Liquid nitrogen freezing device based on liquid nitrogen gravity and air pressure driving and construction method

Abstract

The invention discloses a liquid nitrogen freezing device based on liquid nitrogen gravity and air pressure driving and a construction method. The liquid nitrogen freezing device comprises a freezing outer pipe, a liquid supply pipe and a suspended fan device, wherein the liquid supply pipe is arranged in the freezing outer pipe in a sleeved mode, the bottom end of the liquid supply pipe is closed, and the suspended fan device is arranged in the freezing outer pipe and located at the tail end of the liquid supply pipe. A plurality of open holes are symmetrically formed in the liquid supply pipe along the pipe wall at equal intervals, the suspended fan device comprises a rolling shaft rotationally connected to the liquid supply pipe and a plurality of conical fan blades sequentially arranged on the rolling shaft in the circumferential direction, and gaps exist between the conical fan blades. According to the liquid nitrogen freezing device, the hole is formed in the liquid supply pipe, the suspended fan device is installed, the structure of the freezing pipe is optimized, the temperature field in the pipe is rapidly balanced by accelerating flowing heat exchange of gas in the pipe, and the device is simple in structure and high in convenience and feasibility.

Description

Technical Field

[0001] The invention belongs to the technical field of liquid nitrogen freezing devices, and in particular relates to a liquid nitrogen freezing device driven by liquid nitrogen gravity and gas pressure and a construction method. Background Art

[0002] Artificial liquid nitrogen freezing technology refers to the arrangement of a certain number of freezing pipes in the soil that needs to be frozen and reinforced. The pipes can be set vertically or horizontally. The heat of the soil is absorbed by the liquid nitrogen in these freezing pipes, thereby reducing the temperature of the soil. Although liquid nitrogen freezing technology can quickly achieve water sealing, it is more expensive than other construction methods due to the large consumption of liquid nitrogen. In actual projects, about 1200 to 1500L of liquid nitrogen is consumed per cubic meter of frozen soil. Traditional liquid nitrogen freezing pipes usually consist of freezing outer pipes, liquid supply pipes and exhaust pipes. The boiling point of liquid nitrogen is -196℃. When liquid nitrogen enters the freezing pipe, the surrounding soil temperature is higher than its boiling point, and the liquid nitrogen quickly vaporizes and undergoes intense heat exchange. However, when using traditional freezing pipes, due to the limitations of the liquid supply pipe structure, there is a difference in the temperature of the upper and lower outer pipe walls of the freezing pipe, resulting in uneven freezing temperature of the surrounding soil, which in turn leads to inconsistent thickness of the freezing curtain, affecting the safety of construction.

[0003] Existing research and on-site temperature field measurements show that the bottom of the liquid supply pipe is usually the lowest temperature area in the entire pipeline during the freezing process because the liquid nitrogen flow rate is difficult to accurately control. A large amount of unvaporized liquid nitrogen accumulates at the bottom of the pipe, resulting in a significant difference in the freezing temperature of the soil at the end of the liquid supply pipe and the entrance. Since the supply flow rate to achieve full evaporation of liquid nitrogen is difficult to accurately control, the freezing efficiency of traditional freezing pipes in complex formations is low, and a large amount of liquid nitrogen is required to balance the soil temperature, which increases the freezing cost and time of the project. In order to reduce the construction cost of liquid nitrogen and improve the freezing efficiency, the freezing pipe device for artificial vertical freezing is improved.

[0004] Based on this, a new type of liquid nitrogen freezing device is studied and designed to achieve the average tube wall temperature to speed up the freezing efficiency and reduce the amount of liquid nitrogen, thereby improving the shortcomings of the existing technology. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a new type of liquid nitrogen freezing device, aiming to solve the problem of uneven temperature distribution on the wall of the existing liquid nitrogen freezing tube.

[0006] Technical solution: The present invention is a liquid nitrogen freezing device driven by liquid nitrogen gravity and gas pressure, which includes a freezing outer tube, a liquid supply tube sleeved in the freezing outer tube and sealed at the bottom, and a suspended fan device arranged in the freezing outer tube and located at the tail end of the liquid supply tube;

[0007] The liquid supply pipe is provided with a plurality of openings symmetrically and at equal intervals along the pipe wall. The suspended fan device comprises a rotating shaft rotatably connected to the liquid supply pipe, and a plurality of conical fan blades arranged in sequence along the circumferential direction on the rotating shaft, and gaps are provided between the plurality of conical fan blades.

[0008] The present invention opens a hole on the liquid supply pipe and arranges a suspended fan device at the tail end of the liquid supply pipe, so that the liquid nitrogen flowing out from the hole flushes the fan blades under the action of gravity to drive the fan blades to rotate; at the same time, the liquid nitrogen flows into the bottom of the pipe and accumulates and continuously vaporizes at the bottom of the pipe, forming an air pressure difference between the upper and lower pipes, and rises from the gap between the fan blades to drive the fan blades to rotate again, that is, the fan blades are rotated by means of self-gravity-air pressure coupling, and the heat exchange of gas flow in the pipe is accelerated to quickly balance the temperature field in the pipe.

[0009] Furthermore, the hanging fan device used in the liquid nitrogen freezing device also includes a bracket assembly for fixing and connecting the liquid supply pipe, and the bracket assembly is located below the plurality of hanging fan devices. Preferably, the bracket assembly includes a bracket block for fixing and connecting the liquid supply pipe and a plurality of protective wings arranged along the circumference of the bracket block. Furthermore, the plurality of conical fan blades used in the liquid nitrogen freezing device are a 5-leaf structure, arranged in a conical shape at an angle of 45°.

[0010] Furthermore, the liquid nitrogen freezing device also includes a liquid supply main pipe connected to the top end of the liquid supply pipe, and the liquid supply main pipe is provided with a flow meter and a control valve.

[0011] Furthermore, the top end of the outer freezing tube used in the liquid nitrogen freezing device is provided with an exhaust pipe.

[0012] The present invention is based on the construction method of the above-mentioned liquid nitrogen freezing device, comprising the following steps:

[0013] (1) After the liquid nitrogen freezing device is installed, a small amount of liquid nitrogen is introduced for pre-cooling. After the temperature in the tube is uniform, the liquid nitrogen supply is increased to start the normal freezing process. During the freezing process, the flow meter, the nitrogen temperature at the outlet of the exhaust pipe and the temperature of the temperature measuring tube are monitored in real time, and the three are combined to control the liquid nitrogen flow rate;

[0014] (2) Monitor the temperature of the temperature measuring tube at the end of freezing and wait for the surrounding soil temperature to stabilize to observe whether the freezing plan target has been achieved;

[0015] (3) After the freezing task is completed, the amount of liquid nitrogen introduced is gradually reduced to maintain the stable frozen soil stage, and construction begins according to the on-site construction plan;

[0016] (4) After the construction is completed, stop supplying liquid nitrogen and choose artificial thawing or natural thawing according to the on-site plan.

[0017] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: the liquid nitrogen freezing device optimizes the structure of the freezing pipe by opening a hole on the liquid supply pipe and installing a suspended fan device, and quickly balances the temperature field in the pipe by accelerating the heat exchange of gas flow in the pipe, and the device has a simple structure, high convenience and feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of the liquid nitrogen freezing device of the present invention;

[0019] Figure 2 It is a cross-sectional view of the structure of the suspended fan device;

[0020] Figure 3 This is a structural plan view of the suspended fan device. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0022] like Figure 1 As shown, the liquid nitrogen freezing device of the present invention comprises a freezing outer tube 1, a liquid supply tube 2 sleeved in the freezing outer tube 1, and the bottom end of the liquid supply tube 2 is closed, and a plurality of openings 3 are symmetrically arranged on the tube wall at equal intervals, that is, the liquid nitrogen flows out along the openings 4 during the freezing process, on the one hand, to ensure the uniformity of the temperature distribution of the tube wall of the freezing outer tube 1 and the soil around the tube, and on the other hand, to ensure that there is enough flow at the openings 4 to hydraulically drive the suspension fan device 3 arranged at the bottom end of the freezing outer tube 1 to rotate.

[0023] The suspended fan device 3 includes a rotating shaft 5 rotatably connected to the liquid supply pipe 2 and a plurality of blades 5 arranged in a conical shape at an angle of 45° along the circumferential direction, preferably 5 blades, and the blades are made of aluminum alloy. A plurality of blades 6 are arranged on the rotating shaft 5, and there are gaps between the plurality of blades 6, such as Figure 2 and Figure 3 As shown. In actual application, the liquid nitrogen flowing out from the opening 3 flushes the fan blade 6 under the action of gravity to drive it to rotate; at the same time, the liquid nitrogen flows into the bottom of the tube and accumulates and continuously vaporizes at the bottom of the tube, forming a pressure difference between the upper and lower tubes, and the vaporized liquid nitrogen passes through the gap to drive the fan blade 6 to rotate again, that is, continuous rotation is formed in the whole process, so as to accelerate the heat exchange of gas flow in the tube to quickly balance the temperature field in the tube.

[0024] The suspended fan device 3 also includes a bracket assembly 7 for protecting the fan blades 6 to reduce damage to the fan blade 6 structure during installation and transportation. The bracket assembly 7 includes a bracket block 8 for fixing the liquid supply pipe 2 and a plurality of protective wings 9 arranged circumferentially along the bracket block 8. The bracket block portion is made of ultra-low temperature resistant silicone rubber material to form an inlaid structure so that the tail end of the liquid supply pipe can be embedded to achieve a fixing effect. The protective wings 9 protect the fan blades 6, and the protective wings 9 are non-contacting with the fan blades 6, and the plurality of protective wings 9 do not hinder the dripping of liquid nitrogen and the rising of vaporized liquid nitrogen.

[0025] In addition to the above, the liquid nitrogen freezing device also includes a temperature detection system composed of a temperature measuring tube, a temperature sensor and a temperature recorder, a liquid supply main pipe 10 connected to the top of the liquid supply pipe 2, and the liquid supply main pipe 10 is provided with a flow meter 11 and a control valve 12. An exhaust pipe 13 is provided at the top of the freezing outer pipe 1. One end of the liquid supply main pipe 10 is connected to the drain valve of the liquid nitrogen tank, and the other end is connected to the liquid nitrogen distributor. Liquid nitrogen enters the liquid supply pipe 2 from the liquid nitrogen tank through the liquid supply main pipe 10 and the control valve 12, is discharged from the opening 4, flows through the suspended fan device 3 to drive it to operate, and finally absorbs the heat of the surrounding soil layer in the freezing outer pipe 1 and vaporizes. The nitrogen is discharged into the air through the exhaust pipe, thereby achieving the purpose of low-temperature rapid freezing of the soil. In order to prevent the loss of liquid nitrogen along the liquid supply main pipe 10 during the transportation process, the liquid supply main pipe 10 can be insulated with ceramic fiber insulation cotton.

[0026] The present invention is based on the above-mentioned liquid nitrogen freezing device, and its construction method comprises the following steps:

[0027] (1) According to the requirements of the project conditions, formulate a specific freezing pipe burial plan, including the number of freezing pipes to be buried, the burial distribution, the size and length of the freezing pipes, and the burial plan of the temperature measuring pipes.

[0028] (2) Prepare the corresponding liquid supply pipe and suspended fan device, and prepare the required pipe fittings and monitoring components.

[0029] (3) Each frozen pipe is buried in the predetermined position, and the liquid supply pipe and the suspended fan device are assembled and placed in each pipe; valves and flow meters are installed at each pipe head; at the same time, the temperature measuring pipe is buried according to the established plan, and the sensor component line is connected to the temperature recorder.

[0030] (4) Connect the liquid supply main pipe to the liquid nitrogen tank truck, and wrap the liquid supply main pipe with ceramic fiber insulation cotton for insulation treatment; check whether the components of each subsystem are installed correctly.

[0031] (5) Start freezing the predetermined freezing area. First, introduce a small amount of liquid nitrogen to pre-cool the pipe. After the temperature in the pipe is uniform, increase the liquid nitrogen flow rate to start freezing.

[0032] (6) During the freezing process, the flow meter, the nitrogen temperature at the exhaust pipe outlet, and the temperature of the temperature measuring tube are monitored in real time, and the three are combined to control the liquid nitrogen flow rate.

[0033] (7) At the end of freezing, monitor the temperature of the temperature measuring tube and wait until the temperature of the surrounding soil stabilizes to observe whether the freezing plan objectives have been achieved.

[0034] (8) After the freezing task is completed, the amount of liquid nitrogen introduced is gradually reduced to maintain the frozen soil in a stable stage, and construction is started according to the on-site construction plan.

[0035] (9) After the construction is completed, stop supplying liquid nitrogen and choose artificial thawing or natural thawing according to the on-site plan. Arrange and recycle the usable instruments, pipes and equipment.

Claims

1. A liquid nitrogen freezing device driven by liquid nitrogen gravity and gas pressure, characterized in that: The liquid nitrogen freezing device comprises a freezing outer tube (1), a liquid supply tube (2) which is sleeved inside the freezing outer tube (1) and has a closed bottom end, and a suspended fan device (3) which is arranged inside the freezing outer tube (1) and located at the rear end of the liquid supply tube (2); The liquid supply pipe (2) is provided with a plurality of openings (4) at equal intervals and symmetrically along the pipe wall. The suspended fan device (3) comprises a rotating shaft (5) rotatably connected to the liquid supply pipe (2) and a plurality of conical fan blades (6) arranged in sequence along the circumferential direction on the rotating shaft (5), and gaps are provided between the plurality of conical fan blades (6).

2. The liquid nitrogen freezing device driven by liquid nitrogen gravity and gas pressure according to claim 1, characterized in that: The suspended fan device (3) further comprises a bracket assembly (7) for fixedly connecting the liquid supply pipe (2); the bracket assembly (7) is located below the plurality of suspended fan devices (3).

3. The liquid nitrogen freezing device driven by liquid nitrogen gravity and gas pressure according to claim 1, characterized in that: The bracket assembly (7) comprises a bracket block (8) for fixedly connecting the liquid supply pipe (2) and a plurality of protective wings (9) arranged along the circumference of the bracket block (8).

4. The liquid nitrogen freezing device driven by liquid nitrogen gravity and gas pressure according to claim 1, characterized in that: The plurality of conical fan blades (5) are a five-blade structure and are arranged in a conical shape at an angle of 45°.

5. The liquid nitrogen freezing device driven by liquid nitrogen gravity and gas pressure according to claim 1, characterized in that: The liquid nitrogen freezing device also includes a liquid supply main pipe (10) connected to the top end of the liquid supply pipe (2), and a flow meter (11) and a control valve (12) are provided on the liquid supply main pipe (10).

6. The liquid nitrogen freezing device driven by liquid nitrogen gravity and gas pressure according to claim 1, characterized in that: An exhaust pipe (13) is provided at the top end of the freezing outer pipe (1).

7. A construction method based on the liquid nitrogen freezing device according to claim 1, characterized in that: The steps include: (1) After the liquid nitrogen freezing device is installed, a small amount of liquid nitrogen is introduced for pre-cooling. After the temperature in the tube is uniform, the liquid nitrogen supply is increased to start the normal freezing process. During the freezing process, the flow meter, the nitrogen temperature at the outlet of the exhaust pipe and the temperature of the temperature measuring tube are monitored in real time, and the three are combined to control the liquid nitrogen flow rate; (2) Monitor the temperature of the temperature measuring tube at the end of freezing and wait for the surrounding soil temperature to stabilize to observe whether the freezing plan target has been achieved; (3) After the freezing task is completed, the amount of liquid nitrogen introduced is gradually reduced to maintain the stable frozen soil stage, and construction begins according to the on-site construction plan; (4) After the construction is completed, stop supplying liquid nitrogen and choose artificial thawing or natural thawing according to the on-site plan.

Images