A method and system for regulating oxygen content in a coal-fired boiler

Abstract

This invention discloses a method and system for oxygen regulation in a coal-fired boiler. The method calculates the real-time coal feed rate of a single coal mill using the primary air duct resistance method or coal mill operating parameter modeling. Combined with boiler heat balance calculations or operating parameter modeling, the calorific value of the coal feed rate is obtained. After accumulating the total coal feed rate, operating data is collected at 1-second intervals. The excess air coefficient is calculated, and the oxygen delay time is determined. After establishing a dynamic model of the total air volume, the feedforward correction value of the air supply is calculated and superimposed onto the original control system after upper and lower limit constraints. The system includes modules for data acquisition, coal feed rate and calorific value calculation, delay time determination, total air volume modeling, and feedforward correction. This invention solves the problems of large feedforward deviation and lag in oxygen regulation in traditional control systems, achieving rapid and accurate oxygen tracking, improving the efficiency of boiler operation under varying loads, and is applicable to coal-fired units of different capacities.

Description

Technical Field

[0001] This invention relates to the field of coal-fired boiler operation control technology, specifically to a method and system for regulating oxygen content in a coal-fired boiler. Background Technology

[0002] During the operation of a coal-fired boiler, oxygen content is a crucial parameter affecting combustion efficiency and safety. Currently, oxygen content control in coal-fired boilers is generally achieved through PID control, and its conventional control strategy is shown in Figure 1: using the boiler fuel main control signal and total coal feed rate as feedforward for the air supply, and combining the deviation between the measured oxygen content and the set value, the PID controller generates air supply volume commands and blower opening commands.

[0003] However, this control strategy has significant drawbacks: on the one hand, due to the lag in pulverizing coal by the coal mill, there is a deviation between the boiler fuel command or total coal feed and the actual coal feed during load changes, and the calorific value of the coal feed fluctuates greatly, resulting in a mismatch between the air feedforward and the actual required oxygen, which in turn causes the actual oxygen to deviate significantly from the set value, affecting the boiler efficiency during load changes; on the other hand, oxygen measurement has a lag, and when the air feedforward deviation is large, it takes a long time to adjust the actual oxygen to the set value using oxygen PID control, and some units cannot even put oxygen control into operation, which seriously restricts the economic efficiency of boiler unit operation during load changes. Summary of the Invention

[0004] To address the problems of inaccurate air feedforward and lagging oxygen regulation in existing technologies, this invention provides a method and system for regulating oxygen in coal-fired boilers. By accurately calculating the air feedforward, it achieves rapid and precise regulation of oxygen, reduces oxygen fluctuations during load changes, and improves the operating efficiency of the boiler unit.

[0005] To achieve the above objectives, the present invention provides a method for adjusting the oxygen content of a coal-fired boiler, comprising the following steps:

[0006] Step S1: Calculate the amount of coal fed into the furnace Gj and the calorific value of the coal Qnet for each coal mill in real time;

[0007] Step S2: Calculate the total coal input G: ;

[0008] Step S3: Collect multiple sets of data at 1-second intervals to form a data group. The data group includes: total coal input Gi, calorific value of coal input Qneti, total air volume Qi, and oxygen content O2i, where i is the data sequence number.

[0009] Step S4: Calculate the excess air coefficient : The delay time t0 of oxygen quantity on operating parameters is determined by modeling.

[0010] Step S5: Establish the total air volume model Calculate the theoretical total air volume Q; where: k1 is the modeling coefficient, B is a constant term, and O2sp is the oxygen content setpoint.

[0011] Step S6: Calculate the feedforward correction value of the air supply volume dQ=Q-Q0, and add it to the original control system after upper and lower limit restrictions.

[0012] As a further improvement to the technical solution of the present invention, the amount of coal fed into the furnace, Gj, is obtained by modeling and calculating the primary air duct air-coal resistance method or the operating parameters of the coal mill.

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

[0014] As a further improvement to the technical solution of the present invention, the method for determining the delay time t0 is as follows: using Qi / (Gi*Qneti) as the independent variable, modeling with the excess air coefficient from a delay of 1 second to t seconds, and taking 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 sets collected is not less than 100 sets.

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

[0019] The data acquisition module is used to acquire parameters at 1-second intervals, including total coal input, calorific value of coal input, 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 the coal fed into the furnace, Qnet.

[0021] The delay time determination module is used to determine the oxygen delay time t0 through modeling and analysis.

[0022] The total air volume modeling module is used to build the total air volume model and calculate Q;

[0023] The feedforward correction module is used to calculate dQ and apply 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) with the excess air coefficient of different delay times. 2 The corresponding t0.

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

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

[0027] Precise matching of air supply volume feedforward with combustion demand: By calculating the amount of coal fed into the furnace and its calorific value online and modeling the total air volume, the problem of deviation between fuel command and actual amount of coal fed into the furnace in traditional control is solved, which improves the matching accuracy of air supply volume feedforward with the oxygen required for combustion and avoids large deviation of air supply volume when the load changes.

[0028] Dynamic optimization of oxygen regulation delay time: Based on data modeling, the delay time of oxygen to operating parameters is determined, overcoming the influence of oxygen measurement lag. Compared with traditional PID control, it significantly shortens the time for oxygen to be regulated to the set value and achieves rapid tracking.

[0029] Reduce oxygen fluctuations and blower over-adjustment: By using feedforward correction value limiting control, the deviation of actual oxygen from the set value during load changes is reduced, while avoiding large over-adjustments of air volume and blower opening, thus improving system stability.

[0030] Improving boiler efficiency during variable load operation: Precise oxygen control reduces incomplete combustion losses and flue gas heat losses, thereby improving boiler combustion efficiency during variable load operation, reducing standard coal consumption, and enhancing operational economy.

[0031] Enhanced control strategy adaptability: Through historical data modeling and parameter calibration, this method is applicable to coal-fired units of different capacities and can adapt to changes in operating conditions such as fluctuations in the calorific value of the coal fed into the furnace, thus possessing strong engineering applicability. Attached Figure Description

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

[0033] Figure 1 is a schematic diagram of the conventional strategy for oxygen control in coal-fired boilers in the prior art. The figure shows the traditional control process: the boiler fuel main control signal and the total coal feed rate are used as feedforwards for the air supply volume. The deviation between the measured oxygen value and the set value is used by the PID controller to generate air supply volume commands and blower opening commands.

[0034] Figure 2 is a schematic diagram of the oxygen control strategy of the present invention.

[0035] Figure 3 is a schematic diagram of the framework of the oxygen regulation system for coal-fired boilers of the present invention. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The illustrative 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 indicators (such as up, down, left, right, front, back, upper end, lower end, top, bottom, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0038] In this invention, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0039] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If the combination of technical solutions is contradictory or impossible to implement, such a combination should be considered non-existent and not within the scope of protection claimed by this invention.

[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. The diagram shows that, based on the original control strategy, the present invention calculates the air supply volume feedforward correction value dQ, limits it to upper and lower limits, and then superimposes it onto the original air supply volume feedforward Q0 to achieve precise oxygen regulation. A method for regulating oxygen in a coal-fired boiler includes the following steps:

[0042] Step S1: Calculate the amount of coal fed into the furnace Gj and the calorific value of the coal Qnet for each coal mill in real time;

[0043] Step S2: Calculate the total coal input G: ;

[0044] Step S3: Collect multiple sets of data at 1-second intervals to form a data group. The data group includes: total coal input Gi, calorific value of coal input Qneti, total air volume Qi, and oxygen content O2i, where i is the data sequence number.

[0045] Step S4: Calculate the excess air coefficient : The delay time t0 of oxygen quantity on operating parameters is determined by modeling.

[0046] Step S5: Establish the total air volume model Calculate the theoretical total air volume Q; where: k1 is the modeling coefficient, B is a constant term, and O2sp is the oxygen content setpoint.

[0047] Step S6: Calculate the feedforward correction value of the air supply volume dQ=Q-Q0, and add it to the original control system after upper and lower limit restrictions.

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

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

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

[0051] Specifically, in this embodiment, the modeling coefficient k1 and constant term B in the total air volume model are determined based on the fitting of 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 ±50t / h.

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

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

[0055] The data acquisition module is used to acquire parameters at 1-second intervals, including total coal input, calorific value of coal input, 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 the coal fed into the furnace, Qnet.

[0057] The delay time determination module is used to determine the oxygen delay time t0 through modeling and analysis.

[0058] The total air volume modeling module is used to build the total air volume model and calculate Q;

[0059] The feedforward correction module is used to calculate dQ and apply 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) with the excess air coefficient for different delay times. 2 The corresponding t0.

[0061] Specifically, in this embodiment, the feedforward correction module limits the upper and lower limits of dQ to ±50t / h.

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

[0063] A method for adjusting oxygen content in a coal-fired boiler, specifically including the following:

[0064] (1) The real-time coal feed rate Gj of each coal mill is obtained by applying the primary air duct air-coal resistance method or by modeling and calculating based on the operating parameters of the coal mill.

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

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

[0067] (1)

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

[0069] (5) Calculate the excess air coefficient :

[0070] (2)

[0071] (6) Using Qi / (Gi*Qneti) as the independent variable, and respectively with the dependent variable 1 second delay in dependent variable The dependent variable with a delay of t seconds. Alignment modeling yields the excess air coefficient Correlation coefficient R under different delay times 2 Take R 2 The delay time t0 of the highest value is the delay time of oxygen quantity O2i on parameters such as total coal input Gi and total air volume Qi.

[0072] (7) Using Gi*Qneti* Modeling with Qi as the independent variable and Qi as the dependent variable yields the following modeling relationship:

[0073] (3)

[0074] In the formula: k1 is the modeling coefficient, and 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 content setting value.

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

[0078] dQ=Q-Q0 (4)

[0079] By incorporating dQ into the original control system after setting upper and lower limits, oxygen levels can be quickly and accurately tracked to the set value. Figure 2 As shown.

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

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

[0082] Calculation of total coal feed rate: Assuming that 4 coal mills are in operation during unit operation, and the coal feed rates are G1 = 50 t / h, G2 = 50 t / h, G3 = 50 t / h, and G4 = 50 t / h respectively, then the total coal feed rate (G = 50 + 50 + 50 + 50 = 200 t / h).

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

[0084] Total air volume modeling: Substitute the oxygen setpoint 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 supply feedforward value (Q0 = 980 t / h) is 43 t / h, then the correction value dQ = 1023 - 980 = 43 t / h is added to the original control system after being limited by upper and lower limits (such as ±50 t / h), so that the air supply command is adjusted to 980 + 43 = 1023 t / h, thereby achieving rapid tracking of oxygen content.

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

[0087] Precise matching of air supply volume feedforward with combustion demand: By calculating the amount of coal fed into the furnace and its calorific value online and modeling the total air volume, the problem of deviation between fuel command and actual amount of coal fed into the furnace in traditional control is solved, which improves the matching accuracy of air supply volume feedforward with the oxygen required for combustion and avoids large deviation of air supply volume when the load changes.

[0088] Dynamic optimization of oxygen regulation delay time: Based on data modeling, the delay time of oxygen to operating parameters is determined, overcoming the influence of oxygen measurement lag. Compared with traditional PID control, it significantly shortens the time for oxygen to be regulated to the set value and achieves rapid tracking.

[0089] Reduce oxygen fluctuations and blower over-adjustment: By using feedforward correction value limiting control, the deviation of actual oxygen from the set value during load changes is reduced, while avoiding large over-adjustments of air volume and blower opening, thus improving system stability.

[0090] Improving boiler efficiency during variable load operation: Precise oxygen control reduces incomplete combustion losses and flue gas heat losses, thereby improving boiler combustion efficiency during variable load operation, reducing standard coal consumption, and enhancing operational economy.

[0091] Enhanced control strategy adaptability: Through historical data modeling and parameter calibration, this method is applicable to coal-fired units of different capacities and can adapt to changes in operating conditions such as fluctuations in the calorific value of the coal fed into the furnace, thus possessing strong engineering applicability.

[0092] The technical solutions provided by the embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for helping to understand the principles of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the embodiments of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for adjusting oxygen content in a coal-fired boiler, characterized in that, Includes the following steps: Step S1: Calculate the amount of coal fed into the furnace Gj and the calorific value of the coal Qnet for each coal mill in real time; Step S2: Calculate the total coal input G: ; Step S3: Collect multiple sets of data at 1-second intervals to form a data group. The data group includes: total coal input Gi, calorific value of coal input Qneti, total air volume Qi, and oxygen content O2i, where i is the data sequence number. Step S4: Calculate the excess air coefficient : With Qi / (Gi*Qneti) as the independent variable, and the excess air coefficient delayed from 1 second to t seconds. Model separately and take the correlation coefficient R. 2 The delay time corresponding to the highest value is used as the delay time t0 of oxygen quantity to operating parameters. This t0 provides the basic data for delay matching in the modeling and fitting of the total air volume model, and is used to determine the parameter correspondence required for modeling. Step S5: Establish the total air volume model based on the delay time t0 in step S4. Calculate the theoretical total air volume Q; where: k1 is the modeling coefficient, B is a constant term, and O2sp is the oxygen content setpoint. Step S6: Calculate the feedforward correction value of the air supply volume dQ=Q-Q0, and add it to the original control system after upper and lower limit restrictions.

2. The method for adjusting oxygen content in a coal-fired boiler according to claim 1, characterized in that: The amount of coal fed into the furnace, Gj, is obtained by modeling and calculating using the primary air duct air-coal resistance method or the coal mill operating parameters.

3. The method for adjusting oxygen content in a coal-fired boiler according to claim 1, characterized in that: The calorific value of the coal fed into the furnace, Qnet, is obtained through boiler unit heat balance calculations or operating parameter modeling.

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

1.

5. The method for adjusting oxygen content in a coal-fired boiler according to claim 1, characterized in that: The upper and lower limits of the correction value dQ are ±50t / h.

6. The method for adjusting oxygen content in a coal-fired boiler according to claim 1, characterized in that: In step S2, the number of data sets collected shall not be less than 100 sets.

7. An oxygen regulation system for a coal-fired boiler, implementing the method as described in any one of claims 1-6, characterized in that, include: The data acquisition module is used to acquire parameters at 1-second intervals, including total coal input, calorific value of coal input, 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 the coal fed into the furnace, Qnet. The delay time determination module is used to determine the oxygen delay time t0 through modeling and analysis. The total air volume modeling module is used to build the total air volume model and calculate Q; The feedforward correction module is used to calculate dQ and apply upper and lower limits.

8. The oxygen regulation system for a coal-fired boiler according to claim 7, characterized in that: The delay time determination module obtains the highest correlation coefficient R by modeling Qi / (Gi*Qneti) with the excess air coefficient for different delay times. 2 The corresponding t0.

9. The oxygen regulation system for a coal-fired boiler according to claim 7, characterized in that: The feedforward correction module limits the upper and lower limits of dQ to ±50t / h.

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