Liquefied natural gas cold energy storage device and method based on sleeve

Abstract

The invention provides a liquefied natural gas cold energy storage device and method based on a casing pipe, and belongs to the technical field of energy storage, the liquefied natural gas cold energy storage device comprises an outer pipe and an inner pipe, the outer pipe is buried in soil, the inner pipe is fixed in the outer pipe, an annular space area is formed between the inner pipe and the outer pipe, the outer wall of the inner pipe is coated with an inner heat preservation layer, and the outer wall of the inner pipe is coated with an outer heat preservation layer. The outer pipe is arranged in the annular space and used for insulating heat between the inner pipe and the annular space, the upper portion of the outer side of the outer pipe is coated with an outer heat preservation layer, and the outer heat preservation layer has a set laying depth and is used for insulating heat between the outer pipe and shallow soil. The temperature influence between the inner pipe and the outer pipe can be reduced, cold energy is prevented from being stored in shallow soil, and cold energy loss during energy storage is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of energy storage technology, and in particular relates to a casing-based liquefied natural gas cold energy storage device and method. Background Art

[0002] Liquefied natural gas (LNG) is converted into natural gas through vaporization, releasing approximately 830-860 kJ / kg of cooling energy. Low-grade LNG cooling energy (with a temperature range of -40°C to 0°C) is primarily used in direct cooling applications such as low-temperature cold storage and air conditioning systems. Furthermore, the amount of LNG cooling energy released is related to the amount of LNG transported after vaporization. Since demand for low-grade cooling energy is high in summer and low in winter, summer cooling requires the storage of low-grade LNG cooling energy across seasons to improve its utilization efficiency and expand its application areas.

[0003] Currently, energy storage technology is used to store low-grade cold energy from LNG. Currently, the main energy storage technologies include U-tube cold storage technology and casing heat storage technology. When using U-tubes to store low-grade cold energy from LNG, the installation of the U-tube requires precise bending and positioning, and additional protection measures are required for its bent joints. In addition, the two branches of the U-tube need to maintain a certain distance to ensure sufficient heat exchange. If the distance between the two branches is increased to respond to actual cold storage needs, the construction difficulty is relatively high.

[0004] The casing has the characteristics of flexible burial depth and low drilling construction cost due to its special inner and outer pipe structure. Moreover, the casing can be lowered while drilling, which greatly saves time and resources.

[0005] However, casing is currently commonly used in thermal storage technology. Applying it to the storage of low-grade cold energy from LNG will cause the following problems: (1) Since the inner and outer pipes in the casing are close to each other, the low-grade cold energy of LNG with a large temperature span of -40℃ to 0℃ can easily cause the temperature of the inner and outer pipe media to affect each other, and the cold energy that should be stored in the soil is carried away by the inner pipe fluid, resulting in cold loss.

[0006] (2) When storing heat, the casing inlet temperature is mostly above 0℃. When entering the casing, strong heat exchange may not occur immediately with the shallow soil. When storing low-grade cold energy of LNG, the temperature difference between it and the shallow soil can reach about 50℃. This degree of temperature difference will cause a large amount of cold energy to be concentrated and stored in the shallow soil, which will then be affected by the surface temperature, resulting in loss of stored energy. Summary of the Invention

[0007] In response to the defects or shortcomings in the existing technology, the present invention provides a casing-based liquefied natural gas cold energy storage device and method, which can reduce the temperature impact between the inner and outer pipes, while avoiding the storage of cold energy in shallow soil, reducing cold energy loss during energy storage.

[0008] To achieve the above object, the present invention adopts the following technical solutions: In the first aspect, an embodiment of the present invention provides a casing-based liquefied natural gas cold energy storage device, comprising an outer pipe and an inner pipe, wherein the outer pipe is buried in the soil, the inner pipe is fixed inside the outer pipe, and an annular area is formed between the inner pipe and the outer pipe. The outer wall of the inner pipe is covered with an inner insulation layer for insulating the inner pipe from the annular area, and the upper outer side of the outer pipe is covered with an outer insulation layer, and the outer insulation layer has a set laying depth for insulating the outer pipe from the shallow soil.

[0009] Furthermore, the bottom end of the outer tube is closed and the top end is open.

[0010] Furthermore, the axis of the inner tube coincides with the axis of the outer tube.

[0011] Furthermore, a set distance is provided between the bottom end of the inner tube and the bottom surface of the outer tube, and the inner tube is connected to the annular area from the bottom end.

[0012] Furthermore, a medium inlet is provided at the top end of the outer tube, and the medium inlet is connected to devices such as a compressor and a heat exchanger.

[0013] Furthermore, a medium outlet is provided at the top end of the inner tube, and the medium outlet can be connected to a heat exchanger and a user's cooling equipment.

[0014] Furthermore, the outer side of the outer tube is coated with backfill material, and the backfill material is located between the outer tube and the soil.

[0015] Furthermore, the backfill material is a high thermal conductivity cement-based composite grouting material.

[0016] Furthermore, the outer thermal insulation layer is located between the backfill material and the soil.

[0017] In a second aspect, an embodiment of the present invention provides a casing-based liquefied natural gas cold energy storage method, utilizing the casing-based liquefied natural gas cold energy storage device as described above, comprising the following steps: When cold storage is needed during the heating season, a medium with a temperature between -40°C and 0°C is injected into the annular area through the medium inlet. During the flow of the medium in the annular area, the medium exchanges cold energy with the soil due to the temperature difference. The cold energy is stored in the soil. The temperature of the medium passing through the annular area gradually increases. The high-temperature medium then flows into the inner tube and finally flows out through the medium outlet. The outflowing medium can be recycled and exchanged with the cold energy of LNG. When cooling is needed during the cooling season, the medium that has fully exchanged heat with the high-temperature heat source is injected into the annular area through the medium inlet. During the flow of the medium in the annular area, it exchanges heat with the cold energy stored in the soil. The temperature of the medium passing through the annular area gradually decreases, and the low-temperature medium then flows into the inner tube and finally flows out through the medium outlet. The outflowing medium is used for cooling in summer.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention provides an outer tube and an inner tube. The outer tube is buried in the soil, and the inner tube is fixed inside the outer tube. An annular area is formed between the inner tube and the outer tube. LNG cold energy can exchange heat with the soil in the annular area. The physical properties of the soil are utilized to store LNG cold energy for a long period of time. LNG cold energy can be stored in winter and used in summer, thereby meeting the cross-seasonal storage demand of LNG cold energy and improving the utilization rate of LNG cold energy.

[0019] 2. The present invention completely insulates the annular area from the entire inner tube by coating the outer wall of the inner tube with an inner insulation layer, thereby preventing heat exchange between the medium in the annular area and the medium in the inner tube, thereby preventing the cold energy that should be stored in the soil from being taken away by the inner tube medium, and reducing the cold loss during the cold storage process.

[0020] 3. The present invention provides an outer insulation layer on the upper outer side of the outer tube, and the outer insulation layer is located between the backfill material and the soil, thereby insulating the medium in the annular area from the soil near the surface, avoiding the concentrated storage of the medium near the surface, and preventing the loss of stored cold due to the influence of the surface temperature.

[0021] 4. The present invention coats the outer side of the outer pipe with backfill material, which adopts high thermal conductivity cement-based composite grouting material. Its high thermal conductivity can significantly enhance the heat exchange efficiency between the outer pipe and the soil. At the same time, it relies on structural strength to stabilize drilling and seal cementing, and uses chemical stability to fully protect the pipeline, thereby realizing safe and efficient operation of the buried pipe. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a side sectional view of a storage device in Embodiment 1 of the present invention; Figure 2 is a top cross-sectional view of a storage device in Embodiment 1 of the present invention; Figure 3 The curve of storage device outlet temperature changing with time under different inner insulation layer thicknesses; Figure 4 The heat transfer curve per unit meter with time under different inner insulation layer thicknesses; Figure 5 The curve of storage device outlet temperature changing with time under different outer insulation layer thicknesses; Figure 6 The heat transfer curve per unit meter changes with time under different thicknesses of the external insulation layer; Figure 7 The curve of storage device outlet temperature changing with time at different outer insulation layer depths; Figure 8 The heat transfer curve per unit linear meter at different depths of the external insulation layer changes with time; Among them, 1. outer pipe; 2. inner pipe; 3. annular area; 4. medium inlet; 5. medium outlet; 6. inner insulation layer; 7. outer insulation layer; 8. backfill material; 9. soil; 10. cold energy proposed storage position line. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Example 1 A typical embodiment of the present invention is as follows Figure 1 and Figure 2 As shown, the casing-based liquefied natural gas cold energy storage device includes an outer tube 1 and an inner tube 2. The outer tube 1 is buried below the surface, with its bottom end closed and the top end open. The diameter of the inner tube 2 is smaller than the diameter of the outer tube 1. The inner tube 2 is welded and fixed inside the outer tube 1, and the axis of the inner tube 2 coincides with the axis of the outer tube 1, so that an annular area 3 is formed between the inner tube 2 and the outer tube 1.

[0025] The bottom end of the inner tube 2 is spaced apart from the bottom surface of the outer tube 1 by a set distance, so that the inner tube 2 is connected to the annular area 3 from the bottom end. Figure 1 As shown, a medium inlet 4 is provided at the top of the outer tube 1, and a medium outlet 5 is provided at the top of the inner tube 2. The medium inlet 4 can be connected to a compressor, a heat exchanger, and other devices in sequence. After heat exchange in the heat exchanger, the medium enters the annular space 3 through the medium inlet 4, exchanges heat with the soil 9, and then enters the inner tube 2 from the bottom end and is discharged through the medium outlet 5 at the top end of the inner tube 2. After discharge from the medium outlet 5, the medium enters the user's cooling equipment or re-enters the heat exchanger for circulation.

[0026] Furthermore, since the cold energy is LNG cold energy, its temperature needs to be controlled within the range of -40°C to 0°C. In order to prevent the medium from freezing during flow, gaseous media such as air, nitrogen, and gaseous propane are selected as the medium.

[0027] Since the temperature of LNG cold energy ranges from -40°C to 0°C, the temperature span is large, which can easily cause the temperature between the inner and outer pipes to affect each other. In order to prevent the cold energy that should be stored in the soil 9 from being carried away by the inner pipe medium, resulting in cold loss, the present invention wraps the outer wall of the inner pipe 2 with an inner insulation layer 6 of a predetermined thickness. The inner insulation layer 6 is made of rigid polyurethane foam and is used to completely insulate the annular area 3 from the entire inner pipe 2, preventing heat exchange between the medium in the annular area 3 and the medium in the inner pipe 2.

[0028] In this embodiment, the thickness of the inner insulation layer 6 is 10-15 mm, which can avoid being too thick, which will reduce the area of the annular space 3 and affect the cold storage capacity, and can also avoid being too thin, which will cause the insulation layer to fail to achieve the thermal insulation effect.

[0029] On the premise that other parameters are consistent, different values of the inner insulation layer thickness are taken respectively, and the casing model under different values is simulated using ANSYS software to obtain the changes of the model outlet temperature and heat transfer per unit linear meter over time.

[0030] like Figure 3 As shown in the figure, with the continuous increase of the thickness of the inner insulation layer, the outlet temperature gradually increases. This pattern is consistent with the situation shown in the cloud map. The outlet temperatures of the inner insulation layer with a thickness of 8mm, 10mm, 15mm and 25mm are stable at 4.18℃, 4.71℃, 5.99℃ and 7.71℃ respectively. When the thickness of the inner insulation layer increases from 8mm to 10mm, the outlet temperature increases by 11.3%; when it increases from 10mm to 15mm, the outlet temperature increases by 21.4%; when it increases from 15mm to 25mm, the outlet temperature increases by 22.3%.

[0031] like Figure 4 As shown in the figure, as the thickness of the inner insulation layer increases, the heat transfer per unit meter gradually decreases. The main reason is that under the premise that the other structural parameters remain unchanged, the increase in the thickness of the inner insulation layer will reduce the annular area, thereby increasing the inlet mass flow rate. m The decrease ultimately leads to a decrease in the heat transfer per linear meter. When the thickness of the inner insulation layer increases from 8mm to 10mm, the heat transfer per linear meter changes little, reaching 13.35W / m. Later, the two curves nearly overlap. When the thickness increases from 10mm to 15mm, the heat transfer per linear meter decreases by 1.27%, and when it increases from 15mm to 25mm, the heat transfer per linear meter decreases by 12.22%.

[0032] Increasing the thickness of the inner insulation layer can effectively isolate the mutual influence of the fluid temperature between the inner and outer pipes, but it will reduce the inlet fluid mass flow rate. m , ultimately reducing the cold storage capacity of the casing. The changes in the two curves show that the thickness of the selected inner insulation layer is more suitable in the range of 10mm to 15mm. The heat exchange per linear meter of the two is not much different, and the outlet temperature is relatively high.

[0033] The outer side of the outer pipe 1 is coated with backfill material 8, which is located between the outer pipe 1 and the soil 9. The backfill material 8 adopts a high thermal conductivity cement-based composite grouting material. Its high thermal conductivity can significantly enhance the heat exchange efficiency between the outer pipe 1 and the soil 9. At the same time, it relies on structural strength to stabilize drilling and seal cementing, and uses chemical stability to comprehensively protect the pipeline, thereby realizing safe and efficient operation of the buried pipe.

[0034] Since the temperature of LNG cold energy is between -40℃ and 0℃, the temperature difference with the shallow soil can reach 50℃, which will cause a large amount of cold energy to be concentrated and stored in the shallow soil, and then be affected by the surface temperature. In order to avoid the loss of stored cold energy, an outer insulation layer 7 is also provided on the top of the outer pipe 1. The outer insulation layer 7 is located between the backfill material 8 and the soil 9. The outer insulation layer 7 uses hard polyurethane foam, which can insulate the medium in the annular area 3 from the soil 9 near the surface, avoiding the concentrated storage of the medium near the surface, and preventing the loss of stored cold due to the influence of the surface temperature.

[0035] The outer insulation layer 7 has a set laying depth and thickness. In this embodiment, the laying depth of the outer insulation layer 7 is 2-5m and the thickness is 40-80mm, which can synergistically block the heat exchange between the medium and the soil 9 near the surface and store cold energy below the cold energy intended storage position line 10.

[0036] On the premise that other parameters are consistent, different values of the thickness and depth of the external insulation layer are taken respectively, and the casing model under different values is simulated using ANSYS software to obtain the changes of the model outlet temperature and heat transfer per unit linear meter over time.

[0037] like Figure 5As shown, in the initial stage of operation (days 0-3, partial figure in the upper right corner), all four curves exhibit a steep downward trend, but the temperature drop varies significantly depending on the thickness: the initial temperature of all four curves is 14°C. As the thickness of the external insulation layer increases, the rate of outlet temperature drop gradually decreases. In the first three days, the outlet temperature for the 20mm, 40mm, 80mm, and 100mm external insulation layer thicknesses drops to 8.12°C, 8.27°C, 8.21°C, and 8.19°C, respectively. An inflection point in the outlet temperature change is observed at a thickness of 80mm. In the middle stage (days 4-10), the control effect of insulation layer thickness on the temperature decay rate gradually weakens: the outlet temperature for the 20mm, 40mm, 80mm, and 100mm external insulation layer thicknesses drops to 7.19°C, 7.33°C, 7.27°C, and 7.26°C, respectively, with temperature differences of 0.7°C, 0.67°C, 0.7°C, and 0.69°C, respectively, fluctuating within a range of 0.7°C before gradually stabilizing. By the end of the 14-day operation, the outlet temperatures for 20mm, 40mm, 80mm, and 100mm external insulation thicknesses stabilized at 6.93°C, 7.09°C, 7.02°C, and 7.00°C, respectively. The differences were not significant. The curves clearly show that after three days of operation, the outlet temperature curves for different insulation thicknesses nearly overlapped, with only a small difference. Changing the insulation thickness has little impact on the system's long-term operation, but the curves reveal a threshold for thickness changes. Once the insulation layer exceeds a certain threshold (40mm), further increasing the thickness has diminishing returns on improving temperature stability.

[0038] like Figure 6 As shown in the figure, the curve variation pattern for each outer insulation layer thickness is similar to that of the outlet temperature. When the outer insulation layer thickness is 20 mm, 40 mm, 80 mm, and 100 mm, the heat transfer per linear meter is 23.96 W / m, 24.13 W / m, 24.06 W / m, and 24.04 W / m, respectively. As the outer insulation layer thickness increases, the heat transfer per linear meter first increases and then decreases, with an inflection point at 80 mm. Although the heat transfer per linear meter increases with the thickness of the outer insulation layer, and the amount of cold exchanged with the surrounding environment increases, the cold energy carried by the outlet fluid when it flows through the inner tube also increases, reducing the efficiency. In summary, the outer insulation layer thickness range of 40 to 80 mm is more suitable.

[0039] like Figure 7As shown in the figure, the depth of the external insulation layer exhibits a significant nonlinear effect on the cooling loss rate of the buried pipe. In the initial stage (0-2 days), the outlet temperature drops sharply between 0 and 0.5 days, then slowly decreases between 0.5 and 2 days. The outlet temperature of the shallow insulation layer (2 m) first drops sharply from 14°C to 10.4°C, then slowly decreases to 9.09°C after 2 days. As the insulation layer depth increases, the decline in outlet temperature between 0 and 0.5 days gradually increases, reaching a turning point at a depth of 5 m, where the decline decreases. The outlet temperature of the 7 m deep insulation layer first drops from 14°C to 9.8°C, then slowly decreases to 8.05°C after 2 days. This indicates that excessively deep insulation prevents the timely release of more cooling energy into the soil environment. When the fluid flows back through the deep insulation layer, it carries away some of the cooling energy not released into the soil. Consequently, the outlet temperature is relatively low, resulting in significant cooling loss. In the middle and late stages (2-14 days), the outlet temperature beneath the external insulation layer at different depths shows a slow downward trend, with a daily drop of no more than 0.4°C / day, and the change gradually stabilizes. It is important to note that the fluid outlet temperature curves for external insulation depths of 4m and 5m almost overlap after 2 days, with very little change. However, when the depth increases to 7m, the outlet temperature change gradually increases, suggesting a possible boundary point. When the external insulation layer exceeds 5m, the heat exchange efficiency of the casing-type buried pipe may decline.

[0040] like Figure 8 As shown, the heat transfer rate at each depth reaches its peak at the initial moment (day 0). At day 0.5, the 2m shallow external insulation layer reaches its highest value of 28.1W / m. As the depth increases, the heat transfer rate decreases and then increases. At a depth of 5m, the heat transfer rate increases to 27.15W / m, and then decreases to 27W / m at a depth of 7m. Therefore, the depth range of the external insulation layer is set between 2m and 5m.

[0041] Example 2 This embodiment provides a casing-based liquefied natural gas cold energy storage method, using the casing-based liquefied natural gas cold energy storage device as described in Example 1, including the following steps: When cold storage is needed during the heating season, a medium with a temperature between -40°C and 0°C is injected into the annular area through the medium inlet. During the flow of the medium in the annular area, the medium exchanges cold energy with the soil due to the temperature difference. The cold energy is stored in the soil. The temperature of the medium passing through the annular area gradually increases. The high-temperature medium then flows into the inner tube and finally flows out through the medium outlet. The outflowing medium can be recycled and exchanged with the cold energy of LNG. When cooling is needed during the cooling season, the medium that has fully exchanged heat with the high-temperature heat source is injected into the annular area through the medium inlet. During the flow of the medium in the annular area, it exchanges heat with the cold energy stored in the soil. The temperature of the medium passing through the annular area gradually decreases, and the low-temperature medium then flows into the inner tube and finally flows out through the medium outlet. The outflowing medium is used for cooling in summer.

[0042] The present invention utilizes the physical properties of soil to store LNG cold energy for a long period of time. LNG cold energy can be stored in winter and used in summer, thereby meeting the cross-seasonal storage needs of LNG cold energy and improving the utilization rate of LNG cold energy.

[0043] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A liquefied natural gas cold energy storage device based on a casing, characterized in that: It includes an outer pipe and an inner pipe, the outer pipe is buried in the soil, the inner pipe is fixed inside the outer pipe, an annular area is formed between the inner pipe and the outer pipe, the outer wall of the inner pipe is covered with an inner thermal insulation layer for thermal insulation between the inner pipe and the annular area, the upper outer side of the outer pipe is covered with an outer thermal insulation layer, the outer thermal insulation layer has a set laying depth, and is used to thermally insulate between the outer pipe and the shallow soil.

2. The liquefied natural gas cold energy storage device based on casing according to claim 1, characterized in that: The bottom end of the outer tube is closed and the top end is open.

3. The liquefied natural gas cold energy storage device based on casing according to claim 1, characterized in that: The inner tube axis coincides with the outer tube axis.

4. The liquefied natural gas cold energy storage device based on casing according to claim 1, characterized in that: A set distance is set between the bottom end of the inner tube and the bottom surface of the outer tube, and the inner tube is connected with the annular area from the bottom end.

5. The casing-based liquefied natural gas cold energy storage device according to claim 1, characterized in that: A medium inlet is provided at the top end of the outer tube, and the medium inlet is connected to the compressor and the heat exchanger in sequence.

6. The casing-based liquefied natural gas cold energy storage device according to claim 1, characterized in that: The top end of the inner tube is provided with a medium outlet, which is connected to a heat exchanger or a user's cooling equipment.

7. The liquefied natural gas cold energy storage device based on casing according to claim 1, characterized in that: The outer side of the outer tube is coated with backfill material, and the backfill material is located between the outer tube and the soil.

8. The casing-based liquefied natural gas cold energy storage device according to claim 7, characterized in that: The backfill material is a high thermal conductivity cement-based composite grouting material.

9. The liquefied natural gas cold energy storage device based on casing according to claim 8, characterized in that: The outer thermal insulation layer is located between the backfill material and the soil.

10. A method for storing cold energy of liquefied natural gas based on a casing, using the liquefied natural gas cold energy storage device based on a casing according to any one of claims 1 to 9, characterized in that: The following steps are involved: When cold storage is needed during the heating season, a medium with a temperature between -40°C and 0°C is injected into the annular area through the medium inlet. During the flow of the medium in the annular area, the medium exchanges cold energy with the soil due to the temperature difference. The cold energy is stored in the soil. The temperature of the medium passing through the annular area gradually increases. The high-temperature medium then flows into the inner tube and finally flows out through the medium outlet. The outflowing medium is recycled and re-exchanged with the cold energy of LNG. When cooling is needed during the cooling season, the medium that has fully exchanged heat with the high-temperature heat source is injected into the annular area through the medium inlet. During the flow of the medium in the annular area, it exchanges heat with the cold energy stored in the soil. The temperature of the medium passing through the annular area gradually decreases, and the low-temperature medium then flows into the inner tube and finally flows out through the medium outlet. The outflowing medium is used for cooling in summer.

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