GB2236808A - Power generation using energy storage/transfer - Google Patents

Abstract

Power generated at a first power station 10 is used to compress a gaseous fluid which is passed into a tubular energy transfer element 14 extending between the first station 10 and a second station 12. The energy is stored in the energy transfer element 14 by maintaining the compressed fluid in said element under pressure. At the second power station (12) the fluid is expanded (eg in a turbine) to release the energy stored therein. The first station may comprise a motor 16a driving high and low compressor stages 16 using a gear box 16C and connected via intercoolers 16B. A turbine 17 may alternatively drive the compressor 16. The second station may comprise turbines 18, a combustor 18B, reheater 18A and an electric generator 20, valves 22 and 14A are provided. <IMAGE>

Description

ENERGY STORAGE/TRANSFER SYSTEM The present invention relates to a method and apparatus for the storage and transfer and retiming of delivery of energy in a compressed fluid between two distanced stations.

Energy storage using compressed fluids such as air as the storage medium is well known. In practice the air is compressed and subsequently stored in large underground storage caverns until such time as it is released to drive an expansion turbine which may subsequently drive an electric generator.

In the known method compression, underground cavern storage, and turbine expansion of the working fluid are performed at the same station which is usually in close proximity to a suitable source of electrical energy which drives the compression plant. This energy may be generated by coal, oil, nuclear or other type generating stations which supply electricity to power a motor which subsequently drives the compressor. In the off-peak generation cycle the electric generator which is located in the same station adds to the energy stored in the compressed fluid by using excess electrical energy to drive the compression plant and increase the pressure in the stored working fluid whilst at the same time supplying a base load of electrical energy to closely located transmission and distribution systems supplying domestic and industrial users.During periods of peak demand the energy stored in the compressed working fluid is released to drive a turbine to provide extra electrical energy which can be added to that being supplied to the distribution system directly by the generating station.

Whilst the abovedescribed method has undoubtedly a useful role, its application has been relatively limited to date due to the practical problems of providing sufficiently large capacity storage caverns, not to mention the high cost and construction time involved in relation to the narrow benefits obtained.

It is an object of the present invention to avoid or minimise one or more of the above disadvantages.

According to the present invention there is provided a method of transferring energy between remotely spaced apart first and second power stations, said method comprising the steps of: generating power at said first power station, using said power to compress a gaseous fluid at or in proximity to said first power station, passing the compressed fluid into a tubular energy transfer element extending between the first station to the second station, storing energy in the energy transfer element by maintaining the compressed fluid in said element under pressure, transferring the compressed fluid through the transfer element to the second power station, and expanding the compressed fluid at the second power station so as to release the energy stored therein to the second power station.

As used herein the expression "power station" indicates a station formed and arranged for supplying energy in a desired form, ususually electricity, directly or indirectly, from any suitable source including for example fossil fuel through combustion thereof, water or other fluid through driving of a turbine or the like, thereby etc.

Said method conveniently includes the step of converting energy released from the expanded fluid into electrical energy by means of a fluid driven electrical generator at the second power station. Advantageously energy is added to the expanding fluid,for example, by heating thereof. Thus, for example, where there is used a fluid such as air which supports combustion, it may be burnt with a suitable fuel, e.g. gas or oil.

Thus with the method of present invention substantial amounts of additional energy useful for satisfying peak load demands may be readily stored in a convenient energy distribution system in the form of a pipeline simply by increasing the pressure in the working fluid in the pipeline, thereby avoiding the need for large and expensive additional dedicated storage facilities such as underground caverns.

In a further aspect the present invention provides apparatus for transferring energy between two remotely spaced apart power stations, said apparatus comprising: a compressor formed and arranged at a first power station for using energy generated at said station to compress a fluid in use of the apparatus, a tubular energy transfer element extending between said first power station and a second, remotely spaced therefrom, power station for storing and passing compressed fluid from said compressor to an expander at said second power station, which expander is formed and arranged for receiving the compressed fluid from the tubular energy transfer element and releasing the energy stored therein to said second power station, whereby the amount of energy stored in the tubular energy transfer element can be varied in use of the apparatus by changing the pressure of the fluid in the element.

Conveniently the apparatus includes an expansion turbine at said second power station, which turbine is formed and arranged for converting the energy released from the decompressed fluid into electrical energy.

Preferably also, said tubular energy transfer element comprises a length of pipeline provided with valve means formed and arranged for regulating the flow of compressed fluid therealong.

Any more or less readily compressible fluid may be used in the method and apparatus of the invention. In general the fluid will comprise at least one gas, desirably an environmentally acceptable, readily available, and more or less readily tractable gas or mixture of gases, for example, air, so that fluid may be readily introduced to the tubular element from the atmosphere and/or released from the tubular element to the atmosphere.

Thus by means of the present invention there is simultaneously provided a particularly convenient form of energy transfer system in the form of a tubular element which may conveniently, economically, and safely be installed underground in the same way as distribution systems for other utilities thereby avoiding the need for unsightly high tension overhead electricity power lines stretching across the country, and which system at the same time provides a particularly convenient and readily releasable energy storage means. The tubular elements may moreover be extended over relatively large distances, e.g. from 10 to 500 kilometres or more, without significant power losees.

A preferred embodiment of the present invention will now be described by way of example and with reference to the accompanying drawing in which: Fig. 1 shows schematically apparatus for transferring energy between two remotely spaced apart stations.

With reference to Fig. 1 a method of transferring energy stored in a compressed fluid between two remotely spaced power stations 10, 12 in accordance with the present invention comprises the steps of compressing a fluid such as air at a first power station 10. The compressed air stpres energy and is passed into a tubular energy transfer element 14 in the form of a length of pipeline which connects the first power station 10 with a second remotely spaced power station 12. The energy is stored within the pipeline 14 by maintaining the air under pressure. The compressed air is transferred through the pipeline 14 and a throttle valve 14A provided at a downstream end 14B to the second power station 12 where it is expanded and the energy stored therein is released.

The energy released from the expanded fluid is converted into electrical energy and may subsequently be distributed in any suitable way, for example, using a conventional electrical energy distribution system such as part of the National Grid.

Apparatus for implementing the abovedescribed method include low and high pressure compressors 16 which are driven by a motor 16A using a gearbox coupling 16C.

Intercoolers 16B are connected between the compressors 16A.

The motor 16A is electrically operated using electrical energy generated at the first power station 10 from a suitable fuel source such as coal which is found in close proximity to the first storage station 10 although the compressor 16 could be driven directly by a turbine 17 instead, in which case the energy to drive the turbine would be derived from steam, compressed air or other such means produced using said fuel source.

The pipeline 14 is designed to sustain pressures of between say 500 and 2000 p.s.i. over considerable distances. In one example of the present invention a pipeline run of 42Km between the first 10 and second 12 power stations with a pipeline diameter of 50cm, and operating at a pressure of 2000 p.s.i. of compressed air, could provide about 8 hours energy storage for a 55MW generation station 12 by closing a valve 22 located near to the second power station end 14B of the pipeline 14.

By varying the diameter and length of the pipeline 14 and the operating pressure used, the level and amount of energy stored can be varied. In the example given above the pipeline provides a volume of approximately 2,800 cubic metres over 42Km. To obtain an equivalent volume a spherical underground cavern of 11m diameter would need to be excavated at considerable depth.

The second power station 12 is provided with low and high power expansion turbines 18 which are arranged in use to expand the compressed air which is received from the length of pipeline 14 thereby releasing the energy stored therein. In addition reheat 18A and combuster 18B chambers are provided. The turbines 18 are further connected to a generator 20 which is driven by the released energy and which generates electricity which is distributed to an electrical power distribution system 24.

It will be appreciated that the air used in the apparatus is subject to varying pressures and temperatures. At the first power station before being compressed, air is at atmospheric pressure and ambient temperature while at the pipeline inlet the compressed air is at high pressure and increased temperature say 70 bar at 600C. Over 42Km the air undergoes a limited pressure reduction, for example to 50 bar, while the temperature remains generally constant and after expansion the air is released to the atmosphere at moderate temperature. The transfer process is essentially adiabatic thereby minimising heat loss.

By virtue of the distance between stations, the first power station 10 which requires substantial amounts of energy to compress the air can be conveniently located close to a source of energy such as a coal mine while the second power station 12 which receives most of its energy via the pipeline 14 can be located close to a load centre of the power distribution system such as a small town, with minimal environmental damage, deriving any additional fuel energy requirement from high quality clean fuel sources such as oil or gas.

Finally, the power station 10 is cost efficient since by virtue of the present invention the air transferred from the pipeline 15 to the expansion turbine 18 is already compressed thereby allowing the turbine 18 to deliver its full shaft power to the electrical generator with no loss of power to locally installed compressors.

Claims (8)

1. A method of transferring energy between remotely spaced apart first and second power stations, said method comprising the steps of: generating power at said first power station, using said power to compress a gaseous fluid at or in proximity to said first power station, passing the compressed fluid into a tubular energy transfer element extending between the first station to the second station, storing energy in the energy transfer element by maintaining the compressed fluid in said element under pressure, transferring the compressed fluid through the transfer element to the second power station, and expanding the compressed fluid at the second power station so as to release the energy stored therein to the second power station.

2. A method as claimed in claim 1 wherein said power generated at said first power station is electrical power.

3. A method as claimed in any one of claims 1 or 2 wherein heat energy is added to the expanding fluid.

4. A method as claimed in any one of claims 1 to 3 wherein said compressed gaseous fluid is air and the heat energy is added by burning of a suitable fuel with said air.

5. Apparatus for transferring energy between two remotely spaced apart power stations, said apparatus comprising: a compressor formed and arranged at a first power station for using energy generated at said station to compress a fluid in use of the apparatus1 a tubular energy transfer element extending between said first power station and a second, remotely spaced therefrom, power station for storing and passing compressed fluid from said compressor to an expander at a second power station, which expander is formed and arranged for receiving the compressed fluid from the tubular energy transfer element and releasing the stored energy therein to said second power station, whereby the amount of energy stored in the tubular energy transfer element can be varied in use of the apparatus by changing the pressure of the fluid in the element.

6. Apparatus as claimed in claim 5 which apparatus includes an expansion turbine at said second power station, which turbine is formed and arranged for converting the energy released from the compressed fluid into electrical energy.

7. Apparatus as claimed in claim 6 wherein said expansion turbine comprises low and high power expansion turbines.

8. Apparatus as claimed in any one of claims 5 to 7 wherein said tubular energy transfer element comprises a length of pipeline provided with valve means formed and arranged for regulating the flow of compressed fluid.