DE102014202275A1 - Energy storage for intermediate storage of electrical energy - Google Patents

Abstract

The invention relates to an energy storage device for temporary storage of electrical energy comprising a pressurized water reservoir (2) and a low-temperature cyclic process device (4) and a generator (6), wherein the feed of the pressurized water reservoir (2) by a compression heat pump (50) takes place, the one Exhaust gas stream (52) of a thermal power plant (10) extracts heat.

Description

The invention relates to an energy store for intermediate storage of electrical energy according to claim 1 and to a method for operating an energy store according to claim 5.

Due to the growing feed-in volume of fluctuating renewable energies, thermal power plants are increasingly fulfilling regulatory tasks to offset fluctuation. Thus, the flexibility of thermal power plants is becoming increasingly important. In addition, due to the irregular operation due to the necessary start-up and shutdown processes, the efficiency and service life of the power plants are reduced. This has a negative effect on the efficiency of the systems. Due to the ever increasing fluctuations between electricity supply and electricity demand, there is a need for electricity storage on a scale of several megawatt hours.

The cushioning of demand peaks in the power grid is compensated for example by the use of pumped storage power plants. However, these require large construction measures and are not meaningful to set up in all geographical locations. Another way to store energy on a larger scale between is the establishment of compressed air storage power plants, which, however, have a very low energy density. Furthermore, these are dependent on regional conditions.

The object of the invention is to provide an energy storage for intermediate storage of electrical energy on an industrial scale, which is advantageous from the investment costs over the prior art and independent of the geographical location.

The object is achieved in an energy storage for intermediate storage of electrical energy according to claim 1, as well as in a method for operating an energy storage device according to claim 5.

The energy store according to the invention according to claim 1 comprises a pressurized water reservoir and a low-temperature cyclic process device, such as an Organic Rankine Cycle (ORC) device and a generator. The energy storage is characterized in that the supply of the pressurized water storage tank is effected by a compression heat pump, which extracts heat from an exhaust gas of a thermal power plant.

The advantage of the invention is that a thermal power plant, such as a combined cycle gas and steam power plant, heat, which would otherwise be discharged to the environment, an exhaust gas stream is withdrawn. The exhaust stream, which typically has temperatures between 70 ° C and 150 ° C, is too cold using conventional methods to be accessible for further energy use. With the help of a heat pump, however, the temperature level can be raised. The heat pump heats up the pressurized water tank so that its temperature level is high enough for the economical operation of an ORC plant. With higher demand from the power grid, additional energy can be generated and fed into the grid via the low-temperature cycle device and the connected generator, fed by the pressurized water tank.

In addition, the following terms used here are explained in more detail.

Steam generator:

A steam generator is a steam boiler or a plant for generating water vapor. In such a plant, water is heated and converted into steam. The steam is then used to drive the thermal power plant. In a steam generator pressure, temperature and amount of steam produced are designed so that they are fed to a steam consumer, z. As a power plant turbine are tuned.

• – Der Speisewasservorwärmer (Economizer), in denen Wasser und Verbrennungsluft vorgewärmt werden.
• – Der Verdampfer zur Erzeugung des Dampfes.
• – Der Überhitzer, in dem der Dampf auf die für den Verbraucher benötigte Temperatur erhitzt wird.
• – Der Dampferzeuger kann auch einen Zwischenüberhitzer enthalten, der Wasser bzw. Nassdampf, das eine Hochdruckturbine durchlaufen hat, wieder in den überhitzten Zustand (Heißdampf) bringt, bevor er einer Mitteldruckturbine zugeführt wird.
• – Ein Dampferzeuger kann aus mehreren dieser Komponenten aufgebaut sein und dadurch Dampf auf verschiedenen Druck- und Temperaturstufen erzeugen.
• – Weiterhin gehören Armaturen wie Ventile, Pumpen zu einem Dampferzeuger

Essential components of a steam generator are:

• - The economizer, in which water and combustion air are preheated.
• - The evaporator to generate the steam.
• - The superheater, in which the steam is heated to the temperature required for the consumer.
• - The steam generator can also contain a reheater, the water or wet steam, which has passed through a high-pressure turbine, returns to the superheated state (superheated steam) before it is fed to a medium-pressure turbine.
• - A steam generator can be made up of several of these components and thereby generate steam at various pressure and temperature levels.
• - Furthermore, valves such as valves, pumps belong to a steam generator

Saturated steam and saturated water:

Saturated steam is the boundary between wet and superheated steam. Here, wet steam is supersaturated gaseous water containing condensed water droplets. Superheated steam or superheated steam is steam at a temperature above the boiling point. Of the Steam is "dry" and contains no droplets. In steam boilers, the generated steam is brought into this state by means of the superheater.
Saturated water is water that is in thermodynamic equilibrium with saturated steam, ie water at boiling temperature.

Low-temperature cycle:

This is especially understood to mean the Organic Rankine Cycle or the Kalina Cycle. This is a method of operating steam turbines with a working fluid other than water vapor. As a working medium organic liquids or ammonia are usually used, which have a lower boiling point than water.

Thermal power plant:

Under thermal power plant, in particular, a fossil power plant, such as a gas and steam combined cycle power plant (CCGT) and a biomass power plant, a waste heat and power plant, a nuclear power plant or a solar power plant understood. In particular, the invention is to be used where, by generating steam, a turbine is driven and, as a rule, electrical energy is obtained via a generator.

A further advantageous embodiment of the invention consists in that a throttle is provided between the pressurized water reservoir and the evaporator of the low-temperature cyclic process device, by means of which a reduction of a pressure in the water reservoir to a constant pressure level for the operation of the low-temperature cyclic process device. In this way, the low-temperature cycle, so preferably the ORC or Kalina cycle plant can be operated at the optimum temperature and pressure level for them until the capacity of the memory is exhausted, or its temperature level reaches the temperature level for the low-temperature cycle.

In an advantageous embodiment of the invention, a phase change material is introduced into the pressurized water storage. This allows the storage of a larger amount of heat at a nearly constant temperature by a melting / solidification process. As a result, the storage density of the pressurized water reservoir is increased and the memory can emit more heat at a constant temperature.

A further advantageous embodiment of the invention consists in a method for operating an energy storage device according to claim 5. Here, a low-temperature cycle process device is operated via a pressurized water storage, which in turn drives a generator. The invention is characterized in that the pressurized water reservoir is fed by a heat pump, which extracts heat from an exhaust stream of the thermal power plant. For the method, there are the analog advantages that are already mentioned with respect to the analog device requirement of the energy storage.

In an advantageous embodiment of the method, the pressurized water reservoir is filled during operation of the thermal power plant and supplied with a standby operation of the thermal power plant this with electrical energy. This electrical energy is provided by the generator, which is driven by the operation of the low-temperature cycle process. In this way, the power plant, in particular a reserve power plant, in a standby mode generate its own consumption of energy itself and is not dependent on the network. In particular, in the event of a power outage or a so-called black-out, this is advantageous because the power plant can be restarted by its own power and can go online.

Further advantageous embodiments and further features of the invention will be explained in more detail with reference to the following figures. Features with the same designations, but in different embodiments, are given the same reference numerals.

Showing:

1 a schematic diagram of a thermal power plant with an additionally arranged pressurized water storage and an ORC system;

2 a power plant with energy storage as in 1 but with an alternative feed of steam into the pressurized water storage tank.

In 1 is a schematic representation of a thermal power plant, shown here in particular using the example of a combined cycle power plant. The thermal power plant 10 comprises as essential components on the one hand, the steam generator 8th and a turbo set 16 , The steam generator 8th includes first a feedwater pre-heater 24 (Economizer) in which the water is preheated to produce steam. Furthermore, the steam generator includes 8th an evaporator 25 to which a drum 26 (Pressure vessel) is arranged, is stored in the hot water or steam under pressure. It is followed by a superheater 27 in which the saturated vapor is converted into superheated steam or dry steam.

The superheated steam produced here becomes a high-pressure turbine via a piping system 18 guided, but in this embodiment, on a common shaft 23 with a medium pressure turbine 19 and a low-pressure turbine 20 is arranged. The common wave 23 that over the mentioned turbines 18 to 20 is powered, in turn drives a generator 21 on, which serves to generate electricity and thus to the mains supply. In a condenser 22 In the turbines, the steam is condensed and cooled. The water thus condensed is returned to the economizer or the feedwater pre-heater via various pumps and low pressure preheaters, which will not be discussed further 24 fed. Furthermore, in this embodiment, a reheater 28 provided the steam after passing through the high-pressure turbine 18 and before flowing into the medium pressure turbine 19 overheated again.

In addition, the energy storage comprises a pressurized water storage 2 connected to a low-temperature cycle process device here in the form of an ORC plant 4 stands. The water in the pressurized water tank 2 is stored, comes from the steam generator 8th of the thermal power plant 10 , (The feed itself will be discussed later.) The pressurized water tank 2 contains water at a certain pressure and above it a steam cushion at the same pressure, passing through a throttle valve 14 throttled down to a working pressure necessary for the operation of the ORC plant 4 necessary is. Through the throttle valve 14 can for the ORC facility 4 always a constant pressure and thus a nearly constant temperature of the water vapor are provided, so that they can also be operated constantly and in their optimum efficiency. The steam in the pressurized water tank 2 over the throttle valve 14 into the ORC system 4 is fed into an evaporator 12 led, in turn, a working medium of the ORC plant 4 which has a lower boiling point than the water is evaporated. This steam becomes a turbine 34 the ORC system 4 powered, in turn, a generator 6 the ORC system 4 to generate electricity. The vaporous working fluid is discharged from the turbine 34 led into a recuperator and condensed again. A subsequent capacitor 33 serves for cooling.

The heat supply from the pressurized water storage tank 2 to the evaporator of the ORC plant 4 takes place accordingly by the removal of steam from the pressurized water tank 2 , About the throttle 14 is at the top of the pressurized water tank 2 Taken off steam. The pressure behind the throttle 14 should remain at a constant pressure level for steam extraction, even after the pressure of the pressurized water tank 2 drops by the steam extraction. The supply of steam at a constant pressure level to the evaporator of the ORC 4 allows a more constant upper operating temperature of the ORC 4 , This leads to improved efficiency, simplifies the system design and the selection of the working medium. The extracted steam is in the evaporator of the ORC 4 condenses and gives off its heat. The resulting condensate can be recycled at various points in the steam generation or in the water cycle.

In order to maximize the specific energy content of the store, the difference between top pressure of the pressurized water store should be 2 and the pressure of the steam, the ORC 4 is fed, be as large as possible. However, this leads to low operating pressures and thus to condensation temperatures of the vapor that is the ORC 4 is supplied. This reduces the efficiency of the ORC 4 , It must therefore be found an optimum between storage density and efficiency for reconversion. For example, typical CCGT medium-pressure drums can be used, which allow an upper operating pressure of 30 to 40 bar. For discharging the accumulator, steam can be removed at approx. 15 bar and supplied to the ORC 4 be supplied, which allows a condensation temperature of about 200 ° C. This temperature allows sufficient efficiency for reconversion. If the lower GUD pressure level is used during storage, the heat storage tank can be filled up to 8 bar, for example. The steam production can then take place at about 2 bar and 120 ° C.

In an advantageous embodiment of the invention, a phase change material is introduced into the pressurized water storage. This allows the storage of a larger amount of heat at a nearly constant temperature by a melting / solidification process or a comparable near-isothermal phase change. As a result, the storage density of the pressurized water reservoir is increased and the memory can emit more heat at a constant temperature. When stored at the temperature level of the medium pressure steam turbine (180 ° C to 250 ° C) and a heat transfer to the Niederdruckkreisprozessanlage at about 200 ° C, the following materials offer as phase change materials: LiOH-NaOH (20% / 80% as the preferred mixing ratio) , KNO3-NaNO3 (54/46%) or LiNO3. When stored at the temperature level of the low-pressure steam turbine (110 ° C to 160 ° C) and a heat transfer to the Niederdruckkreisprozessanlage at about 120 ° C, however, offer the following materials as phase change materials: wax; MgCl2 × 6 H2O as an example of a salt hydrate; Erythritol as an example of an organic substance; Polyethylene as an example of a polymer; KNO3 / LiNO3 (67/33% mixture) as an example of a salt mixture. The phase change material can be used in direct material contact with the water in the pressurized water storage. Furthermore, the encapsulation or other inclusion of the phase change material in an inert container material is possible.

To assess the storage capacity under possible power generation capacity by an ORC system 4 one can assume the following parameters. When installing 30 high-pressure drums as accumulator of the pressurized water storage tank 2 a storage volume of approx. 700 m ³ is available. This allows the provision of electricity of the order of 3 MW over a period of approximately 4 hours. The own energy demand of the thermal power plant 10 can thus be covered without external reference from the power grid over this period, if the thermal power plant 10 is in standby mode during this time. In addition, there is the option of using the ORC system 4 power to be added to the grid in case of power fluctuations or in case of power failure, so in a black-out, to use for black start and network recovery.

The pressure in the pressurized water tank 2 is generated by a temperature increase of the water in the pressure water storage. This is done on an exhaust stream 52 of the thermal power plant 10 a heat exchange device 51 appropriate. The heat exchange device 51 withdraws the exhaust gas flow 52 , which typically has a temperature between about 70 ° C and 150 ° C, energy, wherein the exhaust stream is further cooled. At the same time, the energy withdrawn from the exhaust gas flow becomes a heat pump 50 , in particular a compression heat pump, supplied with the use - usually electrical energy - the heat extracted from the exhaust gas flow to the water in the pressurized water tank 2 to a temperature which, as described, is suitable for operating the ORC system. The operating temperature in the pressurized water storage tank when using a heat pump 50 is preferably between 120 ° C and 250 ° C. The operation of the heat pump is due to the design of the heat pump energetically positive, that is, it is for the operation of the heat pump much less electrical energy needed than would be necessary to raise the pressure water storage by electrical resistance heating to the required temperature level. In this way, the exhaust gas flow 52 used by the thermal power plant to provide an excess of electrical energy.

Claims (9)

Energy storage for intermediate storage of electrical energy comprising a pressurized water storage ( 2 ) and a low-temperature cycle process device ( 4 ) as well as a generator ( 6 ), characterized in that the supply of the pressurized water reservoir ( 2 ) by a compression heat pump ( 50 ), which is an exhaust gas flow ( 52 ) of a thermal power plant ( 10 ) Removes heat. Energy store according to claim 1, characterized in that a feed of the pressurized water reservoir ( 2 ) through the steam generator ( 8th ) by saturated or saturated steam. Energy storage according to claim 1 or 2, characterized in that between the pressurized water storage ( 2 ) and an evaporator ( 12 ) of the low-temperature cycle process device ( 4 ) a throttle ( 14 ) is provided by the lowering of the pressure of the pressure water reservoir ( 2 ) for the operation of the low-temperature cyclic process device ( 4 ) constant pressure level occurs. Energy store according to one of the preceding claims, characterized in that the low-temperature cycle process device ( 4 ) is an ORC plant or a Kalina cycle plant. Energy store according to one of the preceding claims, characterized in that a phase change material in the pressurized water storage ( 2 ) is introduced to increase the thermal capacity of the memory. A method according to claim 5 or 6, characterized in that during operation of the thermal power plant ( 10 ) the pressurized water reservoir ( 2 ) and during a standby operation of the thermal power plant ( 10 ) this is supplied with electrical energy by the generator ( 6 ) by operation of the low pressure cycle device ( 4 ) is generated. Method according to claim 6, characterized in that the steam generator ( 8th ) Saturated or saturated steam is withdrawn and the pressurized water storage ( 2 ) is supplied. Method according to claim 6 or 7, characterized in that between the pressurized water reservoir ( 2 ) and the evaporator ( 12 ) of the Low Temperature Circuit Process Device ( 4 ) a throttle ( 14 ) is provided, through which the pressure of the steam in the pressure water reservoir ( 2 ), to a for the operation of the low temperature cycle device ( 4 ) constant operating level is lowered, Method according to one of claims 6 to 8, characterized in that during the operation of the thermal power plant ( 10 ) the pressurized water reservoir ( 2 ) and during a stand-by operation of the thermal power plant ( 10 ), which is supplied with electrical energy by the generator ( 6 ) by operation of the low-temperature cycle process device ( 4 ) is generated.

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