A system and method for online measurement of particle size of wide-screening particles based on multiple wavelengths

Abstract

The present invention discloses an online measurement system for particle size of wide-screened particles based on multiple wavelengths: a laser generating device, including three lasers with different wavelengths, a beam combiner and a fiber collimator, the lasers emitted by the three lasers with different wavelengths are incident on a conveyor belt to form a light spot after passing through the beam combiner and the fiber collimator; a scattered light receiving device, including a lens, a scattered light receiving beam splitter and three receiving channels, the three receiving channels all including a narrow-band filter and a photomultiplier tube, when particles pass through the light spot, a scattered signal is generated, which is focused by the lens and then converted into an electrical signal in sequence through the scattered light receiving beam splitter, the narrow-band filter and the photomultiplier tube; a processing device, which receives the electrical signal and processes it to obtain the particle size. The present invention also discloses an online measurement method for particle size of wide-screened particles using the above device. The device and method can realize online in-situ measurement of particle size of wide-screened distributed particles based on the principle of light scattering, the measurement process does not require manual operation, and the measurement results are accurate and timely.

Description

Technical Field

[0001] The invention relates to the field of online particle size measurement, and in particular to an online particle size measurement system and method for wide screening particles based on multiple wavelengths. Background Art

[0002] The particles in the bed material of a circulating fluidized bed (CFB) boiler are usually distributed in a wide sieve with particle sizes ranging from small to large. Due to the different diameters of the particles, their flow conditions and laws are also different. Practice has shown that the particle size of the fuel entering the furnace has a certain degree of influence on the ignition start-up, operation control, combustion efficiency, and operation of components such as the hood and water-cooled wall of the circulating fluidized bed boiler. For example, when the particles are too large, it may cause problems such as reduced bed pressure and uneven bed surface temperature. CFB boilers usually use conveyor belts to transport fuel to the boiler. Therefore, accurate and rapid measurement of the particle size of the fuel entering the furnace on the conveyor belt is of great significance to the safe and economical operation of the boiler.

[0003] The traditional method for measuring particle size in industrial sites is the sieving method, which is to place a fuel sample of known weight on sieves with different mesh sizes and arranged in sequence and mechanically vibrate them to make the particles continuously pass through the sieves with smaller meshes. The particles retained on the sieves are weighed to calculate the percentage of the mass of each particle size in the total sample weight, and obtain the particle size distribution of the sample. The sieving method has a simple measurement principle and reliable results, but it requires sampling and the detection takes a long time. The measurement results are delayed and cannot meet the rapid changes in industrial production.

[0004] At present, the relatively popular and advanced methods mainly include laser particle size method and machine vision method. For example, Chinese patent with publication number CN107255608A discloses a particle size measuring instrument based on a single photoelectric detector, and Chinese patent with publication number CN109598715A discloses an online material particle size detection method based on machine vision. The laser particle size method obtains the particle size by emitting a laser beam, receiving and analyzing the diffraction or scattered light signal generated after the laser is blocked by particles. This method has fast measurement speed, accurate results and simple operation. The machine vision method converts the target into an image signal through the particle image of a certain area on the particle flow, and then uses the relevant processing algorithm to identify and calculate the target parameters in the image to identify and analyze the particles. This method is low-cost, non-destructive to the sample, and has a wide range of particle sizes to detect, and can simultaneously analyze particles from micrometers to millimeters. Summary of the invention

[0005] The present invention provides a system and method for online measurement of particle size of wide-screen distribution particles based on multiple wavelengths, which can realize online in-situ measurement of particle size of wide-screen distribution particles. The measurement process does not require manual operation, and the measurement results are accurate and timely.

[0006] The present invention provides the following technical solutions:

[0007] A multi-wavelength wide screening particle size online measurement system, the system comprising:

[0008] The laser generating device includes three lasers with different wavelengths, a beam combiner and a fiber collimator. The lasers emitted by the three lasers with different wavelengths are incident on the conveyor belt to form a light spot after passing through the beam combiner and the fiber collimator.

[0009] A scattered light receiving device, comprising a lens, a scattered light receiving beam splitter and three receiving channels, each of which comprises a narrow-band filter and a photomultiplier tube. When particles pass through the light spot, a scattered signal is generated, which is focused by the lens and then converted into an electrical signal by the scattered light receiving beam splitter, the narrow-band filter and the photomultiplier tube in sequence.

[0010] The processing device receives the electrical signal and processes it to obtain the particle size.

[0011] Preferably, the incident light emitted by the optical fiber collimator is incident vertically downward onto the conveyor belt plane, and the incident light and the receiving light path composed of the lens and the scattered light receiving beam splitter are arranged at an angle of 15 to 75. Further preferably, the angle is 30 degrees.

[0012] Preferably, the laser generating device and the scattered light receiving device are both connected and fixed by a cage system.

[0013] Preferably, the cage system is suspended above the conveyor belt via a bracket.

[0014] Preferably, the three lasers with different wavelengths include a solid continuous laser with a wavelength of 400nm to 500nm, a solid continuous laser with a wavelength of 500nm to 600nm, and a semiconductor continuous laser with a wavelength of 600nm to 800nm.

[0015] Preferably, the three lasers with different wavelengths are arranged parallel to each other.

[0016] Preferably, the laser power is 0 to 5W.

[0017] Preferably, the central wavelengths of the narrowband filters in the three receiving channels are 400nm to 500nm, 500nm to 600nm and 600nm to 800nm.

[0018] Preferably, the peak wavelengths of the photomultiplier tubes in the three receiving channels are 400nm to 500nm, 500nm to 600nm and 600nm to 800nm.

[0019] Preferably, the three receiving channels are arranged parallel to each other.

[0020] Preferably, the diameter of the light spot formed on the conveyor belt is 0.05 mm to 1 mm.

[0021] The present invention also provides a method for online measuring the particle size of wide screening particles using the above device, the method comprising: performing Fourier transform on the collected multi-channel scattered light signal as a whole to obtain and The signal is fitted and decomposed to match the components of particles of different sizes in the spectrum to obtain the wide screening particle size distribution data of the fuel; the continuous operation of the conveyor belt drives particles of different sizes to continuously pass through the measuring light spot, and the signal is collected and processed by the calculation program to obtain the fuel particle size distribution in real time;

[0022] The specific steps include:

[0023] (1) Three lasers with different wavelengths are turned on at the same time. The lasers with different wavelengths emitted by each laser are transmitted by optical fiber into the beam combiner. The combined lasers are connected to the optical fiber collimator and irradiated onto the conveyor belt to form a light spot.

[0024] (2) The conveyor belt transports fuel particles at a certain speed. The particles generate scattered signals when they pass through the light spot. The scattered signals are focused by the lens, converted into electrical signals by the scattered light receiving beam splitter, narrow band filter and photomultiplier tube in sequence and transmitted to the computer.

[0025] (3) Computer processing of electrical signals to obtain the response curve of scattered light intensity over time and in and are the scattered light signal intensities generated by the particles under the irradiation of lasers with wavelengths λ1, λ2 and λ3, respectively, and t is the time when the scattered light signal is recorded; and The particles to be tested are identified in the same portion of the durations △t1, △t2 and △t3 under laser irradiation of different wavelengths, and the particle size of the particles to be tested is preliminarily calculated based on the known conveyor belt speed and signal duration;

[0026] (4) Extract the corresponding signal strength during △t1, △t2 and △t3 and By performing Fourier transform, we can obtain the component frequencies F1 (△ω1), F2 (△ω2) and F3 (△ω3) of the particles to be measured in the spectrum, compare them with the calibration results of particles of known particle sizes under laser irradiation of various wavelengths, match the closest calibration particle size, and further determine the particle size of the particles to be measured.

[0027] The measurement is terminated by stopping the conveyor belt or by switching off all three lasers.

[0028] The multi-wavelength based wide screening particle size online measurement system provided by the present invention is arranged beside a fuel conveyor belt, and the fuel is industrial power coal with a particle size above micron level.

[0029] The multi-wavelength based wide-screen particle size online measurement system and method disclosed in the present invention are based on the principle of light scattering. During the conveying process of circulating fluidized bed materials in industrial sites, the online in-situ measurement of particle size data of wide-screen distribution in the circulating fluidized bed materials can be realized. The measurement process does not require manual operation, the measurement results are accurate and timely, and the economic benefits are outstanding. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic structural diagram of the multi-wavelength based wide screening particle size online measurement system provided by the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is necessary to point out that the embodiments are only used to further illustrate the present invention and cannot be understood as a definition of the protection scope of the present invention.

[0032] like Figure 1 As shown, the multi-wavelength based wide screening particle size online measurement system provided by the present invention includes a laser generating device, a scattered light receiving device and a computer.

[0033] The laser generating device includes a first laser 1, a second laser 2, a third laser 3, a beam combiner 4 and a fiber collimator 5. The three lasers are arranged in parallel with each other, and the three laser beams with different wavelengths emitted are combined into one beam of light by the beam combiner 4, and then connected to the fiber collimator 5 via an optical fiber to focus on the conveyor belt 15 to form a light spot.

[0034] The scattered light receiving device includes a lens 6, a scattered light receiving beam splitter 7 and three receiving channels: the first receiving channel includes a first narrowband filter 8 and a first photomultiplier tube 11; the second receiving channel includes a second narrowband filter 9 and a second photomultiplier tube 12; the third receiving channel includes a third narrowband filter and a third photomultiplier tube 13. The three receiving channels are arranged in parallel and connected to a computer 14 for signal transmission and processing.

[0035] The optical path of the laser emitting device and the optical path of the scattered light receiving device are connected and fixed by a cage system to ensure that the optical components are installed along a common optical axis. The incident light emitted by the fiber collimator 5 is vertically downward to the conveyor belt plane, and the incident light and the receiving optical path composed of the lens 6 and the scattered light receiving beam splitter 7 are arranged at an angle of 30 degrees.

[0036] A bracket is provided above the conveyor belt 15, and the laser emitting device and the scattered light receiving device are both suspended on the bracket by a cage system.

[0037] The first laser 1, the second laser 2 and the third laser 3 can respectively emit continuous lasers of 457nm, 532nm and 650nm with a power adjustment range of 0-5W.

[0038] The first photomultiplier tube 11, the second photomultiplier tube 12 and the third photomultiplier tube 13 can convert the received scattered light signals into electrical signals, and amplify the electrical signals and transmit them to a computer. The computer converts the received electrical signals into image signals and obtains the particle size data through software program processing.

[0039] The specific operation process is as follows:

[0040] The first laser 1, the second laser 2 and the third laser 3 respectively emit continuous lasers with wavelengths of 457nm, 532nm and 650nm, which are transmitted into the beam combiner 4 by the optical fiber. Three laser beams with different wavelengths are combined into one laser beam in the beam combiner 4. After the beam combination, the laser beam is connected to the optical fiber collimator 5 by the optical fiber and focused on the conveyor belt 15 to form a light spot with a diameter of 0.1mm. The incident laser light spot irradiates the fuel particles moving with the conveyor belt and scatters. According to the principle of light scattering, the intensity of the scattered light signal is related to the particle size and the laser wavelength. The scattered light is collected by the lens 6 and received by the scattered light receiving beam splitter 7, and is divided into three receiving light paths. The first narrow-band filter 8, the second narrow-band filter 9 and the third narrow-band filter 10 are selective and only allow light of one wavelength to pass through. The first photomultiplier tube 11, the second photomultiplier tube 12 and the point photomultiplier tube 13 respectively record scattered light signals of three specific wavelengths and transmit the scattered light signals to the computer 14. The computer 14 uses the scattered light signal calculation program for further processing to obtain the particle size data.

[0041] When measuring:

[0042] The first laser 1, the second laser 2 and the third laser 3 are turned on at the same time. After the laser beams are combined, the light spot is focused at one place. The conveyor belt 15 transmits the fuel particles at a certain speed. The particles generate scattering signals when passing through the light spot. The first photomultiplier tube 11, the second photomultiplier tube 12 and the third photomultiplier tube 13 collect the electrical signals that change with time and transmit them to the computer.

[0043] The computer obtains the scattered light intensity response curve over time and Among them, λ1, λ2 and λ3 are three laser wavelengths, and t is the time when the scattered light signal is recorded. Since the spot diameter is the same after the laser beams of different wavelengths are combined, the scattered light signal intensity P generated by the same particle under the irradiation of lasers of different wavelengths is different, and the duration △t is the same. and The same part of △t1, △t2 and △t3 is used to identify the particles to be measured, and the particle size of the particles to be measured is preliminarily calculated based on the known conveyor belt speed and signal duration.

[0044] Extract the corresponding signal strength within △t1, △t2 and △t3 and By performing Fourier transform, we can obtain the component frequencies F1 (△ω1), F2 (△ω2) and F3 (△ω3) of the particles to be measured in the spectrum, compare them with the calibration results of particles of known particle sizes under laser irradiation of various wavelengths, and match the closest calibration particle size through a suitable algorithm to further determine the particle size of the particles to be measured.

[0045] Perform Fourier transform on the collected multi-channel scattered light signal as a whole to obtain and Signal fitting and decomposition are performed to match the components of particles of different sizes in the spectrum and obtain the wide screening particle size distribution data of the fuel.

[0046] The conveyor belt 15 continuously runs to drive particles of different sizes to continuously pass through the measuring light spot, and the fuel particle size distribution can be obtained in real time by collecting signals and processing them using a computing program. The measurement can be ended by shutting down the conveyor belt 15 or shutting down the first laser 1, the second laser 2 and the third laser 3 at the same time.

[0047] The above is a detailed description of the present invention in combination with the embodiments, but the implementation methods of the present invention are not limited to the above embodiments, and any other changes, replacements, combination simplifications, etc. made under the core guiding idea of ​​the patent of the present invention are included in the protection scope of the patent of the present invention.

Claims

1. A multi-wavelength wide screening particle size online measurement system, characterized in that: The system comprises: The laser generating device includes three lasers with different wavelengths, a beam combiner and a fiber collimator. The lasers emitted by the three lasers with different wavelengths are incident on the conveyor belt to form a light spot after passing through the beam combiner and the fiber collimator. A scattered light receiving device, comprising a lens, a scattered light receiving beam splitter and three receiving channels, each of which comprises a narrow-band filter and a photomultiplier tube. When particles pass through the light spot, a scattered signal is generated, which is focused by the lens and then converted into an electrical signal by the scattered light receiving beam splitter, the narrow-band filter and the photomultiplier tube in sequence. A processing device receives the electrical signal and processes it to obtain the particle size; The method for measuring the particle size of wide-screened particles online in the system is: Fourier transform the collected multi-channel scattered light signals as a whole to obtain F1(P λ1 ,ω)、F2(P λ2 ,ω) and F3(P λ3 ,ω), perform signal fitting and decomposition, match the components of particles of different sizes in the spectrum, and obtain the wide screening particle size distribution data of the fuel; the continuous operation of the conveyor belt drives particles of different sizes to pass through the measuring light spot continuously, collect signals and use the calculation program to process to obtain the fuel particle size distribution in real time; The specific steps include: (1) Three lasers with different wavelengths are turned on at the same time. The lasers with different wavelengths emitted by each laser are transmitted by optical fiber into the beam combiner. The combined lasers are connected to the optical fiber collimator and irradiated onto the conveyor belt to form a light spot. (2) The conveyor belt transports fuel particles at a certain speed. The particles generate scattered signals when they pass through the light spot. The scattered signals are focused by the lens, converted into electrical signals by the scattered light receiving beam splitter, narrow band filter and photomultiplier tube in sequence and transmitted to the computer. (3) The computer processes the electrical signal to obtain the scattered light intensity response curve f1(P λ1 ,t)、f2(P λ2 ,t) and f3(P λ3 ,t), where P λ1 , P λ1 and P λ3 are the scattered light signal intensities generated by the particles under the irradiation of lasers with wavelengths λ1, λ2 and λ3, respectively, and t is the time when the scattered light signal is recorded; matching f1(P λ1 ,t)、f2(P λ2 ,t) and f3(P λ3 ,t) the part of the particle with the same duration △t1, △t2 and △t3 under the laser irradiation of different wavelengths, identify the particle to be measured, and preliminarily calculate the particle size of the particle to be measured based on the known conveyor belt speed and signal duration; (4) Extract the corresponding signal strength f1(P λ1 ,△t1)、f2(P λ2 ,△t2) and f3(P λ3 ,△t3) and perform Fourier transform to obtain the component frequencies F1(△ω1), F2(△ω2) and F3(△ω3) of the particles to be tested in the spectrum, and compare them with the calibration results of particles of known particle sizes under laser irradiation of various wavelengths to match the closest calibration particle size, and further determine the particle size of the particles to be tested.

2. The multi-wavelength wide screening particle size online measurement system according to claim 1 is characterized in that: The incident light emitted by the optical fiber collimator is incident vertically downward onto the conveyor belt plane, and the incident light is arranged at an angle of 15 to 75 degrees with a receiving light path composed of a lens and a scattered light receiving beam splitter.

3. The multi-wavelength based wide screening particle size online measurement system according to claim 1, characterized in that: The laser generating device and the scattered light receiving device are both connected and fixed by a cage system.

4. The multi-wavelength based wide screening particle size online measurement system according to claim 3 is characterized in that: The cage system is suspended above the conveyor belt through a bracket.

5. The multi-wavelength based wide screening particle size online measurement system according to claim 1, characterized in that: The three lasers with different wavelengths include a solid continuous laser with a wavelength of 400nm to 500nm, a solid continuous laser with a wavelength of 500nm to 600nm, and a semiconductor continuous laser with a wavelength of 600nm to 800nm.

6. The multi-wavelength wide screening particle size online measurement system according to claim 5, characterized in that: The laser power is 0 to 5W.

7. The multi-wavelength based wide screening particle size online measurement system according to claim 1, characterized in that: The central wavelengths of the narrowband filters in the three receiving channels are 400nm to 500nm, 500nm to 600nm and 600nm to 800nm.

8. The multi-wavelength based wide screening particle size online measurement system according to claim 1, characterized in that: The peak wavelengths of the photomultiplier tubes in the three receiving channels are 400nm to 500nm, 500nm to 600nm and 600nm to 800nm.

9. The multi-wavelength wide screening particle size online measurement system according to claim 1, characterized in that: The diameter of the light spot formed on the conveyor belt is 0.05 mm to 1 mm.

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