LNG ship fuel pipeline system and pipeline stress detection and protection method

Abstract

The present invention discloses an LNG ship feed pipeline system and a pipeline protection method, comprising a ship frame and an LNG storage tank, a liquid nitrogen storage tank, an internal combustion engine, a compression recovery mechanism and a pipeline system arranged under the ship frame. The LNG storage tank and the liquid nitrogen storage tank are connected to the pipeline system, and the pipeline system is connected to the compression recovery mechanism and respectively connected to the internal combustion engine, the LNG storage tank and the liquid nitrogen storage tank to form a closed loop. The pipeline system comprises a pipeline group and a control module. The pipeline group comprises an LNG delivery pipe, a nitrogen delivery pipe, a BOG recovery pipe, and a nitrogen recovery pipe, and all are connected to the compression recovery mechanism. The LNG delivery pipe adopts a double-layer pipeline and is connected to a rotary switch at both ends. The two ends of the nitrogen delivery pipe are respectively connected to the liquid nitrogen storage tank and the rotary switch at one end of the LNG delivery pipe away from the LNG storage tank. The present invention adopts pipeline cold stress analysis and simulation, intelligently controls the release of pipeline internal pressure, and re-compresses, recovers and utilizes nitrogen and BOG gas, thereby reducing loss, protecting the pipeline system, and increasing transportation safety.

Description

Technical Field

[0001] The present invention relates to the technical field of LNG ship transportation, and in particular to an LNG ship feed pipeline system and a pipeline protection method. Background Art

[0002] LNG is recognized as the cleanest fossil energy on earth. Its main component is methane. It is colorless, odorless, non-toxic, non-corrosive and has high thermal efficiency. Its volume is about 1 / 625 of the volume of the same amount of gaseous natural gas, and the mass of liquefied natural gas is only about 45% of the same volume of water.

[0003] LNG is natural gas that has been purified, compressed, and cooled to its freezing point to become liquid. It is then transported by special ships and cryogenic pipeline systems and stored in cryogenic storage tanks at -161.5 degrees Celsius and about 0.1 MPa. After a long period of transportation, due to the temperature and pressure requirements of LNG storage, the feed pipeline system of the LNG ship needs to withstand temperature changes of -163℃ to +80℃ and an internal pressure of 10Bar. The pipeline and bracket generate temperature stress due to thermal expansion and contraction, causing the pipeline system to deform. During the voyage of the ship, the secondary stress generated by the flow of LNG in the feed pipeline due to the swaying and speed changes of the ship produces impact force on the pipeline, valves, expansion joints, elbows and other parts, causing the pipeline to deform or even break, causing LNG leakage and wasting resources. During the fuel filling process, the inevitable evaporation of LNG produces BOG flash steam, which increases the pressure in the pipeline. When the pressure in the pipeline reaches the limit, the pipeline expands and breaks and is discharged into the atmosphere, and even explosion danger occurs. Summary of the invention

[0004] To solve the above problems, the present invention proposes an LNG ship feed pipeline system and a pipeline protection method. Through stress analysis of the entire feed pipeline system and in conjunction with a detection unit, the internal pressure of the pipeline system is released in time, and protection is performed according to the cold stress of each component in the pipeline, thereby increasing the transportation safety of the LNG feed pipeline.

[0005] The technical solution adopted by the present invention is:

[0006] The LNG ship feed pipeline system includes a ship frame and an LNG storage tank, a liquid nitrogen storage tank, an internal combustion engine, a compression recovery mechanism and a pipeline system under the ship frame. The LNG storage tank and the liquid nitrogen storage tank are connected to the pipeline system, and the pipeline system is connected to the compression recovery mechanism and respectively connected to the internal combustion engine, the LNG storage tank and the liquid nitrogen storage tank to form a closed loop, wherein:

[0007] The pipeline system includes a pipeline group and a control module. The pipeline group includes an LNG delivery pipe, a nitrogen delivery pipe, a BOG recovery pipe, and a nitrogen recovery pipe, and all of them are connected to a compression recovery mechanism. The LNG delivery pipe adopts a double-layer pipeline and is connected to a rotary switch at both ends. The two ends of the nitrogen delivery pipe are respectively connected to a liquid nitrogen storage tank and a rotary switch at one end of the LNG delivery pipe away from the LNG storage tank. The two ends of the BOG recovery pipe are respectively connected to the compression recovery mechanism and the internal combustion engine. The nitrogen recovery pipe is connected to the bending part of the LNG storage tank. The nitrogen recovery pipe is also connected to the compression recovery mechanism and the liquid nitrogen storage tank. An LNG storage tank is connected between the LNG storage tank and the compression recovery mechanism.

[0008] The compression recovery mechanism includes a fixed frame, an air compressor arranged on the fixed frame, a piston arranged under the air compressor, and a sealing cover fixedly arranged on the outer side of the piston and attached to the inner wall of the fixed frame;

[0009] The control module includes a control unit, a stress analysis unit, a detection unit, a storage unit and a power supply unit. The detection unit includes multiple pressure sensors and temperature sensors and are respectively arranged at the bending part of the LNG delivery pipe, the connection part with other pipelines and the side of the rotary switch close to the LNG delivery pipe. The stress analysis unit, the detection unit, the storage unit and the power supply unit are all electrically connected to the control unit.

[0010] Preferably, the rotary switch comprises a fixed ring, a rotary block and a rotary cylinder disposed on the side wall of the pipeline and connected to the rotary block, and the rotary cylinder is electrically connected to the control unit.

[0011] Preferably, a plurality of introduction holes are provided at equal central angles on the fixed ring and the rotating block and match each other, the center of the fixed ring fits the LNG delivery pipe, and a pressure sensor and a temperature sensor are attached to the inner side of the LNG delivery pipe.

[0012] Preferably, a plurality of through holes are provided on one side and the bottom of the fixed frame, and the sides are respectively connected to the LNG delivery pipe and the nitrogen recovery pipe, and the bottom of the fixed frame is connected to the BOG recovery pipe and the nitrogen recovery pipe. A groove is provided at the bottom of the fixed frame and a control switch is provided inside to rotate and control the closing and opening of the bottom through hole.

[0013] Preferably, the control switch includes a rotating shaft and a rotating blade covering the through hole and fitting the bottom of the fixed frame, and a motor is provided at the bottom of the fixed frame and coaxially with the rotating shaft, and the motor is connected to the rotating shaft and electrically connected to the control unit.

[0014] Based on the above structure, the present invention also proposes a pipeline stress monitoring and protection method, comprising the following steps:

[0015] 1) Before the LNG storage tank is injected, the control unit controls the rotating cylinder to rotate so that the fixed ring and the introduction hole on the rotating block match each other. The liquid nitrogen in the liquid nitrogen storage tank enters the gap in the LNG delivery pipe from the introduction hole on one side through the nitrogen delivery pipe for pre-cooling and the temperature is monitored by the temperature sensor. The generated nitrogen is transported from the bent part of the LNG delivery pipe along the nitrogen recovery pipe to the fixed frame;

[0016] 2) During the navigation of LNG ships, the liquid nitrogen in the liquid nitrogen storage tank maintains the coldness of the LNG delivery pipe and the LNG storage tank. The data of the detection unit is uploaded to the control unit and the cold stress analysis is performed through the stress analysis unit. The simulated flow field data is used as a threshold so that the control unit can control the rotary switch to release the internal pressure of the bending part and the connection part of the LNG storage tank and the LNG delivery pipe;

[0017] 3) In the compression recovery mechanism, the gas enters the fixed frame, the air compressor drives the piston and drives the sealing cover downward to form a sealing mechanism in the fixed frame, the gas in the compressed sealing cover is in liquid state, the control unit drives the motor to rotate and drives the shaft and the control switch to rotate, the vanes rotate to expose the through holes and transport them to the internal combustion engine and the liquid nitrogen storage tank through the through holes for recycling.

[0018] Preferably, in step 1), the control unit controls the stress analysis unit to perform numerical simulation on pre-cooling, takes the allowable stress and strain limit of the pipeline calculated by the data detected by the detection unit as the constraint function, takes the pre-cooling time as the objective function, establishes the cooling flow model of the pre-cooled BOG gas and nitrogen, simulates the pre-cooling time variation curve to estimate the pre-cooling time, and optimizes the operation process.

[0019] Preferably, in step 2), the detection unit performs temperature change and stress detection on the bending parts and connecting parts such as elbows, expansion joints, tees, reducers, etc. in the LNG transmission pipeline. The stress analysis unit combines with the Mixture multiphase flow model to accurately simulate the LNG flow and phase change process in the LNG transmission pipeline, simulate the actual physical process of LNG flow and heat transfer in the LNG transmission pipeline, transfer the flow field data as a thermal load to each component in the LNG transmission pipeline, and accurately calculate the cold stress characteristics of each component and the deformation prediction of the LNG transmission pipe.

[0020] The beneficial effects of the present invention are as follows: during the LNG transportation process, the LNG transportation pipeline is pre-cooled in advance, cold stress analysis of various components in the pipeline is performed according to data from the detection unit during shipping, the control unit promptly controls the rotary switch to release the internal pressure, and the volatile gas is compressed and cooled into a liquid state for recycling, thereby reducing losses and protecting the material delivery pipeline system to achieve safe transportation. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0022] Figure 1 It is a schematic diagram of the structure of the present invention;

[0023] Figure 2 is a schematic diagram of the connection of the control module of the present invention;

[0024] Figure 3 It is a schematic diagram of the structure of the compression recovery mechanism of the present invention;

[0025] Figure 4 It is a front view of a rotary switch of the present invention.

[0026] Marked in the figure: 1. LNG storage tank, 2. liquid nitrogen storage tank, 3. internal combustion engine, 4. compression recovery mechanism, 41. fixed frame, 411. through hole, 412. groove, 413. control switch, 414. rotor, 415. motor, 416. shaft, 42. air compressor, 43. piston, 44. sealing cover, 5. pipeline system, 51. pipeline group, 511. LNG delivery pipe, 512. nitrogen delivery pipe, 513. nitrogen recovery pipe, 514. BOG recovery pipe, 52. control module, 521. control unit, 522. stress analysis unit, 523. detection unit, 5231. pressure sensor, 5232. temperature sensor, 524. storage unit, 525. power supply unit, 6. rotary switch, 61. fixed ring, 611. introduction hole, 62. rotating block, 63. rotating cylinder, 7. ship frame. DETAILED DESCRIPTION

[0027] like Figure 1 As shown, the LNG ship feed pipeline system includes a ship frame 7 and an LNG storage tank 1, a liquid nitrogen storage tank 2, an internal combustion engine 3, a compression recovery mechanism 4 and a pipeline system 5 provided under the ship frame 7. The LNG storage tank 1 and the liquid nitrogen storage tank 2 are connected to the pipeline system 5. The pipeline system 5 is connected to the compression recovery mechanism 4 and respectively connected to the internal combustion engine 3, the LNG storage tank 1 and the liquid nitrogen storage tank 2 to form a closed loop, wherein:

[0028] like Figure 1-4As shown, the pipeline system 5 includes a pipeline group 51 and a control module 52. The pipeline group 51 includes an LNG delivery pipe 511, a nitrogen delivery pipe 512, a BOG recovery pipe 514, and a nitrogen recovery pipe 513, all of which are connected to the compression recovery mechanism 4. The LNG delivery pipe 511 adopts a double-layer pipeline and is connected to a rotary switch 6 at both ends. The two ends of the nitrogen delivery pipe 512 are respectively connected to the liquid nitrogen storage tank 2 and the rotary switch 6 at one end of the LNG delivery pipe 511 away from the LNG storage tank 1. The rotary switch 6 includes a fixed ring 61, a rotating block 62, and a rotating cylinder 63 provided on the side wall of the pipeline and connected to the rotating block 62. The cylinder 63 is electrically connected to the control unit 521. The fixed ring 61 and the rotating block 62 are provided with multiple introduction holes 611 at equal central angles and match each other. The center of the fixed ring 61 is attached to the inner side of the LNG delivery pipe 511, and a pressure sensor 5231 and a temperature sensor 5232 are attached. The two ends of the BOG recovery pipe 514 are respectively connected to the compression recovery mechanism 4 and the internal combustion engine 3. The nitrogen recovery pipe 513 is connected to the bending part of the LNG storage tank 1. The nitrogen recovery pipe 513 is also connected to the compression recovery mechanism 4 and the liquid nitrogen storage tank 2. The LNG storage tank 1 is connected between the LNG storage tank 1 and the compression recovery mechanism 4.

[0029] like Figure 3 As shown, the compression recovery mechanism 4 includes a fixed frame 41, an air compressor 42 arranged on the fixed frame 41, a piston 43 arranged under the air compressor 42, and a sealing cover 44 fixedly arranged on the outer side of the piston 43 and fitted to the inner wall of the fixed frame 41. A plurality of through holes 411 are provided on one side and the bottom of the fixed frame 41, and the sides are respectively connected to the LNG delivery pipe 511 and the nitrogen recovery pipe 513, the bottom of the fixed frame 41 is connected to the BOG recovery pipe 514 and the nitrogen recovery pipe 513, a groove 412 is provided at the bottom of the fixed frame 41, and a control switch 413 is provided inside and rotates to control the closing and opening of the bottom through hole 411, the control switch 413 includes a rotating shaft 416 and a rotating blade 414 covering the through hole 411 and fitting to the bottom of the fixed frame 41, a motor 415 is provided at the bottom of the fixed frame 41 and coaxially with the rotating shaft 416, and the motor 415 is connected to the rotating shaft 416 and electrically connected to the control unit 521;

[0030] like Figure 2 As shown, the control module 52 includes a control unit 521, a stress analysis unit 522, a detection unit 523, a storage unit 524 and a power supply unit 525. The detection unit 523 includes a plurality of pressure sensors 5231 and a temperature sensor 5232, which are respectively arranged at the bending portion of the LNG delivery pipe 511, the connection portion with other pipelines and the side of the rotary switch 6 close to the LNG delivery pipe 511. The stress analysis unit 522, the detection unit 523, the storage unit 524 and the power supply unit 525 are all electrically connected to the control unit 521.

[0031] Based on the above structure, the present invention also proposes a pipeline stress monitoring and protection method:

[0032] 1) Before the LNG storage tank 1 is injected, the control unit 521 controls the rotating cylinder 63 to rotate so that the introduction holes 611 on the fixed ring 61 and the rotating block 62 are matched, and the liquid nitrogen in the liquid nitrogen storage tank 2 enters the gap in the LNG delivery pipe 511 from the one side introduction hole 611 through the nitrogen delivery pipe 512 for pre-cooling and the temperature is monitored by the temperature sensor 5232. The control unit 521 controls the stress analysis unit 522 to perform numerical simulation on the pre-cooling, and the allowable stress and strain limit of the pipeline calculated by the data detected by the detection unit 523 are used as constraint functions, and the pre-cooling time is used as the objective function. A cooling flow model of the pre-cooled BOG gas and nitrogen is established, and the pre-cooling time variation curve is simulated to estimate the pre-cooling time, and the operation process is optimized. The generated nitrogen is transported from the bending part of the LNG delivery pipe 511 along the nitrogen recovery pipe 513 to the fixed frame 41;

[0033] 2) During the shipping process of the LNG ship, the liquid nitrogen in the liquid nitrogen storage tank maintains the coldness of the LNG delivery pipe 511 and the LNG storage tank 1. The data of the detection unit 523 is uploaded to the control unit 521 and the cold stress analysis is performed through the stress analysis unit 522. The detection unit 523 performs temperature change and stress detection on the bending parts and connecting parts such as elbows, expansion joints, tees, reducers, etc. in the LNG delivery pipe 511. The stress analysis unit 522 combines the Mixture multiphase flow model to accurately simulate the LNG flow and phase change process in the LNG delivery pipe 511, simulate the actual physical process of LNG flow and heat transfer in the LNG delivery pipe 511, and transmit the flow field data as the thermal load threshold to each component in the LNG delivery pipe 511, accurately calculate the cold stress characteristics of each component and the deformation prediction of the LNG delivery pipe 511, and the control unit 521 controls the rotary switch 6 to release the internal pressure of the bending parts and connecting parts in the LNG storage tank 1 and the LNG delivery pipe 511;

[0034] 3) In the compression recovery mechanism 4, the gas enters the fixed frame 41, the air compressor 42 drives the piston 43 and drives the sealing cover 44 downward to form a sealing mechanism in the fixed frame 41, and the gas in the compressed sealing cover 44 is in liquid state. The control unit 521 drives the motor 415 to rotate and drives the rotating shaft 416 and the control switch 413 to rotate, the rotating blade 414 rotates to expose the through hole 411 and transport it to the internal combustion engine 3 and the liquid nitrogen storage tank 2 through the through hole 411 for recycling.

[0035] The advantages of the present invention include: pipeline cold stress analysis and simulation, intelligent control of pipeline internal pressure release, and recompression, recovery and utilization of nitrogen and BOG gas, thereby reducing losses, protecting the pipeline system, and increasing transportation safety.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. LNG ship feed pipeline system, including a ship frame and an LNG storage tank, a liquid nitrogen storage tank, an internal combustion engine, a compression recovery mechanism and a pipeline system under the ship frame. The LNG storage tank and the liquid nitrogen storage tank are connected to the pipeline system. The pipeline system is connected to the internal combustion engine, the LNG storage tank and the liquid nitrogen storage tank through the compression recovery mechanism to form a closed loop. The characteristics are: The pipeline system includes a pipeline group and a control module. The pipeline group includes an LNG delivery pipe, a nitrogen delivery pipe, a BOG recovery pipe, and a nitrogen recovery pipe, and all of them are connected to a compression recovery mechanism. The LNG delivery pipe adopts a double-layer pipe and is connected to a rotary switch at both ends. The two ends of the nitrogen delivery pipe are respectively connected to a liquid nitrogen storage tank and a rotary switch at one end of the LNG delivery pipe away from the LNG storage tank. The two ends of the BOG recovery pipe are respectively connected to the compression recovery mechanism and the internal combustion engine. The nitrogen recovery pipe is connected to the bending part of the LNG delivery pipe. The nitrogen recovery pipe is also connected to the compression recovery mechanism and the liquid nitrogen storage tank. The LNG delivery pipe is connected between the LNG storage tank and the compression recovery mechanism. The compression recovery mechanism includes a fixed frame, an air compressor arranged on the fixed frame, a piston arranged under the air compressor, and a sealing cover fixedly arranged on the outer side of the piston and attached to the inner wall of the fixed frame; The control module includes a control unit, a stress analysis unit, a detection unit, a storage unit and a power supply unit. The detection unit includes a plurality of pressure sensors and temperature sensors which are respectively arranged at the bending part of the LNG delivery pipe, the connection part with other pipelines and the side of the rotary switch close to the LNG delivery pipe. The stress analysis unit, the detection unit, the storage unit and the power supply unit are all electrically connected to the control unit; the rotary switch includes a fixed ring, a rotating block and a rotating cylinder which is arranged on the side wall of the pipeline and connected to the rotating block, and the rotating cylinder is electrically connected to the control unit; a plurality of introduction holes are arranged at equal central angles on the fixed ring and the rotating block and match each other, the center of the fixed ring fits the LNG delivery pipe, and the LNG A pressure sensor and a temperature sensor are attached to the inner side of the delivery pipe; a plurality of through holes are provided on one side and the bottom of the fixed frame, and the sides are respectively connected to the LNG delivery pipe and the nitrogen recovery pipe, the bottom of the fixed frame is connected to the BOG recovery pipe and the nitrogen recovery pipe, a groove is provided in the bottom of the fixed frame, and a control switch is provided inside to rotate and control the closing and opening of the bottom through hole; the control switch includes a rotating shaft and a rotating blade covering the through hole and fitting the bottom of the fixed frame, a motor is provided at the bottom of the fixed frame and coaxially with the rotating shaft, the motor is connected to the rotating shaft and electrically connected to the control unit.

2. A pipeline stress monitoring and protection method using the LNG ship feed pipeline system as claimed in claim 1, characterized in that: The following steps are involved: 1) Before the LNG storage tank is injected, the control unit controls the rotating cylinder to rotate so that the fixed ring and the introduction hole on the rotating block match each other. The liquid nitrogen in the liquid nitrogen storage tank enters the gap in the LNG delivery pipe from the introduction hole on one side through the nitrogen delivery pipe for pre-cooling and the temperature is monitored by the temperature sensor. The generated nitrogen is transported from the bent part of the LNG delivery pipe along the nitrogen recovery pipe to the fixed frame; 2) During the navigation of LNG ships, the liquid nitrogen in the liquid nitrogen storage tank maintains the coldness of the LNG delivery pipe and the LNG storage tank. The data of the detection unit is uploaded to the control unit and the cold stress analysis is performed through the stress analysis unit. The simulated flow field data is used as a threshold so that the control unit can control the rotary switch to release the internal pressure of the bending part and the connection part of the LNG storage tank and the LNG delivery pipe; 3) In the compression recovery mechanism, the gas enters the fixed frame, the air compressor drives the piston and drives the sealing cover downward to form a sealing mechanism in the fixed frame, the gas in the compressed sealing cover is in liquid state, the control unit drives the motor to rotate and drives the shaft and the control switch to rotate, the vanes rotate to expose the through holes and transport them to the internal combustion engine and the liquid nitrogen storage tank through the through holes for recycling.

3. The pipeline stress monitoring and protection method according to claim 2 is characterized in that: In step 1), the control unit controls the stress analysis unit to perform numerical simulation on pre-cooling, takes the allowable stress and strain limit of the pipeline calculated by the data detected by the detection unit as the constraint function, takes the pre-cooling time as the objective function, establishes the cooling flow model of the pre-cooled BOG gas and nitrogen, simulates the pre-cooling time variation curve to estimate the pre-cooling time, and optimizes the operation process.

4. The pipeline stress monitoring and protection method according to claim 2 is characterized in that: In step 2), the detection unit performs temperature change and stress detection on the bending part and the connecting part. The stress analysis unit combines the Mixture multiphase flow model to accurately simulate the LNG flow and phase change process in the LNG transmission pipeline, simulates the actual physical process of LNG flow and heat transfer in the LNG transmission pipeline, and transfers the flow field data as a thermal load to each component in the LNG transmission pipeline, accurately calculating the cold stress characteristics of each component and predicting the deformation of the LNG transmission pipe.

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