DE102005060970A1 - Geothermal power station has deep vertical shaft filled with a first good heat conductor and a second thermally insulated section - Google Patents

Abstract

A geothermal power station consists of a deep vertical shaft into the earth through which runs a U-shaped pipe from surface to surface. The first part of the pipe is packed within a material which is a good heat conductor. The last part of the pipe (25) above an inversion layer (Zi) is surrounded by material (50) which is a poor heat conductor. The incoming pipe conveys a cold fluid e.g. brine through the first sections of the pipe as it is progressively heated. On rising above the inversion layer the insulated pipe promotes retention of geothermal heat within the brine. On arrival at the surface, the hot fluid surrenders heat energy to a heat pump. Further claimed is a suitable construction process.

Description

The The invention relates to a geothermal probe after the preamble of claim 1 and a method of introduction a geothermal probe according to the preamble of claim 5.

Known geothermal probes consist essentially of a well with sufficient depth and at least one pipeline introduced into the borehole, which has substantially the shape of a U-tube. Through the laxative pipe legs becomes a fluid, for example brine, oil, a gas or another flowable heat transfer medium, in pumped down the borehole. The fluid decreases inside the borehole geothermal energy through heat transfer between borehole wall, Hole inside volume and pipe wall, heats up and leaves the borehole over an ascending pipe leg. Depending on the initial temperature of the fluid it is also possible to cool the fluid. The geothermal probe can thus both for Heating as well as for cooling purposes be used. If necessary can also several geothermal probes be set. The advantage of geothermal probes is that this one year round usable heat source form with a largely constant temperature and therefore technological very effective with heat pumps can be combined.

there is the by the geothermal energy caused temperature gradient used. This shows up from one Depth of 10 to 25 meters in a temperature increase of about 3K / 100 Meter depth. The installation of known geothermal probes is essentially in two steps. In a drilled hole is a U-profile probe admitted. The borehole is then filled. In general, this will be Bentonite cement-water suspensions used different Aggregates, especially quartz or sand, may contain. Next geological conditions, such as thermal conductivity the upcoming soil, the hydrogeological conditions, the borehole quality or the design of the probe, in particular the fluid, is the well filling for the effectiveness of the geothermal probe of crucial importance. Criteria for assessing the quality of backfilling are in particular the thermal conductivity of the backfill and the thermal contact to the borehole wall or to the pipeline.

The effectiveness Geothermal geothermal probes is also due to the geometry of the pipeline, in particular through the center distance of the up and descending pipe sections, influenced. An enlargement of the Center distance of, for example, 40 to 80 mm leads a constant thermal conductivity of 2.0 W / mK and constant drill hole depth to increase the Heat source temperature around 12.5% and allows a shortening the hole depth by about 6% with maintained heat source temperature. At a thermal conductivity of 3.5 W / mK it is possible to save the probe length by approx. 8%.

To The known state of knowledge is thus characterized by an optimal geothermal probe through one as possible huge Distance between the pipe legs and the greatest possible thermal conductivity of the filling material out. Concentrate on research projects in the field of technologies for geothermal probes therefore exclusively on the increase the thermal conductivity of the filling material or on a maximization of the center distance of the ascending and descending Pipe legs with otherwise unchanged good processing and material properties. However, it is obvious that the heat conduction properties of the filling material can not be increased arbitrarily and both material technology as well as in terms of the resulting costs in real terms are. Likewise, it is practically impossible, the center distance of the pipe legs continued to enlarge, because the thus required larger diameter of the well bore requires an increasing technological or material effort.

It Thus, there is the problem underlying the invention, a geothermal probe or to provide a method for introducing geothermal heat with which the described technological limits with a reasonable cost and workload overcome can be and increased effectiveness the geothermal probe becomes possible.

The Task is with respect to the device aspect with a geothermal probe with the features of claim 1 and with regard to the method aspect with a method for introducing a geothermal probe with the features of Claim 5 solved. The respective subclaims contain appropriate or advantageous embodiments or embodiments of apparatus or Method.

According to the invention Geothermal probe by characterized in that the backfilling in a first section between a maximum drill hole depth to an inversion depth of a temperature gradient between a local well temperature and a fluid temperature with a good heat conducting first backfill material accomplished is and the backfilling from the inversion depth to the borehole edge at least in the area an ascending pipe leg with a heat-insulating second backfill material accomplished is.

The backfilling is therefore not only in the form of a backfill material with good thermal conductivity executed but has a layered structure. This is the upper Part of the pipe legs against heat transport into the soil dammed. A closer look shows that the direction of heat transport between ground and the fluid within the pipeline changes and the direction of the temperature gradient between fluid and Soil at a certain depth depends. The depth at which the direction of heat transport between fluid or pipeline and surrounding soil in one for the mode of action the geothermal probe reverses significant and loss-increasing measures is, in the following called inversion depth. For example, at a warming of the fluid flowing inside the pipeline in the lower part the pipeline a heat transfer from the wall of the borehole into the cooler flowing fluid inside the Pipeline. The temperature gradient between the borehole and the fluid shows in this case of the soil on the backfilling of the Borehole in the flowing fluid into it. Above the inversion depth of the borehole is the heated fluid the collected heat because of the now lower temperature to the backfilling of the Borehole and thus finally to the ground again. The temperature gradient between fluid and Soil now shows above the inversion depth of the lumen the pipeline to the outside. This heat loss causes an efficiency decrease of the geothermal probe in heating mode. In a a similar way is one in the lower sections of the pipeline chilled Fluid above the inversion depth due to the now opposite Temperature gradient reheated. this leads to to a loss of efficiency of the geothermal probe in a cooling operation.

The geothermal probe according to the invention is now executed that a heat transfer above the said inversion depth at least between ascending Pipe legs and soil largely prevented is by filling the backfilling the borehole is made heat-insulating in this section. Here, the backfill below the inversion depth optimal thermal conductivities on. The described loss of efficiency is thus in a simple manner Effectively diminished, without putting on the costly and good thermally conductive backfilling resorted must become.

Conveniently, is the inversion depth larger or the same as the seasonal temperature fluctuations exposed Depth area of the borehole at the geographical location of the geothermal probe. The knowledge is taken into account that especially the seasonal fluctuations in the upper strata of the soil adversely affect the efficiency of the geothermal probe, so that with a corresponding size of the heat-insulating backfilling this Seasonal influence can be largely eliminated.

Advantageous here is an inversion depth of at least 10, expediently at least 25 meters. These amounts arise from known geological studies on the depth-dependent Temperature distribution in their seasonal fluctuations in the soil the temperate climate zone. As heat-insulating backfill are materials with a high porosity provided. Especially can be foaming here and curing Suspensions and / or mixtures are used. The inside of the porous material contained air pockets guarantee experience optimal heat-insulating properties.

One Method for introducing a geothermal probe is by the following Process steps marked: First, the borehole sunk in the ground and the appropriate inversion depth in the borehole considering geological and hydrogeological conditions Location determined. Then the piping arrangement is in the borehole brought in. The drill hole is then connected to the first, good heat conducting backfill from the bottom of the borehole to the inversion depth. Finally that will be Drilling hole from the inversion depth substantially to the edge of the Borehole with the second heat-insulating backfill refilled.

at a conceivable embodiment of the method is a descending Pipe legs separating from the ascending pipe branch, from the inversion depth substantially to the edge of the borehole reaching shuttering introduced. This happens expediently after the introduction of the first good heat-conductive filling material. Next The space between the formwork and rising pipe legs with the heat-insulating second backfilling filled, while the space between the descending pipe legs and the Cladding with the heat transferring first backfilling filled becomes. In this procedure, the amount of the second backfill material be reduced while the ascending pipe leg is still optimally thermally insulated.

The geothermal probe according to the invention or the method for introducing the geothermal probe will now be explained in more detail with reference to exemplary embodiment. To clarify serve the 1 to 3b ,

It shows:

1 an exemplary geothermal probe in a heating operation,

2 the geothermal probe off 1 in a cooling mode,

3a a further embodiment of the geothermal probe in a heating operation,

3b the embodiment of the geothermal probe 3a in a cooling mode.

1 and 2 show an exemplary geothermal probe in a heating or a cooling operation. A drilled hole in the ground 10 contains a pipeline 20 with a rising pipe leg 25 and a descending tubing leg 26 that together with a transverse leg 27 form a U-tube configuration. Within the pipeline, the heat-transporting fluid flows from the descending pipe leg over the transverse leg to the ascending pipe leg. The backfilling 30 fills the space between pipeline 20 and the inner wall of the borehole 10 completely off. It is designed in two parts. In the area of the descending pipe leg and the transverse leg, the backfilling consists of a well-heat-conducting filling material 40 , For example, a known bentonite-cement-water suspension. The good heat-conducting filling extends in the embodiment 1 from the bottom of the borehole at a depth z _B over the area of the transverse leg 27 to the borehole edge at z = 0.

In the area of the rising pipe leg 25 is a heat-insulating filling 50 intended. This extends from the inversion depth z _i to the borehole edge at a depth z = 0. A shuttering 60 separates the heat transfer filling 40 from the heat-insulating backfilling 50 ,

The exact amount of inversion depth z _i depends on several factors. In the embodiment of 1 There is a temperature gradient between a low ambient temperature T _Umg over the edge of the wellbore and a surface temperature T _OB immediately at the edge of the wellbore at a depth of z = 0 to the temperature T _B at the maximum depth of the wellbore at z _B. That by the descending pipeline leg 26 down-flowing cold fluid takes on its way from the surface to the transverse leg 26 Heat up. The fluid has substantially in the region of the transverse leg 27 a maximum temperature, which ideally corresponds to the temperature T _B. When passing through the ascending pipe leg 25 decreases the depth-dependent temperature again. The now heated fluid releases heat to the environment. There is thus a temperature gradient between the fluid in the inner volume of the ascending pipe leg 25 and backfilling 30 in the borehole. The resulting heat loss is due to the line resistance between fluid and backfilling 30 with a certain delay. The temperature gradient thus shows from a certain depth of the inner volume of the pipe branch 25 in the direction of backfilling. This depth is called the inversion depth z _i . It marks the point at which the heat losses begin on the ascending pipe branch. At a certain depth, the seasonal temperature change in the soil structure additionally acts. In this case, especially in the winter months, the heated fluid, a considerable amount of heat additionally withdrawn. The heat-insulating backfilling 50 Accordingly, it extends essentially from the edge of the borehole to the inversion depth z _i and should expediently cover at least the seasonally influenced depth section of the soil. For the in 2 indicated cooling operation of the geothermal probe, for example, during the warm season, the size of the inversion depth z _{i is given} in a simple manner by the depth of the seasonally influenced in its temperature soil in the corresponding climatic zone.

The 3a and 3b show further embodiments of the geothermal probe and concrete application examples for a heating or cooling operation. In the embodiments shown there, the heat-insulating filling extends 50 over the entire cross section of the hole 10 and insulates the descending as well as the ascending tubing legs. 3a shows an exemplary cooling operation. The ambient temperature T _Umg in this case is 0 ° C and can also be considered as the temperature of the upper edge of the terrain, ie the turf. The fluid temperature is about 4 ° C before being introduced into the descending pipe leg. Depending on the depth of the borehole, the temperature is at the bottom of the borehole 8th up to 10 ° C regardless of the seasonal variations on the top of the terrain. This temperature corresponds approximately to a depth of the borehole of approximately 50 meters. The maximization in the heat-conducting backfilling 40 in connection with the thermal insulation in the heat-insulating backfilling 50 causes the heat energy absorbed by the fluid is conducted without environmental losses upwards.

In the application example in 3b the fluid circulating in the pipeline should be cooled. The ambient temperature T _Umg in this case is assumed to be about 20 ° C. Depending on the flow rate of the fluid, cooling takes place up to 8 to 10 ° C. The uprising The resulting fluid traverses the seasonally heated area of the soil and absorbs heat energy from the environment if there is no thermal insulation. The heat-insulating filling in the upper area of the borehole prevents this, so that the fluid when leaving the geothermal probe has a temperature of 8 to 10 ° C and an undesirable heat input is largely avoided.

In order to can the energy loss of the geothermal probe increased by about 10 to 15% and the drilling depth of a geothermal probe be shortened by about 10 to 15%. It can with an assumed fertility of the geothermal probe at a probe length of 100 meters an additional Energy amount of up to 2000 kWh / a be obtained.

As a material for the heat-insulating backfilling 50 Appropriately, especially porous, intumescent and hardening suspensions and mixtures based on plastic foams or foamed slurries and mixtures of granules and binders into consideration.

10

borehole, abgeteuft

20

pipeline

25

Ascending Pipeline leg

26

Descending Pipeline leg

27

transverse leg

30

backfilling

40

heat transfer backfilling

50

heat-insulating filling

60

casing

Claims (6)

Geothermal probe, comprising a hole drilled in the ground ( 10 ), introduced into the bore, flowing through a fluid pipe ( 20 ) and a filling enclosing the pipeline and filling the bore ( 30 ), characterized in that the backfilling in a first section between a maximum borehole depth (z _B ) to an inversion depth (z _i ) of a temperature gradient between a local borehole temperature and a fluid temperature with a first heat-conducting first backfilling material (z) 40 ) is executed and the backfilling from the inversion depth (z _i ) substantially to the borehole edge (z = 0) at least in the region of an ascending pipe leg ( 25 ) with a heat-insulating second filling material ( 50 ) is executed. Geothermal probe according to claim 1, characterized in that the inversion depth (z _i ) is greater than or equal to the seasonal temperature fluctuations exposed depth of the borehole at the geographic location of the geothermal probe. geothermal probe according to claim 2, characterized in that the inversion depth dependent on determined by the geological conditions on site. geothermal probe according to claim 1, characterized in that as a heat-insulating backfill Materials with a high porosity, especially foaming and curing Suspensions and / or mixtures are provided. Method for introducing a geothermal probe, characterized by the method steps: drilling a well in the ground and determining the appropriate inversion depth (z _i ) in the borehole, taking into account the geological and hydrogeological conditions at the intended location, introducing the pipe assembly, filling the well with the first good heat conducting Filling material from the bottom of the borehole to the inversion depth, filling the borehole from the inversion depth substantially to the edge of the borehole with the second heat-insulating filling material. A method according to claim 5, characterized by introducing a descending pipe branch ( 26 ) from the ascending pipeline leg ( 26 ), ranging from the inversion depth (z _i ) substantially to the edge of the borehole shuttering ( 60 ) after the introduction of the first backfill material, filling the space between the casing and rising pipe legs with the heat-insulating second backfill and the space between the descending pipe legs and casing with the heat-transferring first backfilling.