Primary air volume coupling and adjusting system for mixed coal volatile components and ignition distance

Abstract

The invention provides a primary air volume coupling and adjusting system for mixed coal volatile components and ignition distance, and relates to the technical field of energy conservation and environmental protection of power plants. According to the system, coal blending coal types and proportions established by a coal blending system and corresponding parameter information of volatile components, moisture and ash of coal types in a coal yard are read through a relational database interface, and then the coal mixing fuel ratio of a coal mill is calculated; reading primary air quantity and coal feeding quantity data of the SIS system through a real-time system database interface, and calculating a coal mixing air-coal ratio of the coal mill; on the basis of test data, a fuzzy system is constructed, and the coupling relation between the ignition distance and the mixed coal volatile component and the primary air volume is established; based on the sliding window module technology, the offset of the primary air volume set value is calculated in real time through the real-time weighted average value, the real-time primary air volume set value and the real-time ignition distance data; the system interacts with an original coal mill control system in a plug-in mode, and the safety of a power plant is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of energy conservation and environmental protection in power plants, and particularly to a primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance. Background Art

[0002] Coal blending combustion is used to meet the load-carrying capacity of the mill unit and ensure the safety and environmental protection of the combustion process. Coal blending combustion shall not affect the safe and stable operation of the unit and the environmental protection compliance discharge, and ensure that serious incidents such as boiler flameout, severe slagging, large-area high-temperature corrosion of the heating surface, and fire and explosion of the coal pulverizing system caused by the quality of the coal entering the furnace do not occur. Thermal power generation mainly includes coal mills, boilers, steam turbines, and other auxiliary equipment and adopts a DCS / PLC control system. Its operating parameters are mainly designed for early single coal types. However, at present, thermal power enterprises generally operate under the condition of blended coal, making the operating parameters of the original control system non-optimal and the potential of the equipment not fully exerted. Based on this, under the influence of uncertain coal quality parameters of daily blended coal, the adjustment and optimization of the control system of thermal power units are an important topic both in terms of depth and breadth.

[0003] The volatile matter, one of the blended coal parameters, will affect the operation of both the coal mill and the boiler equipment. On the one hand, for blended coal with high volatile matter, the set value of the coal mill outlet temperature cannot be too high, otherwise it will cause an explosion of the coal mill; on the other hand, for blended coal with high volatile matter, the ignition distance of the boiler burner cannot be too close, otherwise the burner nozzle is prone to burning damage and coking, which also requires that the set value of the primary air volume of the coal mill cannot be too small. However, at present, there is a lack of systematic and in-depth research on the adjustment and optimization of the control parameters of unit equipment by integrating the coal quality parameters of blended coal, the coal pulverizing mechanism of the coal mill, and the combustion mechanism of the boiler. Domestic and foreign experts have conducted a preliminary exploration on the primary air ignition distance, given the empirical formula between volatile matter, primary air volume, and ignition distance through experiments, and also studied the influence relationship between primary and secondary air and the burner recirculation zone and ignition distance through experiments; the influence relationship between primary and secondary air and the burner recirculation zone and ignition distance has been studied through experiments.

[0004] In summary, although valuable research results have been obtained on the coupling relationship between volatile matter, ignition distance, and primary air volume, the following problems exist: 1) At present, most thermal power enterprises rely on manual experience for coal blending combustion. The lack of digitalization results in no real-time automatic calculation of the volatile matter of blended coal and no consideration of the impact of the volatile matter of blended coal on the real-time performance of the unit; 2) At present, the coupling relationship between the volatile matter, ignition distance, and primary air volume of single coal types is mainly studied for a small number of discrete experimental points, lacking the study of the relationship between continuous variables; 3) At present, the set value of the primary air volume of the coal mill and the coal feeding amount (equivalent to the load) are adjusted by a simple function relationship, and further, the automatic adjustment problem of the primary air volume for volatile matter and ignition distance needs to be considered. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance on the basis of the previous automatic coal blending, automatically adjust the set value of the primary air volume of the coal mill, promote the high efficiency of the coal mill equipment with digital intelligence on the basis of the existing automation, and fully tap the potential of the coal mill equipment.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance, including a server, a communication module, and a coal mill fuel ratio and air-coal ratio calculation module based on blended coal conditions, a fuzzy system modeling module based on experimental data, a primary air volume set value offset module of the coal mill based on a sliding window, a relational database interface module, and a real-time database interface module formed by software programming and set on the server; the server, as an external system, communicates with the original coal mill control system through the downlink data frame of the communication module; The relational database interface module constructs an interface between the external application program and the relational database, and realizes the interaction of relational database tables with the power plant coal blending system and the coal yard management system through this interface; The real-time database interface module constructs an interface between the external application program and the real-time database, and realizes the interaction of the real-time database with the power plant SIS system through this interface; The coal mill fuel ratio and air-coal ratio calculation module based on blended coal conditions reads the coal blending coal types and proportions established by the coal blending system and the corresponding volatile matter, moisture and ash parameters of the coal types in the coal yard through the relational database interface module, and then calculates the blended coal fuel ratio of the coal mill; reads the primary air volume and coal feeding amount data of the SIS system through the real-time system database interface module and calculates the blended coal air-coal ratio of the coal mill; The fuzzy system modeling module based on experimental data constructs a fuzzy system on the basis of the power plant experimental data to establish the coupling relationship between the ignition distance, the volatile matter of the blended coal and the primary air volume; The primary air volume set value offset module of the coal mill based on a sliding window, aiming at the fact that the current set value of the primary air volume in the power plant does not consider the coupling relationship between the volatile matter of the blended coal and the ignition distance, calculates the offset of the primary air volume set value by using the sliding window technology on the basis of the coupling function relationship between the ignition distance, the volatile matter of the blended coal and the primary air volume, and changes the primary air speed entering the furnace by adjusting the size of the primary air volume set value.

[0007] Preferably, the calculation module for the fuel ratio and air-coal ratio of the coal mill under the condition of blended coal reads the information of the coal types and proportions established by the coal blending system and the corresponding volatile matter, moisture and ash parameters of the coal types in the coal yard through the relational database interface module, and then calculates the fuel ratio of the blended coal in the coal mill; reads the primary air volume and coal feeding amount parameters of the coal mill in the SIS system through the real-time system database interface module and calculates the air-coal ratio of the blended coal in the coal mill. The specific method is as follows: Calculate the weighted average values of the volatile matter, ash and moisture of the coal quality parameters after blending the coal in the coal mill , as shown in the following formula: (1); In the formula, is the number of coal types in the blended coal of the coal mill, are the volatile matter, ash and moisture contents of the th coal type in the blended coal respectively, is the proportion of the th coal type in the blended coal; Calculate the fuel ratio and air-coal ratio of the blended coal in the coal mill; The fuel ratio of the blended coal in the coal mill is the ratio of the coke component to the volatile matter component in the unit coal, as shown in the following formula: (2); In the formula, is the fuel ratio of the blended coal in the coal mill, is the fixed carbon content of the blended coal on the air-dried basis; The air-coal ratio of the blended coal in the coal mill is the ratio of the primary air volume fed into the coal mill to the pulverized coal amount, as shown in the following formula: (3); In the formula, is the air-coal ratio of the blended coal in the coal mill, is the total amount of primary hot air and cold air in the coal mill, is the coal feeding rate of the coal mill, is the conversion efficiency of the coal at the inlet and outlet of the coal mill.

[0008] Preferably, the method for constructing a fuzzy system by the fuzzy system modeling module based on experimental data to establish the continuous function relationship between the ignition distance, the volatile matter of the blended coal and the primary air volume is as follows: Step S1: Using the air-coal ratio and fuel ratio obtained from the power plant experiment as the input vector and the ignition distance as the output variable, construct the input and output data pair set of the fuzzy system, as shown in the following formula: (4); In the formula, is the air-coal ratio and the fuel ratio vector, is the ignition distance variable, is the number of sample sets; Step S2: Set the universe of discourse interval and fuzzify the variables within the universe of discourse interval; Set the air-coal ratio and fuel ratio vectors and the ignition distance variable The universes of discourse are respectively , and , the two variables in the air-coal ratio and fuel ratio vectors , are used as the premise attributes of the fuzzy system, and the ignition distance variable is used as the conclusion attribute of the fuzzy system; each variable in the air-coal ratio and fuel ratio vectors is evenly divided into fuzzy sets, and the corresponding fuzzy sets of the air-coal ratio and fuel ratio vectors and the ignition distance variable are respectively and , is the number of fuzzy sets in the universe of discourse division of the ignition distance variable , and membership functions are assigned to each fuzzy set; Step S3: Use a relational database table to record the data pairs of the air-coal ratio, fuel ratio, and ignition distance, and convert this ordinary record into a fuzzy record; Use a relational database table to record the data pairs of the air-coal ratio, fuel ratio, and ignition distance. Each row of the table represents a record, and each column of the table is an attribute of the record; use to represent the set of attributes, to represent the th record with specific attribute values, and use to describe a set of records containing attribute information, that is: (5); Use to represent the fuzzy set of the premise attribute , to represent the fuzzy set of the conclusion attribute , and obtain the sets and ; for the membership degree value attribute of , use to define a set of fuzzy records containing attribute information: (6); In the formula, is the The membership function of the attribute set corresponding to the records; Through the above formulas (5) and (6), the fuzzy records containing attribute information are saved in another relational record table, where the columns represent attributes , and the rows represent records with values in the range [0, 1].

[0009] Step S4: Create a fuzzy rule base using the nested algorithm; First, traverse all the fuzzy subspaces composed of the fuzzy sets corresponding to the premise attributes and through nested double loops and ; ; Then, for any fuzzy subspace determined by the premise attributes and , for the fuzzy set selected by its conclusion attribute , by looping through each fuzzy set in the fuzzy set , calculate using the following formula: (7); In the formula, and respectively represent the membership function values of the th record; determined by which fuzzy set to select in the conclusion fuzzy subspace ; Finally, after determining the selected fuzzy subspace through the maximum support degree, construct the following IF-THEN fuzzy rule base: (8); In the formula, is the th fuzzy rule, is the number of rules in the fuzzy rule base.

[0010] Step S5: Generate a fuzzy model based on the fuzzy rule base; For the fuzzy rules obtained in Step S4, using single-valued fuzzification, multiplication operation, and weighted average defuzzification, the fuzzy model can be obtained as: (9); In the formula, is the calculated output of the ignition distance of the fuzzy model, is the th rule at the value point where the maximum value is obtained in the fuzzy membership function value, that is, The corresponding value.

[0011] Step S6: Adjust the parameters of the fuzzy model using the gradient descent method; Adjust the output of the fuzzy model in Equation (9) to the following form of vector multiplication: (10); In the formula, is the fuzzy model parameter vector, is the membership function value normalization vector, where is defined as follows: (11); Define the objective error function E composed of the experimental sample data formula (4) as: (12); In the formula, is the experimental data of the ignition distance corresponding to the th record, is the air-coal ratio and fuel ratio vector When taking the data of the th record, the calculated data of the ignition distance of the fuzzy model; Use the gradient descent algorithm to minimize the objective error function (12), thereby dynamically optimizing and adjusting the parameters of the fuzzy model and improving the modeling accuracy of the fuzzy model; The update of the fuzzy model parameter is shown in the following formula: (13); In the formula, is the number of iterations, is a positive learning rate; the learning rate is initially set to 0.02, The initial value of is determined by the fuzzy rules extracted in Steps 1 - Step 6.

[0012] Step S7: Adjust the number of fuzzy sets in the input-output space; improve the prediction accuracy of the fuzzy model by increasing the division of the number of fuzzy sets in the input-output space.

[0013] Preferably, the bias module for the primary air volume set value of the coal mill based on the sliding window calculates the bias of the primary air volume set value using the sliding window technology on the basis of the ignition distance, blended coal volatile matter, and primary air volume calculation data, thereby optimizing the ignition distance and making the ignition distance reasonable; including: First, from , Determine the 2*2 sliding window from the real-time value; from , The real-time value and calculate the ignition distance through formula (9). , if and the corresponding ignition distance is not within the sliding window range, adopt the following strategy to calculate the bias compensation amount of the primary air volume set value : (14); In the formula, are respectively the corresponding primary air volume set values when taking the maximum and minimum ignition distances in the 2×2 sliding window, and the corresponding coal-air ratios ; is the real-time the corresponding primary air volume set value of the original control system; is the ignition distance determined by 4 test points in the 2×2 sliding window; If and the corresponding ignition distance is within the sliding window range, calculate the bias compensation amount of the primary air volume set value according to the following formula : (15); In the formula, are respectively the corresponding primary air volume set values when taking the maximum ignition distances in the first row and the second row within the 2×2 sliding window, and the corresponding coal-air ratios ; are respectively the upper and lower bounds of the corresponding sliding window.

[0014] Preferably, the server is used as an external system to communicate with the original coal mill control system through the downlink data frame of the communication module, and set the bias of the primary air volume set value of the coal mill control system; the original coal mill control system sends a heartbeat digital quantity request frame to the server, and the server simulates the heartbeat signal through the response of the digital quantity switch signal (0,1) designed by the program, and the original coal mill control system detects whether the communication of the external system is normal through the heartbeat frame response; when the original coal mill control system does not detect the heartbeat frame response after exceeding the set time, automatically cut off the external system and switch to the set value signal of the original coal mill control system.

[0015] The beneficial effects produced by adopting the above technical solutions are as follows: The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance provided by the present invention aims at the problems of cracking, deformation, burning damage and coking in the operation of burners in opposed firing boilers of power plants at present. (1) First, aiming at the fact that power plants generally operate under the condition of blended coal, the calculation process of the blended coal fuel ratio and coal-air ratio is given based on the blended coal volatile matter and the primary air volume.

[0016] (2) The coupling relationship among the volatile matter of blended coal, the ignition distance, and the primary air volume was analyzed, revealing the irrationality of the current setting plan for the primary air volume in thermal power plants.

[0017] (3) For different volatile matter parameters of blended coal, a feed-forward compensation plan for the offset of the primary air volume setting value of the coal mill control system was proposed for the first time using fuzzy modeling and sliding window technology, achieving the optimization of the ignition distance and avoiding the problems of burner burnout and coking in the boiler.

[0018] (4) Each module proposed in the present invention is implemented on an external server. The external server is connected to the original primary air volume control system of the coal mill through communication, without modifying the hardware and programs of the original control system. It only changes the original manual experience-based offset method to an algorithm-based external computer control and adjustment implementation method; for the external server, heartbeat pulses and seamless switching are used to ensure system security. Once communication and other faults occur, the original control system can still operate normally.

[0019] The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance proposed in the present invention aims at the problems of cracking, deformation, burnout, and coking in the operation of burners of opposed firing boilers in current power plants. First, considering that thermal power plants generally operate under blended coal conditions, the calculation process of the fuel ratio and air-coal ratio of blended coal and the causes of the problems are given. Then, the coupling relationship among the volatile matter of blended coal, the ignition distance, and the primary air volume was analyzed, revealing the irrationality of the current setting plan for the primary air volume in thermal power plants. Finally, for different operating conditions of blended coal parameters, a feed-forward compensation plan for the offset of the primary air volume setting value of the coal mill control system was proposed for the first time using fuzzy modeling and sliding window technology, achieving the optimization of the ignition distance and avoiding the problems of burner burnout and coking in the boiler.

[0020] In summary, the present invention has considerable anticipated economic value, social value, and scientific value. Brief Description of the Drawings

[0021] Figure 1 It is a diagram showing the implementation route of the primary air volume adjustment technology provided by an embodiment of the present invention; Figure 2 It is a hardware process diagram of the automatic coal distribution system in a power plant provided by an embodiment of the present invention; Figure 3 It is a software interface diagram of the automatic coal distribution system in a power plant provided by an embodiment of the present invention; Figure 4 It is a schematic diagram of the primary air volume ignition distance provided by an embodiment of the present invention; Figure 5 It is a relationship diagram of the ignition distance with the air-coal ratio and fuel ratio provided by an embodiment of the present invention; Figure 6Flow chart of creating a fuzzy rule base using a nested algorithm provided by an embodiment of the present invention; In the figure: 1. Coal bunker; 2. Coal feeder; 3. Coal mill; 4. Conveyor belt; 5. Primary air flow of the burner; 6. Ignition distance; 7. Lower mixing zone; 8. Upper mixing zone; 9. Central primary air flow; 10. Furnace of the boiler. Specific embodiments

[0022] The following combines the accompanying drawings and embodiments to further describe in detail the specific embodiments of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0023] In this embodiment, a primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance is as Figure 1 shown, including a server, a communication module, and a coal mill fuel ratio and air-coal ratio calculation module based on blended coal conditions, a fuzzy system modeling module based on experimental data, a primary air volume set value offset module for the coal mill based on a sliding window, a relational database interface module, and a real-time database interface module formed by software programming and set on the server; the server, as an external system, communicates with the original coal mill control system through a downlink data frame of the communication module to set the offset of the primary air volume set value of the coal mill control system and cancel the traditional manual addition of the offset; the original coal mill control system sends a heartbeat switch quantity request frame to the server, and the server simulates a heartbeat signal through the response of the digital switch signal (0,1) designed by the program. The original coal mill control system then detects whether the communication of the external system is normal through the response of the heartbeat frame; when the original coal mill control system does not detect the response of the heartbeat frame within the set time, the external system is automatically cut off and switched to the set value signal of the original coal mill control system.

[0024] In this embodiment, the relational database interface module constructs an interface between the external application program and the relational database, and realizes the interaction of relational database tables with the power plant coal blending system and the coal yard management system through this interface; The real-time database interface module constructs an interface between the external application program and the real-time database, and realizes the interaction of the real-time database with the power plant SIS system through this interface; The coal mill fuel ratio and air-coal ratio calculation module based on blended coal conditions reads the coal blending types and proportions established by the coal blending system and the corresponding volatile matter, moisture, and ash parameters of the coal yard coal types through the relational database interface module, and then calculates the blended coal fuel ratio of the coal mill; reads the primary air volume and coal feeding amount data of the SIS system through the real-time system database interface module and calculates the blended coal air-coal ratio of the coal mill; The fuzzy system modeling module based on experimental data aims at the problem that there is no quantitative description between the ignition distance, the volatile content of blended coal and the primary air volume. Based on the experimental data of the power plant, a fuzzy system is constructed to establish the functional relationship between the ignition distance, the volatile content of blended coal and the primary air volume, laying a foundation for the adjustment of the primary air volume. The primary air volume set value offset module of the coal mill based on the sliding window aims at the problem that the current primary air volume set value of the power plant does not consider the coupling relationship between the volatile content of blended coal and the ignition distance. Based on the functional relationship between the ignition distance, the volatile content of blended coal and the primary air volume, the sliding window technology is used to calculate the offset of the primary air volume set value, and by adjusting the size of the primary air volume set value, the primary air velocity entering the furnace is changed, and the size of the air velocity will change the ignition distance, avoiding too short ignition distance to burn the burner nozzle and too long ignition distance with low combustion efficiency.

[0025] In this embodiment, for the primary air volume coupling and adjustment system facing the volatile content of blended coal and the ignition distance, the overall implementation process is as Figure 1 shown. Based on the parameter information of each coal type provided by the coal yard coal type management system, the physical hardware and software of the power plant automatic coal blending system are as Figure 2 and Figure 3 shown. The blended coal types are simultaneously fed into the coal bunker 1 from the coal yard by two stacker-reclaimers and two conveyor belts 4. The blended coal in the coal bunker 1 enters the coal mill 3 for grinding through the coal feeder 2. The coal feeding amount of the coal feeder 2 is automatically adjusted according to the power generation load, and the set value of the primary air volume of the coal mill 3 is automatically adjusted according to the coal-air ratio function along with the coal feeding amount. Since the power plant generally adopts the blended coal combustion technology at present, but the original control logic of the coal mill control system is designed for a single coal type and does not consider the influence of the change of the volatile content parameter of blended coal on the boiler combustion performance. Based on this, the present invention will analyze the coupling relationship between the volatile content of blended coal, the ignition distance and the primary air volume of the coal mill on the basis of the automatic coal blending system, and carry out the adjustment of the primary air volume set value.

[0026] In this embodiment, for the calculation module of the fuel ratio and coal-air ratio of the coal mill under the condition of blended coal blending, the specific methods for calculating the fuel ratio and coal-air ratio of the blended coal in the coal mill are as follows: Calculate the weighted average values of the volatile content, ash content and moisture content of the coal quality parameters after the coal mill blends coal, , as shown in the following formula: (1); In the formula, is the number of coal types in the blended coal of the coal mill, are respectively the volatile content, ash content and moisture content of the th coal type in the blended coal, is the proportion of the th coal type in the blended coal; Calculate the fuel ratio and coal-air ratio of the blended coal in the coal mill; The pulverizer mixed coal fuel ratio is the ratio of the coke component to the volatile component in unit coal, as shown in the following formula: (2); In the formula, is the pulverizer mixed coal fuel ratio, is the fixed carbon content of the mixed coal on an air-dried basis; The pulverizer mixed coal air-to-coal ratio is the ratio of the primary air volume fed into the pulverizer to the pulverized coal amount, as shown in the following formula: (3); In the formula, is the pulverizer mixed coal air-to-coal ratio, is the total amount of primary hot air and cold air in the pulverizer, is the coal feeding rate of the pulverizer, is the conversion efficiency of the coal at the inlet and outlet of the pulverizer.

[0027] The ignition distance is an important physical parameter in the combustion process of an opposed firing boiler. If the ignition point is too close to the burner nozzle, phenomena such as nozzle burnout or coking will occur; if the ignition point is too far from the nozzle, the combustion process will be delayed, causing the pulverized coal to leave the furnace before it is completely burned, increasing the heat loss due to mechanical incomplete combustion. In addition, the delayed ignition may also cause the flame center to move upward, easily resulting in overheating of the flue gas in the furnace outlet area and overheating of the high-temperature superheater and reheater tubes in this area, affecting the temperature adjustment of the main steam and reheated steam. In the long run, sudden accidents such as tube bursts will occur.

[0028] As Figure 4 shown, after the primary air flow 5 of the burner enters the furnace, it forms a primary air central flow 9. This flow makes a relative movement with the gas in the furnace 10 of the boiler. Due to the friction entrainment effect, a mixing zone where the primary air flow and the furnace gas are mutually mixed is formed in the area adjacent to the primary air flow and the furnace gas. This mixing zone is divided into an upper mixing zone 8 and a lower mixing zone 7. When it expands along the path to a certain range, the temperature in the mixing zone reaches the ignition point, causing the pulverized coal to burn. Part of the generated heat is transferred to the center of the flow. If the needs of the volatile matter of the pulverized coal and the ignition point of the mixture in the center of the flow can be met, then the ignition point range will rapidly expand to the ignition of the entire flow cross-section. The distance between the location of the entire flow cross-section ignition and the burner nozzle is the ignition distance 6.

[0029] Ignition distance and air-to-coal ratio , fuel ratio The experimental simulation relationship between them is as Figure 5 shown, which is a non-linear function. The ignition distance varies with the change of the volatile matter when the primary air volume remains unchanged; the ignition distance does not show a decreasing relationship with the decrease of the primary air volume when the volatile matter remains unchanged.

[0030] In this embodiment, the method for the fuzzy system modeling module based on experimental data to construct a fuzzy system to establish the continuous function relationship between the ignition distance, the volatile content of the blended coal, and the primary air volume is as follows: Step S1: Using the air-to-coal ratio and fuel ratio obtained from power plant experiments as input vectors and the ignition distance as the output variable, construct a set of input and output data pairs for the fuzzy system, as shown in the following formula: (4); In the formula, is the air-to-coal ratio and the fuel ratio vector, is the ignition distance variable, is the number of sample sets; Step S2: Set the universe of discourse interval and fuzzify the variables within the universe of discourse interval; Set the universe of discourse intervals of the air-to-coal ratio and fuel ratio vectors and the ignition distance variable to be , and respectively. The two variables in the air-to-coal ratio and fuel ratio vectors , serve as the premise attributes of the fuzzy system, and the ignition distance variable serves as the conclusion attribute of the fuzzy system. Each variable in the air-to-coal ratio and fuel ratio vectors is evenly divided into fuzzy sets. The corresponding fuzzy sets of the air-to-coal ratio and fuel ratio vectors and the ignition distance variable are and respectively. is the number of fuzzy sets for the division of the universe of discourse of the ignition distance variable , and a membership function is assigned to each fuzzy set; Step S3: Use a relational database table to record the data pairs of the air-to-coal ratio, fuel ratio, and ignition distance, and convert this ordinary record into a fuzzy record; Use a relational database table to record the data pairs of the air-to-coal ratio, fuel ratio, and ignition distance. Each row of the table represents a record, and each column of the table serves as an attribute of the record; use to represent the set of attributes, to represent the th record with specific attribute values, and use to describe a set of records containing attribute information, that is: (5); Use Denote the premise attribute of the fuzzy set Denote the conclusion attribute of the fuzzy set, obtaining the sets and ; For the membership degree value attribute of use to define a set of fuzzy records containing attribute information: (6); In the formula, is the membership degree function of the th record corresponding to the attribute set; Through the above formulas (5) and (6), save the fuzzy records containing attribute information in another relational record table, where the columns in this table represent the attributes , and the rows represent the records with values in [0, 1].

[0031] Step S4: Create a fuzzy rule base using the nested algorithm; The fuzzy rule base is the foundation for building a fuzzy system and can be obtained through expert knowledge or experimental data. The process of building a fuzzy rule base based on experimental data is given below, as Figure 6 shown; First, traverse all the fuzzy subspaces composed of the fuzzy sets and corresponding to the premise attribute and by nested double loops ; Then, for any fuzzy subspace determined by the premise attribute and , for the fuzzy set selected for its conclusion attribute , by looping through each fuzzy set in the fuzzy set , calculate using the following formula: (7); In the formula, and respectively represent the membership degree function values of the th record; It is determined by which fuzzy set to select in the conclusion fuzzy subspace ; Finally, after determining the selected fuzzy subspace through the maximum support degree, construct the following IF-THEN fuzzy rule base: (8); In the formula, is the a fuzzy rule, which is the number of rules in the fuzzy rule base.

[0032] Step S5: Generate a fuzzy model based on the fuzzy rule base; For the a fuzzy rules obtained in step S4, the fuzzy model can be obtained by using singleton fuzzification, multiplication operation, and weighted average defuzzification as: (9); wherein, is the calculated output of the ignition distance of the fuzzy model, is the th rule at the value point corresponding to the maximum value obtained in the fuzzy membership function value point, that is, the value corresponding to when value.

[0033] Step S6: Adjust the parameters of the fuzzy model by using the gradient descent method; Adjust the output of the fuzzy model in formula (9) to the following form of vector multiplication: (10); wherein, is the fuzzy model parameter vector, is the normalized vector of the membership function values, where is defined as follows: (11); Define the target error function E composed of the experimental sample data formula (4) as: (12); wherein, is the experimental data of the ignition distance corresponding to the th record, is the air-coal ratio and fuel ratio vector When taking the th record data, it is the calculated data of the ignition distance of the fuzzy model; Use the gradient descent algorithm to minimize the target error function (12), so as to dynamically optimize and adjust the parameters of the fuzzy model and improve the modeling accuracy of the fuzzy model; The update of the fuzzy model parameter is shown in the following formula: (13); wherein, is the number of iterations, is a positive learning rate; the learning rate The initial value is set to 0.02, The initial value is determined by the fuzzy rules extracted in steps 1 - 6.

[0034] Step S7: Adjust the number of fuzzy sets in the input - output space; improve the prediction accuracy of the fuzzy model by increasing the division of the number of fuzzy sets in the input - output space.

[0035] In step S1, generally determine the number of fuzzy sets to be divided according to the distribution of data samples within the corresponding universe of discourse, Determine the initial fuzzy region, . Since the fuzzy model is a universal approximator, it is possible to improve its performance by adding new fuzzy sets in the input and output spaces. When the prediction accuracy of the fuzzy model still does not reach the expected prediction accuracy after optimizing the fuzzy model parameters using step 6, consider improving the prediction accuracy of the fuzzy model by increasing the division of the number of fuzzy sets in the input - output space.

[0036] This embodiment uses the root - mean - square error as the performance index to evaluate the fuzzy model, and adjusts the number of fuzzy sets in the input - output space according to this performance index: (14); In the formula, is the root - mean - square error, is the number of input - output data pairs, is the true output of the th sample, is the predicted output of the

[0037] In this embodiment, the bias module for the primary air volume setting value of the coal mill based on the sliding window calculates the bias of the primary air volume setting value using the sliding window technology on the basis of the ignition distance, blended coal volatile matter, and primary air volume calculation data, so as to optimize the ignition distance and make the ignition distance reasonable; it includes: First, taking the experimental data points in Table 1 as an example, from , real - time numerical values (such as is between 2 and 1, is between 3 and 2), the sliding window in Table 1 can be determined.

[0038] Table 1 Experimental data points of ignition distance, air - coal ratio, and fuel ratio

[0039] From , real - time numerical values and calculate the ignition distance through formula (9) , if and The corresponding ignition distance Outside the sliding window, the following strategy is adopted to calculate the offset compensation amount of the primary air volume set value : (15); In the formula, are the corresponding primary air volume set values when taking the maximum and minimum ignition distances in the 2*2 sliding window respectively ; is the real-time primary air volume set value of the original control system corresponding to it; is the ignition distance determined by 4 test points in the 2*2 sliding window; (as shown in Table 1 , , , ); If and the corresponding ignition distance is within the sliding window, calculate the offset compensation amount of the primary air volume set value according to the following formula : (16); In the formula, are the corresponding primary air volume set values when taking the maximum ignition distance in the first row and the second row in the 2*2 sliding window respectively ; are respectively the upper and lower bounds of the corresponding sliding window (as shown in Table 1 , ).

[0040] The reason why the present invention selects the maximum and minimum ignition distances in the 2*2 sliding window and the corresponding primary air volume set values when the corresponding primary air volume maximum set value is calculated is that it is considered that the original coal mill control system does not consider the influence of the volatile content of blended coal on the ignition distance. By appropriately increasing the primary air volume to increase the wind speed, the ignition distance is appropriately increased, thereby weakening the phenomenon of coking at the burner nozzle caused by the volatile content.

[0041] This embodiment takes a 350MW opposed fired boiler unit in one of the four units of a power plant enterprise as an example to illustrate the implementation process of the coupling and adjustment of the primary air volume for the volatile content of blended coal and the ignition distance. Its technical route is implemented as Figure 1 shown.

[0042] Real-time data acquisition: Figure 1The coal blending and co - firing optimization system in stores the coal blending plan and the coal bunker filling plan for each shift every day in the relational database SQL Server according to the time stamp. Therefore, the system of the present invention can read the corresponding blended coal quality parameter information through the database interface and calculate the real - time value of the volatile matter and the fuel ratio. In addition, the real - time coal quantity of the coal feeder can be obtained through the real - time database SIS system, and the set value of the primary air volume and the air - coal ratio can be further obtained through the air - coal ratio curve. Finally, on the basis of obtaining the real - time volatile matter and the set value of the real - time primary air volume, the real - time ignition distance can be obtained through the fuzzy system of the present invention.

[0043] Calculation of the primary air volume offset: First, use the obtained fuel ratio to determine the adjacent upper and lower boundary values in Table 1, and the row position of the 2×2 sliding window can be obtained. Similarly, use the obtained air - coal ratio to determine the adjacent upper and lower boundary values in Table 1, and the column position of the 2×2 sliding window can be obtained. Then calculate the offset of the primary air volume set value, and sum it with the primary air volume set value of the original coal mill control system through the communication module as the new primary air volume set value.

[0044] Table 2 shows the experimental data and test results. First, by reading the blended coal quality database, the weighted average volatile matter, moisture and ash of the corresponding blended coal can be obtained, and the corresponding fuel ratios can be calculated as 4.82 and 1.15 respectively. Then, the corresponding air - coal ratios can be calculated as 1.72 and 0.65; further, through the fuzzy system, the primary air volume ignition distances can be calculated as 3.98 and 2.06 respectively. Finally, the air - coal ratios corresponding to the primary air volume feed - forward compensation values can be calculated as 0.28 and - 0.15 respectively. It can be seen from the experiment that, without changing the air - coal ratio set value of the original coal mill control system, the proposed strategy automatically increases the offset compensation amount, so that the new set value takes into account the influence of the blended coal volatile matter and avoids the problem of affecting the combustion efficiency due to excessive adjustment of the primary air volume.

[0045] Table 2 Experimental data and test data

[0046] Taking the first group of test data as an example to illustrate its calculation process. Since , the sliding window can be determined as the upper - left position of Table 2, and the ignition distance at this time is Within the sliding window range, so the offset of the primary air volume set value at this time is calculated using Equation (16); and since is closer to the upper boundary of the sliding window, the maximum ignition distance test data point in the first row of the sliding window is selected for calculation (at this time differs from the current real - time by 0.28, ), that is, using the test data point corresponding to As the set value of the current real-time primary air volume, at this time , .

[0047] The reason for using as the set value of the current real-time primary air volume is based on the following considerations: 1) The corresponding when the original coal mill control system did not consider the influence of volatile matter and ignition distance, so adjustment is needed; 2) The test data points The corresponding is the comprehensive set value that adds the influence of volatile matter and ignition distance, which is relatively accurate; 3) Using to replace within a permitted small interval range is beneficial to avoid the problem of burner nozzle coking (increasing the primary air volume makes the primary air velocity increase, and the ignition is relatively far from the burner nozzle, solving the current burner coking problem), and is also beneficial to weakening the continuous swing of the primary air damper caused by the continuous fluctuation of the set value, and mechanical wear damages the damper and causes premature damage.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope defined by the claims of the present invention.

Claims

1. A primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance, characterized in that: It includes a server, a communication module, and a calculation module for the fuel ratio and air-coal ratio of a coal mill under the condition of blended coal, a fuzzy system modeling module based on experimental data, a bias module for the set value of the primary air volume of the coal mill based on a sliding window, a relational database interface module, and a real-time database interface module, which are formed by software programming and set on the server; the server, as an external system, communicates with the original coal mill control system through the downlink data frames of the communication module. The relational database interface module constructs an interface between the external application and the relational database, and realizes the interaction with the relational database tables of the power plant coal blending system and the coal yard management system through this interface. The real-time database interface module constructs an interface between the external application and the real-time database, and realizes the interaction with the real-time database of the power plant SIS system through this interface. The calculation module for the fuel ratio and air-coal ratio of the coal mill under the condition of blended coal reads the coal types and proportions established by the coal blending system and the corresponding volatile matter, moisture, and ash parameters of the coal types in the coal yard through the relational database interface module, and then calculates the blended coal fuel ratio of the coal mill; it reads the primary air volume and coal feeding amount data of the SIS system through the real-time database interface module and calculates the blended coal air-coal ratio of the coal mill. The fuzzy system modeling module based on experimental data constructs a fuzzy system on the basis of the experimental data of the power plant to establish the coupling relationship between the ignition distance, the volatile matter of the blended coal, and the primary air volume. Regarding the fact that the current set value of the primary air volume in the power plant does not consider the coupling relationship between the volatile matter of the blended coal and the ignition distance, the bias module for the set value of the primary air volume of the coal mill based on a sliding window calculates the bias of the set value of the primary air volume based on the coupling function relationship between the ignition distance, the volatile matter of the blended coal, and the primary air volume by using the sliding window technology, and changes the primary air velocity entering the furnace by adjusting the size of the set value of the primary air volume.

2. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 1, wherein: The calculation module for the fuel ratio and air-coal ratio of the coal mill under the condition of blended coal reads the coal types and proportions established by the coal blending system and the corresponding volatile matter, moisture, and ash parameters of the coal types in the coal yard through the relational database interface module, and then calculates the blended coal fuel ratio of the coal mill; it reads the primary air volume and coal feeding amount parameter data of the coal mill of the SIS system through the real-time database interface module and calculates the blended coal air-coal ratio of the coal mill. The specific method is as follows: Calculate the weighted mean of the volatile matter, ash content, and moisture content of the coal quality parameters after blending coal in the coal mill , as shown in the following formula: （1）； In the formula, is the number of coal types in the blended coal of the coal mill, are respectively the volatile matter, ash and moisture contents of the th coal type in the blended coal, and is the proportion of the th coal type in the blended coal; Calculate the blended coal fuel ratio and air-coal ratio of the coal mill. The blended coal fuel ratio of the coal mill is the ratio of the coke component to the volatile matter component in the unit coal, as shown in the following formula: （2）； In the formula, is the fuel ratio of blended coal in the coal mill, is the fixed carbon content of the blended coal on an air-dried basis; The blended coal air-coal ratio of the coal mill is the ratio of the primary air volume fed into the coal mill to the pulverized coal amount, as shown in the following formula: （3）； In the formula, is the coal-air ratio of the coal mill for blended coal, is the total amount of primary hot air and cold air in the coal mill, is the coal feeding rate of the coal mill, is the conversion efficiency of coal at the inlet and outlet of the coal mill.

3. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 2, characterized in that: The method for the fuzzy system modeling module based on experimental data to construct a fuzzy system to establish the continuous function relationship between the ignition distance, the volatile matter of the blended coal, and the primary air volume is as follows: Step S1: Using the air-coal ratio and fuel ratio obtained from the power plant experiment as the input vector and the ignition distance as the output variable, construct the input and output data pair set of the fuzzy system, as shown in the following formula: （4）； In the formula, is the air-coal ratio and the fuel ratio vectors, is the ignition distance variable, is the number of sample sets; Step S2: Set the domain interval and fuzzyize the variables within the domain interval. Step S3: Record the data pairs of air-coal ratio, fuel ratio and ignition distance using a relational database table, and convert this ordinary record into a fuzzy record; Step S4: Create a fuzzy rule base using a nested algorithm; Step S5: Generate a fuzzy model based on the fuzzy rule base; Step S6: Adjust the parameters of the fuzzy model using the gradient descent method; Step S7: Adjust the number of fuzzy sets in the input-output space; improve the prediction accuracy of the fuzzy model by increasing the division of the number of fuzzy sets in the input-output space.

4. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 3, characterized in that: The step S2 sets the air-coal ratio and the fuel ratio vector and the ignition distance variable have the universe of discourse intervals of , and respectively. The two variables in the air-coal ratio and the fuel ratio vector , serve as the premise attributes of the fuzzy system, and the ignition distance variable serves as the conclusion attribute of the fuzzy system; each variable in the air-coal ratio and the fuel ratio vector has its universe of discourse evenly divided into fuzzy sets. The corresponding fuzzy sets of the air-coal ratio and the fuel ratio vector and the ignition distance variable are and respectively. is the number of fuzzy sets in the universe of discourse division of the ignition distance variable , and membership functions are assigned to each fuzzy set.

5. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 4, characterized in that: The step S3 uses a relational database table to record the pairs of air-coal ratio, fuel ratio and ignition distance data. Each row of the table represents a record, and each column of the table serves as an attribute of the record; use to represent the set of attributes, to represent the th record with specific attribute values, and use to describe a set of records containing attribute information, that is: （5）； Use to represent the fuzzy set of premise attributes, and use to represent the fuzzy set of conclusion attributes, obtaining the sets and ; for the membership value attributes of , define a group of fuzzy records containing attribute information: （6）； wherein, is the membership function of the attribute set corresponding to the th record; Through the above formulas (5) and (6), the fuzzy records containing attribute information are stored in another relational record table, where the columns in the table represent attributes , and the rows represent records with values in the range [0, 1].

6. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 5, characterized in that: The specific method of step S4 is as follows: First, traverse all the fuzzy subspaces formed by the fuzzy sets corresponding to the premise attributes through nested double loops; Then, for the premise attribute and any fuzzy subspace determined, for its conclusion attribute the selected fuzzy set, by cyclically selecting each fuzzy set in the fuzzy set is calculated by the following formula: （7）； In the formula, and respectively represent the membership function values of the th record; determines which fuzzy set to select in the conclusion fuzzy subspace ; Finally, after determining the selected fuzzy subspace through the maximum support degree, the following IF-THEN fuzzy rule base is formed: （8）； wherein, is the th fuzzy rule, is the number of rules in the fuzzy rule base.

7. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 6, characterized in that: The step S5 is directed to the fuzzy rules obtained in step S4. By using single-value fuzzification, multiplication operation, and weighted average defuzzification, the fuzzy model can be obtained as follows: （9）； In the formula, is the calculated output of the ignition distance of the fuzzy model, is the value corresponding to the maximum value obtained by the fuzzy membership function of the th rule, that is, the value corresponding to the case when .

8. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 7, characterized in that: Step S6 adjusts the output of the fuzzy model in formula (9) to the following form of vector multiplication: （10）； In the formula, is the fuzzy model parameter vector, is the membership function value normalization vector, where is defined as follows: （11）； Define the objective error function E composed of the experimental sample data formula (4) as: （12）； In the formula, is the experimental data of the ignition distance corresponding to the th record, is the vector of air-coal ratio and fuel ratio When taking the data of the th record, it is the calculated data of the ignition distance of the fuzzy model; Use the gradient descent algorithm to minimize the objective error function (12), so as to dynamically optimize and adjust the parameters of the fuzzy model and improve the modeling accuracy of the fuzzy model; Fuzzy model parameters are updated as shown in the following formula: （13）； In the formula, is the number of iterations, is the positive learning rate; the initial value of the learning rate is set to 0.02, and the initial value of is determined by the fuzzy rules extracted in Steps 1 - 6.

9. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 8, characterized in that: The offset module of the primary air volume setting value of the coal mill based on the sliding window calculates the offset of the primary air volume setting value using the sliding window technology on the basis of the ignition distance, volatile matter of blended coal and calculated data of the primary air volume, so as to optimize the ignition distance and make the ignition distance reasonable; it includes: First, from , a 2*2 sliding window is determined from real-time values; from , the real-time values and the ignition distance is calculated through formula (9) . If and the corresponding ignition distance is not within the sliding window range, the offset compensation amount of the primary air volume set value is calculated using the following strategy : （14）； In the formula, are the maximum and minimum ignition distances within the 2×2 sliding window, and the corresponding air-coal ratios corresponding to the primary air flow rate setting values; is the real-time primary air flow rate setting value corresponding to the original control system; is the ignition distance determined by the 4 test points in the 2×2 sliding window; If and the corresponding ignition distance is within the sliding window range, calculate the offset compensation amount of the primary air volume setting value according to the following formula : （15）； In the formula, are respectively the air-coal ratios corresponding to the maximum ignition departure times in the first and second rows within the 2×2 sliding window. They are the corresponding set values of the primary air volume. are respectively the upper and lower bounds of the corresponding sliding window.

10. The primary air volume coupling and adjustment system for blended coal volatile matter and ignition distance according to claim 1, characterized in that: The server, as an external system, communicates with the original coal mill control system through the downlink data frame of the communication module to set the offset of the primary air volume setting value of the coal mill control system; the original coal mill control system sends a heartbeat switch quantity request frame to the server, and the server simulates the heartbeat signal through the response of the digital switch signal (0,1) designed by the program, and the original coal mill control system detects whether the communication of the external system is normal through the heartbeat frame response; When the original coal mill control system does not detect the heartbeat frame response after exceeding the set time, the external system is automatically cut off and switched to the set value signal of the original coal mill control system.

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