JP6994409B2 - Ground freezing method - Google Patents

Description

The present invention relates to a ground freezing method. More specifically, the present invention is a technique for drying pipes (freezing pipes, refrigerant pipes) used in the ground freezing method.

The ground freezing method of freezing the ground in a predetermined area for the purpose of stabilizing the construction ground, impermeable water, and other purposes has been widely used in the past (see, for example, Patent Document 1).
In the ground freezing method, a freezing pipe (refrigerant pipe) is placed in the ground to be frozen, and a refrigerant is allowed to flow in the freezing pipe to take heat from the ground and freeze the target ground.

Here, in the conventional ground freezing method, as the refrigerant produced by chemically synthesizing, the primary side refrigerant (refrigerant on the refrigerator side) is Freon, and the secondary refrigerant (refrigerant circulating on the freezing pipe side) is brine. Is often selected. When the Freon and brine are used as the refrigerant, the diameter of the freezing pipe (particularly the freezing pipe on the secondary side) is increased in order to secure the cold heat required for freezing the ground, and the secondary refrigerant is used. It was necessary to increase the flow rate of brine.
In recent years, a ground freezing method has been implemented in which ammonia is used as the primary refrigerant and a natural refrigerant such as CO ₂ is used as the secondary refrigerant instead of chlorofluorocarbons as the primary refrigerant and brine as the secondary refrigerant.
One of the merits of selecting CO ₂ as a natural refrigerant for the refrigerant, especially the secondary refrigerant, is to reduce the diameter of the freezing pipe (secondary freezing pipe) and reduce the flow rate of the secondary refrigerant. Can be mentioned as a point that can be reduced.

However, if the diameter of the freezing tube is reduced, the secondary refrigerant flows in the freezing tube at a low temperature of about −30 to −45 ° C., so that the water in the freezing tube may freeze and block the freezing tube. Here, the moisture in the freezing tube includes the moisture adhering or accumulating on the inner wall of the freezing tube due to dew condensation or the like, and the moisture existing as water vapor in the space inside the freezing tube. It has long been known that this water freezes into ice, and even if the initial ice is very small with respect to the diameter of the freezing tube, when ice particles come into contact with each other, a bond is formed at the contact portion. , Ice grows inside the freezing tube due to this binding, and eventually an event occurs that occludes the freezing tube. Therefore, when CO ₂ which is a natural refrigerant is allowed to flow through the freezing tube on the secondary side, it is necessary to dry the inside of the freezing tube in advance to remove water from the inside of the freezing tube.
Here, in the conventional ground freezing method using brine as a secondary refrigerant, the diameter of the freezing pipe is large as described above, and since brine is an aqueous solution, even if water is mixed in the brine itself, it is a component. It did not lead to a big problem, and even if the water was frozen in the freezing tube, the freezing tube was not blocked. That is, calcium chloride, which is the main component of brine, is an antifreeze solution, and due to its effect, the presence of water in the freezing tube does not cause obstruction. Therefore, in the conventional ground freezing method, it is not necessary to dry the freezing pipe to remove water from the inside of the freezing pipe before flowing brine, which is a secondary refrigerant.
In other words, the work of drying the freezing pipe to remove water from the inside of the freezing pipe before flowing the refrigerant is necessary only when CO ₂ which is a natural refrigerant is selected as the refrigerant, and brine. It was a work that was not required in the conventional ground freezing method of selecting as the secondary refrigerant. Therefore, a technique for efficiently drying the inside of the freezing pipe before the construction of the ground freezing method has not been proposed in the prior art.

Here, in order to remove water in the refrigerant pipe of the air conditioner, there is a technique of supplying heated nitrogen gas N ₂ to the refrigerant pipe and then drawing a vacuum (for example, Patent Document 2). Nitrogen gas is supplied to the refrigerant pipe because it does not contain water and is an inert gas.
However, even if nitrogen gas _N2 is supplied into the freezing pipe and dried in the ground freezing method, nitrogen is supplied from the nitrogen gas cylinder, so that the flow rate of nitrogen gas is small, especially when there is a lot of air and water in the freezing pipe. Is required for a long time to dry the freezing tube. In addition, it is not possible to continuously supply nitrogen gas, and it is necessary to cut and connect a plurality of nitrogen gas cylinders, which takes time. In addition, if a large amount of nitrogen gas is injected at a construction site (for example, in a tunnel), the construction site becomes oxygen deficient.
Therefore, it is not appropriate to apply the technique of evacuating after supplying nitrogen gas _N2 in order to dry the freezing pipe before the construction of the ground freezing method.

Japanese Unexamined Patent Publication No. 2017-133164 Japanese Unexamined Patent Publication No. 6-148268

The present invention has been proposed in view of the above-mentioned problems of the prior art, and is a ground freezing method using liquefied carbon dioxide (CO ₂ ) as a secondary refrigerant to efficiently dry a freezing pipe. The purpose is to provide a drying mechanism inside the freezing pipe used in the ground freezing method that does not require the use of a large amount of inert gas such as nitrogen gas, and a ground freezing method using a freezing pipe dried by the drying mechanism. There is.

The ground freezing method of the present invention is a ground freezing method using carbon dioxide (CO ₂ ) as the secondary refrigerant of the freezing pipe (1) that takes heat of the object to be frozen.
A step of supplying a drying gas into a freezing tube (1) that circulates carbon dioxide as a secondary refrigerant to remove water in the freezing tube is included.
It is characterized by including a step of circulating the secondary side refrigerant.

In the present invention
In the step of supplying a drying gas into the freezing tube (1) and removing the water content in the freezing tube (1).
The step of measuring the dew point temperature of the drying gas and
It is preferable to have a step of determining whether or not the water content in the freezing tube (1) has been removed based on the measured dew point temperature.

In the present invention, it is preferable to use (dried) air as the drying gas supplied into the freezing tube (1) that circulates carbon dioxide, which is the refrigerant.

Further, in the present invention, the steps for measuring the dew point temperature include the step for measuring the dew point temperature of the drying gas (for example, air) supplied into the freezing tube (1) and the drying discharged from the freezing tube (1). It has a process to measure the dew point temperature of the gas.
In the step of determining whether or not the water in the freezing tube (1) has been removed, the dew point temperature of the drying gas discharged from the freezing tube (1) is supplied to the freezing tube (1). It is preferable to have a step of determining that the moisture in the freezing tube (1) has been removed (dried) when the temperature becomes equal to the dew point temperature of.
Alternatively, in the present invention, the step of measuring the dew point temperature includes a step of measuring the dew point temperature of the drying gas discharged from the freezing tube (1).
In the step of determining whether or not the water in the freezing tube (1) has been removed, the measured dew point temperature of the drying gas discharged from the freezing tube (1) is set to a predetermined temperature (for example, −70 ° C.) or less. It is preferable to have a step of determining that the water in the freezing tube (1) has been removed (dried) when the gas becomes dry.

In the present invention, the predetermined temperature is preferably set according to the atmospheric conditions (for example, temperature and humidity) at the site where the ground freezing method is applied.

The freezing tube drying mechanism (10) used in the ground freezing method of the present invention is
In the freezing pipe drying mechanism (10) that dries the inside of the freezing pipe (1) used in the ground freezing method using carbon dioxide (CO ₂ ) as the secondary refrigerant of the freezing pipe (1) that takes heat of the object to be frozen.
A supply device (2: for example, a compressor) that compresses and discharges the drying gas,
A drying device (3: for example, a refrigerating air dryer 3A and an adsorption type air dryer 3B) for drying the drying gas discharged by the supply device (2).
A first dew point temperature measuring device (4) for measuring the dew point temperature of the dried drying gas discharged from the drying device (3), and a dew point temperature measuring device (4).
It is characterized by being provided with a second dew point temperature measuring device (9) for measuring the dew point temperature of the drying gas (drying gas after flowing in the freezing tube 1) discharged from the freezing tube to be dried. There is.

In the freezing tube drying mechanism (10) used in the ground freezing method of the present invention, the supply device (2) that compresses and discharges the drying gas and the drying gas discharged by the supply device (2) are dried. The device specifications of the drying device (3) are preferably determined at a predetermined temperature set by the atmospheric conditions at the site where the ground freezing method is applied.

The ground freezing method in the present invention uses liquefied carbon dioxide as the secondary refrigerant, compresses the carbon dioxide to about 1 MPa with a refrigerator, and circulates the liquefied secondary refrigerant at about −45 ° C. in a freezing pipe. The subject is frozen by removing heat from the subject to be frozen using latent heat and / or latent heat that vaporizes liquefied carbon dioxide.

In carrying out the present invention, the freezing tube (1) is a member (so-called microchannel) having a flat shape as a whole and having a plurality of rows of fine flow paths inside, and other types. It includes pipes, pipes (5) and (7) for connecting freezing pipes, and joint portions connecting them.
In the present specification, the term "freezing pipe" is used to include all piping systems in a region where a carbon dioxide (CO ₂ ) refrigerant, which is a secondary refrigerant, flows. However, the refrigerator (drying device) is not included in the "freezing tube".
Further, the "moisture in the freezing tube" includes not only the moisture in the state of dew condensation in the freezing tube but also the moisture existing as water vapor in the freezing tube.

According to the present invention having the above-mentioned configuration, in the ground freezing method using CO ₂ as a circulating refrigerant (secondary side refrigerant) for freezing the ground, the water content in the freezing pipe (1) that takes heat of the object to be frozen is efficiently used. Can be removed as a target.
Therefore, CO ₂ is selected as the secondary side refrigerant, and the pipe diameter of the freezing pipe (1) is made smaller to reduce the flow rate of the secondary side refrigerant as compared with the conventional freezing pipe that circulates brine as the secondary side refrigerant. Even so, when the refrigerant (CO ₂ ) is passed through the freezing tube (1) and circulated, the inside of the freezing tube (1) is dry and the water inside is removed, so that the inside of the freezing tube (1) is removed. It prevents the water from freezing and blocking.
Further, whether or not the drying gas is supplied into the freezing tube (1) and the dew point temperature of the drying gas is measured to remove the water in the freezing tube (1) (whether or not the freezing tube 1 is dried). Since the determination is made, it is possible to prevent the inconvenience of stopping the drying work even if water remains in the freezing tube (1) and the inconvenience of continuing the drying work more than necessary.
The freezing pipe (1) used in the ground freezing method has a total length of several meters to several hundreds of meters, but the drying gas is used without exposing the inner surface of the pipe in order to confirm the dry state at the intermediate position. The dew point temperature of the supply port and the discharge port can be used to determine the water removal of the entire length of the freezing pipe (1). That is, it is possible to avoid the risk of water being mixed again because the inner surface of the pipe is exposed at the intermediate position. Further, it can be determined that the entire length of the section to be dried can be dried or dried regardless of the position of the water and the distribution of the concentration such as where the water is accumulated in the total length of the freezing tube (1).
Here, the dew point temperature means the temperature at which condensation, that is, dew condensation starts when a gas containing water vapor is cooled, and the water vapor pressure is calculated by directly measuring with a dew point thermometer or by obtaining the water vapor pressure from the temperature and relative humidity. It can be obtained by determining the temperature to be the saturated water vapor pressure.

In the present invention, whether or not the water in the freezing tube (1) has been removed is determined by drying in which the dew point temperature of the drying gas discharged from the freezing tube (1) is supplied into the freezing tube (1). When it becomes equal to the dew point temperature of the gas, it is judged that the water in the freezing tube (1) has been removed, or the measured dew point temperature of the drying gas discharged from the freezing tube has fallen below the predetermined temperature. Since it is judged that the moisture in the freezing tube (1) has been removed at that time, the moisture in the freezing tube (1) is an objective numerical value of the dew point temperature under the condition that the inside of the freezing tube (1) is too long to be visually recognized. Can be determined to have been removed.

In the present invention, air can be used as the drying gas as the drying gas required for drying the freezing tube (1). If air is used, it may be supplied from the atmosphere into the freezing pipe (1) using a device such as a compressor (2), and it is not necessary to bring a nitrogen gas cylinder or the like to the construction site.
Since the flow rate of the drying gas supplied into the freezing tube (1) can be increased, the working time of the freezing tube drying work is particularly long even when a large amount of water is present in the freezing tube (1). It is prevented from becoming long. In addition, since it is not necessary to cut the cylinder as in the case of using nitrogen gas, the work time of the cutting work is reduced. Further, as in the case of nitrogen gas, even if a large amount of drying gas is injected at the construction site (for example, in the mine), it is possible to prevent the construction site from becoming oxygen deficient.

In the present invention, the predetermined temperature for determining that the water in the freezing pipe (1) has been removed is set according to the atmospheric conditions at the site where the ground freezing method is applied. The atmosphere condition at the site where the ground freezing method is applied refers to the temperature and humidity of the site space where the freezing pipe (1) is installed and the moisture in the freezing pipe (1) is removed. The construction site of the ground freezing method is carried out regardless of the location of the open-air ground or underground space, spring, summer, autumn and winter seasons. Therefore, the temperature and humidity environment of this construction site varies, and the dew point temperature takes into consideration these temperature and humidity conditions, such as under the high temperature of the open air in midsummer, the low temperature of the open air in midwinter, or in the dry open air or in a wet tunnel mine. By setting a predetermined temperature which is the threshold value of, efficient drying can be performed.

It is explanatory drawing which shows the outline of the Embodiment of this invention. It is a block diagram which shows the detail of the freezing tube drying mechanism used in an embodiment. It is a flowchart which shows the freezing tube drying procedure in an embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
First, with reference to FIG. 1, the outline of the ground freezing method for selecting carbon dioxide (CO ₂ ) as the secondary refrigerant will be described.
The present invention is limited to the ground freezing method using CO ₂ as the secondary refrigerant. Although the case where ammonia (NH ₃ ) is used as the primary side refrigerant of the cooling device 20 is exemplified, it is not intended to limit the primary side refrigerant.
The system shown in FIG. 1 includes a cooling device 20 for cooling and liquefying CO ₂ which is a secondary refrigerant and supplying it to the freezing pipe 1, and a refrigerant circulation pump 30. The cooling device 20 includes a CO ₂ liquefier 11 (carbon dioxide liquefier), a condenser 12, and a cooling tower 13. Then, a freezing pipe 1 is arranged in the ground G as an object to be frozen, and liquefied carbon dioxide (liquefied CO ₂ ) which is a secondary side refrigerant is circulated in the freezing pipe 1 to be used as a secondary side refrigerant. A certain CO ₂ absorbs sensible heat and latent heat of vaporization from the ground G and freezes the ground G. In FIG. 1, arrow A indicates the flow of CO ₂ which is a secondary refrigerant.

CO ₂ (gas-liquid mixed state) that has absorbed sensible heat and latent heat of vaporization from the ground G when circulating in the freezing pipe 1 in the ground is liquefied by heat exchange in the CO ₂ liquefier 11 of the cooling device 20. As liquefied CO ₂ , it circulates again in the freezing pipe 1 in the ground G (in the ground).
In the CO ₂ liquefier 11, the primary side refrigerant NH ₃ (natural refrigerant) into which the latent heat of vaporization and the sensible heat taken from the ground by the secondary side refrigerant CO ₂ is input expands and vaporizes. The evaporated and expanded primary side refrigerant NH ₃ exchanges heat with water in the condenser 12, and is liquefied and condensed. The water heated by exchanging heat with the primary side refrigerant NH ₃ is cooled by the cooling tower 13, and the heat input from the temporary side refrigerant NH ₃ is dissipated. That is, the latent heat of vaporization and sensible heat input from the ground G into the secondary refrigerant CO ₂ are passed through the secondary refrigerant CO ₂ , the CO ₂ liquefier 11, the primary refrigerant NH ₃ , the condenser 12, and water. , The heat is dissipated in the cooling tower 13.
Reference numeral 14 in the cooling device is a compressor that circulates the primary side refrigerant NH ₃ .

In the illustrated embodiment, since the refrigerant on the secondary side is carbon dioxide CO ₂ , the diameter of the freezing tube 1 can be made smaller than that in the case where brine is used as the refrigerant in the prior art.
Although not clearly shown in FIG. 1, the freezing tube 1 on the secondary side has a flat shape as a whole and has a plurality of rows of fine flow paths formed inside. For example, "microchannel" can be used, and other types of pipes can be used as freezing pipes, and pipes for connecting freezing pipes can also be used.

When carbon dioxide CO ₂ is selected as the secondary side refrigerant, the pipe diameter of the freezing pipe 1 can be reduced, but the pipe diameter of the freezing pipe is small, and the secondary side refrigerant is carbon dioxide CO ₂ . Therefore, when the secondary side refrigerant CO ₂ is flowed through the freezing pipe 1, there is a possibility that the water content in the freezing pipe 1 freezes and closes the freezing pipe. In order to prevent such a situation, it is necessary to dry the inside of the freezing pipe 1 to remove water from the inside of the freezing pipe 1 before flowing the secondary side refrigerant CO ₂ into the freezing pipe 1.
In FIG. 1, the freezing tube drying mechanism 10 is connectable and removable to the freezing tube 1, and the freezing tube drying mechanism 10 is connected to the freezing tube 1 before flowing the secondary side refrigerant CO ₂ into the freezing tube 1. It has the function of drying the inside and removing water. Then, as shown in FIG. 1, the freezing pipe drying mechanism 10 is provided in, for example, in a region where the secondary refrigerant is input to the ground G to be frozen and a region where the secondary refrigerant is discharged from the target ground G to be frozen. , Connected to the freezing tube 1.
In FIG. 1, the freezing tube 1 and the freezing tube drying mechanism 10 describe a circulating drying gas in a closed system, but are also used in an open system.

The freezing tube drying mechanism 10 of FIG. 1 will be further described with reference to FIG.
In FIG. 2, the freezing tube drying mechanism 10 includes a compressor 2 (gas supply device) and a drying device 3, and the drying device 3 has a refrigerating air dryer 3A and an adsorption air dryer 3B.
Further, the freezing tube drying mechanism 10 includes a drying gas supply pipe 5 that supplies the drying gas to the freezing pipe 1, a drying gas discharge pipe 7 that discharges the drying gas after flowing through the freezing pipe 1, and a drying gas. It has a first dew point temperature measuring device 4 arranged in the supply pipe 5, and a second dew point temperature measuring device 9 arranged in the vicinity of the open air side end portion 7A of the drying gas discharge pipe 7.

The compressor 2 takes in the drying gas, compresses it, and supplies the compressed drying gas to the refrigerating air dryer 3A via the pipe P1.
The refrigerating air dryer 3A cools the compression drying gas supplied from the compressor 2 to, for example, −70 ° C. or lower using a refrigerator, and the moisture contained in the drying gas due to the difference in the amount of saturated water vapor. Is separated, removed and dried. The drying gas dried by the refrigerating air dryer 3A is supplied to the adsorption air dryer 3B via the pipe P2.
In the adsorption type air dryer 3B, the water remaining in the drying gas dried by the refrigerating air dryer 3A is adsorbed on a desiccant (for example, silica gel) or the like to further dry (the drying gas).
In the illustrated embodiment, the refrigerating air dryer 3A and the adsorption air dryer 3B are used in combination to dry the drying gas discharged from the compressor 2 in two stages, thereby improving the drying effect.

When a gas other than air is used as the drying gas, such as nitrogen gas N ₂ , the type of gas stored in the cylinder is selected as the drying gas, and the flow rate of the drying gas (N ₂ ) supplied from the cylinder. If there is a lot of water in the freezing tube, it takes a long time to dry in the freezing tube. In addition, since it is essential to cut and connect the cylinders, extra time is required.
Further, when a large amount of nitrogen gas is injected at the construction site (for example, in the mine) of the drying work, there is a possibility that the construction site (inside the premises) becomes oxygen deficient. Therefore, it is desirable to select air as the drying gas, which can be continuously supplied in large quantities by the compressor and has no risk of oxygen deficiency at the construction site.

In FIG. 2, the discharge port of the adsorption type air dryer 3B of the drying device 3 communicates with the drying gas supply pipe 5, and the other end of the drying gas supply pipe 5 is connected via the first connecting device 6. It communicates with the drying gas supply side end 1A of the freezing tube 1.
Further, the drying gas after flowing through the freezing pipe 1 is discharged from the discharge side end portion 1B of the freezing pipe 1. The discharged drying gas (drying gas after flowing through the freezing pipe 1) flows through the drying gas discharge pipe 7 via the second connecting device 8. The other end 7A of the drying gas discharge pipe 7 (the end opposite to the freezing pipe 1 connection side) is open to the atmosphere. In the illustrated embodiment, the mechanism for removing the water content in the freezing tube 1 by the open system is described for the drying gas, but a mechanism by a closed system is also possible. When air is used as the drying gas, an open system may be applied, and when another nitrogen gas _N2 or the like is used, a closed system may be applied.
Here, as the first and second connecting devices 6 and 8, conventionally known connectors for connecting air pipes can be used.

A first dew point temperature measuring device 4 (dew point thermometer) is provided in the vicinity of the discharge port of the adsorption type air dryer 3B in the drying gas supply pipe 5. The first dew point temperature measuring device 4 has a function of measuring the dew point temperature of the dried drying gas (drying gas supplied into the freezing tube 1) discharged from the adsorption type air dryer 3B. ..
Further, a second dew point temperature measuring device 9 (dew point thermometer) is provided in the vicinity of the atmosphere open side end portion 7A of the drying gas discharge pipe 7. The second dew point temperature measuring device 9 (dew point thermometer) has a function of measuring the dew point temperature of the discharged drying gas (drying gas discharged through the freezing tube 1).
The drying gas supply pipe 5 is provided with an air volume meter 15 for measuring the amount of drying gas supplied into the freezing pipe 1, and the measurement result by the air volume meter 15 is a control device for supplying the drying gas (not shown). It is transmitted to and used for the control described later related to the gas supply for drying.
Although not clearly shown, the compressor 2 of the freezing tube drying mechanism 10, the drying device 3 (refrigerating air dryer 3A, adsorption type air dryer 3B), the drying gas supply pipe 5, and the drying gas discharge pipe 7 are ground-frozen. It is fixed to the equipment placement structure 40 installed at the construction site of the construction method.

When removing the moisture in the freezing tube 1 and drying it, the compressor 2 of the freezing tube drying mechanism 10 and the drying device 3 (refrigerating air dryer 3A, adsorption air dryer 3B) are driven to generate a drying gas. do.
The generated drying gas is discharged from the adsorption type air dryer 3B, and is continuously supplied into the freezing pipe 1 via the drying gas supply pipe 5 and the first connecting device 6. The drying gas supplied to the freezing pipe 1 flows through the freezing pipe 1 and then passes through the second connecting device 8 and the drying gas discharge pipe 7, and is at the end of the drying gas discharge pipe 7 on the open side to the atmosphere. It diffuses into the atmosphere from part 7A. In FIG. 2, the direction in which the drying gas flows is indicated by an arrow B.
When the drying gas flows in the freezing tube 1, the water in the freezing tube 1 is removed and the inside of the freezing tube 1 is dried.

Whether or not the water in the freezing tube 1 has been removed (whether or not the inside of the freezing tube 1 has dried) is determined based on the measurement results of the first dew point thermometer 4 and the measurement results of the second dew point thermometer 9. is doing.
The dew point temperature of the dried drying gas (drying gas supplied into the freezing tube 1) discharged from the drying device 3 (adsorption type air dryer 3B) is set in the freezing tube 1 depending on the atmospheric conditions of the place of construction. Since the dew point temperature of the drying gas to be supplied is set by the drying device 3, the environment on the drying device 3 side is constant and does not change.
In the illustrated embodiment, when the measurement is performed by the first dew point thermometer 4, the measurement is performed in the region immediately after the drying gas is discharged from the adsorption type air dryer 3B. However, when the dew point temperature is measured by the first dew point thermometer 4, it is not limited to the region immediately after the drying gas is discharged from the adsorption type air dryer 3B, and the drying gas supply pipe 5 is used. The first dew point thermometer 4 may be provided in other regions.
When measuring the dew point temperature of the drying gas (drying gas discharged from the freezing pipe 1) after flowing through the freezing pipe 1 with the second dew point thermometer 9, for example, the atmosphere of the drying gas discharge pipe 7 It is preferable to provide a second dew point thermometer 9 in the vicinity of the open side end portion 7A.

As is well known, there is a correlation (at the same temperature) between the dew point temperature and the degree of dryness of the drying gas (for example, air). The gas is dry.
When drying the freezing tube 1, when the dew point temperature of the drying gas discharged from the freezing tube 1 becomes equal to or lower than the predetermined temperature, the ground is set as the predetermined temperature when it is determined that the water in the freezing tube 1 has been removed. Target dew point temperature (for example, -40 ° C to-) of the drying gas based on the atmospheric conditions (temperature, humidity), construction results, etc. at the place where the freezing method is carried out or the place where the drying inside the freezing pipe used for the ground freezing method is carried out. A predetermined temperature is set as 70 ° C.), and it is determined that the water content in the freezing tube 1 has been removed.
Further, by setting a predetermined temperature as the target dew point temperature, the specifications of the drying device 3 (refrigerating air dryer 3A, adsorption air dryer 3B) and the compressor (supply device) 2 are determined in accordance with the predetermined temperature. More efficient drying can be carried out.

When the freezing tube drying mechanism 10 is driven to allow the drying gas to flow through the freezing tube 1 and the freezing tube 1 is gradually dried, the dew point temperature in the freezing tube 1 gradually decreases accordingly.
The dew point temperature of the drying gas discharged from the freezing tube 1 measured by the second dew point thermometer 9 is the dew point of the drying gas supplied into the freezing tube 1 measured by the first dew point thermometer 4. When it becomes equal to the temperature, the dew point temperature of the drying gas in the freezing tube 1 reaches the target dew point temperature, and it can be determined that "drying is completed".
Alternatively, when the dew point temperature of the drying gas discharged from the freezing tube 1 measured by the second dew point thermometer 9 becomes the target dew point temperature (for example, −70 ° C.) or less, “drying is completed. It can be judged. In this case, it is not always necessary to arrange the first dew point thermometer 4 in the region on the drying gas supply side.

Next, with reference to FIG. 3, a procedure for removing (drying) the water content in the freezing pipe 1 used in the ground freezing method will be described in the illustrated embodiment.
In the flowchart of FIG. 3, in steps S1 to S5, the compressor 2 (supply device), the refrigerating air dryer 3A, and the adsorption type air dryer 3B (drying device 3) in the freezing tube drying mechanism 10 are selected, and their respective specifications are determined. Regarding the work to be done. Then, steps S6 to S11 relate to the work of drying the inside of the freezing tube 1 by the freezing tube drying mechanism 10.
In step S1, the volume of the freezing tube 1 is calculated by a conventionally known method.
In step S2, the number of days for drying the freezing pipe 1 is determined with reference to the volume of the freezing pipe 1 calculated in step S1 as needed, based on the entire process of the ground freezing work.

In step S3, the capacity of the compressor 2 is calculated and determined based on the volume of the freezing tube 1 calculated in step S1 and the number of drying days determined in step S2.
In the next step S4, the target dew point temperature of the drying gas supplied to the freezing tube 1 is set.
The target dew point temperature is used to determine that the moisture in the freezing tube 1 has been removed, is used as the dew point temperature set by the drying device 3, and is below a predetermined temperature when the moisture in the freezing tube 1 is removed. It is also used as a control value to judge that.
The target dew point temperature is set based on the atmospheric conditions such as temperature and humidity, with reference to past construction results or experimental verification results.
In the inventor's experiment, the atmospheric pressure of each atmosphere was found in the drying work in the low temperature, medium and low humidity underground space in winter, and the freezing tube drying work in the outdoor atmosphere condition of high temperature and high humidity in summer. The dew point temperature was determined and the target dew point temperature was set to −40 to −70 ° C., and good drying results were obtained.
Considering the actual drying work space atmosphere conditions, the target dew point temperature may be approximately −40 ° C. to −70 ° C.
In step S5, the specifications of the refrigerating air dryer 3A and the adsorption air dryer 3B are determined with reference to the target dew point temperature set in step S4. Then, the process proceeds to step S6.
Here, the dew point temperature list can be suitably used when setting the target dew point temperature in steps S4 and S5 and determining the specifications of the refrigerating air dryer 3A and the adsorption type air dryer 3B. The dew point temperature list can be created from existing numerical values (for example, the saturated vapor pressure of water in "JIS Z 8806 Humidity-Measuring Method").

In step S6, the compressor 2 of the freezing tube drying mechanism 10 and the drying device 3 (refrigerating air dryer 3A, adsorption type air dryer 3B) are driven, and the drying gas is continuously blown (supplied) to the freezing tube 1. .. Then, the process proceeds to step S7.
In step S7, the dew points on the inlet side (the side that supplies the drying gas into the freezing tube 1) and the outlet side (the side where the drying gas that has passed through the freezing tube 1 is discharged) of the freezing tube 1 of the drying gas. Measure the temperature.
The dew point temperature on the inlet side of the freezing tube 1 of the drying gas is measured by the first dew point thermometer 4 arranged near the discharge port of the adsorption type air dryer 3B, and is measured on the outlet side of the freezing tube 1 of the drying gas. The dew point temperature of the above is measured by a second dew point thermometer 9 arranged in the vicinity of the end portion 7A on the open side to the atmosphere in the drying gas discharge pipe 7.
The measurement of the dew point temperature by the first dew point thermometer 4 may be performed only once, for example, at the initial stage of supplying the drying gas. The drying gas whose dew point temperature is measured by the first dew point thermometer 4 is cooled by the refrigerating air dryer 3A and the adsorption type air dryer 3B and dried, so that most of the time while the freezing tube 1 is dried. This is because it does not fluctuate. However, while the freezing tube 1 is being dried, the dew point temperature of the drying gas can be continuously measured by the first dew point thermometer 4.
The dew point temperature of the air discharged from the freezing tube 1 is measured by the second dew point thermometer 9 continuously while the drying gas is supplied into the freezing tube 1.

In the next step S8, the dew point temperature measured by the first dew point thermometer 4, that is, the dew point temperature of the drying gas supplied to the freezing tube 1, and the dew point temperature measured by the second dew point thermometer 9, that is, , The dew point temperature of the drying gas discharged from the freezing tube 1 is compared.
The dew point temperature of the drying gas supplied to the freezing tube 1 (the dew point temperature measured by the first dew point thermometer 4) and the dew point temperature of the drying gas discharged from the freezing tube 1 (the second dew point thermometer 9). If the dew point temperature measured by the above (step S8 is “Yes”) is equal (step S8 is “Yes”), it is determined that the water content in the freezing tube 1 is sufficiently removed and “drying of the freezing tube 1 is completed”. Then, the process proceeds to step S10.

On the other hand, the dew point temperature of the drying gas supplied to the freezing tube 1 (the dew point temperature measured by the first dew point thermometer 4) and the dew point temperature of the drying gas discharged from the freezing tube 1 (the second dew point temperature). When the dew point temperature measured by the total 9 is not equal (step S8 is "No"), that is, the dew point temperature measured by the second dew point thermometer is higher than the dew point temperature measured by the first dew point thermometer. Determines that "the inside of the freezing tube 1 is not dry" because the water content in the freezing tube 1 is not sufficiently removed. Then, the process proceeds to step S9.
Here, the dew point temperature of the drying gas supplied to the freezing tube 1 (the dew point temperature measured by the first dew point thermometer 4) and the dew point temperature of the drying gas discharged from the freezing tube 1 (the second dew point). It is determined whether or not the water content in the freezing tube 1 is sufficiently removed, that is, whether or not the drying of the freezing tube 1 is completed, in an manner other than comparing with the dew point temperature measured by the thermometer 9. Can be done.
For example, the dew point temperature of the drying gas discharged from the freezing tube 1 (the dew point temperature measured by the second dew point thermometer 9) is compared with a predetermined target dew point temperature (for example, −70 ° C.), and the freezing tube 1 It is also possible to determine that "drying of the freezing tube 1 is completed" when the dew point temperature of the drying gas discharged from the above becomes equal to or lower than a predetermined target dew point temperature. As described above, when the control is performed in such an embodiment, the step of measuring the dew point temperature by the first dew point thermometer 4 can be omitted.
In the case of control for comparing the dew point temperature of the drying gas discharged from the freezing tube 1 with the predetermined target dew point temperature, the dew point temperature of the drying gas discharged from the freezing tube 1 and the predetermined target dew point temperature should be equal to each other. For example, in step S8, it is determined that the freezing tube 1 is "dried".

In step S9, the measurement result of the first dew point thermometer 4 (the dew point temperature of the drying gas supplied into the freezing tube 1) and the measurement result of the second dew point thermometer 9 (discharged from the freezing tube 1). Dew point temperature of the drying gas) and the time (elapsed time) spent on the drying work up to that point are referred to to determine whether the work to dry the inside of the freezing tube 1 is proceeding as planned. do.
In the determination in step S9, for example, the measurement result of the second dew point thermometer 9 (the dew point temperature of the drying gas discharged from the freezing tube 1) is the measurement result of the first dew point thermometer 4 (inside the freezing tube 1). If the speed of approaching the dew point temperature of the drying gas supplied to the freezing tube 1 is later than planned, it is determined that the work of drying the inside of the freezing tube 1 is not proceeding as planned.
The mode of comparing the dew point temperature of the drying gas discharged from the freezing tube 1 (the dew point temperature measured by the second dew point thermometer 9) and the predetermined target dew point temperature (for example, −70 ° C.) is controlled. In this case, in step S9, the dew point temperature of the drying gas discharged from the freezing tube 1, the predetermined target dew point temperature, the time spent in the drying work up to that point (elapsed time), and the like are referred to. , It is determined whether or not the work of drying the inside of the freezing tube 1 is proceeding as planned.

As a result of the determination in step S9, if the work of drying the inside of the freezing tube 1 is proceeding as planned (step S9 is "Yes"), the process returns to step S6, the compressor 2, the refrigerating air dryer 3A, and the adsorption type. The drying gas is blown (supplied) to the freezing tube 1 without changing the specifications of the air dryer 3B.
On the other hand, as a result of the determination in step S9, if the work of drying the inside of the freezing tube 1 is not proceeding as planned (step S9 is "No"), the process returns to step S3 and the compressor 2 of the freezing tube drying mechanism 10 or The specifications of the drying device 3 will be reviewed and changed as necessary. Then, step S4 or less is executed to blow (supply) the drying gas to the freezing tube 1.

In step S10, since it is determined in step S8 that the freezing tube 1 has been "dried", the blowing of the drying gas to the freezing tube 1 is stopped.
Then, the process proceeds to step S11, and the inside of the freezing pipe 1 and other pipes (drying gas supply pipe, drying gas discharge pipe) are evacuated to remove the filled drying gas. Evacuation is performed in a conventionally known manner using a conventionally known device.
When step S11 is completed, the work of removing the water in the freezing pipe 1 and drying it is also completed. Therefore, the work of circulating the secondary refrigerant CO ₂ in the freezing pipe 1 and starting the work of freezing the ground can be started. I can.

According to the illustrated embodiment, in the ground freezing method using carbon dioxide CO ₂ as the secondary refrigerant, the inside of the freezing pipe 1 can be efficiently dried by the freezing pipe drying mechanism 10.
Therefore, even if the diameter of the freezing pipe 1 through which the secondary side refrigerant CO ₂ circulates is reduced, or even if the secondary side refrigerant CO ₂ flows through the freezing pipe 1, the inside of the freezing pipe 1 is dry and inside. Since the water content of the above is removed, it is possible to prevent the water content from freezing and clogging in the freezing tube 1.

In the illustrated embodiment, the dew point temperature of the drying gas supplied into the freezing tube 1 is measured by the first dew point thermometer 4, and the dew point temperature of the drying gas discharged from the freezing tube 1 is the second dew point. When the measurement result of the second dew point thermometer 9 becomes equal to the measurement result of the first dew point thermometer, the water content in the freezing tube 1 is removed and the freezing tube 1 is dried. I have decided. Alternatively, when the dew point temperature of the drying gas discharged from the freezing tube 1 becomes equal to the predetermined target dew point temperature, it is determined that the freezing tube 1 has dried.
Therefore, it is possible to easily and accurately determine whether or not water remains in the freezing tube 1, so that the drying work is stopped with the water remaining, or the drying work is continued more than necessary. The inconvenience of getting rid of it is prevented.

Further, according to the illustrated embodiment, as the drying gas required for drying the freezing tube 1, the air in the work space is dried and used as the drying gas. Since air can be taken in from the atmosphere by the compressor 2, a cylinder like nitrogen gas is not required. Therefore, the cylinder cutting work is not required, and it is easy to increase the flow rate of the drying gas (air) supplied into the freezing tube 1 especially when a large amount of water is present in the freezing tube 1. ..
Further, since there is no need to cut and join the cylinder, the work time of the cutting and joining work is reduced.
Further, if the drying gas is air, even if a large amount of the drying gas is sprayed at the construction site (for example, in the mine), it is possible to prevent the construction site from becoming oxygen deficient.

Further, when the drying gas supplied to the freezing tube 1 is dried, the refrigerating air dryer 3A and the adsorption type air dryer 3B are used in combination as the drying device 3, and the drying gas discharged from the compressor 2 is dried in two steps. Therefore, the compressed drying gas protruding from the compressor 2 can be dried to a required degree.
In addition to that, when the work of drying the inside of the freezing tube 1 is performed, it is confirmed whether or not the work is proceeding as planned (step S9 in FIG. 3), and if the work is not progressing as planned, the freezing tube is dried. Since the specifications of the equipment (compressor 2, drying device 3) and others constituting the mechanism 10 are reviewed, the drying operation of the freezing tube 1 can be performed efficiently and reliably.

It should be added that the illustrated embodiment is merely an example and is not a description intended to limit the technical scope of the present invention.

1 ... Freezing tube 2 ... Compressor (supply device)
3 ... Drying device 3A ... Refrigerating air dryer 3B ... Adsorption type air dryer 4 ... First dew point thermometer (first dew point temperature measuring device)
5 ... Drying gas supply pipe 6 ... First connecting device (connector)
7 ... Drying gas discharge pipe 8 ... Second connection device (connector)
9 ... Second dew point thermometer (second dew point temperature measuring device)
10 ... Freezing tube drying mechanism

Claims (8)

In the ground freezing method that uses carbon dioxide as the secondary refrigerant of the freezing pipe that takes away the heat of the object to be frozen.
A step of supplying a drying gas into a freezing tube that circulates carbon dioxide, which is a secondary refrigerant, to remove water in the freezing tube is included.
A ground freezing method comprising a step of circulating the secondary refrigerant. In the step of supplying a drying gas into the freezing tube and removing water in the freezing tube,
The step of measuring the dew point temperature of the drying gas and
The ground freezing method according to claim 1, which comprises a step of determining whether or not the water in the freezing tube has been removed based on the measured dew point temperature. The ground freezing method according to any one of claims 1 and 2, wherein air is used as the drying gas supplied into the freezing pipe. The step of measuring the dew point temperature is
The process of measuring the dew point temperature of the drying gas supplied in the freezing tube,
It has a process of measuring the dew point temperature of the drying gas discharged from the freezing tube.
In the step of determining whether or not the water in the freezing tube has been removed, the inside of the freezing tube is in the freezing tube when the dew point temperature of the drying gas discharged from the freezing tube becomes equal to the dew point temperature of the drying gas supplied in the freezing tube. The ground freezing method according to claim 2 , which comprises a step of determining that the water content of the above has been removed. The step of measuring the dew point temperature is
It has a process of measuring the dew point temperature of the drying gas discharged from the freezing tube.
In the step of determining whether or not the moisture in the freezing tube has been removed, it is determined that the moisture in the freezing tube has been removed when the measured dew point temperature of the drying gas discharged from the freezing tube becomes equal to or lower than a predetermined temperature. The ground freezing method according to claim 2 , which has a step of performing. The ground freezing method according to claim 5, wherein the predetermined temperature is set according to the atmospheric conditions at the site where the ground freezing method is applied. In the mechanism for drying the inside of the freezing pipe used in the ground freezing method that uses carbon dioxide as the secondary refrigerant of the freezing pipe that takes away the heat of the object to be frozen.
A supply device that compresses and discharges the drying gas,
A drying device that dries the drying gas discharged by the supply device,
A first dew point temperature measuring device for measuring the dew point temperature of the dried drying gas discharged from the drying device, and a dew point temperature measuring device.
A freezing tube drying mechanism comprising a second dew point temperature measuring device for measuring the dew point temperature of the drying gas discharged from the freezing tube to be dried. The supply device that compresses and discharges the drying gas, and
The device specifications of the drying device that dries the drying gas discharged by the supply device,
The freezing pipe drying mechanism according to claim 7, which is determined at a predetermined temperature set by the atmospheric conditions at the site where the ground freezing method is applied.

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