Dual-mode anti-freezing cooling system for air compressor of nuclear power plant

Abstract

The present application belongs to the field of nuclear power plant auxiliary support system operation and maintenance and fluid thermodynamics control technology, and particularly relates to a dual-mode anti-freezing cooling system for air compressor of nuclear power plant. A multi-source state sensing and signal preprocessing module is configured to collect state signals of outdoor environment dry bulb temperature, cooling water return temperature, low-level energy storage water tank liquid level, pipe network water supply pressure and external available heat source; a dual-mode intelligent state machine decision module is configured to automatically optimize and switch between wet standby and dry emptying modes according to real-time working conditions; a waste heat coupling closed-loop regulation and control module is configured to perform fine heat management in the wet standby mode; and a fault safety type gravity emptying execution module is configured to control the state of a normally open type vacuum breaking electromagnetic valve arranged at the highest point of the outdoor cooling tower coil and a normally open type backflow bypass valve at the outlet of the circulating pump. The present application significantly improves the intrinsic safety level, energy utilization efficiency and equipment operation reliability of the auxiliary system.

Description

Technical Field

[0001] This invention belongs to the field of operation and maintenance of auxiliary support systems and fluid thermodynamics control technology in nuclear power plants, and specifically relates to a dual-mode antifreeze cooling system for air compressors in nuclear power plants. Background Technology

[0002] As energy facilities with extremely high requirements for continuity and safety, the reliability of key support systems in nuclear power plants directly affects the stable operation of the reactor and accident mitigation capabilities. The instrumentation compressed air system is the nervous system of a nuclear power plant, responsible for providing clean, dry compressed air to all pneumatic control valves, isolation valves, and critical actuators throughout the plant. To ensure the normal operation of the air compressors (usually oil-free screw compressors), a closed-loop cooling water system must be installed to remove the heat of compression. However, due to limitations in plant space layout and heat dissipation requirements, cooling towers and their heat exchange coils are typically located outdoors, while air compressor units and circulating pumps are located indoors. This indoor-outdoor cross-regional physical arrangement exposes units in standby mode to a severe risk of outdoor coil freezing and cracking under low-temperature winter conditions.

[0003] In the past, the antifreeze design of air compressor cooling systems in nuclear power plants typically employed a combined control method of heating cables and circulating pumps based on indoor temperature monitoring points. This involved activating electric heaters or circulating pumps when the pipe water temperature was detected to be below a set value (e.g., 5°C) to prevent freezing. However, this control mode, relying on single-point temperature feedback, suffers from significant thermal hysteresis and temperature measurement blind spots. Since temperature sensors are mostly located indoors or in well-insulated pipe sections, while the coils at the highest risk of freezing are located outdoors with thin walls and rapid heat dissipation, the medium inside the outdoor coils often crystallizes or freezes before the sensors trigger their operation during the static period when the antifreeze pump is off. This difference in physical environment prevents the control system from responding promptly and effectively, easily leading to coil rupture accidents and rendering standby units unusable.

[0004] Furthermore, existing technologies have significant shortcomings in terms of the economic efficiency and thermal stability of freeze protection. On the one hand, the water capacity of the freeze protection circuit is usually small (only enough for water storage in the pipes). When the electric heater is turned on, the water temperature can rise rapidly, causing localized overheating. After it stops, the water cools down quickly, leading to frequent start-stop oscillations in the control system. This not only affects the lifespan of the equipment but also poses safety hazards. On the other hand, in order to keep the standby unit from freezing, the power plant needs to consume high-grade electrical energy to operate the heating device. At the same time, the nearby main air compressor unit is continuously emitting large amounts of low-grade waste heat (compression heat) into the atmosphere. This operating mode, which consumes electrical energy for freeze protection while simultaneously emitting waste heat, is extremely unreasonable in terms of energy utilization.

[0005] More importantly, nuclear power plants have special requirements for passive safety. Existing antifreeze measures are all active, highly dependent on the normal operation of the power supply and control system. In the event of a plant-wide power outage or instrumentation and control power failure, the antifreeze circulating pumps and electric heaters will immediately fail, and the cooling water stagnating in the outdoor coils will become an uncontrollable hazard source, which may freeze at any time, damaging the system boundary and causing a loss of gas supply.

[0006] While some improvements can be made by simply increasing the pump start-up temperature threshold or adding insulation thickness, these are stopgap measures that do not address the root cause. They fail to eliminate the physical property of icing in stagnant fluids and cannot solve the failure problem under power outage conditions. Therefore, a comprehensive solution integrating thermodynamic optimization and fail-safe design is needed. This solution should reduce anti-freezing energy consumption through waste heat recovery technology and achieve intrinsic safety through physical gravity venting mechanisms. Deploying such a dual-mode optimization device in the air compressor cooling system of a nuclear power plant can effectively solve the freezing cracking hazard caused by temperature measurement lag, break the contradiction between energy consumption and safety, and ensure the long-term stability and emergency response capability of nuclear power plant auxiliary systems under extreme weather conditions. Summary of the Invention

[0007] The purpose of this invention is to provide a dual-mode anti-freeze cooling system for air compressors in nuclear power plants. By integrating cross-unit waste heat coupling utilization technology, a fail-safe gravity venting architecture, dual-mode intelligent switching logic, and an automatic vacuum breaking mechanism, it can effectively address the risk of physical freezing and cracking of outdoor coils of standby units due to the static medium under extremely cold winter conditions, the thermal hysteresis effect caused by the difference between the temperature measurement point and the freezing point in traditional heat tracing control, and the excessive energy consumption caused by relying solely on electric heating for anti-freeze. This ensures the inherent safety, low carbon and energy saving, and emergency response capability of the air compressor cooling system, and improves the automation level and operational economy of the nuclear power plant's auxiliary support systems.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A dual-mode anti-freeze cooling system for air compressors in nuclear power plants includes a multi-source state sensing and signal preprocessing module: collecting status signals from outdoor ambient dry-bulb temperature, cooling water return temperature, low-level energy storage tank level, pipeline water supply pressure, and external available heat sources; a dual-mode intelligent state machine decision-making module: automatically optimizing and switching between wet thermal standby and dry venting modes based on real-time operating conditions; a waste heat coupling closed-loop control module: performing refined heat management in wet thermal standby mode; and a fail-safe gravity venting execution module: handling normally open rupture mechanisms located at the highest point of the outdoor cooling tower coils. The vacuum solenoid valve and the normally open reflux bypass valve at the outlet of the circulating pump are subject to status control; the transient rapid charging and recovery module: upon receiving the unit pre-start signal, immediately closes the vent valve and starts the circulating pump at full speed, using a large flow water column to expel air from the pipe and build up pressure, and monitors the pressure build-up rate in real time; the full life cycle self-diagnosis module: during wet operation, it identifies minor leaks by monitoring the abnormal rate of drop in the water tank level; at the moment of low-temperature start-up, it identifies the risk of impeller freezing and jamming by comparing the relationship between the pump motor current and the flow rate, and immediately triggers shutdown protection once an abnormality is detected.

[0009] Multi-source status perception and signal preprocessing module: The module collects outdoor ambient dry bulb temperature, cooling water return temperature, low-level energy storage tank level, pipeline water supply pressure, and status signals of available external heat sources through redundantly configured I / O channels. Available external heat sources include nearby operating units.

[0010] Multi-source state perception and signal preprocessing module: Smooths analog data and removes spike interference through an adaptive moving average filtering algorithm.

[0011] Multi-source state perception and signal preprocessing module: For ambient temperature signals, a trend judgment logic based on time window and a hysteresis comparison mechanism are introduced, and a temperature dead zone of ±1.5℃ is set. The state is only updated when the temperature change exceeds the dead zone.

[0012] The dual-modal intelligent state machine decision module assesses external weather conditions and the availability of internal equipment in real time. When the ambient temperature is higher than the set threshold, it maintains low-power standby. When the ambient temperature is lower than the threshold, it automatically activates the anti-freeze protection logic, prioritizing the check of the availability of external heat sources and the health status of the entire plant's power system to decide whether to use waste heat for low-cost insulation or to perform dry venting to ensure absolute safety.

[0013] Dry exhaust mode Mode drain The triggering criterion is shown in the following formula: (1) For ambient temperature, To prevent freezing, trigger threshold, This is the status bit for the availability of external heat sources; 0 indicates that it is unavailable. This is a major fault signal for the unit. This is a power outage signal for the entire plant.

[0014] Waste heat coupling closed-loop control module: It uses a cascade PID control algorithm to calculate the deviation between the circulating water temperature and the target set value in real time; it dynamically adjusts the opening of the electric regulating valve on the waste heat introduction pipeline according to the deviation, so as to introduce the external high temperature heat medium into the plate heat exchanger of the unit for heat exchange; at the same time, it instructs the anti-freeze circulating pump of the unit to operate at the minimum maintenance frequency to ensure that the pipeline is in a turbulent heat exchange state; the auxiliary electric heater is started only when the regulating valve is fully open and the water temperature continues to drop.

[0015] Auxiliary electric heater start / stop control logic S Heater as follows: (2) For the country's water temperature, For the lowest safe temperature, This refers to the opening degree of the waste heat regulating valve.

[0016] Fail-safe gravity venting module: Once the system determines that it has entered venting mode or a control power loss occurs, the vacuum breaking solenoid valve and the return bypass valve will immediately lose power and open automatically. Atmosphere will then be introduced into the top of the coil to break the siphon effect. Under the action of gravity, the water in the pipe will quickly flow back along the pipe with the designed slope and merge into the indoor low-level energy storage tank. The venting status of the outdoor pipeline is inverted by monitoring the increase in the liquid level of the low-level water tank in real time.

[0017] The empty verification logic is as follows: (3) This represents the volume change corresponding to the rise in the water level in the tank. This refers to the total design volume of outdoor piping and coils. The volume factor is set to 0.95. If the conditions are not met, the pipeline may be blocked by ice or the air vent valve may fail, immediately triggering the highest level of freeze blockage alarm and locking the unit from starting.

[0018] The beneficial effects achieved by this invention are as follows: This invention addresses the challenges of stagnant water freezing during low-load standby in traditional nuclear power plant instrument air systems by integrating waste heat recovery technology, a fail-safe physical venting architecture, and a hierarchical automatic control strategy. These challenges include thermal inertia oscillations in temperature control, and the contradiction between consuming electricity and releasing waste heat simultaneously. It is applicable to winter anti-freezing operation management, energy-saving optimization, and emergency safety assurance scenarios for oil-free screw air compressors in pressurized water reactor nuclear power plants' instrument air systems, significantly improving the intrinsic safety level, energy efficiency, and equipment reliability of auxiliary systems.

[0019] This invention integrates multi-source state perception with dual-modal intelligent state machine decision-making logic to achieve comprehensive real-time monitoring and accurate judgment of the operating conditions and environmental thermal parameters of the air compressor cooling system. The waste heat coupling closed-loop control technology completely changes the traditional high-energy-consuming electric heat tracing mode. By recovering available external heat sources (such as waste heat from nearby operating units) as antifreeze power, it significantly reduces plant power consumption under wet thermal standby conditions, achieving green and low-carbon operation. The fail-safe gravity venting architecture solves the freezing and cracking problem caused by temperature measurement lag or power failure in traditional systems. When extreme low temperatures, heat source loss, or the risk of a plant-wide power outage are detected, the system automatically breaks the vacuum and uses gravity to instantly vent the outdoor medium, physically eliminating the risk of icing. The transient rapid charging recovery mechanism and full life-cycle self-diagnostic function ensure the unit's emergency response speed, enabling rapid elimination of gas locks and pressure establishment under high-flow charging, avoiding the risk of human error, and ensuring the continuity and stability of gas supply to the nuclear power plant under complex winter weather conditions. Attached Figure Description

[0020] Figure 1 This is a flow chart of a dual-mode antifreeze cooling system for an air compressor in a nuclear power plant. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0022] like Figure 1 As shown, a dual-mode anti-freezing cooling system for nuclear power plant air compressors integrates thermodynamic energy flow optimization, passive fail-safe architecture, and full-condition state machine control. Through deep integration of multiple aspects, including real-time acquisition, data fusion, mode discrimination, waste heat scheduling, and venting execution of unit operating conditions, environmental meteorological parameters, fluid thermodynamic characteristics, and pipeline physical topology, the system achieves intrinsic safety protection and zero-energy insulation for the nuclear power plant air compressor cooling system under conditions of low-load standby in winter, extreme cold weather, and power outages. The system includes: a multi-source state perception and signal preprocessing module, a dual-mode intelligent state machine decision-making module, a waste heat coupling closed-loop control module, a fail-safe gravity venting execution module, a transient rapid recharge recovery module, and a full life-cycle self-diagnosis module.

[0023] The multi-source state perception and signal preprocessing module is the nerve ending of the system, responsible for establishing a high-precision system state image. Its implementation process follows a strict data processing sequence. First, this module uses redundantly configured I / O channels to collect high-frequency state signals from outdoor dry-bulb temperature, cooling water return temperature, low-level energy storage tank level, pipeline water supply pressure, and external available heat sources (such as nearby operating units), ensuring the integrity of the raw data. Second, to eliminate signal noise from the complex electromagnetic environment of nuclear power plants, the module integrates an adaptive moving average filtering algorithm to smooth analog data and remove spike interference. Finally, for the ambient temperature signal, which is a key basis for mode switching, the system introduces a trend judgment logic based on a time window and a hysteresis comparison mechanism, setting a temperature dead zone of ±1.5℃. The state is only updated when the temperature change exceeds this dead zone, effectively shielding sensor fluctuations caused by instantaneous gusts or local heat island effects, and preventing destructive frequent oscillations in the control system between "anti-freeze" and "standby" modes.

[0024] The dual-modal intelligent state machine decision-making module is the core logic unit of the system. It has a built-in deterministic finite state machine responsible for automatically optimizing the switching between two physical modes—"wet thermal standby" and "dry venting"—based on real-time operating conditions. This module assesses external weather conditions and internal equipment availability in real time: when the ambient temperature is above a set threshold (e.g., 5°C), the system maintains low-power standby; when the ambient temperature is below the threshold, the system automatically activates anti-freeze protection logic. At this time, the decision-making module prioritizes checking the availability of external heat sources (e.g., whether nearby units are operating) and the overall plant power system health status to determine whether to utilize waste heat for low-cost insulation or perform venting to ensure absolute safety. The core decision logic of this module is the dry venting mode. drain The trigger criterion is as follows: (1) in, For ambient temperature, To prevent freezing, trigger threshold, This is the status bit for the availability of external heat sources (0 represents unavailable, such as when a nearby unit is out of service). This is a major fault signal for the unit. This is a plant-wide power outage signal. This logic ensures that in extreme conditions such as lack of residual heat source, system malfunction, or power loss, the system can be forced into a physical venting state, achieving passive safety.

[0025] The waste heat coupling closed-loop control module is responsible for performing refined heat management in wet standby mode. Its core technology lies in constructing a graded energy consumption control strategy that prioritizes waste heat and uses electric heating as a backup. Specific control steps include: First, using a cascaded PID control algorithm to calculate the deviation between the circulating water temperature and the target setpoint in real time; second, dynamically adjusting the opening of the electric regulating valve on the waste heat introduction pipeline according to the deviation, introducing external high-temperature heat medium (such as return water from the operating unit) into the unit's plate heat exchanger for heat exchange; simultaneously, to prevent dead zone effects, the module instructs the unit's antifreeze circulating pump to operate at the lowest maintenance frequency (e.g., 20Hz) to ensure the pipeline network is in a turbulent heat exchange state. Finally, the module will only start the auxiliary electric heater when the regulating valve is fully open and the water temperature continues to drop (meaning insufficient waste heat). The auxiliary electric heater start / stop control logic (S...) Heater )as follows: (2) in, For the country's water temperature, For the lowest safe temperature, This refers to the opening degree of the waste heat regulating valve. This logic, at the algorithmic level, mandates that high-grade electrical energy is consumed only after all physical waste heat has been completely utilized, thereby achieving significant energy-saving effects.

[0026] The fail-safe gravity venting module constitutes the system's final safety barrier. Its hardware architecture is based on the power-loss safety concept, and its specific execution logic is as follows: First, the module implements state control on the normally open vacuum-breaking solenoid valve located at the highest point of the outdoor cooling tower coil and the normally open return bypass valve at the circulation pump outlet. Second, once the system determines that it has entered venting mode or experiences a power loss, the aforementioned valves will immediately open automatically, allowing atmospheric air to be introduced to the top of the coil to disrupt the siphon effect. Under gravity, the water in the pipes rapidly flows back along the designed slope and into the indoor low-level energy storage tank. Finally, to quantitatively verify the integrity of the venting, the module embeds a diagnostic algorithm based on the principle of volume conservation, which inversely reflects the venting status of the outdoor pipeline by real-time monitoring of the increase in the liquid level in the low-level tank. The venting verification logic is as follows: (3) in, This represents the volume change corresponding to the rise in the water level in the tank. This refers to the total design volume of outdoor piping and coils. This is the volumetric factor, typically taken as 0.95. If this condition is not met, it means that there may be ice blockage in the pipeline or a malfunctioning air vent valve. The system will immediately trigger the highest level of freeze blockage alarm and lock the unit startup.

[0027] The transient rapid charging and recovery module works in conjunction with the full lifecycle self-diagnostic module to ensure high system availability. The specific implementation steps are as follows: First, upon receiving the unit pre-start signal, the charging module immediately closes the vent valve and starts the circulation pump at full speed, using a large flow of water to expel air from the pipes and build pressure within 30 seconds. Second, it monitors the pressure build-up rate dP / dt in real time to confirm system readiness. Simultaneously, the self-diagnostic module continuously monitors the health status of the entire system. During wet operation, it identifies minor leaks by monitoring the abnormal rate of drop in the water tank level. At the moment of low-temperature start-up, it identifies the risk of impeller freezing and jamming by comparing the relationship between the pump motor current and flow rate. Once an abnormality is detected, it immediately triggers shutdown protection to prevent equipment damage.

Claims

1. A dual-mode antifreeze cooling system for an air compressor in a nuclear power plant, characterized in that: Includes a multi-source state perception and signal preprocessing module: collecting outdoor ambient dry bulb temperature, cooling water return temperature, low-level energy storage tank level, pipeline water supply pressure, and status signals from external available heat sources; and a dual-modal intelligent state machine decision-making module: automatically optimizing and switching between wet thermal standby and dry venting modes based on real-time operating conditions. Waste heat coupling closed-loop control module: performs refined heat management in wet standby mode; Fail-safe gravity venting module: implements status control on the normally open vacuum breaking solenoid valve located at the highest point of the outdoor cooling tower coil and the normally open return bypass valve at the outlet of the circulating pump; Transient rapid charging recovery module: upon receiving the unit pre-start signal, immediately closes the venting valve and starts the circulating pump at full speed, using a large flow of water to expel air from the pipes and build up pressure, and monitors the pressure build-up rate in real time; Full life cycle self-diagnosis module: during wet operation, identifies minor leaks by monitoring the abnormal rate of drop in the water tank level; At the moment of low-temperature start-up, the risk of impeller freezing and jamming is identified by comparing the relationship between pump motor current and flow rate. Once an abnormality is detected, the shutdown protection is triggered immediately.

2. The dual-mode anti-freeze cooling system for nuclear power plant air compressors according to claim 1, characterized in that: Multi-source status perception and signal preprocessing module: The module collects outdoor ambient dry bulb temperature, cooling water return temperature, low-level energy storage tank level, pipeline water supply pressure, and status signals of available external heat sources through redundantly configured I / O channels. Available external heat sources include nearby operating units.

3. The dual-mode anti-freeze cooling system for nuclear power plant air compressors according to claim 1, characterized in that: Multi-source state perception and signal preprocessing module: Smooths analog data and removes spike interference through an adaptive moving average filtering algorithm.

4. The dual-mode anti-freeze cooling system for nuclear power plant air compressors according to claim 1, characterized in that: Multi-source state perception and signal preprocessing module: For ambient temperature signals, a trend judgment logic based on time window and a hysteresis comparison mechanism are introduced, and a temperature dead zone of ±1.5℃ is set. The state is only updated when the temperature change exceeds the dead zone.

5. The dual-mode anti-freeze cooling system for nuclear power plant air compressors according to claim 1, characterized in that: The dual-modal intelligent state machine decision module assesses external weather conditions and the availability of internal equipment in real time. When the ambient temperature is higher than the set threshold, it maintains low-power standby. When the ambient temperature is lower than the threshold, it automatically activates the anti-freeze protection logic, prioritizing the check of the availability of external heat sources and the health status of the entire plant's power system to decide whether to use waste heat for low-cost insulation or to perform dry venting to ensure absolute safety.

6. The dual-mode anti-freeze cooling system for nuclear power plant air compressors according to claim 5, characterized in that: Dry exhaust mode Mode drain The triggering criterion is shown in the following formula: （1） For ambient temperature, To prevent freezing, trigger threshold, This is the status bit for the availability of external heat sources; 0 indicates that it is unavailable. This is a major fault signal for the unit. This is a power outage signal for the entire plant.

7. The dual-mode anti-freeze cooling system for air compressors in nuclear power plants according to claim 1, characterized in that: Waste heat coupling closed-loop control module: It uses a cascade PID control algorithm to calculate the deviation between the circulating water temperature and the target set value in real time; it dynamically adjusts the opening of the electric regulating valve on the waste heat introduction pipeline according to the deviation, so as to introduce the external high temperature heat medium into the plate heat exchanger of the unit for heat exchange; at the same time, it instructs the anti-freeze circulating pump of the unit to operate at the minimum maintenance frequency to ensure that the pipeline is in a turbulent heat exchange state; the auxiliary electric heater is started only when the regulating valve is fully open and the water temperature continues to drop.

8. The dual-mode anti-freeze cooling system for air compressors in nuclear power plants according to claim 7, characterized in that: Auxiliary electric heater start / stop control logic S Heater as follows: （2） For the country's water temperature, For the lowest safe temperature, This refers to the opening degree of the waste heat regulating valve.

9. The dual-mode anti-freeze cooling system for air compressors in nuclear power plants according to claim 1, characterized in that: Fail-safe gravity venting module: Once the system determines that it has entered venting mode or a control power loss occurs, the vacuum breaking solenoid valve and the return bypass valve will immediately lose power and open automatically. Atmosphere will then be introduced into the top of the coil to break the siphon effect. Under the action of gravity, the water in the pipe will quickly flow back along the pipe with the designed slope and merge into the indoor low-level energy storage tank. The venting status of the outdoor pipeline is inverted by monitoring the increase in the liquid level of the low-level water tank in real time.

10. The dual-mode antifreeze cooling system for air compressors in nuclear power plants according to claim 9, characterized in that: The empty verification logic is as follows: （3） This represents the volume change corresponding to the rise in the water level in the tank. This refers to the total design volume of outdoor piping and coils. The volume factor is set to 0.

95. If the conditions are not met, the pipeline may be blocked by ice or the air vent valve may fail, immediately triggering the highest level of freeze blockage alarm and locking the unit from starting.

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