WO2007110030A2

WO2007110030A2 - Geothermal probe

Info

Publication number: WO2007110030A2
Application number: PCT/DE2007/000438
Authority: WO
Inventors: Wolfgang Feldmann
Original assignee: Wolfgang Feldmann
Priority date: 2006-03-17
Filing date: 2007-03-10
Publication date: 2007-10-04
Also published as: US20090107650A1; CA2646049A1; EP1996874A2; WO2007110030A3; DE102006012903B3

Abstract

The invention relates to a geothermal probe for the exploitation of geothermal heat, comprising a cluster of several closed heat tubes, which for transporting the heat are filled with a two-phase working medium that can be evaporated by means of the geothermal heat and can be condensed in a heat discharging zone. In this case, the respective heat tubes are subdivided over their length into at least a heat receiving zone, a heat transporting zone and a heat discharging zone, at least two heat tubes in the heat receiving zone and/or in the heat transporting zone being of different lengths.

Description

geothermal probe

The invention relates to a geothermal probe for the use of geothermal heat with a bundle of several closed heat pipes, which are filled for heat transfer with a two-phase working medium, which is vaporized by geothermal and condensable in a heat output zone, wherein the respective heat pipes over the length in at least one Subdivide heat absorption zone, heat transfer zone and heat delivery zone.

Geothermal for heating roads is proposed in DE 35 32 542 A1. The intended use was an automobile test track. In order to safely heat this large area during a test program, very large heat receiving spaces in the ground can be opened up by many long holes. To limit this, the heat was collected in storage tanks and stored and delivered as needed via a guided by climate sensors control to the street to be heated. Therefore, a switchable running system is provided in this heating, which gives off heat when exceeding or falling below of climate-specific limits such as humidity, air temperature, wind speed, surface temperature and surface moisture and thus protects the heat storage of the soil.

The document DE 30 37721 A1 describes a heat pipe for exploiting the heat capacity of the soil and / or groundwater, for example for preventing the freezing of switches. The probe tube is introduced into the soil in the form of a drill core so that the surrounding soil as Heat capacity acts. The heat pipe is here a closed tube with a liquid / gaseous working medium and the surface-increasing deposits for improved heat transfer at the heat source from the heat in the ground to the working medium. A special feature here is an increased by satellite tubes or ribs heat absorption surface mentioned. This measure attempts to maximize the amount of incoming heat. In fact, the inflowing amount of heat is predominantly limited by the conductivity of the surrounding soil, so that an increase in the amount of heat that can be absorbed is achieved primarily by increasing the diameter of the cylindrical receiving surface. For more efficient use of heat switches are installed in the heat pipe, which regulate the heat transfer by interrupting the condensate backflow or by separation of condensation and evaporation or by a switching fluid according to the requirements. The working fluid used here is a water / alcohol mixture, CFC or HFC.

Furthermore, according to a similar method, an executed prototype plant with propane as the working medium is known.

The document EP 1529880 and WO002005045134 concerns a geothermal probe which directly radiates traffic systems, the heat flow of which is conducted via the heat source via the transport zone via at least one heat pipe and split over several heat distribution tubes before the heat is released in the region of a heat sink.

In the patent EP 1194723 B1, an embodiment is shown, in which the liquid medium flows down in a spirally guided tube which winds around the tube with the ascending medium. A similar proposal is made in US5816314.

In the patent DE 4240082 C1, a probe is described in which the flow of the gas from the return of the condensate of the working medium is separated by perforated plates. This happens to already in case of a capillary tube to separate the gas bubbles from the liquid on the transport route and to supply them to the gas stream.

Applications of CO ₂ as a medium in geothermal probes are known as publications DE29824676U1, DE20320409U1, DE20210841 U1.

In DE20210841U1 a probe is described, the condensate stream is separated from the gas stream by the fact that the gas stream rises centrally in a separate, central, perforated tube and the condensate stream flows down along the tube outer wall.

The document DE29824676U1 describes a probe which can be provided with ribs in order to improve the heat transfer.

The document DE20320409U1 describes a stainless steel probe in the form of a corrugated tube, designed as a monotube or a double tube. This is to make it possible that even larger diameter stainless steel tubes can be introduced from a roll in one piece in the wellbore. Another goal here is that at larger wells, large pipe diameter and thus large moving volume of the working medium, the downflowing condensate film is not hindered by the ascending gas flow. With the pipe diameter or volume of the probe tube provided here, this component is subject to stricter provisions of the GPSG (Equipment and Product Safety Act).

In the known versions of geothermal probes and copper pipes, corrosion protected by PE film coating, used with the maximum possible diameter, which still allows easy deformability, so that the tubes unwound from a roll, just shaped, can be sunk into the well. The largest possible pipe diameter is specified by the minimum ductility required for installation. It will be used here several equal-length pipes in a hole. These versions have already been installed in numerous geothermal building heaters. As well It is known in the art to use a downhole grout with the heat conduction enhancing additives. In all known cases, the heat absorption takes place uniformly over the entire borehole depth at least below the neutral zone, the depth that has no temperature fluctuations over the course of the year.

In a majority of the known probes, the heat is either collected in pipes of the largest possible diameter and fed exactly to a use or it is collected in several pipes with a smaller diameter and fed exactly one use, such as a heat exchanger with downstream heat pump.

The invention has the object of developing a device for collecting geothermal heat, which are adapted to the specific requirements of an application purpose and thereby represent a more efficient and economical solution.

The invention is represented by the features of claim 1. The further dependent claims relate to advantageous developments and further developments of the invention.

The invention includes the technical teaching relating to a geothermal probe for the use of geothermal heat with a bundle of several closed heat pipes, which are filled for the heat transport with a two-phase working medium, which can be evaporated by means of geothermal and condensable in a heat delivery zone. In this case, the respective heat pipes are subdivided along their length into at least one heat absorption zone, heat transport zone and heat release zone, wherein at least two heat pipes in the heat absorption zone and / or in the heat transfer zone have different lengths. The invention is based on the consideration that in geothermal probes for the collection of geothermal heat pipes using a liquid-gas working medium is used, the condensation temperature is slightly below the temperature of the heat source used. It preferably serves as a source of heat for freezing of traffic routes and facilities, such as railway systems. This is done predominantly using a small temperature gradient between geothermal and / or the heat contained in the groundwater and / or wastewater compared to the temperatures required for the buildings to be heated or plants at least to the freezing point of water. No additional pumps powered by external energy or other moving parts are required. In this context, geothermal heat means any low-temperature heat source available below the earth's surface, for example also waste heat from sewers.

The invention proposed here operates on the principle of a heat pipe, known in technical language as heatpipes. It is a gas-tight, predominantly vertical or steeply inclined installed pipe in which the working medium evaporated at the heat source, rises to the heat sink, condenses there and flows down into the same pipe back to the heat source.

The mass flow is the main factor influencing transmitted power. The maximum transmittable power results from the chain yield of the soil in the heat receiving area, the thermal conductivity of the soil in the bore environment and the injection material around the hole, the thermal conductivity of the pipe material and the type, orientation and size of the heat receiving surface. The fertility and conductivity as well as the size and orientation of the receiving surface are the main criteria. This shows that the heat conduction of the probe material is of secondary importance.

Since there is the demand for the possibility of several small, sometimes equal-sized services to each exactly the same number of heat sinks It is not proposed to feed a plurality of heat sinks from a probe tube, but to assign each heat sink exactly one heat pipe from a tube bundle to a probe and not to lead the largest possible power from one or more tubes to a heat exchanger. In this case, only the amount of heat that is required for the respective heat sink is taken from the ground via the size of the respective heat absorption surface of a heat pipe.

In this way, the requirement for different temperatures for the respective heat sinks can be met. As the soil also gets warmer with greater depth, the individual tubes can be made of different lengths and then deliver different temperatures through their limited heat-receiving zone from the respective layers. The heat absorption surface is limited by the fact that above it the pipe is thermally insulated, so that a heat absorption area is defined according to temperature and area.

In cases where the receiving zone of a probe extends through several geological layers, each with a different heat capacity, the amount of heat required at the heat sink is adjusted by adjusting the length of the respective heat absorption zone.

From the point of view it is obvious that a high gas flow rate in a pipe leads to high flow velocities. The pipe diameter limits the mass flow rate at a given maximum speed of the medium. This means that the uniform flow of the condensate film on the tube wall, down to the probe foot, is hindered by the ascending gas flow as soon as the flow velocity and / or the mass flow exceeds the critical size. This is prevented here in that the heat absorption surface, the amount of fluid in the pipe and thus the maximum power throughput are limited. The heat absorption surface is limited by the fact that above it, the tube is thermally insulated, thus there is a temperature range and area exactly defined heat absorption area. The particular advantage is that the geothermal probe according to the invention has a surpassing the current level efficiency with respect to heat, material usage and efficiency. The efficiency with regard to the use of heat results from the optimized heat absorption of the heat flowing from the soil via a temperature gradient.

Thus, in the case of a probe, application-specific division of the heat available in the ground into the working medium results in the context of several small heat sinks with precisely defined amounts of heat. A division of the heat flow in a tube bundle with a plurality of heat exchangers improves the operational and functional safety by a plurality of independently operating subsystems. This avoids a source of error in the adaptation of the heat flows which supply the heat quantity to the heat exchangers, as well as a potential source of damage, namely leakage of the probe tube at at least three additional connection points per division.

Different performance requirements of several heat exchangers can be conceptually fulfilled from a single probe. In this case, the cost of materials can be minimized in particular by the different lengths of the probe tubes.

Such geothermal probes with novel components for heat recovery are suitable for the heating of buildings and facilities. In particular for traffic systems, for example in the railway industry for snow and ice clearance of switches, platforms and railroad crossings and other traffic areas outside the railway.

The heat requirement related to the application can be met with heat radiating smaller diameter than usual. The use of a smaller pipe diameter allows for thinner equal wall thickness significantly thinner wall thickness. This results in the following additional advantages: Material savings, better processability and handling and greater flexibility in the choice of materials. In addition, the different probe tube lengths allow further material savings of up to 45%.

Advantageously, at least two heat pipes can have different diameters in the heat absorption zone and / or in the heat transport zone. Alternatively or in combination, different gas pressures can prevail in at least two heat pipes. Furthermore, different working media can be introduced into at least two heat pipes. All of these embodiments open up the possibility of carrying out individual heat pipes with different heat outputs, as required.

In a preferred embodiment of the invention, the heat pipes in the

Heat transfer zone to be thermally insulated. In order to further improve the heat recovery, each tube in the section above the heat receiving zone can be thermally insulated, and indeed against the parallel probe tubes with lower lying heat absorption zones. This ensures that takes place in the heat transport zone of each tube only a negligible small uncontrolled heat exchange with the environment.

In a preferred embodiment, the heat absorption zone is located at the lower end of each heat pipe in the tube bundle to ensure in each case that can accumulate no liquid working fluid at the end of the tube, which would be removed from the heat circulation. In order to achieve a more effective use of the heat source, the different heat absorption zones of a tube bundle are arranged at different depths.

Advantageously, a plurality of heat receiving zones and heat transport zones can be arranged on a heat pipe. In a preferred embodiment of the invention, the heat absorption zones of the individual heat pipes can be arranged in tiers. As a result, several heat pipes with heat absorption zones can be arranged on each floor around the circumference of the tube bundle. The number is based on the fact that each point is taken from the heat in the ground is not significantly affecting the adjacent heat extraction zones. For example, about six heat pipes are arranged circumferentially with heat receiving zones in each floor.

Advantageously, the heat pipes may at least partially have axially extending bulges or guide plates may be arranged in the interior, through whose influence the transport of the refluxing condensate takes place in a targeted manner. In this case, the refluxing condensate is fed into the probe tube in a partially separated by continuous bulges or plates from the gas area and also flows through it in the transport zone down to the heat absorption zone. As a result, the effectiveness is increased by the rising gas has little contact with the refluxing condensate, so that the flow and pressure losses are minimized in the tubes.

Alternatively, the heat pipe can advantageously have a spirally running embossing. The heat pipe as a twisted tube with spiral embossing improves the flow conditions and thus the efficiency. This causes the ascending gas to be charged with a swirl and also the condensate that flows down. Due to the different density of the two states of aggregation of the working medium and the resulting different centrifugal forces, the substantial separation of the gas is achieved by the condensate, the condensate flows down to the outer wall.

Advantageously, the heat receiving surfaces of the heat pipes by helical guiding of the heat pipes in the heat receiving zone around the borehole axis and / or be increased by additional outer ribs. Due to the smaller diameter of the probe tubes, the circumference and thus the receiving surface is correspondingly reduced in relation to a tube of large diameter. Nevertheless, in order to optimally utilize the heat capacity of the soil surrounding the heat absorption zone, the tube can be guided spirally around the tube bundle in the respective heat-absorbing zone, as a result of which the absorption area is multiplied.

In a preferred embodiment of the invention, the heat pipes may be at least partially formed in the heat absorption zone as a surface heat exchanger, which engages wholly or partially around the inner heat pipes of the bundle. As a result, over the entire circumference or even only part of the tube bundle, larger portions of the geothermal energy are collected in a simple manner and, for example, made available to selected heat pipes.

Advantageously, at least in the region of the heat absorption zone, the inner wall of the heat pipes can be rough. As a result, in addition to the increased heat transfer surface, the fluid flowing back can also be distributed to the entire surface in the interior of the tube.

Likewise, at least one heat pipe can be widened in the region of the heat absorption zone at its pipe end. As a result, in particular at the lowest collection point of the returning liquid working medium, an increased heat input takes place.

In a preferred embodiment of the invention, the heat pipes can be twisted about the e-axis in the region of the respective heat absorption zones. A fundamental improvement of the heat absorption is achieved by arranging the tubes such that only absorb the external heat and can additionally be improved by the heat receiving surface is increased by helical guide to the insulated heat pipes, which here form a kind of isolated core, in the receiving zone. This can also be done in the way that several tubes are guided quasi parallel as a multi-start thread with a larger pitch. If this results in a flat slope of the spiral of the heat receiving pipe section and the condensate flows only at the tube sheet and is not evenly distributed on the tube wall, it is proposed that the tube is rotated in the heat receiving area in itself. This ensures that the condensate with each revolution of the tube is at least partially reflected back to the pipe inner wall.

Advantageously, the heat pipe can be made of aluminum or steel.

Embodiments of the invention will be explained in more detail with reference to schematic drawings.

In it show schematically:

2 shows a heat probe with heat pipes of different lengths of the heat transport zone N by an insulation below the earth's surface and heat receiving zones H, arranged in layers, FIG. 2 shows a heat probe with heat pipes of different lengths.

Fig. 3 is a heat probe with tiered spiral guide of

Heat pipes in the heat absorption zone H around the borehole axis,

4 shows a heat probe with a spiral guide of two heat pipes in the heat absorption zone H about the borehole axis,

5 shows a heat probe with heat pipes, which are formed in the heat absorption zone H as surface heat exchanger, which engages around the inner heat pipes of the bundle, 6 A to H show a cross section of different embodiments of surface heat exchangers on different levels of a heat probe, which at least partially engage around the inner heat pipes of the bundle,

7 shows a heat pipe of a heat probe with a wall-side bulge, FIG. 8 shows a cross-section of a heat pipe according to FIG. 7, FIG.

9 shows a heat pipe of a heat probe with inner guide plates, and FIG. 10 shows a cross section of a heat pipe according to FIG. 9.

Corresponding parts are provided in all figures with the same reference numerals.

1 shows a heat probe 1 with heat pipes 2 of different lengths of the heat absorption zone H below the surface of the earth O. The bundle is formed from a plurality of parallel in the ground heat pipes 2, which are filled for the heat transfer with a two-phase working medium. The working medium evaporates due to the geothermal heat in the area of the heat absorption zone H and is transported via the heat transport zone N into a heat emission zone K. In the region of the heat transport zone N, the temperature of the vaporous working medium corresponds approximately to that of the surrounding earth layer, so that no heat is exchanged here. In the heat release zone K, the working fluid condenses after heat release and flows through gravity again in the heat pipe 2 in the depth. The heat transferred in the respective heat pipe 2 depends on the different pipe lengths in the heat absorption zone H.

Also, Fig. 2 shows a heat probe 1 with heat pipes 2 of different lengths in the heat transport zone N. The length of the heat transfer zone N is defined by an insulation 3 below the earth's surface O. The heat is transmitted via the exposed pipe ends of the heat pipes 2 to the working medium. The exposed pipe ends form a heat absorption zone H arranged for the respective heat pipe 2.

Fig. 3 shows a heat probe 1 with floor-wise spiral guiding the heat pipes 2 in the heat absorption zone H around the borehole axis. Another embodiment is shown in FIG. There, a heat probe 1 is shown with a spiral guide two heat pipes 2 in the heat absorption zone H to the borehole axis. Both solutions have in common the enormously enlarged heat absorption surfaces by a helical guiding of the heat pipes 2 in the heat absorption zone H.

Fig. 5 shows a heat probe 1 with heat pipes 2, which are formed in the heat receiving zone H as a surface heat exchanger 7, which engage around the inner heat pipes 2 of the bundle. The pipe end 8 of the deepest heat pipe 2 is widened conically in the region of the heat absorption zone H.

6 A to H show a cross section of different embodiments of surface heat exchangers 7 on different levels of a heat probe 1, which at least partially engage around the inner heat pipes 2 of the bundle. In this case, an annular surface heat exchanger 7 is formed on the lowest floor (Fig. 6A), which opens into the heat pipe 2, which leads centrally upwards. Around the central heat pipe 2, on the first floor (FIG. 6B), three further surface heat exchangers 7 are arranged, each one third of the circumference. The heat pipes 2 opening out of the surface heat exchangers 7 are in turn led as close as possible to the centrally extending heat pipe 2 parallel to this upward. The further floors are shown analogously in FIGS. 6C to 6G. Fig. 6H shows a cross section through the tube bundle, as it is found for example in the heat transport zone N. On each floor, the inside pipe sections are thermally shielded by an insulation. Through these axially extending bulges, the back-flowing condensate is fed into the probe tube in a partially separated by continuous bulges or plates from the gas area and flows through it in the transport zone N down to into the heat absorption zone H. The reflux channel 6 directs the liquid working medium directly into the bulge 4. FIG. 8 shows the cross section of a heat pipe according to FIG. 7.

Alternatively, FIG. 9 shows a heat pipe 2 of a heat probe 1 with inner guide plates by means of which the transport of the refluxing condensate also takes place in a targeted manner. Through both solutions, the effectiveness is increased by the rising gas has little contact with the refluxing condensate, so that the flow and pressure losses are minimized in the tubes. FIG. 10 shows a cross section of a heat pipe according to FIG. 9. FIG.

LIST OF REFERENCE NUMBERS

1 geothermal probe

2 heat pipe

3 insulation

4 bulge

5 guide plate 6 return channel

7 area heat exchanger

8 flared pipe end

H heat absorption zone N heat transport zone

K heat release zone

O earth surface

Claims

Patent claims

1. Geothermal probe (1) for the use of geothermal heat with a bundle of several completed heat pipes (2), which are filled for heat transfer with a two-phase working medium, which can be evaporated by means of geothermal and condensable in a heat delivery zone, wherein the respective heat pipes on their Length in at least one heat absorption zone (H), heat transfer zone (N) and heat output zone (K) subdivide, characterized in that at least two heat pipes (2) in the heat receiving zone (H) and / or in the heat transport zone (N) have different lengths ,

2. geothermal probe according to claim 1, characterized in that at least two heat pipes (2) in the heat receiving zone (H) and / or in the heat transport zone (N) have different diameters.

3. geothermal probe according to claim 1 or 2, characterized in that in at least two heat pipes (2) prevail different gas pressures.

4. geothermal probe according to one of claims 1 to 3, characterized in that in at least two heat pipes (2) different working media are introduced.

5. Geothermal probe according to one of claims 1 to 4, characterized in that the heat pipes (2) in the heat transport zone (N) are thermally insulated.

6. geothermal probe according to one of claims 1 to 5, characterized in that the heat receiving zone (H) of a heat pipe (2) is located at least at the lower end of this tube.

7. geothermal probe according to one of claims 1 to 6, characterized in that on a heat pipe (2) a plurality of heat receiving zones

(H) and heat transfer zones (N) are arranged.

8. Geothermal probe according to one of claims 1 to 7, characterized in that the heat absorption zones (H) of the individual heat pipes (2) are arranged in tiers.

9. Geothermal probe according to one of claims 1 to 8, characterized in that the heat pipes (2) at least partially axially extending bulges (4) or guide plates (5) are arranged in the interior, through the influence of the transport of the back-flowing condensate is targeted.

10. geothermal probe according to one of claims 1 to 8, characterized in that the heat pipe (2) has inwändig a spirally extending embossing.

11. Geothermal probe according to one of claims 1 to 10, characterized in that the heat receiving surfaces of the heat pipe (2) are enlarged by spiraling the heat pipes in the heat absorption zone (H) around the borehole axis and / or by additional outer ribs.

12. geothermal probe according to one of claims 1 to 11, characterized in that in the heat receiving zone (H) the heat pipes are at least partially formed as a surface heat exchanger (7), which is wholly or partially around the inner heat pipes (2) of

Bundle attacks.

13. Geothermal probe according to one of claims 1 to 12, characterized in that at least in the region of the heat absorption zone (H), the inner wall of the heat pipes (2) is rough.

14. Geothermal probe according to one of claims 1 to 13, characterized in that at least one heat pipe (2) in the region of the heat absorption zone (H) is widened at its tube end.

15. Geothermal probe according to one of claims 1 to 14, characterized in that in the region of the respective heat absorption zones (H) the heat pipes (2) are twisted around its own axis.

16. Geothermal probe according to one of claims 1 to 15, characterized in that the heat pipe (2) made of aluminum or steel.