Compressed air energy storage
Compressed air storage power plants are storage power plants, in which compressed air is used to store energy. They are used for network control, such as the provision of balancing power: When will produce more electricity than is consumed, is pumped with the excess energy air under pressure into a reservoir; wherein current flow on demand is produced with compressed air in a gas turbine.
After the English name of compressed air energy storage, these power plants are also abbreviated as CAES power plants.
Only two storage power plants of this type are operated worldwide so far: The Huntorf power plant in Germany and the McIntosh power plant in the U.S..
- 2.1 Compressed air -gas power plant
- 2.2 Adiabatic compressed air energy storage plant 2.2.1 Development Projects
- 2.3.1 Submariner compressed air storage
- 3.1 Completed projects 3.1.1 Huntorf power plant
- 3.1.2 Power Plant McIntosh
- 3.1.3 Power Plant Sesta
- 3.2.1 Compressed air storage Staßfurt ( ADELE )
- 3.2.2 Norton Energy Storage
- 3.2.3 Iowa Stored Energy Park
Operation
Compressed air storage power plants have been designed as a hybrid in combination with a gas turbine power plant to provide electricity at times of peak load. In contrast to a process developed for the same purpose pumped storage power plant in which water from an elevated reservoir flows through downspouts down and it drives turbines and thus generators, a compressed air storage power plant uses the energy contained in compressed air. In off-peak hours, compressed air is stored in an underground cavern with an electrically driven compressor. In times of high demand for electricity at peak load, the compressed air is fed into a gas turbine that delivers its power to a generator hitched. Since expansion of the air heat must be supplied again to prevent the icing of the turbine, a combination of compressed air energy storage and gas turbine power plant is used.
Peak load power plants are technically complicated power plants, and therefore the power generated in them is very expensive. For this reason, they are only used at certain times to cover peak loads.
An essential feature of a compressed air storage power plant - as well as other peak-load and storage power plants - is that they can be started very quickly. Within three minutes, is, for example, in Huntorf Elsfleth at 50 % and after about ten minutes, 100 % of the power available.
The system is also black-start capable, that is, the system can for a large-scale blackout for the reconstruction of the network operation contribute.
Efficiency
Specify the efficiency of compressed air storage power plants is difficult because two different inputs (gas and electricity ) are required. This can not be equated easily. There are two design extremes:
At comparatively high gas prices, it would be possible to scattering generously in the cavern compressed air without any additional supply of heat from gas. The efficiency calculation of the power station would be analogous to that of a pumped storage power plant. The efficiency is due to high losses resulting from the unused heat of compression, significantly lower than that of a modern gas turbine.
At very low gas prices could lower the cavern pressure to save valuable electrical energy for compaction. By burning more gas can compensate for this deficit through higher turbine inlet temperatures within limits. However, this contradicts to some extent the actual purpose of a storage power station, which is to save energy. In addition, so one approaches to the conventional gas turbine process.
Reliable compressed air storage power plants are moving out of technical reasons between these two extremes. In order to produce 1 kWh of electrical energy, 0.8 kWh of electric power and 1.6 kWh of gas must be applied.
The amounts received from the network while saving energy
The energy delivered is significantly higher and is
The difference is provided by additional burning of natural gas.
Importance
CAES power plants could in the future by the energy transition and the resulting construction of new wind turbines and photovoltaic systems, which is accompanied by an increased energy storage requirements, get a bigger meaning. They can be used as pumped storage power plants for electricity finishing. In order to provide a similar amount of balancing energy, need pumped storage power plants either large volumes and so much space or large height differences.
Compressed air storage need hollowed airtight salt domes and are therefore just as pumped storage power plants linked to geologically suitable locations. At the German North Sea coast, there are many salt domes, which could be flushed out, thereby creating caverns for compressed air storage.
This one promises in the face of consistent expansion of wind energy and photovoltaics from the wide use of energy storage a perpetuation of this fluctuating ( volatile ) " supply-dependent forms of energy ." Lack of wind or solar energy could be supplemented from the memories, and the brief but very peak production could be fed into the memory, which increases the power quality characteristics of wind and solar energy. It is advantageous that in the vicinity of the current (coastal area) and future ( North and Baltic Sea) production concentration of wind power production are many geologically suitable sites. The EU promotes a Europe-wide research project on compressed air storage.
Systematization
In the strict sense of the word, there is a compressed air storage power plant only of a current-driven compressor, the compressed air reservoir as a large-volume, hermetically sealed container, a turbine and a generator. The compressor compresses air and presses it into the vessel. The later escaping compressed air drives the turbine. The generator connected to the turbine generates electricity. This elementary execution would in practice lead to significant problems and inefficient operation. It is therefore always extended by additional components.
Compressed air -gas power plant
The compression of the air will automatically lead to an increase in its temperature, see: adiabatic change. Depending on the pressure well over 1,000 ° C can be reached. To protect the system before it is discharged their thermal energy via heat exchangers to the environment and is thus lost for further use. Further cooling takes place through the inevitable temperature compensation with the wall of the compressed air reservoir ( cavern ) in the time to re- taking place. For both processes result in considerable loss of efficiency.
Conversely, the ( already cooled air) would cool down heavily on expansion in the turbine. The residual moisture present in the air would freeze and the turbine freeze. To avoid this, the compressed air is mixed at the inlet to the turbine with a combustible gas, and the mixture ignited. The resulting hot exhaust gases drive the turbine.
Thus, it is a gas turbine power plant, in which the work of belonging to the turbine compressor is taken from the stored compressed air. The power plant Huntorf belongs to this category. In such a power plant, no energy is stored accordingly, the special benefits of such a power plant is the provision of control energy. By operation of the turbine without a compressor coupled significantly higher power may also be provided as this can be done in a conventional gas engine.
Adiabatic CAES plant
In the so-called adiabatic ( ish ) en compressed air storage power plant (Advanced Adiabatic Compressed Air Energy Storage - AA -CAES ), the compressor is not refrigerated and stored between the heat of the compressed air pressure in a heat storage. This is designed as solid storage, similar to a Cowper.
If the air is relaxed again, it goes through before the heat storage and is heated again. It is not natural gas for heating the air needed. Thus, a significantly higher efficiency could be achieved. The prerequisite is that the time between is short and discharging of the memory. During expansion in the turbine, the air is cooled to ambient temperature.
In previously executed power plants, resulting in the compression of the air heat is dissipated to the environment and is therefore not further used. Thus, an adiabatic CAES power plant closer working on an adiabatic change of state, the efficiency is higher.
Development projects
However, the significantly higher efficiencies of pumped storage power plants of about 80 % can be achieved probably never compressed air storage power plants for physical reasons. However, there are efforts in Germany and in the USA for each new building several new compressed air storage power plants in salt dome caverns or in the cavities of disused mines.
In the years 2003 to 2005, worked as part of a European research project of Alstom Power Switzerland on a refinement of the compressed air storage technology ( set ). It is discussed the construction of a compressed air energy storage plant in Staßfurt (RWE, DLR).
Isobaric pressure air storage
During removal of the compressed air from the compressed air reservoir, the pressure in the accumulator, and thus the inlet pressure of the turbine is reduced. Conventional turbines are designed for but largely constant pressure. To keep the pressure in the air space during the removal constant, it can be positioned below a column of liquid. This can be achieved in that the (underground ) cavity is connected to an above-ground storage tanks. During blowing of air into the cavity it displaces the liquid ( water or brine ), from there to the reservoir, while the discharge of the compressed air, the water flows back into the cavity. The change in pressure is reduced to the fluctuation of the surface of the lake. The principle of operation is already in practical use for natural gas storage caverns, for example, from natural gas companies Keyera in Fort Saskatchewan ( Canada).
When submarine compressed air storage, the pressure variations due to the positioning on the seabed automatically reduce to a minimum.
Submariner compressed air storage
The compressed air accumulator is positioned on the seabed, is used as the storage place of the cavity a container having a rigid or flexible sheath. On the cover only very small forces. The pressure of the compressed air at the inside of the container and the water pressure on its outer side are equal, there occurs only small forces. Nevertheless, you can work with high pressures. Thus there is, for example, in 1,000 feet of water, a pressure of about 100 bar.
As a submariner compressed air energy storage with solid shell disused oil tanker or concrete hollow spheres can be used. Submarine compressed air storage are with flexible envelope as " Energy Bag " and developed by the University of Nottingham .. Both versions must be weighted or anchored to the seabed due to the buoyancy occurring.
Professor Seamus Garvey, University of Nottingham, working on compressed air storage in the form of gigantic underwater balloon. In combination with new wind and wave converters, the memory with up to 60 bar pressure and a temperature up to 630 ° C up to 600 m are to work under the sea. The first prototypes are under construction and are supported by a well-known e- group.
Projects
Completed projects
Huntorf power plant
The Huntorf power plant - the world's first CAES power plant - was the late 1970s in Germany, built in Huntorf at Elsfleth, and put into operation in 1978. The plant originally had a capacity of 290 MW; this was increased by a retrofit in 2006 to 321 MW.
The power plant is a combined compressed air reservoir and the gas turbine power plant, that is, the gas turbine is not a pure gas expansion turbine, but an internal combustion engine, in addition to the energy of compressed air and the energy is converted by the combustion of natural gas.
McIntosh Power Plant
Another CAES power plant is located in the U.S. state of Alabama. It was commissioned in 1991. As a further development of the art, a recuperator CAES has been integrated, which uses the hot exhaust gases of the gas turbine to the air pre-heating and thereby reduce the fuel consumption. This power plant can provide a capacity of 110 MW over 26 hours. The air is stored here in a single cavity with a volume of 538,000 m³. The long running time of 26 hours shows that it is not a pure peak load power plant.
In order to win one kWh of electrical energy, 0.69 kWh electric power and 1.17 kWh of gas must be invested before.
In this system, an amount of energy of 2860 MWh retrieved from a Huntorf compared to 1.8 times the storage volume. This corresponds to a factor of about (2860/642) / 1.8 = 2.5 times higher storage density.
Power plant Sesta
In Sesta in Italy a test and demonstration plant with an electrical capacity of 25 MW in operation, the compressed air was from 1986 stored in porous rock. After an earthquake, the plant was shut down in the early 1990s.
Planned investments
Compressed air storage Staßfurt ( ADELE )
As of 2013, a pilot and test plant is to be built according to the principle ADELE ( Adiabatic storage) in Staßfurt in Salzlandkreis in Saxony- Anhalt. The concept is being developed by RWE, General Electric, Züblin and the DLR. The power plant is scheduled after the completion of a capacity of about 90 MWe and a storage capacity of about 360 MWh equipped and operated by RWE.
Norton Energy Storage
In Ohio (USA), the company Norton Energy Storage plans to build the largest ever built compressed air storage power plant. It is to store air in a 700 meter-deep ten million cubic meters of large limestone mine. The first power stage is to have between 200 MW and 480 MW and cost 50-480 million U.S. dollars. In four other stages, the power is to be increased to about 2,500 MW.
Iowa Stored Energy Park
In Iowa (USA), a compressed air storage power plant should be built with about 270 MWe power by 2015. In contrast to other systems should here not be stored in a cavity, but in an aquifer, the compressed air. The hydrostatic pressure of groundwater, it was hoped to use in a weakened form the above-mentioned advantages of the isobaric memory. Completion was scheduled for 2015. Meanwhile, the project was canceled due to geological conditions are not met at the intended location.