SYSTEM AND METHOD FOR STORING AND OUTPUTTING ELECTRIC ENERGY WITH ITS STORAGE AS THERMAL ENERGY

Description

[0001] The invention relates to a system for storing and delivering electrical energy with its storage as thermal energy, according to the preamble of claim 1. The invention also relates to a method for storing and delivering electrical energy with its storage as thermal energy.

[0002] Electricity from renewable energy sources such as wind power and photovoltaics fluctuates greatly in its supply. Demand for electricity also fluctuates throughout the day. Energy storage systems can be used to store electrical energy during times of excess supply and make it available again when demand is high. One option for this is thermoelectric energy storage (TEES), which converts electrical energy into heat during charging and uses this heat to generate electricity again when needed during discharging. Such a system eliminates the need to curtail energy currently unused, increasing security of supply. Furthermore, previously unused heat can be stored and utilized using thermal storage.

[0003] The efficiency of such energy storage systems can be further increased by not generating heat directly via an electrical resistance heater, but indirectly by using the electrical energy to operate a heat pump.

[0004] Such an energy storage system is known, for example, from EP 3 054 155 A1 or from US 2016 / 222 830 A1. It comprises a heat pump, a steam cycle, a first heat storage system, and a second heat storage system. The heat pump system can be any desired system. The preferred working medium is CO2 or air. The first heat storage system contains a heat transfer medium heated by a working medium of the heat pump. The second heat storage system preferably uses water as the heat transfer medium, which is heated with the condensate of the steam cycle during a discharging process. The heated water is stored in a separate hot water tank and fed to the heat pump during a charging process, where it heats the working medium flowing from the expander before being fed into a separate cold water tank. The heat transfer medium of the first heat storage system is heated to its final temperature in two stages.In a first stage, a standard compressor compresses the heat pump's working fluid to a temperature of 300°C to 400°C, which then transfers its heat to the heat transfer medium of the first heat storage system. In a second step, the heat transfer medium is brought to its final temperature using a controlled electric heater. This approach eliminates the need to design the heat pump components for high-temperature conditions. This is only necessary for the components downstream of the electric heater. The disadvantage of this is that the overall efficiency decreases due to the conversion of high-quality electrical energy into low-quality thermal energy. The heat storage systems of the two heat storage systems can be designed as stratified storage systems. The first heat storage system can also receive external heat, for example from a solar power plant.

[0005] A similar energy storage system is known from EP 2 942 492 A1. In this system, heat coupling between the second heat storage system and the heat pump takes place via heat exchangers upstream and downstream of the expander.

[0006] In an energy storage system according to EP 3 444 448 A1 or US 2020 / 248 592 A1, the heat from the second heat storage system can be transferred either to the heat pump or to an air cooler via a controllable valve unit.

[0007] From EP 2 986 825 A1 a power plant is known in which the waste heat of the condenser downstream of the steam turbine is stored in a heat storage unit, wherein the heat storage unit can be designed as a heat pump that supplies a district heating network with heat.

[0008] EP 2 653 668 A1 relates to an energy storage system in which both the charging and discharging cycles are designed as Rankine cycles. Heat can be coupled into the heat pump operating during the charging cycle via a second heat pump.

[0009] Another energy storage system with cascaded heat pumps is disclosed in DE10 2013 006 814 A1. The heat storage system is designed as a large-volume stratified storage tank with an aqueous salt solution as the heat storage medium. The stored heat is released either as thermal energy or as electrical energy via an ORC thermal power process.

[0010] Although the known systems and processes enable flexible storage and withdrawal of electrical energy, the possibilities for optimising the overall efficiency are not yet exhausted.

[0011] This is where the invention is intended to remedy the situation. Its underlying objective is therefore to improve a system and method of the type mentioned above so that they exhibit a higher overall efficiency.

[0012] This object is achieved in a generic system by the characterizing features of claim 1 and in a generic method by the features of claim 13. The subclaims further specify advantageous embodiments.

[0013] The invention is based on the finding that a system (as known, for example, from EP 3 054 155 A1) in which the residual heat of the condensate from the air condenser is transferred to an LT heat transfer medium via a low-temperature (LT) heat exchanger, which is then fed into an LT hot storage tank, has the disadvantage that the condensate must have a higher temperature than the LT heat transfer medium in order for heat to be transferred at all. If the size of the LT heat exchanger is to be minimized, a correspondingly large temperature difference is necessary. Due to operation in the wet steam region, the pressure is also specified for a desired condensate temperature. This has an impact on the upstream system components, i.e. the minimum pressure at the outlet of the steam turbine cannot be less than the condensation pressure. This limits the power of the steam turbine.Alternatively, reducing the condensation temperature leads to a larger heat exchanger. Furthermore, both the condensate as the heating medium and the low-temperature heat transfer medium are liquid, resulting in only limited heat transfer in the liquid-to-liquid low-temperature heat exchanger due to the resulting relatively low mass flow.

[0014] In contrast, the features of the invention increase the efficiency and cost-effectiveness of the overall system. The low-temperature heat exchanger is designed as a condenser and is operated with steam from the steam turbine unit. Steam has the advantage that it has a higher energy content than condensate, and the condensing steam provides better heat transfer. Both factors mean that, with the same heat flow, the heat exchanger according to the invention can be made significantly smaller and is more flexible in operation. A further advantage is achieved by the fact that the steam turbine can expand to lower pressures and temperatures, thereby increasing its efficiency.In this way, the energy input into an energy storage system is utilized to an extremely high degree, thus achieving an economical solution with a high level of efficiency, whereby commercially available components can be used.

[0015] By appropriately dimensioning the HT heat storage circuit, the system can be operated symmetrically or asymmetrically, i.e. loading times and unloading times can differ and the energy input and output - whether electrical or thermal - can also differ and be adapted to the respective boundary conditions.

[0016] The energy source used to charge the thermal storage system is preferably electricity-based, but is not limited to this. It is also possible to couple heat energy directly into the thermal storage system. If the heat is available at a lower temperature than that of the storage system, it can be transferred to the heat pump's working fluid using another heat pump. It is also possible to transfer the heat from the HT heat storage circuit to an external heat consumer. This can be used, for example, to provide process heat, heat a gas stream, or generate useful steam, which can then be used directly or converted back into electricity using a steam turbine and generator. There is also the option of providing cold from the heat pump process.

[0017] The steam turbine unit comprises a high-pressure turbine and a medium-pressure / low-pressure turbine, with a reheater located between the high-pressure turbine and the medium-pressure / low-pressure turbine. Here, too, the high temperature of the reheater, which operates with the high-temperature heat transfer fluid, leads to increased efficiency. A portion of the high-temperature heat transfer fluid flows through the reheater before entering the steam generation unit.

[0018] The low-temperature heat storage circuit is particularly advantageous in locations where no high-temperature heat source is available for the heat pump and ambient air would otherwise be used as a heat source. The higher temperature output level increases the heat pump's coefficient of performance. The heat exchangers can be designed significantly smaller, as heat transfer from the liquid phase to the heat pump's working fluid is significantly better than from air to the heat pump's working fluid.

[0019] Preferably, the heat pump circuit further comprises a recuperator and an expander, and the first working fluid flows successively through the compressor, the high-temperature heat exchanger, the recuperator, the expander, the working fluid heater, and back through the recuperator. This allows the residual heat still present in the first working fluid downstream of the high-temperature heat exchanger to be used to further heat the first working fluid entering the compressor. In a preferred embodiment, the desired inlet temperature of the working fluid entering the HT heat exchanger is provided solely by the compression heat generated in the compressor. For this purpose, the compressor must be designed to be temperature-resistant. Corresponding measures are known from gas turbine technology. By dispensing with thermal support from an electrical resistance heater, this design achieves a particularly high level of efficiency.

[0020] The expander is preferably operated in the positive Celsius temperature range. This increases operational reliability, as phase changes and icing of the working fluid do not occur.

[0021] In a preferred embodiment of the invention, the high-temperature heat storage circuit further comprises a high-temperature cold storage unit and a high-temperature hot storage unit, and the high-temperature heat transfer medium flows successively through the high-temperature cold storage unit, the high-temperature heat exchanger, the high-temperature hot storage unit, and the steam generation unit. The high temperature of the high-temperature heat transfer medium allows steam to be generated with a correspondingly high temperature and high pressure, which has a positive effect on the efficiency of the reconversion cycle.

[0022] Advantageously, the heat pump circuit has a second compressor, and the heat pump circuit and the high-temperature heat storage circuit are connected to a second high-temperature heat exchanger for transferring heat from the first working medium to the high-temperature heat transfer medium. In the heat pump circuit, the second compressor is arranged downstream of the (first) high-temperature heat exchanger, and the second high-temperature heat exchanger is arranged downstream of the second compressor. In the high-temperature heat storage circuit, the second high-temperature heat exchanger can be connected in parallel to the high-temperature heat exchanger. This measure increases efficiency.

[0023] Preferably, the compressor, expander, and second compressor are mechanically coupled via a common gear mechanism. This results in a compact overall design. The reduction in the size of the connecting elements reduces friction losses, which has a positive effect on mechanical efficiency.

[0024] In an advantageous embodiment of the invention, an electric heater is arranged in the high-temperature heat storage circuit between the high-temperature heat exchanger(s) and the high-temperature hot storage tank. This allows the high-temperature heat transfer medium to be heated extremely precisely to the desired target temperature shortly before entering the high-temperature hot storage tank.

[0025] In a preferred embodiment of the invention, the steam generation unit comprises a high-temperature preheater, a steam generator, and a superheater, through which the second working medium flows in this order, and the high-temperature heat transfer medium flows in countercurrent. The high-temperature heat transfer medium outlet of the high-temperature preheater is advantageously connected to the inlet of the high-temperature cold storage tank. The gradual release of the thermal energy of the high-temperature heat transfer medium to generate steam leads to effective utilization.

[0026] In a favorable development of the invention, the low-temperature heat storage circuit has at least one additional condenser downstream of the first condenser. All of these condensers are connected in parallel in the re-conversion circuit. Further condensers arranged downstream in series in the low-temperature heat storage circuit are each connected to a bleed line of the steam turbine unit at points between its inlet and outlet, which are arranged upstream in series in the re-conversion circuit. The size of the condensers decreases with their increasing number. The storage efficiency increases by gradually increasing the temperature of the low-temperature heat transfer medium.

[0027] Preferably, the low-temperature heat storage circuit downstream of the last condenser has a storage device for the low-temperature heat carrier with a storage area for cold low-temperature heat carrier and a storage area for warm low-temperature heat carrier, wherein the inlet of the first condenser is connected to the storage area for cold low-temperature heat carrier and the outlet of the last condenser is connected to the storage area for warm low-temperature heat carrier, and the working medium heater is connected to the storage area for warm low-temperature heat carrier.

[0028] It is advantageous if the storage device for the low-temperature heat transfer medium is a stratified storage tank in which both cold and hot water can be stored together. This design eliminates the need for piping and fittings, resulting in lower investment costs and a smaller footprint. Furthermore, the pressureless operation of the stratified storage tank further reduces investment costs and minimizes operating costs. The different temperature zones are thermally separated from one another using suitable measures. Water at different temperatures is supplied and removed using conventional devices that supply and remove water at different temperatures at suitable points. Optionally, the use of additional heat storage media is possible, such as solids, e.g., stone or ceramics, for storing sensible heat, or phase-change materials for storing latent heat.

[0029] In a preferred embodiment of the invention, the re-electrification circuit comprises at least one low-pressure preheater arranged downstream of parallel-connected condensers and connected to a bleed line of the steam turbine unit at points between its inlet and outlet.

[0030] Advantageously, a bleed line branches off upstream of the at least one further condenser and the at least one low-pressure preheater and is connected to their respective inlets for the second working fluid. This connection allows for flexible use of the thermal energy. Depending on the demand, the proportion of available thermal energy can be adjusted either to benefit the reconversion cycle or the low-temperature heat storage cycle.

[0031] In a favorable development of the invention, at least one high-pressure preheater is arranged in the re-electrification circuit upstream of the steam generation unit, which is connected to the high-pressure turbine for operation via a bleed line.

[0032] Preferably, the re-conversion circuit has a connection for an external heat consumer. This allows the system not only to recover electrical power but also to extract thermal energy from the re-conversion circuit to external heat consumers. The system can thus be flexibly adapted to the needs of a user who requires both thermal energy and electrical energy.

[0033] In a system according to the invention, the (first) high-temperature heat exchanger is preferably designed such that the average temperature difference between the first working medium and the high-temperature heat transfer medium is in a range of 5 K to 30 K, and preferably in a range of 8 K to 12 K. This mode of operation increases the efficiency of the heat exchanger. According to a particularly preferred embodiment, the HT heat exchanger is divided into several units, which are correspondingly smaller and operate with smaller average temperature differences.

[0034] The invention is described in more detail below using the figures as examples. They show: Figure 1 shows a flow diagram of a first embodiment of a system according to the invention; and Figure 2 shows a section of Figure 1 with a second embodiment of the heat pump circuit and the high-temperature heat storage circuit.

[0035] The Fig. 1 The system shown serves to store energy during a charging process and make it available again at a later time during a discharging process. The system according to the invention is particularly suitable for absorbing electrical power from renewable energy sources or surplus power from the power grid. Thermal energy can also be coupled directly or indirectly via heat pumps at various points in the system, with heat also being able to be released to cooling users in the form of cold.

[0036] The system can also be discharged in several ways. The preferred method is reconversion to electricity by generating steam, which drives a steam turbine and a power generator. Another utilization option is to use the generated steam to provide at least some of the process heat. Direct use of the thermal energy is also possible.

[0037] The system comprises a heat pump circuit 1 and a re-electrification circuit 2. Both circuits are thermally coupled to a high-temperature (HT) heat storage circuit 3 and a low-temperature (LT) heat storage circuit 4. A high-temperature (HT) heat transfer medium 5 circulates in the HT heat storage circuit 3, and a low-temperature (LT) heat transfer medium 6 circulates in the LT heat storage circuit 4. The terms "high temperature" and "low temperature" within the context of this invention mean that the entire temperature operating range of the HT heat storage circuit 3 lies above that of the LT heat storage circuit 4 and that there is generally no overlap. Each heat storage circuit also has regions in which the respective heat transfer medium is "hot" or "cold." Within the context of this invention, these terms mean that within a heat transfer circuit, the "hot" heat transfer medium has a higher temperature than the "cold" heat transfer medium.The terms "hot" and "warm" and their derivatives are used synonymously in this publication. The pressures indicated are gauge pressures.

[0038] In the heat pump circuit 1, electrical energy is converted into thermal energy during a charging process. It is a closed circuit in which a working fluid 7 circulates in a reverse Brayton cycle. The type of working fluid 7 is not particularly restricted, but dry air, CO2, water vapor, or helium is preferred, with dry air being particularly preferred as a readily available and cost-effective working fluid.

[0039] The working fluid 7 of the heat pump circuit 1 is first preheated in a recuperator 8. Like all other heat exchangers in the entire system, this is preferably operated in countercurrent. The electrical energy is supplied to the heat pump circuit 1 by an electric motor 9, which drives a compressor 10. The compressor 10 compresses the working fluid 7 flowing from the recuperator 8, which is heated by the compression process. The thus heated working fluid 7 transfers its heat to the HT heat transfer medium 5 in a high-temperature (HT) heat exchanger 11. The working fluid 7 is then passed through the aforementioned recuperator 8, where it heats the working fluid 7 flowing into the compressor 10. This working fluid is then passed into an expander 12. The mechanical work recovered there is transferred to the compressor 10 via a shaft 13.In the example shown, both compressor 10 and expander 12 are single-stage, but they can be designed individually or both as multi-stage.

[0040] Due to the expansion, the temperature of the working fluid 7 decreases. In a working fluid heater 14 operated with the low-temperature heat transfer medium 6, heat is transferred to the working fluid 7 and thus coupled into the heat pump circuit 1. This restores the initial state of the cycle. The heat can be coupled at different temperature levels. Additional heat exchangers not shown here can couple even more heat into the heat pump circuit. The introduced heat can come from various sources, for example, waste heat from industrial processes or from one or more heat pumps.

[0041] In the example shown, dry air is used as the working fluid 7. Downstream of the compressor 10, this air has a pressure of 53 bar and a temperature of 560°C. After heat transfer in the HT heat exchanger 11, the working fluid 7 cools down to, for example, 308°C. After passing through the recuperator 8, it cools down to 104°C. In the expander 12, the working fluid 7 expands to a pressure of 15 bar at a temperature of 2°C. The system is designed so that no liquid forms during expansion in the expander 12. In the working fluid heater 14, the working fluid 7 absorbs heat again and now has a temperature of 90°C. Further heat is absorbed in the recuperator 8, causing the temperature to rise to 298°C. In this state, the working fluid 7 then enters the compressor 10.

[0042] The HT heat storage circuit 3 has an HT cold storage tank 15 for storing the cold HT heat transfer medium 5 and an HT hot storage tank 16 for storing the hot HT heat transfer medium 5. The type of HT heat transfer medium 5 is not particularly limited, but molten salts are preferred, e.g., solar salt, which consists of a mixture of 60 wt.% sodium nitrate and 40 wt.% potassium nitrate. This salt has a wide operating temperature range between 290°C and 570°C, high thermal stability, and the advantage of pressureless operation. The heat storage medium of the HT heat storage tank 16 and, optionally, the HT cold storage tank 15 can consist of the HT heat transfer medium 5 itself or additionally of solid heat storage media such as rock, ceramic, concrete, or phase-change materials. The HT heat storage circuit 3 preferably forms a closed circuit.During the loading process, the HT heat transfer medium 5 is pumped from the HT cold storage tank 15 by a pump 17 through the HT heat exchanger 11, where it absorbs heat from the working fluid 7 of the heat pump circuit 1 and is then fed into the HT hot storage tank 16. The HT heat exchanger 11 thus couples the heat pump circuit 1 with the HT heat storage circuit 3. The HT heat transfer medium 5 can additionally be heated by absorbing heat via separate lines not shown here from external heat sources, such as from thermal solar power plants, electric heaters, or waste heat from other processes.

[0043] In a preferred embodiment, the HT heat transfer medium 5 has a temperature of 298°C in the HT cold tank 15 and is heated to 550°C during the loading process in the HT heat exchanger 14. The HT heat exchanger 11 is designed such that the average temperature difference between the working medium 7 and the HT heat transfer medium 5 is preferably in a range from 5 K to 30 K and particularly preferably in a range from 8 K to 12 K.

[0044] The re-electrification circuit 2 forms the discharge process, in which the thermal energy stored in the high-temperature heat storage circuit 3 is converted back into electrical energy. The thermal energy is coupled into the re-electrification circuit 2 at several points. The re-electrification circuit 2 is also connected to a low-temperature heat storage circuit 4, which stores the residual heat from the re-electrification circuit 2 and returns it to the heat pump circuit 1 during the charging process. This heat transfer from the re-electrification circuit 2 to the low-temperature heat storage circuit 4 also occurs at several points.

[0045] A second working medium 18 circulates in the re-electrification circuit 2. Water / steam is preferably used here. Therefore, the exemplary embodiment of a re-electrification circuit 2 specified here is described using water / steam as the second working medium 18.

[0046] The second working medium 18 passes through the states of matter: liquid, evaporated, condensed.

[0047] Accordingly, in the embodiment described here, reference is made to water 18 or feed water 18 in the liquid state, to steam 18 or water vapor 18 or fresh steam 18 in the evaporated state, and to condensate 18 in the condensed state.

[0048] A steam turbine unit 19 is located in the reconversion circuit 2. This unit is optionally designed in two parts, with a high-pressure (HP) turbine 19a and a medium-pressure / low-pressure (M / LP) turbine 19b. A reheater 21 is arranged between them. The HP turbine 19a and the M / LP turbine 19b are coupled to a common shaft 22, which drives a generator 23 to generate electricity. The expanded steam 18 leaves the M / LP turbine 19b via line 24, which branches into line 25 and line 26. A first bleed line 27, a second bleed line 28, a third bleed line 29 and a fourth bleed line 30 are connected to the IP / LP turbine 19b, and a branch 31 is provided from the HP turbine 19a. There is also a branch 32 from the second bleed line 28. The bleed lines can be equipped with control valves not shown here.

[0049] The steam 18 exiting the medium / low pressure turbine 19b is condensed in a condenser via lines 24 and 25. This condenser can be cooled with various coolants, such as air, river water, or seawater. In this example, the condenser is designed as an air condenser 33. The air serving as the coolant is released into the environment. Alternatively, the air condenser 33 can transfer its heat to a heat pump (not shown here), which couples heat at a higher temperature level into the heat pump circuit 1 via its own heat storage. The working fluid can also be something other than air. To optimize the energy efficiency of the reconversion circuit 2, a regenerative feedwater preheating system is provided.For this purpose, the condensate 18 exiting the air condenser 33 is conveyed via a condensate line 34 and a condensate pump 35 through a first low-pressure (LP) preheater 36 and a second low-pressure (LP) preheater 37 into a feedwater tank 38. The LP preheaters 36 and 37 are designed as condensers in which steam 18 from the bleed lines 32 and 29, respectively, is condensed and pumped into the condensate stream downstream of the respective LP preheater via dedicated condensate pumps 39 and 40. Often, additional LP preheaters are provided, but these are not shown here.

[0050] The feedwater 18 is pumped by a high-pressure (HP) feedwater pump 41 from the feedwater tank 38 through a first high-pressure (HP) preheater 42, a second high-pressure (HP) preheater 43, a high-temperature (HT) preheater 44, a steam generator 45, and a superheater 46. The fresh steam 18 thus generated in several steps is fed to the high-pressure turbine 19a via a fresh steam line 47. Advantageous connecting lines between individual units are not shown here. For example, the steam generator 45 can also have a steam drum, whose separated water 18 is returned to the HT preheater 44.

[0051] To operate the HP preheaters 42 and 43, the second HP preheater 43 is operated with steam 18 from the bleed line 31 connected to the high-pressure turbine 19a. The steam 18 exiting the second HP preheater 43 is fed to the first HP preheater 42. The steam 18 cooled there is fed into the feedwater tank 38 and condensed there. The water 18 in the feedwater tank 38 is also further heated by steam 18 from the bleed line 30 connected to the IP / LP turbine 19b.

[0052] The HT heat storage circuit 3 is coupled to the reconversion circuit 2 via steam generation. For this purpose, a pump 48 successively conveys the HT heat transfer medium 5 from the HT hot tank 16 through line 49 and line 50 to the superheater 46, through line 51 to the steam generator 45, and through line 52 to the HT preheater 44. The HT heat transfer medium 5 gradually releases its heat to the steam 18 and the water 18, respectively. Finally, the cold HT heat transfer medium 5 is returned to the HT cold tank 15 via line 53. Optionally, a partial flow of the HT heat transfer medium 5 is conducted through line 54 to a reheater 21 between the high-pressure turbine 19a and the medium / low-pressure turbine 19b, where it reheats the cooled steam 18 flowing from the high-pressure turbine 19a. The residual heat of the HT heat transfer medium 5 exiting the reheater 21 is further utilized by conducting the HT heat transfer medium 5 to generate steam, e.g.via line 55 to line 51 between superheater 46 and steam generator 45.

[0053] The steam 18 generated in the superheater 46 is preferably fed via line 47 to the steam turbine unit 19 to generate electrical power. However, it is also possible to feed the steam 18, at least partially, via line 56 to an external heat consumer 57 as process heat. After use, the steam 18 is present, depending on the pressure and temperature, as steam 18, condensate 18, or a mixture of both, which can be returned to the re-electricity generation circuit 2 at a suitable point, for example, via line 58 to the air condenser 33 if the released steam 18 is saturated steam.

[0054] In a preferred embodiment, the temperature of the steam 18 is 543°C at the inlet to the HP turbine 19a at a pressure of 141 bar. At the outlet from the HP turbine 19a, the pressure has dropped to 31 bar at a temperature of 330°C. In the reheater 21, the steam 18 is brought back to nearly its initial temperature before being expanded to nearly ambient pressure at 40°C in the IP / LP turbine 19b. At this point, the steam 18 is in the form of wet steam, which has already partially condensed.

[0055] This wet steam 18 is condensed in the air condenser 33. A condensate pump 35 conveys the condensate 18 through low-pressure preheaters 36 and 37, gradually increasing the temperature to 126°C before the condensate 18 is fed into the feedwater tank 38 as feedwater.

[0056] Several bleed lines are connected to the medium / low pressure turbine 19b along the flow path. Bleed line 28 carries steam 18 at 128°C and a pressure of 1.9 bar via branch 32 to the low pressure preheater 36. Bleed line 29 carries steam 18 at 216°C and 2.4 bar to the second low pressure preheater 37. Another bleed line 30 carries steam 18 at 224°C and 6.8 bar to the feedwater tank 38, where it uses its condensation heat to heat the feedwater 18. An high pressure feedwater pump 41 pumps the water 18, heated to 164°C in the feedwater tank 38, through the first high pressure preheater 42 at a pressure of 144 bar, where the temperature rises to 206°C. In the second HP preheater 43, the temperature rises further to 238°C. The second HP preheater 43 is powered by steam 18 from an HP steam line 31 connected to the outlet of the HP turbine 19a. The steam 18 from the HP steam line 31 has a temperature of 331°C and a pressure of 32 bar.After passing through HP preheater 43, it is passed through HP preheater 42 before being fed into the feedwater tank 38 at a temperature of 172°C and a pressure of 16 bar after a throttling not shown here.

[0057] After the feedwater 18 exits the HP preheater 43, the steam 18 is generated in several stages in heat exchangers 44, 45, and 46 operated with the HT heat transfer medium 5. In a first step, the water 18 is heated to 335°C in the HT preheater 44, and in a second step, it is evaporated in the steam generator 45. The steam 18 emerging from this preheater has a temperature of 338°C. This steam 18 is finally heated to 543°C at 141 bar in the superheater 46 and then fed preferably via the live steam line 47 to the HP turbine 19a.

[0058] The high-temperature heat transfer medium 5 for operating the steam-generating devices 44, 45, and 46 is passed through them in reverse order. First, it is pumped through the superheater 46 by pump 48, where it cools from 550°C to 407°C. Heat is released in the evaporator 45, and it cools to 343°C, leaving the high-temperature preheater 44 at a temperature of 298°C. The high-temperature heat transfer medium 5 is then returned to the high-temperature cold tank 15. In a preferred embodiment, a portion of the high-temperature heat transfer medium 5 is branched from line 49 into line 54 and fed into the intermediate superheater 21, where it reheats the steam 18 coming from the high-pressure turbine 19a. The HT heat transfer medium 5 has now cooled to 471°C and is combined with the HT heat transfer medium 5 coming from superheater 46.

[0059] The low-temperature heat storage circuit 4 forms the second link between the reconversion circuit 2 and the heat pump circuit 1. Conversely, during the discharging process of the high-temperature heat storage circuit 3, the low-temperature heat storage circuit 4 is charged with heat. In the following description of the low-temperature heat storage circuit 4, "charging process" thus means the absorption of residual heat from the reconversion circuit 2, and "discharging process" means the transfer of heat to the heat pump circuit 1. The two processes occur with a time offset, as in the heat pump circuit 1. The type of low-temperature heat transfer medium 6, i.e., the working medium of the low-temperature heat storage circuit, is not fundamentally limited. For example, water can be used, or water with additives that change its liquid operating range, such as aqueous salt solutions. However, water is preferred as the low-temperature heat transfer medium and low-temperature heat storage medium.In the following, only this tool will be considered within the framework of the exemplary embodiment described here.

[0060] During the charging process of the LT heat storage circuit 4, in a first step, water 6 is fed from the cold area of ​​a stratified storage tank 59 by a cold water pump 60 into a first condenser 61, where it is heated by the condensing steam 18 from the tap line 26. The water 6 heated in the first condenser 61 is fed to a second condenser 62, where it absorbs further heat from the condensing steam 18 from the tap line 27. In a further step, the water heated in the second condenser 62 is fed to a third condenser 63, which is heated by condensing steam 18 from the tap line 28. The water 6 exiting the third condenser 63 is finally returned to a hot area of ​​the stratified storage tank 59.The condensate 18 of the condensers 61 and 62 is fed into the condensate line 34 coming from the air cooler 33, the condensate 18 of the third condenser 63 is fed into the first low-pressure preheater 36.

[0061] During the discharge process of the LT heat storage circuit 4, hot water 6 from the stratified storage tank 59 is pumped through the working fluid heater 14 by a hot water pump 64, where it transfers its heat to the working fluid 7 of the heat pump circuit 1. The cooled water 6 is then returned to a cold area of ​​the stratified storage tank 59.

[0062] The low-temperature heat storage circuit 4 for absorbing residual heat from the re-electrification circuit 2 is particularly advantageous at locations where no high-temperature heat source is available for the heat pump circuit 1. The increased temperature level of the heat supply increases the coefficient of performance of the heat pump circuit 1. The use of a stratified storage tank as a tank type reduces investment costs.

[0063] In a preferred embodiment, the temperature of the low-temperature heat transfer medium (LTH) water 6 in the cold region of the stratified storage tank 59 is 10°C. The tank is preferably operated under atmospheric pressure. In the first condenser 61, the water 6 is heated to 35°C, in the second condenser 62 to 69°C, and finally in the third condenser 63 to a final temperature just below the boiling point, here 95°C. The thus heated water 6 is fed into the hot region of the stratified storage tank 59. Since hot water has a lower density than cold water, the storage region for warm low-temperature heat transfer medium is located in the upper region of the stratified storage tank 59, and the storage region for cold low-temperature heat transfer medium is located in the lower region.

[0064] During the discharge process, the hot water pump 64 pumps hot water 6 from the stratified storage tank 59 into the working fluid heater 14, which couples the low-temperature heat storage circuit 4 to the heat pump circuit 1. In the working fluid heater 14, the water cools to 10°C and is returned to the cold area of ​​the stratified storage tank 59.

[0065] In Figure 2 is a second embodiment 1', 3' of the heat pump circuit 1 and the HT heat storage circuit 3 from Figure 1 shown with a multi-part heating of working medium 7 and HT heat transfer medium 5.

[0066] In a known manner, compressor 10 compresses the working fluid 7, heating it up. The generated heat is transferred to the HT heat transfer medium 5 in the (first) HT heat exchanger 11. The cooled working fluid 7 is fed to a second compressor 101. The thus compressed and heated working fluid 7 releases its heat in a second HT heat exchanger 102 and is fed in a known manner to the recuperator 8. On the HT heat storage circuit 3 side, the HT heat exchangers 11 and 102 are connected in parallel. The HT heat transfer medium 5 coming from the HT cold storage tank 15 is distributed between the HT heat exchangers 11 and 102 by a three-way valve 103. The three-way valve 103 can also be replaced by a control valve in the supply lines to the HT heat exchangers 11 and 102. After passing through these heat exchangers, the HT heat transfer medium 5 is fed to the HT hot storage tank 16.The additional combination shown here, with the second compressor 101 and the second HT heat exchanger 102, can be followed by further corresponding compressor-heat exchanger combinations, which are not shown here. Alternatively, a serial connection of the HT heat exchangers 11 and 102 is also possible (not shown here).

[0067] A shaft 13 leads from compressor 10 to a gearbox 104. Connected to this shaft is a shaft 105, through which mechanical work is input from expander 12. A shaft 106, which drives compressor 101, is also connected to the same gearbox 104. Additional compressors can be connected accordingly. Preferably, several compressors and also expanders are arranged in a common gearbox housing. Such configurations are known as "geared compressors" and are commercially available.

[0068] To relieve the load on the heat pump circuit 1, an electric heater 107 can be arranged upstream of the HT hot storage tank 16. This reduces the temperature resistance requirements of the upstream parts in the heat pump circuit 1. On the other hand, it reduces the efficiency of the overall system.

[0069] The flow paths are as follows: In the first compressor 10, the first working fluid 7 is compressed to, for example, 40 bar, which heats it to 450°C. In the first HT heat exchanger 11, heat is transferred to the HT heat transfer medium 5. Subsequently, the first working fluid 7, cooled to, for example, 273°C, is compressed to 98 bar by the second compressor 101, which heats it again to 450°C. In the second HT heat exchanger 102, heat is transferred to the HT heat transfer medium 5. The final heating of the HT heat transfer medium 5 to the target temperature specified for the HT hot storage tank 16 is carried out by the electric heater 107.

[0070] The illustrated embodiments are preferred embodiments. They are not to be considered restrictive with regard to suitable configurations. Furthermore, only the essential features of the invention are presented there. They are implemented in a known manner using features typical for such systems, such as fittings, insulation, instrumentation and control technology, safety devices, or devices for filling the working fluid into the heat pump circuit. List of abbreviations and position numbers

[0071] HTHigh temperature NTLow temperature HDHigh pressure MDMedium pressure NDLow pressure 1 Heat pump circuit 2 Reconversion circuit 3 HT heat storage circuit 4 LT heat storage circuit 5 HT heat transfer medium 6 LT heat transfer medium 7 (First) working fluid 8 Recuperator 9 Electric motor 10 (First) compressor 11 (First) HT heat exchanger 12 Expander 13 (First) shaft 14 Working fluid heater 15 HT cold storage tank 16 HT hot storage tank 17 Pump for HT heat transfer medium from HT cold storage tank 18 Second working fluid 19 Steam turbine unit 19a HP turbine 19b Medium / low pressure turbine 21 Reheater 22 Steam turbine shaft 23 Generator 24 Outlet line from medium turbine 25 Line to air condenser 26 Branch LP steam line 27 First bleed line 28 Second bleed line 29 Third bleed line 30 Fourth bleed line 31 Branch HP steam line 32 Branch from second bleed line 33 Air condenser 34 Condensate line 35 Condensate pump 36 First LP preheater 37 Second LP preheater 38 Feedwater tank 39 Condensate pump from first LP preheater 40 Condensate pump from second LP preheater 41 HP feedwater pump 42 First HP preheater43Second HP preheater 44HT preheater 45Steam generator 46Superheater 47Live steam line 48High-temperature heat transfer pump from high-temperature hot tank 49High-temperature heat transfer line from high-temperature pump 50High-temperature heat transfer line to superheater 51High-temperature heat transfer line from superheater to steam generator 52High-temperature heat transfer line from steam generator to high-temperature preheater 53High-temperature heat transfer line from high-temperature preheater to high-temperature cold tank 54High-temperature heat transfer line to reheater 55High-temperature heat transfer line from reheater to steam generator 56Steam line to external heat consumer 57External heat consumer 58Return line of used steam from external heat user 59Stratified storage tank 60Cold water pump 61NT heat exchanger (first condenser) 62Second condenser 63Third condenser 64Hot water pump 1'Heat pump circuit, further embodiment 3'HT heat storage circuit, further embodiment 101Second compressor 102Second HT heat exchanger 103Three-way valve 104Gearbox 105Shaft between expander and gearbox 106Shaft to second compressor 107Electric heater

Claims

1. A system for storing and outputting electric energy stored as heat energy, comprising: • a heat pump circuit (1) having ∘ a first working medium (7) flowing in the circuit and ∘ a compressor (10) having an electric motor (9), • a high-temperature heat storage circuit (3) having ∘ a high-temperature heat transfer medium (5) flowing in the circuit, wherein the heat pump circuit (1) and the high-temperature heat storage circuit (3) are connected to a high-temperature heat exchanger (11) for transferring heat from the first working medium (7) to the high-temperature heat transfer medium (5), • a re-generation circuit (2) having ∘ a second working medium (18) flowing in the circuit, wherein the high-temperature heat storage circuit (3) and the re-generation circuit (2) are connected to a steam generating unit (44, 45, 46) for transferring heat from the high-temperature heat transfer medium (5) to the second working medium (18), and having ∘ a steam turbine unit (19) with power generator (23), which is arranged downstream of the steam generating unit (44, 45, 46), • a low-temperature heat storage circuit (4) having ∘ a low-temperature heat transfer medium (6) flowing in the circuit, wherein the re-generation circuit (2) and the low-temperature heat storage circuit (4) are connected to a low-temperature heat exchanger (61) for transferring heat from the second working medium (18) to the low-temperature heat transfer medium (6), and wherein the low-temperature heat storage circuit (4) and the heat pump circuit (1) are connected to a working medium heater (14) for transferring heat from the low-temperature heat transfer medium (6) to the first working medium (7), wherein the low-temperature heat exchanger (61) is designed as first condenser and in the re-generation circuit (2) its inlet is connected to the outlet of the steam turbine unit (19) and / or to a extraction line (27) on the steam turbine unit (19) in a position between the inlet and outlet of the same, characterised in that the system is configured in such a manner that the steam turbine unit (19) comprises a high-pressure turbine (19a) and a medium-pressure / low-pressure turbine (19b) and between the high-pressure turbine (19a) and the medium-pressure / low-pressure turbine (19b) a reheater (21) is arranged, wherein a part of the high-temperature heat transfer medium flow (5) flows through the reheater (21) before entering the steam generating unit (44, 45, 46).

2. The system according to Claim 1, characterised in that the heat pump circuit (1), further, comprises a recuperator (8) and an expander (12) and the first working medium (7) successively flows through the compressor (10), the high-temperature heat exchanger (11), the recuperator (8), the expander (12), the working medium heater (14) and again through the recuperator (8).

3. The system according to Claim 1 or 2, characterised in that the high-temperature heat storage circuit (3), further, comprises a high-temperature cold store (15) and a high-temperature hot store (16) and the high-temperature heat transfer medium (5) successively flows through the high-temperature cold store (15), the high-temperature heat exchanger (11), the high-temperature hot store (16) and the steam generating unit (44, 45, 46) .

4. The system according to any one of the preceding claims, characterised in that - the heat pump circuit (1') comprises a second compressor (101) and - the heat pump circuit (1') and the high-temperature heat storage circuit (3) are connected to a second high-temperature heat exchanger (102) for transferring heat from the first working medium (7) to the high-temperature heat transfer medium (5), - wherein in the heat pump circuit (1') the second compressor (101) is arranged downstream of the (first) high-temperature heat exchanger (11) and the second high-temperature heat exchanger (102) is arranged downstream of the second compressor (101), and - wherein in the high-temperature heat storage circuit (3) the second high-temperature heat exchanger (102) can be switched on parallel to the high-temperature heat exchanger (11).

5. The system according to Claims 2 and 4, characterised in that the compressor (10), the expander (12) and the second compressor (101) are mechanically coupled to one another via a common gearing (104).

6. The system according to any one of the preceding claims, characterised in that in the high-temperature heat storage circuit (3) between the high-temperature heat exchanger / s (11, 102) and the high-temperature hot store (16) an electric heater (107) is arranged.

7. The system according to any one of the preceding claims, characterised in that the steam generating unit (44, 45, 46) comprises a high-temperature preheater (44), a steam generator (45) and a superheater (46), through which the second working medium (18) flows in this sequence and the high-temperature heat transfer medium (5) in counter-flow.

8. The system according to any one of the preceding claims, characterised in that the low-temperature heat storage circuit (4) comprises at least one further condenser (62, 63) downstream of the first condenser (61), wherein all these condensers (61, 62, 63) are connected in parallel to one another in the re-generation circuit (2) and in the low-temperature heat storage circuit (4) further condensers (62, 63) arranged downstream one behind the other are each connected to a extraction line (27, 28) of the steam turbine unit (19) in positions between the inlet and outlet of the same, which are arranged upstream in the re-generation circuit (2) one behind the other.

9. The system according to Claim 8, characterised in that the low-temperature heat storage circuit (4), downstream of a last condenser (61, 62, 63), comprises a storage device (59) for the low-temperature heat transfer medium, having a storage region for cold low-temperature heat transfer medium (6) and a storage region for warm low-temperature heat transfer medium (6), wherein - the inlet of the first condenser (61) is connected to the storage region for cold low-temperature heat transfer medium (6) and the outlet of the last condenser (61, 62, 63) is connected to the storage region for warm low-temperature heat transfer medium (6), and - the working medium heater (14) is connected to the storage region for warm low-temperature heat transfer medium (6).

10. The system according to Claim 8 or 9, characterised in that the re-generation circuit (2) comprises at least one low-pressure preheater (36, 37), which is arranged downstream of condensers (61, 62) connected in parallel and connected to one of the extraction lines (28, 29) of the steam turbine unit (19) in positions between the inlet and outlet of the same.

11. The system according to the Claims 9 and 10, characterised in that an extraction line (28), upstream of the at least one further condenser (63) and of the at least one low-pressure preheater (36), branches off and is connected to the respective inlet for the second working medium (18) of the same.

12. The system according to any one of the preceding claims, characterised in that the re-generation circuit (2) comprises a connection for an external heat consumer (57) .

13. A method for storing and outputting electric energy stored as heat energy, having the following steps: - providing a system according to any one of the preceding claims; - conducting a part of the high-temperature heat transfer medium flow (5) through the reheater (21) prior to entering the steam generating unit (44, 45, 46) .