A method for correcting the air-coal ratio of a medium-speed mill based on precise air-coal measurement

Abstract

The present invention discloses a method for correcting the air-to-coal ratio of a medium-speed mill based on precise air-to-coal measurement. The method comprises: firstly, using array-type electrostatic induction non-contact full-section air-to-coal monitoring technology, installing a coal powder flow velocity measurement device on each powder pipe at the medium-speed mill outlet, and displaying the measured coal powder flow velocity value in each powder pipe in real time; secondly, installing a coal powder flow balancing valve on the coal powder pipe at the medium-speed mill outlet to balance and adjust the coal powder flow velocity in each coal powder pipe; based on the balanced distribution of coal powder in each primary air-to-coal pipe on the pulverizing side, correcting the mill air-to-coal ratio function according to the coal powder flow velocity under real-time working conditions, and controlling the air-to-coal ratio of the medium-speed mill under the current working conditions to an optimal curve. Thus, based on the balanced distribution of coal powder in each primary air-to-coal pipe on the pulverizing side, the primary air-to-coal ratio of the medium-speed mill can be corrected by precise measurement of the primary air-to-coal flow velocity, thereby achieving optimal control of the air-to-coal ratio.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal automatic control of thermal power plants, and in particular relates to a method for correcting the air-coal ratio of a medium-speed mill based on precise air-powder measurement. Background Art

[0002] Most large-capacity coal-fired units in China use a medium-speed mill direct-fired pulverizing system, which provides reliable coal supply for the boiler combustion process. The medium-speed mill primary air-to-coal ratio is a key parameter for mill operation control. Economical and stable combustion require an appropriate air-to-coal ratio. Both excessively high and insufficient air-to-coal ratios can affect the normal combustion of pulverized coal in the furnace. If the primary air-to-coal ratio is too high, low pulverized coal concentrations can easily result when the mill is under low load, hindering stable combustion. If the primary air-to-coal ratio is too low, pulverized coal can easily become blocked in the mill and cause a high amount of pebbled coal, posing a significant safety risk to the unit. Therefore, an appropriate primary air-to-coal ratio is crucial for the normal operation of the mill and, ultimately, the entire unit.

[0003] Currently, the primary air-to-coal ratio control in coal-fired power plants is still quite extensive. The ratio is set as a function of the coal feed rate to the mill, with different coal feed rates corresponding to different primary air volumes. In actual operation, to prevent mill blockage, the primary air-to-coal ratio is generally set too high. Inaccurate primary air volumes at the mill inlet and inconsistent coal types further complicate optimal primary air-to-coal ratio control. Furthermore, the inability to precisely control the state and distribution of pulverized coal in the pulverizing system can easily lead to problems such as uneven burning and uneven heat load within the furnace, further complicating optimal control of the primary air-to-coal ratio.

[0004] The combustion problem of a boiler ultimately comes down to the precise coordination of air and coal. The primary air pulverized coal flow rate affects the ignition position. If the pulverized coal flow rate is too low, it will cause powder accumulation and blockage in the pulverized coal pipe, and will also cause premature ignition and burnout of the burner. If the pulverized coal flow rate is too high, it will easily cause the flame to scour the water-cooled wall, delaying ignition. Under low load, it is more likely to cause the burner to extinguish and the boiler to burn unstable. The accuracy of the mill primary air volume measurement has always been a major problem in the operation and control of the pulverizing system. The pulverized coal pipe at the mill outlet has sufficient straight pipe sections, and the accuracy and reliability of the pulverized coal flow rate measurement at the mill outlet are higher than those of the inlet air volume device. Therefore, on the basis of balanced pulverized coal distribution in each primary air pulverized coal pipe on the pulverizing side, it is of great practical significance to correct the primary air-to-coal ratio of the medium-speed mill through accurate measurement of parameters such as the primary air pulverized coal flow rate and concentration to achieve optimal control of the air-to-coal ratio. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for correcting the primary air-coal ratio of a medium-speed mill based on precise measurement of air and powder. The method can automatically correct the primary air flow setting at the mill inlet according to the air-powder flow rate under the current operating conditions, and obtain the optimal air-coal ratio under the current operating conditions based on the load requirements and stable combustion needs.

[0006] The present invention provides a method for correcting the air-to-coal ratio of a medium-speed mill based on precise air-to-coal measurement, comprising: step 1, obtaining a real-time coal powder flow rate measurement value in a coal powder pipeline at a coal mill outlet; step 2, performing online adjustment on the real-time coal powder flow rate measurement value so that a deviation between the real-time coal powder flow rate measurement value and an average coal powder flow rate measurement value within a preset time period is not greater than a first preset threshold; step 3, setting a coal powder flow rate requirement value in each coal powder pipeline at a mill outlet according to the load output of the medium-speed mill, and judging whether the difference between the average coal powder flow rate measurement value and the coal powder flow rate requirement value is less than a second preset threshold; step 4, if the difference between the average coal powder flow rate measurement value and the coal powder flow rate requirement value is not less than the second preset threshold, outputting a primary air volume offset to the primary air volume setting value through an air-to-coal ratio correction PID with only integral action, so that the average coal powder flow rate measurement value is adjusted to a difference with the coal powder flow rate requirement value that is less than the second preset threshold by changing the primary air volume.

[0007] Furthermore, in step 1, obtaining the real-time coal powder flow rate measurement value in the powder pipe at the coal mill outlet includes: controlling the coal powder flow rate measuring device provided on the powder pipe to obtain the real-time coal powder flow rate measurement value in the powder pipe at the coal mill outlet.

[0008] Furthermore, in step 2, the online adjustment of the real-time pulverized coal flow rate measurement value includes: controlling a pulverized coal flow balancing electric valve provided on the pulverized coal pipe to online adjust the real-time pulverized coal flow rate measurement value.

[0009] Furthermore, in step 2, the preset threshold is set to 2 m / s.

[0010] Furthermore, the average pulverized coal flow rate measurement value is controlled within a range of 20 m / s to 24 m / s.

[0011] The present application discloses a method for correcting the air-coal ratio of a medium-speed mill based on precise air-powder measurement. First, an array-type electrostatic induction non-contact full-section air-powder monitoring technology is adopted. A coal powder flow rate measuring device is installed on each powder pipe at the outlet of the medium-speed mill to display the measured value of the coal powder flow rate in each powder pipe in real time. Secondly, a coal powder flow balancing valve is installed on the coal powder pipe at the outlet of the medium-speed mill to balance the coal powder flow rate in each coal powder pipe. On the basis of balanced distribution of coal powder in each primary air-powder pipe on the pulverizing side, the mill air-coal ratio function is corrected according to the coal powder flow rate under real-time working conditions, and the air-coal ratio of the medium-speed mill under the current working conditions is controlled within the optimal curve. Therefore, on the basis of balanced distribution of coal powder in each primary air-powder pipe on the pulverizing side, the primary air-coal ratio of the medium-speed mill can be corrected by precise measurement of the primary air-powder flow rate to achieve optimal control of the air-coal ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following is a brief introduction to the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0013] Figure 1 This is a flow chart of a method for correcting the air-coal ratio of a medium-speed mill based on precise air-coal measurement provided by one embodiment of the present invention;

[0014] Figure 2 A SAMA diagram for correcting the primary air volume setting value of a medium-speed mill using the pulverized coal flow rate is provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0016] Reference Figure 1 As shown in FIG, a method for correcting the air-coal ratio of a medium-speed mill based on accurate air-coal measurement includes the following steps:

[0017] Step 1: Obtain the real-time coal powder flow rate measurement value in the coal powder pipeline at the coal mill outlet.

[0018] Adopting array electrostatic induction non-contact full-section air-powder monitoring technology, a coal powder flow rate measuring device is installed at each powder pipe at the outlet of the medium-speed mill to display the coal powder flow rate measurement value in each powder pipe in real time.

[0019] Step 2: Online adjustment is performed on the real-time measured value of the pulverized coal flow rate so that the deviation between the real-time measured value of the pulverized coal flow rate and the average measured value of the pulverized coal flow rate in a preset time period is not greater than a first preset threshold.

[0020] A pulverized coal flow balancing electric valve is installed on each pulverized coal pipeline at the medium-speed mill outlet to adjust the pulverized coal flow rate in each pulverized coal pipeline online to achieve a deviation of the pulverized coal flow rate in each pulverized coal pipeline from the average value of ≤2m / s.

[0021] Step 3: Set the required pulverized coal flow rate in each pulverized coal pipe at the mill outlet according to the load output of the medium-speed mill, and determine whether the difference between the average pulverized coal flow rate measurement value and the required pulverized coal flow rate is less than a second preset threshold.

[0022] Based on a balanced distribution of pulverized coal in each primary air duct on the pulverizing side, a required pulverized coal flow rate in each pulverized coal duct at the mill outlet is determined based on the load output of the medium-speed mill. If the average pulverized coal flow rate deviates from the required control value, provided the load output of the medium-speed mill varies by less than 5%, a primary air volume offset is applied to the set primary air volume. By adjusting the primary air volume, the average pulverized coal flow rate is controlled to near the required value. This method can maintain the mill's air-to-coal ratio near its optimal value.

[0023] Step 4: If the difference between the average pulverized coal flow rate measurement value and the pulverized coal flow rate requirement value is not less than the second preset threshold value, a primary air volume offset is output to the primary air volume set value through an air-coal ratio correction PID with only integral action, so that the average pulverized coal flow rate measurement value is adjusted to a difference with the pulverized coal flow rate requirement value that is less than the second preset threshold value by changing the primary air volume.

[0024] In summary, the method of the present application first adopts array-type electrostatic induction non-contact full-section air-powder monitoring technology, installs a coal powder flow rate measurement device on each powder pipe at the outlet of the medium-speed mill, and displays the coal powder flow rate measurement value in each powder pipe in real time; secondly, a coal powder flow balancing valve is installed on the coal powder pipeline at the outlet of the medium-speed mill to balance the coal powder flow rate in each coal powder pipeline; on the basis of balanced coal powder distribution in each primary air-powder pipeline on the pulverizing side, the mill air-coal ratio function is corrected according to the coal powder flow rate under real-time working conditions, and the air-coal ratio of the medium-speed mill under the current working conditions is controlled within the optimal curve, so that on the basis of balanced coal powder distribution in each primary air-powder pipeline on the pulverizing side, the primary air-coal ratio of the medium-speed mill can be corrected by accurately measuring the primary air-powder flow rate to achieve optimal control of the air-coal ratio.

[0025] The following is an example of a practical application of the present invention to facilitate understanding. After engineering processing, the method described in the present invention is applied to the optimization of the primary air-coal ratio control of a 1000MW supercritical unit in a thermal power plant. Figure 2 As shown, the process is as follows:

[0026] First, a coal powder flow rate measuring device is installed at each powder pipe at the outlet of the medium-speed mill to display the coal powder flow rate measurement value in each powder pipe in real time;

[0027] Secondly, electric pulverized coal flow balancing valves are installed on each pulverized coal pipeline at the medium-speed mill outlet to adjust the pulverized coal flow rate in each pipeline online, so that the deviation of the pulverized coal flow rate in each pipeline from the average value is ≤2m / s;

[0028] On the pulverizing side, the average pulverized coal flow rate in each pulverized coal pipe at the mill outlet is controlled within a reasonable range based on the load output of the medium-speed mill. When the load output of the medium-speed mill varies by less than 5%, the average pulverized coal flow rate is controlled between 20m / s and 24m / s. If the average pulverized coal flow rate deviates from the control requirement (22m / s) by more than 2m / s, a PID correction with an integral-only air-to-coal ratio is used to output a primary air volume offset to the set primary air volume. This offset is then adjusted to bring the average pulverized coal flow rate close to the control value. This offset is reset to zero after the mill primary air volume control is automatically released. The design air-to-coal ratio F1(X) and pulverized coal flow rate F2(X) are shown in Tables 1 and 2, respectively.

[0029] Table 1 Design air-coal ratio F1(X) of coal mill under different load output conditions

[0030]

[0031] Table 2 Corresponding coal powder flow rate F2(X) under different load output conditions of coal mill

[0032]

[0033] The security of the correction process includes:

[0034] (1) In order to ensure the safe and stable operation of the mill, the limit of the correction output size is increased, and only a correction amount of ±10t / h can be added.

[0035] (2) To achieve small dynamic corrections and reduce disturbances to the primary air volume, the PID parameters for the correction coefficient are set to 0, with the proportional coefficient P set to 0 and the integral time I set to 600 seconds. This allows for correction of the primary air volume through slow integral adjustment. Furthermore, when the primary air volume is automatically switched to manual, the correction coefficient PID stops calculating and the PID output is set to zero.

[0036] Specifically, this solution was piloted for optimizing the primary air-to-coal ratio at medium-speed mills at multiple power generation companies, achieving positive results. After optimization, analysis of actual operational performance revealed that the leveling function of the electric valves balancing the pulverized coal flow in each pulverized coal pipeline at the medium-speed mill outlet eliminated uneven combustion caused by pulverized coal flow. This ensured a stable flame center during low-load boiler operation, significantly reduced boiler thermal deviation, maintained steam temperature parameters, and reduced the amount of cooling water at each level. Under stable load, the pulverized coal flow rate at each mill dropped from approximately 30 m / s to 20-24 m / s, increasing mill inlet air temperature and reducing exhaust gas temperature by 10°C compared to pre-optimization levels, thereby improving boiler efficiency. Following optimization, the pulverizing system operated stably, with no significant increase in the amount of pebble coal observed in the mills. Wear on the primary air ducts and burners was alleviated.

[0037] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for correcting the air-coal ratio of a medium-speed mill based on precise air-coal measurement, characterized in that: include: Step 1: obtaining a real-time measured value of the pulverized coal flow rate in the pulverized coal pipeline at the coal mill outlet, wherein obtaining the real-time measured value of the pulverized coal flow rate in the pulverized coal pipeline at the coal mill outlet includes: Adopting the non-contact full-section air-powder monitoring method of array electrostatic induction, a pulverized coal flow rate measuring device is installed on each pulverized coal pipeline at the outlet of the medium-speed mill. The pulverized coal flow rate measuring device installed on the pulverized coal pipeline is controlled to obtain the real-time pulverized coal flow rate measurement value in the pulverized coal pipeline at the outlet of the pulverizer; Step 2: Online adjustment is performed on the real-time pulverized coal flow rate measurement value so that the deviation between the real-time pulverized coal flow rate measurement value and the average pulverized coal flow rate measurement value within a preset time period is no greater than a first preset threshold value; Step 3: setting a required coal flow rate in each coal pulverized pipe at the mill outlet according to the load output of the medium-speed mill, and determining whether the difference between the average coal pulverized flow rate measurement value and the required coal pulverized flow rate is less than a second preset threshold; Step 4: If the difference between the average pulverized coal flow rate measurement value and the pulverized coal flow rate requirement value is not less than the second preset threshold value, a primary air volume offset is output to the primary air volume set value through an air-coal ratio correction PID with only integral action, so that the average pulverized coal flow rate measurement value is adjusted to a difference with the pulverized coal flow rate requirement value that is less than the second preset threshold value by changing the primary air volume.

2. The method for correcting the air-coal ratio of a medium-speed mill based on precise air-coal measurement according to claim 1 is characterized in that: In step 2, the online adjustment of the real-time pulverized coal flow rate measurement value includes: The pulverized coal flow balancing electric valve provided on the pulverized coal pipeline is controlled to perform online adjustment on the real-time pulverized coal flow rate measurement value.

3. The method for correcting the air-coal ratio of a medium-speed mill based on precise air-coal measurement according to claim 1 is characterized in that: In step 2, the first preset threshold is set to 2 m / s.

4. The method for correcting the air-coal ratio of a medium-speed mill based on precise air-coal measurement according to claim 1 is characterized in that: In step 4, the average pulverized coal flow rate measurement value is controlled within a range of 20 m / s to 24 m / s.

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