Intelligent filling control strategy and system for LNG (Liquefied Natural Gas) filling station and LNG filling station

Abstract

The invention discloses an intelligent filling control strategy and system for an LNG filling station and the LNG filling station. The intelligent filling control strategy comprises the following steps that the actual temperature T of LNG from a storage tank to a pump pool liquid outlet pipeline and the actual pressure P of a gas phase space in the storage tank are obtained; inquiring a built-in LNG saturation characteristic curve according to the actual pressure P to obtain a corresponding saturation temperature Ts (P); comparing the actual temperature T with the saturation temperature Ts (P), and judging whether the thermodynamic state of the LNG is an under-saturation state, a saturation state or an over-saturation state; and executing a corresponding filling control strategy according to the thermodynamic state. According to the invention, intelligent protection of the immersed pump and dynamic optimization of the filling process are realized.

Description

Technical Field

[0001] This invention relates to the field of LNG refueling at vehicle refueling stations. More specifically, this invention relates to an intelligent refueling control strategy for LNG refueling stations. Background Technology

[0002] With increasing environmental requirements and considerations of fuel economy, the market application of LNG heavy-duty trucks continues to grow, driving the demand and development of LNG refueling stations and related skid-mounted equipment. During LNG refueling, the thermodynamic characteristics of the cryogenic fluid have a decisive impact on operational safety and efficiency. Currently, the industry's commonly used refueling control strategy is a single pressure-controlled mode, where the system refuels at a fixed or preset pressure target, without considering the actual gas-liquid balance of LNG in the storage tank and pump pool in real time. This simple control method has significant drawbacks: when LNG is undersaturated, the submersible pump is prone to flash cavitation in the flow channel, and the system will increase the pump speed to maintain pressure, creating a vicious cycle that exacerbates cavitation, ultimately leading to pump damage and refueling interruption; conversely, when LNG is in a supersaturated stable liquid phase, single pressure control fails to fully utilize its strong anti-cavitation characteristics, limiting the increase in refueling flow rate and resulting in suboptimal refueling efficiency. Therefore, there is an urgent need for a control strategy that can sense the thermodynamic state of LNG and intelligently adjust it to simultaneously solve the problems of equipment safety and refueling efficiency. Summary of the Invention

[0003] The purpose of this invention is to overcome the cavitation risk and low efficiency problems caused by the single pressure-controlled refueling mode used in existing LNG refueling stations. By identifying the saturation state of LNG in real time and matching differentiated refueling control strategies accordingly, intelligent protection of the submersible pump and dynamic optimization of the refueling process are achieved. This significantly improves the overall efficiency of the refueling operation while ensuring equipment safety and extending its lifespan.

[0004] The technical solution adopted by this invention to solve this technical problem is: an intelligent refueling control strategy for LNG refueling stations, comprising the following steps: Obtain the actual temperature T of LNG in the pipeline from the storage tank to the pump pool, and the actual pressure P of the gas phase space inside the storage tank; Based on the actual pressure P, the built-in LNG saturation characteristic curve is used to obtain the corresponding saturation temperature T. s (P); Compare the actual temperature T with the saturation temperature T s (P) determines whether the thermodynamic state of LNG is undersaturated, saturated, or supersaturated. Execute the corresponding refueling control strategy based on the aforementioned thermodynamic state: If the tank is undersaturated, the filling process is controlled by starting the submersible pump at a reduced frequency or by starting the tank's self-pressurization system. If the system is saturated, then a constant pressure injection mode will be used. If the system is in an oversaturated state, the output pressure will be dynamically increased based on the constant pressure mode to improve the filling rate.

[0005] As a further aspect of the present invention, the determination of the thermodynamic state specifically includes: If T>T s (P) indicates an undersaturated state; If T = T s (P) is determined to be in a saturated state; If T <T s (P) is determined to be in an oversaturated state.

[0006] As a further aspect of the present invention, the refueling control strategy under the undersaturated state includes any of the following: Start the pump at 50% to 80% of its rated frequency and monitor the pump outlet flow and pressure in real time. If the flow drops to less than 10% of the rated flow or the pressure is zero, stop the pump and sound an alarm. The storage tank's self-pressurization system is activated to increase the pressure inside the tank to the saturation pressure P corresponding to the current temperature T. s (T) After the LNG reaches saturation, switch to constant pressure mode for refueling.

[0007] As a further aspect of the present invention, the injection control strategy under the supersaturation state includes: The constant pressure filling is started with the preset initial output pressure; The gas dispenser nozzle pressure is monitored in real time. If the nozzle pressure is lower than the set lower limit, the output pressure of the submersible pump is gradually increased until the nozzle pressure reaches the set upper limit.

[0008] As a further aspect of the present invention, the lower limit is set to 1.3 MPa, the upper limit is set to 1.6 MPa, and the initial output pressure is 1.4 MPa.

[0009] The present invention also provides an intelligent refueling control system for LNG refueling stations, comprising: A temperature sensor is installed on the outlet pipeline from the storage tank to the pump pool to collect the actual temperature T of the LNG. A pressure sensor is installed in the gas phase space at the top of the storage tank to collect the actual pressure P inside the storage tank; The controller has a built-in LNG saturation characteristic curve, which is used to determine the thermodynamic state of LNG based on T and P, and output corresponding control commands. A submersible pump, controlled by the controller, is used to perform the filling operation; The storage tank self-pressurization system, connected to the controller, is used to increase the pressure of the storage tank in an undersaturated state.

[0010] As a further aspect of the present invention, it also includes a gas dispenser data acquisition module, used to acquire the filling pressure at the gas dispenser in real time and feed it back to the controller.

[0011] As a further aspect of the present invention, the controller is also used to control the submersible pump to operate at 50% to 80% of the rated frequency in an undersaturated state, and to monitor the pump outlet flow rate and pressure, triggering an alarm when abnormalities occur.

[0012] As a further aspect of the present invention, the controller controls the submersible pump to gradually increase the output pressure in constant pressure mode under supersaturation conditions until the pressure at the nozzle of the gas dispenser reaches the set upper limit.

[0013] The present invention also provides an LNG refueling station, including the aforementioned intelligent refueling control system.

[0014] This invention offers at least the following advantages: By monitoring and determining the saturation state of LNG in real time and executing differentiated refueling control logic based on different states, this invention fundamentally avoids the risk of submersible pump damage due to cavitation under undersaturated conditions, significantly extending the service life of core equipment. Simultaneously, under favorable supersaturated conditions, the system can safely and automatically increase the refueling pressure, thereby significantly improving the refueling rate, shortening vehicle dwell time, and enhancing the operational efficiency of the refueling station. Furthermore, this strategy achieves complete closed-loop control from state recognition and control mode matching to dynamic parameter adjustment, enhancing the intelligence and adaptability of the refueling process, enabling the system to maintain efficient, stable, and safe operation under various initial thermodynamic conditions.

[0015] 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

[0016] Figure 1 This is a flowchart of an intelligent refueling control strategy for LNG refueling stations according to an embodiment of the present invention. Detailed Implementation

[0017] The present invention will now be described in detail and completely with reference to the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention with reference to the accompanying drawings, it should be particularly noted that the technical solutions and features provided in various parts of the present invention, including the following description, can be combined with each other without conflict.

[0018] Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The specific implementation process is as follows: like Figure 1 As shown, this invention provides an intelligent refueling control strategy for LNG refueling stations, comprising the following steps: Obtain the actual temperature T of LNG in the pipeline from the storage tank to the pump pool, and the actual pressure P of the gas phase space inside the storage tank; Based on the actual pressure P, the built-in LNG saturation characteristic curve is used to obtain the corresponding saturation temperature T. s (P); Compare the actual temperature T with the saturation temperature T s (P) Determine whether the thermodynamic state of LNG is undersaturated (overheated, with the actual temperature higher than the saturation temperature corresponding to the current pressure), saturated, or oversaturated (undercooled, with the actual temperature lower than the saturation temperature corresponding to the current pressure). Execute the corresponding refueling control strategy based on the aforementioned thermodynamic state: If the tank is undersaturated, the filling process is controlled by starting the submersible pump at a reduced frequency or by starting the tank's self-pressurization system. If the system is saturated, then a constant pressure injection mode will be used. If the system is in an oversaturated state, the output pressure will be dynamically increased based on the constant pressure mode to improve the filling rate.

[0020] In the above technical solution, the system collects the actual temperature and system pressure of liquefied natural gas in real time through temperature sensors installed on the pipeline before the pump and pressure sensors on the top of the storage tank. The built-in LNG saturation characteristic curve obtains the LNG saturation pressure at different temperatures by querying data from the NIST database. (The NIST database is a series of scientific databases developed and maintained by the National Institute of Standards and Technology, including datasets from multiple fields such as physics, chemistry, engineering, biology, and information technology). Next, the control system calls its internally stored LNG saturation characteristic database and queries the corresponding theoretical saturation temperature based on the current measured pressure. By directly comparing the measured temperature with the theoretical saturation temperature, the system can accurately identify whether the medium is in a state prone to cavitation (undersaturated), a state of critical equilibrium (saturated), or a stable state (supersaturated). This identification step is the basis of the decision-making process of this invention. Based on the above real-time judgment, the system executes differentiated closed-loop control. If the system is determined to be undersaturated, the pursuit of a constant pressure target is abandoned, and a gentle start-up is implemented by reducing the operating frequency of the submersible pump to weaken the fluid conditions that cause cavitation at the source. Alternatively, the tank's self-pressurization system is activated to increase the overall system pressure and bring the medium back to a saturated state, fundamentally eliminating the risk of cavitation before proceeding with routine filling. If the system is determined to be saturated, a stable and reliable constant pressure mode is used for filling. If the system is determined to be oversaturated, within the framework of the constant pressure mode, the system output pressure is intelligently and gradually increased to raise the filling flow rate to the maximum value allowed by the current physical conditions, while ensuring absolute safety.

[0021] In another embodiment, determining the thermodynamic state specifically includes: If T>T s (P) indicates an undersaturated state. LNG is a two-phase gas-liquid or near-gas phase and is prone to flash cavitation. If T = T s (P) indicates that the LNG is in a saturated state and is in gas-liquid equilibrium with moderate stability. If T <T s (P) indicates a supersaturated state. LNG is a pure liquid phase and has strong resistance to cavitation.

[0022] In the above implementation, the real-time collected liquefied natural gas temperature value before the pump is compared with the saturation temperature value retrieved based on the current pressure. If the former is significantly greater than the latter, the comparison unit outputs an "undersaturated state" flag signal; if the former and the latter are equal within the system's allowable measurement error range, an "saturated state" flag signal is output; if the former is significantly less than the latter, an "oversaturated state" flag signal is output. This judgment rule translates thermodynamic principles into control commands, ensuring that all subsequent control branches can be triggered accurately and reliably.

[0023] In another embodiment, the refueling control strategy under the undersaturated state includes any of the following: Start the pump at 50% to 80% of its rated frequency and monitor the pump outlet flow and pressure in real time. If the flow drops to less than 10% of the rated flow or the pressure is zero, stop the pump and sound an alarm. The storage tank's self-pressurization system is activated to increase the pressure inside the tank to the saturation pressure P corresponding to the current temperature T. s (T) After the LNG reaches saturation, switch to constant pressure mode for refueling.

[0024] In the above implementation, when the control system determines that the system is in an undersaturated state according to the rules, it will immediately initiate the corresponding protective refueling procedure. The first implementation is a frequency reduction soft start: the control system sends a command to the frequency converter to set the operating frequency of the motor driving the submersible pump to a lower range of 50% to 80% of the rated frequency, thereby significantly reducing the rotational speed of the impeller inside the pump. Low-speed rotation effectively weakens the intensity of the low-pressure vortex formed at the pump inlet, thus greatly reducing the possibility of severe flashing of liquefied natural gas at that location. Simultaneously, the system closely monitors the readings of the flow meter and pressure gauge at the pump outlet. Once a sudden drop in flow rate to near-interruption or loss of pressure is detected, an emergency shutdown is immediately executed, and an audible and visual alarm is triggered to prevent damage to the pump body due to idling or cavitation.

[0025] The second implementation method involves adjusting the conditions before refueling. The control system first commands the storage tank's self-pressurization circuit to start. This circuit guides a small amount of liquefied natural gas through the vaporizer, converting it into natural gas and then returning it to the gas phase space of the storage tank, thereby gradually increasing the pressure in the storage tank and the entire pipeline system. The system continuously monitors pressure changes until the pressure rises to the saturation pressure value corresponding to the current liquefied natural gas temperature. At this point, the medium is precisely adjusted from an undersaturated state to a saturated state of gas-liquid equilibrium, thus eliminating the risk of cavitation. Subsequently, the control system automatically switches the refueling mode to the standard constant pressure mode, safely and smoothly completing the subsequent refueling operation. These two methods, one addressing the undersaturation and the other the congestion, provide a complete automated solution for dealing with undersaturated conditions.

[0026] In another embodiment, the refueling control strategy under the oversaturation state includes: The constant pressure filling is started with the preset initial output pressure; The gas dispenser nozzle pressure is monitored in real time. If the nozzle pressure is lower than the set lower limit, the output pressure of the submersible pump is gradually increased until the nozzle pressure reaches the set upper limit.

[0027] In the above implementation, when the system determines that the medium is in a supersaturated state, it first initiates constant-pressure dispensing with a preset, relatively conservative initial output pressure, such as 1.4 MPa, to ensure a smooth dispensing start. After dispensing begins, the system's focus shifts from the pre-pump state to the dispensing terminal. The pressure sensor located at the nozzle of the gas dispenser is activated, feeding back the actual dispensing pressure data from the nozzle to the central controller in real time. The controller has a preset lower safety pressure limit, such as 1.3 MPa. During dispensing, the controller continuously compares the nozzle pressure with this lower limit. Once the nozzle pressure is found to be below this lower limit, indicating that the current pipeline resistance is permissible and the system has a safety margin, the controller will issue a command to the submersible pump to gradually increase its output pressure in a slow, small manner. This process is gradual and controlled; the step size and speed of pressure increase are set to avoid pressure surges. The goal of the increase is to maintain the nozzle pressure near a relatively high, preset upper limit, such as 1.6 MPa, thereby ensuring that the dispensing flow rate remains at the highest level under current operating conditions without overpressure.

[0028] In another embodiment, an intelligent refueling control system for an LNG refueling station includes: A temperature sensor is installed on the outlet pipeline from the storage tank to the pump pool to collect the actual temperature T of the LNG. A pressure sensor is installed in the gas phase space at the top of the storage tank to collect the actual pressure P inside the storage tank; The controller has a built-in LNG saturation characteristic curve, which is used to determine the thermodynamic state of LNG based on T and P, and output corresponding control commands. A submersible pump, controlled by the controller, is used to perform the filling operation; The storage tank self-pressurization system, connected to the controller, is used to increase the pressure of the storage tank in an undersaturated state.

[0029] In the above implementation, the intelligent refueling control system consists of the following core components. The sensing layer includes a temperature sensor installed adjacent to the submersible pump inlet to capture the core temperature of the liquefied natural gas (LNG); and a pressure sensor installed in the gas phase space of the storage tank to obtain the system reference pressure. The decision-making core is a dedicated controller with a built-in LNG property database. It receives signals from the sensors, executes state comparison logic, and makes control decisions. The execution layer includes a submersible pump directly modulated by the controller, and a tank self-pressurization system managed by the controller. This system typically includes a vaporizer and a return pipeline. When an undersaturation state signal is triggered, the controller can directly command the self-pressurization system to start operation. All these components are connected via electrical wiring and a signal network, forming a complete physical system capable of replacing the traditional fixed mode and achieving adaptive refueling control.

[0030] In another embodiment, a gas dispenser data acquisition module is also included to acquire the dispensing pressure at the gas dispenser in real time and feed it back to the controller. The system adds a pressure acquisition module to the dispensing nozzle of the gas dispenser or a nearby return line. This module transmits the actual nozzle pressure data during dispensing operations back to the controller in real time via wired or wireless communication. Especially when performing oversaturation state optimization control, this nozzle pressure signal becomes the sole basis for the controller's decision. The controller no longer relies on a fixed post-pump pressure setting, but instead dynamically and inversely adjusts the submersible pump's operating state based on the pressure feedback from the nozzle, the final point of use, ensuring that the improvement in dispensing efficiency is always constrained by the terminal safety pressure.

[0031] In another embodiment, the controller is also used to control the submersible pump to operate at 50% to 80% of the rated frequency in an undersaturated state, and to monitor the pump outlet flow and pressure, triggering an alarm in case of abnormality.

[0032] In another embodiment, the controller controls the submersible pump to gradually increase the output pressure in a constant pressure mode under supersaturation conditions until the pressure at the nozzle of the gas dispenser reaches the set upper limit.

[0033] In another embodiment, an LNG refueling station includes the aforementioned intelligent refueling control system. The core feature of this novel liquefied natural gas refueling station is that it is equipped with the intelligent refueling control system described in this application. The refueling operation of this station is dominated by an advanced system with state perception, intelligent judgment, and adaptive adjustment capabilities. Whether it is a skid-mounted unit within the station or a stationary refueling station, as long as the core control of its refueling process is entrusted to this system, which includes specific sensor configurations, dedicated controllers, and special actuators, then the refueling station possesses the essential characteristics of automatically optimizing the refueling operation based on the real-time thermodynamic state of liquefied natural gas while simultaneously preventing cavitation risks, thus constituting a novel refueling station entity protected by this invention.

[0034] 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 embodiments shown and described herein.

Claims

1. An intelligent refueling control strategy for LNG refueling stations, characterized in that, Includes the following steps: Obtain the actual temperature T of LNG in the pipeline from the storage tank to the pump pool, and the actual pressure P of the gas phase space inside the storage tank; Based on the actual pressure P, the built-in LNG saturation characteristic curve is used to obtain the corresponding saturation temperature T. s (P); Compare the actual temperature T with the saturation temperature T s (P) determines whether the thermodynamic state of LNG is undersaturated, saturated, or supersaturated. Execute the corresponding refueling control strategy based on the aforementioned thermodynamic state: If the tank is undersaturated, the filling process is controlled by starting the submersible pump at a reduced frequency or by starting the tank's self-pressurization system. If the system is saturated, then a constant pressure injection mode will be used. If the system is in an oversaturated state, the output pressure will be dynamically increased based on the constant pressure mode to improve the filling rate.

2. The intelligent refueling control strategy for LNG refueling stations as described in claim 1, characterized in that, The determination of the thermodynamic state specifically includes: If T > T s (P) indicates an undersaturated state; If T = T s (P) is determined to be in a saturated state; If T < T s (P) is determined to be in an oversaturated state.

3. The intelligent refueling control strategy for LNG refueling stations as described in claim 1, characterized in that, The injection control strategy under the undersaturated state includes any of the following: Start the pump at 50% to 80% of its rated frequency and monitor the pump outlet flow and pressure in real time. If the flow drops to less than 10% of the rated flow or the pressure is zero, stop the pump and sound an alarm. The storage tank's self-pressurization system is activated to increase the pressure inside the tank to the saturation pressure P corresponding to the current temperature T. s (T) After the LNG reaches saturation, switch to constant pressure mode for refueling.

4. The intelligent refueling control strategy for LNG refueling stations as described in claim 1, characterized in that, The injection control strategy under the supersaturation state includes: The constant pressure filling is started with the preset initial output pressure; The gas dispenser nozzle pressure is monitored in real time. If the nozzle pressure is lower than the set lower limit, the output pressure of the submersible pump is gradually increased until the nozzle pressure reaches the set upper limit.

5. The intelligent refueling control strategy for LNG refueling stations as described in claim 4, characterized in that, The lower limit is set at 1.3 MPa, the upper limit is set at 1.6 MPa, and the initial output pressure is 1.4 MPa.

6. An intelligent refueling control system for LNG refueling stations, characterized in that, include: A temperature sensor is installed on the outlet pipeline from the storage tank to the pump pool to collect the actual temperature T of the LNG. A pressure sensor is installed in the gas phase space at the top of the storage tank to collect the actual pressure P inside the storage tank; The controller has a built-in LNG saturation characteristic curve, which is used to determine the thermodynamic state of LNG based on T and P, and output corresponding control commands. A submersible pump, controlled by the controller, is used to perform the filling operation; The storage tank self-pressurization system, connected to the controller, is used to increase the pressure of the storage tank in an undersaturated state.

7. The system as described in claim 6, characterized in that, It also includes a gas dispenser data acquisition module, which is used to acquire the filling pressure at the gas dispenser in real time and feed it back to the controller.

8. The system as described in claim 6, characterized in that, The controller is also used to control the submersible pump to operate at 50% to 80% of the rated frequency in an undersaturated state, and to monitor the pump outlet flow and pressure, triggering an alarm in case of abnormality.

9. The system as described in claim 6, characterized in that, In a supersaturated state, the controller controls the submersible pump to gradually increase the output pressure based on the constant pressure mode until the pressure at the nozzle of the gas dispenser reaches the set upper limit.

10. An LNG refueling station, characterized in that, Including the intelligent refueling control system as described in any one of claims 6-9.

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