ENERGY CONVERTING DEVICE FOR CONVERTING ELECTRIC ENERGY INTO CHEMICAL ENERGY, ELECTRICAL NETWORK COMPRISING SUCH AN ENERGY CONVERTING DEVICE, AND METHOD FOR OPERATING SUCH AN ENERGY CONVERTING DEVICE

Abstract

An energy converting device and method for converting electric energy into chemical energy, including an electrolysis device which can be connected to an electrical network and is designed to split water into hydrogen and oxygen using electric power; a fuel synthesis device which is fluidically connected to the electrolysis device such that the fuel synthesis device can be supplied with hydrogen generated in the electrolysis device as a reactant, wherein the fuel synthesis device is designed to synthesize a fuel from hydrogen and carbon dioxide; and an internal combustion engine which is fluidically connected to the electrolysis device such that the internal combustion engine can be supplied with oxygen generated in the electrolysis device. The internal combustion engine is designed to be operated in a continuous mode using the oxygen generated in the electrolysis device as combustion gas.

Claims

1-10. (canceled)

11. An energy-converting device for converting electrical energy into chemical energy, comprising: an electrolysis device connectable to an electricity network and configured to split water into hydrogen and oxygen by electrical power from the electricity network; a fuel synthesis device connected in terms of flow to the electrolysis device so that hydrogen produced in the electrolysis device is feedable as a starting product to the fuel synthesis device, wherein the fuel synthesis device is configured to synthesize a fuel from hydrogen and carbon dioxide; and a combustion engine connected in terms of flow to the electrolysis device so that oxygen produced in the electrolysis device is feedable to the combustion engine, wherein the combustion engine is configured to be operated in a continuous operation mode with the oxygen produced in the electrolysis device as combustion gas.

12. The energy-converting device according to claim 11, wherein the combustion engine is connected in terms of flow to the fuel synthesis device so that carbon dioxide formed in the combustion engine is feedable as a starting product to the fuel synthesis device.

13. The energy-converting device according to claim 11, wherein a) the combustion engine is configured to be operated, at least in the continuous operation mode, with the fuel synthesized in the fuel synthesis device, and/or b) the combustion engine is connected in terms of flow to the electrolysis device such that hydrogen produced in the electrolysis device is fed to the combustion engine for combustion in a combustion chamber of the combustion engine.

14. The energy-converting device according to claim 11, wherein the combustion engine has an exhaust-gas recirculation device configured to retain carbon-dioxide-containing and water-containing exhaust gas, formed in a previous combustion, in a combustion chamber of the combustion engine, or to recirculate said exhaust gas into the combustion chamber for a subsequent combustion.

15. The energy-converting device according to claim 11, further comprising an electric machine electrically connectable to the electricity network, wherein the combustion engine is operatively connected in terms of drive to the electric machine.

16. The energy-converting device according to claim 11, wherein the combustion engine is configured to be operated with ambient air as combustion gas in a starting operation mode, wherein the combustion engine has a first valve device with a first functional position that shuts off a charging path of the combustion engine with respect to surroundings of the combustion engine, and a second functional position in which ambient air from the surroundings of the combustion engine is fed to the charging path.

17. An electricity network, comprising: at least one regenerative energy source; an energy-converting device according to claim 11; and electrical lines that electrically connect the energy-converting device and the at least one regenerative energy source to one another, wherein the electricity network is configured to feed electrical power from the at least one regenerative energy source to the electrolysis device of the energy-converting device.

18. A method for operating an energy-converting device having an electrolysis device connected to an electricity network and configured to split water into hydrogen and oxygen by electrical power from the electricity network, a fuel synthesis device configured to synthesize a fuel from hydrogen and carbon dioxide, and a combustion engine, the method comprising steps of: feeding hydrogen produced in the electrolysis device as a starting product to the fuel synthesis device; feeding oxygen produced in the electrolysis device to the combustion engine; and operating the combustion engine in a continuous operation mode with the oxygen produced in the electrolysis device as combustion gas.

19. The method according to claim 18, including feeding carbon dioxide produced in the combustion engine as starting product to the fuel synthesis device.

20. The method according to claim 18, including operating the combustion engine with stoichiometric combustion.

Description

[0051] The invention will be discussed in more detail below on the basis of the drawing. Here, the single FIGURE is a schematic illustration of an exemplary embodiment of an electricity network with an energy-converting device, and an embodiment of a method for operating the energy-converting device.

[0052] The single FIGURE is a schematic illustration of an exemplary embodiment of an electricity network 1 with an exemplary embodiment of an energy-converting device 3, and is also a schematic illustration of an embodiment of a method for operating the energy-converting device 3.

[0053] The energy-converting device 3 is configured for converting electrical energy into chemical energy, wherein said energy-converting device has an electrolysis device 5 which is connected to the electricity network 1, wherein the electrolysis device 5 is configured to take electrical power P.sub.el from the electricity network 1 and to split water (H.sub.2O) into hydrogen (H.sub.2) and oxygen (O.sub.2) by means of said electrical power. The energy-converting device 3 furthermore has a fuel synthesis device 7, which is connected in terms of flow to the electrolysis device 5 such that hydrogen produced in the electrolysis device 5 can be fed as starting product to the fuel synthesis device 7, wherein the fuel synthesis device is configured to synthesize a fuel from hydrogen and carbon dioxide (CO.sub.2). The fuel synthesis device 7 is in this case designed in particular as a methane synthesis device or methanizer and configured to synthesize methane (CH.sub.4) from hydrogen and carbon dioxide.

[0054] The energy-converting device 3 furthermore has a combustion engine 9, which is connected in terms of flow to the electrolysis device 5 such that oxygen produced in the electrolysis device 5 can be fed to the combustion engine 9. Here, the combustion engine 9 is configured to be operated in a continuous operation mode with the oxygen produced in the electrolysis device 5 as combustion gas.

[0055] The combustion engine 9 is furthermore preferably connected in terms of flow to the fuel synthesis device 7 such that carbon dioxide formed in the combustion engine 9 can be fed as starting product to the fuel synthesis device 7. During a combustion in a combustion chamber 11 of the combustion engine 9, carbon-dioxide-containing exhaust gas forms, wherein, in the case of the energy-converting device 3 proposed here, the carbon dioxide is not released into the surroundings but rather is fed to the fuel synthesis device 7 as starting product for the production of the fuel, in this case in particular for the synthesis of methane.

[0056] For this purpose, the combustion engine 9 preferably has a separation device 13 which is configured to separate carbon dioxide, as far as possible in pure form, and preferably 100%, out of the exhaust gas of the combustion engine 9, wherein the pure carbon dioxide can then be fed from the separation device 13 via a suitable fluidic connection to the fuel synthesis device 7.

[0057] During the combustion in the combustion chamber 11, water also forms, which can preferably likewise be separated off in the separation device 13, wherein said wateras is schematically illustrated in the FIGUREis in turn fed as starting product to the electrolysis device 5.

[0058] Water also forms as a byproduct in the fuel synthesis device 7, which water is preferably likewise fed as starting product to the electrolysis device 5.

[0059] If the combustion engine 9 is operated with pure oxygen as combustion gas in stoichiometric operation, only carbon dioxide and water form as products of the combustion in the combustion chamber 11, which carbon dioxide and water can be separated from one another in the separation device 13 and fed as separate substance streams to the fuel synthesis device 7, on the one hand, and to the electrolysis device 5, on the other hand. In this case, no combustion products of the combustion engine 9 are released into the surroundings, such that the combustion engine 9 can be operated in a manner free from pollutant emissions and even altogether free from emissions. Owing to the operation of the combustion engine 9 with pure oxygen from the electrolysis device 5, it is in particular the case that no nitrogen oxides form.

[0060] The combustion engine 9 is preferably designed to be operated, at least in the continuous operation mode, with the fuel synthesized in the fuel synthesis device 7, in this case in particular with methane. In this respect, the combustion engine 9 is preferably connected in terms of flow to the fuel synthesis device 7 such that fuel synthesized in the fuel synthesis device 7 can be fed to the combustion engine 9 for combustion in the combustion chamber 11. The combustion engine 9 is designed in particular as a gas engine. It is however not necessary for the combustion engine 9 and the fuel synthesis device 7 to be directly connected to one another in terms of flow. It is possible for a fuel store device to be arranged between the combustion engine 9 and the fuel synthesis device 7. It is also possible for the fuel synthesis device 7, on the one hand, and combustion engine 9, on the other hand, to each be connected to a fuel network, for example an interconnected natural gas network.

[0061] It is however also possible for the combustion engine 9 to draw a fuel, in particular a combustion gas, preferably methane, from a fuel source that is independent of the fuel synthesis device 7, wherein the fuel synthesized in the fuel synthesis device 7 is used in some other way, in particular stored. For example, it is possible for the combustion engine 9 to be connected to the interconnected natural gas network, wherein the fuel produced in the fuel synthesis device 7 is not fed into the interconnected natural gas network but is rather stored in a fuel store device in order to subsequently be fed for some other use.

[0062] It is also possible for the combustion engine 9 to be connected in terms of flow to the electrolysis device 5 such that hydrogen produced in the electrolysis device 5 can be fed to the combustion engine 9 for combustion in the combustion chamber 11. This may be performed in particular in addition or alternatively to the use of a further fuel, in particular of the fuel produced in the fuel synthesis device 7. The hydrogen may thus be used in particular as sole fuel, but also for assisting a combustion in the combustion chamber 11in particular with a small fractionin addition to a further fuel.

[0063] The combustion engine 9 has an exhaust-gas recirculation device 15 which is configured to retain carbon-dioxide-containing and water-containing exhaust gas, formed in the combustion chamber 11 in a previous combustion, in the combustion chamber 11, or to recirculate said exhaust gas into the combustion chamber 11, for a subsequent combustion. For this purpose, exhaust gas may in particular be branched off upstream of the separation device 13 or in the separation device 13 and fed to a charging path 17 of the combustion engine. In this respect, the FIGURE schematically illustrates an external exhaust-gas recirculation arrangement. It is however also possible for the combustion engine 9 to be configured to realize internal exhaust-gas recirculation. A combustion of a fuel with pure oxygen, in particular a combustion of methane with pure oxygen, requires exhaust-gas recirculation and in particular high exhaust-gas recirculation rates in order to lower the flame speed in the combustion chamber 11 to a level suitable for the operation of the combustion engine 9.

[0064] It is possible for the exhaust-gas recirculation device 15 to have an adjusting device (not illustrated here) for adjusting an exhaust-gas recirculation rate, for example an exhaust-gas recirculation flap or the like.

[0065] The combustion engine 9 is preferably operatively connected in terms of drive to an electric machine 19, wherein the electric machine 19 is electrically connected to the electricity network 1. The electric machine 19 is preferably in particular operated as a generator and driven by the combustion engine 9 such that it can generate electrical power and feed this into the electricity network 1. Thus, the combustion engine 9 is in particular configured to provide positive control energy for the electricity network 1.

[0066] The combustion engine 9 may in particular be part of a combined heat and power plant or constitute a combined heat and power plant, wherein it is preferably operated with electricity-based or heat-based control. In particular, it is possible for the combustion engine 9 to be operated at least intermittently in order to produce and provide heat for the fuel synthesis device 7.

[0067] The combustion engine 9 is preferably configured to be operated with ambient air as combustion gas in a starting operation mode. For this purpose, the combustion engine 9 preferably has a first valve device 21, by means of which, in one embodiment, the charging path 17 is, in a first functional position of the first valve device 21, separated from surroundings of the combustion engine 9 and connected in terms of flow to the electrolysis device 5, such that oxygen from the electrolysis device 5 can be fed to the charging path 17. In a second functional position of the first valve device 21, the charging path 17 is preferably connected in terms of flow to the surroundings of the combustion engine 9, such that ambient air can be fed as combustion gas to the charging path 17.

[0068] It is important that the first valve device 21 is designed such that, in the first functional position of the first valve device 21, which corresponds to the continuous operation mode of the combustion engine 9, the flow connection of the charging path 17 to the surroundings of the combustion engine 9 can be shut off such that pure oxygen from the electrolysis device 5 can be fed to the combustion chamber 11.

[0069] It is possible for the first valve device 21as illustrated hereto be provided independently of the fluidic connection between the electrolysis device 5 and the combustion chamber 11 of the combustion engine 9, and to merely be configured to open up and shut off the fluidic connection of the charging path 17 to the surroundings of the combustion engine 9 in accordance with demand. In this case, in the second functional position of the first valve device 21, the combustion chamber 11 can be fed not only with ambient air but also with oxygen from the electrolysis device 5, such that the combustion in the combustion chamber 11 is performed not with pure oxygen, but rather with ambient air enriched with oxygen.

[0070] The second functional position of the first valve device 21 corresponds to the starting operation mode of the combustion engine 9.

[0071] The first valve device 21 is preferably arranged in the charging path 17.

[0072] Here, the combustion engine 9 furthermore has a second valve device 23, by means of which an exhaust-gas path 25, in a first functional position of the second valve device 23, can be separated from the surroundings of the combustion engine 9 and, in a second functional position of the second valve device 23, can be connected in terms of flow to the surroundings. It is also the case here that the second functional position of the second valve device 23 corresponds to the starting operation mode of the combustion engine 9, in whichowing to the nitrogen fed to the combustion chamber 11 by way of the ambient airnitrogen oxides also form in the combustion chamber 11 during the combustion, such that, in any case, the exhaust gas that is formed cannot be completely utilized within the energy-converting device 3, such that at least a part of the exhaust gas, preferably all of the exhaust gas of the combustion engine 9 in the starting operation mode, can be emitted into the surroundings of said combustion engine.

[0073] The first functional position of the second valve device 23 corresponds to the continuous operation mode of the combustion engine 1. In this case, the exhaust gas of the combustion engine 9, which comprises only carbon dioxide and water, is utilized entirely within the energy-converting device 3, on the one hand as starting product for the fuel synthesis device 7 and the electrolysis device 5 and on the other hand for reducing the flame speed in the combustion engine 9 via the exhaust-gas recirculation device 15, such that no fraction of the exhaust gas is then released into the surroundings of the combustion engine 9.

[0074] The electricity network 1 preferably has at least one regenerative energy source 27, in particular a photovoltaic installation, a wind turbine, a hydroelectric power plant or the like, wherein the regenerative energy source 27 and the energy-converting device 3 are electrically connected to one another by means of electrical lines 29 of the electricity network 1. The electricity network 1 preferably has a multiplicity of regenerative energy sources 27, in particular also regenerative energy sources of different type, for example photovoltaic installations and wind turbines, hydroelectric power plants and/or the like.

[0075] The electricity network 1 is configured toat least preferablyfeed electrical power from the regenerative energy source 27 to the electrolysis device 5. In particular, the electrolysis device 5 is preferably utilized, in the presence of an overcapacity ofin particular regeneratively producedelectrical energy in the electricity network 1, for providing negative control energy, that is to say for absorbing electrical power from the electricity network 1.

[0076] The combustion engine 9 is preferably utilized to provide positive control energy for the electricity network 1, that is to say to feed electrical power into the electricity network 1, if an undercapacity of electrical energy is present in the electricity network 1, that is to say a present consumption of electrical power threatens to overshoot a present generation of electrical power in the electricity network 1.

[0077] Provision is particularly preferably made whereby the electrolysis device 5 and the combustion engine 9 can be activated and deactivatedautomatically or manuallyby an operator of the electricity network 1 in accordance with demand.

[0078] The energy-converting device 3 preferably has at least one store device, selected in particular from a group comprising a hydrogen store device, an oxygen store device, a fuel store device, a carbon dioxide store device and a water store device. Such a store device may serve in particular as a buffer or temporary store, such that the various substance flows in the energy-converting device 3 can be maintained independently of the present operation of the individual components, that is to say of the electrolysis device 5, of the fuel synthesis device 7 and of the combustion engine 9. The individual components can thus in particular be operated even when other components are presently not active, because they can thus store their products in correspondingly suitable store devices and/or draw their starting products from correspondingly suitable store devices.

[0079] As already stated, the combustion engine 9 is preferably operated with a stoichiometric ratio of oxygen to fuel, in particular methane, such that the exhaust gas of the combustion engine 9 has exclusively carbon dioxide and water. Stoichiometric operation furthermore has the advantage that the exhaust gas of the combustion engine 9 is free from oxygen. This is rather fully converted in the combustion chamber 11. Operation of the combustion engine 9 with other, non-stoichiometric combustion gas/fuel ratios is however also possible.

[0080] With the energy-converting device 3 proposed here, the electricity network 1 and the method for the operation thereof, a means is created for efficiently operating the individual components of an energy-converting device 3, in particular an electrolysis device 5, a fuel synthesis device 7 and a combustion engine 9, integrally with one another, utilizing a multiplicity of synergistic effects, and in the process considerably reducing, preferably eliminating, pollutant emissions.