Online air speed and pulverized coal concentration monitoring system and method for primary air and pulverized coal pipeline

Abstract

The invention discloses a primary air powder pipeline on-line air speed and pulverized coal concentration monitoring system and method.The system comprises a static pressure difference measuring device and a dynamic and static pressure measuring device, the static pressure difference measuring device is provided with two static pressure measuring points, the two static pressure measuring points are arranged on a vertical pipeline, and micro pressure difference transmitters are arranged at the two static pressure measuring points; the dynamic and static pressure measuring device comprises a standard backrest pipe, an electromagnetic three-way valve, a pressure sensor and a compressed air source; a measuring point of the dynamic and static pressure measuring device is positioned in the center of the two static pressure measuring points; a pressure measuring opening of the standard backrest pipe is connected with an inlet of the electromagnetic three-way valve, an outlet of the electromagnetic three-way valve is connected with the compressed air source and the pressure sensor, and the micro pressure difference transmitter and the pressure sensor are connected with the input end of the data collector. The flow velocity and the pulverized coal concentration of the pulverized coal airflow are obtained by comparing the measured value and the calculated value of the static pressure difference of the pulverized coal airflow at the inlet and the outlet of the test section, the advantages of automatic operation convenience and test reliability are considered, and the reliability and persuasion are high.

Description

Technical Field

[0001] The invention belongs to the technical field of coal-fired boiler combustion monitoring and control, and particularly relates to a system and method for monitoring the online wind speed and coal powder concentration of a primary air-powder pipeline. Background Art

[0002] While the scale of installed renewable energy capacity continues to expand and its share continues to rise, its inherent output volatility and intermittency, coupled with bottlenecks in energy consumption and the lack of maturity in energy storage technology, have yet to yield breakthroughs. Therefore, thermal power will continue to play a vital role in ensuring power supply for a considerable period of time. The rapid development of the new energy industry has not only not diminished the strategic value of thermal power, but has also accelerated the evolution of the thermal power technology system towards efficient and flexible operation, deep peak-shaving response, and clean, low-carbon emissions. Furthermore, during the transitional phase of energy structure transformation, thermal power will gradually shift from being the primary power source to providing system regulation and support.

[0003] Currently, direct-fired pulverized coal systems are widely used in coal-fired units ranging from 300MW to 1000MW. For such systems, the uniformity of the air volume and pulverized coal content in the primary air ducts connecting the burners on the same level significantly impacts the safety and economics of boiler operation and is a key control variable affecting boiler combustion efficiency and stability. Uneven air and pulverized coal distribution in these ducts can lead to flame center deviation, localized slagging, and combustion pulsation in the furnace combustion zone. This not only causes combustion instability but also leads to uneven distribution of flue gas velocity and temperature fields in the superheater area, resulting in steam temperature deviations and even superheater tube bursts. Therefore, regularly measuring the pulverized coal flow rate in the ducts and uniformly controlling the pulverized coal concentration deviations in the pulverized coal pipes at the mill outlet to maintain an optimal air-to-coal ratio in the boiler not only improves efficiency and ensures safe production, but also effectively prevents a range of combustion problems and risks.

[0004] Currently, online measurement methods for primary air dust concentration can be roughly divided into two types: direct and indirect. The main representatives of direct methods include microwave, ultrasonic, laser, and capacitance methods. The main representatives of indirect methods include heat transfer, thermal balance, differential pressure, and temperature methods. Direct measurement methods are easy to use and have good real-time performance, but they also have disadvantages such as susceptibility to measurement changes and high installation or measurement costs, which have prevented the indirect method from being widely used in practice. Although the indirect method has a simple measurement principle, its measurement accuracy is poor due to the presence of intermediate links. A typical offline measurement method for primary air dust concentration is the isokinetic sampling method, which has the advantage of accurate measurement and can be used to calibrate and calibrate online measurement systems or devices. However, it requires manual intervention, and a single sampling takes more than 20 minutes, making it impossible to guide real-time operation.

[0005] Patents with announcement numbers CN202421005U and CN202420571U provide a device for measuring pulverized coal concentration. This device measures the static pressure and total pressure of the airflow before mixing, the static pressure of the airflow after mixing, and the corresponding static pressure difference. The pulverized coal concentration is determined by calculating the flow rate of the pulverized coal airflow. This device is set up for measurement in a horizontal pipe. The flow pattern in the horizontal pipe is complex, the measurement uncertainty is large, and the final calculation is based on a fixed model, and the accuracy may not reflect the actual operating data. Another paper, "Development and Application of a Primary Air Powder Monitoring System for a Direct-Blowing Pulverizing System," introduces the development of an online monitoring system for a direct-blowing pulverizing system for a power plant boiler, as well as the working principle of the differential pressure method for online air-powder monitoring technology. However, its monitoring points are set near the elbow, including a section of horizontal and vertical pipes. The results are also calculated using a fixed model, making it difficult to more realistically reflect the real-time air velocity and pulverized coal concentration in the primary air-powder pipeline. Summary of the Invention

[0006] Low cost, high precision, strong anti-interference and online measurement capabilities are the prerequisites for the large-scale application of air-powder monitoring devices in coal-fired power plants. To this end, the present invention aims to provide a system and method for online monitoring of the wind speed and coal powder concentration in a primary air-powder pipeline, and to achieve self-correction of the two-phase flow model parameters when the coal powder particle size and coal type change by introducing the mass conservation equation, so as to reduce the calibration dependence. The present invention can be used for online precise measurement of the flow rate and coal powder concentration of the coal powder airflow in the primary air-powder pipeline, so as to maintain the optimal air-coal ratio in the boiler and balance the deviation of the powder amount and air-powder flow rate in the pipeline connected to the burner on the same layer. It is suitable for online precise measurement of the flow rate and coal powder concentration of the coal powder airflow in the coal powder conveying pipeline of a coal-fired boiler.

[0007] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: an online wind speed and coal powder concentration monitoring system for a primary air-powder pipeline, including a static pressure difference measurement device and a dynamic and static pressure measurement device. The static pressure difference measurement device is provided with two static pressure measuring points, and the two static pressure measuring points are arranged on the vertical pipeline. A micro-pressure differential transmitter is arranged at the two static pressure measuring points; the dynamic and static pressure measurement device includes a standard backrest tube, an electromagnetic three-way valve, a pressure sensor and a compressed air source; the measuring point of the dynamic and static pressure measurement device is located at the center of the two static pressure measuring points; the pressure measuring port of the standard backrest tube is connected to the inlet of the electromagnetic three-way valve, and the outlet of the electromagnetic three-way valve is connected to the compressed air source and the pressure sensor, and the micro-pressure differential transmitter and the pressure sensor are connected to the input end of the data collector.

[0008] Furthermore, the cross section of the vertical pipe at the static pressure measurement point is constant along the flow direction, and the length of the measured vertical pipe is at least 2 m.

[0009] Furthermore, the inner wall of the pressure taking port of the static pressure measuring point is flush or beveled, the pressure taking port is provided with a compressed air back-blowing device or a diaphragm-type anti-blocking pressure transmitter is selected, the pressure transmitter is installed obliquely on the pressure taking pipe, the angle between the pressure transmitter and the horizontal is ≥60°, and the inner wall of the pressure taking port is inlaid with a ceramic bushing or made of cemented carbide.

[0010] Furthermore, the measuring section is located between the two static pressure measuring points, the lower one is the inlet of the measuring section, four groups of static pressure measuring points are symmetrically arranged at the inlet and outlet of the measuring section, and there is a fully developed flow section in the pipe with a length of at least 2m upstream of the inlet of the measuring section.

[0011] Furthermore, two groups of electromagnetic three-way valves and pressure sensors are provided, including a first electromagnetic three-way valve, a second electromagnetic three-way valve, a first pressure sensor and a second pressure sensor; the windward side of the standard backrest tube is connected to the second pressure sensor through the second electromagnetic three-way valve, the leeward side of the standard backrest tube is connected to the first pressure sensor through the first electromagnetic three-way valve, and the standard backrest tube is connected to the compressed air source through the first electromagnetic three-way valve and the second electromagnetic three-way valve.

[0012] In a second aspect, the present invention provides a method for monitoring the online wind speed and pulverized coal concentration of a primary air-powder pipeline, based on the above-mentioned online wind speed and pulverized coal concentration monitoring system for a primary air-powder pipeline, comprising the following steps: Switch the electromagnetic three-way valve to connect the pressure measuring port to the compressed air source to clean the coal powder in the standard backrest pipe. After cleaning, switch the electromagnetic three-way valve to connect the pressure measuring port to the pressure sensor; Measure the static pressure difference test value Δ of two static pressure measuring points in the vertical pipeline of all air-powder pipes at the same separator outlet p 12,exp ; The dynamic pressure of the pulverized coal airflow at the middle position of the two static pressure measuring points of all air-powder pipes at the same separator outlet is measured through a standard backrest pipe p d and static pressure p p ; Measure and obtain the coal volume and primary air volume data at the outlet of the separator upstream of the calculated air-powder pipe; Based on the initial value of coal powder concentration m Calculate the mixed density of the pulverized coal airflow from all the air-powder pipes at the same separator outlet r , vertically lift pulverized coal to overcome the resistance Δ caused by gravity p g The longitudinal resistance Δ of the air-powder two-phase flow in a straight pipe p f ; The calculated value Δ is based on the resistance caused by vertically lifting coal powder to overcome the gravity pg Calculated value of the longitudinal resistance of the air-powder two-phase flow in a straight pipe Δ p f Calculate the static pressure difference Δ between the first static pressure measuring point 1 and the second static pressure measuring point 2 p 12,cal ; By comparing the static pressure difference between the first static pressure measuring point 1 and the second static pressure measuring point 2 in all the vertical pipes of the air-powder pipe at the same separator outlet, the static pressure difference Δ p 12,cal and the experimental measurement value Δ p 12,exp , and the mass conservation equation of coal and air volume, iteratively calculate the parameters in the along-line resistance calculation model a 、 b The pulverized coal concentration of all pulverized coal airflows from the same separator outlet m ; According to the measured coal powder concentration m Calculate the mixed density of the pulverized coal airflow in all air-powder pipes at the same separator outlet r and speed u .

[0013] Furthermore, real-time cross-checking of multiple signals is performed, mean-median hybrid filtering is used to eliminate abnormal data, and sensor faults are identified in combination with historical trend analysis.

[0014] Furthermore, when calculating the density of the pulverized coal airflow, the received basis moisture content of the coal entering and leaving the furnace, the pulverized coal moisture content at the pulverizer outlet, and the pulverizer outlet temperature are monitored simultaneously.

[0015] Furthermore, according to the mass conservation of pulverized coal and primary air volume, the additional pressure loss coefficient of each air-powder pipe at the outlet of the same separator can be calculated as follows: k The same correction method is used to correct the calculation formula of the resistance overcome by the pulverized coal airflow when it is transported in the vertical pipeline and reduce the calibration dependence, and the flow velocity of the air-powder two-phase flow is calculated. u ,density r and coal powder concentration m The friction coefficient of pure air and k Initial value of k 0, the same separator outlet N Coal powder concentration at the root air-powder pipe m and coal powder air velocity u It needs to be measured and calculated simultaneously.

[0016] Furthermore, the flow velocity of the air-powder two-phase flow is obtained by measuring the dynamic pressure and static pressure of the coal powder airflow in the air-powder pipeline and performing a constant velocity sampling test of the coal powder static pressure zero. u ,density r and coal powder concentration m of the test data.

[0017] Compared with the prior art, the present invention has at least the following beneficial technical effects: the system described in the present invention upgrades the wind speed and coal powder concentration measurement of the primary air-powder pipeline from manual mode to automatic monitoring, which not only reduces labor costs, but also avoids human measurement errors; the proposed primary air-powder pipeline online wind speed and coal powder concentration monitoring system takes into account the advantages of automated operation convenience and test reliability, and has strong reliability and persuasiveness, and the inlet of the electromagnetic three-way valve is connected to the pressure measuring port from the standard backrest pipe through a hose, and the two outlets of the electromagnetic three-way valve are respectively connected to the compressed air source and the pressure sensor, and the electromagnetic three-way valve is used to switch the pressure measuring port of the standard backrest pipe and the compressed air source, or the pressure sensor; the compressed air source of the power plant is used to clean the coal powder in the backrest pipe, which can effectively reduce the blockage in the backrest pipe.

[0018] Furthermore, selecting a vertical pipeline as the measurement section can obtain a larger coal powder airflow pressure drop measurement value and reduce the influencing factors of the resistance along the air-powder two-phase flow in the measurement section; the cross-section of the coal powder pipeline at the measurement section remains unchanged along the flow direction, and the length of the measured vertical pipeline is at least 2m. It is best to have a fully developed flow section in the pipe of more than 2m upstream and downstream of the measurement section to improve the reliability and effectiveness of the detection.

[0019] Furthermore, the pressure port adopts a flush or beveled inner wall design to avoid protrusions obstructing the flow, and a compressed air back-blowing device is installed or a diaphragm-type anti-blocking pressure transmitter is selected, and the pressure pipe is installed at an angle to prevent coal powder deposition and blockage; the inner wall of the pressure port is inlaid with a ceramic bushing or made of cemented carbide. For high-temperature working conditions, a high-temperature resistant sensor is selected or a heat dissipation sleeve is installed.

[0020] Furthermore, when measuring static pressure difference at a single set of measuring points, it is easily affected by local flow field disturbances, measuring point blockage or sensor drift, resulting in data distortion. A pipeline pressure drop measurement method with redundant multi-measuring point arrangement is adopted, and four sets of anti-blocking static pressure measuring points are symmetrically arranged at the inlet and outlet of the test section, which can avoid measurement errors or single-point failure risks.

[0021] Based on the system and method described in the present invention, the static pressure difference between the first static pressure measuring point and the second static pressure measuring point of the pulverized coal airflow is small, so the range of the micro-differential pressure transmitter should be +25Pa~+100Pa. When the pulverized coal airflow flows stably, the static pressure difference between the first static pressure measuring point and the second static pressure measuring point fluctuates relatively little, and a more accurate measurement can be obtained.

[0022] Furthermore, real-time cross-checking is performed on multiple signals, and mean-median hybrid filtering is used to eliminate abnormal data. In combination with historical trend analysis, sensor faults are automatically identified, effectively improving the pressure drop measurement accuracy and system reliability.

[0023] Furthermore, through the coal powder sampling hole, the dynamic pressure and static pressure measurement of the coal powder airflow in the air-powder pipeline, the coal powder static pressure zero-point constant speed sampling and other test contents can obtain a series of flow velocities of the air-powder two-phase flow. u ,density r and coal powder concentration m The experimental data of the flow velocity of the air-powder two-phase flow u ,density r and coal powder concentration m The friction coefficient of pure air is obtained from the experimental data l 0 and correction factor k The experimental values are used to improve the calculation model of the resistance overcome by the pulverized coal airflow when it is transported in the vertical pipeline, thereby ensuring that the calculation of the resistance overcome by the pulverized coal airflow when it is transported from the first static pressure measuring point to the second static pressure measuring point in the straight pipeline is in line with reality. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the device for measuring the static pressure difference of pulverized coal airflow in a vertical pipe section, as well as the installation positions of the two static pressure side holes.

[0025] Figure 2 Schematic diagram of the redundant arrangement of multiple static pressure difference measurement points.

[0026] 1-First static pressure measuring point, 2-Second static pressure measuring point, 3-Micro differential pressure transmitter, 4-Data collector, 5-Pulverized coal pipeline, 6-Standard backrest tube, 7-First solenoid three-way valve, 8-Second solenoid three-way valve, 9-Hose, 10-First pressure sensor, 11-Second pressure sensor, 12-Compressed air source, 13-Pulverized coal sampling hole and pressure measurement calibration hole. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0028] Example 1, reference Figure 1The present invention provides an online air velocity and pulverized coal concentration monitoring system for a primary air-powder pipeline. By introducing the mass conservation equation, the system achieves self-correction of two-phase flow model parameters when the pulverized coal particle size and coal type change, thereby reducing calibration dependency. The system includes a device for measuring the pressure drop of the pulverized coal airflow in the measuring pipeline and a device for measuring the dynamic and static pressures of the pulverized coal airflow. The static pressure differential measurement device includes a static pressure measuring hole, a micro-differential pressure transmitter 3, a data collector 4, and a connected hose 9. The static pressure measuring holes are located in a section of the pipeline where the flow field is stable, avoiding areas of disturbance such as elbows, valves, and reducers. The diameters of the two static pressure measuring holes range from 4 mm to 8 mm, and the edges are burr-free. The static pressure measuring points are designed with flush or chamfered inner walls to avoid protrusions that obstruct flow. When the pulverized coal airflow reaches stability in the vertical pipeline, it is transported from a first static pressure measuring point 1 to a second static pressure measuring point 2. The first static pressure measuring point 1 is a relatively low point, and the second static pressure measuring point 2 is a relatively high point. Two static pressure measurement points are installed on the pipe wall at the same level as the first static pressure measurement point 1 and the second static pressure measurement point 2. In addition, a coal dust sampling hole and a pressure measurement calibration hole 13 are pre-set for conducting zero-point isokinetic sampling of coal dust static pressure and measuring the dynamic and static pressure of the coal dust airflow.

[0029] To prevent clogging, install a compressed air backflush device or use a diaphragm-type anti-clogging pressure transmitter. Install the pressure tapping pipe at an angle to prevent coal dust deposition, with the pressure transmitter at an angle of ≥60° to the horizontal. The inner wall of the static pressure tapping should be inlaid with a ceramic bushing or constructed of carbide. For high-temperature operating conditions, use a high-temperature-resistant sensor (e.g., ≤300°C) or install a heat sink. Use shielded cable for signal transmission, away from strong interference sources, and maintain regular maintenance and cleaning to ensure long-term reliable operation.

[0030] When measuring static pressure difference at a single set of measuring points, it is easily affected by local flow field disturbances, measuring point blockage or sensor drift, resulting in data distortion. In order to avoid measurement errors or single point failure risks, a pipeline pressure drop measurement method with redundant multi-measuring point arrangement is adopted. Four sets of anti-blocking static pressure measuring points are symmetrically arranged at the inlet and outlet of the test section, such as Figure 2 In addition, a data fusion algorithm is used to perform real-time cross-checks on multiple signals, a mean-median hybrid filter is used to eliminate abnormal data, and historical trend analysis is combined to automatically identify sensor faults, effectively improving the pressure drop measurement accuracy and system reliability.

[0031] The dynamic and static pressure measuring device includes a standard backrest tube 6, a first electromagnetic three-way valve 7, a second electromagnetic three-way valve 8, a hose 9, a first pressure sensor 10, a second pressure sensor 11 and a compressed air source 12. The measuring point of the dynamic and static pressure measuring device is located at the center of the first static pressure measuring point 1 and the second static pressure measuring point 2, so that the measured static pressure value can represent the average static pressure of the pulverized coal airflow in the test section, such as Figure 2The windward side of the standard backrest tube 6 is connected to the second pressure sensor 11, and the leeward side of the standard backrest tube 6 is connected to the first pressure sensor 10. Therefore, the pressure measured by the second pressure sensor 11 is the total pressure, and the pressure measured by the first pressure sensor 10 is the static pressure. The difference between the two is the dynamic pressure.

[0032] In the process of pulverized coal airflow being transported from the first static pressure measuring point 1 to the second static pressure measuring point 2 in the vertical pipeline, the first static pressure measuring point 1 is the low point and the second static pressure measuring point 2 is the high point. Figure 1 , the velocity of the pulverized coal airflow is much lower than the speed of sound Yes Generally less than 0.1, and there is no very large local pressure gradient, so the density change caused by the flow is extremely small, and it can be approximately regarded as an incompressible fluid for engineering analysis and calculation. Therefore, the transportation process can be regarded as a steady incompressible flow, which can be described by the Bernoulli equation for the total flow of viscous fluid, expressed as: (1) Where, z 1 and z 2 are the vertical heights from the first static pressure measuring point 1 to the second static pressure measuring point 2 relative to the reference plane, m; p 1 and p 2 are the static pressures of the pulverized coal airflow at the first static pressure measuring point 1 and the second static pressure measuring point 2, Pa; r is the mixed density of the air-powder two-phase flow, kg·m -3 ; g is the acceleration due to gravity, m·s -2 ; α 1 and α 2 are the kinetic energy correction coefficients of the pulverized coal airflow at the first static pressure measuring point 1 and the second static pressure measuring point 2 respectively; u 1 and u 2 are the average flow rates of the pulverized coal airflow at the first static pressure measuring point 1 and the second static pressure measuring point 2, m·s -1 ; h L is the hydraulic loss of pulverized coal airflow in this section of vertical pipe, m.

[0033] If the cross section of the vertical pulverized coal pipeline at the measuring section remains unchanged along the flow direction, when the flow of the pulverized coal airflow in the vertical pipeline reaches stability, it can be considered that the dynamic pressures at the first static pressure measuring point 1 and the second static pressure measuring point 2 on the vertical pipeline are equal, and the hydraulic loss h L It only comes from the resistance along the way. Then formula (1) can be simplified as: (2) Where, Δ p g Indicates the resistance caused by the vertical lifting of pulverized coal airflow to overcome the gravity, Pa; Δp f Indicates the longitudinal resistance of the air-powder two-phase flow in the vertical pipe, Pa. Δ p g It can be expressed as: (3) Where, H Is the vertical height from the first static pressure measuring point 1 to the second static pressure measuring point 2, m. Coal powder concentration m It has a great influence on the mixed density of the pulverized coal airflow, so the vertical lifting of the pulverized coal airflow overcomes the resistance Δ caused by gravity. p g Coal powder concentration m Therefore, Δ p g The size of the pulverized coal airflow can more accurately reflect the concentration of m size.

[0034] The longitudinal resistance Δ of air-powder two-phase flow in a vertical pipe p f It can be expressed as: (4) Where, l μ is the friction resistance coefficient of air-powder two-phase flow; L is the length of the vertical pipe, m; d e is the equivalent diameter of the pipe, m; u is the average velocity of the air-powder two-phase flow in the flow section, m·s -1 Obviously, ru 2 / 2 is the average dynamic pressure of the coal powder airflow. According to the relevant literature, the friction resistance coefficient of the air-powder two-phase flow is l μ Generally calculated according to the following general formula: (5) Where, l 0 is the friction coefficient of pure air for the powder delivery pipeline, l 0 can generally be taken as 0.015; k It can be called the additional pressure loss coefficient, which is used to reflect the additional contribution of pulverized coal particles to the friction pressure drop due to factors such as friction between particles and pipe walls and collisions between particles.

[0035] Additional pressure loss coefficient kIt will be affected by the particle size and type of coal powder. In addition, the coal powder in the pipeline has a significant acceleration in the axial direction, which will also affect the measurement accuracy. If it is assumed that the particle size distribution and coal quality of the coal powder in the air-powder pipe at the same separator outlet are approximately the same, then when the coal powder particle size and coal type change, the present invention can calculate the additional pressure loss coefficient of each air-powder pipe at the same separator outlet based on the mass conservation of coal powder and primary air volume. k The same correction method is used to reduce the calibration dependency. k The correction formula is: (6) Where, k 0 is obtained through calibration test k The initial value of a 、 b is the correction factor. This correction formula takes into account the effects of coal powder particle size, coal powder type and axial acceleration of coal powder in the pipeline.

[0036] (7) Where, N Indicates the number of air-powder pipes at the separator outlet; i Indicates the outlet of the separator i root wind powder tube; A i Describe the separator outlet i Cross-sectional area of the root air powder tube in the measuring section, m 2 ; q m,c Indicates the total coal volume at the separator outlet, kg / s.

[0037] (8) Where, q m,p It indicates the primary air volume at the separator outlet, kg / s. Obviously, the same separator outlet N Coal powder concentration at the root air-powder pipe m and coal powder air velocity u It needs to be measured and calculated simultaneously.

[0038] Mixture density of two-phase flow r and coal powder concentration m According to the "Performance Test of Coal Mill and Pulverizing System for Power Plants" DL / T 467-2019, the density of the pulverized coal airflow is r It can be expressed as: (9) Where, t 2 is the coal mill outlet temperature, °C; p ais the atmospheric pressure, Pa; p p is the static pressure of the airflow, Pa; V c is the volume per kilogram of coal powder, which can generally be taken as V c 0.001m 3 kg -1 ; Δ M It is the water evaporated from the raw coal in the coal mill, kg·kg -1 .

[0039] Evaporated moisture of raw coal in coal mill Δ M It can be expressed as: (10) Where, M ar is the received basic moisture, %; M pc It is the moisture content of pulverized coal, %. It should be noted that the moisture content of pulverized coal at the outlet of the pulverizer should be regularly checked. M pc Conduct laboratory measurements.

[0040] In summary, when the flow of pulverized coal in the vertical pipeline reaches stability, the resistance overcome by the pulverized coal from the first static pressure measuring point 1 to the second static pressure measuring point 2 can be expressed as: (11) Where, Δ p 12 That is, the static pressure difference between the first static pressure measuring point 1 and the second static pressure measuring point 2 ( p 1- p 2).

[0041] The static pressure difference between the first static pressure measuring point 1 and the second static pressure measuring point 2 ( p 1- p 2) It can be measured by a micro differential pressure transmitter and then transmitted to a computer by a data collector, such as Figure 1 The diameters of the two static pressure measurement holes range from 4 mm to 6 mm. Because the static pressure difference between the first and second static pressure measurement points of the pulverized coal airflow is relatively small, the range of the micro differential pressure transmitter should be +25 Pa to +100 Pa. It should be noted that when the pulverized coal airflow is flowing steadily, the static pressure difference between the first and second static pressure measurement points 1 and 2 fluctuates relatively little, allowing for more accurate measurements.

[0042] By measuring the dynamic pressure of the coal powder airflow in the air-powder pipeline p d and static pressure p p, and the static pressure difference between the first static pressure measuring point 1 and the second static pressure measuring point 2 ( p 1- p 2), and combined with equations (1) to (11), the pulverized coal concentration of the pulverized coal airflow can be calculated m , and then the velocity of the pulverized coal airflow can be calculated u .

[0043] Finally, a series of basic tests are required to obtain the friction coefficient of pure air in formula (5): l 0 and additional pressure loss coefficient k Initial value of k 0, ensuring realistic calculations of the drag overcome by the pulverized coal airflow as it is transported from the first static pressure measurement point 1 to the second static pressure measurement point 2 in a straight pipeline. The test primarily included isokinetic sampling of the pulverized coal static pressure at zero point and measurement of the dynamic and static pressures of the pulverized coal airflow in the air-to-powder pipeline.

[0044] The pulverized coal static pressure zero-point constant velocity sampling test can truly obtain the amount of pulverized coal airflow passing through a certain flow cross section at the actual flow rate and pulverized coal concentration under the operating conditions within a certain period of time (three minutes is selected in this invention). M . Pulverized coal concentration m It is defined as the mass flow rate ratio of pulverized coal to air in the pulverized coal / air mixture flow, then the pulverized coal amount M It can be expressed as: (12) Where, M is the mass of pulverized coal taken out through the pulverized coal static pressure zero position isokinetic sampling test, kg; A is the area of the coal pulverized air flow inlet of the coal pulverized static pressure zero position constant velocity sampling device, m 2 ; t is the coal powder sampling time, s.

[0045] The dynamic pressure and static pressure measurement of the pulverized coal airflow in the air-powder pipeline and the constant velocity sampling of the pulverized coal static pressure zero are carried out through the pulverized coal sampling hole. The flow velocity of the air-powder two-phase flow can be obtained by combining equations (4) to (12). u ,density r and coal powder concentration m , and then the friction resistance coefficient of pure air in formula (5) can be obtained l 0 and the parameters in formula (6) k The experimental value of 0 is used to improve the calculation model of the along-the-way resistance overcome by the pulverized coal airflow when it is transported from the first static pressure measuring point 1 to the second static pressure measuring point 2 in the vertical pipeline, thereby ensuring that the calculation of the along-the-way resistance overcome by the pulverized coal airflow when it is transported from the first static pressure measuring point 1 to the second static pressure measuring point 2 in the straight pipeline is consistent with reality.

[0046] Considering that clogging is very likely to occur when using a Pitot tube to measure the dynamic and static pressures of the pulverized coal airflow, a standard backrest tube 6 is used to obtain the dynamic and static pressures of the pulverized coal airflow. In addition, the power plant's compressed air source 12 is used to clean the pulverized coal in the backrest tube at a set frequency to reduce clogging in the standard backrest tube 6. Specifically, the inlet of the electromagnetic three-way valve is connected to the pressure measuring port from the standard backrest tube 6 through a hose, and the two outlets of the electromagnetic three-way valve are connected to the compressed air source 12 and the pressure sensor respectively through hoses. The electromagnetic three-way valve switches the connection between the pressure measuring port of the standard backrest tube 6 and the compressed air source 12, or the pressure sensor.

[0047] In Example 2, the present invention also provides an operating method for the above-mentioned primary air-powder pipeline online wind speed and coal powder concentration monitoring system, comprising the following steps: Switch the electromagnetic three-way valve to the pressure measuring port and connect it to the compressed air source 12 to clean the coal powder in the backrest pipe. After cleaning, switch the electromagnetic three-way valve to the pressure measuring port and connect it to the pressure sensor; Based on the above calculation formulas (9) and (10), the received basis moisture of the coal fed into the furnace is calculated regularly. M ar and the moisture content of pulverized coal at the pulverizer outlet M pc ; Measure the outlet temperature of the coal mill and the static pressure difference test value Δ at the first static pressure measuring point 1 and the second static pressure measuring point 2 in the vertical pipeline of all air-powder pipes at the same separator outlet p 12,exp ; The dynamic pressure of the pulverized coal airflow at the middle position of the two static pressure measuring points of all the air-powder pipes at the same separator outlet is measured through the standard backrest pipe 6 p d and static pressure p p ; Measure and obtain the coal volume and primary air volume data at the outlet of the separator upstream of the calculated air-powder pipe; Assuming the initial value of coal powder concentration m 0, and based on the initial value of coal powder concentration m Calculate the mixed density of the pulverized coal airflow from all the air-powder pipes at the same separator outlet r , and then calculate the resistance Δ caused by vertical lifting of coal powder to overcome gravity p g The longitudinal resistance Δ of the air-powder two-phase flow in a straight pipe p f ; The calculated value Δ is based on the resistance caused by vertically lifting coal powder to overcome the gravity p g Calculated value of the longitudinal resistance of the air-powder two-phase flow in a straight pipe Δp f Obtain the calculated static pressure difference Δ between the first static pressure measuring point 1 and the second static pressure measuring point 2 p 12,cal ; By comparing the calculated value of the static pressure difference between the first static pressure measuring point 1 and the second static pressure measuring point 2 in the vertical pipeline of all air-powder pipes at the same separator outlet, Δ p 12,cal and the experimental measurement value Δ p 12,exp , and the mass conservation equation of coal and air volume, iteratively calculate the parameters in the along-line resistance calculation model a 、 b The pulverized coal concentration of all pulverized coal airflows from the same separator outlet m ; According to the measured coal powder concentration m Calculate the mixed density of the pulverized coal airflow in all the air-powder pipes at the same separator outlet r and speed u .

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A primary air-powder pipeline online wind speed and coal powder concentration monitoring system, characterized in that: The invention comprises a static pressure difference measuring device and a dynamic and static pressure measuring device, wherein the static pressure difference measuring device is provided with two static pressure measuring points, the two static pressure measuring points are arranged on a vertical pipe, and a micro-pressure differential transmitter is arranged at each of the two static pressure measuring points; the dynamic and static pressure measuring device comprises a standard backrest tube (6), an electromagnetic three-way valve, a pressure sensor and a compressed air source (12); the measuring point of the dynamic and static pressure measuring device is located at the center of the two static pressure measuring points; the pressure measuring port of the standard backrest tube (6) is connected to the inlet of the electromagnetic three-way valve, the outlet of the electromagnetic three-way valve is connected to the compressed air source (12) and the pressure sensor, and the micro-pressure differential transmitter and the pressure sensor are connected to the input end of the data collector.

2. The primary air-powder pipeline online wind speed and coal powder concentration monitoring system according to claim 1 is characterized in that: The cross section of the vertical pipeline where the static pressure measurement point is set remains unchanged along the flow direction, and the length of the vertical pipeline to be measured is at least 2m.

3. The online air velocity and pulverized coal concentration monitoring system for primary air-powder pipeline according to claim 1 is characterized in that: The inner wall of the pressure tapping at the static pressure measuring point is flush or beveled. The pressure tapping is provided with a compressed air back-blowing device or a diaphragm-type anti-blocking pressure transmitter. The pressure transmitter is installed obliquely on the pressure pipe. The angle between the pressure transmitter and the horizontal is ≥60°. The inner wall of the pressure tapping is inlaid with a ceramic bushing or made of hard alloy.

4. The online air velocity and pulverized coal concentration monitoring system for a primary air-powder pipeline according to claim 1 is characterized in that: The measuring section is located between the two static pressure measuring points. The lower one is the inlet of the measuring section. Four groups of static pressure measuring points are symmetrically arranged at the inlet and outlet of the measuring section. It is best to have a fully developed flow section in the pipe with a length of 2m upstream and downstream of the measuring section.

5. The on-line air velocity and pulverized coal concentration monitoring system for primary air-powder pipeline according to claim 1 is characterized in that: Two groups of electromagnetic three-way valves and pressure sensors are provided, including a first electromagnetic three-way valve (7), a second electromagnetic three-way valve (8), a first pressure sensor (10) and a second pressure sensor; the windward side of the standard backrest pipe (6) is connected to the second pressure sensor (11) via the second electromagnetic three-way valve (8), the leeward side of the standard backrest pipe (6) is connected to the first pressure sensor (10) via the first electromagnetic three-way valve (7), and the standard backrest pipe (6) is connected to the compressed air source (12) via the first electromagnetic three-way valve (7) and the second electromagnetic three-way valve (8).

6. A method for monitoring the online wind speed and coal powder concentration of a primary air-powder pipeline, characterized in that: The system for monitoring the online wind speed and pulverized coal concentration of the primary air-powder pipeline according to any one of claims 1 to 5 comprises the following steps: Switch the electromagnetic three-way valve to connect the pressure measuring port to the compressed air source (12) to clean the coal powder in the standard backrest pipe (6). After cleaning, switch the electromagnetic three-way valve to connect the pressure measuring port to the pressure sensor; Measure the static pressure difference test value Δ of two static pressure measuring points in the vertical pipeline of all air-powder pipes at the same separator outlet p 12,exp ; The dynamic pressure of the pulverized coal airflow at the middle position of the two static pressure measuring points of all the air-powder pipes at the same separator outlet is measured through the standard backrest pipe (6). p d and static pressure p p ; Measure and obtain the coal volume and primary air volume data at the outlet of the separator upstream of the calculated air-powder pipe; Based on the initial value of coal powder concentration μ Calculate the mixed density of the pulverized coal airflow from all the air-powder pipes at the same separator outlet ρ , vertically lift pulverized coal to overcome the resistance Δ caused by gravity p g The longitudinal resistance Δ of the air-powder two-phase flow in a straight pipe p f ; The calculated value Δ is based on the resistance caused by vertically lifting coal powder to overcome the gravity p g Calculated value of the longitudinal resistance of the air-powder two-phase flow in a straight pipe Δ p f Calculate the static pressure difference Δ between two static pressure measuring points in a vertical pipe p 12,cal ; By comparing the static pressure difference calculation value Δ of the two static pressure measuring points in the vertical pipeline of all air-powder pipes at the same separator outlet p 12,cal and the experimental measurement value Δ p 12,exp , and the mass conservation equation of coal and air volume, iteratively calculate the parameters in the along-line resistance calculation model a 、 b The pulverized coal concentration of all pulverized coal airflows from the same separator outlet μ ; According to the measured coal powder concentration μ Calculate the mixed density of the pulverized coal airflow in all air-powder pipes at the same separator outlet ρ and speed u .

7. The method for monitoring the online wind speed and pulverized coal concentration of a primary air-powder pipeline according to claim 6, characterized in that: Real-time cross-checking of multiple signals is performed, mean-median hybrid filtering is used to eliminate abnormal data, and sensor faults are identified in combination with historical trend analysis.

8. The method for monitoring the online wind speed and pulverized coal concentration of a primary air-powder pipeline according to claim 6, characterized in that: When calculating the density of the pulverized coal airflow, the received basis moisture content of the coal entering and leaving the furnace, the pulverized coal moisture content at the pulverizer outlet, and the pulverizer outlet temperature are monitored simultaneously.

9. The method for monitoring the online wind speed and pulverized coal concentration of a primary air-powder pipeline according to claim 6, characterized in that: According to the mass conservation of pulverized coal and primary air volume, the additional pressure loss coefficient of each air-powder pipe at the outlet of the same separator can be calculated as k The same correction method is used and the flow velocity of the air-powder two-phase flow is calculated. u ,density ρ and coal powder concentration μ The friction coefficient of pure air and k Initial value of k 0, coal powder concentration of all air-powder pipes at the same separator outlet μ and coal powder air velocity u It needs to be measured and calculated simultaneously.

10. The method for monitoring the online wind speed and pulverized coal concentration of a primary air-powder pipeline according to claim 8, characterized in that: The flow velocity of the air-powder two-phase flow is obtained by measuring the dynamic pressure and static pressure of the coal powder airflow in the air-powder pipeline and performing the coal powder static pressure zero-point constant speed sampling test. u ,density ρ and coal powder concentration μ of the test data.

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