are of course also possible. Depending on the weather conditions, the electricity production from renewable energy sources will in that case almost certainly never be zero. Apart from the above-mentioned objectives that have been explicitly described, and which are implicitly known to a person skilled in the art, the big advantage achieved is that the installation costs can be considerably reduced in comparison with a known system. This is because the system according to the invention requires no electrolysis equipment. Likewise, no unnecessary oxygen is produced. As a result, the system according to the present invention is highly effi- cient.

The hydrogen produced in the fuel cell does not need to be stored in storage facilities manufactured especially for this purpose, but may be introduced into existing facilities, such as natural gas fields, gas containers for biomass converters etc.

Since only very little or no residual heat is produced, the performance is further improved.

The invention will now be further elucidated by way of a computation example. When a fuel cell is operated as hy- drogen producer, the total efficiency of the fuel cell increases in comparison with a fuel cell that is operated as electricity producer only. When a fixed amount of fuel (natural gas) is supplied to the fuel cell, it is possible to choose between an operation of mainly electricity production or an operation wherein also a (considerable) amount of hydrogen is produced.

If at a constant supply of natural gas the electricity production is reduced by 190 kW, this reduction in electricity production can be converted into a 727 kW increase of the hydrogen production. Such an operation is possible, for example, if the wind energy increases by 190 kW. The decrease of electricity produced by the fuel cell results in an extra production of 727 kW of carbon monoxide and hydrogen. Hereby an apparent efficiency of (727 : 190 x 100% =) 383% is obtained. The computation example chosen here works with arbitrarily chosen capacities. In practice larger capacities will be required, but the principle of the invention and the ap- parent efficiency obtained apply also to larger capacities. Via a so-called shift reaction with steam, the carbon monoxide can be converted into hydrogen and CO2 in a manner known in the art. The increase in efficiency is obtained due to an increase of the energy stored in the gasses produced, and a reduction of the amount of heat produced in the fuel cell. If the surplus of electricity that was produced by the wind turbines were to be used for the electrolysis of water into hydrogen and oxygen, the return would be only 80 to 90%. In this way therefore, the production of hydrogen would only amount to approximately 150-170 kW.

The system according to the invention is therefore much more efficient than the systems normally used in the art.

As described above, the hydrogen produced may be supplied to a pipeline system for natural gas. It is possible that the fuel cell also produces a nitrogen stream. This nitrogen stream may also, together with the hydrogen or separately, and possibly in the same pipe, be supplied to the natural gas pipeline in order to adjust the total energy con- tent of the gas in the gas pipe to a desired value.

It is further preferred for the electricity production of the fuel cell to be substantially equivalent to the difference between the predetermined value and the measured value . It is also preferred for the method according to the invention to use a system according to the present invention for controlling the operation of the fuel cell.

It is further preferred for the gas stream from the cathode to be subjected to a further treatment in order to remove a residual amount of oxygen therefrom, for example, by feeding the same to a catalytic oxidiser, and after which the treated gas stream is at least partly fed to the natural gas stream. In addition it is preferred for the gas stream from the cathode to be fed to the cathode of a low-temperature fuel cell.

It is further preferred for the hydrogen from an anodic gas stream of the first fuel cell to be fed to the anode of a second fuel cell, and for a cathodic gas stream of the first fuel cell, which in comparison with air has a lower oxygen content, to be fed to the cathode of the second fuel cell. It is also preferred for the fuel cell to which air is fed to be a high-temperature fuel cell, preferably of the internal reforming type, for example an SOFC type or an MCFC type .

It is finally preferred for at least a part of the produced electricity to be supplied to the electricity grid.

The invention is not limited to the supply of the produced hydrogen to a gas pipe. For example, the hydrogen may be stored and later used as fuel in a fuel cell, even in a fuel cell that is designed for hydrogen production. Although in the above reference is made in particular to a natural gas stream, other fuels are also indicated. Therefore the invention is directed at all hydrocarbons (including carbon) that by means of H2O and/or CO2 can be converted into an H2-containing gas stream. A method for the production of nitrogen and hydrogen in a fuel cell is described in the Dutch patent application entitled "Method for the production of nitrogen and hydrogen in a fuel cell" and the Dutch patent application entitled "Method for the integrated operation of a fuel cell and an air separator" filed simultaneously with the present patent application.

The invention is not limited to the above-described embodiments. These relate only to a preferred embodiment of the invention. The invention is limited by the appended claims only.

Claims

1. A system for the integration of renewable energy and a fuel cell for the production of electricity and hydrogen, characterised in that this comprises the use of renewable energy as fluctuating energy source for the production of electricity and at the same time the use of at least one fuel cell, and wherein a control unit controls the operation of the at least one fuel cell such that the total production of electricity lies within to be predetermined limits.

2. A system according to claim 1, characterised in that the fluctuating energy source is chosen from at least one of a heat-controlled total energy plant and a renewable energy source chosen from wind energy, solar energy, biomass energy, hydro-energy and geo-energy.

3. A system according to claim 1, characterised in that a fuel supply to the fuel cell is connected with a fuel pipe, for example, a natural gas pipe.

4. A system according to claim 1 or 3, characterised in that apart from electricity, the fuel cell also produces hydrogen.

5. A system according to claims 1-4, characterised in that the fuel cell comprises a hydrogen product outlet, which may or may not be in direct communication with a gas pipe for supplying the hydrogen produced to a fuel gas pipe, preferably a natural gas pipe.

6. A system according to claims 1-4, characterised in that apart from electricity and hydrogen, the fuel cell also produces nitrogen.

7. A system according to claims 1-6, characterised in that the fuel cell comprises a nitrogen product outlet that may or may not be in direct communication with a gas pipe for supplying the nitrogen produced to a fuel gas pipe, for example, a natural gas pipe, for example, the pipe to which the produced hydrogen is supplied.

8. A system according to claims 1-7, characterised in that heat produced by the fuel cells is conducted to a heat-requiring system.

9. A system according to claim 8, characterised in that the heat-requiring system comprises a device for heating extracted natural gas that is to be expanded.

10. A method for integrating renewable energy as fluctuating energy source, and fuel cell for the production of electricity and hydrogen, characterised in that these steps comprise measuring the electricity production of the fluctuating energy source, comparing the electricity production of the fluctuating energy source with a predetermined production value, and operating a fuel cell for the production of at least electricity, if the measured value is lower than the predetermined value.

11. A method according to claim 10, characterised in that the electricity production of the fuel cell is substantially equivalent to the difference between the predetermined value and the measured value.

12. A method according to claim 10 or 11, characterised in that it uses a system according to claims 1-9 for controlling the operation of the fuel cell.

13. A method according to claim 10, characterised in that the gas stream from the cathode is subjected to a fur- ther treatment in order to remove a residual amount of oxygen therefrom, for example, by feeding the same to a catalytic oxidiser, and after which at least part of the treated gas stream is fed to the natural gas stream.

14. A method according to claim 13, characterised in that the gas stream from the cathode is fed to the cathode of a low-temperature fuel cell.

15. A method according to claim 13 or 14 wherein at least hydrogen is formed in a first fuel cell, characterised in that hydrogen from an anodic gas stream of the first fuel cell is fed to the anode of a second fuel cell, and a ca- thodic gas stream of the first fuel cell, which compared with air has a lower oxygen content, is fed to the cathode of the second fuel cell.

16. A method according to claim 10, characterised in that the fuel cell to which air is supplied is a high- temperature fuel cell, preferably of the internal reforming type, preferably an SOFC type or an MCFC type.

17. A method according to claim 10, characterised in that at least part of the electricity produced is supplied to the electricity grid.