Cold energy recovery system based on natural gas differential pressure change

Abstract

The utility model provides a cold energy recycling system based on natural gas pressure difference change, which relates to the technical field of cold energy recycling of natural gas pressure difference change, and comprises a heat exchanger, the heat exchanger comprises a condensation section and a vaporization section, a plurality of heat pipes are arranged in the condensation section and the vaporization section, and a heat exchange medium is arranged in the heat pipe of the condensation section; a heat medium solution is arranged in the vaporization section, low-temperature natural gas enters the condensation section and is output after exchanging heat with a heat exchange medium, the heat exchange medium exchanges heat with the heat medium solution in the vaporization section after being cooled, and the heat medium solution is output for ice making or air conditioning and other related cold energy utilization after being cooled. According to the utility model, the traditional electric heating or water heating form is solved, the energy is saved, and the cold energy is reasonably utilized; meanwhile, the scheme is simple in structure, does not need other anti-explosion and anti-static devices, reduces the risk and equipment investment of a project, saves the project cost, and is high in stability and reliability.

Description

Technical Field

[0001] The utility model relates to the technical field of natural gas transmission, in particular to a method and system for recovering and utilizing cold energy caused by pressure difference changes during natural gas transmission. Background Art

[0002] Natural gas is one of the most widely used energy sources globally. After extraction, it is transported via high-pressure, 4.0-10.0 MPa, long-distance pipelines to cities, industrial and mining enterprises, and nearby pressure regulating stations for decompression. During this decompression process, the rapid pressure drop caused by the high gas flow causes a significant temperature drop after the pressure regulating valve, potentially reaching 20-40°C. Natural gas contains a wide variety of impurities, including water, heavy hydrocarbons, condensate, and hydrogen sulfide. These impurities typically have a pressure dew point in the pipeline between -10°C and -30°C. This extreme temperature drop causes condensation within the pipeline, which gradually forms ice on the pipe walls, leading to blockages (commonly known as "ice blockages"). Hydrocarbons, under the action of acidic H2S, form a colloid, increasing pipeline corrosion and transmission resistance. More seriously, the precipitation of water and hydrocarbons within the pipeline dissolves hydrogen sulfide, forming acid, which accelerates pipeline corrosion by one to two orders of magnitude. This phenomenon, known as "hydrogen sulfide cold corrosion," poses a serious safety hazard to high-pressure pipelines and associated equipment.

[0003] To prevent ice blockage and cold corrosion during the natural gas transmission and distribution process, the current common approach is to install heat exchangers after the pipeline pressure reducing valves. A more traditional approach involves heating the heat exchangers with conventional energy sources, whether through electricity or by burning nearby natural gas to heat water. This consumes significant energy and poses safety risks due to the installation of heating equipment near the natural gas pipeline. To mitigate these risks, explosion-proof systems must be added, increasing project construction costs. Furthermore, the cold energy generated by the natural gas pressure reduction process is not effectively utilized and is wasted.

[0004] Another existing technology utilizes waste heat generated by power generation equipment during operation. This waste heat is then managed to heat heat exchangers, thereby increasing the temperature of the decompressed natural gas to meet transmission requirements. However, this approach also presents challenges in waste heat management and increases project costs due to equipment investment. Furthermore, the utilization of the cold energy generated by decompressed natural gas is limited. Utility Model Content

[0005] In order to solve the technical problems existing in the prior art, the utility model provides a cold energy recovery and utilization method and system based on the change of natural gas pressure difference.

[0006] In a first aspect, the present invention provides a method for recovering and utilizing cold energy based on changes in natural gas pressure differential, comprising:

[0007] Inlet: The low-temperature natural gas after decompression enters the heat exchanger from the inlet flange;

[0008] Condensation: Low-temperature natural gas exchanges heat with the heat exchange medium in the heat exchanger. After the heat exchange, the temperature of the natural gas increases and is input into the gas pipeline. The heat exchange medium absorbs the cold energy and becomes liquid.

[0009] Vaporization: After the liquid heat exchange medium enters the vaporization section, it exchanges heat with the salt solution through the heat pipe wall and vaporizes. The vaporized heat exchange medium rises into the condensation section and then enters the condensation stage;

[0010] Cold energy utilization: The salt solution exchanges heat with the heat exchange medium in the vaporization section to reach a low temperature. Under the action of the circulating pump, it is discharged from the flange outlet and enters the cold energy utilization link for heat exchange. The salt solution after heat exchange then enters the vaporization section of the heat exchanger through the flange inlet.

[0011] Circulation: Under the action of cold energy and heat energy, the heat exchange medium continuously changes phase, realizing the transfer of cold energy and heat energy in the heat exchanger; under the action of the circulation pump, the heat medium solution circulates and exchanges heat, realizing the transfer of cold energy and heat energy.

[0012] Furthermore, the heat exchanger includes a condensing section and a vaporizing section, which are arranged vertically and with a heat insulation layer in the middle. The heat pipe in the heat exchanger extends from the condensing section through the heat insulation layer and then to the vaporizing section. The low-temperature natural gas exchanges heat with the heat exchange medium in the heat exchanger heat pipe. After the heat exchange, the natural gas reaches the desired temperature and is discharged from the gas outlet flange into the natural gas transmission pipeline. The heat exchange medium condenses and becomes liquid, and flows down the inner wall of the heat pipe to the vaporizing section of the heat exchanger.

[0013] Furthermore, the heat pipe is a gravity heat pipe.

[0014] Furthermore, the heat exchange medium is a mixture of halogenated hydrocarbons.

[0015] Furthermore, the heat medium solution is a salt solution.

[0016] Furthermore, the cold energy utilization link includes at least one of domestic or industrial ice making, air conditioning refrigeration or freezer storage.

[0017] The utility model also provides a cold energy recovery and utilization system based on the change of natural gas pressure difference, including an air intake system, a heat exchange system and a cold energy utilization system;

[0018] The air intake system is used to input the depressurized low-temperature natural gas into the heat exchange system;

[0019] The heat exchange system includes a heat exchanger, which includes a condensing section and a vaporizing section. The condensing section and the vaporizing section are arranged one above the other, and a heat insulation layer is provided between the condensing section and the vaporizing section. A plurality of heat pipes are provided in the heat exchanger, and the heat pipes extend from the condensing section through the heat insulation layer and then to the vaporizing section. The condensing section includes an air inlet flange and an air outlet flange; the air inlet flange is provided above the air outlet flange; and the vaporizing section includes a flange outlet and a flange inlet.

[0020] The cold energy utilization system includes a heat medium solution, a pipeline, a circulation pump, and a cold source terminal.

[0021] Furthermore, the heat pipe is vacuumed and then a halogenated hydrocarbon mixture is injected.

[0022] Furthermore, the heat pipe is a gravity heat pipe.

[0023] Furthermore, the heat pipe is a parallel gravity heat pipe.

[0024] Furthermore, the parallel gravity heat pipe includes a first heat pipe main pipe, a second heat pipe main pipe, a first parallel main pipe, a second parallel main pipe and a plurality of parallel branch pipes. The bottom of the first heat pipe main pipe is connected to the second parallel main pipe. The second parallel main pipe is connected in parallel with a plurality of parallel branch pipes. The parallel branch pipes are connected to the first parallel main pipe. The side of the first parallel main pipe away from the first heat pipe main pipe is connected to the second heat pipe main pipe. The first heat pipe main pipe and the second heat pipe main pipe both pass through the thermal insulation layer to connect the condensing section of the heat exchanger with the vaporizing section of the heat exchanger.

[0025] This utility model provides a cold energy recovery and utilization method and system based on natural gas pressure differentials, resolving the existing issue of high energy consumption associated with adding electric or water heating after conventional pressure regulating gate stations, which requires energy conversion for heating. Specifically, if the natural gas, after decompression, has a flow rate of 10,000 Nm³ / h, a temperature of -25°C, and a pressure of 1 MPa, to prevent condensation, freezing, and cold corrosion, the traditional heating method requires heating the natural gas to -10°C, requiring a heat load of approximately 70.7 kW.

[0026] Assuming 100% heat exchanger efficiency, meaning all electricity is used for natural gas heating, the resulting electrical energy is 70.7 kW. Based on an average thermal-to-electricity conversion rate of 0.38, the thermal energy consumption is 186.1 kW. Similarly, assuming a 90% gas combustion heat exchange efficiency, the required fuel heat is 78.5 kW. Assuming a 12°C hot water inlet and outlet temperature difference, a hot water circulation pump flow rate of 3.7 m³ / h, a head of 30 m, and a 70% pump efficiency, the resulting electrical power is approximately 0.59 kW. Based on an average thermal-to-electricity conversion rate of 0.38, the thermal energy consumption is 1.55 kW, resulting in a total operating thermal energy consumption of 80.10 kW. The two existing conventional natural gas pipeline reheating solutions not only fail to utilize the significant cold energy generated by natural gas decompression, but also consume significant additional energy.

[0027] Take Chongqing in 2022 as an example: Chongqing's annual natural gas consumption in 2022 was 13.163 billion standard cubic meters (data released by the Chongqing Economic and Information Technology Commission), equivalent to 36 million standard cubic meters per day. When long-distance pipeline natural gas reaches the outskirts of natural gas-consuming cities, the pressure is often as high as 3-6 MPa. After being reduced in pressure at nearly 100 high-pressure gate stations outside the city, the pressure drops to 1-1.6 MPa, and then it is transmitted to hundreds of nearly 1,000 regional pressure reducing and regulating stations, where the pressure is further reduced to 0.3-0.4 MPa, and then undergoes a second pressure reduction. This means that the total amount of natural gas that needs to be reduced in pressure in Chongqing every day is 72 million standard cubic meters.

[0028] a. If all 72 million cubic meters per day are heated by electric heating, the heat energy consumed per day is:

[0029] (72 million standard cubic meters / day) X (186.1 kilowatts / 10,000 standard cubic meters) = 1,339,920 kilowatts / day,

[0030] Equivalent to daily electricity consumption (thermoelectric efficiency 0.38): (1339920 kW / day) X0.38 = 509169 kWh / day,

[0031] b. If all 72 million standard cubic meters per day are reheated using gas water heaters, the theoretical daily thermal energy and natural gas consumption (based on the average calorific value of pipeline gas of 8,600 kcal / standard cubic meter) are:

[0032] Thermal energy: (72 million standard cubic meters / day) X (78.5 kilowatts / 10,000 standard cubic meters) = 565,200 kilowatts / day.

[0033] Equivalent natural gas quantity: (565,200 kW / day) / (8,600 kcal / standard cubic meter) X (1 kW / 860 kcal) = 56,520 standard cubic meters / day.

[0034] Secondly, a lot of the cooling energy generated is completely wasted:

[0035] For 10,000 Nm3 / h of natural gas, reheating from -25℃ to -10℃ consumes 70.7kW of energy. If this energy is used for industrial or domestic ice making (the rated energy consumption of brine bath ice making is about 80kW.h / ton), 880kg of ice can be produced, and 21 tons of industrial or domestic ice can be obtained in 24 hours a day.

[0036] In this invention, only the circulation pump requires a certain amount of energy support, while other parts do not. Therefore, compared with traditional heating methods, it can save a lot of energy loss. At the same time, it can also rationally utilize cold energy in various aspects, including domestic or industrial ice making, air conditioning refrigeration or freezer storage, etc.

[0037] Compared with electric heating, it is necessary to configure electric heating elements, explosion-proof and flameproof junction boxes, electrical control cabinets and temperature control systems, and lay high-power explosion-proof cables. For hot water boiler heating, gas hot water boilers and corresponding ancillary buildings must be installed near flammable and explosive stations, and insulated hot water long-distance pipelines must be laid, and special natural gas pipelines for hot water boilers must be laid. Hot water boiler temperature and flow control systems, soft water treatment devices, and regular water replenishment devices must be installed.

[0038] Another existing method of heating and exchanging waste heat from power generation equipment also requires waste heat management, insulation, and transmission, which all involve significant management difficulties, equipment investment, and risk control.

[0039] The cold energy recovery and utilization method and system based on the natural gas pressure difference change of the utility model have the characteristics of simple structure, small number of equipments, flexible layout, stability, reliability and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 A schematic diagram of the overall structure provided for an embodiment of the present utility model;

[0042] Figure 2 A schematic diagram of the structure of the condensing section of the heat exchanger provided in an embodiment of the present utility model;

[0043] Figure 3 A schematic structural diagram of the vaporization section of a heat exchanger provided in an embodiment of the present utility model;

[0044] Figure 4 This is a schematic structural diagram of the heat pipe vaporization section provided in an embodiment of the present utility model.

[0045] Icons: 100-Self-operated pressure regulating valve; 200-Heat exchanger; 300-Municipal pipeline network; 400-Ice making pool; 500-Circulating pump; 210-Condensation section; 220-Vaporization section; 230-Thermal insulation layer; 240-Heat pipe; 211-Inlet flange; 212-Outlet flange; 213-Shell; 214-Insulation layer; 215-Drain plate; 216-Heat exchange medium; 221-Flange inlet; 222-Flange outlet; 223-Heat medium solution; 241-First heat pipe main pipe; 242-Second heat pipe main pipe; 243-First parallel main pipe; 244-Second parallel main pipe; 245-Parallel branch pipe. DETAILED DESCRIPTION

[0046] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0048] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0049] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the utility model product is typically placed when in use. These terms are intended solely to facilitate the description of this utility model and to simplify the description, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on this utility model. Furthermore, the terms "first," "second," and "third," etc., are used solely to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0050] Furthermore, terms such as "horizontal," "vertical," and "overhanging" do not necessarily imply that a component must be absolutely horizontal or overhanging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it can be slightly tilted.

[0051] It should also be noted that, in the description of this utility model, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; mechanical connections, electrical connections; direct connections, indirect connections through an intermediate medium, and internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this utility model based on the specific circumstances.

[0052] The following embodiments of the present invention are described in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0053] like Figure 1 、 Figure 2 and Figure 3 As shown, the utility model provides a cold energy recovery and utilization system based on the change of natural gas pressure difference, including an air intake system, a heat exchange system and a cold energy utilization system;

[0054] The air intake system is used to input the low-temperature natural gas after decompression into the heat exchange system;

[0055] The temperature of the natural gas after being depressurized by the self-operated pressure regulating valve 100 or the turbo expander is reduced by 20-40 degrees. To avoid ice blockage and ice corrosion at low temperatures, the low-temperature natural gas needs to be input into the heat exchange system through the air intake system.

[0056] The heat exchange system includes a heat exchanger 200, which includes a housing 213 with an insulation layer 214 disposed thereon. The heat exchanger 200 includes a condensing section 210 and a vaporizing section 220, which are arranged one above the other. A thermal insulation layer 230 is disposed between the condensing section 210 and the vaporizing section 220. The thermal insulation layer 230 separates the condensing section 210 and the vaporizing section 220, preventing low-temperature natural gas from entering the vaporizing section 220 and preventing a heat medium solution from entering the condensing section 210. Several gravity-fed heat pipes 240 are disposed within the heat exchanger 200. Specifically, the heat pipe 240 extends from the condensation section 210 through the thermal insulation layer 230 to the vaporization section 220; the condensation section 210 includes an air inlet flange 211 and an air outlet flange 212; the vaporization section 220 includes a flange outlet 222 and a flange inlet 221; the flange inlet 221 is located above the flange outlet 222, and the interior of the heat pipe is evacuated and then the heat exchange medium 216 is injected.

[0057] Because heat exchanger 200 is divided into an upper condensing section 210 and a lower evaporating section 220 by an insulating layer 230, low-temperature natural gas enters the cavity of condensing section 210, i.e., between the inner wall of heat exchanger 200 and the outer wall of the heat pipe, through inlet flange 211. Condensing section 210 is used to exchange heat between the low-temperature natural gas and the heat exchange medium 216 within the heat pipe. This involves transferring the low temperature of the natural gas through the heat pipe wall to the heat exchange medium 216. After receiving the cold energy, the heat exchange medium 216 changes from a gas to a liquid, flowing down the heat pipe wall into evaporating section 220. After exchanging heat with the heat exchange medium 216 in condensing section 210, the low-temperature natural gas rises in temperature. Once it reaches the required transmission temperature, it is discharged through outlet flange 212 into the municipal pipeline network 300.

[0058] Vaporization section 220 includes a flange outlet 222 and a flange inlet 221. Flange inlet 221 and flange outlet 222 are used for inputting and outputting a heat medium solution. Heat medium solution 223 is a salt solution. The salt solution enters vaporization section 220 and resides within heat exchanger 200, between the inner wall of heat exchanger 200 and the outer wall of the heat pipe. It then exchanges heat with heat exchange medium 216, which has been condensed by the heat pipe, transferring cold energy to the salt solution. The salt solution, in turn, transfers heat energy to heat exchange medium 216. Heat exchange medium 216, upon receiving the heat energy, becomes gaseous, rises, and reenters condensation section 210, continuing a reciprocating motion. Driven by circulating pump 500, the salt solution can enter a cold energy utilization system through a pipeline, where its cold energy is used for ice making, cold source terminals such as city air conditioners or ice storage.

[0059] In order to increase the heat exchange efficiency and heat exchange effect between the natural gas and the heat exchange medium 216, and to improve the heat exchange efficiency and heat exchange effect between the heat exchange medium 216 and the salt solution, a plurality of guide plates 215 are provided in the radial direction of the heat exchanger 200, i.e., perpendicular to the direction of the heat pipe, to increase the contact path and contact time between the low-temperature natural gas and the salt solution and the heat pipe.

[0060] The heat exchange medium 216 injected into the heat pipe after evacuation is a mixture of halogenated hydrocarbons.

[0061] The heat pipes 240 of the condensing section 210 and the evaporating section 220 in the heat exchanger 200 are symmetrically arranged about the center point of the cavity of the heat exchanger 200 .

[0062] like Figure 4 As shown, the heat pipe 240 in the vaporization section 220 of the heat exchanger 200 is a parallel gravity heat pipe, comprising a first main heat pipe 241, a second main heat pipe 242, a first parallel main heat pipe 243, a second parallel main heat pipe 244, and several parallel branch pipes 245. The bottom of the first main heat pipe 241 is connected to the second parallel main heat pipe 244. Several parallel branch pipes 245 are connected in parallel to the second parallel main heat pipe 244. The parallel branch pipes 245 are connected to the first parallel main heat pipe 243. The side of the first parallel main heat pipe 243 away from the first main heat pipe 241 is connected to the second main heat pipe 242. Both the first main heat pipe 241 and the second main heat pipe 242 pass through the thermal insulation layer 230, connecting the condensing section 210 of the heat exchanger 200 with the vaporization section 220 of the heat exchanger 200. Compared to an independent heat pipe array, the use of parallel heat pipes improves heat exchange efficiency.

[0063] like Figure 1 As shown, the present invention also provides a cold energy recovery and utilization method based on the change of natural gas pressure difference.

[0064] Inlet: The low-temperature natural gas after decompression enters the heat exchanger 200 from the inlet flange 211;

[0065] Condensation: The low-temperature natural gas exchanges heat with the heat exchange medium 216 in the condensing section 210 of the heat exchanger 200. The heat exchange medium 216 absorbs the cold energy and enters the vaporization section 220. The temperature of the natural gas after heat exchange increases and is then fed into the gas pipeline.

[0066] The heat exchanger 200 includes a condensing section 210 and a vaporizing section 220, which are arranged vertically and interspersed with a thermal insulation layer 230. A heat pipe within the heat exchanger 200 extends from the condensing section 210 through the thermal insulation layer 230 to the vaporizing section 220. Low-temperature natural gas exchanges heat with a heat exchange medium 216 within the heat pipe of the heat exchanger 200. The heat exchange medium 216 condenses and becomes liquid, flowing down the inner wall of the heat pipe to the vaporizing section 220 of the heat exchanger 200. The natural gas after heat exchange is discharged from the outlet flange 212 into the natural gas transmission pipeline and into the municipal pipeline network 300.

[0067] Vaporization: After the liquid heat exchange medium 216 enters the vaporization section 220, it exchanges heat with the heat medium solution through the heat pipe wall and vaporizes. The vaporized heat exchange medium 216 rises and enters the condensation section 210, and then enters the condensation stage;

[0068] Cold energy utilization: The heat medium solution exchanges heat with the heat exchange medium 216 in the vaporization section 220 to reach a low temperature. Under the action of the circulation pump 500, it is discharged from the flange outlet 222 and enters the cold energy utilization link for heat exchange. The heat medium solution after heat exchange then enters the vaporization section 220 of the heat exchanger 200 through the flange inlet 221.

[0069] Specifically, the heat medium solution 223 is a salt solution.

[0070] Specifically, the heat exchange medium 216 is a mixture of halogenated hydrocarbons.

[0071] Furthermore, the cold energy utilization link includes ice making in a domestic or industrial ice making pool 400, air conditioning refrigeration or at least one of a freezer.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cold energy recovery system based on natural gas pressure differential changes, characterized in that: Including air intake system, heat exchange system and cold energy utilization system; The air intake system is used to input the depressurized low-temperature natural gas into the heat exchange system; The heat exchange system comprises a heat exchanger (200), the heat exchanger (200) comprising a condensing section (210) and a vaporizing section (220), the condensing section (210) and the vaporizing section (220) being arranged one above the other, a heat insulation layer (230) being arranged between the condensing section (210) and the vaporizing section (220), a plurality of heat pipes (240) being arranged in the heat exchanger (200), the heat pipes (240) extending from the condensing section (210) through the heat insulation layer (230) and then to the vaporizing section (220); the condensing section (210) comprising an air inlet flange (211) and an air outlet flange (212); the air inlet flange (211) being arranged above the air outlet flange (212); the vaporizing section (220) comprising a flange outlet (222) and a flange inlet (221); A heat exchange medium (216) is injected into the heat pipe (240); The cold energy utilization system comprises a heat medium solution, a pipeline, a circulation pump (500), and a cold source terminal.

2. The cold energy recovery system based on natural gas pressure difference change according to claim 1, characterized in that: The heat pipe (240) is a gravity heat pipe.

3. The cold energy recovery system based on natural gas pressure difference change according to claim 2, characterized in that: The heat pipe (240) is a parallel gravity heat pipe.

4. The cold energy recovery system based on natural gas pressure difference change according to claim 3 is characterized in that: The parallel gravity heat pipe comprises a first heat pipe main pipe (241), a second heat pipe main pipe (242), a first parallel main pipe (243), a second parallel main pipe (244) and a plurality of parallel branch pipes (245). The bottom of the first heat pipe main pipe (241) is connected to the second parallel main pipe (244). The second parallel main pipe (244) is connected in parallel with a plurality of parallel branch pipes (245). The parallel branch pipes (245) are connected to the first parallel main pipe (243). The side of the first parallel main pipe (243) away from the first heat pipe main pipe (241) is connected to the second heat pipe main pipe (242). The first heat pipe main pipe (241) and the second heat pipe main pipe (242) both pass through the heat insulation layer (230) so that the condensation section (210) of the heat exchanger (200) is connected to the vaporization section (220) of the heat exchanger (200).

5. The cold energy recovery system based on natural gas pressure difference change according to claim 4 is characterized in that: The heat pipes of the condensation section (210) and the vaporization section (220) are symmetrically arranged about the center point of the heat exchanger (200) cavity.

6. The cold energy recovery system based on natural gas pressure difference change according to any one of claims 1 to 5, characterized in that: A heat insulation layer (214) is provided on the shell of the heat exchanger (200).

7. The cold energy recovery system based on natural gas pressure difference change according to any one of claims 1 to 5, characterized in that: The condensation section (210) and / or the vaporization section of the heat exchanger (200) are provided with a plurality of guide plates (215).

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