Biomass combustion in-situ measurement method based on spectrum and flame imaging

Abstract

The invention provides a biomass combustion in-situ measurement method based on spectrum and flame imaging. The biomass combustion in-situ measurement method comprises the following steps that a biomass sample is pretreated and conveyed to a dropper furnace combustion monitoring system through pneumatic conveying; preheating, and monitoring combustion parameters in real time through a temperature control system and a data acquisition system; the synchronous acquisition system is connected with the Fourier transform infrared spectrometer, the ICCD camera and the intermediate infrared camera; spectral information in a flame heat radiation (200 nm to 20 [mu] m) wave band is obtained, and free radical and smoke component images are collected; and finally, comprehensively processing and analyzing the data, and extracting key parameters such as temperature, radiation characteristics, component concentration and the like. According to the invention, multi-parameter in-situ synchronous measurement is realized, combustion surface temperature and radiation characteristics are accurately calculated in combination with an advanced algorithm, and free radical and flue gas component distribution is quantified through an imaging technology. An efficient and reliable technical means is provided for studying a biomass combustion mechanism, optimizing a combustion process and controlling pollution emission, and the biomass combustion device has important scientific research and application values.

Description

Technical Field

[0001] The present invention relates to the technical field of in-situ measurement of biomass combustion, and specifically to an in-situ measurement method of biomass combustion based on spectroscopy and flame imaging. Background Art

[0002] In the critical period of global energy transformation, biomass energy, as an important renewable energy, its efficient utilization is crucial for alleviating the energy crisis and addressing climate change. The research on the biomass combustion process is the core link to achieve the efficient conversion of biomass energy. Accurately obtaining various parameters during the combustion process, such as temperature distribution, radiation characteristics, free radicals, and changes in the concentration of flue gas components, is of key significance for deeply understanding the combustion mechanism, optimizing combustion technology, improving energy utilization efficiency, and reducing pollutant emissions. However, traditional measurement methods have many limitations when facing the complex multiphase, high-temperature, and dynamic process of biomass combustion, such as being unable to achieve in-situ real-time measurement, being difficult to obtain multiple key parameters simultaneously, and being greatly affected by environmental factors in measurement accuracy. Summary of the Invention

[0003] Aiming at the above-mentioned existing technical deficiencies, the purpose of the present invention is to provide an in-situ measurement method of biomass combustion based on spectroscopy and flame imaging to solve the key problems in the research of biomass combustion.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions: An in-situ measurement method of biomass combustion based on spectroscopy and flame imaging, comprising the following steps: S1. Pretreatment and placement of raw materials Crush, sieve, and dry diverse biomass samples and transport them to the drop-tube furnace combustion system through pneumatic conveying; S2. Start-up and preheating of the drop-tube furnace combustion system Start the drop-tube furnace combustion system and increase the carrier gas flow rate to the experimental set value to complete the preheating of the drop-tube furnace combustion system; S3. Stabilization and monitoring of combustion process parameters Keep the power of the heating system stable and transmit the radiation image of the collected combustion flame to the computer in real time; S4. Construct a data synchronous acquisition system; S5. Acquisition of combustion flame spectral data Continuously monitor the combustion parameters to obtain the emission spectral information of the full radiation band of the combustion flame; S6. Acquisition of combustion flame images Acquire the combustion flame image and the data of the distribution characteristics of the free radical radiation intensity and transmit them to the computer in real time; S7. Acquisition of combustion flue gas images Collect the infrared radiation intensity distribution image data of the combustion flue gas components and transmit it to the computer in real time; S8. Comprehensive data analysis and result presentation Perform baseline correction, smoothing processing and peak splitting fitting on the full radiation band emission spectrum data of the combustion flame, extract the spectral characteristic parameters, perform edge detection and target recognition on the biomass combustion flame image and the infrared flue gas radiation intensity distribution data, extract the distribution characteristics of free radicals and flue gas components, and present the results on the computer.

[0005] Preferably, in step S1, the raw materials are selected from diverse biomass samples by using the random sampling method, which specifically includes the following steps: First, use a vibrating sieve with a mesh size of 0.1 - 1 mm to screen the biomass, and screen out the particles with a relatively concentrated particle size distribution; then, place the screened raw materials in a vacuum drying oven and dry them at a temperature of 60 - 80 °C for 4 - 6 hours to remove the moisture in the raw materials; after the dried biomass is cooled to room temperature, store it in a sealed container for later use; convey the pretreated biomass particles to a pneumatic conveying silo, and a spiral feeder that can precisely control the lifting is connected to the bottom of the pneumatic conveying silo; the rotation speed of the spiral feeder is controlled by a motor, and the feeding rate of the biomass is precisely controlled by adjusting the motor speed, and the feeding rate range is between 0 - 2 g / min; During the feeding process, the carrier gas enters from the inlet, and the flow rate of the carrier gas is precisely controlled by a mass flow controller; the flow rate of the carrier gas is adjusted within the range of 0 - 40 L / min according to the experimental requirements to ensure that the biomass particles can be evenly carried into the drop tube furnace combustion system; a mixing chamber is arranged between the feed hopper and the drop tube furnace combustion system, and a static mixer is installed in the mixing chamber, and the mixing elements inside it can promote the uniform mixing of the gas-solid two phases, so that the biomass particles entering the drop tube furnace combustion system are evenly distributed in the carrier gas, avoiding agglomeration or segregation phenomena.

[0006] Preferably, in step S2, before starting the dropping tube furnace combustion system, check the airtightness of the entire experimental system to ensure no gas leakage; connect the dropping tube furnace combustion system with the gas supply system, temperature control system, and data acquisition system, start the cooling system of the dropping tube furnace combustion system, and ensure that the cooling water flow rate is stable at 2 - 4 L / min to protect the structural integrity of the dropping tube furnace combustion system during high-temperature operation; turn on the gas supply system, first introduce a certain carrier gas at a flow rate of 3 - 5 L / min to purge the dropping tube furnace combustion system and remove air and impurities in the system; then, slowly increase the carrier gas flow rate to the experimental set value and gradually introduce the combustion-supporting gas; the flow rate and proportion of the combustion-supporting gas are precisely controlled according to the experimental purpose; start the heating system of the dropping tube furnace combustion system, and the heating elements of the heating system are arranged around the combustion area of the dropping tube furnace combustion system; the heating system adopts a PID control method, and the temperature of the combustion area is monitored in real time through a temperature sensor, and the temperature signal is fed back to the controller; the controller automatically adjusts the power of the heating elements according to the preset heating curve to slowly raise the temperature of the combustion area to the initial temperature required for the experiment, where the initial temperature is between 400 - 600 °C, and the heating rate is controlled at 10 - 20 °C / min; during the heating process, closely observe the temperature change to ensure a stable heating process and avoid excessive temperature fluctuations affecting the experimental results.

[0007] Preferably, in step S3, when the temperature of the combustion area reaches the initial set value, keep the power of the heating system stable through the temperature control system and continuously monitor various parameters during the combustion process; temperature monitoring is carried out using a platinum-rhodium thermocouple, and the measuring end of the thermocouple is inserted into the outer wall surface of the quartz tube in the combustion area to obtain accurate temperature data; the temperature data is transmitted to the computer in real time through a data acquisition card, and the temperature data is displayed, recorded, and analyzed in real time through the computer; during the combustion process, it is required that the temperature fluctuation range is controlled within ±3 °C. If the temperature fluctuation exceeds this range, the temperature control system will automatically adjust the power of the heating elements to maintain temperature stability; in addition to temperature monitoring, it is also necessary to monitor the gas flow rate during the combustion process in real time; the flow rates of the carrier gas and combustion-supporting gas are precisely controlled and monitored through a mass flow controller, and the accuracy of the mass flow controller reaches ±0.5%FS; the flow rate data is also transmitted to the computer in real time and recorded synchronously with the temperature data for subsequent analysis of the influence of gas flow rate changes on combustion characteristics during the combustion process; at the same time, a pressure sensor is used to monitor the pressure change inside the dropping tube furnace combustion system to ensure that the combustion process is carried out under stable pressure conditions, and the pressure fluctuation range is controlled within ±50 Pa; the radiation image of the combustion flame is collected through an optical collection system.

[0008] Preferably, in step S4, a data synchronous acquisition system is constructed using synchronous triggers and connected to a Fourier transform infrared spectrometer, an ICCD camera of an optical collection system, and a mid-infrared camera; the data synchronous acquisition system is used to ensure the temporal consistency of the data of Fourier transform infrared spectra, ICCD images, and mid-infrared images; the synchronous trigger is connected to the trigger ports of the Fourier transform infrared spectrometer, the ICCD camera, and the mid-infrared camera, and can send trigger signals to the three devices simultaneously; at the start of each measurement, the synchronous trigger issues a synchronous trigger pulse to cause the Fourier transform infrared spectrometer to start scanning, the ICCD camera to perform exposure shooting, and the mid-infrared camera to start image acquisition, ensuring that the three devices start data acquisition at the same moment; during the data acquisition process, the spectral data collected by the Fourier transform infrared spectrometer, the image data captured by the ICCD camera, and the image data collected by the mid-infrared camera are transmitted to the computer through their respective data transmission lines, and the computer receives, stores, and manages these data in real time; to ensure the stability and accuracy of data transmission, the data transmission lines use high-speed and anti-interference cables, and the computer is configured with a data verification and error correction mechanism to ensure that data is not lost or incorrect during transmission.

[0009] Preferably, in step S5, the data acquisition system can efficiently focus the spectral information in the full radiation band of the biomass combustion flame onto the fiber optic inlet of the drop tube furnace combustion system; the optical fiber selected is a full radiation band transmission optical fiber with high transmittance, and transmits the collected spectral information in the full radiation band to the Fourier transform infrared spectrometer; inside the Fourier transform infrared spectrometer, the optical signal is modulated by a Michelson interferometer; the moving mirror of the Michelson interferometer moves at a constant speed driven by a motor, and the moving speed is adjusted between 0.1 - 0.5 cm / s according to the measurement requirements; the movement of the moving mirror causes an optical path difference between the two coherent light beams, thereby forming an interference pattern; the interference pattern is processed by the Fourier transform algorithm to obtain the emission spectrum of the combustion flame; to improve the resolution and accuracy of spectral measurement, the resolution of the Fourier transform infrared spectrometer is set to 1 - 4 cm -1 , the number of scans is selected between 16 - 64 times according to the signal intensity, and the scan range covers the full radiation band.

[0010] Preferably, in step S6, the combustion flame image enters the ICCD camera through the calcium fluoride optical window of the drop tube furnace combustion system. After being dispersed by the dispersion prism of the optical collection system, light of different wavelengths is separated. During the shooting process, the gain of the ICCD camera is adjusted between 10 and 100 according to the flame brightness, and the exposure time is selected between 1 and 100 μs to obtain a clear and high-quality image of the radical radiation intensity distribution. To remove the interference of solid-phase particulate matter and background noise, the steps of the image processing algorithm for the collected ICCD image include: First, an image denoising algorithm based on wavelet transform is used to perform denoising processing on the image to remove high-frequency noise. Then, a background subtraction algorithm is used. By collecting a background image without a combustion flame, the combustion flame image is subtracted from the background image to eliminate the influence of background noise. Through infrared spectroscopy measurement, the radiation energy of particulate matter is continuous in the thermal radiation band. Combining the spectral radiation theory of matter and the change model of emissivity, the radiation characteristics of solid-phase particulate matter in the thermal radiation band are obtained. Next, a threshold segmentation algorithm is used. According to the characteristics of the radical radiation intensity, an appropriate threshold is set to segment the radiation area of the radical from the image. Finally, the segmented image is optimized through morphological processing to make the contour of the radical clearer. There is a certain relationship between the concentration of the radical and the radiation intensity, and a quantitative relationship between the two can be established through a calibration experiment. Assume that the concentration C of the radical and the radiation intensity I satisfy a linear relationship: ; where k and b are calibration coefficients, which are obtained by measuring the radiation intensity under the condition of known radical concentration and fitting using the least squares method.

[0011] Preferably, in step S7, a monochromatic filter corresponding to the characteristic wavelength of the flue gas component is installed in front of the mid-infrared camera. The mid-infrared camera obtains the infrared radiation image of the flue gas component, and the influence of solid-phase particulate matter is removed through an image processing algorithm to obtain the radiation intensity distribution of the flue gas component. According to Lambert-Beer's law, the absorbed light intensity I of the flue gas component and the incident light intensity I 0 , absorption coefficient α, component concentration c, and optical path length l are related as follows: ; By measuring the incident light intensity I 0 and the absorbed light intensity I , knowing the absorption coefficient α and the optical path length l , the concentration c of the flue gas component can be calculated: ; Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention focuses on three aspects: multi-parameter synchronous measurement, precise temperature and radiation characteristic measurement, and free radical and flue gas component measurement. These inventive points cooperate with each other to jointly solve the key problems in biomass combustion research, providing strong support for in-depth exploration of the combustion process, optimization of combustion processes, and control of pollution emissions.

[0012] Multi-parameter synchronous acquisition: It realizes the synchronous acquisition of Fourier transform infrared spectroscopy, combined ultraviolet-enhanced (ICCD) images, and infrared images during the combustion process of a single biomass particle. It breaks through the limitation of traditional measurement methods that can only obtain a certain type of data separately, enabling researchers to observe the combustion state of biomass from multiple dimensions at the same moment and obtain more comprehensive and systematic combustion information. By synchronously analyzing spectral and image data, it is possible to deeply understand the variation laws of substances during the combustion process, providing rich data support for the research of combustion mechanisms.

[0013] Precise temperature and radiation characteristic measurement method: Using the blackbody radiation law, Planck's law, and Wien displacement law, in the case where the emissivity is unknown or variable, by analyzing the radiation characteristics of the target object at multiple different wavelengths, a unique algorithm (substituting the spectral emissivity polynomial into Planck's radiation law and solving the equation using the least squares method) is used to accurately measure the true temperature of the biomass surface and obtain the spectral information in the full radiation band for temperature and radiation characteristic measurement of different components in different bands. This method solves the problem of inaccurate temperature measurement caused by emissivity issues in traditional measurements, greatly improving the accuracy of temperature and radiation characteristic measurements and providing reliable data for studying the thermophysical properties of the combustion process.

[0014] Measurement means for free radicals and flue gas components based on imaging technology: With the help of ICCD imaging and mid-infrared imaging technologies, by installing monochromatic filter plates in front of the corresponding modules, in-situ measurement of biomass combustion free radicals (OH· 310nm, CN· 387nm, CH· 432nm, C2· 470nm) and flue gas components ( 2.72 μm, 4.267 μm, CO 4.642 μm) is realized. By removing the radiation contribution of solid-phase particulate matter, an accurate radiation intensity distribution is obtained, and then a quantitative relationship with the component concentration is established to determine its concentration and variation. Real-time and accurate monitoring of the dynamic changes of free radicals and flue gas components during the combustion process is of great significance for studying the combustion reaction path and evaluating the environmental protection performance of the combustion process. Brief Description of the Drawings

[0015] Figure 1 is a schematic structural diagram of the present invention; Figure 2 is a schematic structural diagram of the dropping furnace combustion system in the present invention.

[0016] Wherein: 1. Optical lens; 2. Optical fiber; 3. Cooling system; 4. Data acquisition system; 5. Fourier transform infrared spectrometer; 6. Synchronous trigger; 7. Computer; 8. Optical collection system; 9. Calcium fluoride optical window; 10. Drop tube furnace combustion system; 11. Temperature control system; 12. Gas supply system. Specific embodiments

[0017] The present invention will be further described below with reference to the accompanying drawings.

[0018] As Figure 1 , Figure 2 shown, a method for in-situ measurement of biomass combustion based on spectroscopy and flame imaging includes the following steps: S1. Pretreatment and placement of raw materials Select raw materials from diverse biomass samples, remove moisture from the raw materials and cool them to room temperature; transport the raw materials into the drop tube furnace combustion system 10 through pneumatic transportation, and introduce carrier gas into the drop tube furnace combustion system 10; the drop tube furnace combustion system 10 is an existing settling furnace combustion system, and the McKenna burner and Hencken burner can be selected and installed; S2. Start-up and preheating of the drop tube furnace combustion system 10 Connect the drop tube furnace combustion system 10 with the gas supply system 12, the temperature control system 11, and the data acquisition system 4; start the cooling system 3 of the drop tube furnace combustion system 10, turn on the gas supply system 12, increase the carrier gas flow rate to the experimental set value, and introduce combustion-supporting gas; start the heating system of the drop tube furnace combustion system 10 for heating; S3. Stabilization and monitoring of combustion process parameters Keep the power of the heating system stable through the temperature control system 11, and continuously monitor various parameters during the combustion process through the data acquisition system 4 and transmit them to the computer 7 in real time; S4. Construct a data synchronous acquisition system Use the synchronous trigger 6 to construct a data synchronous acquisition system, and connect it with the Fourier transform infrared spectrometer 5, the ICCD camera and the mid-infrared camera of the optical collection system 8; S5. Acquisition of combustion flame spectral data Continuously monitor various parameters during the combustion process through the data acquisition system 4 and transmit them to the Fourier transform infrared spectrometer 5 to obtain the emission spectral information of the full radiation band of the combustion flame; S6. Acquisition of combustion flame images Acquire combustion flame images and radical radiation intensity distribution characteristic data through the ICCD camera and transmit them to the computer 7 in real time; S7. Acquisition of combustion flue gas images Collect the infrared radiation distribution image data of the combustion flue gas through the mid-infrared camera and transmit it to the computer 7 in real time; S8. Comprehensive data analysis and result presentation Perform baseline correction, smoothing processing, and peak fitting on the Fourier transform infrared spectroscopy data to extract spectral characteristic parameters. Perform image enhancement, edge detection, and target recognition on the biomass combustion flame image and infrared flue gas radiation intensity distribution data to extract the distribution characteristics of free radicals and flue gas components, and present the results on the computer 7.

[0019] The drop tube furnace combustion system 10 is equipped with a particle inlet, an optical fiber 2 hole, and a cooling water circulation channel; the particle inlet is used to add raw materials into the drop tube furnace combustion system 10; the optical fiber 2 hole is equipped with an optical lens 1, and the optical lens 1 is connected to a Fourier transform infrared spectrometer 5 (FTIR spectrometer) through the optical fiber 2; the cooling water circulation channel is used for the cooling system 3 to adjust the temperature inside the drop tube furnace combustion system 10. The control cabinet of the drop tube furnace combustion system 10 is connected to the silicon molybdenum heating rod and the temperature control system 11 inside the drop tube furnace combustion system 10.

[0020] In this embodiment, in step S1, the random sampling method is used to select raw materials from diverse biomass samples, which specifically includes the following steps: First, use a vibrating sieve with a mesh size of 0.1 - 1 mm to screen the biomass, and screen out particles with a relatively concentrated particle size distribution; then, place the screened raw materials in a vacuum drying oven and dry them at a temperature of 60 - 80 °C for 4 - 6 hours to remove the moisture in the raw materials; after the dried biomass is cooled to room temperature, store it in a sealed container for later use; transport the pretreated biomass particles to a pneumatic conveying bin, and a precisely controllable lifting screw feeder is connected to the bottom of the pneumatic conveying bin; the rotation speed of the screw feeder is controlled by a motor, and the feeding rate of the biomass is precisely controlled by adjusting the motor speed, and the feeding rate range is between 0 - 2 g / min; During the feeding process, the carrier gas (oxygen, nitrogen, carbon dioxide, ammonia) enters from the inlet, and the carrier gas flow rate is precisely controlled by a mass flow controller; the carrier gas flow rate is adjusted within the range of 0 - 40 L / min according to experimental requirements to ensure that the biomass particles can be evenly carried into the drop tube furnace combustion system 10; a mixing chamber is arranged between the pneumatic conveying bin and the drop tube furnace combustion system 10, and a static mixer is installed in the mixing chamber, and the mixing elements inside it can promote the uniform mixing of the gas-solid two phases, so that the biomass particles entering the drop tube furnace combustion system 10 are evenly distributed in the carrier gas, avoiding agglomeration or segregation phenomena.

[0021] In this embodiment, in step S2, before starting the dropping tube furnace combustion system 10, check the airtightness of the entire experimental system to ensure no gas leakage; after connecting the dropping tube furnace combustion system 10 with the gas supply system 12, the temperature control system 11, and the data acquisition system 4, start the cooling system 3 of the dropping tube furnace combustion system 10 to ensure that the cooling water flow rate is stable at 2 - 4 L / min to protect the structural integrity of the dropping tube furnace combustion system 10 during high-temperature operation; turn on the gas supply system 12 and first introduce a certain amount of carrier gas at a flow rate of 3 - 5 L / min to purge the dropping tube furnace combustion system 10 and remove the air and impurities in the system; then, slowly increase the carrier gas flow rate to the experimental set value and gradually introduce the combustion-supporting gas (air, oxygen, or a mixture of the two); the flow rate and proportion of the combustion-supporting gas are precisely controlled according to the experimental purpose, and the volume ratio of oxygen to nitrogen can be set to 1:10 - 1:5; when simulating the actual industrial combustion environment, the proportion of the combustion-supporting gas can be adjusted according to the actual air excess coefficient; start the heating system of the dropping tube furnace combustion system 10, and the heating elements of the heating system are arranged around the combustion area of the dropping tube furnace combustion system 10; the heating system adopts the PID control method, and the temperature sensor is used to monitor the temperature of the combustion area in real time and feedback the temperature signal to the controller; the controller automatically adjusts the power of the heating elements according to the preset temperature rise curve to slowly raise the temperature of the combustion area to the initial temperature required for the experiment, and the initial temperature is between 400 - 600 °C, and the heating rate is controlled at 10 - 20 °C / min; during the temperature rise process, closely observe the temperature change to ensure a stable temperature rise process and avoid excessive temperature fluctuations affecting the experimental results.

[0022] In this embodiment, in step S3, when the temperature of the combustion area reaches the initial set value, keep the power of the heating system stable and continuously monitor various parameters during the combustion process; the temperature is monitored using a platinum-rhodium thermocouple, and the measuring end of the thermocouple is inserted into the outer wall of the quartz tube in the combustion area to obtain accurate temperature data; the temperature data is transmitted to the computer 7 in real time through the data acquisition card, and the computer 7 is used to display, record, and analyze the temperature data in real time; during the combustion process, it is required that the temperature fluctuation range is controlled within ±3 °C. If the temperature fluctuation exceeds this range, the temperature control system 11 will automatically adjust the power of the heating elements to maintain the temperature stability; in addition to temperature monitoring, it is also necessary to monitor the gas flow rate during the combustion process in real time; the mass flow controllers are used to precisely control and monitor the flow rates of the carrier gas and the combustion-supporting gas, and the accuracy of the mass flow controllers reaches ±0.5%FS; the flow rate data is also transmitted to the computer 7 in real time and recorded synchronously with the temperature data for subsequent analysis of the influence of gas flow rate changes on combustion characteristics during the combustion process; at the same time, a pressure sensor is used to monitor the pressure change inside the dropping tube furnace combustion system 10 to ensure that the combustion process is carried out under stable pressure conditions, and the pressure fluctuation range is controlled within ±50 Pa.

[0023] In this embodiment, in step S4, the synchronization acquisition system is used to ensure the temporal consistency of the data of Fourier transform infrared spectroscopy, ICCD images, and mid-infrared images; the synchronization trigger 6 is connected to the trigger ports of the Fourier transform infrared spectrometer 5, the ICCD camera, and the mid-infrared camera, and can send trigger signals to the three devices simultaneously; at the start of each measurement, the synchronization trigger 6 emits a synchronization trigger pulse to cause the Fourier transform infrared spectrometer 5 to start scanning, the ICCD camera to perform exposure shooting, and the mid-infrared camera to start image acquisition, ensuring that the three devices start data acquisition at the same moment; during the data acquisition process, the spectral data collected by the Fourier transform infrared spectrometer 5, the image data captured by the ICCD camera, and the image data collected by the mid-infrared camera are respectively transmitted to the computer 7 through their respective data transmission lines (such as optical fiber 2 and data line), and the computer 7 receives, stores, and manages these data in real time; to ensure the stability and accuracy of data transmission, the data transmission lines use high-speed and anti-interference cables, and the computer 7 is configured with a data verification and error correction mechanism to ensure that the data is not lost or incorrect during transmission.

[0024] In this embodiment, in step S5, the data acquisition system 4 can efficiently focus the spectral information of the full radiation band of the biomass combustion flame onto the entrance of the optical fiber 2 of the drop tube furnace combustion system 10; the optical fiber 2 is selected as an optical fiber for transmitting the full radiation band with high transmittance, and transmits the collected full radiation band to the Fourier transform infrared spectrometer 5; inside the Fourier transform infrared spectrometer 5, the optical signal is modulated by a Michelson interferometer; the moving mirror of the Michelson interferometer moves at a constant speed under the drive of a motor, and the moving speed is adjusted between 0.1 - 0.5 cm / s according to the measurement requirements; the movement of the moving mirror causes an optical path difference between the two coherent light beams, thereby forming an interference pattern; after the interference pattern is processed by the Fourier transform algorithm, the emission spectrum of the combustion flame is obtained; to improve the resolution and accuracy of spectral measurement, the resolution of the Fourier transform infrared spectrometer 5 is set to 1 - 4 cm -1 , and the number of scans is selected between 16 - 64 times according to the signal intensity, and the scanning range covers the full radiation band (400 - 4000 cm -1 ).

[0025] Calculation of temperature and radiation characteristics: According to Planck's radiation law, the spectral radiation intensity I(λ,T) of a blackbody at wavelength λ and temperature T is: ; In this expression, λ represents the wavelength, nm; T represents the temperature, K; I(λ,T) represents the spectral radiation intensity at a specific wavelength λ and temperature T, W / m 3 / sr; ε(λ) is the spectral emissivity; h is Planck's constant, 6.626×10 -34 J·s; c is the speed of light, 3×10 8 m / s; and k is Boltzmann's constant, 1.380649×10 -23 J / K. The spectral emissivity ε(λ) can be approximately described using a polynomial: ; Here, j is the spectral channel; m represents the highest power of the polynomial, and a0, a1, …, a m are the coefficients of the polynomial.

[0026] Substitute the polynomial of the spectral emissivity ε(λ j ) into Planck's radiation law to obtain the temperature (T) relationship of the polynomial coefficients, and establish the relationship between λ, T, and a0, a1, …, a m : ; Use the least squares method to solve this equation and minimize the error function: ; The error function involves fitting the measured values of the spectral intensity at different wavelengths λ. The wavelength measurement points minimize the difference between the model and the measured data, and the polynomial coefficients a0, a1, …, a m and the best estimate of the temperature T can be solved, that is, the spectral emissivity and temperature values are obtained.

[0027] The FTIR spectrum measures only the solid-phase emission in the visible light band. Since the particulate matter radiates energy continuously in the thermal radiation band, by accurately measuring the radiation intensity in the visible light band and its change trend, and combining the spectral radiation theory of the substance and the change model of the emissivity, the radiation characteristics of the solid-phase particulate matter in the ultraviolet and infrared bands can be obtained.

[0028] In this embodiment, in step S6, the combustion flame image enters the optical collection system of the ICCD camera through the calcium fluoride optical window of the drop tube furnace combustion system. After being dispersed by the dispersion prism of the optical collection system, light of different wavelengths is separated. A monochromatic filter of a specific wavelength is installed in front of the ICCD camera, such as a 310 nm filter for detecting OH·, a 387 nm filter for detecting CN·, a 432 nm filter for detecting CH·, and a 470 nm filter for detecting C2·, etc. The ICCD camera has high sensitivity and fast response characteristics, can capture extremely weak optical signals, and complete imaging in a short time. During the shooting process, the gain of the ICCD camera is adjusted between 10 and 100 according to the flame brightness, and the exposure time is selected between 1 and 100 μs to obtain a clear and high-quality image of the radical radiation intensity distribution. To remove the interference of solid-phase particulate matter and background noise, the steps of the image processing algorithm for the collected ICCD images include: First, an image denoising algorithm based on wavelet transform is used to perform denoising processing on the image to remove high-frequency noise. Then, a background subtraction algorithm is used. By collecting a background image without a combustion flame, the combustion flame image is subtracted from the background image to eliminate the influence of background noise. Next, a threshold segmentation algorithm is used. According to the characteristics of the radical radiation intensity, an appropriate threshold is set to segment the radiation area of the radicals from the image. Finally, the segmented image is optimized through morphological processing (such as erosion and dilation operations) to make the contour of the radicals clearer. There is a certain relationship between the concentration of radicals and the radiation intensity, and a quantitative relationship between the two can be established through a calibration experiment. Assuming that the concentration C of the radicals and the radiation intensity I satisfy a linear relationship: ; where k and b are calibration coefficients, which are obtained by measuring the radiation intensity under the condition of known radical concentration and fitting using the least squares method.

[0029] In this embodiment, in step S7, a monochromatic filter corresponding to the characteristic wavelength of the flue gas components is installed in front of the mid-infrared camera. The mid-infrared camera obtains the infrared radiation image of the flue gas components, and the influence of solid-phase particulate matter is removed through an image processing algorithm to obtain the radiation intensity distribution of the flue gas components. According to the Lambert-Beer law, the absorption light intensity I of the flue gas components and the incident light intensity I 0 , the absorption coefficient α, the component concentration c, and the optical path length l are related as follows: ; By measuring the incident light intensity I 0 and the absorption light intensity I , and knowing the absorption coefficient α and the optical path length l , the concentration c of the flue gas components can be calculated: ; Method advantages: This measurement method has significant advantages in many aspects. First, the drop tube furnace combustion system can be equipped with a McKenna burner or a Hencken burner, combined with the gas-carrying feeding method, which can achieve stable and controllable combustion experimental conditions, providing a reliable basis for accurate measurement. Second, the synchronous acquisition of Fourier transform infrared spectroscopy, ICCD images, and infrared images realizes the in-situ synchronous measurement of multiple parameters, enabling the real-time acquisition of key information such as the temperature distribution, radiation characteristics, free radicals, and changes in flue gas component concentrations of the combustion flame without disturbing the combustion process, comprehensively reflecting the dynamic changes of the combustion process. Third, by using advanced algorithms and data processing means, the measurement data is accurately analyzed and processed, effectively improving the measurement accuracy and data analysis ability, and being able to extract valuable information from complex data. In addition, this measurement method has good versatility and scalability and can be flexible according to different research needs and experimental conditions.

[0030] Measurement value of free radicals and flue gas components: Accurately measuring the concentrations of free radicals and flue gas components is of great significance for evaluating the environmental protection performance of the combustion process. It can timely monitor the generation of pollutants during the combustion process, provide data support for the development of cleaner combustion technologies, and contribute to the development of environmental protection.

Claims

1. An in-situ measurement method for biomass combustion based on spectroscopy and flame imaging, characterized in that, It includes the following steps: S1. Pretreatment and placement of raw materials Crush, screen, and dry diverse biomass samples, and then pneumatically transport them into the drop tube furnace combustion system (10). S2. Start-up and preheating of the drop tube furnace combustion system (10) Start the drop tube furnace combustion system (10), increase the carrier gas flow rate to the experimental set value, and complete the preheating of the drop tube furnace combustion system (10). S3. Stabilization and monitoring of combustion process parameters Keep the power of the heating system stable, and transmit the radiation image of the collected combustion flame to the computer (7) in real time. S4. Construct a data synchronous acquisition system S5. Acquisition of combustion flame spectral data Continuously monitor the combustion parameters to obtain the emission spectral information of the full radiation band of the combustion flame. S6. Acquisition of combustion flame images Acquire the combustion flame images and the data of the distribution characteristics of the free radical radiation intensity, and transmit them to the computer (7) in real time. S7. Acquisition of combustion flue gas images Acquire the infrared radiation intensity distribution image data of the combustion flue gas components, and transmit them to the computer (7) in real time. S8. Comprehensive data analysis and result presentation Perform baseline correction, smoothing processing, and peak fitting on the emission spectral data of the full radiation band of the combustion flame to extract spectral characteristic parameters. Conduct edge detection and target recognition on the biomass combustion flame images and the infrared flue gas radiation intensity distribution data to extract the distribution characteristics of free radicals and flue gas components, and present the results on the computer (7).

2. The in-situ measurement method of biomass combustion based on spectroscopy and flame imaging according to claim 1, characterized in that, In step S1, raw materials are selected from diverse biomass samples using the random sampling method, which specifically includes the following steps: First, use a vibrating sieve with a mesh size of 0.1 - 1 mm to screen the biomass and select particles with a relatively concentrated particle size distribution. Then, place the screened raw materials in a vacuum drying oven and dry them at a temperature of 60 - 80 °C for 4 - 6 hours to remove the moisture in the raw materials. After the dried biomass is cooled to room temperature, store it in a sealed container for later use. Transport the pretreated biomass particles to a pneumatic transport bin, and a precisely controllable lifting screw feeder is connected to the bottom of the pneumatic transport bin. The rotation speed of the screw feeder is controlled by a motor, and the feeding rate of the biomass is precisely controlled by adjusting the motor speed. The feeding rate ranges from 0 to 2 g / min. During the feeding process, the carrier gas enters from the inlet, and the carrier gas flow rate is precisely controlled by a mass flow controller. The carrier gas flow rate is adjusted within the range of 0 - 40 L / min according to the experimental requirements to ensure that the biomass particles can be evenly carried into the drop tube furnace combustion system (10). A mixing chamber is set between the pneumatic transport bin and the drop tube furnace combustion system (10), and a static mixer is installed in the mixing chamber. The mixing elements inside it can promote the uniform mixing of the gas-solid two phases, making the biomass particles entering the drop tube furnace combustion system (10) evenly distributed in the carrier gas and avoiding agglomeration or segregation phenomena.

3. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 1, characterized in that In step S2, before starting the dropping tube furnace combustion system (10), check the airtightness of the entire experimental system to ensure no gas leakage; connect the dropping tube furnace combustion system (10) with the gas supply system (12), the temperature control system (11), and the data acquisition system (4), and start the cooling system (3) of the dropping tube furnace combustion system (10) to ensure that the cooling water flow rate is stable at 2 - 4 L / min to protect the structural integrity of the dropping tube furnace combustion system (10) during high-temperature operation; turn on the gas supply system (12), first introduce a certain carrier gas at a flow rate of 3 - 5 L / min to purge the dropping tube furnace combustion system (10) to remove air and impurities in the system; then, slowly increase the carrier gas flow rate to the experimental set value and gradually introduce the combustion-supporting gas; the flow rate and proportion of the combustion-supporting gas are precisely controlled according to the experimental purpose; start the heating system of the dropping tube furnace combustion system (10), and the heating elements of the heating system are arranged around the combustion area of the dropping tube furnace combustion system (10); the heating system adopts the PID control method, and the temperature of the combustion area is monitored in real time through a temperature sensor, and the temperature signal is fed back to the controller; the controller automatically adjusts the power of the heating elements according to the preset heating curve to slowly raise the temperature of the combustion area to the initial temperature required for the experiment, and the initial temperature is between 400 - 600 °C, and the heating rate is controlled at 10 - 20 °C / min; during the heating process, closely observe the temperature change to ensure a stable heating process and avoid excessive temperature fluctuations affecting the experimental results.

4. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 3, characterized in that In step S3, when the temperature of the combustion area reaches the initial set value, keep the power of the heating system stable through the temperature control system (11) and continuously monitor various parameters during the combustion process; temperature monitoring uses a platinum-rhodium thermocouple, and the measuring end of the thermocouple is inserted into the outer wall of the quartz tube in the combustion area to obtain accurate temperature data; the temperature data is transmitted to the computer (7) in real time through a data acquisition card, and the temperature data is displayed, recorded, and analyzed in real time through the computer (7); during the combustion process, it is required that the temperature fluctuation range is controlled within ±3 °C. If the temperature fluctuation exceeds this range, the temperature control system (11) will automatically adjust the power of the heating elements to maintain temperature stability; in addition to temperature monitoring, it is also necessary to monitor the gas flow rate during the combustion process in real time; the flow rates of the carrier gas and the combustion-supporting gas are precisely controlled and monitored through mass flow controllers, and the accuracy of the mass flow controllers reaches ±0.5%FS; the flow rate data is also transmitted to the computer (7) in real time and recorded synchronously with the temperature data for subsequent analysis of the impact of gas flow rate changes on combustion characteristics during the combustion process; at the same time, use a pressure sensor to monitor the pressure change inside the dropping tube furnace combustion system (10) to ensure that the combustion process is carried out under stable pressure conditions, and the pressure fluctuation range is controlled within ±50 Pa; collect the radiation image of the combustion flame through the optical collection system (8).

5. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 4, characterized in that, In step S4, a data synchronous acquisition system is constructed using a synchronous trigger (6), and is connected to the Fourier transform infrared spectrometer (5), the ICCD camera and the mid-infrared camera of the optical collection system (8); the data synchronous acquisition system is used to ensure the temporal consistency of the data of the Fourier transform infrared spectrum, the ICCD image and the mid-infrared image; the synchronous trigger (6) is connected to the trigger ports of the Fourier transform infrared spectrometer (5), the ICCD camera and the mid-infrared camera, and can send trigger signals to the three devices simultaneously; at the start of each measurement, the synchronous trigger (6) issues a synchronous trigger pulse to cause the Fourier transform infrared spectrometer (5) to start scanning, the ICCD camera to perform exposure shooting, and the mid-infrared camera to start image acquisition, ensuring that the three devices start data acquisition at the same moment. During the data acquisition process, the spectral data collected by the Fourier transform infrared spectrometer (5), the image data captured by the ICCD camera, and the image data collected by the mid-infrared camera are respectively transmitted to the computer (7) through their respective data transmission lines, and the computer (7) receives, stores, and manages these data in real time; in order to ensure the stability and accuracy of data transmission, the data transmission lines use high-speed and anti-interference cables, and the computer (7) is configured with a data verification and error correction mechanism to ensure that data is not lost or incorrect during transmission.

6. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 5, wherein In step S5, the data acquisition system (4) can focus the spectral information of the full radiation band of the biomass combustion flame on the entrance of the optical fiber (2) of the drop tube furnace combustion system (10); the optical fiber (2) is selected as the full radiation band transmission optical fiber (2) with high transmittance, and the collected full radiation band is transmitted to the Fourier transform infrared spectrometer (5); inside the Fourier transform infrared spectrometer (5), the optical signal is modulated by a Michelson interferometer; the moving mirror of the Michelson interferometer moves at a constant speed driven by a motor, and the moving speed is adjusted between 0.1 - 0.5 cm / s according to the measurement requirements; the movement of the moving mirror causes an optical path difference between the two coherent light beams, thus forming an interference pattern; after the interference pattern is processed by the Fourier transform algorithm, the emission spectrum of the combustion flame is obtained; in order to improve the resolution and accuracy of the spectral measurement, the resolution of the Fourier transform infrared spectrometer (5) is set to 1 - 4 cm -1 , and the number of scans is selected between 16 - 64 times according to the signal intensity, and the scan range covers the full radiation band.

7. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 5, wherein In step S6, the combustion flame image enters the ICCD camera through the calcium fluoride optical window (9) of the drop tube furnace combustion system (10). After being dispersed by the dispersion prism of the optical collection system (8), light of different wavelengths is separated. During the shooting process, the gain of the ICCD camera is adjusted between 10 and 100 according to the flame brightness, and the exposure time is selected between 1 and 100 μs to obtain a clear and high-quality image of the radical radiation intensity distribution. To remove the interference of solid-phase particulate matter and background noise, the steps of the image processing algorithm for the collected ICCD image include: First, an image denoising algorithm based on wavelet transform is used to perform denoising processing on the image to remove high-frequency noise. Then, a background subtraction algorithm is used. By collecting a background image without a combustion flame, the combustion flame image is subtracted from the background image to eliminate the influence of background noise. Through infrared spectroscopy measurement, the radiation energy of particulate matter is continuous in the thermal radiation band. Combining the spectral radiation theory of matter and the change model of emissivity, the radiation characteristics of solid-phase particulate matter in the thermal radiation band are obtained. Next, a threshold segmentation algorithm is used. According to the characteristics of the radical radiation intensity, a suitable threshold is set to segment the radiation area of the radical from the image. Finally, the segmented image is optimized through morphological processing to make the contour of the radical clearer. There is a certain relationship between the concentration of the radical and the radiation intensity, and a quantitative relationship between the two can be established through a calibration experiment. Assuming that the concentration C of the radical and the radiation intensity I satisfy a linear relationship: ; Among them, k and b are calibration coefficients, which are obtained by measuring the radiation intensity under the condition of known free radical concentration and fitting using the least squares method.

8. The in-situ measurement method of biomass combustion based on spectroscopy and flame imaging according to claim 5, characterized in that In step S7, a monochromatic filter corresponding to the characteristic wavelength of the flue gas components is installed in front of the mid-infrared camera; the mid-infrared camera acquires the infrared radiation image of the flue gas components, and the influence of solid-phase particulate matter is removed through an image processing algorithm to obtain the radiation intensity distribution of the flue gas components; according to the Lambert-Beer law, the absorbed light intensity of the flue gas components I and the incident light intensity I 0 , absorption coefficient α, component concentration c, and optical path length l are related as follows: ; By measuring the incident light intensity I 0 and the absorbed light intensity I , given the absorption coefficient α and the optical path length l , the concentration c of the flue gas components can be calculated as follows: .

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