Liquefied natural gas heat value regulation cascade recovery device

Abstract

The application discloses a liquefied natural gas (LNG) heat value regulation and stepwise recovery device, which comprises a stepwise separation tower, an LNG feeding port and a tangential feeding port, the LNG feeding port is arranged at the top of the stepwise separation tower, the tangential feeding port is arranged at one side of the stepwise separation tower, a three-stage nested tower core is arranged in the stepwise separation tower, the three-stage nested tower core comprises an upper cone which is fixedly installed in the stepwise separation tower, a middle cone which is fixedly installed in the upper cone, a lower cone which is fixedly installed in the middle cone, and a feeding pipe which is fixedly connected with the tangential feeding port. The upper cone, the middle cone and the lower cone are coaxially nested and sequentially penetrated at the lower ends, three independent temperature zones are formed, LNG flows through the outer walls of the cones under the action of gravity, methane is discharged from a first gas extraction port after being gasified in the upper cone, ethane is discharged from a second gas extraction port after being gasified in the middle cone, and heavy hydrocarbon is collected in a bottom liquid collecting groove, so that flexible output of natural gas with different heat values is realized.

Description

Technical Field

[0001] This invention belongs to the field of liquefied natural gas processing technology, and in particular relates to a cascade recovery device for regulating the calorific value of liquefied natural gas. Background Technology

[0002] Liquefied natural gas (LNG) releases a significant amount of cold energy during its vaporization process, with its components vaporizing sequentially at different temperature ranges. In existing technologies, LNG vaporization systems typically include a vaporization pipeline, a power generation circuit, and an ethylene glycol cooling circuit. One end of the vaporization pipeline connects to an LNG storage tank, and the other end connects to a downstream pipeline network via an expander unit. Both the power generation circuit and the ethylene glycol cooling circuit exchange heat with the vaporization pipeline through heat exchanger arrays to recover and utilize the cold energy. Furthermore, some existing technologies employ multiple independently installed heat exchangers or distillation columns to separate the components of LNG to obtain natural gas with different calorific values.

[0003] However, the existing technologies have the following shortcomings: First, cold energy recovery and component separation are carried out in separate equipment, resulting in large equipment footprints, complex pipelines, and high investment costs; Second, existing heat exchanger groups can only achieve cold energy exchange and cannot accurately classify and separate LNG components, leading to a fixed calorific value of the output natural gas, which cannot flexibly adapt to the downstream users' needs for gas with different calorific values; Third, heavy hydrocarbon components in LNG are prone to precipitate in downstream pipelines during gasification and cause freezing blockage, affecting the safe operation of the system; Fourth, existing distillation tower structures suffer from low heat transfer efficiency, insufficient gas-liquid contact, and a limited number of separation stages under cryogenic conditions. To solve the above problems, a liquefied natural gas calorific value regulation and cascade recovery device is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a cascade recovery device for regulating the calorific value of liquefied natural gas, thereby solving the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: This invention relates to a cascade recovery device for liquefied natural gas (LNG) calorific value regulation, comprising a cascade separation tower, an LNG inlet, and a tangential inlet. The LNG inlet is located at the top of the cascade separation tower, and the tangential inlet is located on one side of the cascade separation tower. The cascade separation tower has a three-stage nested tower core, which includes: The upper cone is fixedly installed inside the cascade separation tower. The middle cone is fixedly installed inside the upper cone; The lower cone is fixedly installed inside the middle cone; The lower part of the middle cone passes through the bottom of the upper cone and extends downward, and the lower part of the lower cone passes through the bottom of the middle cone and extends downward; the tangential feed inlet is fixedly connected to a feeding pipe, and the ejection end of the feeding pipe is tangential to the inner wall of the upper cone; When LNG enters from the LNG inlet or tangential inlet, the LNG spirals downward along the inner wall of the upper cone. Methane is preferentially vaporized and discharged from the top of the upper cone. The heavy hydrocarbon liquid flows sequentially through the outer walls of the middle and lower cones. Ethane is vaporized on the outer wall of the middle cone and discharged. The remaining heavy hydrocarbon liquid collects at the bottom of the cascade separation tower.

[0006] Preferably, the outer walls of the upper cone, middle cone, and lower cone are provided with guide fins and guide grooves, the guide fins are provided with guide notches, and the guide grooves and guide notches are connected in a one-to-one correspondence.

[0007] Preferably, the bottom of the guide channel is provided with a plurality of drainage ridges spaced apart along the length direction, and the drainage ridges are semi-cylindrical protrusions.

[0008] Preferably, a guide ring is fixedly provided at the bottom of the inner wall of the upper cone, and the guide ring is inclined downward and faces the outer wall surface of the middle cone.

[0009] Preferably, the bottom of the upper cone is fixedly connected to an extension cylinder, and the circumferential side of the extension cylinder is provided with staggered conical anti-jamming holes.

[0010] Preferably, a Venturi tube is fixedly connected to the bottom end of the middle cone.

[0011] Preferably, a liquid collecting cup is fixedly connected to the bottom end of the lower cone, and a multi-layer degassing grid is fixedly installed inside the liquid collecting cup. Multiple drainage holes are opened at the bottom of the liquid collecting cup.

[0012] Preferably, a liquid collection tank is fixedly installed at the bottom of the cascade separation tower, a siphon breaking pipe is fixedly installed inside the liquid collection tank, and an anti-vortex device is fixedly installed at the bottom of the liquid collection tank.

[0013] Preferably, a first support plate is fixedly connected between the tiered separation tower and the upper cone, a second support plate is fixedly connected between the upper cone and the middle cone, and a third support plate is fixedly connected between the middle cone and the lower cone.

[0014] The present invention has the following beneficial effects: 1. This invention achieves the step-by-step separation and calorific value control of methane, ethane, and heavy hydrocarbon components in LNG within the same tower. Specifically, it forms three independent temperature zones by setting up coaxial nested upper, middle, and lower cones with sequentially protruding lower ends. Under the action of gravity, LNG flows sequentially through the outer walls of each cone. Methane is vaporized in the upper cone and discharged from the first exhaust port, ethane is vaporized in the middle cone and discharged from the second exhaust port, and heavy hydrocarbons are collected in the bottom collection tank, thereby achieving flexible output of natural gas with different calorific values. 2. This invention achieves a significant increase in gas-liquid contact area and an improvement in separation efficiency. Specifically, it involves setting annular guide fins and vertical semi-circular guide grooves on the outer wall of each level of the cone, and opening guide gaps on the guide fins that correspond one-to-one with the guide grooves. This allows the liquid flowing down the outer wall of the cone to be blocked and redistributed at the fins, collected by the guide grooves, and then passing through the gaps to form a continuous and stable liquid film. At the same time, the gas generates turbulence by flowing around the fins in the annular channel, thereby greatly improving the gas-liquid heat and mass transfer efficiency. 3. This invention achieves anti-freezing and self-draining functions under cryogenic LNG conditions. Specifically, it sets the small holes on the extended cylinder at the bottom of the upper cone as conical anti-jamming holes with smaller outer diameters and larger inner diameters, sets semi-cylindrical drainage ridges at intervals at the bottom of the guide channel, and sets the degassing grid in the liquid collection cup as a removable structure. This prevents ice crystals from getting stuck in the small holes, washes them away by the turbulence generated by the flowing liquid, and allows them to be removed and cleaned when the machine is stopped, thereby ensuring long-term stable operation of the device under cryogenic conditions.

[0015] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a three-dimensional structural diagram of the present invention; Figure 2 This is a cross-sectional structural diagram of the present invention; Figure 3 for Figure 2 A magnified schematic diagram of the partial structure at point A in the middle; Figure 4 for Figure 2 A magnified view of the structure at point B in the middle; Figure 5 for Figure 2 A magnified schematic diagram of the local structure at point C; Figure 6 This is a schematic diagram of the internal structure of the present invention; Figure 7 This is a schematic diagram of the nested tower core mechanism of the present invention; Figure 8 This is a schematic diagram of the internal structure of the liquid collection tank of the present invention; Figure 9 for Figure 7 Internal structure diagram; Figure 10 for Figure 9 A magnified schematic diagram of the local structure at point D; Figure 11 for Figure 9 A magnified schematic diagram of the structure at point E in the middle.

[0018] The components represented by each number in the attached diagram are listed below: 1. Cascade Separation Tower; 2. LNG Inlet; 3. Tangential Inlet; 4. Feed Pipe; 5. Upper Cone; 6. Middle Cone; 7. Lower Cone; 8. Collection Tank; 9. Siphon Breaker; 10. Anti-vortex Device; 11. Flow Guide Slot; 12. Drainage Ridge; 13. Flow Guide Fins; 14. Flow Guide Notch; 15. Collection Cup; 16. Degassing Grille; 17. Drain Hole; 18. Extension Cylinder; 19. Conical Anti-jamming Hole; 20. First Support Plate; 21. Second Support Plate; 22. Third Support Plate; 23. Flow Guide Ring; 24. Venturi Tube. Detailed Implementation

[0019] 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.

[0020] In the description of this invention, it should be understood that the terms "upper," "middle," "outer," "inner," etc., which indicate orientation or positional relationship, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0021] Please see Figures 1-11As shown, this invention is a cascade recovery device for liquefied natural gas (LNG) calorific value regulation, comprising a cascade separation tower 1, an LNG inlet 2, and a tangential inlet 3. The LNG inlet 2 is located at the top of the cascade separation tower 1, and the tangential inlet 3 is located on one side of the cascade separation tower 1. The cascade separation tower 1 is equipped with a three-stage nested tower core, which includes an upper cone 5, a middle cone 6, and a lower cone 7 arranged coaxially from top to bottom, thereby forming three independent temperature zones corresponding to the cascade separation of methane, ethane, and heavy hydrocarbons, respectively. The lower part of the middle cone 6 passes through the bottom of the upper cone 5 and extends downward, and the lower part of the lower cone 7 passes through the bottom of the middle cone 6 and extends downward, so that the liquid can flow sequentially through the outer wall of each cone under the action of gravity, realizing continuous and graded separation of components.

[0022] Please combine Figure 2 and Figure 6 A feed pipe 4 is fixedly connected to the tangential feed inlet 3. The spray end of the feed pipe 4 extends into the interior of the stepped separation tower 1 and is tangential to the inner wall of the upper cone 5. This allows LNG to form a spiral downward flowing liquid film after being sprayed tangentially into the inner wall of the upper cone 5. Centrifugal force is used to make the liquid film spread evenly, avoiding local liquid accumulation or dry walls. A guide ring 23 is fixedly installed at the bottom of the inner wall of the upper cone 5. The guide ring 23 is inclined downward and faces the outer wall of the middle cone 6. It is used to guide the heavy hydrocarbon liquid flowing down the inner wall of the upper cone 5 to the outer wall of the middle cone 6, so as to realize the continuous transition between stages.

[0023] Please combine Figures 2 to 5 The outer walls of the upper cone 5, the middle cone 6, and the lower cone 7 are respectively provided with flow guide fins 13 and flow guide grooves 11. The flow guide fins 13 are horizontally annular and equidistantly distributed along the axial direction of the cone. The flow guide fins 13 have flow guide notches 14. The flow guide grooves 11 and the flow guide notches 14 are connected in a one-to-one correspondence. The flow guide grooves 11 extend vertically along the generatrix of the cone and have a semi-circular cross-section. They are used to collect the liquid blocked by the flow guide fins 13 and guide it to the flow guide notches 14, so that the liquid can continue to flow downward after passing through the fins from the flow guide notches 14, forming a continuous and stable liquid film. At the same time, when the gas rises in the annular channel, it flows around the flow guide fins 13 and generates turbulence, thereby greatly improving the gas-liquid heat and mass transfer efficiency.

[0024] Please combine Figure 3 The bottom of the guide channel 11 is provided with multiple drainage ridges 12 at intervals along the length direction. The drainage ridges 12 are semi-cylindrical protrusions. When the liquid flows through the drainage ridges 12, local turbulence is generated, which washes away the ice crystals deposited at the bottom of the guide channel 11 and prevents the ice crystals from clogging the guide channel 11 under cryogenic conditions.

[0025] Please combine Figure 5 , Figure 7 and Figure 10An extension cylinder 18 is fixedly connected to the bottom of the upper cone 5. The circumferential side of the extension cylinder 18 is provided with staggered conical anti-jamming holes 19. The conical anti-jamming holes 19 are conical with a smaller outer diameter and a larger inner diameter. After the gas enters the extension cylinder 18 from below, it is ejected through the conical anti-jamming holes 19 and forms a vertical cross collision with the liquid flowing down the inner wall of the upper cone 5, which enhances the gas-liquid contact. At the same time, the conical structure prevents ice crystals from getting stuck in the small holes, effectively preventing blockage.

[0026] Please combine Figure 4 , Figure 7 and Figure 9 The bottom end of the middle cone 6 is fixedly connected to a venturi tube 24, which consists of a contraction section, a throat, and a diffusion section from top to bottom. When the gas passes through the throat, the flow rate increases dramatically and a local low temperature is generated. The high-speed gas flow impacts the falling droplets, causing them to break up, increasing the gas-liquid contact area, and promoting the escape of ethane components from the liquid phase.

[0027] Please combine Figure 4 and Figure 11 A liquid collecting cup 15 is fixedly connected to the bottom end of the lower cone 7. The liquid collecting cup 15 is cylindrical and closed at the bottom. Multiple degassing grids 16 are fixedly installed inside the liquid collecting cup 15. The degassing grids 16 are made of multiple layers of wire mesh and are installed above the bottom of the liquid collecting cup 15 and immersed below the liquid surface. Multiple drain holes 17 are opened at the bottom of the liquid collecting cup 15 and are evenly distributed in the circumference. When the residual methane bubbles in the liquid rise, they are cut and broken by the degassing grids 16, and the released gas escapes upward. The liquid is continuously discharged through the drain holes 17.

[0028] Please combine Figure 8 A liquid collection tank 8 is fixedly installed at the bottom of the cascade separation tower 1. The liquid collection tank 8 is cylindrical with a conical bottom and its diameter is larger than that of the liquid collection cup 15. An annular gap is formed between the liquid collection tank 8 and the inner wall of the cascade separation tower 1. A siphon breaking pipe 9 is fixedly installed inside the liquid collection tank 8. The siphon breaking pipe 9 is inverted U-shaped. One end of it is inserted into the bottom of the liquid collection tank 8 and the other end is led out of the cascade separation tower 1. A void breaking hole is provided at the top of it. A vortex preventer 10 is fixedly installed at the bottom of the liquid collection tank 8. The vortex preventer 10 is cross-shaped and welded directly above the drain port of the liquid collection tank 8 to prevent vortices from being generated during liquid discharge.

[0029] Please combine Figure 7 A first support plate 20 is fixedly connected between the stepped separation tower 1 and the upper cone 5, a second support plate 21 is fixedly connected between the upper cone 5 and the middle cone 6, and a third support plate 22 is fixedly connected between the middle cone 6 and the lower cone 7. The three cones are fixed inside the stepped separation tower 1 by their respective support plates, thus forming a stable coaxial nested structure. At the same time, the lower ends of each cone are freely suspended, allowing free expansion and contraction along the axial direction during low-temperature shrinkage, thus avoiding thermal stress concentration.

[0030] Through the above technical solution, three independent temperature zones are formed by coaxially nested upper cone 5, middle cone 6, and lower cone 7 with their lower ends extending out sequentially. LNG flows sequentially through the outer walls of each cone under gravity. Methane is vaporized in the upper cone 5 and discharged from the top, while ethane is vaporized in the middle cone 6 and discharged. Heavy hydrocarbons are collected in the bottom collection tank 8, thus achieving flexible output of natural gas with different calorific values. Through the synergistic effect of the guide fins 13, guide grooves 11, and guide notches 14, the liquid forms a continuous and stable liquid film, while the gas flows around the fins, generating turbulence, which greatly improves the gas-liquid heat and mass transfer efficiency. Through the synergistic effect of the conical anti-jamming holes 19, drainage ridges 12, and multi-layer degassing grids 16, the device has good anti-freezing and self-draining capabilities under cryogenic conditions, ensuring long-term stable operation.

[0031] Working principle: The LNG inlet 2 of the cascade separation tower 1 is connected to the LNG storage tank pipeline, the tangential inlet 3 is connected to the LNG pump pipeline, the liquid outlet of the liquid collection tank 8 is connected to the heavy hydrocarbon storage tank pipeline, and the gas phase outlet at the top of the cascade separation tower 1 is connected to the downstream natural gas pipeline network. When performing cascade separation and calorific value control of LNG, LNG enters the cascade separation tower 1 from LNG inlet 2 or tangential inlet 3, and is injected tangentially into the inner wall of the upper cone 5 through the feed pipe 4. LNG flows spirally downward along the inner wall of the upper cone 5. In the low temperature range of the upper cone 5, methane is preferentially vaporized, and methane-rich gas is discharged from the first exhaust port at the top of the upper cone 5. The remaining heavy hydrocarbon liquid continues to flow downward along the inner wall of the upper cone 5, and is guided to the outer wall of the middle cone 6 by the guide ring 23. It then spirals downward along the outer wall of the middle cone 6. In the intermediate temperature range of the middle cone 6, ethane is vaporized, and the ethane-rich gas is discharged from the second exhaust port at the top of the middle cone 6. The remaining heavy hydrocarbon liquid continues to flow downward to the outer wall of the lower cone 7, spiraling downward along the outer wall of the lower cone 7. In the higher temperature range of the lower cone 7, the heavy hydrocarbon components condense into liquid and collect in the liquid collection cup 15 at the bottom of the lower cone 7. After the residual methane bubbles are removed by the degassing grid 16, it is discharged from the drain hole 17 into the liquid collection tank 8, and finally automatically discharged into the heavy hydrocarbon storage tank through the siphon destruction pipe 9. At the same time, the gas flows upward from the bottom of the lower cone 7, passing through the annular gap between the liquid collecting cup 15 and the venturi tube 24, the throat of the venturi tube 24, and the conical anti-jamming hole 19 of the extended cylinder 18 in sequence, forming a countercurrent contact with the downward flowing liquid, and completing multi-stage gas-liquid balance exchange. When it is necessary to adjust the calorific value of the output natural gas, the mixing ratio of methane, ethane and light hydrocarbons can be controlled by adjusting the opening degree of different gas extraction ports, thereby obtaining natural gas with different calorific values ​​to be transported to the downstream pipeline network.

[0032] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0033] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A cascade recovery device for liquefied natural gas (LNG) calorific value regulation, comprising a cascade separation tower (1), an LNG inlet (2), and a tangential inlet (3), wherein the LNG inlet (2) is located at the top of the cascade separation tower (1), and the tangential inlet (3) is located on one side of the cascade separation tower (1), characterized in that, The cascade separation tower (1) is internally equipped with a three-level nested tower core, the three-level nested tower core comprising: The upper cone (5) is fixedly installed inside the cascade separation tower (1); The middle cone (6) is fixedly installed inside the upper cone (5); The lower cone (7) is fixedly installed inside the middle cone (6); The lower part of the middle cone (6) passes through the bottom of the upper cone (5) and extends downward, and the lower part of the lower cone (7) passes through the bottom of the middle cone (6) and extends downward; the tangential feed port (3) is fixedly connected to a feeding pipe (4), and the ejection end of the feeding pipe (4) is tangential to the inner wall of the upper cone (5). When LNG enters from the LNG inlet (2) or the tangential inlet (3), the LNG flows spirally downward along the inner wall of the upper cone (5). Methane is preferentially vaporized and discharged from the top of the upper cone (5). The heavy hydrocarbon liquid flows sequentially through the outer walls of the middle cone (6) and the lower cone (7). Ethane is vaporized on the outer wall of the middle cone (6) and discharged. The remaining heavy hydrocarbon liquid is collected at the bottom of the cascade separation tower (1).

2. The liquefied natural gas calorific value regulation and cascade recovery device according to claim 1, characterized in that, The outer walls of the upper cone (5), middle cone (6) and lower cone (7) are provided with guide fins (13) and guide grooves (11). The guide fins (13) are provided with guide notches (14). The guide grooves (11) and guide notches (14) are connected in a one-to-one correspondence.

3. The liquefied natural gas calorific value regulation and cascade recovery device according to claim 2, characterized in that, The bottom of the guide channel (11) is provided with a plurality of drainage ridges (12) spaced apart along the length direction, and the drainage ridges (12) are semi-cylindrical protrusions.

4. The liquefied natural gas calorific value regulation and cascade recovery device according to claim 1, characterized in that, A guide ring (23) is fixedly provided at the bottom of the inner wall of the upper cone (5), and the guide ring (23) is inclined downward and faces the outer wall of the middle cone (6).

5. A liquefied natural gas calorific value regulation and cascade recovery device according to claim 4, characterized in that, The bottom of the upper cone (5) is fixedly connected to an extension cylinder (18), and the circumferential side of the extension cylinder (18) is provided with staggered conical anti-jamming holes (19).

6. A liquefied natural gas calorific value regulation and cascade recovery device according to claim 1, characterized in that, The bottom end of the middle cone (6) is fixedly connected to a Venturi tube (24).

7. A liquefied natural gas calorific value regulation and cascade recovery device according to claim 6, characterized in that, The bottom end of the lower cone (7) is fixedly connected to a liquid collection cup (15), and the inside of the liquid collection cup (15) is fixedly provided with a multi-layer degassing grid (16), and the bottom of the liquid collection cup (15) is provided with multiple drainage holes (17).

8. A liquefied natural gas calorific value regulation and cascade recovery device according to claim 7, characterized in that, The bottom of the cascade separation tower (1) is fixedly provided with a liquid collection tank (8), a siphon breaking pipe (9) is fixedly provided in the liquid collection tank (8), and an anti-vortex device (10) is fixedly provided at the bottom of the liquid collection tank (8).

9. A liquefied natural gas calorific value regulation and cascade recovery device according to claim 8, characterized in that, A first support plate (20) is fixedly connected between the cascade separation tower (1) and the upper cone (5), a second support plate (21) is fixedly connected between the upper cone (5) and the middle cone (6), and a third support plate (22) is fixedly connected between the middle cone (6) and the lower cone (7).

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