EP3171104A1 - Method for ground freezing - Google Patents

Abstract

The invention relates to a method and a device for freezing soil (9) comprising a freezing pipe (1) which is closed at one end face (2) and an inner pipe (6) projecting into the freezing pipe (1) for supplying a refrigerant. and wherein a hollow body (10) is provided, whose inner diameter is greater than the outer diameter of the freezing tube (1).

Description

The invention relates to a device for freezing soil with a freezing tube, which is closed at one end face, and an inner tube projecting into the freezing tube for supplying a refrigerant. Further, the invention relates to a method for freezing soil with a freezing tube and an inner tube projecting into the freezing tube, wherein a refrigerant is passed through the inner tube into the freezing tube.

In civil engineering and foundation engineering measures must often be taken to seal or support the soil. For temporary tasks, the use of an artificial bottom freezing with liquid nitrogen as a refrigerant.

When bottom freezing, the cold entry via a freezer tube with double pipe system. Liquid nitrogen passes through an inner tube down into the freezer tube, evaporates and gives rise to its rising energy in the annulus cold energy to the surrounding soil. from. By removing heat, the water in the surrounding soil is cooled and frozen.

After icing the freezing tubes usually remain in the ground. In some cases, however, this hinders further construction progress, since, for example, full-cutting machines are not able to pass through the steel or copper pipes used as freezing pipes. In these cases, it is therefore necessary to pull the freezing tubes out of the ground after icing.

The pulling of the freezing tubes, however, presents a problem for several reasons. After completion of the icing of the surrounding soil is still frozen for weeks. The tensile force that can be placed on the freezing tubes, is limited by the material and also a negative pressure is generated when pulling the freezing tube on the underside, which exerts a train of the opposing force on the freezing tube.

Object of the present invention is therefore to provide a device for floor freezing and a corresponding method, which allow easier removal of the freezing pipes from the ground.

This object is achieved by a device for freezing soil with a freezing tube, wherein the freezing tube is closed at one end face, and which has an inner tube projecting into the freezing tube for supplying a refrigerant, and which is characterized in that a hollow body is provided, whose inner diameter is larger than the outer diameter of the freezing tube.

The inventive method for freezing soil with a freezing tube and an inner tube projecting into the freezing tube, wherein a refrigerant is passed through the inner tube in the freezing tube, is characterized in that a hollow body whose inner diameter is greater than the outer diameter of the freezing tube, in the soil is introduced and the freezing tube is introduced into the hollow body.

According to the invention, the removal of the freezing tube from the ground is facilitated by providing a hollow body around the freezing tube. The freezer tube thus does not come into direct contact with the ground and thus does not freeze directly to the ground.

The term hollow body should in particular comprise elongated hollow bodies, such as a tube or a hose. The hollow body may be made of a flexible or inflexible material. As a rule, the hollow body has a circular cross-section. But it can also have a rectangular, oval or other cross-section.

The hollow body remains after removal of the freezing tube in the ground. It is therefore advantageous to manufacture the hollow body in such a way that it does not damage it in contact with soil working machines. This can be done, for example, that the hollow body is made correspondingly thin and the wall thickness of the hollow body is a maximum of 6mm, preferably 1 to 2 mm. Alternatively or in addition, the hollow body can be made of a polymer or plastic material, which does not oppose a tillage machine such a resistance that the machine is damaged.

The hollow body is preferably made at least partially or completely from a polymer material. Here, polytetrafluoroethylene (PTFE) has proven itself. Polytetrafluoroethylene (PTFE) has the advantage that it has a very low coefficient of friction, so that the extraction of the freezing tube is facilitated by the low friction between the freezing tube and cladding tube.

However, it is also possible to use other polymer materials or plastic materials, for example perfluoroalkoxy copolymer, polyethylene, polyamide, polyoxymethylene, ethylene / vinyl acetate, polyetherimide or melamine / phenolic resin or other phenolic resins, as well as epoxy resins. In particular, composite materials which contain polymer materials can also be used. The hollow body can also be made of two or more over- and / or juxtaposed materials. For example, it is possible to connect a hollow body made of a first plastic or of metal with a second plastic.

As a result of the use of the hollow body according to the invention, the freezing tube with its cylindrical or lateral surface no longer comes into direct contact with the surrounding soil and can therefore be removed more easily from the ground. The extraction or pulling of the freezing tube is further facilitated by the fact that the hollow body is closed in a preferred embodiment on one of its end faces, on the front side, which is introduced into the ground. In this way, a freezing of the end face of the freezing tube is prevented on the ground.

In a further embodiment, a contact medium is located between the freezing tube and the hollow body. The contact medium may serve to increase the heat conduction from the freezer tube via the hollow body to the surrounding soil. If appropriate, the contact medium can also compensate for different thermal expansion coefficients and thus a different length contraction of the freezing tube and the hollow body during cooling of the freezing tube. Finally, the freezing tube and / or hollow body can also be produced Have tolerances, so that the heat conduction contact between the freezing tube and the hollow body is not optimal in all places. This too can be improved by the contact medium. The contact medium is advantageously chosen so that one or more of the above advantages are achieved.

The contact medium used is advantageously a substance which has a freezing point of less than 0 ° C or at most 0 ° C. At temperatures greater than 0 ° C, the contact medium is liquid or gaseous.

When cooling the freezing tubes, which preferably takes place by means of liquid nitrogen or an aqueous salt solution (brine), of course, the contact medium is cooled. Depending on how much is cooled and what freezing point the contact medium has, the contact medium can also go into the solid phase. This may in turn mean that the freezing tube is frozen to the hollow body.

It has therefore proven to be advantageous to provide means for heating the contact medium. Before the planned removal of the freezing tube from the hollow body, the contact medium is heated and in particular so far that it passes into the liquid or gaseous state. The freezing tube is then surrounded by a liquid or gaseous substance and can be pulled out of the hollow body relatively easily.

As already stated above, a contact medium is preferably selected which has a freezing point below 0 ° C. The contact medium therefore passes into the liquid state earlier than the water frozen in the surrounding soil to ice. The soil can be left in the frozen state while the contact medium is already liquid.

As the contact medium, any type of liquid or gas can be used. Preference is given to substances with a low freezing point and harmless water hazard class. Examples of such contact media are aqueous alcohol solutions with ethanol and propanol or aqueous salt solutions such as sodium chloride, calcium chloride or magnesium chloride.

The heating of the contact medium takes place, for example, with an electric heater. For this purpose, an electrical heater, such as an electric heating wire, a heating coil, a heating tape or a heating jacket, is provided so that when heated current flows through the heater, the contact medium is heated. For example, a heating wire may be wrapped around the freezing tube prior to introduction of the freezing tube into the hollow body. For example, the heating wire is spirally wound around the freezer tube. It has also proven to be beneficial to lay the heating wire or generally the heating element axially along the freezing tube. In this case, it is also possible to provide a plurality of heating elements connected in series or in parallel.

The electric heater can be inserted or otherwise introduced after the introduction of the freezing tube into the hollow body, but before the supply of the contact medium in the space between the freezing tube and the hollow body. Finally, depending on the choice of contact medium, it may also be possible to apply the electric heater only after the introduction of the contact medium. In general, however, the heating is provided before the cooling of the freezing tube and the freezing of the soil. Instead of a heating wire and the freezer tube itself can be used as a resistance heater. In this case, a power source is connected directly to the freezer tube, so that the freezer tube is traversed by a stream and heats up.

Instead of or in addition to an electric heater may also be provided a heat transfer line for supplying a heat carrier. For this purpose, a heat transfer line, for example a hose or a tube, is provided so that it runs at least in sections through the intermediate space between the freezing tube and the hollow body. The heat carrier line can be inserted from above into the gap or through a hole or similar opening in the shell or the end face of the hollow body. In the latter case, part of the heat carrier line outside the hollow body would pass through the ground. If space permits, it is also possible to provide the heat carrier line wholly or partly inside the freezer tube.

For heating the contact medium, a gas or a liquid having a temperature above the freezing point of the contact medium is supplied via the heat carrier line as a heat transfer medium. Preferably, the temperature is the heat carrier between -30 ° C and +450 ° C, especially when a gaseous heat transfer medium is used. If the heat carrier is a liquid, then its temperature is preferably between 0 ° C and 150 ° C, more preferably 50 ° C to 150 ° C. The heat transfer medium comes into thermal contact with the contact medium and at least heats the contact medium to such an extent that it changes into the liquid state of aggregation.

The means for heating the contact medium, for example an electric heater or a heat carrier line, are preferably at least partially wound around the freezer tube. The means for heating the contact medium are preferably arranged helically around the freezing tube or in one or more axial paths along the freezing tube. The freezing tube is then inserted together with the means for heating the contact medium in the hollow body.

In another embodiment, the heat carrier line has a predetermined breaking point and / or outlet openings for the heat carrier. A part of the heat carrier can then escape via the outlet openings and come into direct contact with the contact medium. The heat transfer to the contact medium can be further intensified. Alternatively or additionally, the heat carrier line may have a predetermined breaking point which breaks at a certain pressure (for example 4 bar). By breaking the predetermined breaking point, the hot or hot heat carrier can escape and circulate around the freezing tube and / or the hollow body, whereby the melting of the contact medium is accelerated. In addition, other hoses or tubes may be placed on e.g. half the length are attached, which allow the removal of already cooled heat transfer medium and thus increase the circulation over the entire length of the freezing tube. When the contact medium is liquid again, the freezer tube can be pulled out.

The supply of the refrigerant medium, for example, liquid nitrogen, in the freezing pipe via the inner tube. As the freezing tube and soil cool, the liquid nitrogen heats and vaporizes. The resulting nitrogen gas can be withdrawn through the annular gap between the inner tube and the freezing tube upwards. However, it can also be provided an additional exhaust pipe in the freezing tube, through which the gaseous nitrogen can escape or subtracted. The exhaust pipe has the advantage that in the freezing tube defined flow conditions can be established and that the gaseous nitrogen does not flow through the freezing pipe over its entire length, but at a defined predetermined height, namely the height of the inlet opening of the exhaust pipe is withdrawn. For example, the uppermost part of the soil can be cooled less or, depending on the design, even frozen at all. Of course, the above statements also apply to other refrigerants than nitrogen.

The invention allows in a simple way the removal, that is, the extraction, of the freezing tube. So that the soil can be frozen first with the help of the freezing tubes. Subsequently, the freezing pipes are removed and only the ducts remain in the ground.

Figur 1

eine erste Ausführungsform einer erfindungsgemäßen Vorrichtung zum Bodengefrieren,

Figur 2

eine zweite Ausführungsform,

Figur 3

eine dritte Ausführungsform,

Figur 4

eine vierte Ausführungsform,

Figur 5

eine fünfte Ausführungsform und

Figur 6

eine sechste Ausführungsform der Erfindung.

The invention and further details of the invention are explained below with reference to embodiments schematically illustrated in the drawings. Hereby show:

FIG. 1

a first embodiment of a device according to the invention for bottom freezing,

FIG. 2

a second embodiment,

FIG. 3

a third embodiment,

FIG. 4

a fourth embodiment,

FIG. 5

a fifth embodiment and

FIG. 6

a sixth embodiment of the invention.

In all figures, the same elements are provided with the same reference numerals.

In FIG. 1 a first embodiment of the invention is shown schematically. A freezing pipe 1 made of a good heat-conducting material, in particular copper, has a diameter of, for example, 50 to 100 mm. The length of the freezing tube is for example 1 to 50 m, often 10m to 30 m.

The freezing tube 1 is closed at its lower end face 2. The upper end face 3 is also closed, but has two passages 4, 5 for an inner tube 6 and an exhaust pipe 7. The inner tube 6 is open at the lower end 8. About a supply line, not shown in the drawing, a nitrogen tank is connected to the inner tube 6.

In the ground to be frosted 9 a borehole is drilled, in which a hollow body 10 is introduced. The hollow body 10 is made of polytetrafluoroethylene and has a wall thickness of 0.5 to 6 mm. The hollow body 10 is designed as a cladding tube and closed at its lower end face 12.

In the hollow body 10, a heat carrier line 11 is then inserted. The heat carrier line 11 can be designed either as a hose or as a flexible or inflexible pipe. The heat carrier line 11 is arranged so that it is as close as possible to the hollow body 10, so that sufficient space for the freezing tube remains. The heat carrier line 11 extends both along the jacket of the hollow body 10 and along its bottom or end face 12. To the heat carrier line, a supply for a hot or hot fluid, in particular air or an aqueous salt solution, connected.

Subsequently, the freezing tube is inserted into the hollow body 10, so that the heat carrier line 11 comes to rest in the intermediate space 13 between the freezing tube 1 and the hollow body 10.

The gap 13 is finally filled with a liquid contact medium 14, for example with an aqueous salt solution or water.

For icing of the soil 9, liquid nitrogen is supplied via the inner tube 6 and passed into the interior of the freezing tube 1. The liquid nitrogen cools the ground 9 via the surrounding contact medium 14. In this case, the nitrogen evaporates. The vaporized, cold gaseous nitrogen, which is also referred to as exhaust gas, draws more heat from the ground. On the temperature of the exhaust gas, a non-illustrated solenoid valve is controlled. In this way a steady flow of nitrogen with optimum efficiency is ensured.

After some time, a frozen area forms around the freezing tube 1. After icing it is convenient in some cases, the freezing tubes 1 from the To remove soil, as this could hinder the further construction progress. For example, full-cutting machines may not be able to pass through the steel or copper pipes used as freezing tubes 1.

According to the invention, the freezing tubes 1 are pulled out of the ground 9 or out of the hollow body 10 in such a case. For this purpose, first a gaseous heat transfer medium is passed through the heat carrier line 11. If the freezing tube has previously been cooled with liquid nitrogen, initially a heat transfer medium with a temperature between, for example, -50 ° C and 0 ° C can be used. For example, at this stage, you can take vaporized gaseous nitrogen directly from a nitrogen tank. In general, however, a heat carrier having a higher temperature of, for example, 50 ° C to 200 ° C, e.g. heated air or heated nitrogen gas used to effect a faster melting and heating of the contact medium.

The heat transfer medium flows through the heat carrier line 11 and thereby heats the surrounding contact medium 14. If the contact medium 14 was in the solid state of aggregation, it is liquefied again. Otherwise, at least the viscosity of the contact medium 14 is reduced by the heating, so that the contact medium 14 is flowable and the freezing tube 1 is easier to move in the contact medium 14.

If the contact medium 14 is liquid or has reached a certain fluidity, the freezing tube 1 is pulled out of the hollow body 10 with a pulling device, not shown in the drawing.

In FIG. 2 an alternative embodiment of the invention is shown. This version is different from the one below FIG. 1 in that the heat carrier line 11 is wound around the freezing tube 1. The heat carrier line 11 is placed helically around the freezing tube 1. This has the advantage that the freezer tube 1 can be easily inserted into the hollow body 10 together with the heat carrier line 11. On the other hand, a uniform heating of the contact medium 14 is achieved by the winding of the heat carrier line 11 to the freezing tube 1. FIG. 3 shows an embodiment of the invention, in which the heat carrier line 11 extends partially through the ground 9. Here, a borehole 15 is first drilled, which has a larger diameter than the hollow body 10. The heat carrier line 11 is guided through the wall of the hollow body 10, extends along the lower end face 12 of the hollow body and is led out again on the opposite side of the hollow body 10.

The hollow body 10 is introduced into the borehole 15 together with the heat carrier line 11. As described above, the freezing pipe 1 and the contact medium 14 are then placed in the hollow body 1. The heat carrier line 11 is guided outside the hollow body 10 upwards and the remaining wellbore 15 is backfilled with soil or aqueous or pasty building materials, such as cement suspension, bentonite or twilight. The heat carrier line 11 may further be provided with a predetermined breaking point 16 in the section in which it runs within the hollow body 10. The predetermined breaking point 16 is designed so that it bursts when a certain pressure, for example 3 bar, is exceeded and releases an opening. The heat transfer medium then flows through this opening into the interior of the hollow body 10, thereby accelerating the melting and heating of the contact medium 14.

The execution according to FIG. 4 is essentially a combination of Figures 2 and 3 , However, instead of the predetermined breaking point 16, a plurality of holes or perforations 17 are provided in the section of the heat carrier line 11 in which it extends within the hollow body 10. The holes or perforations 17 have, for example, a diameter between 0.05 mm and 0.4 mm, for example 0.15 mm or 0.2 mm, so that a part of the heat carrier can flow through these holes 17 into the interior of the hollow body 10.

In the variant after FIG. 5 is provided instead of a heat carrier line, an electric heater 18 for heating the contact medium 14. A heating wire 18 is placed helically around the freezing tube 1 and pushed with the freezing tube 1 in the hollow body 10. The intermediate space 13 between the freezing tube 1 and the hollow body 10 is filled with the contact medium 14. The freezing tube 1 is then cooled as described above with liquid nitrogen and the surrounding soil is frozen. For thawing and heating of the contact medium 14 of the heating wire 18th connected to a power source 19 and a heating current is passed through the heating wire 18.

In the FIG. 5 shown electric heater can be used not only as an alternative to a heat carrier line, but also supplementary. In the latter case, the heating of the contact medium 14 is significantly accelerated by the heat transfer from the heat carrier and by the electric heater.

Finally, in FIG. 6 to see another variant of the invention. In this case, the heating of the contact medium 14 by supplying a heat transfer medium into the freezing tube 1. For this purpose, a heat transfer medium, in particular a hot gas, for example, gaseous nitrogen at a temperature of 50 to 450 ° C is passed into the freezing tube 1. The contact medium 14 is in direct contact with the outside of the freezing tube 1 and is heated by the heat carrier. The heat carrier can be supplied for example via the inner tube 6 and withdrawn via the exhaust pipe 7 again, so that a circulation of the heat carrier is generated. The circulation of the heat carrier can be further improved when the upper end face 3 of the freezing tube 1 is opened.

• Erwärmung durch einen in das Gefrierrohr eingebrachten Wärmeträger
• Erwärmung durch einen Wärmeträger, welcher durch eine mit dem Kontaktmedium in Wärmeaustauschkontakt stehende Wärmeträgerleitung strömt,
• Erwärmung durch einen Wärmeträger, welcher direkt in das Kontaktmedium geleitet wird und/oder
• Erwärmung mittels einer elektrischen Heizung.

The heating of the contact medium 14 via the freezing tube 1, as shown by FIG. 6 of course, can also be complementary to those in the FIGS. 1 to 5 described methods are used. The contact medium 14 may be heated by one or more of the following methods:

• Heating by a heat transfer medium introduced into the freezer tube
• Heating by a heat transfer medium which flows through a heat transfer line in heat exchange contact with the contact medium,
• Heating by a heat transfer medium, which is passed directly into the contact medium and / or
• Heating by means of an electric heater.

Claims (14)

Device for freezing soil with a freezing tube (1), which is closed at one end face (2), and an inner tube (6) projecting into the freezing tube (1) for supplying a refrigerant, characterized in that a hollow body (10) is provided is, whose inner diameter is greater than the outer diameter of the freezing tube (1). Apparatus according to claim 1, characterized in that the hollow body (10) comprises a polymer material, in particular polytetrafluoroethylene. Apparatus according to claim 1 or 2, characterized in that the hollow body (10) is closed at one of its end faces (12). Device according to one of the preceding claims, characterized in that between the freezing tube (1) and the hollow body (10) is a contact medium (14) which has a freezing point of at most 0 ° C. Apparatus according to claim 4, characterized in that means (11, 18) for heating the contact medium (14) are provided. Apparatus according to claim 5, characterized in that the means (11, 18) for heating the contact medium (14) comprises an electric heater (18) and / or a heat carrier line (11) for supplying a heat carrier. Device according to one of claims 5 or 6, characterized in that at least a part of the means (11, 18) for heating the contact medium (14) are wound around the freezing tube (1). Device according to one of claims 6 or 7, characterized in that the means for heating the contact medium (14) comprise a heat carrier line (11) for supplying a heat carrier and that the heat carrier line (11) has a predetermined breaking point (16) and / or outlet openings (17 ) for the Having heat transfer. Device according to one of the preceding claims, characterized in that in the freezing pipe (1) projecting exhaust pipe (7) is provided. A method for freezing soil (9) comprising a freezing tube (1) and an inner tube (6) projecting into the freezing tube (1), wherein a refrigerant is conducted via the inner tube (6) into the freezing tube (1), characterized in that a hollow body (10) whose inner diameter is greater than the outer diameter of the freezing tube (1) is introduced into the soil (9) and the freezing tube (1) is introduced into the hollow body (10). A method according to claim 10, characterized in that a contact medium (14) having a freezing point of at most 0 ° C, in the intermediate space (13) between the hollow body (10) and the freezing tube (1) is introduced. Method according to one of claims 10 or 11, characterized in that the freezing pipe (1) after freezing of the soil (9) from the hollow body (10) is removed. A method according to claim 12, characterized in that the freezing tube (1) and / or the contact medium (14) are heated prior to removal of the freezing tube (1). Method according to one of claims 10 to 13, characterized in that liquid nitrogen or an aqueous salt solution is passed as a refrigerant in the freezing tube (1).

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