SYSTEM FOR PROVIDING ENERGY FROM A GEOTHERMAL SOURCE

SYSTEM FOR PROVIDING ENERGY FROM A GEOTHERMAL SOURCE Technical field

The present specification generally relates to the field of providing energy and particularly discloses a system for providing energy from a geothermal source.

Technical background

Generally, energy can be provided in a numerous of different way, several of them coupled with different problems. Many fuels, such as fossil fuels, are a limited resource, for example oil may be depleted in 20 years, coal in 100 years and uranium in 50 years, and they furthermore pollute the environment. Generating energy from wind, water and sun depend directly on surrounding condition, and are therefore not always suitable. In order to cater for future demands on energy all renewable sources of energy have to be utilized.

Geothermal energy sources tend to offer a robust and environmentally friendly way of providing energy. The basis behind geothermal energy is to collect energy from a liquid that has been heated deep below ground. Existing methods however focuses on high temperature applications. Thus they depend heavily on that surrounding conditions provides a high enough temperature and are mainly suited for usage in regions of high geological activity, such as areas with volcanic activity, areas with faults or where continental plates meet, such as Iceland, Italy, Mexico, Indonesia, California etc. Where a low temperature has been utilized there have been problems with low efficiency.

However, even in favorable locations the concept of extracting geothermal energy is associated with problems. Several additional conditions have to be fulfilled for a successful establishment. For example, the bedrock between the boreholes needs to be permeable for water in order to have a flow of liquid to be heated and the extracted liquid has to be hot enough in order to have an efficient process. Thus, the inventors of the present invention have identified a need for improvements in providing energy from a geothermal source that is designed to overcome the problems stated above, and which provides for system suited for usage in a wider span of regions while still offering in an efficient energy extraction.

An object of the present invention is to provide a system for providing energy from a geothermal source which overcomes the problems stated above.

A further object of the present invention is to provide a system with benefits relating to cost, time for production, flexibility and/or scalability.

Summary of the invention

The above-mentioned requirements are achieved by the present invention according to the independent claims. Preferred embodiments are set forth in the dependent claims.

The invention is based on the insight that a robust turbine allows a more efficient extraction of energy from a geothermal source with less dependence on the geographical conditions. By utilizing a more robust turbine a Rankine cycle may be utilized at a lower temperature, thus the requirements on the temperature extracted from a borehole is decreased. By these decreased requirements a geothermal energy extraction system may be utilized in a wider span of locations. For example, one aspect of the invention relates to a system for providing energy from a geothermal source. The system comprises at least one borehole, at least one heat converting unit and at least one power generating unit. The borehole is adapted for extraction of a geothermally heated liquid. The at least one heat converting unit is adapted to convert heat from the geothermally heated liquid. The at least one power generating unit is adapted to generate energy from the heat and the power generating unit is arranged in connection with the heat converting unit. Furthermore, the temperature of the liquid is below 200°C. A low temperature of the extracted liquid, is

advantageous in that the system may be utilized in a wider span of locations or conditions. The wider span of conditions may for an example be of geological, geographical, safety or economical character. For an example, such systems may be established in locations such as Scandinavia where traditional systems encounter problems.

In one embodiment, the heat converting unit comprises at least one heat exchange unit, at least one expander unit and at least one condenser unit. The heat exchange unit is adapted to cause a refrigerant to collect heat from the liquid, and the expander unit is adapted to convert the heat collected in the refrigerant, the condenser unit is adapted to condense the refrigerant expanded by the expander unit. Furthermore, the power generating unit is arranged in connection with the expander unit. In one embodiment, the expander unit converts the heat collected in the refrigerant by expanding the refrigerant. Aspects of a general expander and the function of a rankine cycle are known and will be described in general terms. When hot water reach the ground surface it is heat exchanged against a refrigerant with a lower boiling point, by the heat transferred from the hot water the refrigerant is turned in to steam. The steam powers a turbine that generates energy. The hot water may be utilized in a cascaded system that gradually extracts energy from the water, in such a system the different parts may be optimized for different temperatures and suitable applications. Such suitable applications may be different rankine cycles, long distance heating, long distance cooling through an absorption heat pump, thermal baths, greenhouses etc. In one embodiment, the at least one borehole is interconnected with a subterranean channel system. The subterranean channel system may for example be bedrock permeable to liquids, natural cracks in the bedrock, porous bedrock or manmade channels. By using a channel system an enlarged subterranean volume may be used for extracting energy.

In one embodiment, the subterranean channel system is a continuous subterranean channel system. The continuous subterranean channel system extends between boreholes or any other source or extraction point for the liquid. This design allows for a complete subterranean coupled and closed channel system that may be filled with water to be heated and circulated.

The term "continuous" in this case means a free connection between two boreholes, a free passage in the bedrock or any other passage having other passages than dead ends.

In one embodiment, the subterranean channel system is made with 3D drilling technology. By utilizing 3D drilling technology the channel system may be optimized for different demands, such as interconnecting different natural system, creating new ones where the bedrock is too solid for traditional systems and reaching volumes not available by traditional drilling. Utilizing a channel system as an extended subterranean heat exchanger allows usage of less deep bore holes, thus a simplified establishment. A further advantage by this design is that unwanted flow between the boreholes are reduced, thus lessening the demands on counter measures such as steel liners. This design will decrease a problem of low flow levels that arise in too deep bore holes.

The term "3D drilling technology" in this case means drilling technology which enables drilling non-straight bore-holes. For an example non-straight bore- holes may be used to extend a bore-hole to a location remote from the location of the surface entrance. Usage of multiple non-straight bore-holes may for an example be used to increase an area in which thermal energy is collected. Further, in one more embodiment, the subterranean channel system made with 3D drilling technology may have a higher complexity below ground. For an example one or more bore-holes may have at least one intermediate point where the bore-hole diverges into several different bore-holes or directions. The diverging bore-holes may extend to a system of tunnels which may be intersecting or non-intersecting. The system may be oriented in different orientations, for an example both vertical and horizontal. This design and variations thereof will at least increase the thermal energy that is possible to extract from one or more bore-holes. By this the impact on the surface can be kept low. A smaller amount of surface equipment and associated surface structures may also be utilized.

Further, in one more embodiment, the subterranean channel system made with 3D drilling technology may be made in a crystalline and/or dense bedrock, for an example such as granite. Since such bedrock has a low liquid permeability, this design allows for bore holes with less demand on lining.

Hence, a dense bedrock is not only utilizable, but may be preferable.

Previous technology mainly depends on a permeable bedrock in order to achieve a flow of heated water.

By utilizing information relating to the composition of the bedrock the subterranean channel system may be optimized, for an example the channels may be directed through volumes of dense rock if bore-hole lining should be kept at a minimum. In a similar way, the channel system may be directed through volumes of permeable bedrock if a flow of water between the boreholes should be utilized.

The term "3D drilling technology" is not limited to complex shapes, but may also be utilized to make straight vertical bore-holes and straight bore-holes which which deviate from vertical boreholes. In one embodiment, the expander unit comprises a turbine adapted to operate in wet steam. By enabling operation in wet steam, no separation of wet and dry steam is needed. Further, a process allowing wet steam is more robust and may be utilized in an enlarged span of temperature at a higher efficiency. Enabling the use of wet steam do not necessarily result in any restrictions in the use of dry stream. In conventional systems for geothermal energy sources there is a need to separate steam and water before the turbine, turbine technology allowing the use of wet steam will decrease the complexity of the process and increase the efficiency.

In one embodiment, the expander unit comprises a turbine where the thickness of the blades is increased from a standard turbine and where the edges of the blades are rounded. The turbine is then preferably a screw turbine or any other turbine fulfilling the specification. This design will result in a more robust turbine that is operational in a wider variety of situations. For an example, the screw turbine may be used to generate electricity at temperatures as low as 50°C.

In one embodiment, the power generating unit is adapted to generate electricity. This may for example be realized by coupling a generator to the turbine.

In one embodiment, the power generating unit is adapted to generate longdistance heating. This may for an example be realized by any one or more from the group including coupling a generator and a heat generating element to the turbine, by utilizing the energy from the condenser and by utilizing any other source of waste heat in the system.

The term "long-distance heating" in this case means a system for distributing heat generated in a centralized location. By utilizing long distance heating the generated heat can be distributed in an efficient way. Further, any waste heat can also be transferred trough the distributing system as it is not limited to generated heat. The term "long-distance cooling" may be defined in a similar way as longdistance heating, but for distributing lack of heat, or cooling, from a

centralized location.

In one embodiment, the system further comprises a refrigerant pump that is adapted to circulate the refrigerant. This design may increase the flow of refrigerant in the heat exchange unit, which results in a more efficient system. A refrigerant pump may also be utilized for additional control over the system.

In one embodiment, the refrigerant is an organic refrigerant. The organic refrigerant is then preferably chosen from the refrigerants properties, such as isentropic saturation vapor curve, freezing point, stability temperature, temperature of vaporization, density, environmental impact, safety and acceptance of different pressures. For an example, an organic refrigerant may be n-pentane or toluene.

In one embodiment, the temperature of the liquid extracted from the borehole is below 150°C, preferably in the span of between 40°C and 140 °C or more preferably in the span of between 50°C and 130 °C. By enabling utilization of an even lower temperature the present system may be used in a wider span of conditions. The wider span of conditions may for an example be of geological, geographical, safety or economical character. In one embodiment, a liquid extracted from the borehole at a temperature below 150°C, preferably in the span of between 40°C and 140 °C or more preferably in the span of between 50°C and 130 °C may be combined with utilization of an organic refrigerant. This design will result in a possibility to output electricity from the system, regardless of the low temperature that may be used. This possibility is in no way limiting to the ability to generate electricity from higher temperatures. For an example, utilizing a lower temperature may allow the usage of more shallow boreholes. In one embodiment, several heat converting units may be utilized, for an example serially attached to a geothermal source, where a heat converting unit adapted to be used at a lower temperature may be attached to use waste energy from a heat converting unit adapted to be used at a higher

temperature. This design provides a solution that may utilize a higher degree of the energy extracted from the geothermal source.

In one embodiment, the liquid extracted from the borehole is adapted to be re-injected into said subterranean channel system. By re-injecting the liquid the life span of the source is prolonged. Re-injecting the liquid also aids in preventing that subsoil water is depleted, and that minerals and other chemicals extracted during the process affects the environment and ground subsidence. A re-injecting system may even allow a completely sealed system, thus minimizing any emissions and decreasing the environmental impact. The re-injection may utilize at least one second borehole.

In a further aspect, the invention relates to a method for providing energy from a geothermal source. The method comprises extracting a geothermally heated liquid from at least one borehole, converting heat from said liquid in at least one heat converting unit, generating energy from said heat in at least one power generating unit, and wherein the temperature of said liquid is below 200°C.

In an embodiment according to the present invention, a geothermal system may be utilized in areas with low geothermal activity where previous establishments were hard or impossible due to for an example by a too low temperature of the liquid extracted from the borehole.

In an embodiment, the heat content of the liquid extracted from the borehole may be utilized in steps in a cascade system. The hot liquid may first be routed to high temperature applications then to medium temperature applications followed by low temperature applications. For an example hot water may first be routed to high temperature applications then to municipal and residential buildings for heating/cooling and tap water, there after the water with a lower heat content can be used in thermal baths and then on to greenhouses and further to a fish farm. This design enables an increased heat usage.

In an embodiment, hot liquid may be converted locally or centrally with an adsorption heat pump into cold liquid which can be used for airconditioning, cooling houses and large scale freezers. This design provides a solution that saves the need of expensive and environmentally harmful cooling systems.

Liquid utilized may be reinjected into the ground in a second bore hole thus obtaining a closed system. The reinjected liquid will be reheated again by the hot bedrock. Through for an example cracks in the ground or a channel system, there is a circulation between the two drill holes and the hot liquid can be used from the first drill hole all over again. This design provides an enviromental friendly system with minimal emissions.

In an embodiment, the bore-holes may as a non-limiting example be between 2 and 6 kilometers deep. The depth depend on specific demands and the location, in some cases no more than one kilometer or less may be

necessary, in some cases even more than 6 kilometers may be needed in order to extract sufficiently hot liquid from a borehole.

A system according to any embodiment may utilize scalable units that may be joined into bigger and more complex compound systems. This design will result in a high degree of flexibility, allow for decreased time in production, increase cost efficiency and speed of establishment.

In an embodiment, more than one turbine may be installed serially one after another. Each turbine reduces the pressure and temperature of the steam that is utilized. Utilizing more than one turbine serially in ordinary techniques means that less and less usage can be extracted from the turbines following the first one. A secondary system where a second liquid having a boiling point which is lower than the boiling point of water may be used, this results in a higher pressure of the steam at a given temperature than the usage of water would. The increased steam pressure can be used to increase the electricity generated in a turbine. The secondary system may be driven by heat transferred from the primary system at any point between the serially installed turbines. The secondary system may be also be installed to directly utilize the heat from the bore-hole. Both the primary system and the secondary system may comprise one or more turbine. The one or more turbine within the primary or secondary system may be installed serially. Heat transfer between different systems may for example be performed by transfer of heated liquid or by heat exchanger.

In an embodiment, more than one turbine may be installed in parallel to each other with a common source of steam, the steam may be directed by a plurality of valves so that the operation of the turbines is optimized. The plurality of valves may be controlled by a control unit. This design allows for operation under a wider span of available steam. Further, a system with a plurality of turbines in parallel may be used to have redundancy of operation and allow for maintenance of non-used turbines during operation of the system.

The term "flashing" may be used for operating turbines serially.

The term "binary cycle technology" may be used to describe the interaction of a primary system with a first liquid and a second system with a second liquid.

In an embodiment, a third system with a third liquid may be implemented to utilize the heat after or from the secondary system. Short description of the appended drawings

The invention is described in the following illustrative and non-limiting detailed description of exemplary embodiments, with reference to the appended drawings, wherein: Figure 1 is a schematic illustration of a system according to a first aspect of the present invention. Figure 2 is a schematic illustration of a system according to one embodiment of the invention.

Figure 3 is a schematic illustration of a method according to a second aspect of the present invention.

All figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested. Throughout the figures the same reference signs designate the same, or essentially the same features.

Detailed description of preferred embodiments of the invention

The invention is described in the following illustrative and non-limiting detailed description of exemplary embodiments, with reference to the appended drawings, wherein:

Figure 1 shows a schematic illustration of a system for providing energy from a geothermal source, according to one embodiment of the present invention. The system comprises a borehole 100, a heat converting unit 200 and a power generating unit 300. The borehole is utilized for extraction of a geothermally heated liquid. The heat converting unit is adapted to convert heat from the geothermally heated liquid. The power generating unit is adapted to generate energy 400 from the converted heat, the power generating unit is arranged in connection with the heat converting unit. Figure 2 shows a schematic illustration of a system for providing energy from a geothermal source, according to one embodiment of the present invention. The system comprises a borehole 100, a subterranean channel system 130, a second borehole (150), a heat exchange unit 210, an expander unit 220, a condenser unit 230 and a power generating unit 300. The borehole is utilized for extraction of a geothermally heated liquid from the continuous

subterranean channel system, which is interconnected with the borehole. The heat exchange unit is adapted to cause a refrigerant to collect heat from the liquid, thereafter the liquid is adapted to be re-injected into the subterranean channel system through the second borehole. The expander unit is adapted to convert the heat collected in the refrigerant. The condenser unit is adapted to condense the refrigerant expanded by the expander unit. The power generating unit is adapted to generate electricity 410 and/or long-distance heating (420) from the heat, the power generating unit is arranged in connection with the expander unit.

Figure 3 shows a schematic illustration of a method for providing energy from a geothermal source, according to one embodiment of the present invention. The method comprises the steps of extracting 500 a geothermally heated liquid (X), converting heat 600 from the liquid and generating 700 energy 400 from the heat.

Aspects of a general system for providing energy from a geothermal source are well known in the art and will not be described in greater detail.

While specific embodiments have been described, the skilled person will understand that various modifications and alterations are conceivable within the scope as defined in the appended claims.