Stratum freezing system and method based on liquid carbon dioxide phase change cold storage

Abstract

The invention discloses a stratum freezing system and method based on liquid carbon dioxide phase change cold storage, liquid carbon dioxide is utilized to cool a cold storage medium, vaporized carbon dioxide is utilized to enter a freezing unit, gradient and cyclic utilization of cooling capacity is achieved, and the freezing efficiency is improved. The low-temperature cold storage medium and the gaseous carbon dioxide are frozen together, waste of part of cooling capacity when the liquid carbon dioxide is directly introduced into the stratum is avoided, the utilization rate of the liquid carbon dioxide is increased, cooling capacity loss is reduced, meanwhile, through common freezing of the low-temperature cold storage medium and the gaseous carbon dioxide, double-cold-source stratum freezing can be achieved, and the freezing efficiency and the uniformity of a freezing curtain are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to freezing construction technology, in particular to stratum freezing technology based on phase change cold storage of liquid carbon dioxide. BACKGROUND

[0002] As a new type of cold carrier, carbon dioxide has a shorter freezing period or economic and environmental benefits compared with traditional brine and liquid nitrogen, so it is widely used in stratum freezing construction.

[0003] The utility model discloses a kind of artificial stratum freezing systems using low-temperature carbon dioxide cycle refrigeration, and the scheme disclosed in it directly uses carbon dioxide to freeze freezing area, since it is directly using liquid carbon dioxide to freeze soil body, this will cause waste of cold quantity;And since liquid carbon dioxide temperature is lower, freezing temperature is too low, also easy to cause uneven problems such as freezing curtain, affect freezing effect.

[0004] And the Chinese patent application with publication number CN119711466A specifically discloses a stratum freezing system and method based on solid and liquid carbon dioxide, and the system scheme disclosed in it is relatively complex as a whole, needs to sublimate solid carbon dioxide first, cool calcium chloride solution to form primary refrigerant, then use liquid carbon dioxide to exchange heat with primary refrigerant in heat exchange mechanism to form secondary refrigerant. Finally, secondary refrigerant is input into freezing area, and secondary refrigerant after heat exchange is transported to the carbon dioxide conveying mechanism to realize the recycling of secondary refrigerant. The system scheme of the patent has complex system;There are three kinds of raw materials for freezing, and there are many equipment, so the initial investment is large.

[0005] Therefore, for the existing carbon dioxide stratum freezing scheme, how to ensure freezing effect, improve cold quantity utilization rate and reduce cost is a technical problem urgently to be solved in the field. SUMMARY

[0006] In view of the defects of the prior art, the purpose of the present application is to provide a stratum freezing system and method based on phase change cold storage of liquid carbon dioxide, to improve the utilization rate of carbon dioxide, reduce cold quantity loss and improve freezing efficiency.

[0007] To achieve the above purpose, the stratum freezing system based on phase change cold storage of liquid carbon dioxide provided by the present application comprises a liquid carbon dioxide storage unit, a phase change cold storage unit, a freezing unit and a monitoring and control system, The phase change cold storage unit is connected with a liquid carbon dioxide storage unit at one end and a freezing unit at the other end. The liquid carbon dioxide storage unit can deliver liquid carbon dioxide to the phase change cold storage unit, exchange heat with the cold storage medium in the phase change cold storage unit, generate cooled cold storage medium and gaseous carbon dioxide, and deliver them to the freezing unit. The cold storage medium is returned to the phase change cold storage unit through the freezing unit for circulation. The monitoring and control system can monitor the temperature and flow of carbon dioxide and cold storage medium in real time, and dynamically adjust the working state of the liquid carbon dioxide storage unit, the phase change cold storage unit and the freezing unit.

[0008] Further, the freezing unit includes carbon dioxide freezing pipes and cold storage medium freezing circulation pipes distributed in the freezing area.

[0009] Further, the liquid carbon dioxide storage unit includes a liquid carbon dioxide storage tank, a carbon dioxide output pipe and a carbon dioxide input pipe. The carbon dioxide output pipe and the carbon dioxide input pipe are connected to the outlet and the inlet of the liquid carbon dioxide storage tank respectively. The carbon dioxide output pipe is also connected to the phase change cold storage unit.

[0010] Further, the phase change cold storage unit includes a phase change heat exchanger and a cold storage medium circulation system. The phase change heat exchanger is provided with a spiral heat exchange pipe for storing cold storage medium, and a heat exchange cavity for accommodating liquid carbon dioxide. The inlet of the heat exchange cavity is connected to the carbon dioxide output pipe, and the outlet is connected to the carbon dioxide freezing pipe. The spiral heat exchange pipe is connected to the cold storage medium circulation system.

[0011] Further, the cold storage medium circulation system includes a cold storage tank. One end of the cold storage tank is connected to the outlet of the spiral heat exchange pipe through a cold storage delivery pipe, and the other end is connected to the cold storage medium freezing circulation pipe. The cold storage medium freezing circulation pipe is also connected to the inlet of the spiral heat exchange pipe.

[0012] Further, the monitoring and control system can monitor the pressure value of the liquid carbon dioxide storage tank in real time, compare it with the preset pressure threshold value, and adjust the outlet valve of the liquid carbon dioxide storage tank.

[0013] Further, the monitoring and control system can monitor the phase change temperature of carbon dioxide and the temperature of cold storage medium in real time, and adjust the recovery circulation flow of cold storage medium after heat exchange with the freezing unit.

[0014] Further, the monitoring and control system further includes a distributed temperature sensing array arranged around the carbon dioxide freezing pipes and the cold storage medium freezing circulation pipes.

[0015] In order to achieve the above-mentioned purpose, the freezing method of the stratum freezing system based on the phase change cold accumulation of liquid carbon dioxide provided by the present application comprises the following steps: The liquid carbon dioxide storage unit delivers liquid carbon dioxide to the phase change cold accumulation unit, the liquid carbon dioxide exchanges heat with the cold accumulation medium in the phase change cold accumulation unit, the cooled cold accumulation medium and the phase changed gaseous carbon dioxide are delivered to the freezing unit to exchange heat with the soil in the freezing area, and the heat exchanged cold accumulation medium returns to the phase change cold accumulation unit through the freezing unit for circulation.

[0016] The stratum freezing system and method based on the phase change cold accumulation of liquid carbon dioxide provided by the present application utilize liquid carbon dioxide to cool the cold accumulation medium first, and then utilize the vaporized carbon dioxide to enter the freezing unit, so that the cascade and recycling utilization of cold energy are realized, the waste of part of cold energy when the liquid carbon dioxide is directly delivered into the stratum is avoided, the utilization rate of liquid carbon dioxide is improved, the cold energy loss is reduced, and meanwhile, the stratum freezing by the double cold sources of the low-temperature cold accumulation medium and the gaseous carbon dioxide can realize the stratum freezing by the double cold sources, so as to improve the freezing efficiency and the uniformity of the freezing curtain. BRIEF DESCRIPTION OF DRAWINGS

[0017] The present application will be further described below in combination with the drawings and specific embodiments.

[0018] Figure 1 The figure is a block diagram of the stratum freezing system based on the phase change cold accumulation of liquid carbon dioxide in the present application. Figure 2 The figure is a schematic diagram of the overall structure of the stratum freezing system based on the phase change cold accumulation of liquid carbon dioxide in the present application. Figure 3 The figure is a schematic diagram of the structure of the phase change heat exchanger in the present application. Figure 4 The figure is a system block diagram of the monitoring and control system in the present application. Figure 5 The figure is a flow chart of the stratum freezing system based on the phase change cold accumulation of liquid carbon dioxide in the present application.

[0019] Reference signs: 1. Liquid carbon dioxide storage unit; 11. Liquid carbon dioxide storage tank; 12. Carbon dioxide output pipeline; 13. Carbon dioxide input pipeline; 2. Phase change cold accumulation unit; 21. Phase change heat exchanger; 211. Spiral heat exchange pipeline; 212. Heat exchange cavity; 22. Cold accumulation medium circulation system; 221. Cold accumulation tank; 222. Cold accumulation delivery pipeline; 3. Freezing unit; 31. Carbon dioxide freezing pipeline; 32. Cold accumulation medium freezing circulation pipeline; 4. monitoring and control system; 41. pressure sensor; 42. first temperature sensor; 43. second temperature sensor; 44. first flow meter; 45. second flow meter; 46. distributed temperature sensor array; 47. first check valve; 48. second check valve; 49. circulating pump. DETAILED DESCRIPTION

[0020] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application is further described below in combination with specific drawings.

[0021] Referring to Figure 1 and Figure 2 , which shows an example of the stratum freezing system based on phase change cold storage of liquid carbon dioxide provided by the present application.

[0022] The stratum freezing system based on phase change cold storage of liquid carbon dioxide in the present example mainly comprises a liquid carbon dioxide storage unit 1, a phase change cold storage unit 2, a freezing unit 3 and a monitoring and control system 4.

[0023] The phase change cold storage unit 2 is connected to the liquid carbon dioxide storage unit 1 at one end and to the freezing unit 3 at the other end. The liquid carbon dioxide storage unit 1 can deliver liquid carbon dioxide to the phase change cold storage unit 2, exchange heat with the cold storage medium in the phase change cold storage unit 2, generate cooled cold storage medium and gaseous carbon dioxide and deliver them to the freezing unit 3, and then return the cold storage medium to the phase change cold storage unit 2 through the freezing unit 3 for circulation. The monitoring and control system 4 can monitor the temperature and flow of carbon dioxide and cold storage medium in real time and dynamically adjust the working state of the liquid carbon dioxide storage unit 1, the phase change cold storage unit 2 and the freezing unit 3, so as to realize stratum freezing with double cold sources, reduce cold loss, improve freezing efficiency and the uniformity of the freezing curtain.

[0024] In combination with Figure 2 , wherein the freezing unit 3 comprises carbon dioxide freezing pipelines 31 and cold storage medium freezing circulation pipelines 32 distributed in the freezing area, the carbon dioxide freezing pipelines 31 and the cold storage medium freezing circulation pipelines 32 are connected to the phase change cold storage unit 2 respectively, and the cold storage medium freezing circulation pipelines 32 are connected to the phase change cold storage unit 2 to form a circulation loop, so that the freezing unit 3 can deliver low-temperature cold storage medium and gaseous carbon dioxide to the freezing area, thereby forming double cold source stratum freezing, effectively improving the freezing efficiency, and returning the cold storage medium after freezing heat exchange to the phase change cold storage unit 2 for circulation to reduce cold loss.

[0025] Further, the liquid carbon dioxide storage unit 1 comprises a liquid carbon dioxide storage tank 11, a carbon dioxide output pipeline 12 and a carbon dioxide input pipeline 13, one end of the carbon dioxide input pipeline 13 is connected to the inlet of the liquid carbon dioxide storage tank 11, and the other end is connected to a liquid carbon dioxide source, and liquid carbon dioxide is transported to the liquid carbon dioxide storage tank 11 through the carbon dioxide input pipeline 13 for storage.

[0026] The other end of the carbon dioxide output pipeline 12 is connected to the outlet of the liquid carbon dioxide storage tank 11, and the other end is connected to the phase change cold storage unit 2, and liquid carbon dioxide is transported to the phase change cold storage unit 2 through the carbon dioxide output pipeline 12, so that the liquid carbon dioxide can exchange heat with the cold storage medium in the phase change cold storage unit 2 to generate low-temperature cold storage medium and gaseous carbon dioxide.

[0027] In combination Figure 2 And Figure 3 In combination, the phase change cold storage unit 2 comprises a phase change heat exchanger 21 and a cold storage medium circulation system 22, the phase change heat exchanger 21 is provided with a spiral heat exchange pipeline 211 for storing cold storage medium, and a heat exchange cavity 212 for containing liquid carbon dioxide is further formed between the spiral heat exchange pipeline 211 and the inner wall of the phase change heat exchanger 21, and the inlet of the heat exchange cavity 212 is connected to the carbon dioxide output pipeline 12, and the outlet is connected to the carbon dioxide freezing pipeline 31 of the freezing unit 3, so that the carbon dioxide output pipeline 12 can transport liquid carbon dioxide into the heat exchange cavity 212 to exchange heat with the cold storage medium in the spiral heat exchange pipeline 211, and after heat exchange, the liquid carbon dioxide changes into gaseous carbon dioxide and is transported into the carbon dioxide freezing pipeline 31 to exchange heat with the soil in the freezing area and then is discharged into the air.

[0028] Further, the spiral heat exchange pipeline 211 is connected to the cold storage medium circulation system 22, the cold storage medium circulation system 22 comprises a cold storage tank 221, one end of the cold storage tank 221 is connected to the outlet of the spiral heat exchange pipeline 211 through a cold storage conveying pipeline 222, and the other end is connected to the cold storage medium freezing circulation pipeline 32 of the freezing unit 3, and the cold storage medium freezing circulation pipeline 32 is further connected to the inlet of the spiral heat exchange pipeline 221, so that after the cold storage medium in the spiral heat exchange pipeline 211 exchanges heat with the liquid carbon dioxide, the low-temperature cold storage medium can be transported into the cold storage tank 221 through the cold storage conveying pipeline 222 for storage, and then flows to the freezing area through the cold storage medium freezing circulation pipeline 32 to exchange heat with the soil in the freezing area, and then returns to the spiral heat exchange pipeline 221 through the cold storage medium freezing circulation pipeline 32 again for circulation.

[0029] In combination Figure 3And, the inlet and outlet of the heat exchange cavity 212 are arranged at the top of the phase change heat exchanger 21, the inlet of the spiral heat exchange pipe 211 is arranged at the bottom of the phase change heat exchanger 21, and the outlet is arranged at the top of the phase change heat exchanger 21, so that the liquid carbon dioxide flows to the bottom of the phase change heat exchanger 21 after entering the heat exchange cavity 212, and the low-temperature gaseous carbon dioxide generated by phase change naturally gathers at the top of the phase change heat exchanger 21. On the contrary, the cold storage medium enters from the bottom of the phase change heat exchanger 21 and spirally flows from bottom to top through the spiral heat exchange pipe 211.

[0030] Therefore, the carbon dioxide and the cold storage medium form reverse flow, which can maintain stable and large average heat transfer temperature difference on the whole heat exchange path, so that the coldest cold storage medium exchanges heat with the liquid carbon dioxide which has not been phase changed, and the cold storage medium which has been preheated exchanges heat with the coldest gaseous carbon dioxide, thereby maximizing the use of cold energy and improving the cold energy utilization rate and heat exchange efficiency.

[0031] Here, the cold storage medium is preferably composed of propylene glycol aqueous solution, so that the chemical properties of the cold storage medium are stable, and the cold storage medium is not flammable and explosive, thereby ensuring the safety of the system.

[0032] The liquid carbon dioxide storage unit 1 and the phase change cold storage unit 2 cooperate to exchange heat between the liquid carbon dioxide and the cold storage medium, and then the low-temperature cold storage medium and the gaseous carbon dioxide generated by phase change are transported to the freezing area in two paths, so as to realize the step-by-step use of the cold energy of the liquid carbon dioxide, reduce the cold energy loss, and simultaneously exchange heat between the low-temperature cold storage medium and the gaseous carbon dioxide and the soil of the freezing area, thereby forming a double-cold-source stratum freezing, and improving the freezing efficiency and the uniformity of the freezing curtain.

[0033] In order to ensure the reliability of the stratum freezing, the system further comprises a monitoring and control system 4, which can monitor the flow and temperature of the carbon dioxide and the cold storage medium in the liquid carbon dioxide storage unit 1 and the phase change cold storage unit 2, and the freezing effect of the freezing area in real time, so as to dynamically adjust the working state of the liquid carbon dioxide storage unit 1, the phase change cold storage unit 2 and the freezing unit 3, and ensure the stable output of the cold energy.

[0034] In combination with Figure 2 and Figure 5 Specifically, the monitoring and control system 4 is provided with a pressure sensor 41 on the liquid carbon dioxide storage tank 11, so as to monitor the pressure value of the liquid carbon dioxide storage tank 11 in real time, compare and judge with a preset pressure threshold value, and adjust the outlet valve of the liquid carbon dioxide storage tank 11 to realize the regulation and control of the pressure in the liquid carbon dioxide storage tank 11.

[0035] Further, the freezing circulation pipeline 32 of the cold storage medium is provided with a circulation pump 49, through which the delivery and recycling of the low-temperature cold storage medium can be realized. The phase-change heat exchanger 21 and the cold storage tank 221 are respectively provided with a first temperature sensor 42 and a second temperature sensor 43, through which the phase-change temperature of the carbon dioxide and the temperature of the low-temperature cold storage medium can be monitored in real time.

[0036] In cooperation therewith, the carbon dioxide output pipeline 12 and the freezing circulation pipeline 32 of the cold storage medium are respectively provided with a first flow meter 44 and a second flow meter 45, through which the delivery flow of the liquid carbon dioxide and the delivery and recycling flow of the low-temperature cold storage medium can be monitored in real time.

[0037] Therefore, the monitoring and control system 4 can compare the phase-change temperature of the carbon dioxide and the temperature of the low-temperature cold storage medium monitored by the first temperature sensor 42 and the second temperature sensor 43 with the preset temperature threshold, and control the working state of the circulation pump 49 in combination with the delivery flow of the liquid carbon dioxide and the recycling flow of the low-temperature cold storage medium monitored by the first flow meter 44 and the second flow meter 45, so as to adjust the recycling flow of the low-temperature cold storage medium, the phase-change temperature of the carbon dioxide and the temperature of the low-temperature cold storage medium, balance the phase-change heat absorption, and ensure the freezing efficiency.

[0038] In order to realize the control of the freezing effect, the carbon dioxide freezing pipeline 31 and the freezing circulation pipeline 32 of the cold storage medium are provided with a distributed temperature sensing array 46 around the periphery, so as to monitor the soil temperature of the freezing area in real time. The monitoring and control system 4 further controls the working state of the circulation pump 49 according to the soil temperature, adjusts the temperature of the freezing area by changing the delivery and recycling flow of the low-temperature cold storage medium, ensures that the phase-change temperature of the carbon dioxide and the temperature of the cold storage medium meet the freezing requirements of the soil, and thus forms a closed-loop control of the freezing effect.

[0039] In addition, the monitoring and control system 4 is further provided with a first check valve 47 and a second check valve 48 on the carbon dioxide input pipeline 13 and the carbon dioxide output pipeline 12 respectively, so as to control the delivery direction of the liquid carbon dioxide and prevent backflow.

[0040] The monitoring and control system 4 thus formed can monitor the flow and temperature of the carbon dioxide and the cold storage medium in the liquid carbon dioxide storage unit 1 and the phase-change cold storage unit 2, and the freezing effect of the freezing area in real time, so as to dynamically adjust the working state of the liquid carbon dioxide storage unit 1, the phase-change cold storage unit 2 and the freezing unit 3, and ensure the stable output of the cold energy and the freezing efficiency.

[0041] The system also comprises a heating device, which is distributed in the freezing area, can heat the cold storage medium freezing circulation pipeline 32 in the thawing stage, make the low-temperature cold storage medium temperature rise, generate high-temperature cold storage medium and flow in the cold storage medium freezing circulation pipeline 32, and transfer heat to the surrounding frozen soil to thaw the frozen soil.

[0042] Therefore, the ground freezing system based on the phase change cold storage of liquid carbon dioxide is provided.

[0043] The application also provides a ground freezing method based on the phase change cold storage of liquid carbon dioxide. The liquid carbon dioxide storage unit 1 delivers liquid carbon dioxide to the phase change cold storage unit 2, the liquid carbon dioxide exchanges heat with the cold storage medium in the phase change cold storage unit 2 to generate low-temperature cold storage medium and gaseous carbon dioxide, which are delivered to the freezing unit 3 to exchange heat with the soil in the freezing area, so as to constitute a double cold source ground freezing, effectively improve the freezing efficiency, and the cold storage medium after heat exchange with the soil returns to the phase change cold storage unit 2 through the freezing unit 3 to circulate, and reduce the cold loss.

[0044] Meanwhile, the monitoring and control system 4 monitors the temperature and flow of carbon dioxide and cold storage medium in real time, and dynamically adjusts the working state of the liquid carbon dioxide storage unit 1, the phase change cold storage unit 2 and the freezing unit 3, to ensure the freezing effect.

[0045] The ground freezing system and method based on the phase change cold storage of liquid carbon dioxide provided by the application utilize liquid carbon dioxide to first cool the cold storage medium, and then utilize the vaporized carbon dioxide to enter the freezing unit, realize the cascade and recycling use of cold, avoid the waste of part of cold when directly passing liquid carbon dioxide into the ground, thereby improve the utilization rate of liquid carbon dioxide and reduce the cold loss, meanwhile, through the common freezing of low-temperature cold storage medium and gaseous carbon dioxide, the double cold source ground freezing can be realized to improve the freezing efficiency and the uniformity of the freezing curtain.

[0046] The basic principle, main features and advantages of the application are shown and described above. It should be understood by those skilled in the art that the application is not limited by the above examples, the above examples and descriptions in the specification are only to illustrate the principle of the application, and various changes and improvements can be made without departing from the spirit and scope of the application, and these changes and improvements all fall within the scope of the claimed application. The scope of protection of the application is defined by the appended claims and their equivalents.

Claims

1. A ground freezing system based on liquid carbon dioxide phase change cold storage, characterized in that, It includes a liquid carbon dioxide storage unit, a phase change cold storage unit, a freezing unit, and a monitoring and control system. One end of the phase change cold storage unit is connected to a liquid carbon dioxide storage unit, and the other end is connected to a freezing unit. The liquid carbon dioxide storage unit can supply liquid carbon dioxide to the phase change cold storage unit, where it exchanges heat with the cold storage medium in the phase change cold storage unit to generate cooled cold storage medium and gaseous carbon dioxide, which is then transported to the freezing unit. The freezing unit then returns the cold storage medium to the phase change cold storage unit for circulation. The monitoring and control system can monitor the temperature and flow rate of carbon dioxide and cold storage medium in real time, and dynamically adjust the working status of the liquid carbon dioxide storage unit, phase change cold storage unit and freezing unit.

2. The formation freezing system based on liquid carbon dioxide phase change cold storage according to claim 1, characterized in that, The freezing unit includes carbon dioxide freezing pipes and cold storage medium freezing circulation pipes distributed in the freezing area.

3. The formation freezing system based on liquid carbon dioxide phase change cold storage according to claim 2, characterized in that, The liquid carbon dioxide storage unit includes a liquid carbon dioxide storage tank, a carbon dioxide output pipe, and a carbon dioxide input pipe. The carbon dioxide output pipe and the carbon dioxide input pipe are respectively connected to the outlet and inlet of the liquid carbon dioxide storage tank. The carbon dioxide output pipe is also connected to the phase change cold storage unit.

4. The formation freezing system based on liquid carbon dioxide phase change cold storage according to claim 3, characterized in that, The phase change cold storage unit includes a phase change heat exchanger and a cold storage medium circulation system. The phase change heat exchanger is provided with a spiral heat exchange pipe for storing the cold storage medium and also forms a heat exchange cavity for containing liquid carbon dioxide. The inlet of the heat exchange cavity is connected to the carbon dioxide output pipe, and the outlet is connected to the carbon dioxide freezing pipe. The spiral heat exchange pipe is connected to the cold storage medium circulation system.

5. The formation freezing system based on liquid carbon dioxide phase change cold storage according to claim 4, characterized in that, The cold storage medium circulation system includes a cold storage tank. One end of the cold storage tank is connected to the outlet of the spiral heat exchange pipe through a cold storage conveying pipe, and the other end is connected to the cold storage medium freezing circulation pipe. The cold storage medium freezing circulation pipe is also connected to the inlet of the spiral heat exchange pipe.

6. The formation freezing system based on liquid carbon dioxide phase change cold storage according to claim 5, characterized in that, The monitoring and control system can monitor the pressure value of the liquid carbon dioxide storage tank in real time, compare it with the preset pressure threshold, and adjust the outlet valve of the liquid carbon dioxide storage tank accordingly.

7. The formation freezing system based on liquid carbon dioxide phase change cold storage according to claim 6, characterized in that, The monitoring and control system can monitor the carbon dioxide phase change temperature and the temperature of the cold storage medium in real time, and adjust the recovery circulation flow rate of the cold storage medium after heat exchange with the freezing unit.

8. The formation freezing system based on liquid carbon dioxide phase change cold storage according to claim 7, characterized in that, The monitoring and control system also includes a distributed temperature sensor array installed around the carbon dioxide freezing pipeline and the cold storage medium freezing circulation pipeline.

9. The freezing method of the formation freezing system based on liquid carbon dioxide phase change cold storage according to any one of claims 1-8, characterized in that, The freezing method includes: The liquid carbon dioxide storage unit supplies liquid carbon dioxide to the phase change cold storage unit. The liquid carbon dioxide exchanges heat with the cold storage medium in the phase change cold storage unit. The cooled cold storage medium and the phase change gaseous carbon dioxide are then transported to the freezing unit to exchange heat with the soil in the frozen area. The cold storage medium after heat exchange then returns to the phase change cold storage unit through the freezing unit for circulation.

Images