An online monitoring system for coal powder fineness based on dust charge

Abstract

The present invention discloses an online monitoring system for coal powder fineness based on dust charge. The system comprises a pair of electrodes, one and two, installed on a straight section of a primary air duct that conveys coal powder airflow to a boiler. The electrodes are connected to a constant voltage power supply via a wire. The constant voltage power supply applies a constant voltage U to the measuring section of the primary air duct during measurement. Cables are drawn from the electrodes to a charge measuring instrument, which measures the charge on the electrodes. The charge measuring instrument transmits the signal to a signal conversion device. The signal conversion device simultaneously collects the primary wind speed measurement signal and the coal feed rate signal obtained by on-site measurement. The signal conversion device converts the collected charge signal, the primary wind speed measurement signal, and the coal feed rate signal into a coal powder fineness signal, which is output via an output instrument. The system can monitor and sense the coal powder fineness before entering the furnace of a power plant in real time, providing a decision-making reference for adjusting the operation of the pulverizer and optimizing furnace combustion.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal powder measurement application in the power generation industry, and in particular relates to an online monitoring system for coal powder fineness based on dust charge. Background Art

[0002] The coal mill is a key auxiliary machine in a power plant's boiler system and the core equipment of the pulverizing system. It is responsible for grinding raw coal from the coal yard into pulverized coal for combustion in the boiler. The fineness of the pulverized coal at the mill outlet can be adjusted on-site. While too coarse pulverized coal saves mill power, it affects boiler efficiency and economics. While too fine pulverized coal facilitates ignition and improves boiler efficiency, it also increases mill power consumption, potentially leading to insufficient mill output and increased equipment wear and depreciation. Therefore, real-time monitoring of the fineness of the pulverized coal entering the furnace is essential.

[0003] However, measuring coal fineness presents numerous challenges. Existing methods typically rely on manual or machine sampling and testing, with results obtained after the fact and limited real-time guidance. While other approaches exist, such as laser diffraction, charge sensing, and high-speed camera imaging, these still suffer from limited accuracy, high maintenance costs, expensive construction, and poor stability. Summary of the Invention

[0004] To overcome these technical challenges, the present invention provides an online monitoring system for pulverized coal fineness based on dust charge. This system, installed in the straight section of the primary air duct, measures the fineness of incoming coal in real time, providing data support for mill operation management and boiler combustion optimization. This system can monitor and sense the fineness of pulverized coal entering the power plant furnace in real time, providing a reference for decision-making on mill operation adjustments and furnace combustion optimization.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] An online monitoring system for coal powder fineness based on dust charge includes an electrode 1 3 and an electrode 2 6 installed on a straight pipe section of a primary air duct 1 that conveys coal powder airflow to a boiler. The electrode 1 3 and the electrode 2 6 are connected to a constant voltage power supply 5 via a wire 4. The constant voltage power supply 5 is used to load a constant voltage U on the measuring pipe section of the primary air duct 1 during measurement. The electrode 1 3 and the electrode 2 6 lead out a cable 2 to a charge measuring instrument 7. The charge measuring instrument 7 is used to measure the amount of charge on the electrodes. The charge measuring instrument 7 transmits the signal to a signal conversion device 8. At the same time, the signal conversion device 8 receives a primary wind speed measurement signal 10 and a coal feed amount signal 11 obtained by on-site measurement. The signal conversion device 8 converts the collected charge signal 7, the primary wind speed measurement signal 10, and the coal feed amount signal 11 into a coal powder fineness signal, which is output through an output meter 9.

[0007] The electrode 1 3 and the electrode 2 6 are symmetrically installed in the upper and lower arc segments of the straight pipe section of the primary air duct 1. The electrode length l is required to be no less than 2 times the inner diameter d of the primary air duct and no more than 1 / 3 of the total length L of the straight pipe section where it is installed, that is, 2d≤l≤L / 3.

[0008] The included angle θ between the arc segments of the electrode 1 3 and the electrode 2 6 and the center of the pipeline is in the range of 15°<θ<60°.

[0009] The primary air duct 1 contains a flowing coal powder airflow 12 , and the other parts of the primary air duct 1 connected to the electrodes are made of insulating materials to prevent the charge on the electrodes from being lost through the primary air duct 1 .

[0010] There is no special requirement for the positive and negative poles of the electrode 1 3 and the electrode 2 6 , and one positive pole and one negative pole can be freely set according to the on-site conditions.

[0011] The power supply 5 for applying voltage to the electrode 1 3 and the electrode 2 6 is a constant low voltage power supply, which is less than 36V. The specific voltage value can be adjusted according to the on-site measurement signal.

[0012] Beneficial effects of the present invention:

[0013] Based on the physical properties of pulverized coal, this invention designs a simple and easy-to-implement measurement device that senses changes in coal fineness and converts and outputs electrical signals, enabling real-time monitoring of the actual coal fineness within the primary air duct. This provides a new option for measuring coal fineness in power plants, offering ease of implementation and low maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a diagram of the system device of the present invention.

[0015] Figure 2 Cross-sectional installation diagram of electrodes arranged in the primary air duct. DETAILED DESCRIPTION

[0016] The present invention will be described in further detail below with reference to the accompanying drawings.

[0017] like Figure 1 、 Figure 2 As shown:

[0018] Step 1: Arrange the main devices of the online monitoring system: Arrange a pair of electrodes 1 3 and 2 6 at appropriate locations in the primary air duct 1 and connect them to a constant voltage power supply 5 via a wire 4. When a voltage U is applied to the electrodes, the charge characteristics of the pulverized coal are utilized to generate charge on the surface of the pulverized coal, and the charge gradually accumulates on the electrodes under the action of the applied voltage.

[0019] Step 2: Determine the main theoretical basis and measurement parameters of the online monitoring system: Assuming that the chargeability of coal powder remains constant, that is, the charge per unit area n remains unchanged, then the charge of coal powder at this position depends on the specific surface area of ​​coal powder. When the coal powder concentration c remains unchanged, the specific surface area is a function of the coal powder fineness, so the charge carried by coal powder is a function of the coal powder fineness. Connect electrode 1 3 and electrode 2 6 to the charge measuring instrument 7 through the shielded signal cable 2 to monitor the charge on the electrodes. When voltage is applied to electrode 1 3 and electrode 2 6 on the measuring section of the primary air duct 1, the measuring section is equivalent to a capacitor. The charge carried by the coal powder between the two poles of the capacitor determines the size of the capacitor. Therefore, the size of the capacitor is a function of the coal powder fineness and the coal powder concentration, as shown in formula (1):

[0020] C=f1(R 90 ,c) (1)

[0021] Step 3: Collect necessary data through the monitoring system: obtain the air flow G and pulverized coal flow F in the pipeline through the primary air velocity measuring device 10 and the coal feed signal measuring device 11, thereby obtaining the pulverized coal concentration in the primary air duct:

[0022] c=F / G (2)

[0023] By measuring the voltage U of the load power supply 5 of the pipe section and the charge Q obtained by the charge measuring instrument 7, the capacitance of the measuring pipe section corresponding to the coal powder concentration c is obtained, as shown in formula (3):

[0024] C=Q / U (3)

[0025] Step 4: The functional relationship between the collected data signal and the coal fineness is obtained by deduction and mathematical fitting: the charge measuring instrument 7, the primary air velocity measuring device 10 and the coal feed signal measuring device 11 are connected to the signal conversion device 8, and each measurement signal is converted and calculated on the 8 to obtain the coal fineness value R 90 , the data information directly collected and the coal powder fineness R 90 The existing relationship can be derived from equations (1) to (3) as shown in (4):

[0026] R 90 =f2(Q,U,F / G) (4)

[0027] From formula (4), we can know that the coal powder fineness R 90 There is a functional relationship between the electrode loading voltage U, the charge signal Q on the electrode, the pulverized gas amount F, and the primary air volume G. Therefore, in this monitoring system, the independent variable parameters in formula (4) are collected in real time, and the pulverized coal is sampled and tested regularly to obtain the pulverized coal fineness data R. 90 ; The coal powder fineness R measured regularly offline 90The results are mathematically fitted with the parameters U, Q, F, and G collected in real time to obtain the coal powder fineness R 90 Functional relationship f2 with the collected monitoring operating parameters:

[0028] Mathematical fitting can be done using polynomial or exponential functions and can be corrected regularly;

[0029] Step 5: Convert the real-time measured parameters into coal powder fineness values ​​through the signal conversion device 8 according to the fitting function relationship: In the real-time measurement system, the signal conversion device 8 collects and summarizes the primary air flow G, coal powder amount F, the voltage U loaded on the pipeline electrode 1 3 and the electrode 2 6, and the measured charge Q, and sends the real-time coal powder fineness data to the instrument 9 for output according to the function relationship f2 obtained in step 4. The output result is calculated according to the formula (4) obtained by regular fitting in step 4.

[0030] like Figure 2 As shown, electrodes 1 3 and 2 6 are symmetrically installed in the upper and lower arcs of the straight section of the primary air duct 1. To ensure sufficient electric field effect generated by the electrodes and not affect the flow and safety of the pulverized coal airflow within the duct, the electrode length l is required to be no less than twice the primary air duct inner diameter d and no greater than 1 / 3 of the total length L of the straight section in which they are installed, that is, 2d ≤ l ≤ L / 3. If the length of a straight section of the primary air duct is too short to meet the above installation requirements, then that section is not suitable for installing the electrode pair measurement device, and another straight section that meets the requirements must be found.

[0031] There are also requirements for the arc segments of electrode 1 3 and electrode 2 6. If they are too large, the shape of the electrode plate will be distorted, and if they are too small, the electric field strength will be insufficient. Figure 2 As shown, the angle θ between the electrode arc segment and the center of the pipe is in the range of: 15°

Claims

1. An online monitoring system for coal powder fineness based on dust charge, characterized by: The invention comprises an electrode 1 (3) and an electrode 2 (6) installed on a straight pipe section of a primary air duct (1) for conveying pulverized coal airflow to a boiler, wherein the electrode 1 (3) and the electrode 2 (6) are connected to a constant voltage power supply (5) via a conductor (4), wherein the constant voltage power supply (5) is used to load a constant voltage U on the measuring pipe section of the primary air duct (1), wherein the electrode 1 (3) and the electrode 2 (6) lead out a cable (2) to a charge measuring instrument (7), wherein the charge measuring instrument (7) is used to measure the charge amount on the electrodes, wherein the charge measuring instrument (7) transmits the signal to a signal conversion device (8), and at the same time, the signal conversion device (8) receives a primary wind speed measurement signal (10) and a coal feeding amount signal (11) obtained by on-site measurement, wherein the signal conversion device (8) converts the collected charge signal, the primary wind speed measurement signal (10) and the coal feeding amount signal (11) into a coal powder fineness signal, which is outputted through an output instrument (9); The electrode 1 (3) and the electrode 2 (6) are symmetrically installed in the upper and lower arc sections of the straight pipe section of the primary air duct (1). The electrode length l The required diameter is not less than the inner diameter of the primary air duct d 2 times, not more than 1 / 3 of the total length L of the straight pipe section where it is installed, that is, 2 d ≤ l ≤L / 3; The angle between the arc segments of the electrode 1 (3) and the electrode 2 (6) and the center of the pipeline θ Range: 15°< θ < 60°; There are no special requirements for the positive and negative poles of the electrode 1 (3) and the electrode 2 (6), and one positive pole and one negative pole can be freely set according to the on-site conditions; The power supply (5) for applying voltage to the electrode 1 (3) and the electrode 2 (6) is a constant low voltage power supply, which is less than 36V. The specific voltage value can be adjusted according to the on-site measurement signal.

2. The on-line monitoring system for coal powder fineness based on dust charge according to claim 1 is characterized in that: The primary air duct (1) contains a flowing coal powder airflow (12), and the other parts of the primary air duct (1) connected to the electrodes are made of insulating materials to prevent the charge on the electrodes from being lost through the primary air duct (1).

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