Automatic control method for combustion-supporting air supply system of annealing furnace

Abstract

The invention belongs to the technical field of electric power metallurgy automatic control, and provides an annealing furnace combustion-supporting air supply system automatic control method which comprises the steps that a temperature detection element is arranged on an outlet pipeline of a combustion-supporting fan, the temperature of combustion-supporting air is detected in real time, and the optimal rotation speed of the combustion-supporting fan is automatically matched through piecewise linear control according to different combustion-supporting air temperatures on site. On the basis of the optimal rotating speed of the combustion-supporting fan, feedforward control is matched with a PID feedback control algorithm to control the opening degree of an outlet blow-off valve of the combustion-supporting fan so as to adjust the actual combustion-supporting air pressure value; according to the method, a combustion-supporting air temperature detection loop and a piecewise linear control module are added, and automatic matching and giving of the optimal fan rotating speed are achieved. The opening control mode of the blow-off valve is optimized, feed-forward control and PID control are combined, and the pressure stability is improved.

Description

Technical Field

[0001] This invention belongs to the field of power metallurgical automation control technology, and relates to the control of the combustion air supply system of the combustion system of an annealing furnace, specifically an automatic control method for the combustion air supply system of an annealing furnace. Background Technology

[0002] The combustion system of the annealing furnace is the core process system for achieving hot stretching and smoothing. It mainly consists of a gas supply system, a combustion air supply system, a burner system, and a flue gas system. The stable operation of these four systems is crucial to ensuring the stability, safety, and efficiency of the entire annealing furnace combustion system. The original control method of the combustion air supply system was as follows: the fan operated at a fixed speed, and the setpoint of the combustion air pressure was determined by the factory-calibrated pressure of the burner, which was a fixed value. The actual pressure of the combustion air was dynamically controlled by adjusting the opening of the fan outlet vent valve through PID control.

[0003] In actual production, the large temperature difference between day and night in the factory leads to drastic changes in air density, causing significant fluctuations in the actual load on the fan and the combustion air pressure. As the ambient temperature rises and air density decreases, the fan load decreases and the combustion air pressure drops even with a constant fan speed. This results in a smaller fan outlet vent valve opening, and in severe cases, the vent valve opening becomes zero, causing a sharp decrease in airflow. This leads to an excessive pressure difference between the fan inlet and outlet, causing fan surge, which further results in insufficient combustion air pressure. Surge can easily damage the fan, and insufficient combustion air pressure causes the burner's air-fuel ratio to deviate from the optimal combustion state, leading to substandard flue gas emissions and safety risks. Furthermore, when the burner's combustion power changes significantly, the PID control of the valve opening exhibits lag, resulting in large fluctuations in air pressure. To overcome these problems, a manual fan speed control method was adopted. While simple, this method requires frequent manual adjustments based on on-site conditions, demanding high personnel skill and having poor reliability. Summary of the Invention

[0004] This invention proposes an automatic control method for the combustion air supply system of an annealing furnace. Based on different combustion air temperatures on site, segmented linear control is used to automatically match the optimal combustion air fan speed, avoiding combustion air pressure fluctuations, fan surge, and fan overload tripping. The burner combustion power is used as feedforward control and combined with pressure PID regulation to control valve opening, thereby improving air pressure stability.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows: An automatic control method for an annealing furnace combustion air supply system includes the following steps: S1. Install a temperature detection element in the outlet pipe of the combustion fan to detect the temperature of the combustion air in real time and connect the signal to the PLC control system. S2. Divide the temperature range, match the optimal fan speed for different combustion air temperature ranges, establish the piecewise linear relationship between combustion air temperature and the fan frequency converter, and establish a piecewise linear control function block in the PLC control system to control the fan frequency converter. S3. Based on automatically matching the optimal combustion fan speed, the PLC control system adjusts the actual combustion air pressure value PV to approximate the set value SV of the combustion air pressure by controlling the opening of the vent valve at the outlet of the combustion fan; the opening adjustment model of the vent valve adopts feedforward control combined with PID feedback control algorithm.

[0006] Furthermore, the feedforward control combined with the PID feedback control algorithm includes: Formula 1: PWz = PD1*S1 + PD2*S2 + ... + PDx*Sx; PDx is the rated power of a single burner, S1 is the total number of burners with that power, and PWz is the rated power of all burners. Formula 2: PWs = PD1 * D1 + PD2 * D2 + ... + PDx * Dx; PDx is the rated power of a single burner, Dx is the number of burners that can be ignited at that power, and PWs is the actual operating power of the ignited burners. Formula 3: P = (1 - (PWs / PWz)) * 100; PWs / PWz represents the percentage of burner power used, and P represents the percentage of burner power not used, expressed as a percentage (%). Equation 4: Ps = P * k; k is the proportional coefficient, which is adjusted according to the actual regulation situation and is used to change the influence of the feedforward control. Its value range is 0-1; Ps is the output value of the feedforward control. Equation 5: PCV = LMN + Ps; LMN is the output value of the PID control module, derived from the pressure setpoint and pressure feedback value. PCV is the opening value sent to the vent valve by the PLC control system.

[0007] Furthermore, methods for matching the optimal fan speed to different combustion air temperature ranges include: First, collect historical data on the actual temperature of the combustion air, the manually set speed of the combustion air blower, the pressure of the combustion air, the opening value of the blower outlet vent valve, and the actual current value of the blower. Then, based on historical data, multiple temperature ranges are divided, and the corresponding optimal fan speed is matched for each temperature range.

[0008] The beneficial effects of this invention are: The method of this invention effectively avoids the phenomenon of fan surge and insufficient combustion air pressure under high temperature conditions in summer by real-time detection of combustion air temperature and automatic optimal matching between it and fan speed. This not only improves the operating conditions of the fan, but also ensures the stability and safety of the combustion system and ensures that the flue gas emissions of the annealing furnace meet the standards. At the same time, it also effectively avoids fan overload tripping under low temperature conditions in winter, ensuring the safe and stable operation of the continuous unit and reducing fan energy consumption. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the automatic control system of the method of the present invention; Figure 2 This is a schematic diagram illustrating the segmented linear correspondence between the combustion air temperature and the fan speed percentage in this invention; Figure 3 This is a flowchart illustrating the automatic control application of the combustion air supply system in this invention. Detailed Implementation

[0010] The present invention will be further described below with reference to embodiments and accompanying drawings: Example

[0011] The present invention will be specifically described using the combustion air supply system of the company's hot stretching and leveling unit as an example.

[0012] Automatic control method for the combustion air supply system of annealing furnace, such as Figure 1 As shown, it includes: S1. Install a PT100 thermal resistor as a temperature detection element TE in the outlet pipeline of the combustion fan to detect the temperature of the combustion air at the outlet of the fan M in real time, and connect the temperature signal to the PLC control system. S2. Divide the temperature range, match the optimal fan speed for different combustion air temperature ranges, establish the piecewise linear relationship between combustion air temperature and the fan frequency converter, and establish a piecewise linear control function block in the PLC control system to control the fan frequency converter. Methods for matching the optimal fan speed to different combustion air temperature ranges include: First, collect 24 months of historical data on five types of variables: actual combustion air temperature, manually set combustion air speed, combustion air pressure, fan outlet vent valve opening, and actual fan current. Then, by statistically analyzing the long-term trend data of the actual combustion air temperature, combustion air pressure, fan outlet vent valve opening, and actual fan current corresponding to the manually set percentage of combustion air fan speed in the PLC control system, the optimal fan speed percentage corresponding to different combustion air temperatures was selected, thus obtaining... Figure 2 The figure shows a piecewise linear relationship between the optimal combustion air temperature and the percentage of fan speed.

[0013] The piecewise linear control function block takes the combustion air temperature value as its input IN, and processes it through a piecewise linear correspondence as follows: Figure 2 As shown, the optimal fan speed value is automatically matched as the output OUT, which is given to the combustion fan frequency converter as the set value SV of the fan speed. S3. Based on automatically matching the optimal combustion fan speed SV, the PLC control system adjusts the actual combustion air pressure value PV detected by PT to approximate the set value SV by controlling the opening degree PCV of the combustion fan outlet vent valve; the vent valve opening adjustment model adopts feedforward control combined with PID feedback control algorithm.

[0014] Feedforward control combined with PID feedback control algorithm includes: Formula 1: PWz = PD1*S1 + PD2*S2 + ... + PDx*Sx; PDx is the rated power of a single burner, S1 is the total number of burners with that power, and PWz is the rated power of all burners. Formula 2: PWs = PD1 * D1 + PD2 * D2 + ... + PDx * Dx; PDx is the rated power of a single burner, Dx is the number of burners that can be ignited at that power, and PWs is the actual operating power of the ignited burners. Formula 3: P = (1 - (PWs / PWz)) * 100; PWs / PWz represents the percentage of burner power used, and P represents the percentage of burner power not used, expressed as a percentage (%). Equation 4: Ps = P * k; k is the proportional coefficient, which is adjusted according to the actual regulation situation and is used to change the influence of the feedforward control. Its value range is 0-1; Ps is the output value of the feedforward control. Equation 5: PCV = LMN + Ps; LMN is the output value of the PID control module, derived from the pressure setpoint and pressure feedback value. PCV is the opening value sent to the vent valve by the PLC control system.

[0015] From the start-up of the combustion system to the shutdown of the combustion air pressure control system, the entire control system application process is as follows: Figure 3 As shown.

[0016] This invention utilizes a piecewise linear control function block and a venting valve opening adjustment model to automatically match different fan speeds to varying combustion air temperatures. This avoids fan overload tripping at low temperatures, ensuring safe, stable, and low-energy operation of the continuous unit. Simultaneously, it effectively prevents fan surge and insufficient combustion air pressure at high temperatures, improving fan operating conditions, enhancing the stability of the air-fuel ratio in the combustion system, and further meeting the environmental requirements for low emissions in the combustion system. This invention reduces abnormal downtime by 15 hours annually, generating a benefit of 565,000 yuan and increasing production by 195 tons.

Claims

1. An automatic control method for an annealing furnace combustion air supply system, characterized in that: Includes the following steps: S1. Install a temperature detection element in the outlet pipe of the combustion fan to detect the temperature of the combustion air in real time and connect the signal to the PLC control system. S2. Divide the temperature range, match the optimal fan speed for different combustion air temperature ranges, establish the piecewise linear relationship between combustion air temperature and the fan frequency converter, and establish a piecewise linear control function block in the PLC control system to control the fan frequency converter. S3. Based on automatically matching the optimal combustion fan speed, the PLC control system adjusts the actual combustion air pressure value PV to approximate the set value SV of the combustion air pressure by controlling the opening of the vent valve at the outlet of the combustion fan; the opening adjustment model of the vent valve adopts feedforward control combined with PID feedback control algorithm.

2. The automatic control method for the combustion air supply system of an annealing furnace according to claim 1, characterized in that: This includes feedforward control combined with PID feedback control algorithms, including: Formula 1: PWz = PD1*S1 + PD2*S2 + ... + PDx*Sx; PDx is the rated power of a single burner, S1 is the total number of burners with that power, and PWz is the rated power of all burners. Formula 2: PWs = PD1 * D1 + PD2 * D2 + ... + PDx * Dx; PDx is the rated power of a single burner, Dx is the number of burners that can be ignited at that power, and PWs is the actual operating power of the ignited burners. Formula 3: P = (1 - (PWs / PWz)) * 100; PWs / PWz represents the percentage of burner power used, and P represents the percentage of burner power not used, expressed as a percentage (%). Equation 4: Ps = P * k; k is the proportional coefficient, which is adjusted according to the actual regulation situation and is used to change the influence of the feedforward control. Its value range is 0-1; Ps is the output value of the feedforward control. Equation 5: PCV = LMN + Ps; LMN is the output value of the PID control module, derived from the pressure setpoint and pressure feedback value. PCV is the opening value sent to the vent valve by the PLC control system.

3. The automatic control method for the combustion air supply system of an annealing furnace according to claim 1, characterized in that: The method for matching the optimal fan speed to different combustion air temperature ranges includes: First, collect historical data on the actual temperature of the combustion air, the manually set speed of the combustion air blower, the pressure of the combustion air, the opening value of the blower outlet vent valve, and the actual current value of the blower. Then, based on historical data, multiple temperature ranges are divided, and the corresponding optimal fan speed is matched for each temperature range.

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