LNG loading system

Abstract

This invention provides an LNG loading system. The LNG loading system includes: a cryogenic storage tank containing LNG; a loading pipeline system including an outlet pipeline, a return pipeline, a return regulating valve, and an orifice flow meter; the inlet end of the outlet pipeline is connected to a discharge port, and the outlet end of the outlet pipeline supplies LNG from the tank to the outside, extending to the tank truck loading area; the inlet end of the return pipeline is connected to the outlet pipeline, and the outlet end of the return pipeline is connected to a return port; the orifice flow meter is installed on the outlet pipeline to detect the flow rate; the return regulating valve is installed on the return pipeline to regulate the flow rate; and a control assembly is electrically connected to the orifice flow meter and the return regulating valve; the control assembly controls the opening of the return regulating valve based on the flow signal fed back from the orifice flow meter, thereby adapting to changes in the number of tank trucks to be loaded, achieving a high degree of automation.

Description

Technical Field

[0001] This invention relates to the field of LNG transportation equipment technology, and in particular to an LNG loading system. Background Technology

[0002] Cryogenic ceiling-mounted storage tanks are commonly used containers for storing LNG (liquefied natural gas), and the demand for them is increasing at LNG receiving terminals and LNG liquefaction plants. Most of the LNG stored in these tanks is transported throughout the country via LNG tank trucks, so most storage tanks are equipped with LNG loading systems.

[0003] Traditional LNG loading systems mostly use external pumps, meaning the plunger pumps or submersible pumps used for loading are located outside the storage tank. However, this type of system is relatively simple, only capable of loading LNG and lacking a high degree of automation. A smaller number of storage tanks use in-tank pump systems, where the submersible pumps are located inside the storage tank. However, these systems are often not well-designed, with generally low levels of automation and safety. This makes them unable to meet the constantly changing loading conditions and handle unexpected situations during the loading process. Summary of the Invention

[0004] The purpose of this invention is to provide an LNG loading system to solve the problem that existing loading systems cannot flexibly meet the ever-changing loading conditions.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] An LNG loading system includes: a cryogenic storage tank storing LNG, with a drain port and a reflux port communicating with the tank's interior at the top; a loading pipeline system including an outlet pipeline, a reflux pipeline, a reflux regulating valve, and an orifice flow meter; the inlet end of the outlet pipeline is connected to the drain port, and the outlet end of the outlet pipeline supplies LNG from the tank to the outside, extending to the tank truck loading area; the inlet end of the reflux pipeline is connected to the outlet pipeline, and the outlet end of the reflux pipeline is connected to the reflux port; the orifice flow meter is installed on the outlet pipeline to detect the flow rate; the reflux regulating valve is installed on the reflux pipeline to regulate the flow rate; and a control assembly electrically connected to the orifice flow meter and the reflux regulating valve; the control assembly controls the opening degree of the reflux regulating valve based on the flow signal fed back by the orifice flow meter.

[0007] According to one aspect of the invention, the orifice plate flow meter is located downstream of the connection node between the outlet pipeline and the return pipeline.

[0008] According to one aspect of the present invention, at least two drain ports are provided; at least two submersible pumps are provided inside the cryogenic storage tank, and the outlet of each submersible pump is provided with a pump column; the pump column extends outward from the tank through the drain ports; the outlet pipeline includes two branch pipes and an outlet collection pipe; one end of each branch pipe is connected to the top of each pump column, and the other ends of the two branch pipes are connected and merged and connected to the outlet collection pipe; the two submersible pumps operate alternately, one starting and one stopping.

[0009] According to one aspect of the invention, the outlet manifold is connected to the return pipe; the orifice flow meter is disposed on the outlet manifold.

[0010] According to one aspect of the invention, the control assembly includes a pump frequency converter control cabinet, and a pump motor and a pump operating column respectively electrically connected to the pump frequency converter control cabinet.

[0011] According to one aspect of the present invention, the control assembly includes a PLC control cabinet, and the PLC control cabinet and the pump frequency converter control cabinet are electrically connected.

[0012] According to one aspect of the present invention, at least two drain ports are provided; at least two submersible pumps are provided inside the cryogenic storage tank, and each submersible pump has a pump column at its outlet; the pump column extends outward from the tank through the drain port; two outlet pipes and two return pipes are provided respectively, the inlet end of each outlet pipe is connected to the top end of each pump column, and each return pipe is connected and communicates with each outlet pipe; two return regulating valves and two orifice plate flow meters are also provided respectively.

[0013] According to one aspect of the invention, the loading pipeline system further includes a pressure transmitter, a cryogenic shut-off valve, a cryogenic check valve, and a temperature transmitter sequentially disposed upstream of the outlet pipeline near the cryogenic storage tank.

[0014] According to one aspect of the invention, the loading pipeline system further includes a liquid outlet switch valve disposed on the liquid outlet pipeline, the liquid outlet switch valve being located downstream of the orifice flow meter.

[0015] According to one aspect of the present invention, the LNG loading system further includes a venting system, the venting system including a venting pipe and a cryogenic safety valve; the two ends of the venting pipe are respectively connected to the cryogenic storage tank and the liquid outlet pipeline, and the cryogenic safety valve is provided on the venting pipe to control the opening and closing of the venting pipe.

[0016] As can be seen from the above technical solution, the LNG loading system provided by the present invention has at least the following advantages and positive effects: The LNG return line is connected to the outlet line to achieve LNG diversion. An orifice flow meter detects the flow rate in the outlet line, while a reflux regulating valve adjusts the flow rate in the return line. The orifice flow meter and reflux regulating valve are interlocked. The control assembly controls the opening of the reflux regulating valve based on the flow signal from the orifice flow meter, thereby regulating the LNG flow rate at the outlet of the outlet line. This adapts to changes in the number of tank trucks waiting to be loaded, resulting in a high degree of automation and practicality. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the loading pipeline system in the first embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the operation of the pump start-stop system, DCS control system and automatic valve control system in the first embodiment of the present invention.

[0019] Figure 3 This is a schematic diagram of the loading pipeline system in the second embodiment of the present invention.

[0020] The annotations in the attached figures are explained as follows: 200-tank truck, 100 - Cryogenic storage tank, 101 - Drain port, 102 - Reflux port, 103 - Submersible pump, 104 - Pump column 1-Loading piping system; 11-Pressure transmitter; 12-Cryogenic shut-off valve; 13-Cryogenic check valve; 14-Temperature transmitter; 15-Orifice plate flow meter; 16-Condensation induction valve; 17-Discharge switch valve; 18-Return regulating valve; 191-Discharge piping; 1911-Branch pipe; 1912-Discharge main pipe; 192-Return piping; 193-Common return piping. 2-Vent system, 20-Vent pipe, 21-Cryogenic shut-off valve, 22-Bypass valve, 23-Cryogenic shut-off valve, 24-Cryogenic safety valve 3-Pump start / stop system, 31-Pump frequency converter control cabinet, 32-Pump motor, 33-Pump operating column, 4-DCS control system, 41-PLC control cabinet, 42-monitoring computer 5-Automatic valve control system, 51-Filter pressure reducer, 52-Solenoid valve, 53-Valve positioner. Detailed Implementation

[0021] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various variations in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations herein are for illustrative purposes only and not intended to limit the present invention.

[0022] This embodiment provides an LNG loading system, mainly used for cryogenic storage tanks. The system automatically controls the built-in submersible pump in the storage tank to transport the LNG stored in the storage tank to the loading area for LNG tank truck filling, etc.

[0023] First Specific Embodiment of LNG Loading System Please refer to the above as well. Figure 1 and Figure 2 These components together illustrate the specific structure of an LNG loading system provided in this embodiment. The LNG loading system mainly includes a cryogenic storage tank 100, a loading pipeline system 1, a venting system 2, a pump start-stop system 3, a DCS control system 4, and an automatic valve control system 5. The pump start-stop system 3, the DCS control system 4, and the automatic valve control system 5 together constitute the control assembly.

[0024] like Figure 1 As shown, the aforementioned cryogenic storage tank 100 is a large LNG cryogenic ceiling-mounted storage tank, and is not limited to storing other cryogenic liquids such as liquid ammonia. The top of the cryogenic storage tank 100 is respectively provided with a drain port 101 for LNG to flow out and a return port 102 for LNG to flow back into the tank, which are connected to the inside of the tank.

[0025] The storage tank is equipped with two submersible pumps 103 (A / B) immersed in LNG. The submersible pumps 103 serve as a power source to lift the LNG from the tank to the outside. Each submersible pump 103 is equipped with a pump column 104, which is vertically arranged. The lower end of the pump column 104 is connected to the outlet of the submersible pump 103, and the upper end of the pump column 104 extends outward from the tank through the drain port 101.

[0026] The loading pipeline system 1 is mainly divided into two parts according to its function: the liquid discharge process pipeline and the reflux process pipeline.

[0027] The liquefaction process pipeline mainly includes a liquefaction pipeline 191, an orifice flow meter 15, and a liquefaction switch valve 17 installed on the liquefaction pipeline 191. The inlet end of the liquefaction pipeline 191 is connected to the pump column 104, and the outlet end of the liquefaction pipeline 191 supplies LNG from the tank to the outside, extending to the loading area of ​​the LNG tanker truck 200. The orifice flow meter 15 is used to detect the flow rate of the liquefaction pipeline 191. The liquefaction switch valve 17 is located downstream of the orifice flow meter 15 and is used to control the on / off state of the liquefaction pipeline 191.

[0028] In this embodiment, the two submersible pumps 103 (A / B) are configured with one in operation and one on standby, and cannot be turned on simultaneously. The two pumps share a single outlet pipe 191 and return pipe 192. Specifically, the outlet pipe 191 includes two branch pipes 1911 and an outlet manifold pipe 1912; one end of each branch pipe 1911 is connected to the top of each pump column 104, and the other ends of the two branch pipes 1911 are connected together and connected to the outlet manifold pipe 1912. The outlet manifold pipe 1912 is connected to the return pipe 192; an orifice plate flow meter 15 is installed on the outlet manifold pipe 1912.

[0029] The reflux process pipeline includes a reflux line 192 and a reflux regulating valve 18 installed on the reflux line 192. The inlet end of the reflux line 192 is connected to the outlet line 191, and the outlet end of the reflux line 192 is connected to the reflux port 102 of the cryogenic storage tank 100. Essentially, a portion of the LNG flowing through the outlet line 191 is diverted into the reflux line 192 and then flows back into the storage tank through the reflux line 192. The reflux regulating valve 18 is installed on the reflux line 192 to regulate the flow rate through the reflux line 192.

[0030] Both the orifice plate flow meter 15 and the reflux regulating valve 18 are electrically connected to the control assembly to achieve interlocking control.

[0031] like Figure 1 As shown, the node connecting the return line 192 and the outlet line 191 is defined as the diversion node S. The orifice flow meter 15 is located downstream of this diversion node S and is actually used to measure the LNG flow rate in the outlet line used for loading after diversion in real time. The working principle of the orifice flow meter 15 is as follows: when the medium flows through the orifice plate in the pipeline, the flow velocity will form a local contraction at the orifice plate, increasing the flow velocity and generating a pressure difference across the orifice plate. The flow rate is calculated by measuring the pressure difference; the larger the medium flow rate, the larger the pressure difference across the orifice plate.

[0032] When the number of tank trucks 200 that need to be filled changes, the flow rate of LNG output from the storage tank pump also needs to change. The control assembly (specifically the DCS control system 4) uses a PID controller to control the opening of the return regulating valve 18 based on the flow signal from the orifice flow meter 15, so that a portion of the LNG in the outlet pipeline 191 is transported back to the storage tank through the return pipeline 192, thereby adjusting the LNG flow rate to meet the tank truck filling requirements.

[0033] Specifically, the LNG output flow rate of the submersible pump 103 can be adjusted by changing the pump speed. However, the speed of the submersible pump 103 is already set during pre-cooling and commissioning, and adjusting the pump speed will cause instability in the output flow rate, resulting in inaccurate data measured by the orifice plate flow meter 15. To ensure that the submersible pump 103 speed remains constant and the pumped LNG flow rate is constant, The flow rate of LNG output needs to be controlled by adjusting the opening of the pump backflow regulating valve 18.

[0034] When the number of tank trucks 200 to be filled is small, the DCS control system 4 receives the actual flow signal from the orifice flow meter 15 and converts it into a corresponding value Q1. Q1 is then compared with the preset loading demand flow value Q2. This loading demand flow value Q2 can come from feedback from the monitoring device in the tank truck loading area or from manual input by on-site personnel. Generally, the flow rate of a single submersible pump 103 is sufficient to meet the flow requirements for a small number of tank trucks. If Q1 is greater than Q2, it indicates that the flow rate is sufficient to meet the loading demand. At this time, the DCS control system 4 sends a control signal to the automatic valve control system 5. The valve positioner 53 uses a PID controller to open the post-pump reflux regulating valve 18 and adjusts its opening. This allows a portion of the LNG in the outlet pipeline 191 to be returned to the storage tank through the post-pump reflux regulating valve 18, thereby regulating the LNG flow rate to meet the tank truck filling requirements. After the LNG begins to divert, the LNG flow rate detected by the orifice flow meter 15 will gradually decrease until it drops to Q2.

[0035] When the number of tank trucks 200 requiring filling increases, the required flow rate for loading becomes larger, Q3. Clearly, the flow rate Q2 from the previous outlet pipeline 191 cannot meet the loading demand. At this point, the DCS control system 4, after comparing the flow rate difference, outputs a control signal to the automatic valve control system 5. The valve positioner 53 uses a PID controller to reduce or even close the post-pump return regulating valve 18 (i.e., close the return pipeline 192), thereby ensuring that all LNG in the outlet pipeline 191 is used entirely for tank truck filling, thus meeting the tank truck filling requirements.

[0036] When not loading, the cryogenic pump maintains a small flow rate of reflux through the return line 192 in the loading pipeline system 1 to even out the LNG density within the storage tank. Because LNG is a mixture with varying densities of its components, LNG can stratify if left stagnant for an extended period. This stratification can cause the LNG to churn, rapidly vaporizing and causing a sudden increase in pressure within the tank, potentially leading to tank damage and a safety accident. Therefore, to prevent LNG stratification and churn, the pump's return line can be used to even out the LNG density across the tank layers, ensuring safe operation.

[0037] In addition, when the outlet pipeline 191 needs to be refrigerated, the pump can be started by the DCS control system 4 to transport the LNG in the storage tank to the outlet pipeline 191. The pump backflow regulating valve 18 is opened, and the LNG returns to the tank through the pump backflow regulating valve 18. The pipeline is refrigerated repeatedly to achieve the purpose of pre-cooling. During this process, the outlet switch valve 17 is in the closed state.

[0038] like Figure 1 As shown, the loading pipeline system 1 is used for LNG transportation and is equipped with a pressure transmitter 11, a cryogenic shut-off valve 12, a cryogenic check valve 13, a temperature transmitter 14, and a condensate release valve 16, sequentially located upstream of the cryogenic storage tank 100 on the outlet pipeline 191. The pressure transmitter 11 provides local display and monitors pressure changes within the pipeline during the unloading process, transmitting the pressure signal to the DCS control system 4. The cryogenic shut-off valve 12 allows for manual switching to control LNG transportation within the pipeline. The cryogenic check valve 13 prevents LNG backflow within the pipeline. The temperature transmitter 14, with local display, monitors temperature changes within the pipeline during the loading process and transmits the temperature signal to the DCS control system 4. The condensate release valve 16 can be used to release residual gas or liquid within the pipeline. The discharge switch valve 17, equipped with a solenoid valve 52, receives electrical signals from the DCS control system 4 and can remotely interlock to control the LNG delivery within the pipeline. The reflux regulating valve 18, equipped with a valve positioner 53, receives electrical signals from the DCS control system 4 and can remotely interlock to control the valve opening to regulate the LNG flow rate within the pipeline. During normal operation of the storage tank, except for the bypass valve 22 and the condensate trap valve 16 which are closed, all other cryogenic shut-off valves are normally open.

[0039] like Figure 2 As shown, the pump start-stop system 3 is applied to the submersible pump 103, including a pump frequency converter control cabinet 31, and a pump motor 32 and a pump operating column 33 that are electrically connected to the pump frequency converter control cabinet 31. The pump frequency converter control cabinet 31 can control the start and stop of the pump motor 32 according to the frequency or speed signal given by the DCS control system 4, and can provide feedback signals such as fault, operation, current, and speed to the DCS control system 4; the pump motor 32 can control the start and stop of the pump bearing to transport the LNG stored in the storage tank to the loading pipeline system 1; the pump operating column 33 is equipped with three buttons: start, stop, and emergency stop, as well as running and start-allowed indicator lights. According to the actual operating conditions, when the DCS control system 4 allows manual start, the start and stop of the pump motor 32 can be manually controlled according to the indicator lights on the operating column. In case of emergency, whether in manual or automatic control, the pump can be stopped immediately by pressing the emergency stop button on the pump operating column 33. In addition, the pump operation column 33 is set in a safe area on site. When the DCS control system 4 allows manual operation, the on-site personnel can manually operate the pump according to the indicator lights on the operation column and the on-site working conditions. When an abnormal situation occurs during the pump loading process, the pump loading can be terminated by the emergency stop button on the pump operation column 33, thus providing safety protection for the entire pump loading system.

[0040] The automatic valve control system 5 mainly includes a filter pressure reducer 51, a solenoid valve 52, and a valve positioner 53. The filter pressure reducer 51 is used to reduce the instrument gas pressure and filter impurities in the instrument gas; the solenoid valve 52 receives signals from the DCS control system 4 to control the opening or closing of the liquid outlet switch valve 17, thereby controlling the delivery of LNG in the pipeline; the valve positioner 53 receives signals from the DCS control system 4 to adjust the opening of the pump backflow regulating valve 18, thereby controlling the flow rate of LNG in the pipeline.

[0041] The DCS control system 4 mainly includes a PLC control cabinet 41 and a monitoring computer 42, typically located in the central control room. The PLC control cabinet 41 is electrically connected to the pump frequency converter control cabinet 31. The PLC control cabinet 41 receives and transmits signals, allowing staff to monitor the pump loading status in real time on the monitoring computer 42. The DCS control system 4 can transmit signals to the solenoid valves 52 and electric valve positioners 53 within the pump start-stop system 3 and the automatic valve control system 5, enabling remote control of pump start-stop and pneumatic valve opening, closing, and opening degree adjustment, thereby controlling pump loading.

[0042] In this embodiment, as Figure 1 As shown, the LNG loading system also includes a venting system 2.

[0043] The venting system 2 mainly includes a venting pipe 20, and a cryogenic shut-off valve 21, a bypass valve 22, a cryogenic shut-off valve 23, and a cryogenic safety valve 24 installed on the venting pipe 20.

[0044] The cryogenic safety valve 24 automatically opens when the pressure in the process pipeline reaches its set pressure, releasing overpressure gas into the storage tank to protect the transmitters and valves in the loading pipeline system 1. Cryogenic shut-off valves 21 and 23 are only closed during the calibration or maintenance of the cryogenic safety valve 24; they are normally open during normal operation. The bypass valve 22 is only manually opened during the calibration or maintenance of the cryogenic safety valve 24 to release pressure in the process pipeline; it is normally closed in all other situations. The purpose of the venting system 2 is to ensure that the process pipeline system is always under safe operating conditions.

[0045] When there are LNG tank trucks to be loaded in the loading area, the staff in the central control room transmits the signal to the frequency converter in the pump frequency converter control cabinet 31 through the DCS control system 4 on the monitoring computer 42. The pump motor 32 adjusts its speed according to the frequency output of the frequency converter to transport the LNG stored in the storage tank to the liquid outlet pipeline 191. At the same time as the pump motor 32 starts, the DCS control system 4 opens the liquid outlet switch valve 17 through the automatic valve control system 5. The LNG stored in the storage tank is transported to the loading area for LNG tank truck filling through the cryogenic shut-off valve 12, cryogenic check valve 13, orifice flow meter 15, liquid outlet switch valve 17 and other components in the loading pipeline system 1.

[0046] When the pressure in the loading pipeline system 1 exceeds the pressure set by the cryogenic safety valve 24 in the venting system 2, the cryogenic safety valve 24 automatically opens to release the pressure into the storage tank, thereby protecting the transmitters and valves in the loading pipeline system 1.

[0047] Specific Second Embodiment of LNG Loading System Please refer to Figure 3 The difference in this embodiment is that the two submersible pumps 103 (A / B) can be turned on simultaneously. Each pump has a separate outlet pipeline and return pipeline 192, meaning that the outlet pipeline 191 and the return pipeline 192 are both independent and do not affect each other. The simultaneous operation of the two pumps can provide a larger flow rate to meet the loading needs of a larger number of LNG tank trucks 200.

[0048] The inlet end of each liquid outlet pipeline 191 is connected to the top end of each pump column 104, and the outlet ends of the two liquid outlet pipelines 191 extend far away and converge in the LNG tanker area.

[0049] Each return line 192 is connected to each outlet line 191, and their common node is marked as S. The ends of the two return lines 192 furthest from node S merge together and return to the storage tank 100 through the same common return line 193. Two return regulating valves 18 and two orifice flow meters 15 are also provided, each valve corresponding to its respective pipeline. In addition, two other control valves, such as pressure transmitters 11, are also provided, each respectively on its respective pipeline.

[0050] When there are LNG tank trucks to be loaded in the loading area (the flow rate of a single pump is sufficient for tank truck filling, and any pump can be started for tank truck filling), taking submersible pump A as an example, the staff in the central control room transmits the signal to the frequency converter in the pump frequency converter control cabinet 31 through the DCS control system 4 on the monitoring computer 42. The motor 32 of pump A adjusts its speed according to the frequency output of the frequency converter, and delivers the LNG stored in the storage tank to the outlet pipeline 191. At the same time as pump motor 32 of pump A starts, the DCS control system 4 opens the outlet switch valve 17 through the automatic valve control system 5. The LNG stored in the storage tank is delivered to the loading area for LNG tank truck filling through the cryogenic shut-off valve 12, cryogenic check valve 13, orifice flow meter 15, outlet switch valve 17 and other components in the loading pipeline system 1.

[0051] During the loading process, while maintaining a constant speed of the operating submersible pump 103 and a constant LNG flow rate, the LNG output flow rate needs to be controlled by adjusting the opening of the post-pump reflux regulating valve 18. When the number of tank trucks to be filled is small, the DCS control system 4 sends the signal from the orifice flow meter 15 to the automatic valve control system 5. The valve positioner 53 uses a PID controller to open the post-pump reflux regulating valve 18, allowing a portion of the LNG in the outlet pipeline 191 to be returned to the storage tank, thus regulating the LNG flow rate to meet the tank truck filling requirements. When the number of tank trucks to be filled increases, the DCS control system 4 sends the signal from the orifice flow meter 15 to the automatic valve control system 5. The valve positioner 53 uses a PID controller to close the post-pump reflux regulating valve 18 (i.e., close the reflux pipeline 192), ensuring that the LNG in the outlet pipeline 191 is entirely used for tank truck filling, thereby meeting the tank truck filling requirements.

[0052] When the flow rate of a single submersible pump 103 is insufficient for tanker filling, the staff in the central control room transmits a signal to the frequency converter in the pump frequency converter control cabinet 31 via the DCS control system 4, starting submersible pump B. Pump motor 32 of pump B adjusts its speed according to the frequency output of the frequency converter, transporting the LNG stored in the storage tank to the outlet pipeline 191. Simultaneously with the start of pump motor 32 of pump B, the DCS control system 4 opens the outlet switch valve 17 on the second outlet pipeline 191 via the automatic valve control system 5. The LNG stored in the storage tank is then transported to the loading area for LNG tanker filling via the cryogenic shut-off valve 12, cryogenic check valve 13, orifice flow meter 15, outlet switch valve 17, and other components in the loading pipeline system 1. The DCS control system 4 sends the signal fed back by the orifice plate flow meter 15 to the automatic valve control system 5. The valve positioner 53 uses the PID controller to close the pump backflow regulating valve 18 (i.e., close the backflow pipeline 192), ensuring that the LNG in the outlet pipeline 191 is used entirely for tank truck filling to meet the tank truck filling requirements.

[0053] Although the invention has been described with reference to several typical embodiments, it should be understood that the terminology used is illustrative and exemplary, and not restrictive. Since the invention can be embodied in many forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims. Therefore, all variations and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A LNG loading system, characterized in that, include: A cryogenic storage tank that stores LNG, with a drain port and a return port at the top that communicate with the inside of the tank; The loading pipeline system includes an outlet pipeline, a return pipeline, a return regulating valve, and an orifice flow meter. The inlet end of the outlet pipeline is connected to the discharge port, and the outlet end of the outlet pipeline supplies LNG from the tank to the outside, extending to the tank truck loading area. The inlet end of the return pipeline is connected to the outlet pipeline, and the outlet end of the return pipeline is connected to the return port. The orifice flow meter is installed on the outlet pipeline to detect the flow rate. The return regulating valve is an adjustable valve installed on the return pipeline to regulate the flow rate of the return pipeline. The control assembly is electrically connected to the orifice plate flow meter and the reflux regulating valve, respectively; the control assembly controls the opening degree of the reflux regulating valve according to the flow signal fed back by the orifice plate flow meter. When the number of tank trucks to be filled changes, the control assembly controls the opening of the reflux regulating valve by comparing the flow signal of the orifice plate flow meter with the preset loading demand flow value, so that part of the LNG in the outlet pipeline is transported back to the cryogenic storage tank through the reflux pipeline, and the flow of LNG is adjusted to meet the tank truck filling requirements. When not loading, the return pipeline maintains a small flow rate to ensure uniform LNG density within the storage tank.

2. The LNG loading system of claim 1, wherein, The orifice plate flow meter is located downstream of the connection node between the outlet pipeline and the return pipeline.

3. The LNG loading system according to claim 1, characterized in that, At least two drain ports are provided; at least two submersible pumps are provided inside the cryogenic storage tank, and the outlet of each submersible pump is provided with a pump column; the pump column extends outward from the tank through the drain ports; the outlet pipeline includes two branch pipes and an outlet collection pipe; one end of each branch pipe is connected to the top of each pump column, and the other ends of the two branch pipes are connected to the outlet collection pipe; the two submersible pumps operate alternately, one starting and one closing.

4. The LNG loading system according to claim 3, characterized in that, The outlet collection pipe is connected to the return pipe; the orifice plate flow meter is installed on the outlet collection pipe.

5. The LNG loading system according to claim 3, characterized in that, The control assembly includes a pump frequency converter control cabinet, and a pump motor and a pump operating column that are electrically connected to the pump frequency converter control cabinet.

6. The LNG loading system according to claim 5, characterized in that, The control assembly includes a PLC control cabinet, which is electrically connected to the pump frequency converter control cabinet.

7. The LNG loading system according to claim 1, characterized in that, At least two drain ports are provided; at least two submersible pumps are provided inside the cryogenic storage tank, and each submersible pump has a pump column at its outlet; the pump column extends out of the tank through the drain port; two outlet pipes and two return pipes are provided respectively, the inlet end of each outlet pipe is connected to the top of each pump column, and each return pipe is connected to each outlet pipe; two return regulating valves and two orifice plate flow meters are also provided respectively.

8. The LNG loading system according to claim 1, characterized in that, The loading pipeline system also includes a pressure transmitter, a cryogenic shut-off valve, a cryogenic check valve, and a temperature transmitter, which are sequentially installed upstream of the outlet pipeline near the cryogenic storage tank.

9. The LNG loading system according to claim 1, characterized in that, The loading pipeline system also includes a liquid outlet switch valve located on the liquid outlet pipeline, which is downstream of the orifice flow meter.

10. The LNG loading system according to claim 1, characterized in that, The LNG loading system also includes a venting system, which includes a venting pipe and a cryogenic safety valve. The two ends of the venting pipe are connected to the cryogenic storage tank and the liquid outlet pipeline, respectively. The cryogenic safety valve is installed on the venting pipe to control the opening and closing of the venting pipe.

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