Cryogenic LPG loading system with automatic venting and depressurization

Abstract

This invention discloses a cryogenic LPG loading system with automatic venting and pressure relief, comprising: an LPG loading main pipe, a BOG return pipe, an LPG loading / unloading arm connected to the LPG loading main pipe, and a BOG return arm connected to the BOG return pipe. A pressure relief riser is installed at the highest point of the LPG loading main pipe, and the pressure relief riser is connected to the BOG return pipe via a return gas pipe. A first shut-off valve is installed on the return gas pipe, and the first shut-off valve is interlocked with the LPG delivery pump. A differential pressure level gauge is installed on the pressure relief riser, and a pressure regulating valve is installed downstream of the first shut-off valve on the return gas pipe. The differential pressure level gauge is interlocked with the pressure regulating valve so that when the differential pressure level gauge outputs a high level signal, the pressure regulating valve closes, and when it outputs a low level signal, the pressure regulating valve opens. This invention eliminates the need for an LPG cold circulation system, ensuring the LPG loading main pipe remains in a safe state.

Description

Technical Field

[0001] This invention relates to the field of chemical terminal storage and transportation technology. More specifically, this invention relates to a cryogenic LPG loading system with automatic venting and depressurization capabilities. Background Technology

[0002] LPG is an important chemical feedstock and fuel. Large-scale LPG trade typically involves liquefying the gas and then transporting it by pipeline to ships for ocean shipping. LPG is generally available in two types: ambient temperature / high pressure and cryogenic / atmospheric pressure. Cryogenic LPG includes propane (C3, storage temperature -43°C) and butane (C4, storage and transportation temperature -7°C). Traditional cryogenic LPG loading systems include... Figure 1 As shown, liquid LPG from the land-based tank farm is transported to the LPG ship via the LPG loading main pipe, and BOG gas from the LPG ship's hold is returned to the land-based tank farm for reliquefaction and storage via the BOG return pipe. During non-loading operations, because LPG is a cryogenic medium, ambient heat entering the pipeline causes residual liquid LPG in the loading main pipe to vaporize. This vaporization increases the pressure within the loading main pipe, creating a safety hazard. Furthermore, some liquid LPG is pre-cooled and consumed before the next loading. Therefore, a small flow of LPG must be output from the land-based tank farm along the loading main pipe and then returned to the land-based tank farm via a dedicated cold circulation pipe to ensure the loading main pipe remains in a cryogenic environment and within the design pressure range. Due to the long length of the wharf pier, installing a dedicated cold circulation pipeline requires continuous operation, which not only consumes energy but also increases pipeline infrastructure, complicates system control, occupies space in the pier's pipe rack and wharf, and significantly increases installation and maintenance costs. Therefore, proposing a facility that ensures the safety of the loading process system without requiring a dedicated cold circulation system is of great significance. Summary of the Invention

[0003] The purpose of this invention is to provide a low-temperature LPG loading system that can automatically vent and depressurize, thereby ensuring that the LPG loading main is in a safe state without the need for an LPG cold circulation system.

[0004] To achieve these objectives and other advantages according to the present invention, an automatically venting and depressurizing cryogenic LPG loading system is provided, comprising: an LPG loading main extending from an LPG land-based tank farm to a terminal, a BOG return pipe extending from the terminal to the LPG land-based tank farm, an LPG loading arm disposed at the terminal berth and connected to the LPG loading main, and a BOG return arm disposed at the terminal berth and connected to the BOG return pipe, wherein a depressurization riser is disposed at the highest point of the LPG loading main and connected thereto, and the depressurization riser is connected to the BOG return pipe via a return gas pipe;

[0005] The return gas pipe is equipped with a first shut-off valve, which is interlocked with the LPG delivery pump so that the first shut-off valve is closed when the LPG delivery pump starts and opened when the LPG delivery pump stops.

[0006] A differential pressure level gauge is installed on the pressure relief riser, and a pressure regulating valve is installed downstream of the first shut-off valve on the return gas pipe. The differential pressure level gauge is interlocked with the pressure regulating valve so that when the differential pressure level gauge outputs a high liquid level signal, the pressure regulating valve is closed, and when it outputs a low liquid level signal, the pressure regulating valve is opened.

[0007] Preferably, a second shut-off valve is also provided on the return gas pipe downstream of the pressure regulating valve.

[0008] Preferably, an exhaust bypass pipe communicating with the return gas pipe is provided on the return gas pipe between the upstream of the first shut-off valve and the downstream of the second shut-off valve. The diameter of the exhaust bypass pipe is the same as that of the return gas pipe, and a third shut-off valve is provided on the exhaust bypass pipe.

[0009] When the differential pressure level gauge outputs a high liquid level signal, it triggers a first alarm signal; when the differential pressure level gauge outputs a low liquid level signal, it triggers a second alarm signal.

[0010] Preferably, the diameter of the pressure relief riser is the same as that of the LPG loading main pipe, the elevation difference between the upper and lower pressure taps of the differential pressure level gauge on the pressure relief riser is not less than 600 mm, the lower pressure tap of the differential pressure level gauge on the pressure relief riser is 100 mm from the bottom of the pressure relief riser, and the upper pressure tap of the differential pressure level gauge on the pressure relief riser is 100 mm from the top of the pressure relief riser.

[0011] Preferably, the pressure regulating valve is a tight shut-off type, and the pressure regulating valve automatically regulates the pressure in its downstream return gas pipe to not exceed 10 kPaG.

[0012] Preferably, a fourth shut-off valve is provided on the LPG loading main pipe, and a fifth shut-off valve is provided on the BOG return pipe.

[0013] Preferably, the pressure relief riser is provided with a cap at the top, and the return air pipe is connected to the cap.

[0014] Preferably, the LPG is propane, butane, or a mixture of propane and butane.

[0015] The present invention has at least the following beneficial effects:

[0016] 1. No need to install cold circulation pipelines, saving investment in pipelines, instruments and control systems, reducing the space occupied by docks and trestle layout, and saving construction costs and time;

[0017] 2. After loading is completed, the exhaust and pressure relief facilities will be automatically activated. The residual low-temperature LPG in the loading main pipe will naturally vaporize and accumulate in the pressure relief riser at the highest point, causing the liquid level in the pressure relief riser to drop. When the differential pressure level gauge outputs a low liquid level signal, the pressure regulating valve will open, and the gas phase will return to the land tank area along the BOG return pipe, thereby avoiding the safety hazards caused by excessive pressure in the loading main pipe.

[0018] 3. The gas phase formed by heat leakage of low-temperature LPG in the loading main pipe can not only be automatically discharged, but also absorb heat during the phase change process of natural vaporization, so that the LPG loading main pipe is kept at a low temperature. At the same time, the gas phase continues to absorb heat as it returns to the land tank area along the BOG return pipe, which can also keep the BOG return pipe cold.

[0019] 4. The system's venting and depressurization process is fully automated. The low-level regulating valve opens for natural venting, while the high-level regulating valve closes tightly to prevent liquid from entering the gaseous BOG system. No special monitoring is required, making the design safer and operation simpler.

[0020] 5. Compared with the traditional method of laying dedicated cold circulation pipelines, the present invention does not require the output of a small flow of LPG to keep the main loading pipe cold. Therefore, there is no continuous energy consumption during operation, which can achieve the purpose of energy saving and environmental protection.

[0021] 6. This invention can also be applied to LPG unloading systems, as well as loading and unloading systems for liquid ammonia and other substances that have similar physical properties to LPG, thus having a wide range of applications.

[0022] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0023] Figure 1 A schematic diagram of the piping system for a traditional cryogenic LPG loading system.

[0024] Figure 2 This is a schematic diagram of the piping of the low-temperature LPG loading system with automatic venting and depressurization as described in this invention.

[0025] Figure 3 A schematic diagram of the structure of the low-temperature LPG loading system with automatic venting and depressurization described in this invention;

[0026] Among them, 1-LPG loading main pipe, 2-BOG return pipe, 3-pressure relief riser, 4-differential pressure level gauge, 5-first shut-off valve, 6-exhaust bypass pipe, 7-pressure regulating valve, 8-third shut-off valve, 9-second shut-off valve, 10-return gas pipe, 11-LPG loading and unloading arm, 12-BOG return arm, 13-fourth shut-off valve, 14-fifth shut-off valve, 21-dedicated cold circulation pipe. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0028] It should be noted that in the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0029] This example illustrates the practical application of an overseas project. In this project, the LPG terminal berth is located 800 meters away from the land-based tank farm, and the LPG carrier has a capacity of 35,000 m³. 3 The loading medium is cryogenic propane. Based on the ship type, the designed loading flow rate is 2600 m³ / h. 3 / h, net loading time is 14h.

[0030] To meet the above project requirements, this embodiment provides a cryogenic LPG loading system with automatic venting and depressurization capabilities. Please refer to [link to relevant documentation]. Figures 2-3 Specifically, it includes:

[0031] The LPG loading main 1 extends from the LPG land-based tank farm to the terminal, the BOG return pipe 2 extends from the terminal to the LPG land-based tank farm, the LPG loading arm 11 is located at the terminal berth and connected to the LPG loading main 1, and the BOG return arm 12 is located at the terminal berth and connected to the BOG return pipe 2.

[0032] Specifically, the LPG loading main pipe 1 is designed to be DN500 with a flow velocity of 3.7m / s; the LPG loading and unloading arm 11 is designed to be DN300 with a flow velocity of approximately 10m / s.

[0033] The highest point of the LPG loading main pipe 1 is equipped with a pressure relief riser 3 connected to it, and the pressure relief riser 3 is connected to the BOG return pipe 2 through the return air pipe 10.

[0034] The return gas pipe 10 is equipped with a first shut-off valve 5, which is interlocked with the LPG delivery pump so that the first shut-off valve 5 is closed when the LPG delivery pump starts and opened when the LPG delivery pump stops.

[0035] A differential pressure level gauge 4 is installed on the pressure relief riser 3, and a pressure regulating valve 7 is installed on the return gas pipe 10 downstream of the first shut-off valve 5. The differential pressure level gauge 4 and the pressure regulating valve 7 are interlocked so that when the differential pressure level gauge 4 outputs a high liquid level signal, the pressure regulating valve 7 is closed, and when it outputs a low liquid level signal, the pressure regulating valve 7 is opened.

[0036] Specifically, since the main loading pipe is 800m long, the heat loss of the pipe is calculated as 32W / m. 2 Considering the design, the upstream return gas pipe section 10 of the pressure regulating valve 7 is DN25. Under non-ship loading conditions, the pressure of the upstream return gas pipe section 10 is assumed to be 2 barg based on the static pressure difference between the LPG storage tank and the pressure relief riser 3. The downstream return gas pipe section 10 of the pressure regulating valve 7 is designed to be DN50. The downstream return gas pipe section 10 is considered to be operating at a maximum pressure of 10 kPag in the land-based tank farm, and the calculated exhaust volume is 45 Nm. 3 / h, the pressure regulating valve 7 is selected as a tight shut-off type shut-off valve, which can meet the adjustment requirements of pressure drop from 2 barg to 10 kPag.

[0037] Specifically, the diameter of the pressure relief riser 3 is the same as that of the LPG loading main pipe 1. The elevation difference between the upper and lower pressure taps of the differential pressure level gauge 4 on the pressure relief riser 3 is not less than 600 mm. This allows for a certain duration of liquid level change between the upper and lower pressure taps, providing a certain interval for the pressure regulating valve 7 to operate, thus preventing the pressure regulating valve 7 from being triggered too frequently due to a small elevation difference between the upper and lower pressure taps. The lower pressure tap of the differential pressure level gauge 4 on the pressure relief riser 3 is H3 = 100 mm from the bottom of the pressure relief riser 3, and the upper pressure tap of the differential pressure level gauge 4 on the pressure relief riser 3 is H4 = 100 mm from the top of the pressure relief riser 3. This design meets the pressure requirements of the pipeline, preventing both excessively high liquid level and excessively high pressure in the pressure relief riser 3. In this example, the pressure relief riser 3 is designed to be DN500, H1 = 1m, and the elevation difference H2 between the upper and lower pressure taps is designed to be 0.8m.

[0038] Furthermore, a fourth shut-off valve 13 is provided on the LPG loading main pipe 1 to cut off or connect the LPG loading main pipe 1 pipeline, and a fifth shut-off valve 14 is provided on the BOG return pipe 2 to cut off or connect the BOG return pipe 2 pipeline.

[0039] Furthermore, in order to make it easier to collect gas at the top of the pressure relief riser 3, a pipe cap can be installed at the top of the pressure relief riser 3, and the return gas pipe 10 can be connected to the pipe cap.

[0040] Furthermore, to avoid the formation of liquid and gas bags that could cause pipeline vibration, the return gas pipeline downstream of pressure regulating valve 7 can be arranged in a step-low manner.

[0041] The specific steps for loading LPG onto ships using the aforementioned low-temperature LPG loading system with automatic venting and depressurization are as follows:

[0042] 1. After the vessel waiting to load LPG docks at the berth, connect the LPG loading arm 11 to the liquid phase manifold of the LPG vessel and the BOG return arm 12 to the gas phase manifold of the LPG vessel. Conduct leak checks and necessary safety tests to confirm that the control system and related operations are in working condition.

[0043] 2. Open the fourth shut-off valve 13, the fifth shut-off valve 14, and the LPG transfer pump. Since the LPG transfer pump is interlocked with the first shut-off valve 5, the first shut-off valve 5 automatically closes when the LPG transfer pump starts, thus preventing cryogenic liquid propane from entering the pressure relief riser 3 and the return gas pipe 10. Cryogenic liquid propane enters the LPG ship's hold via the LPG loading main pipe 1 and the LPG loading / unloading arm 11, displacing BOG from the hold. The displaced BOG is then sent back to the land-based tank farm via the BOG return arm 12 and the BOG return pipe 2 under pressure differential to balance the tank pressure. Excess BOG will be reliquefied.

[0044] 3. After loading is completed, close the fourth shut-off valve 13 and the fifth shut-off valve 14, shut down the LPG transfer pump, drain the loading and unloading arm, and disconnect the LPG loading and unloading arm 11 and the BOG return arm after checking that the drain is complete.

[0045] IV. After loading is completed, the LPG loading main pipe 1 is still filled with cryogenic liquid propane. Due to the influence of ambient temperature, even with a cold insulation layer, heat can leak into the loading main pipe. The temperature and pressure of the cryogenic liquid propane inside the loading main pipe will rise, which can easily lead to leakage and even fire or explosion hazards. Therefore, when the LPG transfer pump is shut down, the first shut-off valve 5 automatically opens, connecting the LPG loading main pipe 1 with the pressure regulating valve 7 on the pressure relief riser 3 and the return gas pipe 10.

[0046] 5. Because the differential pressure level gauge 4 on the pressure relief riser 3 is interlocked with the pressure regulating valve 7, when the liquid level in the pressure relief riser 3 reaches the pressure tapping point on the differential pressure level gauge 4, the pressure regulating valve 7 will be tightly closed to prevent cryogenic liquid propane from entering the return gas pipe 10 downstream of the pressure regulating valve 7. As heat enters, the cryogenic liquid propane in the loading main pipe and the pressure relief riser 3 gradually vaporizes, causing the gas phase to accumulate at the higher part of the pressure relief riser 3. The liquid level in the pressure relief riser 3 will gradually decrease. When the liquid level reaches the lower pressure tapping point on the differential pressure level gauge 4, the pressure regulating valve 7 will automatically open, and the gaseous propane will enter the BOG return pipe 2 from the return gas pipe 10 downstream of the pressure regulating valve 7, and then return to the land-based tank area along the BOG return pipe 2. Because the gas phase generated in the system can be automatically and promptly removed, the system pressure and temperature will stabilize within a safe range.

[0047] Based on the above description of the loading process, it is easy to see that: after loading is completed, the above embodiment automatically activates the venting and depressurization facilities. The residual low-temperature LPG in the loading main pipe undergoes heat leakage and natural vaporization, entering the depressurization riser 3, which lowers the liquid level in the depressurization riser 3. When the differential pressure level gauge 4 outputs a low liquid level signal, the pressure regulating valve 7 opens, and the gas phase returns to the land-based tank area along the BOG return pipe 2, thereby avoiding safety hazards caused by excessive pressure in the loading main pipe. The phase change process of the residual low-temperature LPG in the loading main pipe undergoing heat leakage and natural vaporization absorbs heat, keeping the LPG loading main pipe 1 at a low temperature. At the same time, the gas phase continues to absorb heat as it returns to the land-based tank area along the BOG return pipe 2, which can also continue to keep the BOG return pipe 2 cold. The system's venting and depressurization process is fully automated and requires no special monitoring, thus making operation simpler.

[0048] Meanwhile, compared with traditional low-temperature LPG loading systems, the above embodiments do not require the installation of cold circulation pipelines, saving investment in pipelines, instruments, and control systems, reducing the space occupied by the dock and trestle layout, saving construction costs and time, and eliminating the need to output a small flow of LPG to keep the loading main pipe cold. Therefore, there is no continuous energy consumption during operation, achieving the goal of energy conservation and environmental protection.

[0049] In the aforementioned embodiments, since the pressure regulating valve 7 is interlocked with the differential pressure level gauge, the pressure regulating valve 7 needs to frequently operate based on the level signal output by the differential pressure level gauge 4. Therefore, it requires frequent maintenance and repair to prevent the pressure regulating valve 7 from failing. During the maintenance and repair period of the pressure regulating valve 7, the connection between the pressure regulating valve 7 and the return gas pipe 10 needs to be disconnected. To achieve this, the following embodiments further improve upon the aforementioned embodiments:

[0050] Specifically, a second shut-off valve 9 is also provided on the return gas pipe 10 downstream of the pressure regulating valve 7. In this way, when the pressure regulating valve 7 malfunctions, the first shut-off valve 5 upstream of the pressure regulating valve 7 and the second shut-off valve 9 downstream of the pressure regulating valve 7 can be manually closed. Here, the first shut-off valve 5 is manually operated so as not to trigger its interlock function with the LPG transfer pump.

[0051] In the aforementioned embodiments, when the pressure regulating valve 7 malfunctions, the operator manually closes the first shut-off valve 5 upstream of the pressure regulating valve 7 and the second shut-off valve 9 downstream of the pressure regulating valve 7. However, this prevents the system from releasing pressure. To ensure the system continues to perform its pressure release function during the maintenance and warranty period of the pressure regulating valve 7, the following embodiments further improve upon the aforementioned embodiments:

[0052] Specifically, an exhaust bypass pipe 6 is provided on the return pipe 10 between the upstream of the first shut-off valve 5 and the downstream of the second shut-off valve 9, and is connected to the return pipe 10. The diameter of the exhaust bypass pipe 6 is the same as that of the return pipe 10, and a third shut-off valve 8 is provided on the exhaust bypass pipe 6.

[0053] When the differential pressure level gauge 4 outputs a high liquid level signal, it triggers a first alarm signal; when the differential pressure level gauge 4 outputs a low liquid level signal, it triggers a second alarm signal.

[0054] In the specific operation of this embodiment, since both the upstream and downstream of the pressure regulating valve 7 are cut off, the pressure relief riser 3 is connected to the exhaust bypass pipe 6. When the differential pressure level gauge 4 outputs a high liquid level signal, the system triggers a first alarm signal and displays it on the system's touch panel. The operator can then use this first alarm signal to know the high liquid level in the pressure relief riser 3 and manually close the third shut-off valve 8 to prevent liquid propane from entering the downstream of the return gas pipe 10 through the exhaust bypass pipe 6. When the differential pressure level gauge 4 outputs a low liquid level signal, the system triggers a second alarm signal and displays it on the system's touch panel. The operator can then use this second alarm signal to know the low liquid level in the pressure relief riser 3 and manually open the third shut-off valve 8 to release the accumulated gaseous propane in the pressure relief riser 3. This allows for manual pressure relief of the system.

[0055] Although the LPG in the foregoing embodiments is propane, the above-mentioned low-temperature LPG loading system is also applicable when the LPG is butane or a mixture of propane and butane.

[0056] In addition, the above embodiments can also be applied to LPG unloading systems, as well as loading and unloading systems for liquid ammonia and other substances that have similar physical properties to LPG, thus having a wide range of applications.

[0057] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A low temperature LPG loading system capable of automatic venting and pressure relief, comprising: The LPG loading main pipe extending from the LPG land tank area to the wharf, the BOG return pipe extending from the wharf to the LPG land tank area, the LPG loading and unloading arm arranged on the wharf berth and communicated with the LPG loading main pipe, and the BOG return arm arranged on the wharf berth and communicated with the BOG return pipe are characterized in that the highest point of the LPG loading main pipe is provided with a pressure relief stand pipe communicated therewith, and the pressure relief stand pipe is further communicated with the BOG return pipe through a gas return pipe. The first cut-off valve is interlocked with the LPG delivery pump to realize that the first cut-off valve is closed when the LPG delivery pump is started and the first cut-off valve is opened when the LPG delivery pump is stopped. The pressure relief stand pipe is provided with a differential pressure type liquid level meter, and the gas return pipe is provided with a pressure regulating valve downstream of the first cut-off valve, and the differential pressure type liquid level meter is interlocked with the pressure regulating valve to realize that the pressure regulating valve is closed when the differential pressure type liquid level meter outputs a high liquid level signal and the pressure regulating valve is opened when the differential pressure type liquid level meter outputs a low liquid level signal.

2. The self-ventable and pressure-relievable cryogenic LPG loading system of claim 1, wherein, The gas return pipe is further provided with a second cut-off valve downstream of the pressure regulating valve.

3. The self-ventable and pressure-relievable cryogenic LPG loading system of claim 2, wherein, The gas return pipe is provided with a third cut-off valve between the first cut-off valve upstream and the second cut-off valve downstream. The differential pressure type liquid level meter outputs a high liquid level signal to trigger a first alarm signal, and outputs a low liquid level signal to trigger a second alarm signal.

4. The self-ventable and pressure-relievable cryogenic LPG loading system of claim 1, wherein, The pressure relief stand pipe has the same diameter as the LPG loading main pipe, the differential pressure type liquid level meter has a height difference between the upper and lower pressure points on the pressure relief stand pipe of not less than 600 mm, the lower pressure point of the differential pressure type liquid level meter is 100 mm away from the bottom of the pressure relief stand pipe, and the upper pressure point of the differential pressure type liquid level meter is 100 mm away from the top of the pressure relief stand pipe.

5. The self-ventable and pressure-relievable cryogenic LPG loading system of claim 1, wherein, The pressure regulating valve is a tightly closed type, and the pressure regulating valve adjusts the pressure in the gas return pipe downstream of the pressure regulating valve to be not more than 10 kPaG.

6. The self-ventable and pressure-relievable cryogenic LPG loading system of claim 1, wherein, The LPG loading main pipe is provided with a fourth cut-off valve, and the BOG return pipe is provided with a fifth cut-off valve.

7. The self-ventable and pressure-relievable cryogenic LPG loading system of claim 1, wherein, The top end of the pressure relief stand pipe is provided with a pipe cap, and the gas return pipe is connected to the pipe cap.

8. The self-ventable and pressure-relievable cryogenic LPG loading system of claim 1, wherein, The LPG is propane or butane or a mixture of propane and butane.

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