Combined power plant and method for operating a combined power plant

Abstract

The invention relates to a combined power plant and to a method for storing and discharging thermal energy, wherein, in a first operating mode, thermal energy is stored and, in a second operating mode, thermal energy is converted into rotational energy, wherein, in the first operating mode, the thermal energy of a medium is increased in a compressor (7, 9, 14), and a first storage medium is heated by means of a first heat exchanger (8) using the increased thermal energy and is conducted into a first heat store (2), wherein, in the second operating mode, the thermal energy of the first storage medium leads, in the first heat exchanger (8), to an increase of the thermal energy of the medium, and the increased thermal energy of the medium is converted, in a first turbine section (19), into rotational energy.

Description

[0001] Description

[0002] Combined plant and method for operating a combined plant

[0003] The invention relates to a combined system and a method for operating a combined system, wherein thermal energy is stored in a first operating mode and thermal energy is converted into rotational energy in a second operating mode.

[0004] Electrical energy generation is complex and requires sustainable action to optimise the use of limited energy sources. Many efforts are being made to minimise the use of fossil fuels and increase the use of renewable energies. Many nations have set themselves the goal of increasing the share of renewable energies in the electricity and heating grids in order to reduce greenhouse gas emissions. However, the share of guaranteed output can only be increased in part by increasing the installed capacity of renewable energy generators. The reason for this is that renewable energy cannot be reliably planned in terms of when it will be available and how much energy it will supply. It is therefore necessary to be able to guarantee a temporal decoupling of energy supply and energy demand.

[0005] Another aspect of sustainable action with regard to electrical energy generation is energy storage. Here, too, greater efforts are being made to decouple the generation and demand of electrical energy. If the current supply of electrical energy generation exceeds demand, it makes sense to store the excess capacity. If demand falls short at a later date, the energy can be withdrawn from the storage facility.

[0006] The temporal imbalance between supply and demand also leads to fluctuations between high and low electricity prices. Therefore, it also makes economic sense to store energy during periods of low electricity prices and withdraw energy from storage during periods of high electricity prices.

[0007] There are very different technologies for storing electrical energy on demand. These can include pumped-storage power plants or chemical batteries. Another option for storing energy would be thermal energy storage. These differ in the choice of working medium and the design of the thermodynamic cycle.

[0008] Thermodynamic cycles use working fluids such as air, argon, or carbon dioxide (CO2). These cycles employ the so-called Brayton cycle, in which the working fluid remains in the gas phase. In a Clausius-Rankine cycle, a phase transition between gaseous and liquid occurs and is also widely used.

[0009] The object of the invention is to provide an improved combination system and an improved method with which energy can be temporarily stored.

[0010] This object is achieved by a system according to claim 1 and a method according to claim 11.

[0011] An essential feature of the invention is that the combined system is characterized by two operating modes. In a first operating mode, thermal energy is stored, and in a second operating mode, rotational energy is generated using the thermal energy.

[0012] The present invention proposes a thermal energy storage device. Electrical energy is converted into heat and transferred to the thermal energy storage device. When needed, the heat is extracted from the thermal energy storage device and converted into electrical energy. Such an energy storage device is called a "Carnot battery."

[0013] Advantageous further developments are specified in the subclaims.

[0014] In an advantageous further development, water is used as the working medium for storing and extracting heat in a Clausius-Rankine cycle. The charging cycle, which can also be referred to as the first operating mode, is comparable to a heat pump process, while the discharging cycle, which can also be referred to as the second operating mode, is comparable to a heat engine process.

[0015] In the first operating mode (charging circuit), compressors, evaporators, heat pumps, throttles, heat exchangers and heat storage units are used.

[0016] In the second operating mode (discharge circuit), turbines, condensers, pumps, heat exchangers and heat storage are used.

[0017] In the charging cycle (first operating mode), the working fluid is first evaporated by heat provided by a heat pump or heat extracted from a storage tank. The working fluid is then compressed once or multiple times.

[0018] After each compression process, the heat generated is transferred to a high-temperature storage unit as sensible heat.

[0019] The working fluid after the last compressor is preferably, but not necessarily, in the supercritical range, which allows for the storage of sensible heat after the compressor stages. The heat extracted from the working fluid during a possible, but preferential, cooling is also transferred to a heat storage unit before the working fluid is throttled or expanded. The throttling or expansion closes the charging circuit.

[0020] In the discharge circuit (second operating mode), the medium is ideally brought to a higher pressure level in the liquid state by means of a pump and preheated by the heat that was released during the possible cooling in the charging circuit.

[0021] The working medium is then superheated, depending on the compressor stages in the charging circuit, but not necessarily, alternately with the heat from the high-temperature storage and expanded in one or more turbines.

[0022] In order to close the discharge circuit, the working medium is deheated if necessary after the last expansion and is completely condensed by heat release, possibly into a storage tank.

[0023] The invention achieves the advantage that a Clausius-Rankine cycle is used to charge and discharge a Carnot battery and that the charging and discharging of heat storage devices is carried out using heat exchangers.

[0024] The heat is generated in one or more compression steps and is fed into the circuit during discharge via one or more superheating steps.

[0025] A further advantage of the invention is that the heat to be dissipated during the intermediate cooling is not sprayed off, but is stored with the help of sensitive storage media.

[0026] A further advantage of the invention is that the process is designed in such a way ( in so - called supercritical operation ) that all thermal energies can be stored sensitively .

[0027] A further advantage of the invention lies in the very high overall efficiency that can be achieved. This is due to the fact that, using the Clausius-Rankine cycle, heat can be converted very efficiently into mechanical energy. The high efficiency of the inventive arrangement results in the use of only small specific amounts of stored thermal energy.

[0028] The use of the Clausius-Rankine cycle has a significant impact on the volumetrics of the cycle components.

[0029] The high heat capacity of water and its partially liquid state mean that the piping, heat exchangers and rotating machines can be designed more compactly than in cycles of comparable capacity based on a Brayton cycle.

[0030] The possible supercritical heat release after the last compressor enables more effective heat transfer. This results in smaller driving temperature differences and thus smaller heat transfer gradients.

[0031] The solution according to the invention is suitable for supplementing or converting existing fossil power plants with steam turbines, since the existing infrastructure for operation with steam is already in place.

[0032] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of the exemplary embodiments, which are explained in more detail in conjunction with the drawings. Identical components or components with the same function are designated by the same reference numerals.

[0033] Examples of embodiments of the invention are described below with reference to the drawings. These are not intended to represent the examples to scale; rather, where useful for explanation, the drawings are presented in a schematic and / or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art.

[0034] It shows :

[0035] Figure 1 is a schematic representation of the combined system in a first operating mode (charging mode)

[0036] Figure 2 shows a schematic representation of the combined system in a second operating mode (discharge mode)

[0037] Figures 1 and 2 show a combination system 1 in two different operating modes, with Figure 1 showing a charging mode and Figure 2 showing a discharging mode.

[0038] The combined system 1 is designed to store thermal energy in a first operating mode. The combined system 1 comprises a counterclockwise thermodynamic cycle, which is symbolized by the arrows in Figure 1.

[0039] A first thermal storage unit 2 can be filled with a storage medium. The storage medium can be salt or a similar medium. A heat source 3 is fluidly connected to a throttle 5 on the inlet side 4 and to a compressor 7 on the outlet side 6. The heat source 3 is designed to evaporate the medium, whereby the heat source 3 can be designed as a heat pump or as a heat storage unit. The working medium, here water, is first evaporated by means of heat provision by the heat source 3 (a heat pump or heat extraction from a storage unit) (step 1-c 2a-c ) .

[0040] The medium is then compacted once or several times (step 2-c 3-c). After each compression process, the heat generated is transferred to a high-temperature storage unit 2 as sensible heat. (Step 3-c 2-c or

[0041] Step 3-c 4-c ) .

[0042] For this purpose, the compressor 7 is coupled to a first heat exchanger 8, wherein the compressor 7 is designed such that the pressure and the temperature of the medium are increased, wherein the first heat exchanger 8 is designed such that the thermal energy of the medium can be transferred to the first storage medium 2.

[0043] The medium after the last compressor 9 is preferably, but not necessarily, in the supercritical range, which makes it possible to store sensible heat after the compressor stages.

[0044] The heat extracted from the medium is transferred into a second thermal storage 10 during a possible but preferred cooling (step 4-c 5-c ) . The second thermal storage

[0045] 10 is filled with a second storage medium, the thermal energy being transferred via a second heat exchanger 11.

[0046] The second storage medium may be an oil, a salt or a similar medium.

[0047] The combination system 1 has at least one further compressor 14, which is fluidly connected on the inlet side to the first heat exchanger 8 and on the outlet side to a further heat exchanger 15. The further compressor 15 is designed such that the pressure and temperature of the medium are increased, wherein the further heat exchanger 15 is designed such that the thermal energy of the medium can be transferred to the first storage medium 2.

[0048] The second heat exchanger 11 is fluidically connected on the inlet side 12 to the first heat exchanger 8 and on the outlet side 13 to the throttle 5.

[0049] The throttle 5 is designed to liquefy the medium.

[0050] In step 5-c 1-c, the medium is throttled or expanded. Throttling or expansion closes the charging circuit.

[0051] Figure 2 shows the second operating mode, which can also be referred to as the discharge cycle. The discharge cycle runs clockwise and is symbolized by the arrows.

[0052] In the discharge circuit, the medium is ideally brought to a higher pressure level in the liquid state by means of a feed water pump 16 (step 1-g 2-g) and by the

[0053] Heat that was released during possible cooling in the charging circuit, preheated (step 2-g 3-g) .

[0054] The combined system in the discharge circuit is designed to generate energy.

[0055] The feedwater pump 16 is designed to pump the medium to the second heat exchanger 11, wherein the second heat exchanger 11 is designed in the second operating mode to transfer the thermal energy of the second storage medium to the medium. Subsequently, the medium is superheated alternately with the heat from the first thermal storage device, depending on the compressor stages in the charging circuit, but not necessarily.

[0056] (Step 3-g 4-g or step 5-g 4-g) and expanded in one or more sub-turbines (step 4-g 5-g) .

[0057] The first partial turbine 19 is fluidically connected on the inlet side 17 to the heat exchanger 18, wherein the first partial turbine 19 is designed such that the thermal energy of the medium is converted into rotational energy.

[0058] For this purpose, the first partial turbine 19 is fluidly connected on the output side to the first heat exchanger 8, wherein the first heat exchanger 8 is designed to transfer the thermal energy of the first storage medium 2 to the medium in the second operating mode.

[0059] Further partial turbines 20, 21 are arranged in the flow direction of the medium.

[0060] The combined system further comprises a condenser 22 that is fluidically coupled to the turbine section 21, wherein the condenser 22 is designed to condense the medium. On the output side, the condenser 22 is fluidly connected to the feedwater pump 16.

[0061] To close the discharge circuit, the medium is deheated after the last relaxation if necessary and completely condensed by heat release, possibly into a storage tank (step 5-g 1-g) .

Claims

Patent claims 1. Combined system (1) for storing thermal energy in a first operating mode, comprising a first thermal storage device (2) filled with a first storage medium, further comprising a heat source (3) which is fluidically connected on the inlet side (4) to a throttle (5) and on the outlet side (6) to a compressor (7), wherein the heat source (3) is designed to evaporate a medium, wherein the compressor (7) is provided with a first heat exchanger (8), wherein the compressor (7) is designed such that the pressure and the temperature of the medium are increased, wherein the first heat exchanger (8) is designed such that the thermal energy of the medium can be transferred to the first storage medium, wherein the throttle (5) is fluidically connected on the inlet side to the first heat exchanger (8) and on the outlet side to the heat source (3), wherein the throttle (5) is designed to liquefy the medium.

2. Combined system (1) according to claim 1, wherein the medium is water.

3. Combined system (1) according to claim 1 or 2, wherein the heat source (3) is designed as a heat pump.

4. Combined system (1) according to claim 1 or 2, wherein the heat source (3) is designed as a heat accumulator.

5. Combined system (1) according to one of the preceding claims, wherein the first storage medium is a salt.

6. Combined system (1) according to one of claims 1 to 5, further comprising a second thermal storage (10) filled with a second storage medium, further comprising a second heat exchanger (11), wherein the second heat exchanger (11) is designed such that the thermal energy of the medium can be transferred to the second storage medium, wherein the second heat exchanger (11) is fluidly connected on the inlet side to the first heat exchanger (8) and on the outlet side to the throttle (5). Combined system (1) according to claim 6, wherein the second storage medium is oil. Combined system (1) according to one of the preceding claims, with at least one further compressor (14, 9) which is fluidly connected on the inlet side to the first heat exchanger (8) and on the outlet side to a further heat exchanger (15), wherein the further compressor (14, 9) is designed such that the pressure and the temperature of the medium are increased, wherein the further heat exchanger (15) is designed such that the thermal energy of the medium can be transferred to the first storage medium.Combined system (1) according to one of the preceding claims, wherein the system is designed to generate energy in a second operating mode, comprising a feedwater pump (16) which is designed to pump the medium to the second heat exchanger (11), wherein the second heat exchanger (11) is designed in the second operating mode to transfer the thermal energy of the second storage medium to the medium, wherein the medium is fluidically coupled to the further heat exchanger (18) via a line, wherein the further heat exchanger (18) is designed to transfer the thermal energy of the first storage medium to the medium, further comprising a first partial turbine (19) which is fluidically connected on the inlet side to the further heat exchanger (18), wherein the first partial turbine. (19) is designed such that the thermal energy of the medium is converted into rotational energy, wherein the first partial turbine (19) is fluidically connected on the output side to the first heat exchanger (8), wherein the first heat exchanger (8) is designed to transfer the thermal energy of the first storage medium to the medium in the second operating mode, wherein the second partial turbine (21) is designed such that the thermal energy of the medium is converted into rotational energy, further comprising a condenser (22) which is fluidically coupled to the second partial turbine (21), wherein the condenser (22) is designed to condense the medium, wherein the condenser (22) is fluidically coupled on the output side to the feedwater pump (16). Combined system (1) according to claim 9, wherein a further partial turbine (20) is arranged between the first partial turbine (19) and the second partial turbine (21).Method for operating a combination plant, wherein in a first operating mode thermal energy is stored and in a second operating mode thermal energy is converted into rotational energy, wherein in the first operating mode the thermal energy of a medium is increased in a compressor (8, 15) and the increased thermal energy is used via a first heat exchanger (8) to heat a first storage medium which is fed into a first thermal storage device (2), wherein in the second operating mode the thermal energy of the first storage medium in the first heat exchanger (8) leads to an increase in the thermal energy of the medium, wherein the increased thermal energy of the medium is converted into rotational energy in a first partial turbine (19).

12. The method according to claim 11, wherein in the first operating mode a second heat exchanger (11) is used, with which the thermal energy of the medium after the first heat exchanger (8) is transferred to a second storage medium which is led into a second thermal storage device (10).

13. The method according to claim 11 or 12, wherein in the first operating mode further compressors (14, 9) and further heat exchangers (15) are arranged to transfer the thermal energy of the medium to the first heat medium.

14. Method according to one of claims 11 to 13, wherein in the first operating mode a throttle (5) is used to convert the medium present as vapor into liquid.

15. Method according to one of claims 11 to 14, wherein in the first operating mode a heat source (3) is used to convert the medium from liquid to vapor.

16. The method according to any one of claims 11 to 15, wherein in the second operating mode the second thermal storage device (10) with the second storage medium is used to increase the thermal energy of the medium.

17. Method according to one of claims 11 to 16, wherein in the second operating mode further partial turbines (20, 21) and further heat exchangers (15, 8) are used to convert the thermal energy of the medium into rotational energy.

18. The method according to any one of claims 11 to 17, wherein water is used as the medium.

19. The method according to any one of claims 11 to 18, wherein the heat source (3) is designed as a heat pump or a heat accumulator.

20. The method according to any one of claims 11 to 19, wherein a salt is used as the first heat medium.

21. Method according to one of claims 11 to 20, wherein an oil is used as the second heat medium.

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