A method and system for on-line measurement of coal fineness of a boiler

Abstract

The present application belongs to the technical field of boiler monitoring, and discloses a kind of boiler coal powder fineness on-line measurement method and system, method includes: using matrix method to establish the quantitative physical corresponding relation between particle size and scattered light intensity, obtain light energy coefficient matrix;Using iterative algorithm to inverse, with the ratio of measured light intensity and current distribution calculation light intensity, according to the weight proportion of light energy coefficient matrix, correct the distribution value of each particle size range;Two wavelengths of red light and near infrared light are used respectively to independently inverse the measurement data, obtain two groups of particle size distribution and fusion, obtain the particle size distribution after fusion;The corrected continuous particle size distribution is converted into the coal powder fineness index commonly used in power plant, and the fineness parameter is output, which is used for real-time guidance of combustion adjustment and optimization of pulverizing system.The present application eliminates the uneven full-range accuracy defect of traditional single-wavelength instrument, which is not accurate for fine and coarse or not accurate for coarse and fine, and solves the problem of large hysteresis of traditional offline screening method, which cannot guide the operation in real time.

Description

Technical Field

[0001] This invention belongs to the field of boiler monitoring technology, specifically relating to an online measurement method and system for the fineness of pulverized coal in boilers. Background Technology

[0002] Existing laser diffraction technology for measuring the fineness of coal powder has the following drawbacks: Limitations of single-wavelength measurement: Current technologies mostly use single-wavelength lasers. For coal powder, which has a wide distribution, is non-spherical, and has a high concentration, the inversion error of a single wavelength is relatively large, and it is difficult to simultaneously guarantee the measurement accuracy at both the fine and coarse particle ends. Lack of automatic calibration mechanism: Factors such as optical window contamination, light source attenuation, and detector drift cause system errors to accumulate over time. Existing technologies lack closed-loop self-calibration functions, resulting in poor long-term operational reliability.

[0003] Chinese patent publication number CN119124944A, entitled "Online Detection Method for Coal Powder Fineness Based on Adaptive Filtering and Laser Diffraction," describes a method comprising: achieving constant-velocity cyclic sampling by changing the compressed air flow rate through pressure measurement in a coal powder conveying pipeline; irradiating the coal powder particle flow with a laser beam generated by a laser emitting device; suppressing environmental noise using the LMS algorithm; collecting diffracted light using a charge-coupled device and converting it into a digital signal; constructing a fineness information detection model after preprocessing the diffraction rings, calculating the center coordinates and radius of the diffraction rings, and fitting the fineness information. The diffraction rings are collected using CCD pixels. However, this patent application uses a single wavelength, resulting in significant inversion errors and a lack of closed-loop self-calibration. Summary of the Invention

[0004] In order to overcome the problems existing in the prior art, the present invention aims to provide an online measurement method and system for boiler pulverized coal fineness. By using dual-wavelength laser diffraction spectral fusion and closed-loop self-calibration, the problem of large lag and inability to guide operation in real time in traditional offline screening methods is solved, and accurate and real-time online measurement of pulverized coal fineness is achieved.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides an online method for measuring the fineness of pulverized coal in a boiler, comprising the following steps: A quantitative physical correspondence between particle size and scattered light intensity was established using the matrix method, resulting in the light energy coefficient matrix. An iterative algorithm is used for inversion. In each iteration, the ratio of the measured light intensity to the light intensity calculated from the current distribution is used to correct the distribution values ​​of each particle size range according to the weight ratio of the light energy coefficient matrix. If the calculated light intensity of a certain particle size range is less than the measured value, the proportion of that range is increased; if the calculated light intensity of a certain particle size range is greater than or equal to the measured value, it is decreased. The particle size distribution is obtained by independently inverting the measurement data of red light and near-infrared light wavelengths, respectively, and then fused to obtain the fused particle size distribution. The system drift is calibrated using standard particles of known size. Correction coefficients for the entire particle size range are obtained by linear interpolation. The particle size distribution after fusion is then corrected based on the correction coefficients to obtain the final continuous particle size distribution. The corrected continuous particle size distribution is converted into a coal powder fineness index commonly used in power plants, and the fineness parameter is output for real-time guidance of combustion adjustment and pulverizing system optimization.

[0006] Optionally, after obtaining the two sets of particle size distributions, they can be fused by weighting the signal-to-noise ratio.

[0007] Optionally, in the step of establishing a quantitative physical correspondence between particle size and scattered light intensity using the matrix method, a quantitative physical correspondence between particles of each size range and the scattered light intensity on each detection ring of the photodetector is established.

[0008] Optionally, before the overall drift step of the standard particle calibration system with known particle size, the temperature and pressure values ​​in the primary air duct of the boiler are measured in real time. The current air refractive index is calculated based on the measured temperature and pressure values, and the mapping relationship between the diffraction angle and the particle size is corrected in real time using the refractive index. The particle size mapping is corrected for the fused particle size distribution, and the corrected particle size distribution is corrected using a correction coefficient.

[0009] Optionally, the calculation formula for the iterative algorithm is:

[0010] Where W is the particle size distribution vector, A is the M×N optical energy coefficient matrix, Ii is the total light intensity received by the i-th ring of the detector, j is the j-th particle size, and the value range corresponds to N particle size levels, M is the total number of rings of the annular photodetector, and k is the current iteration round.

[0011] Optionally, in the iterative algorithm, the initial distribution adopts the Rosin-Rammler distribution, and the convergence condition is that the residual R < 10^(-4) or the number of iterations k > 100.

[0012] Optionally, in the step of converting the corrected continuous particle size distribution into the fineness index of pulverized coal commonly used in power plants, the residue at a 90μm sieve, the residue at a 200μm sieve, the volume average particle size, and the median particle size are calculated respectively.

[0013] Secondly, the present invention provides a measurement system for the online measurement method of boiler pulverized coal fineness, comprising: a multi-wavelength laser unit, a measurement chamber unit, and a ring photodetector unit; the multi-wavelength laser unit includes a red semiconductor laser, a near-infrared semiconductor laser, a dichroic mirror, and a collimating beam expander lens, the dichroic mirror being disposed at the beam convergence point of the lasers emitted by the red semiconductor laser and the near-infrared semiconductor laser, the emitting end of the dichroic mirror facing the collimating beam expander lens, and the collimating beam expander lens facing the measurement chamber unit; a photodetector is disposed on the side of the measurement chamber unit facing away from the collimating beam expander lens.

[0014] Optionally, the red semiconductor laser has an emission wavelength of 650 nm, and the near-infrared semiconductor laser has an emission wavelength of 850 nm.

[0015] Optionally, the measuring chamber unit includes a Laval nozzle, which comprises a converging conduit and an ejector conduit. One end of the ejector conduit is connected to a pulverized coal conduit, and the other end is connected to the side of the converging conduit. One end of the converging conduit is open to the atmosphere, and the other end is connected to a throat conduit. The other end of the throat conduit is connected to a diverging conduit, and the other end of the diverging conduit is connected to a return coal conduit. Optical windows are respectively provided on a set of opposite sides of the throat conduit, with one optical window facing the collimating beam expander lens.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention employs independent inversion using both red and near-infrared wavelengths. The two wavelengths are used to obtain two sets of particle size distributions through scattering forward modeling and iterative inversion, respectively. The fused distribution simultaneously ensures the measurement accuracy of both the fine end (high resolution) and the coarse end (good stability), eliminating the uneven accuracy across the entire measurement range that is either too fine or too coarse, which is a problem with traditional single-wavelength instruments.

[0017] This invention systematically solves the problems of large lag and inability to provide real-time operational guidance in traditional offline screening methods by establishing a physical model using a matrix method, performing dual-wavelength inversion fusion, self-calibration correction, and outputting engineering indicators in a closed-loop process. It can output fineness parameters in real time that can directly guide combustion adjustments, significantly improving the economy and response speed of boiler operation.

[0018] Furthermore, by performing weighted fusion based on signal-to-noise ratio after dual-wavelength inversion, this invention can dynamically utilize the high signal-to-noise ratio advantage of 650nm in the fine particle segment and the stability advantage of 850nm in the coarse particle segment, achieving complementary advantages, effectively eliminating the measurement blind zone of a single wavelength at the fine or coarse end, ensuring balanced measurement accuracy across the entire particle size range (1~1000μm), and significantly improving the accuracy and reliability of the inversion results.

[0019] Furthermore, this invention adds a real-time compensation step before self-calibration. It uses measured temperature and pressure values ​​to correct the air refractive index using the Edlen formula and corrects the mapping relationship between diffraction angle and particle size in real time. This compensation eliminates the 3%–5% systematic error caused by large fluctuations in boiler primary air duct temperature (60–180°C) and pressure (80–120 kPa) at its physical source. Subsequently, self-calibration corrects for slow drift, improving the system's measurement accuracy and long-term stability in complex field environments.

[0020] Furthermore, this invention achieves high-precision acquisition of optical emission, uniform sampling of gas-solid two-phase flow, and scattering signals through a multi-wavelength laser unit, a measurement gas chamber unit, and a ring photoelectric detection unit. The dual-wavelength beam combining and common optical path design ensures that the two lasers irradiate the same particle group, guaranteeing the spatiotemporal consistency of data fusion.

[0021] Furthermore, the present invention provides optical windows on both sides of the throat to facilitate the penetration of light beams, and the coal powder return pipe realizes the recovery of coal powder, thus avoiding sample waste and environmental pollution. Attached Figure Description

[0022] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely schematic to aid in understanding the invention and do not specifically limit the shapes and proportions of the components. In the drawings: Figure 1 This is a schematic diagram of the laser diffraction measurement structure according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a Laval nozzle according to an embodiment of the present invention; Figure 3 This is a structural diagram of the photodetector according to an embodiment of the present invention; Figure 4 This is a particle size diagram of pulverized coal according to an embodiment of the present invention; Figure 5 This is a velocity cloud diagram of pulverized coal particles according to an embodiment of the present invention; Among them, 1. Red semiconductor laser; 2. Near-infrared semiconductor laser; 3. Dichroic mirror; 4. Collimating and expanding lens; 5. Laval nozzle; 6. Photodetector; 7. Pulverized coal pipeline; 51. Tapered pipeline; 52. Ejector pipeline; 53. Throat pipeline; 54. Expanding pipeline; 55. Pulverized coal return pipeline; 61. Optical protection window; 62. Silicon photodetector; 63. Data acquisition unit; 64. Data processor. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0024] Therefore, the following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0025] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed during use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0026] When an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments. The use of the term "horizontal" does not imply that the component is required to be absolutely horizontal, but rather that it may be slightly tilted. "Horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but rather that it may be slightly tilted.

[0027] It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the specification and appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0029] The present invention will now be described in detail with reference to the accompanying drawings.

[0030] To reduce costs, coal-fired power plants commonly employ coal blending, but fluctuations in coal quality negatively impact boiler operation. Therefore, precise control of pulverized coal fineness is crucial, as this parameter directly affects boiler combustion efficiency, pulverizing system power consumption, equipment wear, and pollutant emissions. Currently, pulverized coal fineness measurement primarily employs offline sampling and sieving methods, which suffer from significant time lag, cumbersome manual operation, and an inability to provide real-time guidance for operational adjustments.

[0031] Existing laser diffraction technology for measuring the fineness of coal powder has the following drawbacks: Limitations of Single-Wavelength Measurement: Existing technologies mostly use single-wavelength lasers. For widely distributed, non-spherical, and high-concentration particles like pulverized coal, single-wavelength inversion errors are significant, and it's difficult to simultaneously guarantee measurement accuracy at both the fine and coarse particle ends. Lack of Real-Time Compensation: Boiler site temperatures and pressures vary greatly, and changes in air refractive index directly affect diffraction angle calculations. Existing technologies do not consider real-time compensation for operating conditions, resulting in poor on-site measurement accuracy. Lack of Automatic Calibration Mechanism: Factors such as optical window contamination, light source attenuation, and detector drift cause system errors to accumulate over time. Existing technologies lack closed-loop self-calibration functionality, leading to poor long-term operational reliability. Susceptibility to Optical Window Contamination: The harsh environment of pulverized coal sites makes optical windows easily contaminated by coal dust. Existing purging mechanisms are ineffective, affecting measurement stability.

[0032] The present invention provides an online method for measuring the fineness of pulverized coal in boilers, comprising the following steps: A quantitative physical correspondence between particle size and scattered light intensity was established using the matrix method, resulting in the light energy coefficient matrix. An iterative algorithm is used for inversion. In each iteration, the ratio of the measured light intensity to the light intensity calculated from the current distribution is used to correct the distribution values ​​of each particle size range according to the weight ratio of the light energy coefficient matrix. If the calculated light intensity of a certain particle size range is less than the measured value, the proportion of that range is increased; if the calculated light intensity of a certain particle size range is greater than or equal to the measured value, it is decreased. The particle size distribution is obtained by independently inverting the measurement data of red light and near-infrared light wavelengths, respectively, and then fused to obtain the fused particle size distribution. The system drift is calibrated using standard particles of known size. Correction coefficients for the entire particle size range are obtained by linear interpolation. The particle size distribution after fusion is then corrected based on the correction coefficients to obtain the final continuous particle size distribution. The corrected continuous particle size distribution is converted into a coal powder fineness index commonly used in power plants, and the fineness parameter is output for real-time guidance of combustion adjustment and pulverizing system optimization.

[0033] Before the overall drift step of the calibration system using standard particles of known particle size, the temperature and pressure values ​​in the primary air duct of the boiler are measured in real time. The current air refractive index is calculated based on the measured temperature and pressure values, and the mapping relationship between the diffraction angle and the particle size is corrected in real time using this refractive index. The particle size distribution after fusion is corrected by particle size mapping, and the corrected particle size distribution is corrected by correction coefficient.

[0034] This invention systematically solves the problems of large lag and inability to provide real-time operational guidance in traditional offline screening methods by establishing a physical model using a matrix method, performing dual-wavelength inversion fusion, self-calibration correction, and outputting engineering indicators in a closed-loop process. It can output fineness parameters in real time that can directly guide combustion adjustments, significantly improving the economy and response speed of boiler operation.

[0035] This invention adds a real-time compensation step before self-calibration, using measured temperature and pressure values ​​to correct the air refractive index through the Edlen formula, and corrects the mapping relationship between diffraction angle and particle size in real time, thereby improving the measurement accuracy and long-term stability of the system in complex field environments.

[0036] Example 1 This embodiment of a method for online measurement of pulverized coal fineness in boilers includes the following steps: Step 1: Establish a quantitative physical correspondence between particle size and scattered light intensity using the matrix method to obtain the light energy coefficient matrix.

[0037] Step 2: Using the Rosin-Rammler distribution naturally conforming to industrial pulverized coal as the initial value for iteration, the Chahine iterative algorithm is used for inversion. In each iteration, the ratio of the measured light intensity to the light intensity calculated from the current distribution is used to adjust the distribution values ​​of each particle size range according to the weight proportions of the light energy coefficient matrix. If the calculated light intensity of a certain particle size range is less than the measured value, the proportion of that range is increased; otherwise, it is decreased.

[0038] Two sets of particle size distributions were obtained by independently inverting measurement data at two wavelengths: red light and near-infrared light. Then, they were fused by weighting the results according to the signal-to-noise ratio.

[0039] Step 3: Perform real-time refractive index correction and substitute the corrected refractive index into the diffraction angle formula. Based on the measured temperature and pressure values, correct the correspondence between particle size and diffraction angle in real time to eliminate systematic errors caused by operating condition fluctuations.

[0040] Step 4: Use standard particles of known size to calibrate the overall drift of the system, obtain the correction factor for known particle size points, and then obtain the correction coefficient for the entire particle size range through linear interpolation.

[0041] Step 5: Convert the continuous particle size distribution obtained after inversion and correction into a coal powder fineness index commonly used in power plants, and output the fineness parameters to guide combustion adjustment and pulverizing system optimization in real time.

[0042] The measurement algorithm in this embodiment is based on the physical theory of Mie scattering electromagnetics. It achieves high-precision online measurement of coal powder fineness under complex working conditions through a complete technical chain of forward scattering modeling, ill-conditioned equation inversion, multi-wavelength data fusion, operating condition error compensation, system self-calibration, and engineering parameter output.

[0043] The specific steps are as follows: Step 1: Use Mie scattering theory and light energy coefficient matrix to construct an algorithm.

[0044] Based on rigorous Mie scattering theory, for a spherical particle with diameter D and complex refractive index m, under plane wave illumination with wavelength λ, the scattering coefficient a n b n Calculated by the following formula:

[0045] Where α = πD / λ is the size parameter, and ψ n Let ξ be the Ricardi-Bessel function. n Let be the Ricardi-Hankel function. The above equations are rigorous analytical solutions based on Maxwell's equations in spherical coordinates. , These are the series expansion coefficients for the perpendicular and parallel polarization components of the scattered light, respectively. Modeling using the matrix method, this can represent the normalized scattered light energy produced by a particle of a certain size on the corresponding detector ring. It establishes a quantitative physical correspondence between particle size and diffracted light intensity, forming the theoretical basis for all inversion calculations.

[0046] Step 2: Employing a granularity distribution inversion and dual-wavelength data fusion algorithm The improved Chahine iterative algorithm is used to solve the first kind of Fredholm integral equations:

[0047] The physical meaning of this fundamental equation is: the total light intensity Ii received by the i-th ring of the detector is equal to the linear superposition of the scattered light produced by all particles of different sizes in that ring.

[0048] Where A is an M×N light energy coefficient matrix and W is a particle size distribution vector.

[0049] The iterative formula is:

[0050] Iterative correction formula: A multiplicative correction mode is adopted, and each iteration uses the measured light intensity. Calculate light intensity with the current distribution The ratio, according to The weighting ratio is adjusted to correspond to the particle size distribution value. If the calculated light intensity of a certain particle size is less than the measured value, the distribution ratio of that size is adjusted upwards; otherwise, it is adjusted downwards.

[0051] The initial distribution adopts the Rosin-Rammler distribution: W j (0) ∝D j n exp(-(D j / D') n The convergence condition is that the residual R < 10^(-4) or the number of iterations k > 100. Where W j (0) D represents the initial volume distribution percentage of the j-th particle size. j Let be the characteristic size of the j-th particle size, D' be the characteristic particle size, and n be the uniformity index.

[0052] Dual-wavelength data fusion weighted by signal-to-noise ratio:

[0053] The particle size distribution of industrial coal powder naturally conforms to the RR distribution law. Using this as the initial value for iteration can significantly reduce the number of iterations, accelerate the convergence speed, and meet the real-time requirements of online measurement.

[0054] Single-wavelength lasers have inherent measurement blind spots: short wavelengths exhibit strong scattering response to fine particles but are prone to multiple scattering interference with coarse particles; long wavelengths provide stable measurements for coarse particles but suffer from low signal-to-noise ratios at the fine particle end. This invention achieves complementary advantages through signal-to-noise ratio weighted fusion: Two sets of particle size distribution results were obtained by independently inverting the measurement data of two wavelengths respectively; the weighting coefficients were dynamically determined by the measurement signal-to-noise ratio of the corresponding particle size range: 650nm has a high signal-to-noise ratio and high weight in the fine particle range (<30μm); 850nm has good stability and high weight in the coarse particle range (>60μm).

[0055] After fusion, the measurement accuracy of both fine and coarse particles can be guaranteed simultaneously, solving the problem of uneven accuracy across the entire range of traditional single-wavelength laser particle size analyzers.

[0056] The particle size inversion is essentially an ill-conditioned first-kind Fredholm integral equation, which cannot be directly inverted. The algorithm uses the ratio of measured light intensity to calculated light intensity as a correction factor and updates the particle size distribution round by round using multiplication iteration, which naturally satisfies the physical constraint that the particle proportion is non-negative and avoids numerical oscillation.

[0057] The complete particle size distribution of pulverized coal can be stably and accurately deduced from the measured light intensity signal of the ring detector.

[0058] Step 3: Implement real-time compensation and closed-loop self-calibration algorithm for operating conditions: The air temperature in the boiler's primary air duct typically fluctuates between 60 and 180°C, and the air pressure fluctuates between 80 and 120 kPa. The air refractive index changes with temperature and pressure, leading to a shift in the diffraction angle. Directly using parameters under standard conditions introduces a 3% to 5% systematic error, which is one of the core reasons for the poor on-site measurement accuracy of existing online measurement devices. Therefore, the Edlen formula for air refractive index correction is used: Where n0=1.000292, P0=101325Pa, T0=273.15K, α=3.661×10^(-3)K^(-1).

[0059] Classical diffraction formulas are derived based on a vacuum (refractive index = 1). However, the actual measurement medium is air, and changes in refractive index will cause a shift in the diffraction angle for particles of the same size. This formula introduces a real-time refractive index... Correcting the correlation between diffraction angle and particle size eliminates systematic errors caused by fluctuations in operating conditions at their source. Diffraction angle correction formula:

[0060] Self-calibration employs piecewise linear correction using standard particles:

[0061] Where k(D) is the correction factor at particle size D.

[0062] Step 4: Perform piecewise linear calibration: Calibrate the overall system drift using standard particles of known size, and obtain correction coefficients for the entire particle size range through two-point interpolation to offset slowly varying errors such as light source attenuation, window contamination, and detector aging. For example, obtain correction factors k10 and k100 at two particle size points of 10μm and 100μm, and obtain correction coefficients for the entire particle size range through two-point interpolation.

[0063] Step 5: Calculation of coal powder fineness characteristic parameters: The 90μm sieve residue R90, the 200μm sieve residue R200, the volume average particle size D[4,3], and the median particle size D50 are calculated according to the following formulas:

[0064] Where D is the particle diameter. It is volume frequency density. This represents the total volume contribution of particles in that particle size range. For pulverized coal, the density is approximately the same, so the volume percentage is equivalent to the mass percentage. The numerator represents the total volume of all particles larger than 90 μm, and the denominator represents the total volume of particles of all sizes. R90 represents the mass percentage of pulverized coal particles larger than 90 μm. The lower the R90, the finer the pulverized coal is ground.

[0065]

[0066]

[0067] D[4,3] is the average particle size obtained by weighting the particle volume (mass) as the weight. The formula is essentially "the average value of all particle sizes weighted by their volume". Since the volume (D3) of large particles contributes greatly, D[4,3] is extremely sensitive to the coarse particle end and is often used to quantify the overall coarseness level of large particles ground by the powdering system.

[0068]

[0069] Where F is the cumulative distribution function.

[0070] D50 represents the particle size at which the accumulated coal powder particles, arranged from smallest to largest, reach exactly 50% of the total. It represents the median size of the coal powder distribution; 50% of the particles are smaller than this size, and 50% are larger. This index directly reflects the overall distribution shift and is unaffected by extreme interference from a very small number of ultra-coarse or ultra-fine particles, exhibiting good stability.

[0071] The continuous particle size distribution obtained by inversion is converted into engineering indicators commonly used in power plants: R90 / R200 is the volume percentage of particles larger than the corresponding particle size (equivalent to the mass percentage, directly comparable to the traditional sieving method); D[4,3] is the volume-weighted average particle size; D50 is the median particle size, which is accurately located by linear interpolation.

[0072] Example 2 This embodiment provides a measurement system for the online measurement method of boiler pulverized coal fineness described in Embodiment 1, comprising: a multi-wavelength laser unit, a measurement gas chamber unit, and a ring photoelectric detection unit.

[0073] The online coal powder fineness measurement system for boilers in this embodiment is used to measure the coal powder pipeline 7.

[0074] The pulverized coal pipeline 7 is used to transport pulverized coal from the primary air of the boiler and to provide a sampling source.

[0075] The multi-wavelength laser unit includes a red semiconductor laser 1 and a near-infrared semiconductor laser 2. The red semiconductor laser 1 emits at a wavelength of 650 nm, and the near-infrared semiconductor laser 2 emits at a wavelength of 850 nm.

[0076] The red semiconductor laser 1 is used to generate short-wavelength laser light, which is more sensitive to the scattering response of fine particles with a diameter of less than 30 μm and can provide high-resolution fine-end measurements.

[0077] The near-infrared semiconductor laser 2 is used to generate long-wavelength lasers, which provides more stable measurement of coarse particles with a diameter greater than 60 μm and provides high signal-to-noise ratio data for coarse particles.

[0078] Optionally, the red semiconductor laser 1 is a stable semiconductor laser with a power of 5mW. The near-infrared semiconductor laser 2 is a near-infrared semiconductor laser with a power of 5mW.

[0079] The multi-wavelength laser unit also includes a dichroic mirror 3 and a collimating beam expander lens 4. The emission ports of the red semiconductor laser 1 and the near-infrared semiconductor laser 2 are both directed towards the entrance end of the dichroic mirror 3, and the emission port of the dichroic mirror 3 is directed towards the collimating beam expander lens 4. The collimating beam expander lens 4 is directed towards the measuring gas chamber unit.

[0080] The dichroic mirror 3 is used to combine two laser beams into a coaxial beam, realizing a dual-wavelength common optical path. The dichroic mirror 3 can reflect 650nm laser light and transmit 850nm laser light.

[0081] The dichroic mirror 3 is positioned at the point where the laser beams emitted by the red semiconductor laser 1 and the near-infrared semiconductor laser 2 converge.

[0082] The collimating and expanding lens 4 is used to expand the combined laser beam and collimate it into a parallel beam with a diameter of 10mm to ensure uniform irradiation of the particle group.

[0083] Two laser beams emitted by red semiconductor laser 1 and near-infrared semiconductor laser 2 are combined into a coaxial beam by dichroic mirror 3, and then collimated and expanded by collimating lens 4 to form a parallel beam with a diameter of 10 mm. The dual-wavelength design utilizes the difference in scattering response of different wavelengths to particles of different sizes; 650 nm is more sensitive to fine particles, while 850 nm is more sensitive to coarse particles. High-precision measurement across the entire range is achieved through data fusion.

[0084] Optionally, the collimating and beam-expanding lens 4 is a multi-piece collimating and beam-expanding lens group.

[0085] The measuring chamber unit includes a Laval nozzle 5. Specifically, the Laval nozzle 5 includes a converging conduit 51 and an ejector conduit 52. One end of the ejector conduit 52 is connected to the pulverized coal conduit 7, and the other end is connected to the side of the converging conduit 51. One end of the converging conduit 51 is connected to the external atmosphere, and the other end is connected to a throat conduit 53. The other end of the throat conduit 53 is connected to a diverging conduit 54, and the other end of the diverging conduit 54 is connected to a return pulverized coal conduit 55.

[0086] Compressed air is injected and accelerated through the converging pipe 51, creating a negative pressure that draws in pulverized coal from the pulverized coal pipe 7. The mixture of pulverized coal and compressed air is kept at a constant speed in the throat pipe 53 and ejected through the expanding pipe 54, returning to the pulverized coal return pipe 55.

[0087] Optical windows are provided on a set of opposite sides of the throat pipe 53, with one of the optical windows facing the collimating beam expander lens 4.

[0088] A photodetector 6 is provided on the side of the throat pipe 53 facing away from the collimating beam expander lens 4; the center of the dichroic mirror 3, the center of the collimating beam expander lens 4, the center of the Laval nozzle 5, and the center of the photodetector 6 are arranged on the same axis.

[0089] The photodetector 6 includes: an optical protection window 61, one end of which faces the Laval nozzle 5, and a silicon photodetector 62 at the other end. The other end of the silicon photodetector 62 is connected to a data acquisition unit 63, and the data acquisition unit 63 is communicatively connected to a data processor 64.

[0090] Optionally, the optical protection window 61 is made of sapphire and has a thickness of 3 mm.

[0091] The silicon photodetector 62 employs a 32-ring concentric ring detection system, with each ring independently amplifying and acquiring data, achieving a dynamic range of 10^5. The data acquisition unit 63 is used for time-division multiplexing of dual-wavelength signals. The data processor 64 is used to analyze the data from the data acquisition unit 63. Optionally, a switchable filter wheel is provided between the silicon photodetector 62 and the data acquisition unit 63, with the filters being bandpass filters of 640nm to 660nm and 840nm to 860nm respectively, to achieve time-division multiplexing of dual-wavelength signals.

[0092] Example 3 This embodiment of a method for online measurement of pulverized coal fineness in boilers includes the following steps: Preparation phase: Check that the multi-wavelength laser unit (power 5mW), the measuring chamber window is clean, and the ring detector signal is normal. Start compressed air at 0.2MPa and pulverized coal flow rate at 0.5kg / min. Self-calibrate using standard particles D50=50μm.

[0093] Detection steps: Emit a dual-wavelength beam (10mm diameter).

[0094] Powdered coal passes through throat pipe 53 (flow velocity 20m / s) and light intensity signals are collected.

[0095] The distribution is obtained through inversion fusion.

[0096] Operating condition compensation (T=120°C, P=100kPa, n=1.00028). Output R90=18.5%, R200=2.3%, D[4,3]=55.2μm, D50=48.7μm. Result: Deviation <2%, efficiency improved.

[0097] like Figure 4 The figure shown is a particle size distribution of pulverized coal. This figure shows a typical wide-distribution pulverized coal particle size distribution (RR distribution), which verifies that the measurement accuracy is balanced across the entire range (fine and coarse particles) after multi-wavelength fusion. However, there are blind spots in single wavelengths (deviation at the coarse end of 650nm and low signal-to-noise ratio at the fine end of 850nm).

[0098] like Figure 5 The figure shows the velocity cloud map of pulverized coal particles. This figure shows the flow field of the throat pipe 53 of the Laval nozzle 5. The pulverized coal airflow velocity is uniform (20 m / s), which ensures that the particles pass through the measurement area uniformly and reduces the influence of flow field disturbance on the scattered signal.

[0099] Simulation results show that the system has an error of less than 1% under complex working conditions. Working condition compensation and self-calibration effectively eliminate 3-5% of the system error, verifying the reliability and field applicability of the invention.

[0100] Unless otherwise specified, the equipment components involved in the above embodiments are all conventional equipment components, and the structural settings, working methods or control methods involved are all conventional settings, working methods or control methods in the art unless otherwise specified.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for online measurement of the fineness of pulverized coal in boilers, characterized in that, Includes the following steps: A quantitative physical correspondence between particle size and scattered light intensity was established using the matrix method, resulting in the light energy coefficient matrix. An iterative algorithm is used for inversion. In each iteration, the ratio of the measured light intensity to the light intensity calculated from the current distribution is used to correct the distribution values ​​of each particle size range according to the weight ratio of the light energy coefficient matrix. If the calculated light intensity of a certain particle size range is less than the measured value, the proportion of that range is increased; if the calculated light intensity of a certain particle size range is greater than or equal to the measured value, it is decreased. The particle size distribution is obtained by independently inverting the measurement data of red light and near-infrared light wavelengths, respectively, and then fused to obtain the fused particle size distribution. The system drift is calibrated using standard particles of known size. Correction coefficients for the entire particle size range are obtained by linear interpolation. The particle size distribution after fusion is then corrected based on the correction coefficients to obtain the final continuous particle size distribution. The corrected continuous particle size distribution is converted into a coal powder fineness index commonly used in power plants, and the fineness parameter is output for real-time guidance of combustion adjustment and pulverizing system optimization.

2. The method for online measurement of pulverized coal fineness in boilers according to claim 1, characterized in that, After obtaining the two sets of particle size distributions, they are fused according to the signal-to-noise ratio weighting.

3. The method for online measurement of pulverized coal fineness in boilers according to claim 1, characterized in that, In the step of establishing a quantitative physical correspondence between particle size and scattered light intensity using the matrix method, a quantitative physical correspondence is established between particles of each size range and the scattered light intensity on each detection ring of the photodetector.

4. The method for online measurement of pulverized coal fineness in boilers according to claim 1, characterized in that, Before the overall drift step of the calibration system using standard particles of known particle size, the temperature and pressure values ​​in the primary air duct of the boiler are measured in real time. The current air refractive index is calculated based on the measured temperature and pressure values, and the mapping relationship between the diffraction angle and the particle size is corrected in real time using this refractive index. The particle size mapping is corrected for the fused particle size distribution, and the corrected particle size distribution is corrected using a correction coefficient.

5. The method for online measurement of pulverized coal fineness in boilers according to claim 1, characterized in that, The calculation formula for the iterative algorithm is: Where W is the particle size distribution vector, A is the M×N optical energy coefficient matrix, Ii is the total light intensity received by the i-th ring of the detector, j is the j-th particle size, and the value range corresponds to N particle size levels, M is the total number of rings of the annular photodetector, and k is the current iteration round.

6. The method for online measurement of pulverized coal fineness in boilers according to claim 1, characterized in that, In the iterative algorithm, the initial distribution adopts the Rosin-Rammler distribution, and the convergence condition is that the residual R < 10^(-4) or the number of iterations k > 100.

7. The method for online measurement of pulverized coal fineness in boilers according to claim 1, characterized in that, In the step of converting the corrected continuous particle size distribution into the pulverized coal fineness index commonly used in power plants, the residue at a 90μm sieve, the residue at a 200μm sieve, the volume average particle size, and the median particle size are calculated respectively.

8. A measurement system applied to the online measurement method for boiler pulverized coal fineness according to any one of claims 1 to 7, characterized in that, include: The unit comprises a multi-wavelength laser unit, a measuring gas chamber unit, and a ring photodetector unit. The multi-wavelength laser unit includes a red semiconductor laser (1), a near-infrared semiconductor laser (2), a dichroic mirror (3), and a collimating beam expander (4). The dichroic mirror (3) is located at the point where the laser beams emitted by the red semiconductor laser (1) and the near-infrared semiconductor laser (2) converge. The emitting end of the dichroic mirror (3) faces the collimating beam expander (4), and the collimating beam expander (4) faces the measuring gas chamber unit. A photodetector (6) is provided on the side of the measuring gas chamber unit that faces away from the collimating beam expander (4).

9. The measurement system according to claim 8, characterized in that, The red semiconductor laser (1) emits at a wavelength of 650 nm, and the near-infrared semiconductor laser (2) emits at a wavelength of 850 nm.

10. The measurement system according to claim 8, characterized in that, The measuring gas chamber unit includes a Laval nozzle (5), which includes a tapered pipe (51) and an ejector pipe (52). One end of the ejector pipe (52) is connected to the pulverized coal pipe (7), and the other end is connected to the side of the tapered pipe (51). One end of the tapered pipe (51) is connected to the atmosphere, and the other end is connected to a throat pipe (53). The other end of the throat pipe (53) is connected to a diffuser pipe (54), and the other end of the diffuser pipe (54) is connected to a return pulverized coal pipe (55). Optical windows are respectively provided on a set of opposite sides of the throat pipe (53), and one of the optical windows faces the collimating beam expanding lens (4).

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