Long distance cold energy pipeline transportation system and control method

Abstract

The application discloses a long-distance cold energy pipeline transportation system and a control method, which comprises a receiving station, a cold energy exchange station, an LNG pipeline, an NG pipeline, an LNG circulation line, an LNG discharge line, an isolation valve, a flow meter and an adjusting valve; the receiving station is connected with the cold energy exchange station through the LNG pipeline, and the cold energy exchange station is connected with the receiving station through the NG pipeline; the LNG pipeline is connected with the LNG circulation line at the end, and the other end of the LNG circulation line is connected with the receiving station; the LNG discharge line is connected with the LNG pipeline in parallel; the cold energy exchange station is used for realizing the step-by-step utilization of the cold energy of LNG, avoiding the waste of directly discharging the cold energy of LNG gasification, eliminating the cold pollution and remarkably improving the energy utilization efficiency; and the LNG pipeline and the LNG circulation line adopt a multilayer composite cold insulation structure of a wear-resistant layer, a foamed glass layer and a PIR polyisocyanurate layer, have excellent heat insulation performance and minimize the cold loss in the long-distance transportation process.

Description

Technical Field

[0001] This invention belongs to the field of cold energy recovery technology, specifically relating to a long-distance cold energy pipeline transportation system and control method. Background Technology

[0002] With the country's optimization and adjustment of its energy structure and increasing emphasis on environmental protection, liquefied natural gas (LNG) has experienced rapid industrial development due to its alignment with the development direction of a low-carbon economy and energy conservation and environmental protection, as well as its ability to solve the dual problems of supply security and ecological environment improvement. However, refrigerated pipelines, as the main facilities for transporting LNG, present the following technical challenges:

[0003] 1. The conventional transportation distance of LNG pipelines does not exceed 1km. During long-distance transportation, low-temperature LNG is prone to significant cold loss and temperature rise, leading to a degradation of cold energy.

[0004] 2. If insulation fails during the operation of cold energy pipelines, LNG vaporization will significantly reduce transportation efficiency and pose a serious safety hazard.

[0005] 3. In existing LNG receiving terminals, LNG is directly vaporized through seawater or vaporizers, and a huge amount of cold energy is directly released into the environment, which not only wastes energy but also easily causes local ecological cold pollution.

[0006] Therefore, we propose a long-distance cold energy pipeline transportation system and control method. Summary of the Invention

[0007] The purpose of this invention is to provide a long-distance cold energy pipeline transportation system and control method to solve the problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a long-distance cold energy pipeline transportation system, comprising a receiving station, a cold energy exchange station, an LNG pipeline, an NG pipeline, an LNG circulation line, an LNG venting line, an isolation valve, a flow meter, and a regulating valve;

[0009] The receiving station is connected to the cold energy exchange station via the LNG pipeline for LNG export, and the cold energy exchange station is connected to the receiving station via the NG pipeline for LNG to be vaporized into NG and then returned.

[0010] The LNG pipeline is connected at one end to the LNG circulation line, and the other end of the LNG circulation line is connected to the receiving station, which is used to maintain the LNG pipeline in a cold standby circulation and cold preservation state.

[0011] The LNG venting line is connected in parallel to the LNG pipeline and is used to safely discharge LNG from the LNG pipeline.

[0012] One or more of the isolation valve, the flow meter, and the regulating valve are installed on the LNG pipeline, the NG pipeline, the LNG circulation line, and the LNG venting line.

[0013] Preferably, the cold energy exchange station is an integrated heat exchange device with an internal intermediate baffle that divides the cold energy exchange station cavity into an upper cavity and a lower cavity.

[0014] The upper cavity is filled with gaseous refrigerant 1, the lower cavity is filled with liquid refrigerant 1, and the middle baffle is provided with through holes for the gaseous refrigerant 1 and liquid refrigerant 1 to flow together.

[0015] The LNG pipeline is connected to the upper cavity, and the lower cavity is equipped with a refrigerant pipeline, which is connected to a cold energy user.

[0016] Preferably, the first refrigerant is a phase change refrigerant R404A, and the second refrigerant flows through the refrigerant pipeline. The second refrigerant is a non-phase change ethylene glycol aqueous solution or brine.

[0017] Preferably, the isolation valve and the regulating valve are integral valve bodies made of austenitic stainless steel, and the isolation valve and the regulating valve are subjected to cryogenic treatment. The cryogenic treatment process is as follows: the valve is immersed in liquid nitrogen, and after the temperature of the parts stabilizes at -196℃, it is kept at this temperature for 2-4 hours, and then naturally restored to room temperature.

[0018] Preferably, both the LNG pipeline and the LNG circulation line include a pipeline body and a cold insulation structure disposed on the outside of the pipeline body. The cold insulation structure includes, from the inside to the outside, a wear-resistant layer, a foam glass layer, a PIR polyisocyanurate layer, a moisture-proof layer, and a protective layer.

[0019] Preferably, the thickness of the foam glass layer is not less than 12.7 mm;

[0020] When the thickness of the PIR polyisocyanurate layer is greater than 40 mm, it shall be laid in layers.

[0021] The cold insulation structure is laid in a staggered joint pattern with overlapping joints between inner and outer layers, and is secured with stainless steel straps or tape.

[0022] Preferably, the foam glass layer uses a spliced ​​profile:

[0023] When the diameter of the pipeline body is less than 300mm, a semi-concave profile is selected;

[0024] When the diameter of the pipeline body is 300mm-600mm, an arc plate profile is selected;

[0025] When the diameter of the pipeline body is greater than 600mm, a 90° arc plate profile is selected.

[0026] A method for controlling long-distance cold energy pipeline transportation includes the following steps:

[0027] S1, LNG transportation: The receiving station outputs liquefied natural gas at -162℃, which is transported through the LNG pipeline. The flow rate is monitored by a flow meter, the transportation flow rate is regulated by a regulating valve, and the pipeline is controlled by an isolation valve to transport the LNG to the cold energy exchange station.

[0028] S2, Cold Energy Exchange: LNG enters the upper cavity of the cold energy exchange station, exchanges heat with gaseous refrigerant 1 and is vaporized into room temperature natural gas, which flows back to the receiving station through the NG pipeline. Gaseous refrigerant 1 exchanges heat, cools down and condenses into liquid refrigerant 1, which flows into the lower cavity through the intermediate baffle hole.

[0029] S3, Cold Energy Supply: The liquid refrigerant 1 in the lower cavity exchanges heat with the refrigerant 2 in the refrigerant pipe. After the refrigerant 2 is cooled down, it is delivered to the cold energy user to realize the cold energy supply. The liquid refrigerant 1 exchanges heat and heats up to evaporate into gaseous refrigerant 1, which flows back to the upper cavity through the middle baffle through the hole to complete the refrigerant 1 cycle.

[0030] S4. Pipeline cold preservation: Start the LNG circulation line and control a small amount of LNG to circulate slowly between the LNG pipeline and the receiving station to continuously absorb pipeline heat and maintain the LNG pipeline in a low-temperature cold state.

[0031] S5. Safety relief control: When the LNG pipeline needs maintenance, venting, or when the pressure is abnormal, the isolation valve corresponding to the LNG relief line will be opened to safely and orderly discharge the LNG or natural gas in the pipeline, ensuring the safe operation of the system.

[0032] Preferably, in step S3, the refrigerant circulation process maintains the stability of the gas-liquid two-phase system within the cold energy exchange station cavity, and the output temperature of refrigerant after heat exchange is dynamically adjusted according to the cold energy user's needs via a regulating valve.

[0033] Preferably, in step S4, the LNG circulation flow rate is monitored in real time by a flow meter, and the regulating valve controls the circulation flow rate within a preset low flow range.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] 1. This invention realizes the cascade utilization of LNG cold energy through a cold energy exchange station, avoiding the waste of LNG gasification cold energy directly emitted in traditional processes, eliminating cold pollution, and significantly improving energy utilization efficiency;

[0036] 2. In this invention, the LNG pipeline and LNG circulation line adopt a multi-layer composite cold insulation structure consisting of a wear-resistant layer, a foam glass layer, and a PIR polyisocyanurate layer. Combined with the laying process, it has excellent thermal insulation performance, minimizes cold loss during long-distance transportation, and avoids degradation of cold energy.

[0037] 3. This invention includes an LNG circulation line to maintain the pipeline in a cold standby state, preventing fatigue damage from thermal expansion and contraction and LNG blockage; an LNG discharge line to safely discharge during pipeline maintenance and in case of abnormal pressure; and valves made of austenitic stainless steel and cryogenically treated to adapt to low-temperature conditions and ensure reliable pipeline connection and disconnection. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the system of the present invention;

[0039] Figure 2 This is a schematic diagram of the structure of the cold energy exchange station of the present invention;

[0040] Figure 3 This is a schematic diagram of the structure of the LNG pipeline or LNG circulation line of the present invention;

[0041] Figure 4 This is a cross-sectional structural schematic diagram of the LNG pipeline or LNG circulation line of the present invention.

[0042] Figure 5 This is a schematic diagram of the half-tile profile structure of the foam glass layer of the present invention;

[0043] Figure 6 This is a schematic diagram of the arc-shaped profile structure of the foam glass layer of the present invention.

[0044] In the diagram: 1-Receiving station, 2-Cold energy exchange station, 201-Intermediate baffle, 202-Upper cavity, 203-Lower cavity, 204-Refrigerant pipeline, 205-Cold energy user, 3-LNG pipeline, 4-NG pipeline, 5-LNG circulation line, 6-LNG venting line, 7-Isolation valve, 8-Flow meter, 9-Regulating valve, 10-Pipeline body, 11-Wear-resistant layer, 12-Foam glass layer, 13-PIR polyisocyanurate layer, 14-Moisture-proof layer, 15-Protective layer. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] Please see Figures 1-6 The long-distance cold energy pipeline transportation system provided by the present invention includes a receiving station 1, a cold energy exchange station 2, an LNG pipeline 3, an NG pipeline 4, an LNG circulation line 5, an LNG discharge line 6, an isolation valve 7, a flow meter 8, and a regulating valve 9.

[0047] Receiving station 1 is connected to cold energy exchange station 2 via LNG pipeline 3 to achieve the export of liquefied natural gas at -162℃.

[0048] The cold energy exchange station 2 is connected to the receiving station 1 through the NG pipeline 4, and the ambient temperature natural gas after LNG heat exchange and vaporization is returned to the receiving station 1;

[0049] The LNG pipeline 3 is connected to the LNG circulation line 5 at one end, and the other end of the LNG circulation line 5 is connected back to the receiving station 1 to form a small flow circulation loop, which maintains the LNG pipeline 3 in a continuous low temperature and cold state, avoids fatigue damage caused by pipeline temperature fluctuations, and prevents LNG vaporization and gas blockage.

[0050] LNG vent line 6 is connected in parallel to LNG pipeline 3. When the pipeline needs to be repaired, emptied, or the pressure exceeds the standard, the medium inside the pipeline can be safely discharged to avoid safety risks.

[0051] The LNG external transmission and return loop realizes cold energy transportation and natural gas closed-loop recovery; the LNG circulation line 5 allows a small amount of LNG to flow slowly and continuously in the pipeline, continuously absorbing the heat that seeps into the pipe wall and maintaining the stable low temperature of LNG pipeline 3. On the one hand, it avoids the fatigue damage caused by thermal expansion and contraction due to frequent hot and cold alternation in the pipeline and extends the service life of the pipeline. On the other hand, it prevents the large amount of LNG from evaporating due to heat, which may cause gas blockage or sudden pressure rise. It solves the problems of large cold loss and cold energy degradation in long-distance transportation, significantly reduces cold loss and stabilizes transportation efficiency.

[0052] Isolation valves 7, flow meters 8, and regulating valves 9 are installed as needed on LNG pipeline 3, NG pipeline 4, LNG circulation line 5, and LNG discharge line 6. Isolation valve 7 controls the opening and closing of the pipeline, flow meter 8 monitors the medium flow in real time, and regulating valve 9 regulates the medium delivery flow to ensure the stability of system operating parameters.

[0053] The cold energy exchange station 2 is an integrated sealed heat exchange cavity with an internal intermediate baffle 201. The intermediate baffle 201 divides the cavity into an upper cavity 202 and a lower cavity 203. Multiple through holes are evenly opened on the intermediate baffle 201 to allow the refrigerant to flow in both gas and liquid phases.

[0054] LNG pipeline 3 is connected to the upper cavity 202 from the side wall, and refrigerant pipeline 204 is connected to the lower cavity 203 from the side wall. The other end of refrigerant pipeline 204 is connected to the cold energy user 205.

[0055] Refrigerant 1 uses phase change refrigerant R404A, which circulates within the cavity: gaseous refrigerant 1 in the upper cavity 202 condenses into liquid after heat exchange with LNG, and flows into the lower cavity 203 through the through hole of the intermediate baffle 201; liquid refrigerant 1 in the lower cavity 203 evaporates into gas after heat exchange with refrigerant 2, and then flows back to the upper cavity 202 through the through hole of the intermediate baffle 201, and the cycle repeats. Refrigerant 2 uses ethylene glycol aqueous solution, which is a non-phase change medium. After heat exchange, it directly delivers cold energy to the cold energy user 205. Refrigerant 1 circulates naturally in the cavity, with a short heat exchange path and low thermal resistance. LNG cold energy can be directly and efficiently transferred to refrigerant 2, realizing the cascade utilization of cold energy, avoiding the waste of direct emission of cold energy in traditional gasification processes, eliminating local cold pollution, and significantly improving energy utilization.

[0056] Isolation valve 7 and regulating valve 9 are made of austenitic stainless steel integral valve body, and after processing, they are subjected to deep cryogenic treatment: the valve is immersed in liquid nitrogen, and after the temperature stabilizes at -196℃, it is kept at the temperature for 3 hours, and then naturally heated to room temperature to improve the structural stability and sealing performance of the valve under low temperature conditions.

[0057] The pipeline body 10 of LNG pipeline 3 and LNG circulation line 5 is provided with a cold insulation structure, which consists of a wear-resistant layer 11, a foam glass layer 12, a PIR polyisocyanurate layer 13, a moisture-proof layer 14, and a protective layer 15 from the inside to the outside.

[0058] The thickness of the foam glass layer 12 is not less than 12.7 mm;

[0059] When the thickness of the PIR polyisocyanurate layer 13 is greater than 40 mm, it is laid in layers.

[0060] The cold insulation structure is laid with staggered joints in the same layer and overlapping joints in the inner and outer layers, and is fixed by binding with stainless steel strips or tape.

[0061] Foam glass layer 12 uses spliced ​​profiles:

[0062] When the diameter of the pipeline body 10 is less than 300mm, a half-roof profile should be selected;

[0063] When the diameter of the pipeline body 10 is 300mm-600mm, an arc plate profile is selected;

[0064] When the diameter of the pipeline body 10 is greater than 600mm, a 90° arc plate profile shall be selected;

[0065] Moisture-proof layer 14 prevents moisture from entering the insulation layer, and protective layer 15 protects against external mechanical damage;

[0066] The innermost wear-resistant layer 11 protects the pipeline body and prevents the insulation material from wearing off. The foam glass layer 12 has a low thermal conductivity and is resistant to low temperatures. As the main insulation layer, it blocks heat intrusion to the maximum extent and reduces cold loss. The outer PIR polyisocyanurate layer 13 further enhances the insulation. When the thickness exceeds 40mm, it is laid in layers to meet the insulation requirements of large-diameter pipes. The moisture-proof layer 14 prevents water vapor from seeping into the insulation layer and causing freezing failure. The protective layer 15 resists external mechanical impact. The splicing profiles and laying process are designed according to the pipe diameter. The insulation layer is tightly bonded, without cold bridges, and has a stable insulation effect. It is suitable for low-temperature pipes of different specifications, and the construction is convenient and the insulation life is long.

[0067] The long-distance cold energy pipeline transportation control method provided by this invention, based on system operation, includes the following specific steps:

[0068] S1, LNG transportation: Receiving station 1 outputs -162℃ liquefied natural gas, opens isolation valve 7 on LNG pipeline 3, monitors the flow rate through flow meter 8, and regulates the transportation flow rate to the rated value through regulating valve 9, and stably delivers it to cold energy exchange station 2.

[0069] S2, Cold Energy Exchange: LNG enters the upper cavity 202 of the cold energy exchange station 2 and exchanges heat with gaseous R404A refrigerant 1. LNG absorbs heat and vaporizes into room temperature natural gas, which flows back to receiving station 1 through NG pipeline 4. Gaseous refrigerant 1 releases heat and condenses into liquid, which flows into the lower cavity 203 through the through hole of the intermediate baffle 201.

[0070] S3, Cold Energy Supply: Liquid refrigerant 1 in the lower cavity 203 exchanges heat with refrigerant 2 in the refrigerant pipe 204. After the refrigerant 2 is cooled, it is delivered to the cold energy user 205. Liquid refrigerant 1 absorbs heat and evaporates into gas, flowing back to the upper cavity 202 to complete the refrigerant 1 cycle. During operation, the gas and liquid phases in the cavity are kept stable. The output temperature of refrigerant 2 is adjusted by regulating valve 9 according to user needs.

[0071] S4. Maintaining cold insulation in pipelines: Open the isolation valve 7 on the LNG circulation line 5, monitor the circulation flow through the flow meter 8, and control the small flow of LNG to circulate slowly between the LNG pipeline 3 and the receiving station 1 through the regulating valve 9 to maintain the low temperature of the pipeline and prevent damage from thermal expansion and contraction and gas blockage.

[0072] S5. Safety relief control: When LNG pipeline 3 needs maintenance, close the upstream and downstream isolation valves 7 and open the isolation valve 7 of LNG relief line 6 to safely discharge LNG or natural gas from the pipeline; automatically open the relief valve when the pressure is abnormal to ensure system safety.

[0073] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A long-distance cold energy pipeline transportation system, characterized in that, Including receiving station (1), cold energy exchange station (2), LNG pipeline (3), NG pipeline (4), LNG circulation line (5), LNG discharge line (6), isolation valve (7), flow meter (8) and regulating valve (9); The receiving station (1) is connected to the cold energy exchange station (2) through the LNG pipeline (3) for LNG export. The cold energy exchange station (2) is connected to the receiving station (1) through the NG pipeline (4) for LNG to be vaporized into NG and then returned. The LNG pipeline (3) is connected to the LNG circulation line (5) at one end, and the other end of the LNG circulation line (5) is connected to the receiving station (1) to maintain the LNG pipeline (3) in a cold standby circulation and cold preservation state. The LNG discharge line (6) is connected in parallel to the LNG pipeline (3) and is used to safely discharge LNG from the LNG pipeline (3); One or more of the isolation valve (7), the flow meter (8), and the regulating valve (9) are installed on the pipelines of the LNG pipeline (3), the NG pipeline (4), the LNG circulation line (5), and the LNG discharge line (6).

2. The long-distance cold energy pipeline transportation system according to claim 1, characterized in that: The cold energy exchange station (2) is an integrated heat exchange device with an internal intermediate baffle (201). The intermediate baffle (201) divides the cavity of the cold energy exchange station (2) into an upper cavity (202) and a lower cavity (203). The upper cavity (202) is filled with gaseous refrigerant 1, the lower cavity (203) is filled with liquid refrigerant 1, and the intermediate baffle (201) is provided with a through hole for gaseous refrigerant 1 and liquid refrigerant 1 to flow through. The LNG pipeline (3) is connected to the upper cavity (202), and the lower cavity (203) is provided with a refrigerant pipeline (204), which is connected to a cold energy user (205).

3. A long-distance cold energy pipeline transportation system according to claim 2, characterized in that: The first refrigerant is a phase change refrigerant R404A, and the second refrigerant flows through the refrigerant pipe (204). The second refrigerant is a non-phase change ethylene glycol aqueous solution or brine.

4. A long-distance cold energy pipeline transportation system according to claim 1, characterized in that: The isolation valve (7) and the regulating valve (9) are integral valve bodies made of austenitic stainless steel. The isolation valve (7) and the regulating valve (9) are subjected to cryogenic treatment. The cryogenic treatment process is as follows: the valve is immersed in liquid nitrogen, and after the part temperature stabilizes at -196℃, it is kept at the temperature for 2-4 hours, and then naturally restored to the normal temperature.

5. A long-distance cold energy pipeline transportation system according to claim 1, characterized in that: Both the LNG pipeline (3) and the LNG circulation line (5) include a pipeline body (10) and a cold insulation structure disposed on the outside of the pipeline body (10). The cold insulation structure includes, from the inside to the outside, a wear-resistant layer (11), a foam glass layer (12), a PIR polyisocyanurate layer (13), a moisture-proof layer (14), and a protective layer (15).

6. A long-distance cold energy pipeline transportation system according to claim 5, characterized in that: The thickness of the foam glass layer (12) is not less than 12.7 mm; When the thickness of the PIR polyisocyanurate layer (13) is greater than 40 mm, it is laid in layers; The cold insulation structure is laid in a staggered joint pattern with overlapping joints between inner and outer layers, and is secured with stainless steel straps or tape.

7. A long-distance cold energy pipeline transportation system according to claim 6, characterized in that: The foam glass layer (12) is made of spliced ​​profile: When the diameter of the pipeline body (10) is less than 300mm, a semi-tile profile is selected; When the diameter of the pipeline body (10) is 300mm-600mm, an arc plate profile is selected; When the diameter of the pipeline body (10) is greater than 600 mm, a 90° arc plate profile is selected.

8. A long-distance cold energy pipeline transportation control method based on the system described in any one of claims 1-7, characterized in that, Includes the following steps: S1, LNG transportation: The receiving station (1) outputs liquefied natural gas at -162℃, which is transported through the LNG pipeline (3). The flow rate is monitored by the flow meter (8), the transportation flow rate is adjusted by the regulating valve (9), and the isolation valve (7) controls the pipeline opening and closing, so as to transport the LNG to the cold energy exchange station (2). S2, Cold Energy Exchange: LNG enters the upper cavity (202) of the cold energy exchange station (2), and after exchanging heat with gaseous refrigerant I, it is vaporized into room temperature natural gas, which flows back to the receiving station (1) through the NG pipeline (4). The gaseous refrigerant I is cooled down and condensed into liquid refrigerant I, which flows into the lower cavity (203) through the through hole of the intermediate baffle (201). S3, Cold energy supply: The liquid refrigerant 1 in the lower cavity (203) exchanges heat with the refrigerant 2 in the refrigerant pipe (204). After the refrigerant 2 is cooled down, it is delivered to the cold energy user to realize the cold energy supply. The liquid refrigerant 1 exchanges heat and heats up to evaporate into gaseous refrigerant 1, which flows back to the upper cavity (202) through the through hole of the middle baffle (201) to complete the refrigerant 1 cycle; S4. Maintaining cold in the pipeline: Open the LNG circulation line (5) and control a small amount of LNG to circulate slowly between the LNG pipeline (3) and the receiving station (1) to continuously absorb heat from the pipeline and maintain the LNG pipeline (3) in a low-temperature cold state. S5. Safety release control: When the LNG pipeline (3) needs maintenance, venting or pressure abnormality, open the isolation valve (7) corresponding to the LNG release line (6) to safely and orderly release the LNG or natural gas in the pipeline and ensure the safe operation of the system.

9. The long-distance cold energy pipeline transportation control method according to claim 8, characterized in that: In step S3, the refrigerant circulation process keeps the gas and liquid phases stable in the cavity of the cold energy exchange station (2), and the output temperature of the refrigerant after heat exchange is dynamically adjusted according to the cold energy user's needs through the regulating valve (9).

10. A long-distance cold energy pipeline transportation control method according to claim 8, characterized in that, In step S4, the LNG circulation flow rate is monitored in real time by the flow meter (8), and the regulating valve (9) controls the circulation flow rate within the preset low flow range.

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