LNG liquefaction device mixed refrigerant intelligent supplement device and control method
The intelligent refrigerant replenishment device with online detection and closed-loop control solves the problem of imbalance in the proportion of refrigerant components, and achieves efficient and safe operation of the refrigeration system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HOUPU CLEAN ENERGY GROUP SICHUAN ENGINEERING TECHNOLOGY CO LTD
- Filing Date
- 2026-06-12
- Publication Date
- 2026-07-21
AI Technical Summary
In existing technologies, the proportion of components in mixed refrigerants becomes unbalanced due to leakage, separation, and discharge during long-term operation, resulting in reduced refrigeration efficiency, increased energy consumption, and system instability. Furthermore, there is a lack of real-time monitoring and precise intelligent replenishment capabilities.
Real-time multi-component concentration detection is performed using an online gas chromatograph or infrared spectrometer. Combined with the PID control algorithm of an industrial-grade PLC or DCS system, precise component replenishment is achieved through an independent refrigerant storage tank, pneumatic regulating valve, and mass flow meter. Safety monitoring is provided by a mixing tank and pressure sensor, forming a closed-loop control system.
It enables real-time and precise adjustment of the proportion of mixed refrigerant components, improves detection accuracy and response speed, avoids resource waste and system instability, and ensures the long-term efficient operation and safety of the refrigeration system.
Smart Images
Figure CN122429520A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of natural gas liquefaction refrigeration equipment technology, and more specifically, to an intelligent refrigerant replenishment device and control method for LNG liquefaction plants. Background Technology
[0002] Currently, in systems requiring mixed refrigerant refrigeration cycles, such as natural gas liquefaction, petrochemicals, and air separation, the mixed refrigerant (such as a mixture of nitrogen, methane, ethane, propane, isopentane, etc.) may experience component imbalances due to leakage, separation, or emissions during long-term operation. This can reduce refrigeration efficiency, increase energy consumption, and even affect the stable operation of the system.
[0003] In existing technologies, the replenishment of mixed refrigerants mainly relies on the following methods: First, manual periodic testing and replenishment: operators sample and analyze refrigerant components, determine the missing types, and manually replenish. This method has a slow response, low accuracy, high labor intensity, and is prone to improper replenishment due to human error. Second, timed and quantitative replenishment: replenishing refrigerant at fixed times or in fixed amounts cannot reflect actual component changes, easily leading to over- or under-replenishment, wasting resources and affecting system performance. Third, single-component pressure-controlled replenishment: replenishing only one type of refrigerant based on changes in the total system pressure ignores the proportional coordination between multiple components, and after long-term operation, the components deviate significantly from the design values.
[0004] In summary, existing technologies lack the ability to monitor and accurately and intelligently replenish mixed refrigerant components, making it difficult to ensure the long-term efficient operation of refrigeration systems. Summary of the Invention
[0005] The present invention aims to provide an intelligent refrigerant replenishment device and control method for LNG liquefaction plants, so as to solve the problems of existing technologies that rely on manual replenishment, have slow response, low accuracy, and cannot maintain the balance of component ratios.
[0006] This invention is implemented as follows: This invention provides an intelligent replenishment device for mixed refrigerant in an LNG liquefaction unit, applied to a mixed refrigerant circulation refrigeration system. The mixed refrigerant circulation refrigeration system includes a refrigerant compressor and a mixed refrigerant circulation pipeline. The intelligent replenishment device includes a sampling and detection module installed on the mixed refrigerant circulation pipeline. The control unit is communicatively connected to the aforementioned sampling and detection module; The refrigerant replenishment execution module includes multiple independent refrigerant storage tanks, multiple regulating valves, multiple flow meters, and a junction box; each of the above-mentioned refrigerant storage tanks stores a pure component refrigerant, and its outlet is connected in series with one of the above-mentioned regulating valves and one of the above-mentioned flow meters, and the outlets of all the regulating valves are connected to the mixed refrigerant replenishment main pipe; the above-mentioned regulating valves and flow meters are all electrically connected to the above-mentioned control unit through the above-mentioned junction box. The mixing safety module includes a mixing tank, a shut-off valve, and a pressure sensor connected in series on the aforementioned mixing refrigerant replenishment main pipe; the shut-off valve and the pressure sensor are both electrically connected to the aforementioned control unit. A one-way valve is provided on the main mixed refrigerant supply pipe between the pressure sensor and the mixed refrigerant circulation pipeline.
[0007] Preferably, the aforementioned refrigerant storage tanks include a methane storage tank, a nitrogen storage tank, an ethylene storage tank, a propane storage tank, and an isopentane storage tank; the aforementioned regulating valves include a first regulating valve, a second regulating valve, a third regulating valve, a fourth regulating valve, and a fifth regulating valve; the aforementioned flow meters include a first flow meter, a second flow meter, a third flow meter, a fourth flow meter, and a fifth flow meter; the outlet of the methane storage tank is connected in series with the first flow meter and the first regulating valve, the outlet of the nitrogen storage tank is connected in series with the second flow meter and the second regulating valve, the outlet of the ethylene storage tank is connected in series with the third flow meter and the third regulating valve, the outlet of the propane storage tank is connected in series with the fourth flow meter and the fourth regulating valve, and the outlet of the isopentane storage tank is connected in series with the fifth flow meter and the fifth regulating valve.
[0008] Preferably, the above sampling and detection module is an online gas chromatograph or an infrared spectrometer.
[0009] Preferably, the control unit is an industrial-grade PLC or DCS system with a built-in PID control algorithm.
[0010] Preferably, the regulating valve is a pneumatic regulating valve with continuous adjustment of opening from 0% to 100%; the flow meter is a mass flow meter.
[0011] Preferably, the above-mentioned mixing tank is a static mixer or a buffer tank.
[0012] In one embodiment of the present invention: a control method for an intelligent replenishment device for a mixed refrigerant in an LNG liquefaction unit is also provided, comprising the following steps: S1. Preset the ideal target concentration values and lower concentration thresholds of each component of the mixed refrigerant in the control unit; S2. Collect the actual concentration data of each component in the mixed refrigerant circulation pipeline through the sampling and detection module, and calculate the concentration deviation value of each component through the control unit; S3. When the actual concentration of a certain component is lower than the above-mentioned lower limit threshold, the required replenishment amount is calculated based on the concentration deviation value of the component, the system operating load and the total amount of refrigerant. The control unit controls the corresponding regulating valve to open for replenishment. The replenishment flow is fed back in real time through the corresponding flow meter to form a closed-loop control. After the replenishment amount is reached, the corresponding regulating valve is closed. S4. The pressure of the mixed refrigerant replenishment main pipe is monitored in real time by a pressure sensor. When an abnormal pressure or refrigerant leak is detected, the control unit controls the shut-off valve to close to cut off the replenishment circuit and issues an alarm signal.
[0013] Preferably, in S2, the actual concentration data of each component in the mixed refrigerant is collected once at a preset time interval.
[0014] Preferably, in S3, when the actual concentrations of multiple components are simultaneously lower than the aforementioned lower concentration threshold, they are supplemented sequentially according to the priority of each component's impact on refrigeration efficiency, or simultaneously according to the concentration deviation ratio of each component.
[0015] Preferably, in step S3, after the replenishment is completed, the actual concentration data of each component in the mixed refrigerant are collected again. After confirming that the concentration of each component is within the allowable deviation range, the replenishment process ends.
[0016] Preferably, in step S3, after the replenishment is completed, the actual concentration data of each component in the mixed refrigerant are collected again. After confirming that the concentration of each component is within the allowable deviation range, the replenishment process ends.
[0017] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. A qualitative leap has been achieved in detection accuracy and response speed: This invention employs an online gas chromatograph or infrared spectroscopy analyzer to achieve real-time, continuous, and online detection of the concentrations of multiple components in a mixed refrigerant. It completely eliminates the lag associated with traditional manual sampling and offline analysis, reducing the detection response time from several hours to minutes, enabling immediate detection of component ratio deviations. Simultaneously, it offers high detection accuracy, accurately obtaining the volumetric or mass concentration of each component, providing a reliable data foundation for subsequent intelligent supplementation decisions. This fundamentally solves the problems of low accuracy, large errors, and high labor intensity associated with manual detection.
[0018] 2. Intelligent control enables precise, on-demand replenishment, eliminating resource waste: This invention uses the deviation between the actual and target concentrations of components to drive replenishment decisions, rather than traditional timed and quantitative or single-component pressure control. It can accurately identify missing refrigerant components and calculate the optimal replenishment amount. The control unit employs an industrial-grade PLC or DCS system with built-in PID, fuzzy logic, rule base, and other control algorithms. It can flexibly adjust the control strategy based on dynamic parameters such as system load and total refrigerant volume. For situations where multiple components are simultaneously missing, it provides two modes: priority-based sequential replenishment and proportional synchronous replenishment. This ensures rapid recovery of the system's core cooling capacity while avoiding temporary proportional imbalances caused by excessive replenishment of a single component.
[0019] 3. Independent execution structure enables closed-loop precise control, ensuring stable component ratios: This invention provides separate storage tanks, pneumatic regulating valves, and mass flow meters for each of the five core refrigerant components: methane, nitrogen, ethylene, propane, and isopentane. This enables individual metering and independent adjustment of each component, completely avoiding mutual interference during multi-component replenishment. The pneumatic regulating valves can achieve continuous stepless adjustment from 0% to 100% opening, ensuring smooth and stable replenishment flow and preventing system pressure fluctuations. The mass flow meters are unaffected by changes in operating conditions such as temperature and pressure, offering high metering accuracy. Together with the control unit, they form a complete closed-loop flow control, effectively preventing over- or under-replenishment and quickly restoring the mixed refrigerant component ratio to within the design tolerance range.
[0020] 4. Multiple safety and mixed-flow designs ensure safe and reliable system operation: This invention incorporates a mixing tank (static mixer or buffer tank) before the refrigerant inlet point to ensure thorough mixing of the replenished refrigerant with the existing refrigerant in the system, preventing localized concentration unevenness from affecting the cooling effect. It also features a pressure sensor and an emergency shut-off valve; when abnormal pressure or refrigerant leakage is detected in the replenishment main pipe, the replenishment circuit is automatically shut off and an alarm is triggered to prevent the accident from escalating. Furthermore, a one-way valve is installed at the end of the replenishment main pipe, preventing refrigerant backflow and providing a safe isolation method for system maintenance, further enhancing system safety and operational flexibility.
[0021] 5. Excellent system integration, low modification cost, and wide applicability: This invention employs a modular design, allowing for seamless integration with existing PLC or DCS control systems in LNG liquefaction plants. It eliminates the need for large-scale modifications to existing refrigeration systems, significantly reducing implementation difficulty and modification costs. Beyond natural gas liquefaction, this device can also be directly applied to industrial systems employing mixed refrigerant cycles, such as ethylene cold boxes and air separation equipment, demonstrating broad engineering versatility.
[0022] 6. Full lifecycle optimization for long-term high-efficiency operation: This invention employs a complete closed-loop process of "detection-supplementation-verification," performing a secondary concentration test after supplementation to confirm the supplementation effect and ensure that the supplementation meets the standards. Attached Figure Description
[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0024] Figure 1 This is a process flow diagram of an intelligent refrigerant replenishment device for an LNG liquefaction unit according to an embodiment of the present invention; Figure 2 This is a logic block diagram of a control method for an intelligent refrigerant replenishment device for an LNG liquefaction unit, as described in an embodiment of the present invention.
[0025] Icons: 1-Refrigerant compressor, 2-Mixed refrigerant circulation pipeline, 3-Sampling and detection module, 4-Control unit, 5-Refrigerant replenishment execution module, 6-Refrigerant storage tank, 7-Regulating valve, 8-Flow meter, 9-Jack box, 10-Mixed refrigerant replenishment main pipe, 11-Mixed flow safety module, 12-Mixed flow tank, 13-Shut-off valve, 14-Pressure sensor, 15-Check valve, 16-Methane storage tank, 17-Nitrogen storage tank, 18-Ethylene storage tank, 19-Propane storage tank, 20-Isopentane storage tank, 21-First regulating valve, 22-Second regulating valve, 23-Third regulating valve, 24-Fourth regulating valve, 25-Fifth regulating valve, 26-First flow meter, 27-Second flow meter, 28-Third flow meter, 29-Fourth flow meter, 30-Fifth flow meter, 31-Mixed refrigerant inlet, 32-Mixed refrigerant outlet. Detailed Implementation
[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0027] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0028] Example See Figure 1 and Figure 2 This embodiment proposes an intelligent replenishment device for mixed refrigerant in an LNG liquefaction unit, which is applied to a mixed refrigerant circulation refrigeration system. The mixed refrigerant circulation refrigeration system includes a refrigerant compressor 1 and a mixed refrigerant circulation pipeline 2. The intelligent replenishment device includes a sampling and detection module 3, which is installed on the mixed refrigerant circulation pipeline 2 and is used to detect the concentration of each component in the mixed refrigerant in real time online. The control unit 4 is connected to the sampling and detection module 3 to receive component concentration data, compare it with the preset ideal component target value and calculate the deviation value, and determine the replenishment amount of each component based on the deviation value, system operating load and total amount of refrigerant. The refrigerant replenishment execution module 5 includes multiple independent refrigerant storage tanks 6, multiple regulating valves 7, multiple flow meters 8, and a junction box 9; each refrigerant storage tank 6 stores a pure component refrigerant, and its outlet is connected in series with a regulating valve 7 and a flow meter 8. The outlets of all regulating valves 7 are connected to the mixed refrigerant replenishment main pipe 10; the regulating valves 7 and the flow meters 8 are both electrically connected to the control unit 4 through the junction box 9. The mixing safety module 11 is located between the mixed refrigerant replenishment main pipe 10 and the low-pressure side or suction side of the mixed refrigerant circulation pipe 2. It includes a mixing tank 12, a shut-off valve 13 and a pressure sensor 14 connected in series on the mixed refrigerant replenishment main pipe 10. The mixing tank 12 is used to fully mix the replenished refrigerant with the refrigerant in the system. The shut-off valve 13 and the pressure sensor 14 are both electrically connected to the control unit 4. A one-way valve 15 is provided on the main manifold for replenishing the mixed refrigerant between the pressure sensor 14 and the mixed refrigerant circulation line 2.
[0029] The intelligent refrigerant replenishment device for an LNG liquefaction unit disclosed in this embodiment adopts an intelligent control architecture with real-time online multi-component concentration detection and deviation drive, combined with an execution structure that allows for independent storage and metering of each refrigerant component. This completely eliminates the drawbacks of traditional manual detection and replenishment, timed and quantitative replenishment, or single-component pressure replenishment. It can accurately identify the actual missing amount of each refrigerant component and achieve closed-loop precise replenishment. At the same time, the mixing tank 12 ensures that the replenished refrigerant is fully mixed with the system refrigerant, and the shut-off valve 13 and pressure sensor 14 provide safety protection for abnormal operating conditions. The one-way valve 15 further enhances the safety and flexibility of system operation, effectively maintaining the long-term stability of the mixed refrigerant component ratio, significantly improving the operating efficiency of the refrigeration system, reducing energy consumption, greatly reducing the intensity of manual labor and the risk of human error, and ensuring the long-term efficient, stable, and safe operation of the LNG liquefaction unit.
[0030] See Figure 1 and Figure 2 In this embodiment, the refrigerant storage tank 6 includes a methane storage tank 16, a nitrogen storage tank 17, an ethylene storage tank 18, a propane storage tank 19, and an isopentane storage tank 20; the regulating valve 7 includes a first regulating valve 21, a second regulating valve 22, a third regulating valve 23, a fourth regulating valve 24, and a fifth regulating valve 25; the flow meter 8 includes a first flow meter 26, a second flow meter 27, a third flow meter 28, a fourth flow meter 29, and a fifth flow meter 30; the outlet of the methane storage tank 16 is connected in series with the first flow meter 26 and the first regulating valve 21, the outlet of the nitrogen storage tank 17 is connected in series with the second flow meter 27 and the second regulating valve 22, the outlet of the ethylene storage tank 18 is connected in series with the third flow meter 28 and the third regulating valve 23, the outlet of the propane storage tank 19 is connected in series with the fourth flow meter 29 and the fourth regulating valve 24, and the outlet of the isopentane storage tank 20 is connected in series with the fifth flow meter 30 and the fifth regulating valve 25.
[0031] Specifically, by configuring independent storage, metering, and regulation units for the five core refrigerant components—methane, nitrogen, ethylene, propane, and isopentane—in the LNG mixed refrigerant cycle system, individual and precise metering and independent closed-loop control of each refrigerant component are achieved. This completely avoids mutual interference during the replenishment of multiple components, accurately matches the actual missing amount of each component, and quickly restores the proportion of mixed refrigerant components to the design value, effectively ensuring the refrigeration efficiency and long-term operational stability of the refrigeration system. At the same time, the standard configuration of the unit for mainstream MRC processes is clearly defined, significantly improving the versatility and engineering practicality of the unit.
[0032] See Figure 1 and Figure 2 In this embodiment, the sampling and detection module 3 is an online gas chromatograph or infrared spectrometer, used to obtain the volume concentration or mass concentration of each component in the mixed refrigerant.
[0033] Specifically, by using an online gas chromatograph or infrared spectrometer as the sampling and detection module 3, real-time, continuous, and online detection of the concentration of each component in the mixed refrigerant can be achieved without manual sampling and analysis. This reduces labor intensity and significantly improves the detection response speed and data timeliness. At the same time, it can accurately obtain the volume concentration or mass concentration of each component, with high detection accuracy and comprehensive component coverage. This provides a reliable data foundation for the control unit 4 to accurately calculate component deviations and replenishment amounts, ensuring the accuracy and effectiveness of intelligent replenishment of the mixed refrigerant from the source.
[0034] See Figure 1 and Figure 2 In this embodiment, the control unit 4 is an industrial-grade PLC or DCS system with built-in PID control algorithm, fuzzy logic algorithm or rule base algorithm.
[0035] Specifically, by using an industrial-grade PLC or DCS system as the control unit 4, it possesses excellent anti-interference capabilities in industrial environments and long-term operational reliability. It can be seamlessly integrated with the existing control system of the LNG liquefaction plant, significantly reducing system modification costs and on-site implementation difficulties. At the same time, it has built-in multiple control algorithms such as PID, fuzzy logic, and rule base, which can flexibly adapt the optimal control strategy according to different system loads and component deviation conditions, significantly improving the calculation accuracy and control response speed of refrigerant replenishment, ensuring a stable and controllable replenishment process, and avoiding interference with the normal operation of the original refrigeration system.
[0036] See Figure 1 and Figure 2 In this embodiment, the regulating valve 7 is a pneumatic regulating valve, which can achieve continuous adjustment of the opening degree from 0% to 100%; the flow meter 8 is a mass flow meter.
[0037] Specifically, a pneumatic regulating valve capable of continuous adjustment from 0% to 100% opening is adopted, enabling smooth and stepless precise control of the refrigerant replenishment flow rate. This avoids sudden flow changes and system pressure fluctuations caused by on / off regulation, ensuring a smooth and shock-free replenishment process. Simultaneously, a mass flow meter is used to measure the refrigerant replenishment amount, unaffected by changes in on-site temperature, pressure, and other operating conditions. It boasts high measurement accuracy and stability. The combination of these two devices enables precise closed-loop control of the refrigerant replenishment amount, effectively preventing over- or under-replenishment issues and further improving the accuracy of restoring the proportions of the mixed refrigerant components and the reliability of system operation.
[0038] See Figure 1 and Figure 2 In this embodiment, the mixing tank 12 is a static mixer or a buffer tank.
[0039] Specifically, by limiting the mixing tank 12, two mature and reliable industrial structures can be adopted: a static mixer or a buffer tank. The static mixer can utilize the characteristics of having no moving parts, high mixing efficiency, and small installation space to quickly and fully homogenize the supplementary refrigerant of different components within a short distance, avoiding local concentration changes that may affect the cooling effect of the cold box. The buffer tank can utilize its excellent pressure buffering capacity to stabilize the flow and pressure fluctuations in the mixed refrigerant supplementary main pipe 10, while also having a certain mixing function. The optimal solution can be flexibly selected according to the installation conditions and operating requirements of different engineering sites, which significantly improves the engineering applicability and operational stability of the device.
[0040] In one embodiment of the present invention: a control method for an intelligent replenishment device for a mixed refrigerant in an LNG liquefaction unit is also provided, comprising the following steps: S1. Preset the ideal target concentration values and lower concentration thresholds of each component of the mixed refrigerant in the control unit 4; S2. The actual concentration data of each component in the mixed refrigerant circulation pipeline 2 are collected by the sampling and detection module 3, and the concentration deviation value of each component is calculated by the control unit 4. S3. When the actual concentration of a certain component is lower than the lower limit threshold, the required replenishment amount is calculated based on the concentration deviation value of the component, the system operating load and the total amount of refrigerant. The control unit 4 controls the corresponding regulating valve to open for replenishment. The replenishment flow is fed back in real time through the corresponding flow meter to form a closed loop control. After the replenishment amount is reached, the corresponding regulating valve is closed. S4. The pressure of the mixed refrigerant replenishment main pipe 10 is monitored in real time by the pressure sensor 14. When an abnormal pressure or refrigerant leakage is detected, the control unit 4 controls the shut-off valve 13 to close to cut off the replenishment circuit and issues an alarm signal.
[0041] See Figure 1 and Figure 2 In this embodiment, in S2, the actual concentration data of each component in the mixed refrigerant is collected once at a preset time interval.
[0042] Specifically, by setting a step to collect the actual concentration data of each component in the mixed refrigerant at preset time intervals, the system ensures the timeliness of the component concentration data, enabling timely detection of component ratio deviations and triggering replenishment operations. This effectively avoids problems such as reduced refrigeration efficiency, increased energy consumption, and system instability caused by long-term accumulation of deviations. It also avoids the waste of system resources and excessive wear and tear on detection equipment caused by continuous and uninterrupted data collection. At the same time, the preset time interval can be flexibly adjusted according to actual conditions such as system operating load and operating conditions, balancing detection accuracy and system operating economy, thus laying the foundation for the timeliness and reliability of intelligent refrigerant replenishment control.
[0043] See Figure 1 and Figure 2 In this embodiment, in S3, when the actual concentrations of multiple components are simultaneously below the lower concentration threshold, they are replenished sequentially according to the priority of each component's influence on refrigeration efficiency, or simultaneously according to the concentration deviation ratio of each component.
[0044] Specifically, by setting two flexible replenishment strategies for operating conditions where multiple components are simultaneously missing, the system can replenish components sequentially according to their priority of impact on refrigeration efficiency, prioritizing and quickly restoring the core refrigeration capacity of the system and avoiding a significant decline in system performance. Alternatively, it can replenish components synchronously according to their concentration deviation ratios, allowing the proportions of each component to return to the design values simultaneously, avoiding temporary imbalances and system pressure fluctuations caused by excessive replenishment of a single component. These two strategies adapt to different operating conditions, significantly improving the adaptability, stability, and accuracy of the intelligent replenishment process, and ensuring the continuous, efficient, and stable operation of the refrigeration system.
[0045] See Figure 1 and Figure 2 In this embodiment, in step S3, after the replenishment is completed, the actual concentration data of each component in the mixed refrigerant are collected again. After confirming that the concentration of each component is within the allowable deviation range, the replenishment process ends.
[0046] Specifically, by adding a secondary acquisition and confirmation step of the mixed refrigerant component concentration after replenishment, a complete closed-loop control process of "detection-replenishment-verification" is formed. This can effectively verify the accuracy of a single replenishment operation, promptly correct over-replenishment or under-replenishment caused by calculation errors, metering deviations, or uneven refrigerant mixing, ensure that the concentration of each component accurately returns to the allowable deviation range, completely eliminate the situation of premature termination of the replenishment process or invalid repeated replenishment, fundamentally guarantee the stability of the mixed refrigerant component ratio, and provide reliable support for the continuous, efficient and stable operation of the refrigeration system.
[0047] See Figure 1 and Figure 2In this embodiment, the two ends of the mixed refrigerant circulation pipeline 2 are respectively a mixed refrigerant inlet 31 and a mixed refrigerant outlet 32, and the mixed refrigerant inlet 31 and the mixed refrigerant outlet 32 are respectively connected to the outlet and inlet of a flow channel of the cold box.
[0048] See Figure 1 and Figure 2 In this embodiment, the refrigerant compressor 1 is the core power source and pressure control core that ensures the replenished refrigerant does not flow back. By continuously operating on the suction side, it constructs and maintains the lowest pressure zone of the entire mixed refrigerant circulation system, fundamentally establishing the pressure basis for unidirectional flow from a fluid mechanics perspective: the refrigerant compressor 1 continuously draws and compresses the refrigerant from the suction side (the end of the refrigerant compressor 1 closest to the mixed refrigerant inlet) and sends it to the high-pressure side of the system (the end of the refrigerant compressor 1 closest to the mixed refrigerant outlet), making the suction side operating pressure much lower than the storage pressure of the refrigerant storage tank 6 on the replenishment device side and the operating pressure of the mixed refrigerant replenishment main pipe 10, forming a situation where "the pressure of the refrigerant storage tank 6 is greater than the pressure of the mixed refrigerant inlet pipe 10." The stable three-stage positive pressure gradient of "compensation main pipe pressure > compressor suction side pressure" forces the refrigerant to flow unidirectionally from the high-pressure replenishment device to the low-pressure circulation system. At the same time, the compressor's suction capacity can fully cover the maximum replenishment flow condition. Even when multiple components are replenished simultaneously, the incoming refrigerant can be promptly removed and pressurized for circulation, preventing abnormal increases in suction side pressure and reversal of the pressure gradient. Combined with the control logic of "first closing component regulating valve 7, and then closing emergency shut-off valve 13 after the compressor has completely removed the remaining refrigerant from the mixed refrigerant replenishment main pipe 10" after replenishment, the possibility of refrigerant backflow towards the replenishment device in the circulation system is completely eliminated.
[0049] See Figure 1 and Figure 2 In this embodiment, the emergency shut-off valve 13, pressure sensor 14, and one-way valve 15 are connected in series and finally connected to the compressor suction side. During normal operation, the three-stage positive pressure gradient of "refrigerant tank 6 pressure > mixing tank 12 pressure > compressor suction side pressure" always exists, and the refrigerant can only flow in one direction. The one-way valve 15 acts as a physical barrier, allowing refrigerant to flow from the mixed refrigerant replenishment main pipe 10 to the circulation system. Once an abnormality such as the refrigerant compressor 1 stopping causes the circulation side pressure to rise, the valve disc of the shut-off valve 13 will automatically close, blocking the backflow path. The pressure sensor 14 monitors the pressure of the mixing tank 12 on the mixed refrigerant replenishment main pipe 10 in real time. When the pressure exceeds the set threshold or a sudden pressure rise (leakage signs) is detected, the control unit 4 closes the emergency shut-off valve 13 within 1 second and issues an audible and visual alarm, cutting off the replenishment circuit. In the non-replenishment state, the emergency shut-off valve 13 remains normally closed, disconnecting the replenishment device from the circulation system at the source.
[0050] See Figure 1 and Figure 2 In this embodiment, the control unit principle is as follows: The output signal of the sampling and detection module follows the Modbus-RTU communication protocol and is transmitted to the control unit via shielded twisted-pair cable. The output signals of the flow meter and pressure sensor are typically 4mA to 20mA analog signals, connected to the analog input module of the control unit via a junction box and shielded computer cable. The input signal of the regulating valve is connected to the analog output module of the control unit via a junction box and shielded computer cable. The solenoid coil of the shut-off valve is connected to the digital output module of the control unit via a junction box and shielded computer cable. The control unit collects the mixed refrigerant component data from the detection module, compares it with the target component, and obtains the deviation value. After calculation by the logic controller, the PID function block outputs the regulating valve opening signal to adjust the addition amount of the corresponding component. The control unit collects the real-time signal from the pressure sensor and compares it with the preset interlock value of the logic controller. When the detected real-time pressure sensor value is greater than or equal to the preset interlock value, the logic controller outputs a low-level signal to the digital output module, causing the shut-off valve to close.
[0051] See Figure 1 and Figure 2 The specific principle of the intelligent refrigerant replenishment device for the LNG liquefaction unit in this embodiment is as follows: The intelligent refrigerant replenishment device for the LNG liquefaction unit in this embodiment is based on the characteristics of the MRC mixed refrigerant cycle process. It constructs an automated replenishment system driven by deviation and controlled in a closed loop, completely replacing traditional manual detection, timed and quantitative, or single-component pressure replenishment modes. The device relies on the high-pressure potential energy of the refrigerant storage tank 6 and the continuous negative pressure on the suction side of the refrigerant compressor 1 to form a stable three-stage positive pressure gradient: "storage tank pressure > replenishment main pipe pressure > compressor suction side pressure." This provides natural power for refrigerant replenishment without the need for additional pressurization equipment, establishing the unidirectional flow trend of the refrigerant from a fluid dynamics perspective.
[0052] The device uses an online gas chromatograph or infrared spectrometer to collect real-time concentration data of five core components—methane, nitrogen, ethylene, propane, and isopentane—in the circulating refrigerant at preset time intervals, and transmits this data to an industrial-grade PLC or DCS control unit 4. The control unit 4 compares the measured concentrations with preset ideal target values to calculate the deviation. Combined with parameters such as system operating load and total refrigerant volume, it accurately calculates the replenishment amount of each component using algorithms such as PID and fuzzy logic. For operating conditions where multiple components are simultaneously missing, it can flexibly select either priority-based sequential replenishment or proportional synchronous replenishment modes.
[0053] Each refrigerant component employs an independent storage tank, independent mass flow meter, and independent pneumatic regulating valve, achieving precise metering and stepless flow regulation for each component. This avoids mutual interference from multiple component replenishments and, combined with real-time feedback from the flow meter, forms a closed-loop flow control system. The replenished refrigerant is first homogenized and mixed in the mixing tank 12 before entering the circulation system. Simultaneously, a triple anti-backflow and safety protection system is constructed through physical shut-off by the one-way valve 15, rapid response by the emergency shut-off valve 13, and source control by the control logic. After replenishment, a secondary concentration test verifies the effect, forming a complete closed loop of "detection-decision-execution-verification," ensuring the long-term stability of the mixed refrigerant component ratio and guaranteeing the refrigeration efficiency and safe operation of the LNG liquefaction cold box.
[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A smart refrigerant replenishment device for an LNG liquefaction unit, applied to a mixed refrigerant circulation refrigeration system, the mixed refrigerant circulation refrigeration system comprising a refrigerant compressor (1) and a mixed refrigerant circulation pipeline (2), characterized in that: The intelligent replenishment device includes a sampling and detection module (3), which is installed on the mixed refrigerant circulation pipeline (2); The control unit (4) is communicatively connected to the sampling and detection module (3); The refrigerant replenishment execution module (5) includes multiple independent refrigerant storage tanks (6), multiple regulating valves (7), multiple flow meters (8), and a junction box (9); each of the refrigerant storage tanks (6) stores a pure component refrigerant, and its outlet is connected in series with one of the regulating valves (7) and one of the flow meters (8), and the outlets of each regulating valve (7) are connected to the mixed refrigerant replenishment main pipe (10); the regulating valves (7) and the flow meters (8) are both electrically connected to the control unit (4) through the junction box (9); The mixing safety module (11) includes a mixing tank (12), a shut-off valve (13) and a pressure sensor (14) connected in series on the mixing refrigerant replenishment main pipe (10); the shut-off valve (13) and the pressure sensor (14) are both electrically connected to the control unit (4); A one-way valve (15) is provided on the main mixed refrigerant supply pipe (10) between the pressure sensor (14) and the mixed refrigerant circulation pipeline (2).
2. The intelligent refrigerant replenishment device for an LNG liquefaction unit according to claim 1, characterized in that: The refrigerant storage tank (6) includes a methane storage tank (16), a nitrogen storage tank (17), an ethylene storage tank (18), a propane storage tank (19), and an isopentane storage tank (20); the regulating valve (7) includes a first regulating valve (21), a second regulating valve (22), a third regulating valve (23), a fourth regulating valve (24), and a fifth regulating valve (25); the flow meter (8) includes a first flow meter (26), a second flow meter (27), a third flow meter (28), a fourth flow meter (29), and a fifth flow meter (30). The outlet of the methane storage tank (16) is connected in series with the first flow meter (26) and the first regulating valve (21); the outlet of the nitrogen storage tank (17) is connected in series with the second flow meter (27) and the second regulating valve (22); the outlet of the ethylene storage tank (18) is connected in series with the third flow meter (28) and the third regulating valve (23); the outlet of the propane storage tank (19) is connected in series with the fourth flow meter (29) and the fourth regulating valve (24); and the outlet of the isopentane storage tank (20) is connected in series with the fifth flow meter (30) and the fifth regulating valve (25).
3. The intelligent refrigerant replenishment device for an LNG liquefaction unit according to claim 1, characterized in that: The sampling and detection module (3) is an online gas chromatograph or an infrared spectrometer.
4. The intelligent refrigerant replenishment device for an LNG liquefaction unit according to claim 1, characterized in that: The control unit (4) is an industrial-grade PLC or DCS system with a built-in PID control algorithm.
5. The intelligent refrigerant replenishment device for an LNG liquefaction unit according to claim 1, characterized in that: The regulating valve (7) is a pneumatic regulating valve with continuous adjustment of opening from 0% to 100%; the flow meter (8) is a mass flow meter.
6. The intelligent refrigerant replenishment device for an LNG liquefaction unit according to claim 1, characterized in that: The mixing tank (12) is a static mixer or a buffer tank.
7. A control method for an intelligent refrigerant replenishment device for an LNG liquefaction plant according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. The ideal target concentration value and lower limit threshold of each component of the mixed refrigerant are preset in the control unit (4); S2. The actual concentration data of each component in the mixed refrigerant circulation pipeline (2) is collected by the sampling and detection module (3), and the concentration deviation value of each component is calculated by the control unit (4). S3. When the actual concentration of a component is lower than the lower limit threshold of the concentration, the required amount of replenishment is calculated based on the concentration deviation of the component, the system operating load and the total amount of refrigerant. The control unit (4) controls the corresponding regulating valve to open for replenishment. The replenishment flow is fed back in real time through the corresponding flow meter to form a closed loop control. After the replenishment amount is reached, the corresponding regulating valve is closed. S4. The pressure of the mixed refrigerant replenishment main pipe (10) is monitored in real time by the pressure sensor (14). When an abnormal pressure or refrigerant leakage is detected, the control unit (4) controls the shut-off valve (13) to close and issues an alarm signal.
8. The control method for an intelligent refrigerant replenishment device for an LNG liquefaction unit according to claim 7, characterized in that: In S2, the actual concentration data of each component in the mixed refrigerant is collected once at preset time intervals.
9. The control method for an intelligent refrigerant replenishment device for an LNG liquefaction unit according to claim 7, characterized in that: In S3, when the actual concentrations of multiple components are simultaneously lower than the lower concentration threshold, they are supplemented sequentially according to the priority of each component's influence on refrigeration efficiency, or simultaneously according to the concentration deviation ratio of each component.
10. The control method for an intelligent refrigerant replenishment device for an LNG liquefaction unit according to claim 7, characterized in that: In step S3, after the replenishment is completed, the actual concentration data of each component in the mixed refrigerant are collected again. After confirming that the concentration of each component is within the allowable deviation range, the replenishment process ends.