1

The present invention relates to a system and a method of extracting geothermal energy from the earth. The present invention further relates to a method for building of a substantially vertical energy stave or drilled tunnel for a system for extracting geothermal energy from the earth.

Background of the invention

Utilization of geothermal energy in depths above 5 km (i.e. deep into the earth's crust) could contribute considerably to resolving the global problems related to a lack of energy and to glasshouse gases from fossil fuels.

US 2010/0224408 Al describes an equipment which makes deep holes in geological formations (rock) by disintegrating the soil into blocks carried to the land surface through the excavated hole filled with liquid, using transport modules yielded up by gas buoyancy interaction in the transport module utilizing super-cavitation. In an opposite direction - by help of negative buoyancy - the necessary energy carriers, materials and components, or entire devices required for rock excavation, are carried to the bottom. The opportunity to transport rock in entire blocks reduces energy consumption considerably, because the rock is disintegrated in the section volumes only. Some of the extracted rock and material carried from the surface is used to make a casing of the hole using a part of the equipment. The equipment also allows the generation of the necessary high pressure of liquid at the bottom of the hole, to increase permeability of adjacent rock. The equipment as a whole allows by its function that there is almost linear dependence between the price and depth (length) of the produced tunnel.

US 3,786,858 relates to hydraulic fracturing which is used to interconnect two or more holes penetrating a previously dry geothermal reservoir, and to produce within the reservoir a sufficiently large heat-transfer surface so that heat can be extracted from the reservoir at a usefully high rate by a fluid entering it through one hole and leaving it through another. Introduction of a fluid into the reservoir to remove heat from it and establishment of natural (unpumped) convective circulation through the reservoir to accomplish continuous heat removal are important and novel features of the method.

Although that throughout the years there has been developed some systems and methods for retrieving geothermal energy from the ground, there is still need for better and more efficient systems and methods for doing so, since many of the previously suggested methods and systems for retrieving geothermal energy from the ground are quite complicated, are not very reliable, and/or have some drawbacks in relation to efficiency, robustness, and/or secure or uninterrupted operation. Some systems cannot manage the heat as some metals soften at temperatures above about 185-200°C.

Summary of the invention

It is an object of the present invention to provide a more compact and reliable system and method for extracting geothermal energy.

Another object of the present invention is to provide a more efficient system and method for extracting geothermal energy.

Yet another object of the present invention is to provide an alternative system and method for extracting geothermal energy.

It is a further object of the present invention to provide a method for building a system for extracting geothermal energy.

Yet another object of the present invention is to provide a system and method for extracting geothermal energy that can endure high temperatures.

This is obtained by the independent claims according to the present invention.

Additional features of the invention are given in the dependent claims.

Short description of the drawings

Figure 1 shows one embodiment of the system for extracting geothermal energy from the earth according to the present invention.

Figure 2 shows cross sections of the drilled tunnel or energy stave according to one embodiment of the system of the present invention.

Figure 3A-3C show different embodiments of the system for extracting geothermal energy from the earth according to the present invention.

Figure 4 shows an alternative embodiment of the system for extracting geothermal energy from the earth according to the present invention.

Figure 5 shows another alternative embodiment of the system for extracting geothermal energy from the earth according to the present invention. Figure 6 shows yet another alternative embodiment of the system for extracting geothermal energy from the earth according to the present invention.

Detailed description of the invention

Figure 1 shows one embodiment of the energy system 1 for extracting geothermal energy from the earth. The energy system 1 according to the present invention comprises a substantially vertical drilled tunnel or hole 10 having a predetermined depth or length L and a predetermined diameter D. The depth or length L of the tunnel or energy stave 10 can be in the range of about 10 to 70 km, starting from the earth or ground surface 3 and stretching down into layers 30 of rock, and more particularly in the range of about 40-45 km. The rock temperature at such depths (about 40-45 km) is about between 1080-1200°C. The diameter D of the tunnel or energy stave 10 can be in the range of about 2-19 m, and particularly about 3-7 m, and even more particularly about 5 m. The wall 11 and bottom 12 of the tunnel or energy stave 10 are thermally and physically isolated 13 from the surrounding rock layers 30 with the help of a tunnel insulation 13 which is adapted to bear or endure high temperatures of up to about 1800°C, and particularly of about 1100-1800°C, and more particularly of about 1100- 1300°C in sections of the energy stave 10 that are closer to the earth surface 3 and possibly of about 1500- 1800°C in sections of the energy stave 10 that are closer to the bottom 12. For that purpose geopolymer composites comprising ceramics and having the necessary material properties, or other materials used in the spaceship or rocket industry, can be used for the insulation plates or sections. The circumference or periphery of the wall insulation 13' is supplied with a number of evenly distributed longitudinal channels 14 placed therein (i.e. in the thickness of the insulation 13). Reference is herein made to the cross section in fig. 2. These channels 14 are adapted for transportation of a fluid 2, e.g. water, but not limited thereto, from the earth or ground surface 3 to the tunnel bottom 12 in order to be heated or "charged" with geothermal energy.

The insulation 13, 13', 13" of the energy stave or tunnel 10 serves to increase the efficiency as it isolates the energy stave or tunnel 10 from the surrounding rock layers 30. In addition the insulation 13, 13', 13" serves to stabilize the rock layers 30 and to counteract the heat in the rock layers 30 around the energy stave or tunnel 10.

The thickness of the insulation 13, 13', 13" can be up to about 1,5 m, alternatively up to about 1 m, and the channels 14 therein can be up to about 3" (3 inches), alternatively up to about 2" (2 inches), and more particularly up to about 1" (1 inch). A bottom portion of the tunnel or energy stave 10 has a predetermined height H and is adapted to be able to serve as a boiler arrangement 4 for the fluid 2. The predetermined height H is in the range of about 10000-30000 m, and particularly in the range of about 15000-30000 m, and even more particularly in the range of about 20000-30000 m. The bottom portion or boiler arrangement 4 is closed at its top side 15 in such a way that the heated fluid or steam 2 is to be returned to the ground surface 3 through a return pipe 20 arranged in the tunnel 10. Preferably the return pipe is arranged in the proximity of the center of the tunnel 10. The return pipe 20 has an inner diameter dl and an outer diameter d2. The return pipe 20 can be from about 6" (6 inches) to about 12" (12 inches) pipe, preferably an 8" pipe, and can be made of hard metal, e.g. steel, or metal sections welded together. Special enforced composite materials withstanding high temperatures can also be used for the return pipe.

In fig. 3A a schematic alternative embodiment of the invention is shown, wherein the diameter Dl of the boiler arrangement 4 can be bigger than the diameter D of the tunnel or energy stave 10 (i.e. Dl > D) in order to increase the contact area with the rock layer(s). By making Dl > D, it is also possible to decrease the height H of the bottom portion or boiler arrangement 4. Alternatively the boiler arrangement 4 can have a conical form or shape getting from D to Dl (fig. 3B), or a combination of the previous two embodiments (fig. 3C).

In fig. 4 yet another schematic alternative embodiment of the invention is shown, wherein the boiler arrangement 4 can be drilled with an inclination having a certain angle Alpha (a) from about 0 to about 90 degrees. When the inclination angle a is about 0 degrees then the longitudinal axis of the tunnel or energy stave 10 is substantially concurrent or falling together with the longitudinal axis of the boiler arrangement 4. When the inclination angle a is about 90 degrees then the longitudinal axis of the tunnel or energy stave 10 is substantially perpendicular to the longitudinal axis of the boiler arrangement 4.

Having in mind how much strain the rock layer(s) can take, the fluid circulation volume and the contact area can be calculated as well as some other parameters, e.g. D and/or Dl, H, temperature, etc.

The packer arrangement closing the top side 15 of the boiler arrangement 4, can be shaped in such a manner that the top side 15 of the boiler arrangement 4 can have a funnel-form going or narrowing towards the return pipe 20 which can be arranged in the proximity of the tunnel's center. The packer arrangement 15 can be firmly fixed to the wall insulation 13 and possibly even deep into the rock layer. The number of circumferential longitudinal channels 14 distributed within the tunnel insulation 13 are running out in the boiler arrangement 4 through outlets or holes (see the cross section in fig. 2) that are arranged on the wall insulation 13' in the proximity of the boiler arrangement's 4 bottom 12, or alternatively the outlets can be spread or arranged in a certain manner over the circle area of the bottom insulation 13", or alternatively a combination of the two previous alternatives. The outlets for the channels arranged on the wall insulation 13' can be placed in a predetermined manner and at only one

(vertical) level in the wall, or alternatively on at least two levels.

A suitable energy conversion means 5 is arranged in fluid connection with the longitudinal channels 14 and the return pipe 20 and is further placed or arranged on or in the proximity of the earth or ground surface 3, wherein the geothermal energy is being extracted from the heated fluid or steam 2. In this embodiment of the invention the suitable energy conversion means 5 is a turbine, e.g. a steam turbine, and can comprise a generator for producing electricity (e.g. from 40 MW to 2 GW power plant). For capacities higher than 40-50 MW or 1 GW, the dimensions of the energy stave design should be recalculated. The higher the temperature, the higher the contribution or gross margin ratio of the project.

Cooling means (not shown) can be arranged for the turbine or the energy conversion means 5.

In a first embodiment of the invention the suitable energy conversion means 5 can be placed or arranged or built on of the earth or ground surface 3. Additionally, the energy conversion means 5 or the entire power plant can be placed or arranged or built directly above the tunnel 10, so that it will completely cover the tunnel 10.

In a second embodiment of the invention, shown also in fig. 4, the suitable energy conversion means 5 or the entire power plant can be placed or arranged or built in the proximity of the earth or ground surface 3, and particularly slightly below the surface 3, so that only transformation means (transformer) 55 and/or at least one power supply cable 56 can be arranged on the earth or ground surface 3.

As it can be seen in fig. 1, the area created between the outer diameter d2 of the return pipe 20, the inner diameter of the wall insulation and the top closed side of the boiler arrangement 4, is filled with a fluid, e.g. and preferably, but not limited, water 21.

The return pipe 20 can be arranged to have its longitudinal axis falling within or in the proximity of the longitudinal axis of the drilled tunnel or energy stave 10. In addition the return pipe 20 can be arranged to be held in a fixed position in relation to the tunnel wall 11 at predetermined length intervals. This can be done with the help of holding means, e.g. but not limited to stand-off pieces or spacers. This also stabilizes the return pipe 20. The holding means can be firmly fixed to the wall insulation and possibly even deep into the into the rock layer.

As mentioned above, the heated fluid or steam 2 comes up to the ground surface 3 from/through the return pipe 20 and is carrying the geothermal energy that is to be supplied to the suitable energy conversion means 5, in this case the turbine with the generator (e.g. 40-50 MW or even 1 GW), where the used fluid 2 therein is then fed or delivered back into the number of circumferential longitudinal channels 14 distributed within the tunnel insulation 13 in order to be recirculated.

Although that natural convective circulation of the fluid 2 is established (e.g. about 500- 1500 l/s, and more particularly about 800 l/s), pumping means can be supplied in a further embodiment of the invention in order to help with or ease the fluid 2 circulation.

In order to ease the building of the tunnel or energy stave 10, the tunnel insulation 13, and more particularly the wall insulation 13', can be made of insulation sections that are firmly fixed together, e.g. glued or welded or cemented or casted together, and in such a way that these joints or connections or seams will be able to bear the high temperatures mentioned above. Alternatively, the insulation can be casted or build during the drilling process.

All channels 14 in the insulation 13, 13', 13" are arranged in a controlled channel system. The fluid circulation in all channels 14 therein and/or the return pipe 20 can be completely or fully controlled by a circulation controlling means 50. The circulation controlling means 50 can be arranged as a part or element of said suitable energy conversion means 5.

Sometimes, some of the channels 14 can be closed for circulation, which is something that can depend on different circumstances and/or needs.

In an alternative embodiment, shown schematically in fig. 5, a certain number of the channels can be dedicated for the transportation of the fluid from the earth surface 3 to the tunnel bottom 12 and the rest of the channels 14 can be dedicated for the heated fluid transportation from the proximity of the tunnel bottom 12 to the ground surface 3, omitting thus the need for a return pipe. In this case the outlets of a predetermined number of channels 14 dedicated for the heated fluid transportation from the proximity of the tunnel bottom 12 to the ground surface 3 should be arranged at at least one level in tunnel wall(s) of the boiler arrangement 4 and in close proximity to the closing packer arrangement 15.

In another alternative solution, shown schematically in fig. 6, the return pipe 20 can be used in combination with the predetermined number of channels 14 dedicated for the heated fluid transportation from the proximity of the tunnel bottom 12 to the ground surface 3.

The invention concerns also a method for extracting geothermal energy from the earth, comprising the following steps:

transportation of a fluid 2, e.g. water, from the earth or ground surface 3 to a tunnel bottom 12 through a number of circumferential longitudinal channels 14 evenly distributed within a thermal and physical insulation 13 of substantially vertical drilled tunnel 10, all the channels 14 therein having controlled fluid circulation and a certain number or all of them being adapted for transportation of the fluid 2 from the earth or ground surface 3 to the tunnel bottom 12 to be heated and voluntarily a predetermined number of them being adapted for heated fluid transportation from the proximity of the tunnel bottom 12 to the earth or ground surface 3;

distributing the fluid 2 into a bottom portion of the drilled tunnel 10, having a predetermined height H and serving as a boiler arrangement 4 for heating the fluid 2, through outlets arranged at the proximity of or on the boiler arrangement's 4 bottom 12; returning the heated fluid 2 to the ground surface 3 through a return pipe 20 starting from a closed top side 15 of the boiler arrangement 4 and/or through the predetermined number of dedicated longitudinal channels 14 of the controlled channel system in the tunnel insulation 13; and

extracting the geothermal energy from the fluid by a suitable energy conversion means 5 in fluid connection with the longitudinal channels 14 and possibly the return pipe 20 and arranged on or in the proximity of the earth or ground surface 3.

The fluid 2, e.g. water, can be recirculated. Pumping means can be used in order to help with or ease the circulation itself.

And finally, the invention is aimed to also provide a method for building of an energy stave or drilled tunnel 10 for the above mentioned system 1 for extracting geothermal energy from the earth, comprising the following steps:

a) drilling a first section of the energy stave or tunnel 10 with the help of a drilling or boring means or tunnel boring machine (TBM);

b) arranging a first tunnel insulation 13' section onto the tunnel wall 11 with the help of an assembling means that for example can be mounted on the drilling means;

c) drilling a second or following section of the energy stave or tunnel 10 with the help of the drilling means;

d) arranging a second or subsequent tunnel insulation 13' section onto the tunnel wall 11 with the help of an assembling means that for example can be mounted on the drilling means;

e) firmly fixing together, e.g. by gluing or welding or cementing or casting together, the first and second / subsequent tunnel insulation 13' sections;

f) repeating step a)-e) until the whole length or depth L of the drilled energy stave or tunnel 10 is completely drilled.

Under the drilling operation the drilling machine or means can be working in water that can be used as a coolant for the process. Cold water can also be used to break the rock layers under drilling. Alternatively, electricity can be used to break the rock layers. Other suitable drilling methods should not be excluded. The drilling machine or means can be milling the rocks and all mixed with water can be pumped up to the ground surface.

According to this building method, the return pipe 20 sections can be placed, assembled and/or welded while the drilled energy stave or tunnel 10 is being drilled, or alternatively after completion of the tunnel drilling operation and then the return pipe can be built downwards up.

After the completion of the tunnel drilling operation the bottom insulation 13" can be arranged on the tunnel bottom 12, and further fixed, e.g. glued or welded or cemented or casted, to the end or final tunnel insulation 13' section on the tunnel wall 11.

The closing packer arrangement 15 is assembled at a boiler top depth (which is equal to/= L-H) for the top side 15 of the boiler arrangement 4, thus closing the top side of boiler arrangement 4 in such a way that the return pipe 20 is the only opening thereof.

In addition each wall insulation 13' section can be made of at least two circumferential parts or elements that are firmly fixed together, e.g. glued or welded or cemented or casted together, prior to or alternatively during installation, and having a number of circumferential longitudinal channels 14 evenly distributed therein.

It should be noted that the wall insulation 13' sections or parts with the number of circumferential longitudinal channels 14 evenly distributed therein, should be fixed, e.g. glued or welded or cemented or casted, to a subsequent wall insulation 13' section or part in such a way that a continuation of the circumferential longitudinal channels 14 is created from the top surface 3 and down to the end or final tunnel insulation 13' section on the tunnel wall 11. As mentioned above holding means, such as but not limited to stand-off pieces or spacers, can be arranged at predetermined length intervals. Furthermore, this operation can be done during or alternatively after completion of the tunnel drilling operation.

The energy stave system according the invention can be built within approximately 18-24 months, wherein the drilling speed can be approximately 20-40 meters per day depending on the drilling conditions.

It should be noted that alternative embodiments, not mention herein but falling within the range of the patent claims, are also to be considered as part of the present invention.