Patent Application
20140360191
This application claims priority to and the benefit of German Application No. DE 102013210430.8 filed Jun. 5, 2013, incorporated by reference herein in its entirety.
The present invention relates to an energy storage apparatus for the storage of thermal energy, with a charging and a discharge circuit, said apparatus being suitable for preheating feed water in a water/steam circuit. Energy storage apparatuses of this type are preferably integrated into power plants.
Since electrical energy is increasingly being fed into the current distribution networks from renewable energy sources, there is a growing need to be able to store electrical energy intermediately for a period of time. The aim in this case is to have the ability, in the event of a surplus, to extract the electrical energy from the current distribution networks and make it available to the current distribution networks once again for later utilization, in order thereby to stabilize the distribution networks.
The technical literature often follows the approach of converting the available electrical energy into thermal energy and storing it intermediately for a period of time. When there is a renewed demand for additional electrical energy, the thermal energy thus stored intermediately can be converted into electrical energy again by means of a reverse conversion method.
Such a proposal for a technical solution is described, for example, in PCT/EP2012/072450, which proposes to connect a heat store thermally to a compressor and to an expansion turbine, in order, when the compressor is in operation, to introduce the compression heat in this case occurring into the heat store and store it. The heat store is in this case additionally connected to a water/steam circuit, so that the energy contained in the heat store can be provided for the provision of steam in the water/steam circuit. The heat store may likewise serve for the intermediate superheating of steam carried in the water/steam circuit.
The disadvantage of this technical solution known from the prior art, however, is that the temperature which may prevail in the heat store is in most cases not sufficiently high to provide steam in the water/steam circuit in an operating state which is typical in a power plant. To be precise, the heat store is supplied with storage heat by means of an adiabatic heat process (compression of a working medium in the compressor). The compression temperatures in this case occurring typically amount to not appreciably more than 300° C. However, the provision of steam at this temperature level necessitates a very high heat transmission rate of heat from the heat store to the water in the water/steam circuit. However, efficient heat transmission for steam provision is thereby possible to only an inadequate extent, since the water quantities conducted in the water/steam circuit are very high. In other words, at a temperature level of only 300° C., heat is not transmitted to the water in the water/steam circuit sufficiently to ensure that the provision of steam with sufficient thermal energy would be readily possible.
A set technical object, therefore, is to avoid these disadvantages known from the prior art. In particular, an energy storage apparatus is to be proposed, which enables thermal energy stored intermediately in a heat store to be made available efficiently to a steam process taking place in a power plant. Furthermore, the transmission of heat from the heat stores to the water in such a water/steam circuit is to be capable of taking place at a technically advantageous heat transmission rate. Moreover, a technical solution is to allow for the fact that such heat provision is to be capable of being achieved, even in conventional power plants, by simple restructuring measures.
These objects on which the invention is based are achieved by an energy storage apparatus as claimed.
In particular, these objects on which aspects of the invention are based are achieved by an energy storage apparatus for the storage of thermal energy, with a charging circuit, comprising a compressor, a heat store and an expansion turbine, the compressor being connected on the outlet side to the inlet of the expansion turbine via a first line for a first working gas, and the heat store being inserted into a second line, and the first line being connected to a first heat exchanger, by which the first line and the second line are coupled thermally, and, furthermore, comprising a discharge circuit which comprises a water/steam circuit which is equipped with a steam generator and which has at least one feed water preheater preceding the steam generator with respect to the direction of flow of the water in the water/steam circuit, and thermal coupling between the charging circuit and discharge circuit being achieved by the feed water preheater, in particular being achieved solely by the feed water preheater.
The charging circuit according to aspects of the invention may in this case have both an open and a closed configuration.
The aspects of the invention provide for supplying heat from the heat store to the water/steam circuit via a feed water preheater of the discharge circuit. Utilization of the thermal energy thus serves for the thermal conditioning of the water in the water/steam circuit or for preheating this feed water even before the water is delivered to the steam generator in which the water can be supplied with sufficient heat for steam generation. The steam generator in this case ensures a sufficiently high heat transmission rate to the water in the water/steam circuit, so that steam can be generated at sufficiently high temperatures and with sufficiently high thermal energy. Thermal conditioning by the transmission of heat from the heat store by the feed water preheater consequently serves only for preheating the water, but without generating steam which could be used in a steam process for energy generation. Water treatment may in this case take place at a temperature level which, on the one hand, allows advantageous transmission of heat from the heat store, but, on the other hand, is not the sole energy source for steam generation. Thus, thermal energy from the heat store can be supplied in an advantageous way to the feed water in the water/steam circuit, but at the same time process reliability and process constancy in steam generation by the steam generator can be ensured. The steam generator may in this case be, for example, a fossil-fired combustion boiler or a suitable waste heat recovery steam generator of, for example, a combined-cycle power plant.
It should be pointed out at this juncture that the feed water preheater is preferably designed as a heat exchanger or as a number of individual heat exchangers.
According to a first embodiment of the invention, there is provision whereby the feed water preheater is designed as a heat exchanger which is likewise coupled thermally to a low-temperature steam line which, in particular, emanates from a low-pressure steam part of a steam turbine connected to the water/steam circuit. A low-temperature steam line, in the sense of a bleed steam line of a low-pressure steam turbine (low-pressure steam part), may typically have water at a temperature level of about 150° C. The implemented combination of two heat sources (heat store and low-pressure steam part) is thus suitable for transmitting heat to water in the water/steam circuit, in order to provide heat energy at a temperature level of at most about 150° C.
According to a further embodiment of this invention, there is provision whereby the feed water preheater is designed as a heat exchanger which is likewise coupled thermally to a medium-temperature steam line which, in particular, emanates from a medium-pressure steam part of a steam turbine connected to the water/steam circuit. A medium-temperature steam line, in the sense of a bleed steam line of a medium-pressure steam turbine (medium-pressure steam part), may in this case have a typical temperature level of at most about 230° C. This embodiment, too, allows thermal coupling of heat from the steam process and of heat which is extracted from the heat store.
According to a further advantageous embodiment of the invention, there is provision whereby the feed water preheater is designed as a heat exchanger which is likewise coupled thermally to a high-temperature steam line which, in particular, emanates from a high-pressure steam part of a turbine connected to the water/steam circuit. High-temperature steam lines, in the sense of bleed steam lines of a high-pressure steam turbine (high-pressure steam part), may in this case have a typical temperature level of at most up to 350° C. This coupling of a high-temperature steam line and a heat store by the one feed water preheater allows an energy-efficient utilization of heat from two different heat sources.
It should also be pointed out at this juncture that the feed water preheater is preferably designed as a heat exchanger or as a number of individual heat exchangers. In this case, thermal coupling of these heat stores to a steam line which discharges steam and therefore heat from the water/steam circuit is suitable especially for thermal conditioning in the sense of a preheating of the feed water. To be precise, depending on the temperature level of the thermal energy stored intermediately in the heat store, different heat sources having similar temperature levels can thus be combined efficiently with one another in order to ensure an advantageous overall transmission of heat to the feed water.
It remains to be taken into account that, after the intermediate storage of heat in the heat store which lasts for a long period of time, a lowering of temperature due to heat losses may occur. Nevertheless, even with lowered temperature levels, efficient heat release or a combination of various heat sources can still be made possible at a comparable temperature level for feed water preheating. If, for example, a heat store is initially charged completely and has a temperature level of about 300° C., this heat can be combined efficiently with heat from a high-temperature steam line by a feed water preheater suitable for this purpose and can be transmitted to feed water in the water/steam circuit. However, should the temperature level in the heat store fall on account of a lengthy period of storage time, for example to about 150° C., the transmission of heat to the feed water can nevertheless continue to be carried out efficiently, in that, for example, the heat is combined with the heat of a low-temperature steam line and transmitted to the feed water.
According to an advantageous embodiment of the invention, there is provision whereby the feed water preheater comprises at least two, in particular exactly two, heat exchangers which are in each case connected thermally to a steam line and can transmit heat at different temperature levels. In particular, these steam lines are designed either as a low-temperature steam line, as a medium-temperature steam line or as a high-temperature steam line according to the above description. On account of the combination of a plurality of feed water preheaters, the transmission of heat from the heat store to the feed water in the water/steam circuit can be made thermally more flexible. In particular, it is thereby possible also to take into account the temperature level of the heat store which may vary in the course of the intermediate storage of heat.
According to a further advantageous embodiment of the invention, there is provision whereby the compressor and the expansion turbine are arranged on a common shaft. Alternatively, however, the compressor and the expansion turbine may also be arranged so as to be decoupled mechanically from one another.
Furthermore, it is conceivable that the compressor and the expansion turbine are connected via an essentially closed line circuit for the first working gas which comprises the first line. Such a closed line circuit comprises, for example, the first line, which carries working gas compressed by the compressor to the expansion turbine, and a return line, which returns the expanded working gas to the compressor again. According to a particular embodiment, the first line and the return line may be coupled to one another via a further second heat exchanger, so that, for example, thermal energy not stored in the heat store can still be transmitted at least partially to the working gas introduced into the compressor. An essentially closed line circuit makes it possible to use a working gas which, in particular, is not air, but which allows especially efficient thermodynamic state changes.
According to a further advantageous embodiment of the invention, there is provision whereby the first line comprises an electrically operated heating device. By this heating, electrical energy can be introduced into the first line for suitable thermal conditioning. Thus, for example, if there is a current surplus, this electrically operated heating device can provide additional thermal energy which, for example, can be stored intermediately in the heat store. Likewise, the electrically operated heating device can also ensure that the working gas introduced into the expansion turbine has a sufficiently high temperature level so that, during the expansion process, there is no fear of any cold damage in or downstream of the expansion turbine.
Alternatively or else additionally, additional electrical heating may be inserted into the charging circuit upstream of the heat store. Such additional heating makes it possible to provide additional thermal energy which can be stored intermediately in the heat store. Such provision is advantageous in energy terms particularly when, for example, in the case of a current surplus, electrical energy can be extracted from the public distribution networks and utilized.
According to a further preferred embodiment of the invention, there is provision whereby the heat store contains a porous storage medium which comprises sand, gravel, rock, concrete, water, salt and/or thermal oil. Consequently, any suitable material for sensitive and latent heat storage is basically appropriate for the heat store. It is likewise conceivable to design the heat store as a thermochemical heat store.
According to a further especially preferred embodiment, there is provision whereby, furthermore, a steam turbine plant capable of being operated by steam from the water/steam circuit is inserted into the discharge circuit. This steam turbine plant ensures the reverse conversion of thermal energy for the provision of electrical energy and is located in many power plants already installed. Consequently, by simple structural changes, an already existing power plant can be reequipped so that it can also utilize heat from the heat store suitably for the thermal conditioning of feed water.
The invention will be explained in more detail below by means of a drawing. It should be pointed out, here, that the drawing is merely in diagrammatic form, but this does not signify any restriction with regard to the implementability of the invention.
It should likewise be pointed out that the technical components shown in the drawing are claimed for themselves alone and in any combination with one another, insofar as a solution of the technical problem on which the invention is based can be achieved by means of the combination.
Furthermore, it should be pointed out that the components given the same reference symbols in the figure have identical actions.
Thus:
If, then, during regular operation, the compressor 4 is driven by the motor M, the first working gas 3 sucked into the compressor 4 is compressed, as a result of which, under adiabatic compression, thermal energy is transmitted to the working gas 3. This thermal energy, which can be provided at a temperature level of at most about 300° C. to 350° C., is transmitted via the first heat exchanger 20 to a second working gas, not given a reference symbol, in the second line 8. The second working gas may in this case be identical to the first working gas 3. By virtue of the circulation of the second working gas in the second line 8, thermal energy is increasingly conducted into the heat store 5 and deposited there.
After the thermal interaction of the first working gas 3 in the region of the first heat store 20, the first working gas is delivered to the expansion turbine 6 in the first line 7. In this case, the first working gas 3, before entering the expansion turbine 6, may be thermally conditioned further by an electrical heating device 9. When the first working gas 3 is expanded in the expansion turbine 6, the expansion of the gas to a lower pressure level takes place. The expansion turbine 6 can be operated by the pressure-dynamic energy which is released in this case and is converted into kinetic energy, and electrical energy can consequently be generated by the generator G.
After emerging from the expansion turbine 6, the first working gas 3 can either be supplied to the surroundings if there is an open circuit or else, if a closed circuit is implemented, be delivered once again to the compressor 4 via a return line 11. In the event of closed line routing, for example, the first working gas 3 carried in the return line 11 can thus be thermally conditioned again via a second heat exchanger 25 which makes it possible to extract heat from the first working gas 3 after heat transmission in the first heat exchanger 20 even before delivery to the expansion turbine 6, in order to transmit this heat to the returned first working gas 3 even before delivery to the compressor 4. The second heat exchanger 25 is inserted on the primary side into the first line 7 and on the secondary side into the return line 11.
The discharge circuit 30 has a water/steam circuit 40 which is connected to a steam turbine 60. The steam turbine 60 has three different steam parts which differ from one another according to the temperature level and pressure level of the steam in the water/steam circuit 40. Thus, as implemented here, the steam turbine 60 provides a low-pressure steam part 61 (low-pressure steam turbine), a medium-pressure steam part 62 (medium-pressure steam turbine) and a high-pressure steam part 63 (high-pressure steam turbine). For the provision of steam, the discharge circuit 30 comprises a steam generator 41, for example a fossil-fired steam generator (fossil-fired burner space or waste heat recovery steam generator). Further, the discharge circuit 30 has, upstream of this steam generator 41, two feed water preheaters 42 which are in each case connected thermally to the heat store 5 via the second line 8. At the same time, the feed water preheaters 42 are likewise connected thermally to steam lines of individual steam parts of the steam turbine 60. Thus, for example, the first feed water preheater 42 arranged downstream of the condenser 70 is connected to the low-pressure steam part 61 of the steam turbine 60 via a low-temperature steam line 51. The low-temperature steam line 51 enables bleed steam to be supplied from the low-pressure steam part 61 to the feed water preheater 42. This feed water preheater 42 is followed downstream by a further preheater which, in the present case, is not given a reference symbol. This preheater is connected solely to a medium-temperature steam line 52 from the medium-pressure steam part 62 of the steam turbine 60. This preheater is further followed downstream by a second feed water preheater 42 which is at the same time connected to the high-pressure steam part 63 of the steam turbine 60 by a high-temperature steam line 53.
In the extraction of heat from the heat store 5, then, the second working gas can be conducted in a second line 8 in such a way that it first extracts heat from the heat store 5 and then delivers this to the two feed water preheaters 42. The feed water preheaters 42 enable heat to be transmitted from the second working gas in the second line 8 to feed water in the water/steam circuit 40. Depending on the prevailing temperature levels, the feed water preheaters 42 can also extract thermal energy from the steam lines 51 and 53. In this case, therefore, the heat from the heat store 5 is combined together with heat which is extracted at predetermined locations in the water/steam circuit 40.
As implemented here, the water extracted from the condenser 70 has, for example, a temperature level of 20° C. If the storage medium itself, arranged in the heat store 5, has a temperature level of about 300° C., a temperature level of 150° C. can be stipulated downstream of the condenser 70, for example, by the first feed water preheater 42. The feed water, after renewed preheating, is heated to a temperature level of 200° C. by the preheater which is not given a reference symbol. The further feed water preheater 42 which follows this downstream then makes it possible, for example, to have thermal conditioning to a temperature level of about 300° C. After these steps of the thermal conditioning of the feed water, the latter is carried into the steam generator 41 for further thermal steam provision. The reverse conversion process can thereafter be carried out by the steam turbine 60, utilizing the steam contained in the water/steam circuit 40.
Further embodiments may be gathered from the subclaims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102013210430.8 | Jun 2013 | DE | national |
