BOG (Boil Off Gas) recondenser for recycling cold energy of high-pressure supercooled LNG (Liquefied Natural
By resetting the high-pressure pump return port and improving the gas inlet distributor in the BOG recondenser, the problems of incomplete condensation and temperature and pressure fluctuations are solved, efficient gas-liquid mass transfer and heat transfer and energy utilization are achieved, and equipment is reduced Volume and investment.
Patent Information
- Application Number
- CN202323575546.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-27
- Publication Date
- 2024-12-27
- Estimated Expiration
- 2033-12-27
AI Technical Summary
In the BOG processing system, the BOG in the recondenser is not completely condensed and the return flow of the high-pressure pump is too large, resulting in temperature and pressure fluctuations. The traditional recondenser equipment is large in size and has a high investment.
Design a BOG recondenser for reuse of high-pressure supercooled LNG cooling energy, reset the high-pressure pump return port, adopt the BOG gas inlet distributor and improved outlet end structure of the downstream pipe, and use the supercooled liquid cooling of the high-pressure pump return port It can achieve uniformity and stability of gas-liquid mass and heat transfer.
The problems of gas-liquid mass transfer heat transfer flow field disturbance and temperature and pressure fluctuations in the recondenser are solved, which improves the mass transfer efficiency of gas-liquid contact, reduces process energy consumption, improves energy utilization, and simplifies the manufacturing process.
Smart Images
Figure CN222257269U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to a liquefied natural gas (LNG) boil-off gas (BOG) recovery and processing device, in particular to a recondenser for BOG processing used for LNG storage, unloading and transfer at an LNG receiving station. Background Art
[0002] As a clean energy, natural gas plays an important role in reducing carbon emissions, and its proportion in primary energy is increasing year by year. The huge market growth brings corresponding market space and supply pressure, which requires a larger-scale natural gas infrastructure. LNG pipeline transportation can be transported as needed, but for large LNG transport ships, LNG receiving stations are required. The production system of the LNG receiving station includes unloading system, storage system, BOG (Boil Off Gas) processing system, transportation system, external transmission and metering system, etc. The main equipment includes storage tanks, BOG compressors, high and low pressure delivery pumps, recondensers, vaporizers, etc. Among them, the recondenser is a key process equipment in the BOG processing system, and its functions mainly include: 1) ensuring that BOG and LNG (Liquefied natural gas) have sufficient contact space and contact time, and using the supercooled LNG to condense BOG into liquid; 2) as the inlet buffer tank of the LNG high-pressure pump in the BOG processing system; 3) ensuring the stability of the pressure and liquid level in the recondenser, and the internal liquid level height of the recondenser must meet the NPSH (permissible cavitation margin of the pump) requirements at the inlet of the LNG high-pressure pump.
[0003] By analyzing the factors that affect the unstable operation of the recondenser, it was found that the following problems exist in the operation of the recondenser in the BOG treatment system: (1) The BOG in the recondenser is not completely condensed; (2) When the reflux rate of the high-pressure pump is too large, the recondenser has temperature and pressure fluctuations, which significantly affects its operating state; (3) The traditional BOG recondenser equipment is large in size and has high investment.
[0004] In 2022, the applicant applied for a downstream BOG recondenser (publication number CN115507618A). Subsequent experimental analysis found that: (1) Within a small flow range, the high-pressure pump reflux port is directly introduced into the channel distributor, which will not cause disturbances in the gas-liquid mass transfer and heat transfer flow field and cause changes in the temperature and pressure of the recondenser. However, when the reflux volume of the high-pressure reflux pump reaches a certain flow rate, it is directly introduced into the channel distributor, which will cause pressure and temperature fluctuations in the recondenser. (2) The design of the BOG inlet distributor is crucial for the uniform distribution of BOG gas on the cross-sectional area of the recondenser. It is necessary to eliminate turbulence, achieve uniform distribution, and control the pressure drop. (3) The downcomer enters the straight-through liquid collecting tank, which will cause the liquid level in the straight-through liquid collecting tank to be unstable, and thus cannot deliver a stable liquid flow to the downstream channel distributor. In response to the above problems, a solution to optimize the internal structure of the recondenser is proposed. Utility Model Content
[0005] The utility model provides a BOG recondenser for recycling cold energy of high-pressure supercooled LNG, and resets the installation position of a high-pressure pump reflux port to avoid fluctuations in internal pressure and temperature.
[0006] The technical solution adopted by the utility model is: a BOG recondenser for recycling cold energy of high-pressure supercooled LNG, a BOG inlet is provided on the top of the shell, the lower part of the BOG inlet is connected to the BOG gas inlet distributor, an LNG inlet is provided on the side wall of the shell, a liquid collecting tank is provided inside the shell, and a downcomer, a straight-through collecting tank, a flow channel distributor, and a structured packing component are connected in sequence below the liquid collecting tank, an LNG outlet is provided at the center of the bottom head of the shell, a high-pressure pump reflux port is provided on the side wall of the shell, the LNG inlet is connected to the liquid collecting tank through the LNG guide pipe, and the high-pressure pump reflux port is connected to the liquid collecting tank through the reflux guide pipe, the liquid collecting tank has a certain depth, and the bottom ends of the LNG guide pipe and the bottom ends of the reflux guide pipe are vertically extended into the liquid collecting tank.
[0007] Preferably, the BOG gas inlet distributor is composed of an upper ring plate, a lower circular plate, and guide vanes, and a plurality of guide vanes are fixed between the upper ring plate and the lower circular plate in a circular matrix along the radial direction of the ring, wherein the central circular hole of the upper ring plate is connected to the BOG inlet, and the lower circular plate is a circular plate.
[0008] Further preferably, the angle between adjacent guide blades is 30° to 45°.
[0009] More preferably, the vertical distance between the upper ring plate and the lower circular plate is 250-350 mm.
[0010] Furthermore, the outlet end of the downcomer is in the shape of a rectangular bar, and there are slots between the rectangular bars.
[0011] Preferably, the bottom ends of the LNG guide pipe and the return guide pipe extend into the liquid collecting tank to a depth of 100 to 150 mm.
[0012] The straight-through collecting tank is provided with anti-impact filler, which is irregular filler.
[0013] The channel distributor comprises a distribution trough and a cyclone mixer. The distribution trough is connected with the side opening of the straight-through collecting trough. The cyclone mixer is fixed on the outside of the distribution trough. The inlet of the cyclone mixer is connected with the outlet of the side wall of the distribution trough.
[0014] The top of the shell is provided with an air supply port, an exhaust port, and a pressure gauge port, and the liquid cavity at the bottom of the shell is provided with a liquid level gauge, which is connected to the liquid level gauge through the liquid level gauge port and the liquid level gauge port.
[0015] The beneficial effects of the utility model are as follows: 1) A reflux guide pipe is added to the liquid collecting tank at the reflux port of the high-pressure pump, and the supercooled liquid LNG at the reflux port of the high-pressure pump enters the downcomer through the liquid collecting tank to the flow channel distributor, which can fully utilize the residual cold energy of the high-pressure supercooled LNG at the reflux port of the high-pressure pump to achieve uniform liquid distribution, so that the high-pressure supercooled LNG at the reflux port of the high-pressure pump can fully exchange heat with BOG. The problem of the intermittent feeding of the high-pressure pump reflux port disturbing the gas-liquid mass transfer and heat transfer flow field in the recondenser and causing changes in the temperature and pressure of the recondenser is solved. 2) A BOG gas inlet distributor different from the publication number CN115507618A is adopted to solve the problem of uneven distribution of the cross-sectional area of BOG gas entering the recondenser and being in a turbulent state, thereby improving the gas-liquid contact mass transfer and heat transfer efficiency. 3) The structural design at the outlet end of the downcomer is improved, and it is designed as a rectangular guide port, which effectively solves the problem of unstable liquid level in the straight-through liquid collecting tank. 4) The improved recondenser has safe and reliable process performance, low process energy consumption, and improves the flexibility of production process operation and energy utilization. It is simple to manufacture and has good economy. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Figure 1 —Schematic diagram of the structure of the recondenser of the utility model;
[0017] Figure 2 —Schematic diagram of the structure of the BOG gas inlet distributor of the utility model;
[0018] Figure 3 —Schematic diagram of the utility model's rectangular strip-shaped guide port downcomer;
[0019] Figure 4 —Schematic diagram of the middle cross-section structure of the flow channel distributor of the utility model;
[0020] Figure 5 — A schematic diagram of the structure of the flow channel distributor of the utility model from a top view (both sides of the straight-through collecting tank are connected to the distribution tank, and only one side of the distribution tank is shown in the figure);
[0021] Figure 6 —Schematic diagram of the structure of the cyclone mixer of the utility model;
[0022] Figure 7 —Enlarged view of the structure between the LNG draft tube and the structured packing assembly;
[0023] Figure numerals: 1. Shell, 2. BOG inlet, 3. LNG inlet, 4. High-pressure pump reflux port, 5. LNG outlet, 6. Air supply port, 7. Exhaust port, 8. Pressure gauge port, 9A. Upper liquid level gauge port, 9B. Lower liquid level gauge port, 10. Thermometer port, 11. BOG gas inlet distributor, 12. LNG guide pipe, 13. Reflux guide pipe, 14. Collecting tank, 15. Downcomer, 16. Straight-through collecting tank, 17. Anti-impact packing assembly, 18. Cyclone mixer, 19. Distribution tank, 20. Channel distributor, 21. Structured packing assembly, 22. Support grid, 23. Vortex breaker, 1101. Upper ring plate, 1102. Guide vane, 1103. Lower circular plate. DETAILED DESCRIPTION
[0024] The utility model is further described below in conjunction with the accompanying drawings.
[0025] As shown in the figure, a BOG recondenser for recycling cold energy of high-pressure subcooled LNG includes a shell BOG inlet 1, an LNG inlet 2, a high-pressure pump reflux port 4, an LNG outlet 5, an air supply port 6, an exhaust port 7, a pressure gauge port 8, an upper liquid level gauge port 9A, a lower liquid level gauge port 9B, a thermometer port 10, and a manhole. The air supply port 6, the exhaust port 7, and the pressure gauge port 8 are arranged on the top head of the shell 1, and the liquid level gauge is connected through the upper liquid level gauge port 9A and the lower liquid level gauge port 9B of the liquid cavity at the bottom of the shell 1, and the thermometer port 10 is connected to the thermometer. Among them, the BOG inlet 1 is designed at the center position of the top of the upper head of the shell 1, the LNG inlet 3 and the high-pressure pump reflux port 4 are designed on the upper side wall of the shell 1, and the LNG outlet 5 is designed at the center position of the bottom head of the recondenser. Among them, the bottom of the BOG inlet 2 is connected to the BOG gas inlet distributor 11. The LNG inlet 3 and the high-pressure pump reflux port 4 are connected to the liquid collecting tank 14 in the shell 1 through the LNG guide pipe 12 and the reflux guide pipe 13 respectively. The liquid collecting tank 14 has a sufficient depth, so that the bottom end of the LNG guide pipe 12 and the bottom end of the return guide pipe 13 extend into the liquid collecting tank 14 to a depth of 100 to 150 mm. The high-pressure pump reflux port 4 adds the return guide pipe 13 to the liquid collecting tank 14, and the high-pressure supercooled LNG at the high-pressure pump reflux port 4 enters the downcomer 15 to the channel distributor 20 through the liquid collecting tank 14, which can fully utilize the residual cold energy of the high-pressure supercooled LNG, realize uniform liquid distribution, and make the high-pressure supercooled LNG and BOG fully exchange heat, solving the problem that the intermittent feeding high-pressure pump reflux port 4 disturbs the gas-liquid mass transfer and heat transfer flow field in the recondenser and causes changes in temperature and pressure in the recondenser.
[0026] The BOG gas inlet distributor 11 is composed of an upper ring plate 1101, a lower circular plate 1103, and guide vanes 1102 arranged in a circular matrix along the radial direction of the ring between the upper ring plate 1101 and the lower circular plate 1103, wherein the central circular hole of the upper ring plate 1101 is connected to the BOG inlet 2, and the bottom of the lower circular plate 1103 is a closed circular plate. The distribution angle of the guide vanes 1102 along the circumferential direction is 30°~45°. The vertical distance between the upper ring plate 1101 and the lower circular plate 1103 is 250~350mm. After BOG flows into the BOG gas inlet distributor 11, it is evenly dispersed to the surroundings along the guide vanes 1102 and then flows downward under the action of its own weight, so that the BOG gas entering the equipment is evenly distributed on the cross-sectional area, reducing turbulence and improving the gas-liquid contact mass transfer and heat transfer efficiency.
[0027] A downcomer 15 is provided directly below the liquid collecting tank 14, and a straight-through collecting tank 16 corresponds to the downcomer 15 below, and a flow channel distributor 20 corresponds to the straight-through collecting tank 16 below. The flow channel distributor 20 includes a distribution tank 19 and a cyclone mixer 18, and the distribution tank 19 is connected to the side opening of the straight-through collecting tank 16, and the cyclone mixer 18 is fixed to the outside of the distribution tank 19, and the inlet of the cyclone mixer 18 is connected to the outlet of the side wall of the distribution tank 19. Below the cyclone mixer 18 is a structured packing assembly 21, and the structured packing is inside, and the structured packing assembly 21 is supported by a support grid 22 fixed to the inner wall of the shell 1.
[0028] In order to solve the problem of the unstable liquid level in the straight-through collecting tank 16 caused by the impact of the high flow velocity in the downcomer, the structure at the outlet end of the downcomer 15 is designed as a rectangular guide port, which plays the role of guiding and stabilizing the flow. The rectangular guide port is a plurality of rectangular strips arranged in a ring, and there are slots between the rectangular strips. Further, an anti-impact filler assembly 17 is arranged on the upper part of the straight-through collecting tank 16, and an anti-impact filler (usually irregular filler) is placed, which can further stabilize the flow of LNG coming down the downcomer 15.
[0029] The working process of the utility model is as follows: BOG gas enters from the BOG inlet 1, and the gas is distributed and discharged through the BOG gas inlet distributor 11, and the BOG gas uniformly descends from the inner diameter surface of the equipment to the channel distributor 20. The supercooled LNG liquid enters the liquid collecting tank 14 continuously and stably from the LNG inlet 3 through the LNG guide pipe 12, and the high-pressure supercooled LNG liquid intermittently enters the liquid collecting tank 14 from the high-pressure pump reflux port 4 through the reflux guide pipe 13. The LNG liquid in the liquid collecting tank 14 flows down from the downcomer 15 to the straight-through collecting tank 16, and flows into the distribution tank 19 through the side opening of the straight-through collecting tank 16, so as to achieve rapid and uniform distribution. The side wall of the distribution tank 19 is provided with small holes at equal intervals, and the LNG liquid passes through the small holes and enters the cyclone mixer 18. The LNG liquid swirls downward through the cyclone mixer 18, and is mixed and contacted with the descending BOG, so as to achieve the purpose of condensing the BOG. The uncondensed BOG continues to descend, and continues to contact with the structured packing when passing through the structured packing assembly 21, and continues to condense, so that the BOG is completely condensed and phase-changed into LNG, and finally flows out through the LNG outlet 5 (the bottom inner wall near the LNG outlet 5 is connected to the vortex breaker 23 to prevent the formation of vortex, and the vortex breaker 23 is a prior art structure), and enters the next process.
Claims
1. A BOG recondenser for recycling cold energy of high-pressure subcooled LNG, wherein a BOG inlet (2) is provided on the top of a shell (1), the lower part of the BOG inlet (2) is connected to a BOG gas inlet distributor (11), an LNG inlet (3) is provided on the side wall of the shell (1), a liquid collecting tank (14) is provided inside the shell (1), and the lower part of the liquid collecting tank (14) is connected in sequence to a downcomer (15), a straight-through collecting tank (16), a flow channel distributor, and a structured packing assembly (21), and an LNG outlet (5) is provided at the center of the bottom head of the shell (1), wherein: A high-pressure pump return port (4) is provided on the side wall of the shell (1); the LNG inlet (3) is connected to the liquid collecting tank (14) via the LNG guide pipe (12); and the high-pressure pump return port (4) is connected to the liquid collecting tank (14) via the return guide pipe (13); the liquid collecting tank (14) has a certain depth; the bottom ends of the LNG guide pipe (12) and the return guide pipe (13) both extend vertically into the liquid collecting tank (14).
2. The BOG recondenser for recycling cold energy of high-pressure subcooled LNG according to claim 1 is characterized in that: The BOG gas inlet distributor (11) is composed of an upper ring plate (1101), a lower circular plate (1103), and guide vanes (1102); a plurality of guide vanes (1102) are fixed between the upper ring plate (1101) and the lower circular plate (1103) in a circular matrix along the radial direction of the circular ring; a central circular hole of the upper ring plate (1101) is connected to the BOG inlet (2); and the lower circular plate (1103) is a circular plate.
3. The BOG recondenser for recycling cold energy of high-pressure subcooled LNG according to claim 2 is characterized in that: The angle between adjacent guide blades (1102) is 30° to 45°.
4. The BOG recondenser for recycling cold energy of high-pressure subcooled LNG according to claim 2 is characterized in that: The vertical distance between the upper ring plate (1101) and the lower circular plate (1103) is 250 to 350 mm.
5. The BOG recondenser for recycling cold energy of high-pressure subcooled LNG according to claim 1 is characterized in that: The outlet end of the downcomer (15) is in the shape of a rectangular strip, with slots between the rectangular strips.
6. The BOG recondenser for recycling cold energy of high-pressure subcooled LNG according to claim 1, characterized in that: The bottom ends of the LNG guide pipe (12) and the return guide pipe (13) extend into the liquid collecting tank (14) to a depth of 100 to 150 mm.
7. The BOG recondenser for recycling cold energy of high-pressure subcooled LNG according to claim 1, characterized in that: The straight-through collecting tank (16) is provided with an anti-impact filler assembly (17) which is an irregular filler.
8. The BOG recondenser for recycling cold energy of high-pressure subcooled LNG according to claim 1, characterized in that: The flow channel distributor (20) comprises a distribution trough (19) and a cyclone mixer (18). The distribution trough (19) is connected to a side opening of a straight-through collecting trough (16). The cyclone mixer (18) is fixed to the outside of the distribution trough (19). The inlet of the cyclone mixer (18) is connected to a flow outlet of the side wall of the distribution trough (19).
9. The BOG recondenser for recycling cold energy of high-pressure subcooled LNG according to claim 1, characterized in that: The top of the shell (1) is provided with an air supply port (6), an air exhaust port (7), and a pressure gauge port (8); the liquid cavity at the bottom of the shell (1) is provided with a liquid level gauge and a thermometer, which are connected to the liquid level gauge via an upper liquid level gauge port (9A) and a lower liquid level gauge port (9B).