A primary fan static blade and variable frequency combined optimization control method

Abstract

The present application relates to the technical field of coal-fired unit boiler auxiliary machine control, and discloses a primary air fan static vane and variable frequency combined optimization control method, which comprises the following steps: a collection end acquires primary air pressure, static vane opening, variable frequency and denitration inlet nitrogen oxide concentration and sends them to a calculation end. The calculation end compares the current parameters with the safety constraint boundary values. When the pressure is reduced and the nitrogen oxide concentration exceeds the standard, the excess air volume is cut off according to the time sequence logic of first reducing the variable frequency drive frequency to the lower limit and then closing the small static vane opening within the safety constraint. When the pressure is increased, the air volume is increased according to the time sequence logic of first opening the large static vane opening to the upper limit and then increasing the variable frequency drive frequency. The present application breaks the operation limit of single variable frequency drive equipment and solves the problem of nitrogen oxide emission exceeding the standard caused by excess primary air volume under deep peak regulation and extremely low load conditions.

Description

Technical Field

[0001] This invention relates to the field of auxiliary equipment control technology for coal-fired boiler units, and in particular to a method for combined optimized control of primary air fan stator blades and frequency converter. Background Technology

[0002] Coal-fired boiler operation relies on primary air fans to provide air with appropriate head and flow rate for drying and transporting pulverized coal. The boiler combustion system needs to adjust the total primary air supply in real time according to changes in actual operating conditions. A single stator vane adjustment method controls airflow by changing the physical cross-sectional area of ​​the fan inlet guide vane opening, while a single variable frequency drive (VFD) method controls airflow by changing the fan motor's power frequency. A combined optimized control method integrates stator vane opening adjustment and VFD speed adjustment to control the air supply system. Under normal load conditions, the control system instructs the stator vanes to maintain a low-resistance channel at maximum opening, while simultaneously instructing the VFD to dynamically change its speed frequency to adapt to the actual pulverized coal transport requirements. However, the VFD equipment is constrained by the physical properties of the motor, resulting in a minimum operating frequency limit. This leads to physical condition conflicts in the conventional combined control logic when the generator unit enters extremely low load conditions.

[0003] Existing primary air fan joint optimization control technology suffers from the following technical challenges: Under extremely low loads, the frequency converter reaches its lower limit, leading to excessive primary air volume and increased nitrogen oxide (NOx) generation and emissions exceeding standards. During deep peak-shaving operations in coal-fired boilers, the overall operating load of the generator unit is extremely low, resulting in a significant reduction in the primary air volume required by the boiler pulverizing system. Limited by the physical protection thresholds of the equipment, the primary air fan frequency converter cannot further reduce its output frequency; this lower frequency limit causes the actual air volume supplied by the fan to far exceed the air volume required for pulverized coal combustion. Excessive air entering the furnace causes a sudden increase in oxygen concentration in the main combustion zone, promoting the oxidation reaction between nitrogen and oxygen in the furnace and significantly increasing the total NOx generation of the coal-fired unit. For example, during off-peak grid conditions, when the generator unit responds to dispatch commands by reducing its operating load, the boiler coal feeding control system reduces the coal feed accordingly, and the automatic control system synchronously issues a command to reduce the primary air volume based on a fixed coal-air ratio logic. After receiving the frequency reduction command, the frequency converter reaches the minimum safe operating frequency and stops reducing the frequency drive frequency. The actual output speed is limited, causing excess primary air to continuously enter the coal-fired unit, triggering a localized oxygen-rich combustion state inside the furnace. This localized oxygen-rich combustion causes a significant increase in nitrogen oxide concentration at the inlet of the denitrification equipment. The abnormally high gas concentration exceeds the maximum reduction processing capacity of the denitrification control system, ultimately causing the unit's exhaust gas emission data to violate standards. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for the combined optimized control of primary air fan stator blades and frequency converter. This invention solves the technical problem of excessive primary air volume caused by the frequency converter reaching its lower limit under extremely low load, resulting in increased nitrogen oxide generation and excessive emissions.

[0005] To solve the above-mentioned technical problems, the specific contents of the present invention are as follows: This invention provides a method for joint optimization control of primary air fan stator blades and frequency converter, comprising: The acquisition terminal obtains the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current nitrogen oxide concentration at the denitrification inlet of the coal-fired unit, and sends the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current nitrogen oxide concentration at the denitrification inlet to the processing terminal; The computing terminal receives the current primary air pressure, the current stationary blade opening, the current variable frequency drive frequency, and the current nitrogen oxide concentration at the denitrification inlet; The computing terminal extracts the pre-stored target primary air pressure, primary air pressure safety lower limit, static blade opening safety lower limit, frequency safety lower limit, and concentration upper limit threshold. The computing terminal compares the current primary wind pressure with the lower limit of the primary wind pressure, and compares the current stator blade opening with the lower limit of the stator blade opening. When the current primary air pressure is greater than the target primary air pressure and the current nitrogen oxide concentration at the denitrification inlet is greater than or equal to the upper limit threshold of the concentration, the computing terminal generates a frequency reduction command and sends the frequency reduction command to the variable frequency drive terminal to instruct the variable frequency drive terminal to reduce the current variable frequency drive frequency according to the frequency reduction command; When the current variable frequency drive frequency is equal to the frequency safety lower limit, the current denitrification inlet nitrogen oxide concentration is greater than or equal to the concentration upper limit threshold, the current stationary blade opening is greater than the stationary blade opening safety lower limit, and the current primary air pressure is greater than the primary air pressure safety lower limit, the computing terminal generates a stationary blade closing instruction and sends the stationary blade closing instruction to the stationary blade drive terminal to instruct the stationary blade drive terminal to reduce the current stationary blade opening according to the stationary blade closing instruction.

[0006] Furthermore, the primary wind turbine stator blade and frequency converter joint optimization control method of the present invention, after the frequency reduction command or stator blade closing command is generated at the computing terminal and before the frequency reduction command is sent to the frequency converter drive terminal or the stator blade closing command is sent to the stator blade drive terminal, further includes: The computing terminal extracts the expected target frequency value corresponding to the frequency reduction instruction or the expected target opening value corresponding to the closing silent leaf instruction; The computing terminal calculates the expected target frequency value or the expected target opening value by multiplying them according to the preset pressure opening mapping coefficient to obtain the estimated primary wind pressure and the estimated stationary blade opening. When the estimated primary wind pressure is lower than the safe lower limit of primary wind pressure, or when the estimated stator blade opening is lower than the safe lower limit of stator blade opening, the computing terminal stops sending the frequency reduction command to the frequency converter drive terminal, or stops sending the stator blade closing command to the stator blade drive terminal.

[0007] Furthermore, in the primary air turbine stator blade and frequency converter joint optimization control method of the present invention, the computing terminal generates a frequency reduction command and sends the frequency reduction command to the frequency converter drive terminal, including: The computing terminal calculates the pressure difference between the current primary wind pressure and the target primary wind pressure; The computing terminal extracts a pre-established table of correspondence between pressure difference and frequency reduction amplitude, and queries the table of correspondence between pressure difference and frequency reduction amplitude to find the preferred frequency reduction amplitude value that matches the pressure difference. When the difference between the current variable frequency drive frequency and the preferred frequency reduction magnitude value is greater than or equal to the frequency safety lower limit value, the computing terminal generates the frequency reduction command according to the preferred frequency reduction magnitude value and sends the frequency reduction command to the variable frequency drive terminal. When the difference between the current variable frequency drive frequency and the preferred frequency reduction amplitude value is less than the frequency safety lower limit value, the computing terminal updates the preferred frequency reduction amplitude value using the difference between the current variable frequency drive frequency and the frequency safety lower limit value, generates the frequency reduction command based on the updated preferred frequency reduction amplitude value, and sends the frequency reduction command to the variable frequency drive terminal.

[0008] Furthermore, in the primary wind turbine stator blade and frequency converter joint optimization control method of the present invention, the computing terminal generates a stator blade closing command and sends the stator blade closing command to the stator blade drive terminal, including: The computing terminal receives the current feedback frequency sent by the frequency conversion drive terminal. When the current feedback frequency is equal to the frequency safety lower limit, the computing terminal generates a frequency lock status identifier. When the computing terminal detects the frequency lock status flag, the computing terminal calculates the concentration difference between the current nitrogen oxide concentration at the denitrification inlet and the upper limit threshold concentration. The computing terminal extracts a pre-stored table of correspondence between concentration difference and target excess air volume reduction value, and queries the table of correspondence between concentration difference and target excess air volume reduction value to find the target excess air volume reduction value corresponding to the concentration difference. The computing terminal converts the target excess air volume reduction value into a stator blade opening adjustment parameter, generates the stator blade closing command based on the stator blade opening adjustment parameter, and sends the stator blade closing command to the stator blade drive terminal.

[0009] Furthermore, the primary air fan stator and frequency converter joint optimization control method of the present invention further includes: The computing terminal extracts the pre-stored safe upper limit value of the still blade opening; When the current primary wind pressure is less than the target primary wind pressure, the computing terminal generates a command to open the stator blades and sends the command to the stator blade drive terminal. The acquisition terminal acquires the value of the opening degree of the stationary blade after executing the command to open the stationary blade and sends it to the processing terminal. The processing terminal receives the value of the stationary blade opening degree after it is opened larger; When the value of the stator blade opening after the opening is increased is equal to the safe upper limit of the stator blade opening and the current primary wind pressure is less than the target primary wind pressure, the computing terminal generates an up-frequency command and sends the up-frequency command to the frequency converter drive terminal.

[0010] Furthermore, the primary air fan stator blade and frequency converter joint optimization control method of the present invention, wherein the acquisition terminal obtains the current denitrification inlet nitrogen oxide concentration of the coal-fired unit, and the calculation terminal receives the current denitrification inlet nitrogen oxide concentration sent by the acquisition terminal, includes: The acquisition terminal acquires the furnace temperature distribution matrix, coal supply value, and secondary air supply value of the coal-fired unit, and sends the furnace temperature distribution matrix, coal supply value, and secondary air supply value to the computing terminal. The computing terminal receives the furnace temperature distribution matrix, the coal supply value, and the secondary air supply value; The computing terminal concatenates the furnace temperature distribution matrix, the coal supply value, and the secondary air supply value into a multi-dimensional physical state feature vector. The computing terminal extracts pre-stored dot product calculation rules, which include a node weight matrix. The computing terminal calculates the dot product of the multidimensional physical state feature vector and the node weight matrix according to the dot product result calculation rules, and uses the dot product result as the current nitrogen oxide concentration at the denitrification inlet.

[0011] Furthermore, in the primary air fan stator and frequency converter joint optimization control method of the present invention, before the computing terminal extracts the pre-stored primary air pressure safety lower limit value and stator opening safety lower limit value, it further includes: The acquisition terminal acquires the coal powder fineness value, coal powder moisture value, and pipeline fluid resistance value of the coal-fired unit's pulverizing pipeline transportation line, and sends the coal powder fineness value, coal powder moisture value, and pipeline fluid resistance value to the computing terminal. The computing terminal receives the coal powder fineness value, the coal powder moisture value, and the pipeline fluid resistance value; The computing terminal performs weighted summation calculations on the coal powder fineness value, the coal powder moisture value, and the pipeline fluid resistance value according to the preset weight ratio parameters, to obtain the critical wind speed standard value for maintaining the suspended fluidized state of coal powder. The computing terminal multiplies the critical wind speed standard value with the preset safety margin coefficient to obtain the updated primary wind pressure safety lower limit value and the updated stator blade opening safety lower limit value. The computing terminal uses the updated primary wind pressure safety lower limit and the updated stationary blade opening safety lower limit to overwrite the pre-stored primary wind pressure safety lower limit and the pre-stored stationary blade opening safety lower limit.

[0012] Furthermore, the primary air fan stator blade and frequency converter joint optimization control method of the present invention, after the acquisition terminal obtains the current denitrification inlet nitrogen oxide concentration of the coal-fired unit, further includes: The acquisition terminal obtains the current operating load value of the coal-fired unit and sends the current operating load value to the processing terminal; The processing terminal receives the nitrogen oxide concentration at the denitrification inlet from multiple sampling cycles continuously sent by the acquisition terminal; The computing terminal calculates the arithmetic mean of the nitrogen oxide concentration at the denitrification inlet for multiple sampling periods, and uses the arithmetic mean as a smoothed concentration value; The computing terminal calculates the absolute value of the concentration deviation between the smoothed concentration value and the redundant concentration values ​​fed back from the pre-stored adjacent detection points. When the absolute value of the concentration deviation is greater than the preset detection failure deviation limit value, the computing terminal extracts the historical calibration concentration empirical value that matches the current operating load value; The computing terminal uses the historical calibrated concentration empirical value to replace the current nitrogen oxide concentration at the denitrification inlet.

[0013] Furthermore, in the primary air turbine stator blade and frequency converter joint optimization control method of the present invention, after the computing terminal generates a frequency reduction command or a stator blade closing command, it further includes: The acquisition terminal continuously acquires the concentration of nitrogen oxides at the denitrification inlet according to a preset time step, generates a numerical gradient sequence composed of concentration values ​​at consecutive time points, and sends the numerical gradient sequence to the computing terminal. The computing terminal receives the numerical gradient sequence; The computing terminal calculates the difference between the first and last parts of the numerical gradient sequence. When the difference between the first and last parts is negative and the current concentration of nitrogen oxides at the denitrification inlet is less than the upper limit threshold of the concentration, the computing terminal generates a parameter locking command and sends it to the frequency converter drive terminal and the stationary blade drive terminal. Furthermore, the primary air fan stator and frequency converter joint optimization control method of the present invention further includes: The acquisition terminal monitors the current operating load value of the coal-fired unit and sends it to the processing terminal; When the current operating load value is greater than the preset peak load upper limit threshold, the computing terminal extracts the pre-stored initial coal-air ratio curve value and sends a load recovery command to the frequency converter drive terminal and the stationary blade drive terminal according to the initial coal-air ratio curve value.

[0014] Beneficial effects of this invention; The primary air fan stator blade and frequency converter joint optimization control method provided by this invention receives real-time data from the acquisition terminal, including the current primary air pressure, current stator blade opening, current frequency converter drive frequency, and current nitrogen oxide concentration at the denitrification inlet. When the current primary air pressure is greater than the target primary air pressure and the current nitrogen oxide concentration at the denitrification inlet is greater than or equal to the upper concentration threshold, the acquisition terminal prioritizes issuing a frequency reduction command to the frequency converter drive. Lowering the current frequency converter drive frequency reduces the total primary air supply to the coal-fired unit, suppresses the oxidation reaction rate in the locally oxygen-rich environment inside the furnace, and reduces the total amount of nitrogen oxides generated at the combustion source.

[0015] After the current variable frequency drive frequency is reduced to the lower limit of frequency safety, resulting in physical operational limitations, if the current nitrogen oxide concentration at the denitrification inlet is still greater than or equal to the upper limit threshold, the computing terminal executes extended control judgment. Under the objective physical conditions that the current stator blade opening is greater than the lower limit of stator blade opening and the current primary air pressure is greater than the lower limit of primary air pressure, the computing terminal issues a stator blade closing command to the stator blade drive. Reducing the current stator blade opening utilizes the shrinking of the inlet guide vane's physical cross-sectional area to cut off excess primary airflow into the coal-fired unit. This control logic breaks the physical constraint of the minimum operating frequency of a single variable frequency drive device, eliminating the risk of overload on the denitrification equipment caused by excessive primary airflow under deep peak shaving and extremely low load conditions.

[0016] Throughout the regulation command issuance process, the primary air pressure safety lower limit and the stator blade opening safety lower limit are consistently set as the underlying protection boundaries. The command interception and numerical comparison mechanism executed at the computing end prevents primary air fan stall and pulverized coal dust accumulation and blockage in the pulverizing pipeline network caused by excessive airflow reduction. The joint optimization control steps, following a strict priority sequence, logically couple the variable frequency speed regulation and stator blade section regulation, simultaneously meeting the environmental emission requirements for exhaust gas in the low-load operating range of the coal-fired unit and the safety assurance requirements for the basic physical operation of the boiler auxiliary equipment. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the method for combined optimization control of primary air fan stator blades and frequency converter according to the present invention. Detailed Implementation

[0019] To make the technical solution of the present invention clearer, the present invention will be clearly and completely described below with reference to specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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. The present invention provided by various embodiments will be described in detail below with reference to the accompanying drawings. To better understand the purpose of the present invention, the present invention will be described in further detail below.

[0020] Please see Figure 1 The present invention provides a method for joint optimization control of primary air fan stator blades and frequency converter, comprising: Step 1: The acquisition terminal obtains the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current nitrogen oxide concentration at the denitrification inlet of the coal-fired unit, and sends the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current nitrogen oxide concentration at the denitrification inlet to the processing terminal. Step 2: The computing terminal receives the current primary air pressure, the current stationary blade opening, the current variable frequency drive frequency, and the current nitrogen oxide concentration at the denitrification inlet; Step 3: The computing terminal extracts the pre-stored target primary air pressure, primary air pressure safety lower limit, stationary blade opening safety lower limit, frequency safety lower limit, and concentration upper limit threshold. Step 4: The computing terminal compares the current primary wind pressure with the lower limit of the primary wind pressure and compares the current stator blade opening with the lower limit of the stator blade opening. Step 5: When the current primary air pressure is greater than the target primary air pressure and the current nitrogen oxide concentration at the denitrification inlet is greater than or equal to the upper limit threshold of the concentration, the computing terminal generates a frequency reduction command and sends the frequency reduction command to the variable frequency drive terminal to instruct the variable frequency drive terminal to reduce the current variable frequency drive frequency according to the frequency reduction command. Step 6: When the current variable frequency drive frequency is equal to the frequency safety lower limit, the current denitrification inlet nitrogen oxide concentration is greater than or equal to the concentration upper limit threshold, the current stationary blade opening is greater than the stationary blade opening safety lower limit, and the current primary air pressure is greater than the primary air pressure safety lower limit, the computing terminal generates a stationary blade closing instruction and sends the stationary blade closing instruction to the stationary blade drive terminal to instruct the stationary blade drive terminal to reduce the current stationary blade opening according to the stationary blade closing instruction.

[0021] In the application scenario of deep peak shaving technology for coal-fired power units, the generator unit enters the extremely low load range, causing a sharp drop in the primary air volume required by the boiler pulverizing system. The acquisition end obtains the current primary air pressure, current stationary blade opening, current variable frequency drive frequency, and current denitrification inlet nitrogen oxide concentration of the coal-fired power unit, and sends the current primary air pressure, current stationary blade opening, current variable frequency drive frequency, and current denitrification inlet nitrogen oxide concentration to the computing end. Among them, the current primary air pressure represents the fluid pressure state inside the primary air header and is measured in kPa; the current stationary blade opening indicates the open ratio of the physical cross-sectional area of ​​the primary air fan inlet guide vanes and is measured in %. The current variable frequency drive frequency reflects the AC frequency output from the frequency converter to the primary air fan motor and is measured in Hz; the current denitrification inlet nitrogen oxide concentration reflects the nitrogen oxide content of the flue gas between the furnace outlet and the selective catalytic reduction unit inlet and is measured in mg per cubic meter. After receiving the current primary air pressure, current stationary blade opening, current variable frequency drive frequency, and current nitrogen oxide concentration at the denitrification inlet, the computing terminal extracts the pre-stored target primary air pressure, primary air pressure safety lower limit, stationary blade opening safety lower limit, frequency safety lower limit, and concentration upper limit threshold. The target primary air pressure is a set target dynamically issued by the main control system based on the coal feed command. The primary air pressure safety lower limit and the stationary blade opening safety lower limit together define the physical boundary for preventing the primary air fan from stalling and ensuring that coal powder transportation does not experience sedimentation and pipe blockage. The frequency safety lower limit is jointly determined by the motor heat dissipation conditions and the variable frequency drive hardware protection settings. Subsequently, the computing unit compares the current primary air pressure with the lower limit of primary air pressure and the current stator blade opening with the lower limit of stator blade opening. When the logical judgment conditions of the current primary air pressure being greater than the target primary air pressure and the current nitrogen oxide concentration at the denitrification inlet being greater than or equal to the upper limit of concentration threshold are met, the computing unit generates a frequency reduction command and sends it to the frequency converter drive end to instruct the frequency converter drive end to reduce the current frequency converter drive frequency according to the frequency reduction command, thereby reducing the air supply volume and directly suppressing the oxidation reaction rate inside the furnace. When the joint judgment conditions of the current frequency converter drive frequency being equal to the lower limit of frequency, the current nitrogen oxide concentration at the denitrification inlet being greater than or equal to the upper limit of concentration threshold, the current stator blade opening being greater than the lower limit of stator blade opening, and the current primary air pressure being greater than the lower limit of primary air pressure are met, the computing unit generates a stator blade closing command and sends it to the stator blade drive end to instruct the stator blade drive end to reduce the current stator blade opening according to the stator blade closing command.

[0022] After generating a frequency reduction command or a deceleration command at the computing end, and before sending the frequency reduction command to the frequency converter drive end or the deceleration command to the deceleration command to the deceleration drive end, the computing end extracts the expected target frequency value corresponding to the frequency reduction command or the expected target opening value corresponding to the deceleration command. Then, based on the pre-set pressure opening mapping coefficient, it multiplies the expected target frequency value or the expected target opening value to obtain the estimated primary wind pressure and the estimated deceleration command. The pressure opening mapping coefficient is set as an empirical transfer function matrix based on the similarity law of fluid mechanics, representing the linear approximation relationship between the rate of change of physical frequency and the rate of change of wind pressure. When the estimated primary wind pressure is lower than the safe lower limit of primary wind pressure, or the estimated deceleration command is lower than the safe lower limit of deceleration command, the computing end stops sending the frequency reduction command to the frequency converter drive end or stops sending the deceleration command to the deceleration drive end.

[0023] The data processing path for constructing the correspondence table between pressure difference and frequency reduction amplitude at the computing end is as follows: the acquisition end collects historical numerical sequences of primary air pressure steady-state deviation under different operating load nodes from the historical operation log of the coal-fired unit, as well as the corresponding historical numerical sequences of inverter frequency compensation. The computing end uses the least squares method to fit a polynomial curve to calculate the nonlinear mapping function between the historical numerical sequences of primary air pressure steady-state deviation and the historical numerical sequences of inverter frequency compensation. The computing end substitutes the independent variable of air pressure deviation into the nonlinear mapping function with an discrete step size of 0.1 kPa and outputs the corresponding dependent variable of frequency compensation. The computing end pairs and stores the independent variable of air pressure deviation and the dependent variable of frequency compensation to generate a correspondence table between pressure difference and frequency reduction amplitude. The data processing path for constructing the correspondence table between concentration difference and target excess air volume reduction amplitude at the computing end is as follows: the computing end extracts pre-stored furnace cross-sectional area parameters of the coal-fired unit and values ​​from the burner air distribution dynamic field test report. The computing end calculates the theoretical air mass flow rate reduction required to restore the nitrogen oxide concentration per unit volume to the standard value based on the law of conservation of mass and the chemical reaction equivalence ratio calculation formula. The computing unit uses the air density constant under standard conditions to convert the theoretical air mass flow rate into the difference in air volume flow rate under standard conditions. The computing unit iterates the above calculation logic in steps of 1 milligram per cubic meter of concentration difference. The computing unit combines the calculated difference in air volume flow rate under standard conditions with the corresponding concentration difference node and writes it into the database, finally generating a table of correspondence between concentration difference and target excess air volume reduction value.

[0024] The processing unit calculates the pressure difference between the current primary wind pressure and the target primary wind pressure. It then extracts a pre-established table mapping pressure difference to frequency reduction magnitude and queries the table for the preferred frequency reduction magnitude that matches the pressure difference. This table internally stores discrete mapping node data of wind pressure deviation and frequency compensation values ​​under different operating conditions. When the logical condition that the difference between the current variable frequency drive frequency and the preferred frequency reduction magnitude is greater than or equal to the lower frequency safety limit is met, the processing unit generates a frequency reduction command based on the preferred frequency reduction magnitude and sends it to the variable frequency drive. When the logical condition that the difference between the current variable frequency drive frequency and the preferred frequency reduction magnitude is less than the lower frequency safety limit is met, the processing unit updates the preferred frequency reduction magnitude using the difference between the current variable frequency drive frequency and the lower frequency safety limit, generates a frequency reduction command based on the updated preferred frequency reduction magnitude, and sends it to the variable frequency drive.

[0025] The processing unit receives the current feedback frequency from the frequency converter drive. When the current feedback frequency equals the lower limit of frequency safety, it generates a frequency lock status flag and sets this flag as a high-level trigger signal within the control logic status register for subsequent calculations. Upon detecting the frequency lock status flag, the processing unit calculates the concentration difference between the current inlet nitrogen oxide concentration and the upper limit threshold. It then extracts a pre-stored table of correspondence between concentration differences and target excess airflow reduction values. The corresponding target excess airflow reduction value is then retrieved from this table, defining the target excess airflow reduction value as the standard state air volume flow rate difference required to bring the nitrogen oxide concentration back to the normal range, measured in m³ / h. The processing unit converts the target excess airflow reduction value into a stator blade opening adjustment parameter, generates a stator blade closing command based on this parameter, and sends the command to the stator blade drive.

[0026] When the operating load command of a coal-fired unit increases rapidly, causing a significant increase in the air supply demand of the boiler combustion system, the primary air pressure tends to decrease. The computing unit retrieves the pre-stored safe upper limit value for the stationary vane opening. When the current primary air pressure is less than the target primary air pressure, the computing unit generates a command to open the stationary vanes and sends it to the stationary vane drive. This utilizes the increased cross-sectional area of ​​the stationary vane channel, which causes a synchronous decrease in the fluid resistance of the air supply channel. Subsequently, the acquisition unit collects the value of the stationary vane opening after the command is executed and sends it to the computing unit. The computing unit receives the value of the opened stationary vane opening. When the combined logical conditions of the opened stationary vane opening value being equal to the safe upper limit value and the current primary air pressure being less than the target primary air pressure are met, the computing unit generates a frequency upsampling command and sends it to the frequency converter drive.

[0027] The acquisition unit collects the furnace temperature distribution matrix, coal supply values, and secondary air supply values ​​of the coal-fired power unit, and sends these data to the processing unit. The furnace temperature distribution matrix aggregates real-time temperature node values ​​from multiple thermocouple sensors located around the burner elevation, measured in °C. The coal supply values ​​represent the mass of fuel transported per unit time by the feeder conveyor belt, measured in t / h. The processing unit receives the furnace temperature distribution matrix, coal supply values, and secondary air supply values, and concatenates them into a multidimensional physical state feature vector. It then extracts pre-stored dot product calculation rules, which include a node weight matrix containing a mapping constant array representing the connection strength of hidden layer neurons corresponding to the input layer physical quantities. The processing unit calculates the dot product between the multidimensional physical state feature vector and the node weight matrix according to the dot product calculation rules, and uses the result as the current nitrogen oxide concentration at the denitrification inlet.

[0028] When the physical properties of coal are altered during combustion in a boiler, the data acquisition unit collects data on the fineness, moisture content, and fluid resistance of the pulverized coal from the coal-fired unit's pulverizing pipeline. This data is then transmitted to the processing unit. The fineness of the pulverized coal indicates the average particle size distribution of the coal particles and is measured in μm. The moisture content records the mass fraction of bound water within the fuel. The fluid resistance is calculated from the difference in readings of pressure transmitters along the pipeline and is measured in Pa. The processing unit receives these data and performs a weighted summation based on pre-set weighting parameters to obtain the critical wind speed standard value for maintaining the suspended fluidized state of the pulverized coal. Since the increased moisture content increases the drag required for the suspended airflow of the pulverized coal particles, the weighted summation dynamically calculates the minimum oxygen-carrying wind speed limit. The computing unit multiplies the critical wind speed standard value with the preset safety margin coefficient to obtain the updated primary wind pressure safety lower limit value and the updated stator blade opening safety lower limit value. The updated primary wind pressure safety lower limit value and the updated stator blade opening safety lower limit value are then used to overwrite the pre-stored primary wind pressure safety lower limit value and the pre-stored stator blade opening safety lower limit value.

[0029] The acquisition unit obtains the current operating load value of the coal-fired power unit and sends it to the processing unit. The current operating load value is defined as representing the active power output parameter of the generator stator, with the unit of measurement being MW. The processing unit receives the denitrification inlet nitrogen oxide concentration from multiple sampling periods continuously sent by the acquisition unit, specifying the sampling period as the digital scanning cycle value of the control system. The processing unit calculates the arithmetic mean of the denitrification inlet nitrogen oxide concentration from multiple sampling periods, using this arithmetic mean as the smoothed concentration value. The arithmetic mean calculation method filters out high-frequency spikes and abrupt changes caused by power frequency electromagnetic interference. Subsequently, the processing unit calculates the absolute value of the concentration deviation between the smoothed concentration value and the redundant concentration values ​​fed back from pre-stored adjacent detection points. When the absolute value of the concentration deviation exceeds a preset detection failure deviation threshold, the processing unit extracts a historical calibration concentration empirical value that matches the current operating load value. This historical calibration concentration empirical value comes from a dictionary of benchmark performance curves measured by the unit performance testing equipment at various load conditions. Finally, the processing unit replaces the current denitrification inlet nitrogen oxide concentration with the historical calibration concentration empirical value.

[0030] After the unit resumes operation at increased load following a period of stagnation in the peak-shaving depth range, the acquisition unit continuously collects the concentration of nitrogen oxides at the denitrification inlet at a preset time step, generating a numerical gradient sequence composed of concentration values ​​at consecutive time points. This numerical gradient sequence is then sent to the processing unit, which sets a preset time step to match the dynamic response time constant limit of the denitrification chemical reaction. The processing unit receives the numerical gradient sequence and calculates the difference between the first and last values. When the difference is negative and the current nitrogen oxide concentration at the denitrification inlet is less than the upper concentration threshold, the processing unit generates a parameter locking command and sends it to the frequency converter drive and the stationary blade drive. A negative difference indicates that the flue gas nitrogen oxide concentration parameter is in a monotonically decreasing state. The acquisition unit monitors the current operating load of the coal-fired unit and sends it to the processing unit. When the current operating load is greater than the preset peak-shaving load upper limit threshold, the processing unit extracts the pre-stored initial coal-air ratio curve value and sends a load recovery command to the frequency converter drive and the stationary blade drive according to the initial coal-air ratio curve value.

[0031] The processing unit receives the furnace temperature distribution matrix, coal supply values, and secondary air supply values ​​sent by the acquisition unit, and concatenates these values ​​into a multidimensional physical state feature vector. The processing unit extracts pre-stored dot product calculation rules, which include a node weight matrix. Following these rules, the processing unit calculates the dot product of the multidimensional physical state feature vector and the node weight matrix, and uses this result as the current nitrogen oxide concentration at the denitrification inlet. The specific dot product formula is as follows: In the above formula for dot product: This represents the current concentration of nitrogen oxides at the denitrification inlet, measured in mg per cubic meter. The node weight matrix represents a mapping constant array that reflects the connection strength of neurons in the hidden layer corresponding to the physical quantities in the input layer. It represents a multidimensional physical state feature vector, which is composed of the furnace temperature distribution matrix, coal supply values, and secondary air supply values ​​spliced ​​together in the data dimension.

[0032] The computational end internally constructs a nitrogen oxide (NOx) generation prediction model, which is set as a single-layer perceptron network topology. The single-layer perceptron network topology includes an input layer and an output layer. The number of nodes in the input layer is equal to the data dimension of the multi-dimensional physical state feature vector. The output layer is set as a single node to output the predicted value of the NOx concentration at the denitrification inlet. A node weight matrix is ​​configured between the input and output layers, representing the connection weights of different physical quantities from the input nodes to the output nodes. During the NOx generation prediction model training phase, the acquisition end collects multiple sets of operating data from the coal-fired unit under historical stable load conditions. The historical furnace temperature distribution matrix, historical coal supply values, and historical secondary air supply values ​​are concatenated and combined to form a historical multi-dimensional feature vector sample set. Simultaneously, the acquisition end collects the measured values ​​of the NOx concentration at the denitrification inlet at the time nodes corresponding to the historical multi-dimensional feature vector sample set, using these measured values ​​as the true label data. The computational end inputs the historical multi-dimensional feature vector sample set into the NOx generation prediction model and executes internal calculations to obtain the predicted label data. The computational end uses the mean squared error loss function to calculate the physical concentration error between the predicted and actual label data. It employs a gradient descent optimization algorithm, iteratively updating the numerical variables within the node weight matrix according to the gradient direction that reduces the physical concentration error. When the physical concentration error is less than a preset convergence tolerance value, or when the number of iterations reaches the set maximum iteration limit, the computational end stops training and stores the currently fixed node weight matrix as the dot product calculation rule in its storage space. The input and output data of the multidimensional physical state feature vector have a physical reaction mapping relationship. The furnace temperature distribution matrix directly determines the generation rate of thermal nitrogen oxides, the coal supply value reflects the total amount of fuel-type nitrogen elements participating in combustion, and the secondary air supply value determines the oxygen distribution concentration in the combustion zone. The computational end uses these three dimensions of physical quantities as input data to comprehensively cover the key reaction boundary conditions for nitrogen oxide generation, establishing a rigorous mathematical correlation model between the combustion-side input variables and the exhaust gas emission-side output variables.

[0033] When the physical properties of coal used in boiler combustion change, the data acquisition unit collects the coal powder fineness, coal powder moisture content, and pipeline fluid resistance values ​​from the coal-fired unit's pulverizing pipeline. These values ​​are then sent to the processing unit. The processing unit performs a weighted summation calculation on these values ​​based on pre-set weighting parameters to obtain the critical wind speed standard value for maintaining the suspended fluidized state of the coal powder. The weighted summation calculation dynamically calculates the minimum oxygen-carrying wind speed requirement. The specific formula for the weighted summation calculation is as follows: In the above weighted summation formula: This represents the standard value of the critical wind speed, measured in m / s. This represents a pre-defined weighting parameter for the fineness of pulverized coal. This represents the fineness of pulverized coal, measured in μm. This represents the pre-set weighted ratio of coal powder moisture content. This represents the moisture content of pulverized coal, expressed as a percentage by mass. This represents a pre-defined parameter that accounts for the weighting of fluid resistance in the pipeline. This represents the fluid resistance value in the pipeline, measured in Pa. After obtaining the standard value of the critical wind speed, the calculation terminal multiplies this value by a preset safety margin coefficient to obtain the updated lower limit of primary wind pressure and the updated lower limit of stator blade opening. The specific formula for the multiplication operation is as follows: In the above product operation formula: This represents the updated lower limit of primary wind pressure, measured in kPa. This represents the standard value of the critical wind speed, measured in m / s. This represents the pre-set safety margin factor for wind pressure conversion; This represents the updated lower safety limit for the stationary blade opening, measured in % (%). This represents the pre-set safety margin factor for the stationary blade opening conversion.

[0034] To verify the engineering feasibility of the aforementioned data processing path and computational logic, a complete overall implementation example of data processing is provided. The acquisition end collects the physical state parameters of the coal-fired unit in real time and sends these parameters to the computation end. The computation end combines the scalarized values ​​of the furnace temperature distribution matrix (1000), coal supply (50), and secondary air supply (120) to generate a multidimensional physical state feature vector X. The computation end extracts the internally recorded node weight matrix W, which includes corresponding values ​​of 0.2, 1.5, and 0.8 for three dimensions. The computation end performs a dot product operation to calculate the result of the multidimensional physical state feature vector multiplied by the node weight matrix, yielding the current denitrification inlet nitrogen oxide concentration Nact value of 371 mg / m³. Simultaneously, the acquisition end collects and sends the coal powder fineness value Cf (20 μm), coal powder moisture value Mw (10%), and pipeline fluid resistance value Rp (1500 Pa) of the pulverizing pipeline transportation line to the computation end. The computational end extracts the following weighting parameters: coal powder fineness weighting α = 0.5, coal powder moisture weighting β = 1.2, and pipeline fluid resistance weighting γ = 0.01. A weighted summation operation is performed to obtain the critical wind speed standard value Vc = 37 m / s. Finally, the computational end extracts the wind pressure conversion safety margin coefficient Kp = 0.1 and the stationary blade opening conversion safety margin coefficient Kv = 0.8. A product operation is performed to obtain the updated primary wind pressure safety lower limit Pmin = 3.7 kPa and the updated stationary blade opening safety lower limit Vmin = 29.6%. The computational end uses the updated primary wind pressure safety lower limit of 3.7 kPa and the updated stationary blade opening safety lower limit of 29.6% to overwrite the pre-stored primary wind pressure safety lower limit and the pre-stored stationary blade opening safety lower limit, completing the dynamic optimization and adjustment of the physical parameters throughout the entire process.

[0035] The present invention provides a method for joint optimization control of primary air fan stator blades and frequency converter, which is applied to a joint optimization control system for primary air fan stator blades and frequency converter. The joint optimization control system for primary air fan stator blades and frequency converter includes: The data receiving module is used to control the acquisition terminal to acquire the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current denitrification inlet nitrogen oxide concentration of the coal-fired unit, and to send the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current denitrification inlet nitrogen oxide concentration to the computing terminal, and to control the computing terminal to receive the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current denitrification inlet nitrogen oxide concentration; The threshold extraction module is used to control the computing terminal to extract the pre-stored target primary air pressure, primary air pressure safety lower limit, still blade opening safety lower limit, frequency safety lower limit, and concentration upper limit threshold. The numerical comparison module is used to control the computing terminal to compare the current primary wind pressure obtained by the data receiving module with the safe lower limit value of the primary wind pressure extracted by the threshold extraction module, and to compare the current stator blade opening obtained by the data receiving module with the safe lower limit value of the stator blade opening extracted by the threshold extraction module, and output the physical state comparison result. The frequency reduction control module is used to control the computing terminal to generate a frequency reduction command and send the frequency reduction command to the frequency converter drive terminal when the physical state comparison result is that the current primary air pressure is greater than the target primary air pressure and the current nitrogen oxide concentration at the denitrification inlet is greater than or equal to the upper limit threshold of the concentration. This command instructs the frequency converter drive terminal to reduce the current frequency converter drive frequency according to the frequency reduction command. The stator blade control module is used to control the computing terminal to generate a stator blade closing instruction and send the stator blade closing instruction to the stator blade drive terminal when the physical state comparison result is that the current variable frequency drive frequency is equal to the frequency safety lower limit, the current denitrification inlet nitrogen oxide concentration is greater than or equal to the concentration upper limit threshold, the current stator blade opening is greater than the stator blade opening safety lower limit, and the current primary air pressure is greater than the primary air pressure safety lower limit.

[0036] The various control thresholds extracted by the computing end are supported by physical basis and engineering operation data. The computing end calculates the target primary air pressure based on the current coal feed rate. At an operating load of 180 MW, the control system sets the target primary air pressure to 7.00 kPa. The control system sets the lower safety limit for primary air pressure to 6.84 kPa, which is the minimum hydrodynamic value required to ensure that pulverized coal remains suspended in long-distance conveying pipelines without sedimentation or blockage. The control system sets the lower safety limit for stator blade opening to 37.05%, which is a physical protection boundary to prevent the primary air fan from triggering stall, surge, and aerodynamic instability conditions when operating in extremely low flow areas. The control system sets the lower safety limit for frequency to 30.00 Hz, which comprehensively considers the minimum switching frequency limit of the inverter's insulated gate bipolar transistor module and the minimum cooling airflow requirement of the primary air fan drive motor's built-in cooling fan at low speeds. The control system sets the upper limit threshold for nitrogen oxide concentration at 350 mg / m³, corresponding to the ultra-low emission assessment standard for coal-fired power generating units issued by the national environmental protection department. The control system sets the detection failure deviation limit at 30 mg / m³, representing the maximum physical distribution error of redundantly configured nitrogen oxide sensors on the same measurement cross-section within the allowable range of normal measurement. The control system sets the upper limit threshold for peak load at 220 MW, which is the load division node where the boiler's main burner switches to the stabilizing oil gun and all pulverized coal burners operate independently. The control system sets the safe upper limit for stator vane opening at 85.00%, which is the physical opening state when the stator vane adjustment mechanism's transmission linkage is in the maximum mechanical travel limit switch contact position.

[0037] When a coal-fired unit enters a low-load operating range under deep peak-shaving conditions, the actual air supply required by the boiler combustion system is significantly reduced. To establish accurate physical safety boundaries and environmental variable prediction benchmarks, the data acquisition unit collects real-time data on the coal powder fineness (25 μm), coal powder moisture content (12%), and pipeline fluid resistance (1600 Pa) of the pulverizing pipeline. These data are then sent to the processing unit. Upon receiving these physical parameters, the processing unit extracts pre-set weighted parameters for coal powder fineness (0.6), coal powder moisture content (1.5), and pipeline fluid resistance (0.015). The processing unit performs a continuous algebraic summation of the product of the coal powder fineness and its corresponding weighted parameter, the product of the coal powder moisture content and its corresponding weighted parameter, and the product of the pipeline fluid resistance and its corresponding weighted parameter, yielding a critical wind speed standard of 57 m / s for maintaining the suspended fluidized state of the coal powder. The processing unit extracts the pre-set safety margin coefficients of 0.12 for wind pressure conversion and 0.65 for stator blade opening conversion. It then performs independent multiplication of the critical wind speed standard value with each of the two safety margin coefficients to obtain an updated lower limit for primary wind pressure of 6.84 kPa and an updated lower limit for stator blade opening of 37.05%. The processing unit uses 6.84 kPa and 37.05% to cover the initial corresponding boundary values ​​pre-stored by the system. In the synchronous prediction step, the acquisition unit collects the characteristic values ​​representing the furnace temperature distribution matrix of the coal-fired unit (1050℃), coal supply (60 t / h), and secondary air supply (150 t / h) and sends them to the processing unit. The processing unit sequentially concatenates and combines 1050℃, 60 t / h, and 150 t / h along the data dimension to generate a multi-dimensional physical state feature vector. The processing unit extracts the pre-stored dot product calculation rules and retrieves the node weight matrix containing the corresponding dimension mapping values ​​of 0.25, 1.20, and 0.85. Following the dot product calculation rules, the processing unit performs a one-to-one multiplication of each element in the multidimensional physical state feature vector with each element in the node weight matrix, and then globally accumulates the results. The resulting value of 382 mg / m³ is used as the benchmark value for the current nitrogen oxide concentration at the denitrification inlet for subsequent logical comparisons.

[0038] After completing the physical boundary definition and predicted state assessment, the data acquisition unit obtains the current primary air pressure (7.50 kPa), current stator blade opening (45.00%), current variable frequency drive frequency (32.00 Hz), and the measured current denitrification inlet nitrogen oxide concentration (382 mg / m³) of the coal-fired unit. It also sends the measured fluid pressure, physical cross-sectional area ratio, AC frequency, and flue gas pollutant content data to the processing unit. The processing unit extracts the pre-stored target primary air pressure (7.00 kPa), primary air pressure safety lower limit (6.84 kPa), stator blade opening safety lower limit (37.05%), frequency safety lower limit (30.00 Hz), and concentration upper limit (350 mg / m³). The processing unit compares the current primary air pressure (7.50 kPa) with the primary air pressure safety lower limit (6.84 kPa) to determine that the fluid pressure has not exceeded the lower limit, and compares the current stator blade opening (45.00%) with the stator blade opening safety lower limit (37.05%) to determine that the equipment is not in the stall range. Under the combined physical conditions that the current primary air pressure (7.50 kPa) is greater than the target primary air pressure (7.00 kPa) and the current nitrogen oxide concentration at the denitrification inlet (382 mg / m³) is greater than the upper limit threshold (350 mg / m³), the computing unit initiates the pressure reduction and emission reduction execution logic. The computing unit calculates the pressure difference between the current and target primary air pressures to be 0.50 kPa. It then extracts a pre-established table of the correspondence between pressure difference and frequency reduction amplitude, finding that the preferred frequency reduction amplitude matching the 0.50 kPa pressure difference is 3.00 Hz. Finally, the computing unit calculates the current variable frequency drive frequency (32.00 Hz) minus the preferred frequency reduction amplitude of 3.00 Hz to obtain the estimated operating frequency of 29.00 Hz. Under the condition that the estimated operating frequency of 29.00Hz is less than the frequency safety lower limit of 30.00Hz, the computing end uses the current inverter drive frequency of 32.00Hz to subtract the frequency safety lower limit of 30.00Hz to obtain the updated difference of 2.00Hz, and uses 2.00Hz to update the preferred frequency reduction amplitude value. The computing end extracts the expected target frequency value of 30.00Hz corresponding to the updated preferred frequency reduction amplitude value of 2.00Hz, extracts the pre-set pressure opening mapping coefficient of 0.05, which represents the linear correspondence between the rate of change of physical frequency and the rate of change of wind pressure, and performs the product calculation of the expected target frequency value and the pressure opening mapping coefficient to obtain the estimated primary wind pressure of 7.10kPa. Under the condition that the estimated primary wind pressure of 7.10kPa is not lower than the primary wind pressure safety lower limit of 6.84kPa, the computing end generates a frequency reduction command according to the updated preferred frequency reduction amplitude value of 2.00Hz and sends the frequency reduction command to the inverter drive end. The frequency converter drive reduces the frequency of the AC power output from the internal inverter to 30.00Hz according to the frequency reduction command.

[0039] After the frequency converter driver completes the frequency reduction action, the computing terminal receives the current feedback frequency of 30.00Hz from the frequency converter driver. When the current feedback frequency equals the frequency safety lower limit of 30.00Hz, the computing terminal generates a high-level frequency lock status flag. When the computing terminal detects the frequency lock status flag, it re-receives the real-time operating data from the acquisition terminal and finds that the current nitrogen oxide concentration at the denitrification inlet has decreased to 365mg / m³ but is still greater than the upper limit threshold of 350mg / m³. The computing terminal calculates that the concentration difference between the current nitrogen oxide concentration at the denitrification inlet (365mg / m³) and the upper limit threshold (350mg / m³) is 15mg / m³. The computing terminal retrieves the pre-stored correspondence table between the concentration difference and the target excess air volume reduction value, and queries the data table to find that the target excess air volume reduction value corresponding to 15mg / m³ is 8000m³ / h. The calculation unit divides the target excess air volume reduction value in volumetric flow rate form by the constant coefficient recorded on the equipment nameplate to convert it into a stator vane opening adjustment parameter of 5.00%. The calculation unit extracts the current stator vane opening of 45.00% and subtracts the stator vane opening adjustment parameter of 5.00% to obtain the expected target opening value of 40.00%. After verifying that the expected target opening value does not exceed the physical limit by performing a product calculation according to the aforementioned logic, the calculation unit generates a stator vane closing command according to the stator vane opening adjustment parameter of 5.00% and sends the stator vane closing command to the stator vane drive unit. The stator vane drive unit drives the servo motor to perform mechanical action, reducing the current stator vane opening of the guide vanes to 40.00% according to the stator vane closing command, thus blocking excess air from entering the furnace to participate in the oxidation reaction from the perspective of physical channel cross-sectional area.

[0040] During the entire cycle of deep peak shaving and low load control, the acquisition terminal obtains the current operating load value of 180MW for the coal-fired unit and sends it to the processing terminal. The processing terminal continuously receives the nitrogen oxide concentration measurement data at the denitrification inlet from the acquisition terminal for five consecutive sampling cycles. The processing terminal performs an arithmetic mean calculation by adding the five consecutive measurement data and dividing by 5, and uses the smoothed arithmetic mean as the smoothed concentration value in the correction calculation. The processing terminal calculates the absolute value of the concentration deviation between the smoothed concentration value and the redundant concentration values ​​fed back from adjacent detection points in the pre-stored data. When the absolute value of the concentration deviation suddenly rises to 45mg / m³ due to ash buildup in the thermal measurement sensor pipeline, which exceeds the preset detection failure deviation limit of 30mg / m³, the processing terminal extracts the historical calibration concentration empirical value of 340mg / m³ that matches the current operating load value of 180MW from the internal dictionary. The processing terminal replaces the current denitrification inlet nitrogen oxide concentration that has drifted with the historical calibration concentration empirical value of 340mg / m³. As the combustion material ratio reaches a new steady-state equilibrium, the acquisition unit continuously collects the nitrogen oxide concentration at the denitrification inlet according to a preset time step, generating a numerical gradient sequence composed of concentration values ​​at continuous time points, which is then sent to the calculation unit. The calculation unit calculates that the difference between the latest value at the end of the numerical gradient sequence and the historical value at the beginning is -12 mg / m³. When the difference is negative and the current nitrogen oxide concentration at the denitrification inlet gradually decreases to 338 mg / m³, which is less than the upper limit threshold of 350 mg / m³, the calculation unit generates a parameter locking command and simultaneously sends it to the frequency converter drive and the stationary blade drive to keep the mechanical actuators stationary. After a period of peak-shaving dwell time, the power grid dispatch center issues a load increase command. The acquisition unit monitors the current operating load value of the coal-fired unit and it climbs to 250 MW and sends it to the calculation unit. When the current operating load value of 250 MW is greater than the preset upper limit threshold of peak-shaving load of 220 MW, the boiler system's air supply demand surges, causing the current primary air pressure to drop to 6.50 kPa, which is less than the target primary air pressure of 7.50 kPa. The processing unit extracts the pre-stored safe upper limit value of the stator blade opening (85.00%), generates a stator blade opening command, and sends it to the stator blade drive. The acquisition unit collects the stator blade opening value (85.00%) after the stator blade drive completes its action and sends it to the processing unit. When the stator blade opening value after opening equals the safe upper limit value of the stator blade opening (85.00%) and the current primary air pressure is still less than the target primary air pressure, the processing unit extracts the pre-stored initial coal-air ratio curve value, generates a frequency increase command according to the initial coal-air ratio curve value, and sends it to the frequency converter drive, instructing the frequency converter to significantly increase the output frequency to fully meet the pulverized coal conveying airflow requirements of the high-load burnout zone after the coal-fired unit exits deep peak shaving.

[0041] To further verify the practical engineering application effect of the primary air turbine stator blade and frequency converter joint optimization control method provided by this invention, the following objective explanation is based on comparative experimental data from a 600 MW coal-fired power plant unit. In the first test phase, the coal-fired power plant unit operated at a deep peak-shaving, extremely low load condition of 180 MW, and the control system used conventional frequency converter individual adjustment logic. The testing instrument recorded that the frequency converter drive frequency stopped decreasing when it reached the hardware threshold of 30.00 Hz. At this time, the measured primary air pressure was 7.45 kPa, and the nitrogen oxide concentration at the denitrification inlet continued to rise and remained at 395 mg / m³, significantly exceeding the environmental protection limit of 350 mg / m³. Simultaneously, the ammonia injection rate of the denitrification system reached 120 kg / hour, indicating a serious risk of ammonia escape. In the second test phase, the coal-fired power plant unit remained at a deep peak-shaving, extremely low load condition of 180 MW, and the control system was switched to the joint optimization control method. After detecting that the frequency converter drive frequency reached 30.00 Hz and the nitrogen oxide concentration at the denitrification inlet was 395 mg / m³, the computing terminal issued a command to close the stationary blades according to the timing logic. The stationary blade drive reduced the current stationary blade opening from the initial 45.00% to 38.50%. After a 15-minute stabilization period of furnace combustion conditions, the testing instrument recorded that the measured primary air pressure steadily decreased to 6.95 kPa, and the primary air pressure did not trigger the alarm at the 6.84 kPa safety lower limit. The nitrogen oxide concentration at the denitrification inlet decreased significantly and stabilized at 320 mg / m³, fully meeting the upper limit threshold requirement of below 350 mg / m³. At the same time, the ammonia injection rate of the denitrification system decreased to 85 kg / h. The experimental data fully demonstrates that the joint optimization control method can effectively cut off the excess primary air volume under extremely low load conditions, significantly reducing the total nitrogen oxide generation and alleviating the operating load of the denitrification equipment while ensuring the fluid pressure safety of the boiler pulverizing system.

Claims

1. A method for joint optimization control of primary air fan stator blades and frequency converter, characterized in that, include: The acquisition terminal obtains the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current nitrogen oxide concentration at the denitrification inlet of the coal-fired unit, and sends the current primary air pressure, current stator blade opening, current variable frequency drive frequency, and current nitrogen oxide concentration at the denitrification inlet to the processing terminal; The computing terminal receives the current primary air pressure, the current stationary blade opening, the current variable frequency drive frequency, and the current nitrogen oxide concentration at the denitrification inlet; The computing terminal extracts the pre-stored target primary air pressure, primary air pressure safety lower limit, still blade opening safety lower limit, frequency safety lower limit, and concentration upper limit threshold. The computing terminal compares the current primary wind pressure with the safe lower limit of the primary wind pressure, and compares the current stator blade opening with the safe lower limit of the stator blade opening. When the current primary air pressure is greater than the target primary air pressure and the current nitrogen oxide concentration at the denitrification inlet is greater than or equal to the upper limit threshold of the concentration, the computing terminal generates a frequency reduction command and sends the frequency reduction command to the variable frequency drive terminal to instruct the variable frequency drive terminal to reduce the current variable frequency drive frequency according to the frequency reduction command; When the current variable frequency drive frequency is equal to the frequency safety lower limit, the current denitrification inlet nitrogen oxide concentration is greater than or equal to the concentration upper limit threshold, the current stationary blade opening is greater than the stationary blade opening safety lower limit, and the current primary air pressure is greater than the primary air pressure safety lower limit, the computing terminal generates a stationary blade closing instruction and sends the stationary blade closing instruction to the stationary blade drive terminal to instruct the stationary blade drive terminal to reduce the current stationary blade opening according to the stationary blade closing instruction.

2. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 1, characterized in that, After the arithmetic terminal generates a frequency reduction command or a stator blade closing command, and before sending the frequency reduction command to the inverter drive terminal or the stator blade closing command to the stator blade drive terminal, the method further includes: The computing terminal extracts the expected target frequency value corresponding to the frequency reduction instruction or the expected target opening value corresponding to the closing silent leaf instruction; The computing terminal calculates the expected target frequency value or the expected target opening value by multiplying them according to the preset pressure opening mapping coefficient to obtain the estimated primary wind pressure and the estimated stationary blade opening. When the estimated primary wind pressure is lower than the safe lower limit of primary wind pressure, or when the estimated stator blade opening is lower than the safe lower limit of stator blade opening, the computing terminal stops sending the frequency reduction command to the frequency converter drive terminal, or stops sending the stator blade closing command to the stator blade drive terminal.

3. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 2, characterized in that, The processing terminal generates a frequency reduction command and sends the frequency reduction command to the frequency converter drive terminal, including: The computing terminal calculates the pressure difference between the current primary wind pressure and the target primary wind pressure; The computing terminal extracts a pre-established table of correspondence between pressure difference and frequency reduction amplitude, and queries the table of correspondence between pressure difference and frequency reduction amplitude to find the preferred frequency reduction amplitude value that matches the pressure difference. When the difference between the current variable frequency drive frequency and the preferred frequency reduction magnitude value is greater than or equal to the frequency safety lower limit value, the computing terminal generates the frequency reduction command according to the preferred frequency reduction magnitude value and sends the frequency reduction command to the variable frequency drive terminal. When the difference between the current variable frequency drive frequency and the preferred frequency reduction amplitude value is less than the frequency safety lower limit value, the computing terminal updates the preferred frequency reduction amplitude value using the difference between the current variable frequency drive frequency and the frequency safety lower limit value, generates the frequency reduction command based on the updated preferred frequency reduction amplitude value, and sends the frequency reduction command to the variable frequency drive terminal.

4. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 3, characterized in that, The processing terminal generates a command to close the stator blades and sends the command to the stator blade driver terminal, including: The computing terminal receives the current feedback frequency sent by the frequency conversion drive terminal. When the current feedback frequency is equal to the frequency safety lower limit, the computing terminal generates a frequency lock status identifier. When the computing terminal detects the frequency lock status flag, the computing terminal calculates the concentration difference between the current nitrogen oxide concentration at the denitrification inlet and the upper limit threshold concentration. The computing terminal extracts a pre-stored table of correspondence between concentration difference and target excess air volume reduction value, and queries the table of correspondence between concentration difference and target excess air volume reduction value to find the target excess air volume reduction value corresponding to the concentration difference. The computing terminal converts the target excess air volume reduction value into a stator blade opening adjustment parameter, generates the stator blade closing command based on the stator blade opening adjustment parameter, and sends the stator blade closing command to the stator blade drive terminal.

5. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 4, characterized in that, Also includes: The computing terminal extracts the pre-stored safe upper limit value of the still blade opening; When the current primary wind pressure is less than the target primary wind pressure, the computing terminal generates a command to open the stator blades and sends the command to the stator blade drive terminal. The acquisition terminal acquires the value of the opening degree of the stationary blade after executing the command to open the stationary blade and sends it to the processing terminal. The processing terminal receives the value of the stationary blade opening degree after it is opened larger; When the value of the stator blade opening after the opening is increased is equal to the safe upper limit of the stator blade opening and the current primary wind pressure is less than the target primary wind pressure, the computing terminal generates an up-frequency command and sends the up-frequency command to the frequency converter drive terminal.

6. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 5, characterized in that, The acquisition terminal obtains the current nitrogen oxide concentration at the denitrification inlet of the coal-fired power unit, and the processing terminal receives the current nitrogen oxide concentration at the denitrification inlet sent by the acquisition terminal, including: The acquisition terminal acquires the furnace temperature distribution matrix, coal supply value, and secondary air supply value of the coal-fired unit, and sends the furnace temperature distribution matrix, coal supply value, and secondary air supply value to the computing terminal. The computing terminal receives the furnace temperature distribution matrix, the coal supply value, and the secondary air supply value; The computing terminal concatenates the furnace temperature distribution matrix, the coal supply value, and the secondary air supply value into a multi-dimensional physical state feature vector. The computing terminal extracts pre-stored dot product result calculation rules, which include a node weight matrix; The computing terminal calculates the dot product of the multidimensional physical state feature vector and the node weight matrix according to the dot product result calculation rules, and uses the dot product result as the current nitrogen oxide concentration at the denitrification inlet.

7. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 6, characterized in that, Before the computing terminal extracts the pre-stored primary wind pressure safety lower limit value and the stator blade opening safety lower limit value, it also includes: The acquisition terminal acquires the coal powder fineness value, coal powder moisture value, and pipeline fluid resistance value of the coal-fired unit's pulverizing pipeline transportation line, and sends the coal powder fineness value, coal powder moisture value, and pipeline fluid resistance value to the computing terminal; The computing terminal receives the coal powder fineness value, the coal powder moisture value, and the pipeline fluid resistance value; The computing terminal performs weighted summation calculations on the coal powder fineness value, the coal powder moisture value, and the pipeline fluid resistance value according to the preset weight ratio parameters, to obtain the critical wind speed standard value for maintaining the suspended fluidized state of coal powder. The computing terminal multiplies the critical wind speed standard value with the preset safety margin coefficient to obtain the updated primary wind pressure safety lower limit value and the updated stator blade opening safety lower limit value. The computing terminal uses the updated primary wind pressure safety lower limit and the updated stationary blade opening safety lower limit to overwrite the pre-stored primary wind pressure safety lower limit and the pre-stored stationary blade opening safety lower limit.

8. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 7, characterized in that, After acquiring the current nitrogen oxide concentration at the denitrification inlet of the coal-fired power unit, the acquisition terminal also includes: The acquisition terminal obtains the current operating load value of the coal-fired unit and sends the current operating load value to the processing terminal; The processing terminal receives the nitrogen oxide concentration at the denitrification inlet from multiple sampling cycles continuously sent by the acquisition terminal; The computing terminal calculates the arithmetic mean of the nitrogen oxide concentration at the denitrification inlet for multiple sampling periods, and uses the arithmetic mean as a smoothed concentration value; The computing terminal calculates the absolute value of the concentration deviation between the smoothed concentration value and the redundant concentration values ​​fed back from the pre-stored adjacent detection points. When the absolute value of the concentration deviation is greater than the preset detection failure deviation limit value, the computing terminal extracts the historical calibration concentration empirical value that matches the current operating load value; The computing terminal uses the historical calibrated concentration empirical value to replace the current nitrogen oxide concentration at the denitrification inlet.

9. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 8, characterized in that, After the computing terminal generates a frequency reduction instruction or a silent blade closing instruction, it also includes: The acquisition terminal continuously acquires the concentration of nitrogen oxides at the denitrification inlet according to a preset time step, generates a numerical gradient sequence composed of concentration values ​​at consecutive time points, and sends the numerical gradient sequence to the computing terminal. The computing terminal receives the numerical gradient sequence; The computing terminal calculates the difference between the first and last parts of the numerical gradient sequence. When the difference is negative and the current nitrogen oxide concentration at the denitrification inlet is less than the upper limit threshold, the computing terminal generates a parameter locking command and sends it to the frequency converter drive and the stationary blade drive.

10. The method for joint optimization control of primary air fan stator blades and frequency converter according to claim 9, characterized in that, Also includes: The acquisition terminal monitors the current operating load value of the coal-fired unit and sends it to the processing terminal; When the current operating load value is greater than the preset peak load upper limit threshold, the computing terminal extracts the pre-stored initial coal-air ratio curve value and sends a load recovery command to the frequency converter drive terminal and the stationary blade drive terminal according to the initial coal-air ratio curve value.

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