Method and system for adjusting oxygen content of coal-fired boiler

Abstract

The invention discloses a coal-fired boiler oxygen amount adjusting method and system, and the method comprises the steps: calculating the real-time as-fired coal amount of a single coal mill through a primary air pipe air powder resistance method or coal mill operation parameter modeling, obtaining the as-fired coal heat value through boiler heat balance calculation or operation parameter modeling, carrying out the accumulation to obtain the total as-fired coal amount, collecting operation data at an interval of 1 second, and obtaining the oxygen amount of the coal-fired boiler. And calculating an excess air coefficient, determining oxygen delay time, establishing a total air volume dynamic model, calculating an air supply volume feed-forward correction value, and superposing the air supply volume feed-forward correction value to an original control system after upper and lower limit limitation. The system comprises a data acquisition module, a coal as fired quantity and heat value calculation module, a delay time determination module, a total air volume modeling module and a feedforward correction module. The problems that in traditional control, the feed-forward deviation of the air supply amount is large, and oxygen amount adjustment lags are solved, the oxygen amount is rapidly and accurately tracked, the variable-load operation efficiency of the boiler is improved, and the method is suitable for coal-fired units with different capacities.

Description

Technical Field

[0001] The present invention relates to the technical field of coal-fired boiler operation control, and in particular to a method and system for regulating the oxygen content of a coal-fired boiler. Background Art

[0002] During the operation of coal-fired boilers, oxygen content is an important parameter that affects the combustion efficiency and safety of the boiler. At present, the oxygen content control of coal-fired boilers is generally achieved through PID control. Its conventional control strategy is as follows: Figure 1 As shown: The boiler fuel master control signal and the total coal feed rate are used as the air volume feedforward, and the deviation between the oxygen measurement value and the set value is combined to generate the air volume command and the blower opening command through the PID controller.

[0003] However, this control strategy has significant defects: on the one hand, due to the hysteresis of the pulverized coal in the pulverizer, there is a deviation between the boiler fuel instruction or total coal feed and the actual coal feeding amount under variable load, and the calorific value of the coal feeding into the furnace fluctuates greatly, resulting in a mismatch between the air supply volume feedforward and the actual required oxygen content, which in turn causes the actual oxygen content to deviate significantly from the set value, affecting the boiler efficiency under variable load; on the other hand, there is a hysteresis in the oxygen measurement. When the air supply volume feedforward deviation is large, it takes a long time to adjust the actual oxygen content to the set value by relying on the oxygen PID control. Some units are even unable to put oxygen control into operation, which seriously restricts the economic efficiency of the variable load operation of the boiler unit. Summary of the Invention

[0004] In response to the problems of inaccurate air volume feedforward and delayed oxygen regulation in the prior art, the present invention provides a method and system for regulating the oxygen content of a coal-fired boiler. By accurately calculating the air volume feedforward, rapid and precise regulation of the oxygen content is achieved, reducing oxygen content fluctuations during load changes and improving the operating efficiency of the boiler unit.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solution: a method for regulating the oxygen content of a coal-fired boiler, comprising the following steps:

[0006] Step S1, calculating the amount of coal fed into each coal mill Gj and the calorific value of the coal fed into the mill Qnet in real time;

[0007] Step S2: Calculate the total amount of coal fed into the furnace G: ;

[0008] Step S3, collecting multiple groups of data at 1 second intervals to form a data group, the data group including: total coal quantity Gi, coal calorific value Qneti, total air volume Qi, oxygen content O2i, where i is the data sequence number;

[0009] Step S4: Calculate excess air coefficient : , determine the delay time t0 of oxygen quantity to operating parameters through modeling;

[0010] Step S5: Establishing a total air volume model , calculate the theoretical total air volume Q; where: k1 is the modeling coefficient, B is the constant term, and O2sp is the oxygen content setting value;

[0011] Step S6: Calculate the air supply volume feedforward correction value dQ=Q-Q0, and add it into the original control system after being limited by upper and lower limits.

[0012] As a further improvement to the technical solution of the present invention, the amount of coal entering the furnace Gj is calculated by using a primary air duct air-powder resistance method or coal mill operating parameter modeling.

[0013] As a further improvement to the technical solution of the present invention, the calorific value Qnet of the coal entering the furnace is obtained by thermal balance calculation of the boiler unit or operating parameter modeling.

[0014] As a further improvement of the technical solution of the present invention, the method for determining the delay time t0 is: using Qi / (Gi*Qneti) as the independent variable and modeling the excess air coefficient from 1 second to t seconds, the correlation coefficient R 2 The delay time corresponding to the highest value.

[0015] As a further improvement to the technical solution of the present invention, in the total air volume model, the modeling coefficient k1 and the constant term B are determined based on the historical operating data of the unit. For a 660MW unit, k1=0.0172 and B=-15.1.

[0016] As a further improvement to the technical solution of the present invention, the upper and lower limits of the correction value dQ are limited to ±50t / h.

[0017] As a further improvement to the technical solution of the present invention, in step S2, the number of data groups collected is no less than 100.

[0018] As a further improvement to the technical solution of the present invention, a coal-fired boiler oxygen regulation system includes:

[0019] Data acquisition module, used to collect parameters at 1 second intervals, including total coal quantity, coal calorific value, total air volume and oxygen content;

[0020] The module for calculating the amount of coal fed into the furnace and its calorific value is used to calculate the amount of coal fed into the furnace Gj and the calorific value of coal fed into the furnace Qnet;

[0021] A delay time determination module is used to determine the oxygen delay time t0 through modeling analysis;

[0022] Total air volume modeling module, used to establish the total air volume model and calculate Q;

[0023] Feedforward correction module, used to calculate dQ and set upper and lower limits.

[0024] As a further improvement to the technical solution of the present invention, the delay time determination module obtains the highest correlation coefficient R by modeling Qi / (Gi*Qneti) and the excess air coefficient with different delay times. 2 Corresponding t0.

[0025] As a further improvement to the technical solution of the present invention, the upper and lower limit ranges of dQ by the feedforward correction module are ±50t / h.

[0026] The present invention has the following beneficial effects:

[0027] Air volume feedforward precisely matches combustion requirements: Through online calculation of the amount of coal entering the furnace and its calorific value and total air volume modeling, the problem of deviation between the fuel command and the actual amount of coal entering the furnace in traditional control is resolved. This improves the accuracy of matching the air volume feedforward with the oxygen required for combustion, avoiding large deviations in the air volume during variable load conditions.

[0028] Dynamic optimization of oxygen adjustment delay time: Based on data modeling, the delay time of oxygen adjustment to operating parameters is determined to overcome the hysteresis effect of oxygen measurement. Compared with traditional PID control, it significantly shortens the time it takes to adjust oxygen to the set value and achieves fast tracking.

[0029] Reduce oxygen content fluctuations and fan overshoot: Through feedforward correction value limiting control, the deviation of actual oxygen content from the set value under variable load is reduced, while avoiding large overshoots of air volume and fan opening, thereby improving system stability.

[0030] Improve the variable load operation efficiency of the boiler: Accurate oxygen control reduces incomplete combustion losses and exhaust heat losses, thereby improving the combustion efficiency of the boiler during variable load, reducing standard coal consumption, and enhancing operational economy.

[0031] Enhanced control strategy adaptability: Through historical data modeling and parameter calibration, this method can be applied to coal-fired units of different capacities and can adapt to operating conditions such as fluctuations in the calorific value of the incoming coal, demonstrating strong engineering applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0033] Figure 1 This diagram illustrates a conventional oxygen control strategy for coal-fired boilers. The diagram illustrates the traditional control process: the boiler's fuel master control signal and total coal feed rate are used as feedforwards for air flow. The deviation between the measured oxygen level and the setpoint is used by a PID controller to generate air flow commands and fan opening commands.

[0034] Figure 2 Schematic diagram of the oxygen control strategy of the present invention.

[0035] Figure 3 It is a schematic diagram of the framework of the oxygen regulation system for a coal-fired boiler of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The exemplary embodiments and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0037] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, upper end, lower end, top, bottom...) are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0038] In the present invention, unless otherwise specified or limited, the term "connection" should be understood in a broad sense. For example, "connection" can mean fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two elements, or interaction between two elements, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0039] In addition, the terms "first," "second," and so on, used in this disclosure are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly indicating the number of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include at least one such feature. Furthermore, the technical solutions of various embodiments may be combined with each other, but only on the basis that they can be implemented by a person of ordinary skill in the art. If the combination of technical solutions contradicts or cannot be implemented, it shall be deemed that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this disclosure.

[0040] The present invention will be further described in detail below with reference to the accompanying drawings.

[0041] Reference Figure 2 ( Figure 2 This is a schematic diagram of the oxygen control strategy of the present invention. This diagram shows that, based on the original control strategy, the present invention calculates the air volume feedforward correction value dQ, which is then added to the original air volume feedforward Q0 after being limited by upper and lower limits, achieving precise oxygen regulation. A method for regulating oxygen in a coal-fired boiler includes the following steps:

[0042] Step S1, calculating the amount of coal fed into each coal mill Gj and the calorific value of the coal fed into the mill Qnet in real time;

[0043] Step S2: Calculate the total amount of coal fed into the furnace G: ;

[0044] Step S3, collecting multiple groups of data at 1 second intervals to form a data group, the data group including: total coal quantity Gi, coal calorific value Qneti, total air volume Qi, oxygen content O2i, where i is the data sequence number;

[0045] Step S4: Calculate excess air coefficient : , determine the delay time t0 of oxygen quantity to operating parameters through modeling;

[0046] Step S5: Establishing a total air volume model , calculate the theoretical total air volume Q; where: k1 is the modeling coefficient, B is the constant term, and O2sp is the oxygen content setting value;

[0047] Step S6: Calculate the air supply volume feedforward correction value dQ=Q-Q0, and add it into the original control system after being limited by upper and lower limits.

[0048] Specifically, in this embodiment, the amount of coal fed into the furnace Gj is calculated by using the primary air duct air-powder resistance method or coal mill operating parameter modeling.

[0049] Specifically, in this embodiment, the calorific value Qnet of the incoming coal is obtained through thermal balance calculation of the boiler unit or operating parameter modeling.

[0050] Specifically, in this embodiment, the method for determining the delay time t0 is: using Qi / (Gi*Qneti) as the independent variable and modeling the excess air coefficient from 1 second to t seconds, taking the correlation coefficient R 2 The delay time corresponding to the highest value.

[0051] Specifically, in this embodiment, in the total air volume model, the modeling coefficient k1 and the constant term B are determined based on the historical operating data of the unit. For a 660MW unit, k1=0.0172 and B=-15.1.

[0052] Specifically, in this embodiment, the upper and lower limits of the correction value dQ are within a range of ±50 t / h.

[0053] Specifically, in this embodiment, in step S2, the number of data groups collected is no less than 100.

[0054] Reference Figure 3 Specifically, in this embodiment, a coal-fired boiler oxygen regulation system includes:

[0055] Data acquisition module, used to collect parameters at 1 second intervals, including total coal quantity, coal calorific value, total air volume and oxygen content;

[0056] The module for calculating the amount of coal fed into the furnace and its calorific value is used to calculate the amount of coal fed into the furnace Gj and the calorific value of coal fed into the furnace Qnet;

[0057] A delay time determination module is used to determine the oxygen delay time t0 through modeling analysis;

[0058] Total air volume modeling module, used to establish the total air volume model and calculate Q;

[0059] Feedforward correction module, used to calculate dQ and set upper and lower limits.

[0060] Specifically, in this embodiment, the delay time determination module obtains the highest correlation coefficient R by modeling Qi / (Gi*Qneti) and the excess air coefficient with different delay times. 2 Corresponding t0.

[0061] Specifically, in this embodiment, the upper and lower limit ranges of dQ set by the feedforward correction module are ±50 t / h.

[0062] Taking a 660MW coal-fired unit as an example, the specific implementation of the present invention is further explained:

[0063] A method for regulating oxygen content in a coal-fired boiler, comprising:

[0064] (1) Apply the primary duct air-powder resistance method or calculate the real-time coal input Gj of each coal mill based on the coal mill operating parameters.

[0065] (2) The calorific value Qnet of the coal fed into the boiler is obtained by heat balance calculation of the boiler unit or by modeling the operating parameters.

[0066] (3) Calculate the total amount of coal fed into the furnace G:

[0067] (1)

[0068] (4) Obtain enough data sets at 1 second intervals. The data sets include: total coal quantity Gi, calorific value of coal quantity Qneti, total air volume Qi, boiler oxygen quantity O2i, etc., where i is the data sequence number.

[0069] (5) Calculation of excess air coefficient :

[0070] (2)

[0071] (6) Take Qi / (Gi*Qneti) as the independent variable and compare it with the dependent variable , strain after 1 second delay , ..., strain after a delay of t seconds Align modeling to obtain excess air coefficient Correlation coefficient R under different delay times 2 , take R 2 The maximum delay time t0 is the delay time of the oxygen amount O2i to the total coal amount Gi, total air volume Qi and other parameters.

[0072] (7) Gi*Qneti* The independent variable and Qi are the dependent variables for modeling, and the modeling relationship is obtained as follows:

[0073] (3)

[0074] Where: k1 is the modeling coefficient. For a specific 660MW unit, k1=0.0172;

[0075] B is a constant term. For a specific 660MW unit, B=-15.1;

[0076] O2sp is the oxygen setting value.

[0077] (8) Obtain the air supply volume feedforward value Q0 of the original control system and calculate the correction value dQ:

[0078] dQ=Q-Q0 (4)

[0079] After limiting dQ to upper and lower limits, add it to the original control system to achieve rapid and accurate tracking of oxygen content to the set value. Figure 2 shown.

[0080] Taking a 660MW coal-fired unit as an example, it should be noted that:

[0081] Calculation of coal quantity and calorific value: The coal quantity Gj entering each pulverizer is calculated in real time using the primary air duct air-powder resistance method, and the calorific value of the coal entering the furnace, Qnet = 23 MJ / kg, is obtained through boiler heat balance calculation.

[0082] Calculation of total coal input: Assuming that 4 coal mills are put into operation, and the coal input is G1 = 50 t / h, G2 = 50 t / h, G3 = 50 t / h, G4 = 50 t / h, then the total coal input (G = 50 + 50 + 50 + 50 = 200 t / h.

[0083] Data collection and delay time determination: 100 sets of data were collected at 1 second intervals, Qi / (Gi*Qneti) was used as the independent variable, and the excess air coefficient with different delay times was modeled. When the delay time t0 = 3 seconds, the correlation coefficient R 2 = 0.95 is the highest value, which determines the delay time to be 3 seconds.

[0084] Total air volume modeling: Substitute the oxygen set value O2sp = 3.5% into the model , the theoretical total air volume Q is calculated to be 0.0172 *200 * 23 *21 / 17.5- 15.1≈1023 t / h.

[0085] Feedforward correction: If the original control system's air volume feedforward value (Q0 = 980 t / h, then the correction value dQ = 1023 -980 = 43 t / h. After being limited by upper and lower limits (such as ±50 t / h), dQ = 43 t / h is added to the original control system, so that the air volume instruction is adjusted to 980 + 43 = 1023 t / h, achieving rapid tracking of oxygen content.

[0086] In summary, the present invention has the following beneficial effects:

[0087] Air volume feedforward precisely matches combustion requirements: Through online calculation of the amount of coal entering the furnace and its calorific value and total air volume modeling, the problem of deviation between the fuel command and the actual amount of coal entering the furnace in traditional control is resolved. This improves the accuracy of matching the air volume feedforward with the oxygen required for combustion, avoiding large deviations in the air volume during variable load conditions.

[0088] Dynamic optimization of oxygen adjustment delay time: Based on data modeling, the delay time of oxygen adjustment to operating parameters is determined to overcome the hysteresis effect of oxygen measurement. Compared with traditional PID control, it significantly shortens the time it takes to adjust oxygen to the set value and achieves fast tracking.

[0089] Reduce oxygen content fluctuations and fan overshoot: Through feedforward correction value limiting control, the deviation of actual oxygen content from the set value under variable load is reduced, while avoiding large overshoots of air volume and fan opening, thereby improving system stability.

[0090] Improve the variable load operation efficiency of the boiler: Accurate oxygen control reduces incomplete combustion losses and exhaust heat losses, thereby improving the combustion efficiency of the boiler during variable load, reducing standard coal consumption, and enhancing operational economy.

[0091] Enhanced control strategy adaptability: Through historical data modeling and parameter calibration, this method can be applied to coal-fired units of different capacities and can adapt to operating conditions such as fluctuations in the calorific value of the incoming coal, demonstrating strong engineering applicability.

[0092] The technical solutions provided by the embodiments of the present invention are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present invention. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, according to the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present invention.

Claims

1. A method for regulating oxygen content in a coal-fired boiler, characterized in that: The following steps are involved: Step S1, calculating the amount of coal fed into each coal mill Gj and the calorific value of the coal fed into the mill Qnet in real time; Step S2: Calculate the total amount of coal fed into the furnace G: ; Step S3, collecting multiple groups of data at 1 second intervals to form a data group, the data group including: total coal quantity Gi, coal calorific value Qneti, total air volume Qi, oxygen content O2i, where i is the data sequence number; Step S4: Calculate excess air coefficient : , determine the delay time t0 of oxygen quantity to operating parameters through modeling; Step S5: Establishing a total air volume model , calculate the theoretical total air volume Q; where: k1 is the modeling coefficient, B is the constant term, and O2sp is the oxygen content setting value; Step S6: Calculate the air supply volume feedforward correction value dQ=Q-Q0, and add it into the original control system after being limited by upper and lower limits.

2. The method for regulating oxygen content in a coal-fired boiler according to claim 1, wherein: The amount of coal fed into the furnace Gj is calculated by the primary air duct air-powder resistance method or the coal mill operating parameter modeling.

3. The method for regulating oxygen content in a coal-fired boiler according to claim 1, wherein: The calorific value Qnet of the incoming coal is obtained through thermal balance calculation of the boiler unit or operating parameter modeling.

4. The method for regulating oxygen content in a coal-fired boiler according to claim 1, wherein: The method for determining the delay time t0 is as follows: using Qi / (Gi*Qneti) as the independent variable and modeling the excess air coefficient from 1 second to t seconds, the correlation coefficient R 2 The delay time corresponding to the highest value.

5. The method for regulating oxygen content in a coal-fired boiler according to claim 1, wherein: In the total air volume model, the modeling coefficient k1 and the constant term B are determined based on the historical operating data of the unit. For a 660MW unit, k1=0.0172 and B=-15.

1.

6. The method for regulating oxygen content in a coal-fired boiler according to claim 1, wherein: The upper and lower limits of the correction value dQ are within the range of ±50t / h.

7. The method for regulating oxygen content in a coal-fired boiler according to claim 1, wherein: In step S2, the number of data groups collected is no less than 100.

8. A coal-fired boiler oxygen regulation system, implementing the method according to any one of claims 1 to 7, characterized in that: include: Data acquisition module, used to collect parameters at 1 second intervals, including total coal quantity, coal calorific value, total air volume and oxygen content; The module for calculating the amount of coal fed into the furnace and its calorific value is used to calculate the amount of coal fed into the furnace Gj and the calorific value of coal fed into the furnace Qnet; A delay time determination module is used to determine the oxygen delay time t0 through modeling analysis; Total air volume modeling module, used to establish the total air volume model and calculate Q; Feedforward correction module, used to calculate dQ and set upper and lower limits.

9. The coal-fired boiler oxygen regulation system according to claim 8, characterized in that: The delay time determination module obtains the highest correlation coefficient R by modeling Qi / (Gi*Qneti) and the excess air coefficient at different delay times. 2 Corresponding t0.

10. The coal-fired boiler oxygen regulation system according to claim 8, characterized in that: The upper and lower limits of dQ set by the feedforward correction module are ±50t / h.

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