JPH0733819B2 - How to extract and use geothermal energy - Google Patents

Description

The present invention relates to a method for extracting and utilizing thermal energy existing inside the earth and a geothermal plant for implementing the method.

It is well known to extract and utilize geothermal heat in existing heat plants and heat pumps. Existing geothermal plants generate heat from deep inside the earth in the form of hot water or steam flowing through geological bedrock containing geothermal heat (ie, natural hot water or steam present in the ground). Extracting. This can result in very toxic condensate water that sometimes causes serious environmental problems.

In heat pumps, on the other hand, it has been established as a practice to use heat exchangers with a fairly large surface area at relatively shallow depths, which makes sense even when the temperature gradient is relatively small. High thermal efficiency can be obtained. However, known heat pump devices have structural limitations that result in a relatively small contact surface area between the heat transfer medium and the interior of the Earth, which limits the efficiency of the heat pump device. .

An object of the present invention is to extract and utilize geothermal energy,
It is to provide an improved method.

Another object of the present invention is to provide a method of extracting and utilizing geothermal energy which is considerably more efficient than currently known methods.

Another object of the present invention is to provide a geothermal plant capable of implementing the above method.

According to the present invention, in a method for extracting heat energy from the inside of the earth for use on the ground, (a) a step of forming a vertical shaft in the ground downward, and (b) a crushing means in the vertical shaft A step of forming an intrusion passage outward from the shaft in addition to the existing intrusion passage by crushing surrounding rocks, and (c) rinsing the existing intrusion passage and the intrusion passage formed by the crushing by a pressurized fluid means. And (d) a step of re-digging the vertical shaft and crushing rock around the vertical shaft by a crushing means in the vertical shaft to form an additional intrusion path, and (e) an existing intrusion path and newly formed (F) pushing the substance in the form of a slurry of carrier liquid, binder, and granular material having high thermal conductivity into the invasion passage, and (g) in the intrusion passage. Hardening the slurry; and (h) inserting a casing into the shaft and fixing the casing to the slurry in the intrusion passage and surrounding rocks with a grout containing a granular material having high thermal conductivity. (I) expanding the bottom area of the shaft by reamer excavation in the blast; (j) inserting an inner pipe into the casing to a depth near the bottom area; (k) the bottom area of the shaft. To lower the heat transfer medium through one passage inside at least one of the casing and the inner pipe so as to convey the heat to the ground, and the other inside the at least one of the casing and the inner pipe. And a step of raising through the passage.

To obtain the desired results, the shaft will be excavated underground to a depth of more than 1,500 m. Preferably at least
It is recommended to excavate underground to a depth of 5,000m or more. In the bottom area of the shaft, intrusion passages that extend outward from the shaft into the bedrock are formed, and these intrusion passages are large.
It has the shape of a small crack or crevice.

The most part of the invasion passage is filled with a heat conductive substance. As a result, compared to a vertical shaft with a cylindrical peripheral surface,
The contact area in the bottom area of the shaft is significantly increased, and thus a large amount of heat can be extracted from the surrounding rock mass.
The hardened thermally conductive material (actually, the hardened thermally conductive material constitutes cracked rock plugs or plugs) is a good thermal conductor and is concentrated from surrounding rock Since it absorbs heat, a large amount of heat can be made to flow.

Deep shaft (preferably over 1,500 m depth, eg 5,00 m
For drilling (depths of 0 to 10,000 m), known drilling techniques used for extracting oil from deep oil wells and other purposes are used. Next, the rocks are crushed by explosion (blasting), high-pressure liquid, gas, or spraying of grout (mixed liquid of cement, sand, water, etc.), etc., and penetrate into the bottom area of the shaft over a range of 1,500 to 2,000 m. Forming a passage. These entry channels or fissures and fissures are formed in addition to the naturally occurring fissures and fissures.

The rock mass around the shaft is blast fractured and then washed away to form a long bottom region surrounded by an intrusion passage formed by any of the above methods. This work is performed upward from the bottom of the shaft, and the shaft is redrilled every time this work is performed once.

Next, the entry passage is filled with a thermally conductive material. The thermally conductive material may be water or cement based, to which one or more of silica gel, finely ground metal powder (preferably silver and / or copper and / or aluminum powder) is provided. Added. This thermally conductive substance is in the form of a fluid and is used for pressure filling (grouting). After being injected into the intrusion passage, it is left to solidify.

Next, a casing having a closed bottom is inserted into the shaft and thermally joined to the heat conductive material. In particular, the bottom area of the shaft is expanded by blasting or reamer drilling to a larger diameter than the casing, thereby forming a substantially cylindrical underground chamber. The casing is then placed against the surrounding rock mass (the invasion passage of which is filled with a heat-conducting substance) and a contact matrix (cement containing a mixture of strong heat-conducting substances of metal and / or silicate). Is preferred), and then grout. This causes the casing to form the outer surface of the heat exchanger.

Into this casing or supply pipe is inserted a return pipe for the heat transfer medium, which is in the form of an inner pipe. Unlike the supply pipe, the bottom of this return pipe is open.

The heat transfer medium is caused to flow downward between the inner wall surface of the supply pipe (casing) and the outer wall surface of the return pipe, and the heat transfer medium and rock mass in the bottom region of the shaft (as described above for this rock mass,
The heat is absorbed by the temperature difference between the heat treatment and the heat treatment). At least the top of the return tube is insulated to minimize heat loss while the heat transfer medium rises through the return tube. For this purpose of insulation, at least one of special iron, asbestos cement or synthetic resin is used.

For convenience, water can be used as the heat transfer medium.
Corrosion resistant formulations may be added to the water if desired. The absorbed heat is transferred to the ground surface as steam or hot water,
Used in one of several well known methods. When the steam has condensed, the water is again introduced into the closed circuit and returned to the shaft.

The flow rate of the heat transfer medium can be large because a given amount of heat per unit time flows through the geothermal plant, which is determined by the heat exchange surface area, the temperature gradient in the bottom area of the shaft and the temperature of the heat transfer medium in the bottom area. The more
The temperature of the heat transfer medium rising in the return pipe will be lower. However, in many cases it is desirable to perform heat recovery at the highest temperature possible. To this end, the invention allows the heat transfer medium to be alternately supplied and withdrawn to at least two separate shafts of the type described above. Therefore, a pulsating flow can be generated in the heat transfer medium. In this case, the heat transfer medium circulates in the closed circuit of one shaft, during which it is temporarily not used for heat extraction. The temperature of the heat transfer medium thus rises to the level required to effect a favorable heat extraction. During this time, thermal energy is extracted from the heat transfer medium circulating in another vertical shaft. The pressure of the heat transfer medium circulating in the dormant shaft is preferably used to determine when heat extraction operation should be performed by the heat transfer medium.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in Fig. 1a, a deep shaft (borehole) 3 is formed in the bedrock 1 to a depth considerably deeper than 1,500 m (preferably 5,
It has been excavated. Next, as shown in FIG. 1b, an intrusion passage 7 is provided in the rock around the bottom area 5 of the shaft 3. The entry path 7 to the bedrock is composed of cracks, fissures, capillary cracks, etc. These cracks cause an explosion (blasting) in the bottom region 5 or the bedrock by fluid pressure. It is preferably formed by crushing.

The explosion can be performed by slow-delayed explosion such as the blister method, and it is desirable to wash with a chemical (especially acid) after the explosion.

By carrying out such an explosion, the bottom area 5 of the bedrock is relaxed, and desired cracks and crevices are formed. Generally, this relaxation starts from the bottom of the shaft 3 and gradually rises from the lower end of the shaft to a height of 1,000 m, for example. The rock fragments accumulated in the shaft after the explosion are flushed out from the top by a pressure medium (preferably water), or the bottom area 5 of the shaft 3 is repeatedly re-excavated, as schematically shown in Figure 1b. . When excavating such a deep shaft, it is necessary to use a known technique for excavating a deep oil well, for example.

As shown in FIG. 1c, when the substantially cylindrical bottom region 5 reaches the required height h, the
As shown schematically in the figure, a substance S having a high thermal conductivity is injected. This substance S flows into the open invasion passage 7 and fills most of the invasion passage 7. The substance S hardens to form a heat conduction connection from the sponge-like heat exchange area AF to the axial direction of the bottom area 5. At the same time, the inner wall of the bottom region 5 is coated with the thermally conductive material S, as shown in FIG. The thermally conductive substance S is injected as a fluid, in which case it is preferable to use water as the carrier. The heat conductive material S is introduced from the upper part of the vertical shaft into the intrusion passage 7, that is, the crevice or the hole. The heat conductive material S is preferably composed of silica gel and finely pulverized metal powder made of silver and / or aluminum and / or copper.

After evaporating or allowing the carrier fluid to evaporate or soak, into the connecting or ingress passage 7 and into the gap between the bottom region 5 of the shaft 3 and the outer surface of the tube of the casing 9 (Fig. 3), The substantially solid heat conductive material S remains and diffuses in the bedrock 1 in the form of a sponge. In this way, the shaft 3
The contact surface, that is, the heat exchange area AF between the base rock 1 surrounding the shaft 3 and the shaft 3 is expanded, and the speed of extracting heat can be significantly increased.

As shown in FIG. 3, the first closed-end casing 9 is inserted into the shaft 3 which has already been treated with the heat conductive material S as described above. The lower end of the casing 9 needs to be made of a highly heat-conductive material such as metal.

By introducing a suitable compound (compound) M, the outer surface of the casing 9 in the bottom region 5 comes into thermal contact with the thermally conductive material S and the rock mass in the bottom region 5. Formulation M should consist primarily of cement and / or silica in which metal powders, metal fibers, etc. are dispersed. This formulation M, as shown schematically in FIG.
It is injected under pressure along the outer surface of the casing 9.

FIG. 4 shows the completed state of the shaft constructed according to the requirements of the present invention. After the casing 9 has been thermally joined to the rock surrounding it by means of a heat-conducting substance, ie the compound M, a return pipe 11 with an open end is inserted. This return pipe 11 is particularly insulated in its upper region (the part below the ground surface). This is to minimize the heat exchange that occurs between the heat transfer medium W flowing down in the annular space between the casing 9 and the return pipe 11 and this heat transfer medium W rising in the return pipe 11. . For this purpose, the return pipe 11 is either made of special steel, asbestos cement and / or synthetic resin, or is insulated with asbestos cement or synthetic resin.

The heat transfer medium W is pressure-fed between the inner wall of the casing 9 and the outer surface of the return pipe 11, and ascends in the return pipe 11 again as shown in the figure, so that the heat transfer medium W has a function of carrying heat from the inside of the earth to the ground surface. Eggplant

Due to the enlarged contact surface due to the outwardly extending ingress passage 7, a considerable amount of heat is supplied to the heat transfer medium W from the natural rock mass, the heat conductive substance S and the heat conductive compound M. .

Recirculation of the heat transfer medium and extraction of heat at the surface of the earth are carried out using methods well known, for example, in district heating of steam power plants. Vertical shaft 3 as heat transfer medium
Water or other low boiling liquid is used which evaporates in the bottom region 5 of the water, condenses after extracting the available heat and then flows through the shaft 3 into the closed circuit.

For the above device, the shaft 3 prepared and equipped according to the invention forms a "geothermal furnace" with high efficiency. This geothermal furnace has a very large contact surface compared to the cylindrical surface of the shaft casing 9 itself, so that a considerable amount of heat can be extracted from the earth per unit of time, and therefore from the bedrock 1. A large amount of heat can flow into the heat transfer medium and be carried out to the ground surface.

FIG. 5 shows a layout of a geothermal power plant constructed according to the present invention. This geothermal power generation plant is equipped with, for example, three geothermal utilization vertical shafts 13a to 13c, and each vertical shaft is preferably configured like the vertical shaft shown in FIGS. These shafts 13a-13c can be fluidly interconnected or configured to operate separately.

In the case where a natural karst-like continuous crossing channel is formed in rock between adjacent shafts close to each other, a heat transfer liquid is introduced from one shaft to circulate the circulating flow between the shafts. And the heated liquid or vapor can be removed from the adjacent shaft. With such a configuration, the amount of heat extracted from the earth is increased as compared with the embodiment forming the first problem of the present invention (that is, the embodiment configured to recover heat separately from each shaft). Can be increased. By conducting a geothermal survey in advance, a rock mass with a high thermal conductivity, such as a granite, and / or a depth where heat can be used, where a karst-like geological structure can be expected. It is advisable to install a vertical shaft here.

In a preferred embodiment of the invention, the heat transfer medium return pipes 15a-15c are linked to heat utilization units (heat extraction units) 19a, 19b via control valves 17a-17c, or the heat transfer medium is pitted. Supply pipe 21a for returning directly to 13a to 13c
It is connected to ~ 21c in a closed circuit. The control valves 17a-17c are connected to the control unit 23 so that some of the shafts can be operated in a closed circuit without looping to the heat extraction units 19a, 19b.

In this case, the temperature of the heat transfer medium is
1b) asymptotically rises to a high level equal to the bedrock temperature, while the other shafts (shafts where the heat transfer medium has already reached the required temperature available) have control unit 23 and control valves 17a-17c. Is switched to the heat extraction unit 19a, 19b. The control unit 23 can perform temperature control and / or pressure control. The temperature and / or pressure are detected in the pipes leading the heated liquid from the respective shafts and the connection to the extraction units 19a, 19b takes place when the pressure and / or temperature reaches a predetermined level.

The degree of improvement when the thermal conductivity of rock is increased by injecting metal into the natural opening exposed in the shaft or the opening formed by blasting the rock is roughly based on the type of rock. It can be roughly calculated and the natural thermal conductivity is improved by about 2 to 10 times in the case of basalt and about 2 to 6 times in the case of granite.

The smaller numerical value corresponds to the case where aluminum is used as the implantation metal, and the larger numerical value corresponds to the case where copper or silver is used. You can get these or higher magnifications near the shaft walls,
Depending on the condition of the bedrock, the magnification decreases significantly as it moves away from the shaft.

The results of these calculations will also differ depending on the volume that can be filled with metal (grouting) in the fractures in the rock around the shaft. By proper selection of the strength and time of the explosion in the shaft, every effort can be made to create a high proportion of ingress passages 7 and to make these intrusion passages 7 widespread within the continuous network. . If possible from a rock type and environmental point of view, pouring in an acid or other chemical solvent can extend or smooth the surface of leaching or cracks in the rock.

Natural hot water (hot springs) and underground steam sources (eg intermittent springs)
As is commonly done in existing geothermal plants utilizing the heat transfer pipe, separators 22a to 22c for separating hot water and steam may be provided at the front stage of the heat extraction unit. is necessary. Is hot water carried directly out for industrial, building heating, agricultural or other uses,
Alternatively, it is returned to the shaft again. The steam removed in the separators 22a to 22c is guided to a pressure equalizing / storage tank (boiler) and used for power generation and / or various industrial applications.

By the above method utilizing the thermal energy inside the earth and the geothermal power palant based on the method, it is possible to generate energy with high efficiency without causing serious environmental damage. Geothermal power plants built on this principle are as harmless as existing hydro or thermal power plants and, from a biological point of view, are much more harmful than these hydro or thermal power plants. Be beneficial.

[Brief description of drawings]

FIGS. 1a-1c schematically show the three stages of excavating a shaft in the interior of the earth and forming an ingress passage outward from the bottom region of the shaft according to the invention. FIG. 2 is an enlarged schematic view showing a state where an intrusion passage of a vertical shaft is filled with a suitable heat conductive material according to the present invention. FIG. 3 is a schematic view showing a state in which a closed end casing is inserted into a shaft according to the present invention. FIG. 4 is a schematic view showing a state in which the shaft processing is completed by the method of FIGS. 1 to 3 and a state in which a return pipe for the heat transfer medium is provided according to the present invention. FIG. 5 is a schematic diagram showing a geothermal plant having a plurality of shafts according to the present invention, which is controllable so that the heat extracted from different shafts can be obtained almost continuously. 1 ... Base rock, 3 ... Vertical shaft, 5 ... Bottom area, 7 ... Invasion passage 9 ... Casing, 11 ... Return pipe, 13a, 13b, 13c ... Vertical shaft, 15a, 15b, 15c ... Heat Transmission medium, 17a, 17b, 17c ... Control valve, 19a, 19b ... Heat utilization unit (heat extraction unit), 22a, 22b, 22c ... Separator, 23 ... Control unit, M ... Compound, S ... … Heat conductive material, W …… Heat transfer medium, AF …… Heat exchange area.

Claims (7)

[Claims] 1. A method for extracting thermal energy from the inside of the earth for use on the ground, comprising the steps of (a) forming a vertical shaft downward in the ground, and (b) surrounding the vertical shaft by crushing means in the vertical shaft. Forming an intrusion passage outward from the shaft in addition to the existing intrusion passage by crushing the rocks of (1), and (c) washing away the existing intrusion passage and the intrusion passage formed by the crushing by the pressurized fluid means. And (d) a step of re-digging the shaft and crushing rock around the shaft by a crushing means in the shaft to form an additional intrusion passage, and (e) an existing intrusion passage and a newly formed intrusion Flushing the passages again, (f) pushing a carrier liquid, a binder, and a substance in the form of a slurry of granular material having high thermal conductivity into the entry passages, (g) in the entry passages Hardening the slurry; (h) inserting a casing into the shaft, and fixing the casing to the slurry in the intrusion passage and surrounding rock by a grout containing a granular material having high thermal conductivity; (I) expanding the bottom area of the shaft by blasting or reaming; (j) inserting an inner pipe into the casing to a depth near the bottom area; (k) heat in the bottom area of the shaft. The heat transfer medium through one passage inside at least one of the casing and the inner pipe so as to carry heat to the ground, and through the other passage inside at least one of the casing and the inner pipe. And a step of increasing. 2. The method according to claim 1, wherein the shaft is excavated in the ground at a depth of 1,500 m or more. 3. The method according to claim 2, wherein the shaft is excavated in the ground at a depth of at least 5,000 m. 4. The heat conductive material comprises water, cement, and
The method according to claim 1, characterized in that it comprises at least one of the following substances: (a) silica gel and (b) finely ground metal powder. 5. The finely ground metal powder is silver and / or
Alternatively, the method according to claim 4, comprising copper and / or aluminum. 6. The method according to claim 1, wherein the casing is brought into close contact with a base rock that has been sprayed with a heat conductive material by a seal composition. 7. The method according to claim 6, wherein the seal composition comprises cement and / or silica containing iron file or copper whiskers or copper fibers.