A cooling tower intelligent variable frequency energy-saving and water-saving control method and system for a stainless steel hot rolling line

Abstract

This invention discloses an intelligent variable frequency energy-saving and water-saving control method and system for cooling towers in stainless steel hot rolling lines, relating to the field of stainless steel production technology. This intelligent variable frequency energy-saving and water-saving control method for cooling towers in stainless steel hot rolling lines collects the inlet and outlet water temperatures and ambient temperature and humidity of each cooling tower system, dynamically calculates fan speed adjustment commands using an adaptive PID algorithm, and performs load balancing and global optimization scheduling of the three systems (turbid loop, laminar flow cooling, and clean loop) based on a multi-system linkage and coordination strategy. It executes protective actions when temperatures exceed limits or equipment malfunctions. Compared with existing technologies that rely on constant fan speed operation, manual start / stop control, and independent operation of each system, this method achieves on-demand cooling and optimal global energy efficiency, resulting in a comprehensive power saving rate of ≥20%, water temperature fluctuation control within ±0.5℃, and fully automatic unattended operation.

Description

Technical Field

[0001] This invention relates to the field of stainless steel production technology, specifically to an intelligent frequency conversion energy-saving and water-saving control method and system for cooling towers used in stainless steel hot rolling lines. Background Technology

[0002] In the production process, stainless steel hot rolling production lines (such as the 1780 line) require multiple independent cooling tower systems, including a turbid ring cooling system, a laminar flow cooling system, and a clean ring cooling system. These systems are used for cooling the rolling mill equipment, the strip laminar flow cooling, and auxiliary equipment such as the hydraulic station. The above-mentioned cooling tower systems typically use axial flow fans for forced ventilation and heat exchange to reduce the circulating water temperature and ensure the stable operation of the rolling line equipment. Currently, the cooling tower systems in stainless steel hot rolling plants generally adopt the traditional fixed-speed control mode, that is, the fans run at a constant speed of 50Hz, and the water temperature control depends on the operators to manually start and stop the fans based on experience. Moreover, the turbid ring, laminar flow, and clean ring systems operate independently without data exchange or coordinated scheduling between them.

[0003] The existing cooling tower control methods described above have the following shortcomings in practical applications: First, the fan operates at full load at industrial frequency for a long time, maintaining a constant speed regardless of production load or changes in ambient temperature, resulting in serious energy waste, which does not meet the industry's requirements for energy conservation and emission reduction. Secondly, the water temperature relies on manual start-stop control, which has a large response lag and lacks a precise closed-loop regulation mechanism. The water temperature fluctuation range usually reaches ±3℃, which can easily lead to over-cooling or under-cooling, affecting the working stability of the rolling mill, coiling side guide plate and hydraulic station. Third, when the wind turbine is running at high speed, the circulating water inside the tower is easily carried away by the airflow and drifts outside the tower, resulting in a "drifting water" phenomenon, which wastes water resources and increases the cost of replenishing fresh water. Fourth, the three systems of turbid loop, laminar cooling, and clean loop operate independently and cannot be coordinated and scheduled according to the real-time heat load of each system. When the load of a certain system is high, it cannot obtain the support of the surplus cooling capacity of other systems, resulting in low overall energy efficiency and high equipment failure rate. Therefore, there is an urgent need for an intelligent cooling tower control solution that can automatically adjust according to real-time operating conditions, achieve precise temperature control and energy and water conservation, and support the coordinated operation of multiple systems. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an intelligent frequency conversion energy-saving and water-saving control method and system for cooling towers in stainless steel hot rolling lines, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a smart frequency conversion energy-saving and water-saving control method for cooling towers in stainless steel hot rolling lines, wherein the stainless steel hot rolling line comprises three independent cooling tower systems: a turbid ring cooling system, a layer cooling system, and a clean ring cooling system. The method includes the following steps: Step S1: Data collection step, real-time collection of inlet water temperature, outlet water temperature, and ambient temperature and humidity of each cooling tower system; Step S2: Calculation step, based on the difference between the collected outlet water temperature and the preset target water temperature, and the real-time heat load calculated from the inlet water temperature and the outlet water temperature, as the control input quantity; Step S3: Adaptive PID adjustment step, based on the control input, executes an adaptive PID algorithm to dynamically calculate and output the fan speed adjustment command; wherein, the proportional coefficient Kp, integral coefficient Ki, and derivative coefficient Kd of the adaptive PID algorithm are adjusted in real time according to the current magnitude of the difference and / or the rate of change of the difference; Step S4: Variable frequency speed control step, according to the fan speed adjustment command, control the frequency converter to change the operating frequency of the cooling tower fan, thereby steplessly adjusting the cooling air volume; Step S5: Multi-system linkage and coordination step, interconnecting the three independent cooling tower systems through an industrial communication network; based on a preset global optimization strategy and priority rules, coordinating the operation frequency of the fans in the three systems to achieve load sharing; Step S6: Protection Step. When the outlet water temperature of any cooling tower system exceeds the limit or a equipment failure occurs, the preset protection action is executed.

[0006] Preferably, the adaptive PID algorithm in step S3 specifically includes: Obtain the current temperature difference Δe between the outlet water temperature and the target water temperature; The absolute value of the current temperature difference Δe is compared with the preset first temperature difference threshold A and second temperature difference threshold B, where A > B > 0; When |Δe|≥A, it is determined to be a large deviation working condition, and the proportional coefficient Kp is adjusted to the first proportional coefficient Kp1, where Kp1>Kp0 and Kp0 is the basic proportional coefficient; When B is less than |Δe| and less than A, it is determined to be a medium deviation condition, and the proportional coefficient Kp is kept at the basic proportional coefficient Kp0. When |Δe|≤B, it is determined to be a small deviation condition, and the proportional coefficient Kp is adjusted to the second proportional coefficient Kp2, where Kp2 is less than Kp0.

[0007] Preferably, the adaptive PID algorithm in step S3 further includes: Calculate the rate of change of the current temperature difference Δe over time, de / dt, in real time; The absolute value of the rate of change de / dt is compared with a preset rate of change threshold C; When |de / dt|≥C, it is determined to be a rapid temperature change condition. The differential coefficient Kd is adjusted to the first differential coefficient Kd1, where Kd1>Kd0 and Kd0 is the basic differential coefficient. When |de / dt| is less than C, it is determined to be a stable operating condition, and the differential coefficient Kd is adjusted to the second differential coefficient Kd2, where Kd2 is less than Kd0.

[0008] Preferably, the global optimization strategy and priority rules in step S5 further include: The net ring cooling system is set to the highest priority, followed by the turbid ring cooling system, and then the laminar cooling system. When the hot rolling line is detected to be in rolling production, a high-load mode is executed: priority is given to ensuring that the outlet water temperature of the net ring cooling system does not exceed its first target temperature, and partial cooling capacity of the turbid ring and / or laminar cooling system is allowed to be used for auxiliary cooling. When the hot rolling line is detected to be in a waiting or shutdown state for more than a predetermined time, the energy-saving mode is executed: under the premise of ensuring that the outlet water temperature of each system does not exceed its upper limit alarm temperature, the operating frequency of all fans is reduced to the lower limit frequency of energy saving.

[0009] Preferably, the multi-system linkage and coordination step in step S5 specifically includes: The PLC controllers of each cooling tower system share their current outlet water temperature, current operating frequency, and calculated real-time heat load in real time via industrial Ethernet. Based on the shared information and the priority rules, the PLC controller of any system executes the load sharing algorithm: when the heat load of a high-priority system exceeds its rated cooling capacity, it sends a frequency increase request to one or more low-priority systems to temporarily increase the cooling air volume of the low-priority systems in order to share the heat load of the high-priority systems. Once the thermal load of the high-priority system returns to normal, a frequency recovery command is sent to the low-priority system.

[0010] Preferably, in step S4, when controlling the frequency converter to change the operating frequency of the cooling tower fan, the operating frequency is limited to a preset minimum operating frequency fmin and a maximum operating frequency fmax; the minimum operating frequency fmin is a lower limit value set based on the safety operation requirements of the cooling tower fan and the asynchronous motor.

[0011] Preferably, the protection action in step S6 includes: When the outlet water temperature of any cooling tower system exceeds its corresponding first temperature alarm threshold, the fan frequency of the system is controlled to increase stepwise at the first rate until it operates at full frequency or the temperature drops. When the outlet water temperature exceeds its corresponding second temperature alarm threshold, a global audible and visual alarm is triggered, and the system's fan is forced to run at full frequency, wherein the second temperature alarm threshold is greater than the first temperature alarm threshold. When the outlet water temperature is lower than its corresponding low temperature protection threshold, the fan frequency of the control system is gradually reduced to the minimum operating frequency fmin. When a fault is detected in the frequency converter or fan, the power supply to the fan is immediately cut off and a fault alarm signal is issued.

[0012] Preferably, the calculation step in step S2 further includes: Construct a real-time heat load calculation model: Q=C×M×(Tin-Tout), where Q is the real-time heat load, C is the specific heat capacity of water, M is the circulating water flow rate, Tin is the inlet water temperature, and Tout is the outlet water temperature; Construct a global total load calculation model: Qt=Σ(Qi), where Qi is the real-time heat load of the i-th cooling tower system; The coordinated scheduling in step S5 further adjusts the reference operating frequency of each system dynamically based on the ratio of the global total load Qt to the total system load.

[0013] Preferably, in step S4, the frequency converter adopts a stepless speed regulation method, which receives an analog signal from the PLC controller and linearly outputs a power frequency of 0 to 50 Hz according to the signal to drive the cooling tower fan motor.

[0014] This invention also discloses an intelligent variable frequency energy-saving and water-saving control system for cooling towers in stainless steel hot rolling lines, used to execute the intelligent variable frequency energy-saving and water-saving control method for cooling towers in stainless steel hot rolling lines as described in any one of claims 1 to 9, the system comprising: The temperature acquisition unit includes a PT100 temperature sensor and a temperature and humidity sensor installed on the inlet water main pipe, outlet water main pipe and outside the tower body of each cooling tower system, for performing step S1; The intelligent control unit includes a PLC controller, which has a built-in adaptive PID module, a multi-system linkage module and an edge computing module, for executing steps S2, S3, S5 and S6; The variable frequency drive unit includes multiple dedicated low-voltage frequency converters that correspond one-to-one with the cooling tower fan and are power-matched, for performing step S4; The execution unit includes a cooling tower fan configured with a low-drift structure, wherein the low-drift structure includes airfoil-shaped twisted FRP blades, a U-shaped sealing ring, an annular water baffle ring and a central guide cone, and the sealing gap between the fan and the air duct is no more than 1 mm. An industrial communication network connects the intelligent control units of the three cooling tower systems (turbid ring, laminar cooling, and clean ring) to enable data exchange and collaborative command issuance.

[0015] The technical effects and advantages of this invention are as follows: This intelligent variable frequency energy-saving and water-saving control method for cooling towers used in stainless steel hot rolling lines firstly collects the inlet and outlet water temperatures and ambient temperature and humidity of each cooling tower system, dynamically calculates the fan speed adjustment command using an adaptive PID algorithm, and performs load mutual assistance and global optimization scheduling of the three systems (turbid loop, laminar flow cooling, and clean loop) based on a multi-system linkage and coordination strategy. It executes protective actions when the temperature exceeds the limit or equipment malfunctions. Compared with existing technologies that rely on constant fan speed at industrial frequency, manual start / stop control, and independent operation of each system, this method achieves on-demand cooling and optimal global energy efficiency, resulting in a comprehensive power saving rate of ≥20%, water temperature fluctuation control within ±0.5℃, and fully automatic unattended operation.

[0016] Secondly, by using a PLC controller with a built-in adaptive PID module and a cooling tower fan equipped with a low-drift structure, the adaptive PID module adjusts the proportional, integral, and derivative coefficients in real time according to the current temperature difference and the rate of temperature change. This solves the problem that traditional fixed PID cannot adapt to the water temperature overshoot or oscillation caused by the drastic load fluctuations of the hot rolling line. At the same time, the low-drift structure, through the integrated design of airfoil-shaped twisted FRP blades, U-shaped sealing rings, annular water baffles, and a central guide cone, combined with variable frequency low-speed operation, controls the sealing gap between the fan and the air duct to within 1mm, reducing the degree of water droplet dispersion carried by the airflow. Compared with the existing technology where the high-speed operation of the fan causes a drift rate greater than 0.3%, this achieves the technical effect of narrowing the water temperature fluctuation from ±3℃ to ±0.5℃, reducing the drift rate to below 0.1%, and achieving a comprehensive water saving rate of ≥20%.

[0017] Third, this invention interconnects the intelligent control units of the three cooling tower systems (turbid ring, laminar cooling, and clean ring) through an industrial communication network, and incorporates a multi-system linkage and coordination module to execute a load sharing algorithm. When the heat load of a high-priority system exceeds its rated cooling capacity, it sends a frequency increase request to a low-priority system to share the heat load. After returning to normal, it sends a frequency recovery command. At the same time, it automatically switches between high-load mode and energy-saving mode according to the mill's operating status. Compared with the existing technology where the three systems operate independently without coordinated scheduling, this invention achieves dynamic allocation of cross-system cooling capacity and global energy efficiency optimization, thus achieving the technical effects of avoiding equipment overcooling, reducing ineffective energy consumption, and extending the service life of fans and motors. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of the overall method of the present invention; Figure 2 This is a diagram of the overall system architecture of the present invention; Figure 3 This is the adaptive PID logic decision diagram of the present invention; Figure 4 This is a diagram illustrating the multi-system linkage and collaboration strategy of the present invention. Figure 5 This is a logic diagram of the protection steps of the present invention; Figure 6 This is the adaptive PID coefficient tuning logic diagram of the present invention. Detailed Implementation

[0020] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This embodiment discloses an intelligent frequency conversion energy-saving and water-saving control method and system for cooling towers in stainless steel hot rolling lines. The stainless steel hot rolling line specifically includes three independent cooling tower systems: a turbid ring cooling system, a layer cooling system, and a clean ring cooling system. The following description, in conjunction with the appendix... Figure 1 To be continued Figure 6 The specific embodiments of the present invention will be described in detail below.

[0022] The system of this invention mainly includes: a temperature acquisition unit, an intelligent control unit, a frequency conversion drive unit, an execution unit, and an industrial communication network.

[0023] Furthermore, the temperature acquisition unit includes PT100 platinum resistance temperature sensors and temperature and humidity sensors installed on the inlet and outlet water pipes of each cooling tower system and on the outside of the tower body. The PT100 temperature sensor has an accuracy of ±0.1℃ and a sampling frequency of 1Hz. The signal is transmitted to the intelligent control unit through a shielded cable. The inlet water pipe temperature sensor is used to collect the inlet water temperature Tin, the outlet water pipe temperature sensor is used to collect the outlet water temperature Tout, and the temperature and humidity sensor on the outside of the tower body is used to collect the ambient temperature and humidity as a basis for feedforward compensation.

[0024] Furthermore, the intelligent control unit adopts a Siemens S7-1200 series PLC controller or a compatible model. This PLC controller has an adaptive PID module, a multi-system linkage module, and an edge computing module programmed into it. The edge computing module is used to perform real-time heat load calculation: the real-time heat load Q of each cooling tower system is calculated according to the formula Q=C×M×(Tin-Tout), where C is the specific heat capacity of water (can be taken as 4.2×10³J / (kg·℃)), M is the system circulating water flow rate (unit: m³ / h), Tin is the inlet water temperature, and Tout is the outlet water temperature. The intelligent control unit is also used to perform global total load calculation: Qt=Σ(Qi), where Qi is the real-time heat load of the i-th cooling tower system.

[0025] Furthermore, the variable frequency drive unit includes multiple dedicated low-voltage frequency converters that correspond one-to-one with the cooling tower fan and are power-matched. In this embodiment, depending on the fan power, 11kW or 15kW frequency converters are configured. The frequency converter adopts stepless speed regulation. It receives 4-20mA or 0-10V analog signals from the analog output module of the PLC controller and linearly outputs a power frequency of 0 to 50Hz according to the signal to drive the cooling tower fan motor. The frequency converter has built-in protection functions such as overload, overcurrent, overheating, and phase loss.

[0026] Furthermore, the execution unit includes cooling tower fans equipped with a low water drift structure. In this embodiment, a total of 18 cooling tower fans cover three systems: turbid ring, laminar cooling, and clean ring. Specifically disclosed, the low water drift structure includes: airfoil-shaped twisted FRP blades, U-shaped sealing ring, annular water baffle ring, and central guide cone. The sealing gap between the fan and the fan casing is no more than 1mm. This integrated structure design can reduce water mist dispersion when the fan is running at low speed.

[0027] Furthermore, the industrial communication network adopts industrial Ethernet (Profinet / Modbus TCP protocol) to interconnect the intelligent control units of the three cooling tower systems (turbid loop, laminar flow, and clean loop) to achieve real-time sharing of information such as the current outlet water temperature, current operating frequency, and real-time heat load of each system, which is used for collaborative scheduling and command issuance.

[0028] The functional module architecture inside the intelligent control unit includes: a data acquisition module, a load calculation module, an adaptive PID control module, a multi-system linkage and coordination module, a frequency converter output module, and a fault protection module. The modules are connected to each other through an internal data bus.

[0029] Furthermore, the adaptive PID control module has a built-in dynamic parameter tuning algorithm. Unlike traditional fixed PID, this invention adjusts the proportional coefficient Kp, integral coefficient Ki, and derivative coefficient Kd in real time based on the magnitude of the current temperature difference Δe and the rate of change of the temperature difference de / dt. In this embodiment, the specific tuning rules are as follows: (a) Adaptive adjustment of the proportional coefficient Kp: Set the first temperature difference threshold A to 2℃ and the second temperature difference threshold B to 0.5℃.

[0030] When |Δe|≥2℃, it is determined to be a large deviation condition, requiring a rapid response. The proportional coefficient is adjusted to Kp=Kp0×1.5, where Kp0 is the basic proportional coefficient (in this embodiment, Kp0 is 2.0).

[0031] When 0.5℃ is less than |Δe| and less than 2℃, it is determined to be a medium deviation condition, and Kp=Kp0×1.0 is maintained, which is the basic proportional coefficient.

[0032] When |Δe|≤0.5℃, it is judged as a small deviation condition. Overshoot and oscillation need to be suppressed, and the proportional coefficient should be adjusted to Kp=Kp0×0.6.

[0033] (ii) Adaptive adjustment of integral coefficient Ki: To prevent integral saturation during system startup or sudden load changes, Ki is set to 0.

[0034] When the outlet water temperature approaches the set value (i.e., |Δe|≤1℃), the integral action is gradually engaged, Ki=Ki0×(0.4~1.0), where Ki0 is the basic integral coefficient (in this embodiment, Ki0 is 0.5).

[0035] Once the system has been running stably for more than 300 seconds, Ki = Ki0 × 0.7 to maintain a constant temperature and prevent drift.

[0036] (III) Adaptive adjustment of differential coefficient Kd: Set the rate of change threshold C to 1℃ / min.

[0037] When |de / dt|≥1℃ / min, it is determined to be a rapid temperature change condition, and anti-fluctuation measures need to be taken in advance. The differential coefficient is adjusted to Kd=Kd0×1.4, where Kd0 is the basic differential coefficient (Kd0 is 1.0 in this embodiment).

[0038] When |de / dt| is less than 1℃ / min, it is determined to be a stable operating condition. The sensitivity to disturbance is reduced and adjusted to Kd=Kd0×0.7.

[0039] When the ambient temperature and humidity fluctuate significantly, the anti-interference effect can be further enhanced by adjusting Kd=Kd0×1.2.

[0040] As attached Figure 3 As shown, the multi-system linkage and collaboration module has built-in global optimization strategies and priority rules. Specifically, the system priority is set as follows: the net-loop cooling system is the highest, followed by the turbid-loop cooling system, and the laminar cooling system is the lowest. The specific time-based strategies are as follows: Furthermore, the specific method by which the multi-system linkage and coordination module executes the load sharing algorithm is as follows: the PLC controllers of each cooling tower system share their current outlet water temperature, current operating frequency, and calculated real-time heat load in real time through industrial Ethernet. When the heat load of a high-priority system (such as the net loop system) exceeds 80% of its rated cooling capacity, it sends a frequency increase request to the turbid loop system or laminar cooling system to temporarily increase the cooling air volume of the low-priority system in order to help share the heat load of the high-priority system. When the heat load of the high-priority system returns to normal, it sends a frequency recovery command to the low-priority system.

[0041] As attached Figure 4 As shown, in the variable frequency drive unit, the operating frequency of the cooling tower fan is limited to between the preset minimum operating frequency fmin and the maximum operating frequency fmax. It should be particularly emphasized that in this embodiment, the minimum operating frequency fmin is set to 20Hz. This value is a safe operating lower limit obtained by comprehensively measuring the self-heating requirements of the asynchronous motor, the bearing lubrication characteristics, and the mechanical resonance frequency of the cooling tower fan. Long-term operation below 20Hz will lead to insufficient self-heating of the motor (the fan speed decreases as the cooling air volume decreases cubically), the bearing oil film cannot be established, and the operating stability will decrease. 20Hz can ensure that the fan can run continuously at low speed, which not only meets the basic cooling air volume and equipment safety, but also maximizes energy and water saving under low load conditions. The maximum operating frequency fmax is set to 50Hz, which corresponds to the rated frequency of the motor.

[0042] As attached Figure 5 As shown, the fault protection logic flow of this invention is as follows. It should be particularly emphasized that the specific temperature threshold for the protection action is set as follows: Clean loop system: target water temperature 32℃; first temperature alarm threshold (upper limit alarm) is 36℃; second temperature alarm threshold (over-temperature forced) is 38℃; low temperature protection threshold is 28℃.

[0043] Turbidity circulation system: target water temperature 40℃; upper limit alarm threshold 44℃; low temperature protection threshold 36℃.

[0044] Laminar cooling system: target water temperature 38℃; upper limit alarm threshold 42℃; low temperature protection threshold 34℃.

[0045] Furthermore, the specific sequence of protective actions is as follows: When the outlet water temperature exceeds the first temperature alarm threshold, the PLC controls the system's frequency converter to increase the fan frequency at a rate of 2Hz every 30 seconds until it runs at full frequency or the temperature drops.

[0046] When the outlet water temperature exceeds the second temperature alarm threshold, a global audible and visual alarm is triggered, and the system's fan is forced to run at full frequency of 50Hz.

[0047] When the outlet water temperature is lower than the low temperature protection threshold, the PLC controls the inverter of the system to reduce the fan frequency at a rate of 2Hz or 4Hz every 30 seconds until the minimum operating frequency of 20Hz is reached.

[0048] The recovery criterion is: the emergency mode can only be exited when the outlet water temperature returns to within 0.5℃ above or below the target water temperature and remains there for more than 60 seconds.

[0049] When a fault such as inverter overload, overcurrent, phase loss, excessive vibration of fan bearing, or motor overheating is detected, the power supply to the fan should be immediately cut off and a fault alarm signal should be issued.

[0050] The complete workflow of the present invention will be described in detail below with reference to specific embodiments: Example 1: This example uses a stainless steel hot rolling line in its normal daytime rolling production stage as an example, combined with the attached... Figure 1 Appendix Figure 2 Appendix Figure 3 The workflow is explained in detail below: Step S1: Data Acquisition; The temperature acquisition unit acquires the inlet water temperature, outlet water temperature, and ambient temperature and humidity of each cooling tower system in real time. Taking the net loop system as an example, the PT100 sensor in the inlet water main pipe measures Tin=35℃, and the sensor in the outlet water main pipe measures Tout=33.5℃, which exceeds the target water temperature of 32℃. The sampling frequency is 1Hz, and all data are transmitted to the PLC controller through a shielded cable.

[0051] Step S2: Load calculation and deviation calculation; After receiving the data, the intelligent control unit performs real-time heat load calculations using the edge computing module: Q = C × M × (Tin - Tout), assuming the net loop system circulating water flow rate M = 500 m³ / h; Therefore, Q = 4.2 × 10³ × 500 × (35 - 33.5) / 3600 ≈ 875 kW. Simultaneously, calculate the current temperature difference: Δe=Tout-32℃=33.5-32=+1.5℃.

[0052] Step S3: Adaptive PID control; The adaptive PID module obtains Δe = +1.5℃, which is determined to be a medium deviation condition (0.5℃ is less than |Δe| is less than 2℃). Therefore, Kp remains at the base value of 2.0. The temperature difference change rate de / dt is +0.8℃ / min, which is less than the threshold of 1℃ / min. Therefore, Kd is reduced to Kd0 × 0.7 = 0.7. The integral term is gradually added, Ki = Ki0 × 0.6 = 0.3. The PID algorithm outputs the fan speed adjustment command, and it is calculated that the frequency needs to be increased by about 4Hz.

[0053] Step S4: Variable frequency speed control; The PLC sends a 4-20mA analog signal (corresponding to 46Hz) to the corresponding low-voltage frequency converter. The frequency converter outputs a 46Hz power frequency to drive the cooling tower fan, increasing the cooling air volume and causing the outlet water temperature to drop.

[0054] Step S5: Multi-system linkage and collaboration; At the same time, the multi-system linkage module detected through the industrial Ethernet that the outlet water temperature of the laminar cooling system was only 36.5℃ (lower than the target of 38℃), and determined that the laminar cooling system had spare cooling capacity. According to the priority rule (the mill operation signal is ON, and the high load mode is executed), it sent a frequency reduction request to the PLC of the laminar cooling system. The frequency of the laminar cooling system fan was reduced from 42Hz to 35Hz, realizing global energy efficiency optimization.

[0055] Step S6: Protection monitoring; The system continuously monitors the outlet water temperature. When the net loop outlet water temperature drops to 31.8℃, the PID controller starts to adjust in reverse, gradually reducing the frequency, and eventually stabilizing within the range of 32℃±0.3℃. The protection module is not triggered.

[0056] Example 2: This example uses a stainless steel hot rolling line entering a nighttime shutdown or waiting-to-roll state as an example to illustrate the workflow under energy-saving mode in detail as follows: Triggering conditions: The PLC detects that the mill operation signal has been continuously OFF for more than 30 minutes, and the outlet water temperature of each system has been running stably within 1°C above or below the target value for more than 10 minutes.

[0057] Perform the following actions: Priority switching: The system automatically switches from "rolling production mode" to "energy saving priority mode", and the multi-system linkage module adjusts the global optimization goal from "ensuring net cooling" to "lowest global energy consumption".

[0058] Frequency reduction: The PLC controller executes a unified frequency reduction command, and the frequency of the fan in the clean air system is gradually reduced from the original average of 42Hz to 25Hz; the frequency of the turbid air system is reduced from 40Hz to 22Hz; and the frequency of the laminar cooling system is reduced from 38Hz to 20Hz (minimum operating frequency fmin).

[0059] Effect verification: Under this operating condition, the fan power decreases cubically with the speed. Taking the net ring system as an example, the speed decreases by about 40%, and the theoretical power decreases to (0.6)³=21.6% of the original, that is, the power saving rate is about 78.4%. The water drift rate decreases from the conventional 0.3% to below 0.1% due to the low wind speed, which shows the water saving effect.

[0060] Low temperature protection: If the outlet water temperature of any system drops below the low temperature protection threshold (net ambient temperature less than 28℃) due to low ambient temperature (such as at night in winter), the PLC will automatically perform frequency reduction protection action until the minimum operating frequency of 20Hz is reached to ensure that the equipment is not damaged due to excessive cooling.

[0061] Recovery mechanism: When the mill operation signal turns ON again, the system recognizes the signal change within 1 second, automatically exits the energy-saving mode, and gradually restores the frequency allocation strategy to the high-load mode.

[0062] Example 3: This example uses the abnormal rise in the outlet water temperature of the clean circulation system caused by high summer temperatures and continuous full-load production on the rolling mill as an example to illustrate the emergency protection process in detail as follows: Triggering condition: The outlet water temperature of the clean loop system continues to rise, exceeding the first alarm threshold of 36℃, and continues to rise to the second alarm threshold of 38℃.

[0063] Action sequence: Phase 1 (T > 36℃): The PLC controller sends a warning signal to the central control room. At the same time, the adaptive PID module enters the large deviation mode (|Δe| ≥ 2℃), Kp is increased to 1.5 times the base value, and the frequency converter is adjusted with the fastest response speed. The frequency converter increases by 2Hz every 30 seconds.

[0064] Phase 2 (T > 38℃): Trigger a global audible and visual alarm, execute the high-temperature emergency plan with the multi-system linkage module, ignore priority energy-saving strategies, and send a "full frequency" forced command to the turbid circulation and laminar cooling systems. All 18 cooling tower fans in the three systems will run at full frequency of 50Hz to achieve maximum cooling capacity output.

[0065] Load sharing: During full-frequency operation, if the outlet water temperature of the turbid circulation system is still within a controllable range (e.g., 42℃), while the net circulation temperature remains high, the multi-system linkage module can further adjust the cooling tower water distribution valve or request the water treatment system to increase the net circulation water flow rate to achieve cross-system resource allocation.

[0066] Recovery Criteria: The PLC continuously monitors the outlet water temperature of the clean loop system. When the temperature drops to within the range of 31.5℃ to 32.5℃ and remains there for more than 60 seconds, the danger is deemed to be over, the system automatically exits the emergency mode, the fan frequency gradually decreases according to the PID adjustment result, and the alarm signal is cleared.

[0067] Fault redundancy: If a frequency converter or fan fails during an emergency, the fault protection module immediately cuts off the power supply to the faulty equipment and reports the fault information to the central control room. The remaining normally operating fans are redistributed their load by the multi-system linkage module to ensure that critical equipment (clean-loop system) always has air-cooled supply.

[0068] The above detailed embodiments, in conjunction with examples, illustrate the technical solution of the present invention. It should be emphasized that the specific values ​​of the first temperature difference threshold A, the second temperature difference threshold B, the rate of change threshold C, the minimum operating frequency fmin, and various temperature alarm thresholds are all preferred solutions in this embodiment. Those skilled in the art can make reasonable adjustments according to actual equipment parameters and operating conditions, which does not depart from the protection scope of the present invention. The core of the present invention lies in the organic integration of adaptive PID dynamic temperature control algorithm, variable frequency speed regulation technology, and multi-system linkage and coordination strategy to form an intelligent, precise, and energy-saving control method and system for cooling towers of stainless steel hot rolling lines.

[0069] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for intelligent frequency conversion energy-saving and water-saving control of cooling towers for stainless steel hot rolling lines, characterized in that, The stainless steel hot rolling line comprises three independent cooling tower systems: a turbid ring cooling system, a laminar cooling system, and a net ring cooling system. The method includes the following steps: Step S1: Data collection step, real-time collection of inlet water temperature, outlet water temperature, and ambient temperature and humidity of each cooling tower system; Step S2: Calculation step, based on the difference between the collected outlet water temperature and the preset target water temperature, and the real-time heat load calculated from the inlet water temperature and the outlet water temperature, as the control input quantity; Step S3: Adaptive PID adjustment step, based on the control input, executes an adaptive PID algorithm to dynamically calculate and output the fan speed adjustment command; wherein, the proportional coefficient Kp, integral coefficient Ki, and derivative coefficient Kd of the adaptive PID algorithm are adjusted in real time according to the current magnitude of the difference and / or the rate of change of the difference; Step S4: Variable frequency speed control step, according to the fan speed adjustment command, control the frequency converter to change the operating frequency of the cooling tower fan, thereby steplessly adjusting the cooling air volume; Step S5: Multi-system linkage and coordination step, interconnecting the three independent cooling tower systems through an industrial communication network; based on a preset global optimization strategy and priority rules, coordinating the operation frequency of the fans in the three systems to achieve load sharing; Step S6: Protection Step. When the outlet water temperature of any cooling tower system exceeds the limit or a equipment failure occurs, the preset protection action is executed.

2. The intelligent frequency conversion energy-saving and water-saving control method for a cooling tower used in a stainless steel hot rolling line according to claim 1, characterized in that, The adaptive PID algorithm in step S3 specifically includes: Obtain the current temperature difference Δe between the outlet water temperature and the target water temperature; The absolute value of the current temperature difference Δe is compared with the preset first temperature difference threshold A and second temperature difference threshold B, where A > B > 0; When |Δe|≥A, it is determined to be a large deviation working condition, and the proportional coefficient Kp is adjusted to the first proportional coefficient Kp1, where Kp1>Kp0 and Kp0 is the basic proportional coefficient; When B is less than |Δe| and less than A, it is determined to be a medium deviation condition, and the proportional coefficient Kp is kept at the basic proportional coefficient Kp0. When |Δe|≤B, it is determined to be a small deviation condition, and the proportional coefficient Kp is adjusted to the second proportional coefficient Kp2, where Kp2 is less than Kp0.

3. The intelligent frequency conversion energy-saving and water-saving control method for a cooling tower in a stainless steel hot rolling line according to claim 2, characterized in that, The adaptive PID algorithm in step S3 further includes: Calculate the rate of change of the current temperature difference Δe over time, de / dt, in real time; The absolute value of the rate of change de / dt is compared with a preset rate of change threshold C; When |de / dt|≥C, it is determined to be a rapid temperature change condition. The differential coefficient Kd is adjusted to the first differential coefficient Kd1, where Kd1>Kd0 and Kd0 is the basic differential coefficient. When |de / dt| is less than C, it is determined to be a stable operating condition, and the differential coefficient Kd is adjusted to the second differential coefficient Kd2, where Kd2 is less than Kd0.

4. The intelligent frequency conversion energy-saving and water-saving control method for a cooling tower used in a stainless steel hot rolling line according to claim 1, characterized in that, The global optimization strategy and priority rules in step S5 further include: The net ring cooling system is set to the highest priority, followed by the turbid ring cooling system, and then the laminar cooling system. When the hot rolling line is detected to be in rolling production, a high-load mode is executed: priority is given to ensuring that the outlet water temperature of the net ring cooling system does not exceed its first target temperature, and partial cooling capacity of the turbid ring and / or laminar cooling system is allowed to be used for auxiliary cooling. When the hot rolling line is detected to be in a waiting or shutdown state for more than a predetermined time, the energy-saving mode is executed: under the premise of ensuring that the outlet water temperature of each system does not exceed its upper limit alarm temperature, the operating frequency of all fans is reduced to the lower limit frequency of energy saving.

5. The intelligent frequency conversion energy-saving and water-saving control method for a cooling tower used in a stainless steel hot rolling line according to claim 4, characterized in that, The multi-system linkage and coordination steps in step S5 specifically include: The PLC controllers of each cooling tower system share their current outlet water temperature, current operating frequency, and calculated real-time heat load in real time via industrial Ethernet. Based on the shared information and the priority rules, the PLC controller of any system executes the load sharing algorithm: when the heat load of a high-priority system exceeds its rated cooling capacity, it sends a frequency increase request to one or more low-priority systems to temporarily increase the cooling air volume of the low-priority systems in order to share the heat load of the high-priority systems. Once the thermal load of the high-priority system returns to normal, a frequency recovery command is sent to the low-priority system.

6. The intelligent frequency conversion energy-saving and water-saving control method for a cooling tower in a stainless steel hot rolling line according to claim 1, characterized in that, In step S4, when the frequency converter is controlled to change the operating frequency of the cooling tower fan, the operating frequency is limited to a preset minimum operating frequency fmin and a maximum operating frequency fmax; the minimum operating frequency fmin is a lower limit value set based on the safety operation requirements of the cooling tower fan and the asynchronous motor.

7. The intelligent frequency conversion energy-saving and water-saving control method for a cooling tower used in a stainless steel hot rolling line according to claim 1, characterized in that, The protective actions in step S6 include: When the outlet water temperature of any cooling tower system exceeds its corresponding first temperature alarm threshold, the fan frequency of the system is controlled to increase stepwise at the first rate until it operates at full frequency or the temperature drops. When the outlet water temperature exceeds its corresponding second temperature alarm threshold, a global audible and visual alarm is triggered, and the system's fan is forced to run at full frequency, wherein the second temperature alarm threshold is greater than the first temperature alarm threshold. When the outlet water temperature is lower than its corresponding low temperature protection threshold, the fan frequency of the control system is gradually reduced to the minimum operating frequency fmin. When a fault is detected in the frequency converter or fan, the power supply to the fan is immediately cut off and a fault alarm signal is issued.

8. The intelligent frequency conversion energy-saving and water-saving control method for a cooling tower in a stainless steel hot rolling line according to claim 1, characterized in that, The calculation steps in step S2 further include: Construct a real-time heat load calculation model: Q=C×M×(Tin-Tout), where Q is the real-time heat load, C is the specific heat capacity of water, M is the circulating water flow rate, Tin is the inlet water temperature, and Tout is the outlet water temperature; Construct a global total load calculation model: Qt=Σ(Qi), where Qi is the real-time heat load of the i-th cooling tower system; The coordinated scheduling in step S5 further adjusts the reference operating frequency of each system dynamically based on the ratio of the global total load Qt to the total system load.

9. The intelligent frequency conversion energy-saving and water-saving control method for a cooling tower used in a stainless steel hot rolling line according to claim 1, characterized in that, In step S4, the frequency converter adopts a stepless speed regulation method. It receives analog signals from the PLC controller and linearly outputs a power frequency of 0 to 50 Hz according to the signal to drive the cooling tower fan motor.

10. A smart frequency conversion energy-saving and water-saving control system for cooling towers in stainless steel hot rolling lines, characterized in that, A smart frequency conversion energy-saving and water-saving control method for a cooling tower in a stainless steel hot rolling line, as described in any one of claims 1 to 9, wherein the system comprises: The temperature acquisition unit includes a PT100 temperature sensor and a temperature and humidity sensor installed on the inlet water main pipe, outlet water main pipe and outside the tower body of each cooling tower system, for performing step S1; The intelligent control unit includes a PLC controller, which has a built-in adaptive PID module, a multi-system linkage module and an edge computing module, for executing steps S2, S3, S5 and S6; The variable frequency drive unit includes multiple dedicated low-voltage frequency converters that correspond one-to-one with the cooling tower fan and are power-matched, for performing step S4; The execution unit includes a cooling tower fan configured with a low-drift structure, wherein the low-drift structure includes airfoil-shaped twisted FRP blades, a U-shaped sealing ring, an annular water baffle ring and a central guide cone, and the sealing gap between the fan and the air duct is no more than 1 mm. An industrial communication network connects the intelligent control units of the three cooling tower systems (turbid ring, laminar cooling, and clean ring) to enable data exchange and collaborative command issuance.

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