Patent Application
20100052326
The present invention relates to the use of renewable energy sources for the production of electrical energy. Moreover, the present invention includes a method and a system to recover energy in two different power generation systems using the same energy source.
The traditional use of wind, water, and solar power is well known in the art, and an increasing yet still minor contributor of electrical energy in developed as well as developing countries. Environmental issues are the major promoting force for mass production of electricity by the use of renewable energy sources to resist increasing risks of climate change due to carbon emission and other pollution, exhaustion of fossil fuels and the environmental risks associated with nuclear power.
It is well known in the art to generate hydroelectricity from hydropower plants by the load of elevated water sources (the hydraulic head) to drive a water turbine and generator to produce electrical energy. This process of producing electrical energy is dependent on volume as well as a natural difference in height between the intake of water and the outlet of the water, by allowing the water to run through a tunnel shaped structure (penstock). Frequently, large dams are required, which are costly and affect the environment.
Another way of energy production is the use of geothermal power plants in areas of the world where geothermal heat is present at relatively shallow depth. By drilling tunnels or wells until they reach natural fractures in the ground, hot water or steam either flows up or is pumped up. Geothermal energy can be generated several ways such as using dry steam to drive turbines and generators or by using steam-water separators to separate steam from boiling water flowing from an underground source and then using the steam to drive a turbine, which spins a generator.
Methods of deep drilling are being developed and geothermal power plants being built which reach deeper into the earth to reach heat. In such power systems, wells are drilled into known geothermal reservoirs where temperatures often exceed 360° C. Steam or super-heated water is brought to the surface under its own pressure where the energy, in the form of steam, is utilized to turn the turbines of an electrical generator. In these systems, the carrier in the form of pressurised water or steam is essential, which limits useful areas for unleashing geothermal energy.
Methods have also been investigated where water is pumped down and passed through fractures sufficiently deep underground where the rock has a temperature of 140° C. or higher, thus the rock is used as a heat exchanger and the water penetrating the fracture is brought to the surface again where its heat is tapped. This technology has been referred to as “Hot Dry Rock” technology. Experimental systems have been setup (Los Alamos, USA, Hijion, Japan and Cornwall, UK), providing temporary power plants of a few MW and further experiments are ongoing, e.g. in Soultz-sous-Forêts in France and in Urach, Germany. The initial “Hot Dry Rock” concept was based on the assumption that deep crystalline basement rock formations are nearly dry and impermeable for fluids due to the pressure of the overburden rock. Therefore, it was suggested to induce artificial fractures acting as heat exchange surfaces, through which fluid could be circulated via boreholes penetrating these fractures.
Alternative methods to produce energy on large-scale from renewable non-polluting sources are still very much appreciated and useful.
The invention provides a method and system for tapping geothermal energy, which are not limited by plentiful supplies of hot ground water. The invention is based on the premise that heat is ubiquitous underneath earth's surface although the temperature-depth gradient varies depending on local variations in the crust of the earth. Useful geothermal areas using available technologies are primarily found in volcanic regions in vicinity of tectonic plate boundaries where the crust is thin and hot magma is closer to earth's surface. The continental crust is generally 20-70 km thick, however, the oceanic crust (sima) is thinner, generally 5-10 km thick. Underneath the crust lies the upper mantle layer. The temperature of the crust ranges from the air temperature to about 900° C. close to the upper mantle.
Instead of relying on underground hot water supplies in geothermal areas or pumping down water through a ‘Hot Dry Rock’ heat exchanger, the invention introduces a novel concept of guiding seawater/freshwater to geothermal vaults where the water is heated and acts as a heat carrier to bring thermal energy from hot underground areas to the surface where the thermal heat is converted to electrical energy.
Several basic configurations have been developed based on the same main concept and the choice of a particular configuration will depend on the local geographic circumstances and the desired amount of energy.
The method utilises seawater/freshwater as a carrier of thermal energy from underground geothermal heat sources. In preferred embodiments the difference in height of the sea water source and the geothermal heat source is used to create a hydrodynamic head which is utilised to drive a hydropower plant and thus the water serves as a dual energy carrier, of potential energy and thermal energy.
In a first aspect the present invention relates to a method for power generation. The method comprises in its simplest form the steps of:
It is a premise of the invention to find a suitable geothermal underground dry space. State of the art methods for exploring the earth's crust, e.g. developed in the field of searching for oil and gas reserves are very useful in this regard. It is contemplated that in several locations in the world suitable conditions exist, especially in the vicinity of volcanic areas and close to coastal areas with a shallow coastal shelf close to the bathyal zone, i.e. where the land is close to deep sea. Such areas are often found by volcanic islands, e.g. the Westmann Islands south of Iceland.
In an embodiment the method further comprises guiding seawater/freshwater from an intake at the bottom of the ocean into a first penstock tunnel leading downwardly towards a lower point beneath the ocean bottom. Seawater/freshwater is guided through the tunnel into an underground hydropower unit comprising means to extract mechanical energy from the flowing seawater/freshwater and means for converting the mechanical energy into electrical energy. Thereafter the seawater/freshwater is lead from the hydropower unit into the geothermal underground dry space, where the seawater/freshwater absorbs heat from the surrounding hot rock and consequently temperature and pressure of the water increases. The pressurised hot water or steam from the underground dry geothermal area is then allowed to escape through one or more ducts to the surface of the earth into a geothermal power station leading the hot water or steam through means to extract thermal energy and converting the thermal energy into electrical energy.
In a second aspect the present invention relates to a power generation system which operates based on the principles and methods of the invention. The power generation system comprises
The seawater/freshwater is guided through a first underground powerhouse at the end of the inlet tunnel, where the powerhouse comprises means to extract mechanical energy from the flowing seawater/freshwater and means for converting the mechanical energy into electrical energy. After the seawater/freshwater flows from the powerhouse it is lead into one or more transport tunnels for guiding the seawater/freshwater from into an underground dry geothermal area, where the seawater/freshwater is heated up to a boiling point. The system further comprises one or more outlet ducts for allowing hot water or steam from the geothermal underground dry space to the surface of the earth, where it goes through a power station comprising means to extract thermal energy and means for converting the thermal energy into electrical energy.
An embodiment of the “basic” configuration of the invention is shown in
In one embodiment of the present invention an energy recovery system is disclosed, where sea water is used to generate power in two different power plant systems. The first system generates hydroelectricity through a hydropower system using water turbine(s) and generator(s). The second system a geothermal power plant using steam turbines to retrieve thermal heat and convert to electricity. Details of a particular configuration of this embodiment are shown in
The second system (the geothermal power plant) is positioned above the geothermal dry space, where several vertical or semi-vertical ducts or tunnels 7 allow hot water and/or steam to escape from the geothermal space.
The penstock tunnel 13 receives seawater from an intake structure 2 which can comprise a valve as shown in
The second system consists of a plurality of tunnels which are drilled from land, into the geothermal area. A geothermal power plant 6 is positioned over the tunnels 7, where steam turbines harness thermal energy from steam/pressurised water from the tunnels.
The system shown in
In an embodiment of the present invention a method is disclosed for energy recovery where the same natural source is used to generate energy in two different power generation processes. The first power generation processes uses a hydropower station to generate hydroelectricity and the second power generation processes involves a geothermal power plant to generate electricity from steam. The natural source used in the method of the present invention is seawater. Seawater is received through an intake unit at the bottom of the ocean and directed to an underground power station through a diagonal or a vertical penstock. The seawater passes through a powerhouse driving one or more turbines. The mechanical energy produced by the turbines is converted to electrical energy by generators using electromagnetic induction. An optional step is leading the seawater further underground through a second penstock to a second powerhouse generating additional mechanical energy to be converted by generators into electrical energy. The next step involves leading the water optionally through a check valve into one or more tailrace tunnels into the dry geothermal area. When the water enters the geothermal area the temperature of the water increases and pressure will build up. The steam is lead through tunnels between the main land/island and the geothermal area to a geothermal power plant over the tunnels. The steam from the geothermal area drives the turbines geothermal power plant to generate mechanical energy which is converted to electrical energy by generators. The drainage from the geothermal power plant can be lead through tunnels, which have power house(s) comprising water turbines, back into the underground geothermal area. In this manner a circulation is created, where geothermal energy and hydraulic energy are generated in one system.
In an embodiment of the present invention, the water from the last powerhouse is lead through a closed system into the underground geothermal area and up through the tunnels to the geothermal power plant.
In an embodiment of the present invention, the intake of seawater is on land and the seawater is pumped for a shorter or longer distance to the intake. This embodiment is useful, where drilling for penstock at the bottom of the ocean is difficult or impossible. The power required for pumping seawater for a shorter distance onto land is proportionally small as compared to the energy generated in the power generation system of the present invention. Other advantages by pumping seawater onto land are better filtering options in order to protect the underground power generation system (generators and turbines), as well as causing less environmental damage to the bottom of the ocean.
In another embodiment of the present invention, the intake of water into the system is intake of freshwater from an estuary of a river. The estuary is near the sea, where fresh water and salt water mix. In this embodiment the water intake collects the water before it mixes with the seawater. In this embodiment the water is moving as it approaches and enters the intake, which is beneficial to the velocity of the water in the penstock. Such a set up requires a filtering mechanism/strainer or sift to prevent mud and sand or rocks carried forward by the river to end up in the energy recovery system. Freshwater can also be collected from a freshwater lake, which solves problems caused by salt in the power houses. Examples of such lakes are lagoons or reservoirs which are filled by glacier-melt-water. The intake for this embodiment can be placed in a pier of a bridge crossing a river. The pier will then serve as an access point to the intake for service etc.
In an embodiment of the present invention the penstock leads from the bottom of the sea and to a underground geothermal area situated under a dry area or a desert, such as the Sahara desert. The steam or hot water will be guided from the hot area up to the desert. In this manner energy is generated by power stations in the pipeline from the bottom of the sea and to the hot area. The steam and water that is guided from the hot area through the steam power plant and can be used to facilitate growth of plants in dry areas, where growth of plants is difficult or impossible.
In an embodiment of the present invention the penstock can be directed around a igneous intrusion such as a laccolith in order to heat the water from the intake.
In the present context the term “penstock” relates to tunnels, sluices or gates for enclosed flow of water, such as an enclosed pipe structure that deliver water to hydraulic turbines in a hydraulic power generation system. The penstock of the present invention can be formed by drilling or using explosions or both. In certain areas, it is advantageous to heat/burn the inner surface of the penstock to prevent the seawater to mix/react with chemical substances in the rock. The penstock can also be provided with a liner/feed such as a tube/pipe or moulded.
In the present context the term “tailrace” refers to a duct, a race or a tunnel for conveying water away from a power station after having released its kinetic energy to a turbine. The diameter of a tailrace can be of various sizes, depending on the nature of the geothermal area, such as in the range of 25-100 cm in diameter, but also from 100-5000 cm.
In the present context the terms “powerhouse”, “power station” and “power plant” refer to a facility for the generation of electric power. Such a facility comprises means for extracting mechanical energy from flowing water, usually a turbine, as well as means for converting mechanical energy into electrical energy, generally a generator. The generator may also be placed in a separate housing (transformer hall).
Generators and turbines are well known in the art will not be their function will not be discussed herein.
Calculations of flow to power plant and production of electricity thereof.
Approximation; it is assumed that there is no pressure difference and that there is no influence from the high pressure hot area (such as in a closed system).
The calculations show that there is a tremendous amount of energy to be recovered from such a system (see
| Number | Date | Country | Kind |
|---|---|---|---|
| 8580 | Dec 2006 | IS | national |
| 8610 | Feb 2007 | IS | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IS07/00023 | 12/17/2007 | WO | 00 | 7/7/2009 |
