Aod furnace waste heat recovery flue gas temperature self-adaptive control method

Abstract

This invention belongs to the field of automatic control technology for waste heat recovery in industrial furnaces and kilns, and relates to an adaptive control method for flue gas temperature in AOD furnace waste heat recovery. The method includes: collecting flue gas temperature monitoring data and calculating the temperature deviation term and the first-order backward differential change term; comparing the algebraic polarity of the temperature deviation term and the first-order backward differential change term, reducing the proportional gain coefficient and integral gain coefficient when the polarities are opposite, and calculating the control increment; resetting the internal value of the integral accumulator to zero during a large thermal shock, and restoring it after the shock subsides; and correcting the valve opening control by superimposing the reverse idle compensation value of the mechanism during commutation. This invention overcomes the feedback delay caused by temperature sensing time lag, avoids integral saturation under large thermal shocks, eliminates low-frequency oscillations caused by the dead zone of the regulating valve commutation, and improves the dynamic tracking accuracy of general control systems.

Description

Technical Field

[0001] This invention belongs to the field of automatic control technology for waste heat recovery in industrial furnaces and kilns, and relates to an adaptive control method for flue gas temperature in AOD furnace waste heat recovery. Background Technology

[0002] Currently, utilizing industrial furnaces for high-temperature smelting or heating production while simultaneously recovering waste heat from flue gas has become a core approach for energy conservation and emission reduction in modern industry. However, existing technologies still have significant limitations in handling multivariate coupling impacts, control loop timing delays, and physical constraints during highly dynamic combustion processes.

[0003] First, there is the PID control technology for flue gas based on flow dead zone locking. For example, Chinese invention patent application publication number CN122041592A discloses a PID control method for automatic flue gas control of heating furnaces. By setting the target flue gas temperature and flow rate data, the opening of the flue gas regulating valve and the power of the induced draft fan are adjusted by calculating the deviation, and a flow dead zone limit is introduced to lock the valve output. Its drawback is that when the actual temperature is lower than the set temperature trigger limit, the rigid dead zone command is used to lock the current flow valve output value. The control logic lacks the dynamic adaptability to continuous fine-tuning of multiple variables. Moreover, its furnace pressure interlock control has a fixed 5-second automatic adjustment frequency converter time delay when the feedback pressure exceeds the set value, which easily causes drastic changes in furnace pressure and instantaneous control failure during the high dynamic combustion transition stage.

[0004] Second, there is the anti-integral saturation control technology based on fixed timing switching. For example, Chinese invention patent authorization announcement number CN109856958B discloses a control method to prevent integral saturation. It adds auxiliary override logic to the classic PID closed-loop control. When the actuator command reaches the limit value, it forcibly tracks the high / low limit value and switches back to the original adjustment mode after a set time and cyclically judges. Its drawback is that this technology relies on a fixed first set time of 2 seconds for tracking and a third set time of 15 seconds for restoring normal adjustment. This strategy is mainly suitable for large inertia and smooth processes such as thermal power plants. It fails to adaptively correlate the rigid parameter switching on the time axis with the high-frequency pulsating control response. When facing loops with rapidly changing heat loads and violent instantaneous pressure surges, the rigid waiting timing is very likely to miss the optimal adjustment window, causing the controller to frequently experience secondary saturation or even triggering large-scale system resonance.

[0005] Third, physical flue gas recovery technology based on multi-stage heat exchange and heat storage; for example, Chinese invention patent authorization announcement number CN111595166B discloses an efficient waste heat recovery system for AOD furnace flue gas. By sequentially connecting a dust removal device and a heat storage furnace body with multiple built-in heat storage sections in the flue gas recovery pipeline, the intermittent flue gas temperature fluctuations are physically smoothed out by switching the path of the valve pipeline. Its shortcomings are: this scheme focuses on using multi-stage heat storage bricks and mechanical valve switching for passive physical heat capacity buffering, lacking a refined fully automated dynamic decoupling control strategy, and cannot actively and in real time map the induced draft fan power, the opening degree of the frequency conversion regulating baffle and the explosive instantaneous surge pressure at the furnace mouth in a closed loop. The lag in the action of the mechanical valve channel makes it difficult to fundamentally eliminate the drastic jump in furnace pressure under extreme disturbances of multiple variables.

[0006] Therefore, how to construct a control architecture with high dynamic multivariable adaptive sensing capability, so that efficient recovery of flue gas waste heat and flexible continuous anti-saturation furnace pressure regulation converge to the true physical safety boundary throughout the entire process cycle, is the technical problem to be solved by this invention. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and solve the technical problems that the prior art is prone to causing drastic changes in furnace pressure, integral saturation of the controller and low-frequency oscillation when dealing with multivariable coupling impact, control loop timing delay and physical constraints in high dynamic combustion processes. The invention provides an adaptive control method for flue gas temperature in AOD furnace waste heat recovery.

[0008] To achieve the above-mentioned objective, the present invention provides an adaptive temperature control method for waste heat recovery flue gas in an AOD furnace, comprising the following steps:

[0009] Step S1: Collect flue gas temperature data and calculate the deviation and first-order backward difference term: Collect flue gas temperature monitoring data in the waste heat recovery channel of AOD furnace, and calculate the flue gas temperature deviation term and first-order backward difference change term for the current control cycle. Step S2, reduce the gain coefficient and calculate the control increment when the polarities are opposite: compare the algebraic polarity of the flue gas temperature deviation term and the first-order backward differential change term; when the algebraic polarity of the flue gas temperature deviation term and the first-order backward differential change term is opposite, reduce the proportional gain coefficient and integral gain coefficient corresponding to the velocity-type discrete control algorithm, and calculate the valve opening control increment based on the reduced proportional gain coefficient and integral gain coefficient. Step S3: Reset the integral gain to zero when the limit is exceeded, and restore it after the safety condition is met: When the absolute value of the flue gas temperature deviation term is greater than the temperature deviation control limit, and the first-order backward differential change term continuously exceeds the temperature change rate threshold, the integral gain coefficient is reset to zero to cut off the integral accumulation effect of the velocity-type discrete control algorithm; after the flue gas temperature monitoring data falls back to the safe control range, the integral gain coefficient is restored. Step S4, superimpose the backlash compensation value and send a drive signal when reversing: retrieve the pre-stored mechanism backlash compensation value in the memory, compare the valve opening control increment with the direction of the electronic control adjustment command of the previous control cycle; when the valve opening control increment is opposite to the direction of the electronic control adjustment command, superimpose the mechanism backlash compensation value into the valve opening control increment and send a drive control signal for the air valve mechanism.

[0010] Step S2 of the present invention includes the following sub-steps: Step S21, when the algebraic polarity is opposite, multiply the reference coefficients stored in the reference parameter library step by step by a physical attenuation factor less than 1, and reduce the proportional gain coefficient and integral gain coefficient of the current cycle online; Step S22, import the reduced proportional gain coefficient and integral gain coefficient into the velocity-type discrete control algorithm, and combine them with the flue gas temperature deviation term of the current control cycle to complete the calculation of the valve opening control increment.

[0011] Step S3 of the present invention includes the following sub-steps: Step S31, continuously read the first-order backward differential change term for 3 control cycles. When the absolute value of the first-order backward differential change term in each control cycle is greater than the temperature change rate threshold, and the absolute value of the flue gas temperature deviation term in the current control cycle is greater than the temperature deviation control limit, it is determined that a sudden thermal load shock has occurred in the controlled process; Step S32, write a zero value to the integral accumulator register in the velocity-type discrete control algorithm to suspend the integral regulation action, so that the regulation loop switches to the proportional-derivative control state.

[0012] Step S3 of the present invention further includes the following sub-steps: Step S33, after the value inside the integral accumulator register is reset to zero, the flue gas temperature monitoring data is continuously compared with the target temperature; Step S34, when the absolute value of the flue gas temperature deviation term is maintained within the temperature deviation control limit for 5 consecutive control cycles, it is determined that the controlled process has entered the safe control range, and the control weight of the integral gain coefficient in the velocity-type discrete control algorithm is gradually restored by a progressively increasing method.

[0013] Step S4 of the present invention includes the following sub-steps: Step S41, read the sign of the valve opening control increment calculated in the current control cycle, and retrieve the actual action symbol of the previous control cycle; Step S42, compare the current sign with the actual action symbol, and when the two are opposite, determine that the mechanical transmission direction of the air valve mechanism has changed, and directly add the mechanism reverse idle compensation value to the valve opening control increment to correct the air valve mechanism drive control signal.

[0014] In step S2 of the present invention, the operation of reducing the integral gain coefficient and the proportional gain coefficient is achieved by modifying the gain setting value in the hardware register by the control chip, so as to limit the number of commutations of the wind valve mechanism drive control signal near the steady-state equilibrium point.

[0015] The present invention includes the following long-term monitoring steps: Step S5, accumulate the number of times the integral gain coefficient is reset to zero within the smelting cycle, calculate the statistical variance of the flue gas temperature deviation term, and calculate the degradation index characterizing the wear state of the transmission connecting rod idle stroke; Step S6, when the value of the degradation index is greater than the preset wear threshold, reduce the temperature deviation control limit in step S3, and issue a high-risk over-temperature alarm signal for the heat exchange bag.

[0016] The sampling period of the controlled process described in this invention is 1s to 3s; in step S3, the temperature deviation control limit is 3% to 5% of the target temperature; in step S4, the mechanism reverse idle compensation value accounts for 0.5% to 1.5% of the preset adjustment opening stroke.

[0017] In step S4 of the present invention, sending the air valve mechanism drive control signal includes: distributing the air valve mechanism drive control signal to the speed regulation drive interface of the variable frequency fan, adjusting the speed of the variable frequency fan within a loop response time of 0.5s to 1.5s, and suppressing the large-scale thermal deviation disturbance of the flue gas temperature monitoring data caused by the blowing conditions.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: 1. In the adaptive control of flue gas temperature for waste heat recovery in AOD furnaces, by simultaneously utilizing the flue gas temperature deviation term, the first-order backward differential change term, and the second-order backward differential term to determine the deviation direction and trend of flue gas temperature, the proportional gain coefficient and integral gain coefficient can be adjusted in advance before the temperature sensor fully reflects the actual flue gas temperature change. This can reduce the impact of heat transfer resistance and detection delay on the control response, enabling the damper mechanism and variable frequency fan to follow the flue gas temperature change more promptly, thereby improving the dynamic response capability of waste heat recovery flue gas temperature control.

[0019] 2. When the flue gas temperature deviation term has the opposite algebraic polarity to the first-order backward differential change term, and the flue gas temperature is falling back towards the target temperature, timely reduction of the proportional gain coefficient and integral gain coefficient can make the valve opening control increment converge smoothly, avoiding the controller maintaining a large adjustment range when approaching the target temperature. This eliminates the need to establish a complex fluid dynamics prediction model, reduces the reverse overshoot caused by control lag, and reduces the frequent reversing and mechanical shock of the damper mechanism and variable frequency fan, making the adjustment process near steady state more stable.

[0020] 3. Under sudden thermal load shock, by cutting off the integral accumulation action and temporarily switching to proportional-derivative control, it is possible to prevent large flue gas temperature deviations from continuously accumulating in the integral term, reducing integral saturation and the resulting long-term over-adjustment. After the flue gas temperature drops back to the safe control range, the integral gain coefficient is gradually restored. This can avoid premature or one-time restoration of the integral action, which could cause new temperature fluctuations. At the same time, it takes into account both rapid adjustment during thermal shock and control accuracy under stable operating conditions. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the basic steps of the adaptive flue gas temperature regulation of the present invention. Figure 2 This is a schematic diagram of the multi-dimensional underlying technical element collaboration and signal interaction architecture of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings.

[0023] Example 1: This embodiment discloses an adaptive control method for flue gas temperature in AOD furnace waste heat recovery, including the following steps: Step S1: Collect flue gas temperature data and calculate the deviation and first-order backward difference term: Collect flue gas temperature monitoring data in the waste heat recovery channel of AOD furnace, and calculate the flue gas temperature deviation term and first-order backward difference change term for the current control cycle. Step S2, reduce the gain coefficient and calculate the control increment when the polarities are opposite: compare the algebraic polarity of the flue gas temperature deviation term and the first-order backward differential change term; when the algebraic polarity of the flue gas temperature deviation term and the first-order backward differential change term is opposite, reduce the proportional gain coefficient and integral gain coefficient corresponding to the velocity-type discrete control algorithm, and calculate the valve opening control increment based on the reduced proportional gain coefficient and integral gain coefficient. Step S3: Reset the integral gain to zero when the limit is exceeded, and restore it after the safety condition is met: When the absolute value of the flue gas temperature deviation term is greater than the temperature deviation control limit, and the first-order backward differential change term continuously exceeds the temperature change rate threshold, the integral gain coefficient is reset to zero to cut off the integral accumulation effect of the velocity-type discrete control algorithm; after the flue gas temperature monitoring data falls back to the safe control range, the integral gain coefficient is restored. Step S4, superimpose the backlash compensation value and send a drive signal when reversing: retrieve the pre-stored mechanism backlash compensation value in the memory, compare the valve opening control increment with the direction of the electronic control adjustment command of the previous control cycle; when the valve opening control increment is opposite to the direction of the electronic control adjustment command, superimpose the mechanism backlash compensation value into the valve opening control increment and send a drive control signal for the air valve mechanism.

[0024] Step S2 in this embodiment includes the following sub-steps: Step S21, when the algebraic polarity is opposite, multiply the reference coefficients stored in the reference parameter library step by step by a physical attenuation factor less than 1, and adjust the proportional gain coefficient and integral gain coefficient of the current cycle online; Step S22, import the adjusted proportional gain coefficient and integral gain coefficient into the velocity-type discrete control algorithm, and combine them with the flue gas temperature deviation term of the current control cycle to complete the calculation of the valve opening control increment.

[0025] Step S3 in this embodiment includes the following sub-steps: Step S31, continuously read the first-order backward differential change term for 3 control cycles. When the absolute value of the first-order backward differential change term in each control cycle is greater than the temperature change rate threshold, and the absolute value of the flue gas temperature deviation term in the current control cycle is greater than the temperature deviation control limit, it is determined that a sudden thermal load shock has occurred in the controlled process; Step S32, write a zero value to the integral accumulator register in the velocity-type discrete control algorithm to pause the integral regulation action and switch the regulation loop to the proportional-derivative control state.

[0026] Step S3 in this embodiment further includes the following sub-steps: Step S33, after the value inside the integral accumulator register is reset to zero, the flue gas temperature monitoring data is continuously compared with the target temperature; Step S34, when the absolute value of the flue gas temperature deviation term is maintained within the temperature deviation control limit for 5 consecutive control cycles, it is determined that the controlled process has entered the safe control range, and the control weight of the integral gain coefficient in the velocity-type discrete control algorithm is gradually restored by a progressively increasing method.

[0027] Step S4 in this embodiment includes the following sub-steps: Step S41, read the sign of the valve opening control increment calculated in the current control cycle, and retrieve the actual action symbol of the previous control cycle; Step S42, compare the current sign with the actual action symbol, and when they are opposite, determine that the mechanical transmission direction of the air valve mechanism has changed, and directly add the mechanism reverse idle compensation value to the valve opening control increment to correct the air valve mechanism drive control signal.

[0028] In step S2 of this embodiment, the operation of reducing the integral gain coefficient and the proportional gain coefficient is achieved by modifying the gain setting value in the hardware register by the control chip, so as to limit the number of commutations of the air valve mechanism drive control signal near the steady-state equilibrium point.

[0029] The following long-term monitoring steps are described in this embodiment: Step S5, accumulate the number of times the integral gain coefficient is reset to zero within the smelting cycle, calculate the statistical variance of the flue gas temperature deviation term, and calculate the degradation index characterizing the wear state of the transmission connecting rod idle stroke; Step S6, when the value of the degradation index is greater than the preset wear threshold, reduce the temperature deviation control limit in step S3, and issue a high-risk over-temperature alarm signal for the heat exchange bag.

[0030] The sampling period of the controlled process described in this embodiment is 1s to 3s; in step S3, the temperature deviation control limit is 3% to 5% of the target temperature; in step S4, the mechanism reverse idle compensation value accounts for 0.5% to 1.5% of the preset adjustment opening stroke.

[0031] In step S4 of this embodiment, sending the air valve mechanism drive control signal includes: distributing the air valve mechanism drive control signal to the speed regulation drive interface of the variable frequency fan, adjusting the speed of the variable frequency fan within a loop response time of 0.5s to 1.5s, and suppressing the large-value thermal deviation disturbance of the flue gas temperature monitoring data caused by the blowing conditions.

[0032] Example 2: In this embodiment, during decarburization blowing in the AOD furnace, the staged oxygen supply and oxidation reaction cause nonlinear fluctuations in the flue gas temperature within the waste heat recovery channel. A single-point temperature sensor is installed in the flue gas pipeline; its protective sleeve and heat transfer structure create thermal resistance, causing a time delay between the sensor output and the actual flue gas temperature. The damper mechanism used to adjust the cold air intake is affected by machining tolerances, resulting in reverse backlash during reversal. When using fixed parameters for feedback adjustment, the control loop struggles to keep up with rapid changes in heat load. As the flue gas temperature deviation continues to increase, integral saturation easily occurs, causing significant changes in the cold air intake within a short period and increasing the risk of overheating damage to the downstream heat exchanger bag filter. The control unit acquires the raw output of the single-point temperature sensor at 20Hz via a digital input bus, with a 2s sampling period for the controlled process. Within each control cycle, the continuously sampled data is cumulatively resampled to obtain the... Flue gas temperature monitoring data for each control cycle ;in, To control the periodic index, The unit is °C. The control unit uses a fifth-order rolling median filter to sort the sampled sequence, remove glitch data that exceed the thermal response slope, and output the cleaned effective temperature parameter. ; control unit according to Calculate the flue gas temperature deviation term for the current control cycle. ,in, To preset the target temperature, and The units are all in °C. The unit is ℃. The difference between the current flue gas temperature deviation term and the flue gas temperature deviation term of the previous control cycle is divided by 2s to obtain the first-order backward difference term. Its unit is ℃ / s; the difference between the current first-order backward difference term and the previous control cycle's first-order backward difference term is divided by 2s to obtain the second-order backward difference term. Its unit is ℃ / s², and the control unit will , and Combined into time-varying eigenvectors , This is a column vector composed of the three components mentioned above.

[0033] When flue gas temperature deviation With the first-order backward difference change term The algebraic polarities are the same and all are positive, and the second-order backward difference terms have the same polarity. Also, when the discrete state space three-zone symbolic arbitration logic determines that the flue gas temperature is in a state of accelerating deviation from the target temperature, the control unit multiplies the reference proportional gain coefficient and the reference integral gain coefficient by an exponential increase term. This exponential increase term has a base of natural constant and uses the ratio of the first-order backward differential change term to the heat transfer delay time constant as the exponent, thereby increasing the proportional gain coefficient and the integral gain coefficient, increasing the adjustment amplitude of the control command before the sensor has completed its thermal response; when the flue gas temperature deviation term... With the first-order backward difference change term When the algebraic polarity is opposite, it indicates that the flue gas temperature is falling back towards the preset target temperature. The control unit reads the reference proportional gain coefficient and the reference integral gain coefficient from the reference parameter library, multiplies the two reference coefficients step by step by a physical attenuation factor less than 1, and writes the resulting values ​​into the gain setting register of the control chip. In this embodiment, the physical attenuation factor used is 0.85, and its value ranges from 0.75 to 0.90. This physical attenuation factor is determined according to the rated response time of the damper mechanism, so that the attenuation rate of the valve opening control increment is greater than 1.2 times the attenuation rate of natural heat dissipation of the flue gas. The control unit imports the reduced proportional gain coefficient and integral gain coefficient into the velocity-type discrete control algorithm, and combines them with the flue gas temperature deviation term of the current control cycle. Calculate valve opening control increment This reduces the number of reverse overshoots and commutations near the steady-state equilibrium point.

[0034] In this embodiment, the temperature deviation control limit is set to 5% of the preset target temperature. At a temperature of 560℃, the temperature deviation control limit is 28℃. During a sudden heat load shock, the flue gas temperature deviation item... The absolute value exceeds 50℃, and the first-order backward difference term If the temperature exceeds 15℃ / s for three consecutive control cycles, the integral dynamic cutoff gate block determines that a sudden thermal load shock has occurred in the controlled process. It writes a zero value to the integral accumulator register of the velocity-type discrete control algorithm and simultaneously sets the integral gain coefficient to zero to pause integral accumulation, switching the control loop to proportional-derivative control. Effective temperature parameter After the thermal disturbance peak is passed and begins to recede, the control unit continues to compare the flue gas temperature deviation. Temperature deviation control limit; when the flue gas temperature deviation item When the absolute value remains below 28℃ for five consecutive control cycles, the controlled process is determined to have entered the safe control range. The integral dynamic cutoff gate stops writing zero values ​​to the integral accumulator register. The control unit then gradually restores the control weight of the integral gain coefficient over multiple control cycles until it is restored to the corresponding reference integral gain coefficient, thus avoiding the integral regulation being activated all at once before the flue gas temperature has stabilized. The reverse idle compensation value of the mechanism is pre-stored in the memory. In this embodiment, The absolute value is 1% of the preset adjustment stroke, and the sign is based on the current valve opening control increment. Once the direction is determined, the control unit reads the current valve opening increment to control the valve. The control unit determines the sign of the control signal and retrieves the actual action symbol recorded in the previous control cycle. This actual action symbol is used to represent the direction of the electronic control adjustment command in the previous control cycle. When the two signs are opposite, the control unit determines that the mechanical transmission direction of the damper mechanism has changed, and the dynamic dead zone reverse compensation operator compensates for the reverse idle travel value of the mechanism. Directly superimposed on the valve opening control increment In the middle; when the absolute value of the current valve opening control increment is less than the mechanism reverse backlash compensation value, the compensation amount is used to make up for the mechanical backlash in the initial stage of reversal.

[0035] The control unit converts the corrected valve opening control increment into a 4mA to 20mA damper mechanism drive control signal to adjust the position of the mixing valve. This drive control signal is then distributed to the speed control interface of the variable frequency fan. Within a loop response time of 0.5s to 1.5s, the variable frequency fan speed and cold air intake are adjusted. Using this control method, the flue gas temperature in the waste heat recovery channel is maintained around 560℃, with temperature fluctuations controlled within ±15℃. The thermal resistance formed by the protective sleeve is an inherent physical inertia of the flue gas temperature detection circuit; the control algorithm does not change the physical properties of the heat exchange pipeline and temperature sensor. Based on the transmission characteristics, the control unit extracts the slope and acceleration information of the flue gas temperature change through the first-order backward differential term and the second-order backward differential term. When the second-order backward differential term is positive and the flue gas temperature deviation continues to increase, the proportional gain coefficient of the current control cycle is increased, so that the control command increases the amount of cold air adjustment before the sensor has fully reflected the actual flue gas temperature change. This processing makes the control signal have an equivalent phase lead relative to the temperature feedback. In conjunction with clearing the integral accumulator register, modifying the gain setting register, and compensating for the reverse idle distance of the mechanism, the influence of heat transfer delay, integral saturation, and damper reversing idle distance on the flue gas temperature control is reduced.

[0036] Example 3: In this embodiment, a three-dimensional fluid dynamics thermal balance model of the heat exchange pipeline in the waste heat recovery channel of the AOD furnace is established on a thermophysical control simulation test bench. Using the Navier-Stokes governing equations of mass conservation, momentum conservation, and energy conservation, as well as the convection heat transfer differential equation, the model simulates the flue gas temperature change caused by the step thermal shock during the decarburization blowing stage. The simulation temperature range is 400℃ to 750℃. Under typical blowing conditions with an oxygen supply intensity of 55 m³ / min, the bottom-level analog-to-digital conversion interface collects flue gas temperature monitoring data with a period of 50 ms, corresponding to a sampling frequency of 20 Hz. Gaussian white noise with a signal-to-noise ratio of 25.1 dB is superimposed on the sampled signal. A random power frequency interference harmonic with an amplitude of 1.2℃ is used to simulate on-site electromagnetic interference and flue gas turbulence fluctuations. The control unit performs rolling filtering and cumulative resampling on the data collected in 50ms cycles, and sets the sampling period of the controlled process to 2s. This value is within the control range of 1s to 3s. The sampling period is determined according to the flue gas temperature change rate and the shortest response time of the damper mechanism. When the flue gas temperature changes rapidly, the bottom layer sampling frequency is kept at 20Hz to reduce sampling distortion during the rapid temperature rise process. The velocity-type discrete control algorithm still calculates the flue gas temperature deviation term, the first-order backward differential change term, and the valve opening control increment according to the 2s controlled process sampling period.

[0037] During the calibration of the damper mechanism, the test bench measured the uncorrected mechanical backlash of the transmission linkage to be 2.0% of the preset adjustment opening stroke. After conversion according to the transmission lever ratio, the mechanical backlash compensation value stored in the control unit was 1.0% of the preset adjustment opening stroke, which is within the set range of 0.5% to 1.5%. During long-term operation, the control unit calculates the degradation index based on the statistical variance of the reset action frequency and the flue gas temperature deviation term according to the integral gain coefficient. When the degradation index is greater than the wear threshold, the temperature deviation control limit is reduced from 5% to 3% of the target temperature, and a high-risk over-temperature alarm signal for the heat exchange bag is issued to identify the continuous deviation of the flue gas temperature in advance after the transmission wear worsens. The test group, control group, partially missing control group, and out-of-range control group were set up. The control group used a fixed proportional gain coefficient and a fixed integral gain coefficient. The partially missing control group retained the velocity-type discrete control algorithm, but did not perform the algebraic polarity comparison between the flue gas temperature deviation term and the first-order backward differential change term, nor did it write a zero value to the integral accumulator register. The out-of-range control group set the temperature deviation control limit to 120℃ to observe the response change after the limit significantly exceeded the normal control range. The test group adjusted the proportional gain coefficient and integral gain coefficient according to the algebraic polarity of the flue gas temperature deviation term and the first-order backward differential change term, and cut off the integral accumulation action when the sudden heat load shock condition was met.

[0038] At the initial stage of blowing, the same step thermal shock was applied to all groups. The maximum temperature rise rate of the flue gas temperature monitoring data reached 22.4℃ / s. In the control group, because the proportional gain coefficient and integral gain coefficient remained unchanged, the valve mechanism reciprocated near zero opening and full opening, and the maximum overshoot of the flue gas temperature reached 84.3℃. After the integral term continued to accumulate, the transition time required for the controlled process to return to stability was 245.3s. The partially missing control group did not reduce the gain according to the algebraic polarity, nor did it reset the integral accumulator register during the large thermal shock. The valve opening control increment remained at a large value in the saturation range, causing the cold air introduction valve to produce an overmodulation action of 14.8s. The flue gas cooling rate increased accordingly, and acidic condensation formed locally on the bag filter frame. The low-frequency limit cycle oscillation period of the flue gas temperature reached 112.5s. Under the same thermal shock, the flue gas temperature deviation term calculated by the experimental group was... The initial value is 65.2℃, and the first-order backward difference term is... It is 21.3℃ / s, second-order backward difference term. The absolute value of the flue gas temperature deviation term was 4.6℃ / s², exceeding the temperature deviation control limit. Furthermore, the sampling period of the first-order backward differential change term exceeded 15℃ / s for three consecutive controlled processes. Based on this, the control unit determined that a sudden thermal load shock had occurred in the controlled process. It wrote a zero value to the integral accumulator register of the velocity-type discrete control algorithm and reset the integral gain coefficient to zero, switching the control loop to proportional-derivative control. After the integral accumulation action was cut off, the maximum overshoot of the flue gas temperature in the test group decreased to 11.6℃, and the transition time shortened to 32.4s. This process was jointly triggered by the flue gas temperature deviation term and the first-order backward differential change term. The integral accumulator register remained at zero during the thermal shock. After the flue gas temperature dropped and entered the safe control range, the control weight of the integral gain coefficient was restored through a gradual increase.

[0039] To observe the impact of the temperature deviation control limit on the control response, the limit was extended to 5℃ and 80℃ respectively during the test. Within the range of 5℃ to 80℃, the regulating loop could still recover stability. When the temperature deviation control limit was below 5℃, residual pulses caused by noise frequently triggered integral reset, and the steady-state variance of the flue gas temperature deviation term increased from 0.45 to 16.82. When the temperature deviation control limit was above 80℃, the gain adjustment and integral cutoff actions were significantly delayed, and the control response gradually approached the fixed parameter control group. After the limit was further set to 120℃ for the out-of-range control group, the flue gas temperature continued to deviate in the early stage of thermal shock and failed to trigger the corresponding control action within the effective regulation period. During the polarity judgment process, when the flue gas temperature deviation term, the first-order backward differential term, and the second-order backward differential term are all positive, the control unit increases the proportional gain coefficient and the integral gain coefficient. When the flue gas temperature deviation term and the first-order backward differential term have opposite algebraic polarities, the control unit multiplies the reference coefficient step by step by a physical attenuation factor less than 1, reducing the proportional gain coefficient and the integral gain coefficient of the current control cycle. When the flue gas temperature deviation term and the first-order backward differential term have the same sign, while the second-order backward differential term has the opposite sign, the current proportional gain coefficient remains unchanged, and the integral cutoff condition continues to be monitored. The above processing corresponds to the processes of continuous deviation of flue gas temperature, return to the target temperature, and the beginning of slowing down of the rate of change, respectively.

[0040] In the reversing steady-state test, the uncorrected mechanical backlash of the damper drive linkage remained at 2.0%. In the control group, after the valve opening control increment changed direction, the electronic control command could not immediately drive the valve stem to move in the opposite direction, resulting in a 2.6s positional pause in the damper mechanism and a low-frequency limiting cycle oscillation with an amplitude of 24.3℃ in the flue gas temperature. The experimental group read the valve opening control increment for the current control cycle. The control unit determines the sign of the valve mechanism and retrieves the actual action sign from the previous control cycle. When the two signs are opposite, the control unit determines that the mechanical transmission direction of the valve mechanism has changed. It then directly adds the converted 1.0% mechanism backlash compensation value to the valve opening control increment, and converts the correction result into a 4mA to 20mA valve mechanism drive control signal. The sign of the mechanism backlash compensation value is consistent with the direction of the current valve opening control increment, used to allow the valve stem to overcome the mechanical backlash in the initial stage of reversal. After adopting this compensation method, the delay from receiving the reverse electronic control adjustment command to the valve stem producing an actual action is reduced from 2... The timeout was reduced from 0.6s to 95.0ms, with a target flue gas temperature of 560℃ and an allowable error of ±15℃. Under the continuous presence of Gaussian white noise and random power frequency interference harmonics, the steady-state flue gas temperature was between 558.4℃ and 561.2℃. The test results show that by adjusting the proportional gain coefficient and integral gain coefficient according to the algebraic polarity of the flue gas temperature deviation term and the first-order backward differential change term, resetting the integral gain coefficient during sudden thermal load shocks, and superimposing the reverse idle compensation value of the mechanism when the damper mechanism reverses, it is possible to simultaneously reduce the flue gas temperature overshoot, the duration of integral saturation, and the damper mechanism reversal pause.

[0041] Example 4: This embodiment combines Figures 1 to 2 This paper describes an adaptive control method for flue gas temperature in an AOD (Aeration Overheating) furnace waste heat recovery system. Figure 1 As shown, the method includes the following steps: S1, collecting flue gas temperature data and calculating the deviation and first-order backward differential term by establishing a connection through unidirectional signal transmission in the order of process steps; S2, reducing the gain coefficient and calculating the control increment when the polarity is opposite; S3, resetting the integral gain to zero when the limit is exceeded and restoring it after safety; and S4, superimposing the idle compensation value and sending the drive signal when the reverse is achieved. The nodes of each step together constitute the basic execution logic of the entire control method.

[0042] like Figure 2 As shown, the adaptive control process of flue gas temperature for AOD furnace waste heat recovery involves four sets of collaborative inputs from underlying components. The first set of input logic relates to the signal transmission between flue gas temperature monitoring data, single-point temperature sensors, and the first-order backward differential change term. The second set of input logic relates to the signal collaboration between the integral dynamic truncation gate block, sudden heat load impacts, and the integral accumulator register. The third set of input logic relates to the parameter transmission between the velocity-type discrete control algorithm and the algebraic polarity opposite and physical attenuation factors. The fourth set of input logic relates to the signal correction between the damper mechanism drive control signal, the mechanism reverse idle compensation value, and the dynamic dead zone reverse inverse compensation operator. The parallel interactive logic of the above four sets of technical elements ultimately converges to the core processing node of the adaptive control of flue gas temperature for AOD furnace waste heat recovery.

[0043] Example 5: In this embodiment, when the transient oxygen blowing rate reaches 60 m³ / min at the end of the AOD furnace blowing process, the heat released by the nonlinear oxidation reaction causes the flue gas temperature in the waste heat recovery channel to approach 750°C in a short time, with a transient temperature rise rate of 30°C / s. The heat transfer delay time constant of the single-point temperature sensor protective sleeve increases to 4.5s, and the collected flue gas temperature monitoring data lags behind the actual flue gas temperature in the channel. If the control unit continues to use a fixed proportional gain coefficient and integral gain coefficient, the velocity-type discrete control algorithm will continuously increase the valve opening control increment during this delay period, which can easily cause the actuator to reach the upper limit saturation opening. When the flue gas temperature exceeds the peak and begins to fall, the integral accumulation will still hinder the timely reverse action of the damper mechanism, thereby increasing the risk of condensation on the heat exchange tubes or overheating damage to the heat exchange bag frame. After the control program is started, the bottom layer... The interface reads flue gas temperature monitoring data at 20Hz. The measurement accuracy of the single-point temperature sensor is 0.1℃. The control unit filters and accumulates resampling of the original sampled data, sets the sampling period of the controlled process to 2s, and calculates the flue gas temperature deviation term, the first-order backward differential change term, and the second-order backward differential term according to this period. When the absolute value of the flue gas temperature deviation term reaches 80℃, the control unit compares the algebraic polarity of each component in the time-series rate characteristic vector. When the flue gas temperature deviation term, the first-order backward differential change term, and the second-order backward differential term are all positive, it is determined that the flue gas temperature is accelerating away from the target temperature. The proportional gain coefficient is increased from 1.5 to 3.2, while the integral gain coefficient is decreased to 0.1 to increase the adjustment range of the current control cycle and limit the integral accumulation rate. The velocity-type discrete control algorithm sets the output boundary for the valve opening control increment. ,in, To preset the allowable incremental saturation threshold, which is 5.0%, after calculating the valve opening control increment, the control unit first limits the amplitude according to this threshold, and then generates the air valve mechanism drive control signal to avoid the opening change in a single control cycle from exceeding the allowable range of the actuator.

[0044] In this embodiment, the temperature deviation control limit is set within the range of 3% to 5% of the target temperature. When the flue gas temperature deviation reaches 80℃ and the first-order backward differential change term reaches 30℃ / s for three consecutive controlled process sampling periods, the absolute value of the flue gas temperature deviation exceeds the temperature deviation control limit, and the first-order backward differential change term also continuously exceeds the temperature change rate threshold. Based on this, the control unit determines that a sudden thermal load shock has occurred in the controlled process, writes a zero value to the integral accumulator register, and resets the integral gain coefficient to zero, switching the regulation loop to proportional-derivative control mode. Completing the above register writing before valve action can prevent the flue gas temperature deviation during the thermal shock from continuing to enter the integral accumulation term; flue gas temperature After the peak value is exceeded, the first-order backward differential term changes direction as the temperature drops. When the flue gas temperature deviation term has the opposite algebraic polarity to the first-order backward differential term, the control unit multiplies the reference proportional gain coefficient and the reference integral gain coefficient by a physical attenuation factor less than 1 in steps, thereby reducing the proportional gain coefficient and integral gain coefficient of the current control cycle and reducing the absolute value of the valve opening control increment. The integral gain coefficient remains truncated at this time. Only when the absolute value of the flue gas temperature deviation term is within the temperature deviation control limit for five consecutive controlled process sampling cycles, the control unit determines that the controlled process has entered the safe control range and gradually restores the control weight of the integral gain coefficient through a progressively increasing method.

[0045] During the adjustment of the cold air intake, the uncorrected mechanical backlash of the damper drive linkage was measured to be 3.5% of the preset adjustment stroke. The control unit converted this measured value according to the transmission lever ratio and the actual opening stroke of the damper. The converted value within the range of 0.5% to 1.5% of the preset adjustment stroke was stored in the memory as the mechanism backlash compensation value. The 3.5% uncorrected mechanical backlash was not directly added to the control command. When the damper mechanism reverses direction, the control unit reads the sign of the valve opening control increment in the current control cycle and retrieves the actual action sign of the previous control cycle. When the two signs are opposite, it is determined that the mechanical transmission direction of the damper mechanism has changed. The mechanism backlash compensation value in the memory is directly added to the valve opening control increment. The sign of the compensation value is consistent with the direction of the current valve opening control increment, which is used to make up for the mechanical backlash of the valve rod at the initial stage of reversal. The control unit will then correct the backlash. The valve opening control increment is converted into a damper mechanism drive control signal and distributed to the speed control drive interface of the variable frequency fan. Within a loop response time of 0.5s to 1.5s, the variable frequency fan speed and cold air intake are adjusted. The local response delay of the damper mechanism from receiving the reverse control command to the valve stem starting to produce actual action is reduced from 3.8s to 110ms. This local response delay is used to characterize the valve stem starting time after the mechanical idle stroke is compensated, and is measured separately from the loop response time corresponding to the variable frequency fan completing the speed adjustment. After adopting the above control process, the flue gas temperature in the waste heat recovery channel drops back to the target temperature of 560℃, and the steady-state temperature control deviation is maintained within ±15℃. The control unit processes the sensor lag, integral saturation, and damper mechanism reversing idle stroke respectively through gain adjustment, clearing the integral accumulator register, and mechanism reverse idle stroke compensation, so that the damper mechanism can still complete forward adjustment and reverse correction with the flue gas temperature change under extreme heat load conditions.

[0046] Example 6: In this embodiment, before the start of the AOD furnace smelting cycle, the control unit calibrates the process control parameters required for adaptive flue gas temperature control. The calibration includes the temperature change rate threshold, the mechanism reverse idle compensation value, and the temperature deviation control limit. During the calibration of the temperature change rate threshold, the control unit retrieves flue gas temperature monitoring data collected by a single-point temperature sensor from historical smelting cycles, calculates the average temperature rise slope during the normal decarburization blowing stage, and uses the maximum value of the average temperature rise slope from each smelting cycle as the temperature change rate threshold. The calibration uses three sets of blowing conditions (high, medium, and low) with oxygen supply intensities of 60 m³ / min, 55 m³ / min, and 40 m³ / min, respectively, to cover the main operating range of flue gas temperature changes. At an oxygen supply intensity of 60 m³ / min... Under operating condition n, the heat transfer delay time constant of the single-point temperature sensor protective sleeve is 4.5s, and the maximum transient temperature rise rate of the flue gas is 30℃ / s. During the calibration of the mechanism's reverse backlash compensation value, the control unit sends unidirectional increasing opening command and unidirectional decreasing opening command to the air valve mechanism during the shutdown interval, and reads the valve stem displacement through the position sensor. The control unit records the moment when the opening command starts to change and the moment when the valve stem actually produces displacement. Based on the change in the opening command during this period, the mechanical reverse backlash is determined, and then converted into the mechanism's reverse backlash compensation value corresponding to the actual opening stroke of the air valve according to the transmission lever ratio. The converted value is written into the memory as the reference mechanism reverse backlash compensation value and is kept within the preset adjustment range of 0.5% to 1.5% of the opening stroke.

[0047] During the calibration of temperature deviation control limits, the control unit determines the usable temperature safety margin based on the difference between the material's temperature tolerance limit of the heat exchange bag and the target temperature. It then selects a temperature deviation control limit within the range of 3% to 5% of the target temperature. This limit is used to determine whether the flue gas temperature deviation exceeds the steady-state regulation range and, together with the temperature change rate threshold, constitutes the criteria for judging sudden heat load shocks. After wear and tear on the damper mechanism, the control unit corrects the mechanism's reverse idle compensation value according to the following formula: ,in, The corrected reverse backlash compensation value is expressed in % (%). , where is the connecting rod wear correction factor, and is a dimensionless value; The reference mechanism reverse backlash compensation value is pre-stored in the memory, in units of %; after each periodic maintenance or after accumulating 500 smelting cycles, the control unit sends a reverse full-stroke pulse command to the air valve mechanism and measures the pause time from receiving the command to the valve stem producing actual displacement through a displacement sensor. The measured pause time is divided by the reference pause time of 100ms when the new equipment leaves the factory, and the resulting ratio is used as the connecting rod wear correction coefficient. As the wear degree of the transmission connecting rod increases, this coefficient gradually increases between 1.00 and 1.35; after the air valve mechanism has run for 2000 smelting cycles, the calibrated connecting rod wear correction coefficient is 1.15. Based on this, the control unit calculates the corrected mechanism reverse backlash compensation value and writes the calculation result into the memory.

[0048] During long-term monitoring, the control unit accumulates the frequency of resetting the integral gain coefficient to zero within a single smelting cycle and calculates the statistical variance of the flue gas temperature deviation term within that cycle. The cumulative frequency of resetting the integral gain coefficient is divided by the upper limit of the baseline reset frequency (50 times) to obtain the frequency normalized value; the statistical variance of the flue gas temperature deviation term is divided by the upper limit of the allowable variance (25℃²) to obtain the variance normalized value. The control unit multiplies the frequency normalized value by a first weighting factor of 0.6 and the variance normalized value by a second weighting factor of 0.4, and then adds the two products to obtain the degradation index characterizing the wear state of the transmission connecting rod idle stroke. When the degradation index exceeds the wear threshold of 0.85, the control unit determines that the mechanical wear of the transmission link has affected the reversing response of the damper mechanism. It reduces the temperature deviation control limit from 5% to 3% of the target temperature and issues a high-risk over-temperature alarm signal for the heat exchange bag filter. After the temperature deviation control limit is reduced, the flue gas temperature deviation can meet the judgment condition of sudden heat load impact earlier, so that the integral gain coefficient is reset to zero in advance when the mechanical transmission idle distance increases. After completing the parameter calibration, the control unit writes the temperature change rate threshold, temperature deviation control limit, reference mechanism reverse idle distance compensation value and link wear correction coefficient into the corresponding register. Under the blowing conditions with an oxygen supply intensity of 60 m³ / min, the control system calls the calibrated process control parameters. The maximum overshoot of the effective temperature parameter is 11.6℃, and the transition time of the controlled process is 32.4 s. Under the control conditions without temperature change rate threshold calibration, when the control system faces a step thermal shock of the same intensity, it cannot determine the integral cutoff time based on the temperature rise slope of the normal decarburization blowing stage. The air valve mechanism generates an overmodulation action of 14.8 s, and a low-frequency limiting loop oscillation with an amplitude of 24.3℃ is formed in the waste heat recovery channel. After adopting the above calibration parameters, the flue gas temperature is adjusted around the target temperature of 560℃, and the steady-state temperature deviation is kept within ±15℃.

Claims

1. A method for adaptive temperature control of flue gas in AOD (Aeration Oxygen Depletion) furnace waste heat recovery, characterized in that, Includes the following steps: Step S1: Collect flue gas temperature monitoring data in the waste heat recovery channel of the AOD furnace, and calculate the flue gas temperature deviation term and the first-order backward differential change term for the current control cycle. Step S2: Compare the algebraic polarity of the flue gas temperature deviation term with that of the first-order backward differential change term; when the algebraic polarity of the flue gas temperature deviation term and the first-order backward differential change term is opposite, reduce the proportional gain coefficient and integral gain coefficient corresponding to the velocity-type discrete control algorithm, and calculate the valve opening control increment based on the reduced proportional gain coefficient and integral gain coefficient. Step S3: When the absolute value of the flue gas temperature deviation term is greater than the temperature deviation control limit and the first-order backward differential change term continuously exceeds the temperature change rate threshold, the integral gain coefficient is reset to zero to cut off the integral accumulation effect of the velocity-type discrete control algorithm. After the flue gas temperature monitoring data falls back to the safe control range, the integral gain coefficient is restored; Step S4: Retrieve the pre-stored mechanism reverse idle compensation value in the memory, compare the valve opening control increment with the direction of the electronic control adjustment command of the previous control cycle; when the valve opening control increment is opposite to the direction of the electronic control adjustment command, add the mechanism reverse idle compensation value to the valve opening control increment, and send the air valve mechanism drive control signal.

2. The adaptive temperature control method for waste heat recovery flue gas in an AOD furnace according to claim 1, characterized in that, Step S2 includes the following sub-steps: Step S21, when the algebraic polarity is opposite, multiply the reference coefficients stored in the reference parameter library step by step by a physical attenuation factor less than 1, and adjust the proportional gain coefficient and integral gain coefficient of the current cycle online; Step S22, import the adjusted proportional gain coefficient and integral gain coefficient into the velocity-type discrete control algorithm, and combine them with the flue gas temperature deviation term of the current control cycle to complete the calculation of the valve opening control increment.

3. The adaptive temperature control method for waste heat recovery flue gas in an AOD furnace according to claim 1, characterized in that, Step S3 includes the following sub-steps: Step S31, continuously read the first-order backward differential change term for 3 control cycles. When the absolute value of the first-order backward differential change term in each control cycle is greater than the temperature change rate threshold, and the absolute value of the flue gas temperature deviation term in the current control cycle is greater than the temperature deviation control limit, it is determined that a sudden thermal load shock has occurred in the controlled process; Step S32, write a zero value to the integral accumulator register in the velocity-type discrete control algorithm to pause the integral regulation action and switch the regulation loop to the proportional-derivative control state.

4. The adaptive temperature control method for waste heat recovery flue gas in an AOD furnace according to claim 1, characterized in that, Step S3 also includes the following sub-steps: Step S33, after the value inside the integral accumulator register is reset to zero, the flue gas temperature monitoring data is continuously compared with the target temperature; Step S34, when the absolute value of the flue gas temperature deviation term is maintained within the temperature deviation control limit for 5 consecutive control cycles, it is determined that the controlled process has entered the safe control range, and the control weight of the integral gain coefficient in the velocity-type discrete control algorithm is gradually restored by a progressively increasing method.

5. The adaptive temperature control method for waste heat recovery flue gas in an AOD furnace according to claim 1, characterized in that, Step S4 includes the following sub-steps: Step S41, read the sign of the valve opening control increment calculated in the current control cycle, and retrieve the actual action symbol of the previous control cycle; Step S42, compare the current sign with the actual action symbol, and when they are opposite, determine that the mechanical transmission direction of the damper mechanism has changed, and directly add the mechanism's reverse idle compensation value to the valve opening control increment to correct the damper mechanism drive control signal.

6. The adaptive temperature control method for waste heat recovery flue gas in an AOD furnace according to claim 1, characterized in that, In step S2, the operation of reducing the integral gain coefficient and the proportional gain coefficient is achieved by modifying the gain setting value in the hardware register by the control chip, so as to limit the number of commutations of the air valve mechanism drive control signal near the steady-state equilibrium point.

7. The adaptive temperature control method for waste heat recovery flue gas in an AOD furnace according to claim 1, characterized in that, The long-term monitoring steps include: Step S5, accumulating the number of times the integral gain coefficient is reset to zero within the smelting cycle, calculating the statistical variance of the flue gas temperature deviation term, and calculating the degradation index characterizing the wear state of the transmission connecting rod idle stroke; Step S6, when the value of the degradation index is greater than the preset wear threshold, reducing the temperature deviation control limit in Step S3, and issuing a high-risk over-temperature alarm signal for the heat exchange bag.

8. The adaptive temperature control method for waste heat recovery flue gas in an AOD furnace according to claim 1, characterized in that, The sampling period of the controlled process is 1s to 3s; in step S3, the temperature deviation control limit is 3% to 5% of the target temperature; in step S4, the mechanism reverse idle compensation value accounts for 0.5% to 1.5% of the preset adjustment opening stroke.

9. The adaptive temperature control method for waste heat recovery flue gas in an AOD furnace according to claim 1, characterized in that, In step S4, sending the air valve mechanism drive control signal includes: distributing the air valve mechanism drive control signal to the speed regulation drive interface of the variable frequency fan, adjusting the speed of the variable frequency fan within a loop response time of 0.5s to 1.5s, and suppressing the large-value thermal deviation disturbance of the flue gas temperature monitoring data caused by the blowing operation.

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