An in-situ measurement method for biomass combustion based on spectroscopy and flame imaging

Abstract

This invention provides an in-situ measurement method for biomass combustion based on spectroscopy and flame imaging. The method comprises the following steps: pretreating a biomass sample and pneumatically conveying it to a dropper furnace combustion monitoring system; preheating the sample, and real-time monitoring of combustion parameters using a temperature control system and data acquisition system; connecting a Fourier transform infrared spectrometer, an ICCD camera, and a mid-infrared camera to the synchronous acquisition system; acquiring spectral information within the flame thermal radiation band (200 nm-20 μm), and capturing images of free radicals and flue gas components; and finally, comprehensively processing and analyzing the data to extract key parameters such as temperature, radiation characteristics, and component concentrations. This method achieves simultaneous in-situ measurement of multiple parameters, combines advanced algorithms to accurately calculate combustion surface temperature and radiation characteristics, and uses imaging technology to quantify the distribution of free radicals and flue gas components. This method provides an efficient and reliable technical means for studying biomass combustion mechanisms, optimizing combustion processes, and controlling pollution emissions, and has significant scientific and application value.

Description

Technical Field

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

[0002] At a critical time in the global energy transition, biomass energy, as an important renewable energy source, is of vital importance for alleviating the energy crisis and addressing climate change. The study of biomass combustion processes is the core link in achieving efficient conversion of biomass energy. Accurately acquiring various parameters during the combustion process, such as temperature distribution, radiation characteristics, and changes in free radical and flue gas component concentrations, is crucial for a deeper understanding of combustion mechanisms, optimizing combustion technology, improving energy efficiency, and reducing pollutant emissions. However, traditional measurement methods have many limitations when faced with complex multiphase, high-temperature, and dynamic processes such as biomass combustion. These include the inability to achieve in-situ real-time measurement, difficulty in simultaneously acquiring multiple key parameters, and measurement accuracy being significantly affected by environmental factors. Summary of the Invention

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

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for in-situ measurement of biomass combustion based on spectroscopy and flame imaging comprises the following steps:

[0006] S1. Pretreatment and placement of raw materials

[0007] A variety of biomass samples are crushed, screened, dried and transported to the drop tube furnace combustion system through pneumatic conveying;

[0008] S2. Start-up and preheating of the dropper furnace combustion system

[0009] Start the dropper furnace combustion system and increase the carrier gas flow rate to the experimental setting value to complete the preheating of the dropper furnace combustion system;

[0010] S3. Combustion process parameter stabilization and monitoring

[0011] Maintaining the power of the heating system stable, the collected radiation images of the burning flame are transmitted to the computer in real time;

[0012] S4. Build a data synchronization acquisition system;

[0013] S5. Combustion flame spectrum data collection

[0014] Continuously monitor combustion parameters to obtain the full-radiation band emission spectrum information of the combustion flame;

[0015] S6. Combustion flame image acquisition

[0016] Collect combustion flame images and free radical radiation intensity distribution characteristic data, and transmit them to the computer in real time;

[0017] S7. Combustion smoke image acquisition

[0018] Collect infrared radiation intensity distribution image data of combustion flue gas components and transmit it to the computer in real time;

[0019] S8. Comprehensive data analysis and results presentation

[0020] The emission spectrum data of the full radiation band of the burning flame is baseline corrected, smoothed and peak fitted to extract the spectral characteristic parameters. The edge detection and target recognition are performed on the biomass burning flame image and infrared flue gas radiation intensity distribution data to extract the distribution characteristics of free radicals and flue gas components, and the results are presented on the computer.

[0021] Preferably, in step S1, a random sampling method is used to select raw materials from a diverse biomass sample, specifically comprising the following steps:

[0022] First, the biomass is screened using a vibrating screener with a 0.1-1 mm pore size screen to select particles with a relatively concentrated particle size distribution. The screened raw material is then placed in a vacuum drying oven and dried at 60-80°C for 4-6 hours to remove moisture. The dried biomass is cooled to room temperature and stored in a sealed container for later use. The pretreated biomass pellets are then transported to a pneumatic conveying silo, the bottom of which is connected to a precisely controlled screw feeder. The screw feeder's speed is controlled by a motor, which precisely adjusts the biomass feed rate to a range of 0-2 g / min.

[0023] During the feeding process, the carrier gas enters from the air inlet, and the carrier gas flow rate is precisely controlled by a mass flow controller; the carrier gas flow rate is adjusted in 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; a mixing chamber is set between the feed hopper and the drop tube furnace combustion system, and a static mixer is installed in the mixing chamber. The mixing element inside the mixing chamber can promote uniform mixing of the gas and solid phases, so that the biomass particles entering the drop tube furnace combustion system are evenly distributed in the carrier gas, avoiding agglomeration or segregation.

[0024] Preferably, in step S2, before starting the dropper furnace combustion system, check the air tightness of the entire experimental system to ensure that there is no gas leakage; connect the dropper furnace combustion system with the gas supply system, temperature control system, and data acquisition system, start the cooling system of the dropper 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 dropper furnace combustion system during high-temperature operation; turn on the gas supply system, and first introduce a certain carrier gas at a flow rate of 3-5 L / min to purge the dropper furnace combustion system 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 dropper furnace combustion system, and the heating elements of the heating system are arranged around the combustion area of the dropper furnace combustion system; the heating system adopts PID control mode, and monitors the temperature of the combustion area in real time through the temperature sensor, and feeds back the temperature signal to the controller; the controller automatically adjusts the power of the heating element according to the preset heating curve, so that the temperature of the combustion area slowly rises to the initial temperature required for the experiment, and the initial temperature is between 400-600 ℃, and the heating rate is controlled at 10-20℃ / min; during the heating process, closely observe the temperature changes to ensure a smooth heating process and avoid excessive temperature fluctuations that may affect the experimental results.

[0025] Preferably, in step S3, after the combustion zone temperature reaches the initial set value, the power of the heating system is maintained stable by a temperature control system, and various parameters during the combustion process are continuously monitored. Temperature monitoring is performed using a platinum-rhodium thermocouple, with the measuring end of the thermocouple inserted into the outer wall of the quartz tube in the combustion zone to obtain accurate temperature data. The temperature data is transmitted in real time to a computer via a data acquisition card, and the temperature data is displayed, recorded, and analyzed in real time by the computer. During the combustion process, the temperature fluctuation range is required to be controlled within ±3°C. If the temperature fluctuation exceeds this range, the temperature control system will automatically adjust the power of the heating element to maintain temperature stability. In addition to temperature monitoring, the gas flow rate during the combustion process must be monitored in real time. The flow rates of the carrier gas and the combustion-supporting gas are precisely controlled and monitored by a mass flow controller with an accuracy of ±0.5%FS. The flow rate data is also transmitted in real time to the computer and recorded synchronously with the temperature data to facilitate subsequent analysis of the impact of gas flow changes on combustion characteristics during the combustion process. At the same time, a pressure sensor is used to monitor pressure changes within the dropper 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 by an optical collection system.

[0026] Preferably, in step S4, a synchronous trigger is used to construct a data synchronization acquisition system and is connected to the Fourier transform infrared spectrometer, the ICCD camera of the optical collection system, and the mid-infrared camera; the data synchronization acquisition system is used to ensure the temporal consistency of the Fourier transform infrared spectrum, ICCD image, and mid-infrared image data; 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 at the same time; at the beginning of each measurement, the synchronous trigger sends a synchronous trigger pulse to start scanning by the Fourier transform infrared spectrometer, exposure and shooting by the ICCD camera, and image acquisition by the mid-infrared camera, ensuring that the three devices start data acquisition at the same time; 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 respectively transmitted to the computer via their respective data transmission lines, and the computer receives, stores, and manages the data in real time; to ensure the stability and accuracy of data transmission, the data transmission line uses a high-speed, interference-resistant cable, and the computer is configured with a data check and error correction mechanism to ensure that data is not lost or erroneous during transmission.

[0027] Preferably, in step S5, the data acquisition system can efficiently focus the full-radiation band spectral information of the biomass combustion flame to the optical fiber inlet of the drop tube furnace combustion system; the optical fiber uses a full-radiation band transmission optical fiber with high transmittance to transmit the collected full-radiation band spectral information 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 the two coherent light beams to produce an optical path difference, 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; in order to improve the resolution and accuracy of the 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 and 64 times according to the signal strength, and the scanning range covers the entire radiation band.

[0028] Preferably, in step S6, the combustion flame image enters the ICCD camera through the calcium fluoride optical window of the dropper furnace combustion system, and after being split by the dispersion prism of the optical collection system, the light of different wavelengths is separated; during the shooting process, the gain of the ICCD camera is adjusted between 10-100 according to the flame brightness, and the exposure time is selected between 1-100 μs to obtain a clear, high-quality free radical radiation intensity distribution image; in order to remove the interference of solid-phase particles and background noise, the steps of performing an image processing algorithm on the collected ICCD image include: first, using an image denoising algorithm based on wavelet transform to perform denoising on the image and remove high-frequency noise; then, using a background subtraction algorithm, by collecting a background image without a combustion flame, subtracting the background image from the combustion flame image to eliminate the influence of background noise; measuring the continuous radiation energy of the particles in the thermal radiation band by infrared spectroscopy, combining the spectral radiation theory of the material and the emissivity change model, the radiation characteristics of the solid-phase particles in the thermal radiation band are obtained. Next, a threshold segmentation algorithm is used to set an appropriate threshold based on the characteristics of the free radical radiation intensity to segment the free radical radiation area from the image. Finally, the segmented image is optimized through morphological processing to make the outline of the free radical clearer. There is a certain relationship between the concentration of free radicals and the radiation intensity, and a quantitative relationship between the two can be established through calibration experiments. It is assumed that the concentration C of free radicals and the radiation intensity I satisfy the linear relationship:

[0029] C=kI+b;

[0030] Where k and b are calibration coefficients, which are obtained by measuring the radiation intensity under conditions of known free radical concentration and fitting using the least squares method.

[0031] Preferably, in step S7, a monochromatic filter corresponding to the characteristic wavelength of the smoke component is installed in front of the mid-infrared camera; the mid-infrared camera obtains the infrared radiation image of the smoke component, removes the influence of solid phase particles through the image processing algorithm, and obtains the radiation intensity distribution of the smoke component; according to the Lambert-Beer law, the absorption intensity of the smoke component is I With incident light intensity I 0 , absorption coefficient α, component concentration c and optical path length l The relationship between them is:

[0032] ;

[0033] By measuring the incident light intensity I 0 and absorption intensity I , the absorption coefficient α and the optical path length are known l , the concentration c of the flue gas component can be calculated:

[0034] .

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention focuses on three aspects: simultaneous measurement of multiple parameters, precise measurement of temperature and radiation characteristics, and measurement of free radicals and flue gas components. These inventive points work together to solve key problems in biomass combustion research, providing strong support for in-depth exploration of the combustion process, optimization of combustion technology, and control of pollution emissions.

[0037] Multi-parameter simultaneous acquisition: This system enables simultaneous acquisition of Fourier transform infrared spectra, combined ultraviolet-enhanced coherent density (ICCD) images, and infrared images of individual biomass pellet combustion processes. This overcomes the limitations of traditional measurement methods, which can only capture a single type of data. It enables researchers to observe biomass combustion from multiple dimensions simultaneously, providing more comprehensive and systematic combustion information. By simultaneously analyzing spectral and image data, researchers can gain a deeper understanding of the dynamics of substances during combustion, providing rich data support for combustion mechanism research.

[0038] Precise temperature and radiation characteristic measurement method: Utilizing the blackbody radiation law, Planck's law, and Wien's displacement law, this method analyzes the radiation characteristics of the target object at multiple wavelengths when the emissivity is unknown or varying. A unique algorithm (substituting the spectral emissivity polynomial into Planck's radiation law and solving the equation using the least squares method) accurately measures the true temperature of the biomass surface. This method also obtains spectral information across the entire radiation band for temperature and radiation characteristic measurements across different wavelengths for different components. This method overcomes the problem of inaccurate temperature measurements caused by emissivity issues in traditional measurements, significantly improving the accuracy of temperature and radiation characteristic measurements and providing reliable data for studying the thermophysical properties of combustion processes.

[0039] Imaging-based free radical and flue gas component measurement: Utilizing ICCD imaging and mid-infrared imaging technologies, monochromatic filters installed in front of the corresponding modules enable in-situ measurement of biomass combustion free radicals (OH 310nm, CN 387nm, CH 432nm, C2 470nm) and flue gas components (H2O 2.72 μm, CO2 4.267 μm, CO 4.642 μm), respectively. By removing the radiation contribution from solid particulate matter, an accurate radiation intensity distribution is obtained, which is then quantitatively correlated with component concentrations to determine their concentrations and variations. Real-time and accurate monitoring of the dynamic changes of free radicals and flue gas components during combustion is crucial for studying combustion reaction pathways and evaluating the environmental performance of combustion processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural schematic diagram of the present invention;

[0041] Figure 2 It is a structural schematic diagram of the drop tube furnace combustion system in the present invention.

[0042] in:

[0043] 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. Dropper furnace combustion system; 11. Temperature control system; 12. Gas supply system. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the accompanying drawings.

[0045] like Figure 1 、 Figure 2 As shown, a method for in-situ measurement of biomass combustion based on spectroscopy and flame imaging includes the following steps:

[0046] S1. Pretreatment and placement of raw materials

[0047] Raw materials are selected from a variety of biomass samples, moisture is removed from the raw materials, and the raw materials are cooled to room temperature; the raw materials are transported to the drop tube furnace combustion system 10 by pneumatic conveying, and carrier gas is introduced into the drop tube furnace combustion system 10; the drop tube furnace combustion system 10 is an existing settling furnace combustion system and can be equipped with McKenna burners and Hencken burners as options;

[0048] S2. Start-up and preheating of the dropper furnace combustion system 10

[0049] Connect the drop tube furnace combustion system 10 to 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, open the gas supply system 12, increase the carrier gas flow rate to the experimental set value, and introduce the combustion-supporting gas; start the heating system of the drop tube furnace combustion system 10 to heat;

[0050] S3. Combustion process parameter stabilization and monitoring

[0051] The power of the heating system is kept stable by the temperature control system 11, and the various parameters of the combustion process are continuously monitored by the data acquisition system 4 and transmitted to the computer 7 in real time;

[0052] S4. Build a data synchronization acquisition system

[0053] A data synchronization acquisition system is constructed using a synchronization trigger 6 and connected to the Fourier transform infrared spectrometer 5, the ICCD camera and the mid-infrared camera of the optical collection system 8;

[0054] S5. Combustion flame spectrum data collection

[0055] The various parameters of the combustion process are continuously monitored by the data acquisition system 4 and transmitted to the Fourier transform infrared spectrometer 5 to obtain the emission spectrum information of the full radiation band of the combustion flame;

[0056] S6. Combustion flame image acquisition

[0057] The combustion flame image and free radical radiation intensity distribution characteristic data are collected by ICCD camera and transmitted to computer 7 in real time;

[0058] S7. Combustion smoke image acquisition

[0059] Collect infrared radiation distribution image data of combustion flue gas through a mid-infrared camera and transmit it to computer 7 in real time;

[0060] S8. Comprehensive data analysis and results presentation

[0061] The Fourier transform infrared spectral data were baseline corrected, smoothed and peak fitted to extract the spectral characteristic parameters. The biomass combustion flame image and infrared flue gas radiation intensity distribution data were subjected to image enhancement, edge detection and target recognition to extract the distribution characteristics of free radicals and flue gas components, and the results were presented on computer 7.

[0062] The drop-tube furnace combustion system 10 is equipped with a particle inlet, an optical fiber hole, and a cooling water circulation channel. The particle inlet is used to add raw materials to the drop-tube furnace combustion system 10. The optical fiber hole 2 is installed with an optical lens 1, which is connected to a Fourier transform infrared spectrometer (FTIR spectrometer) 5 via an optical fiber 2. The cooling water circulation channel is used by the cooling system 3 to regulate 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 rods and the temperature control system 11 inside the drop-tube furnace combustion system 10.

[0063] In this embodiment, in step S1, a random sampling method is used to select raw materials from a diverse biomass sample, specifically including the following steps:

[0064] First, the biomass is screened using a vibrating screener with a 0.1-1 mm pore size screen to select particles with a relatively concentrated particle size distribution. The screened raw material is then placed in a vacuum drying oven and dried at 60-80°C for 4-6 hours to remove moisture. The dried biomass is cooled to room temperature and stored in a sealed container for later use. The pretreated biomass pellets are then transported to a pneumatic conveying silo, the bottom of which is connected to a precisely controlled screw feeder. The screw feeder's speed is controlled by a motor, which precisely adjusts the biomass feed rate to a range of 0-2 g / min.

[0065] During the feeding process, carrier gas (oxygen, nitrogen, carbon dioxide, ammonia) enters from the air 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 set between the pneumatic conveying silo and the drop tube furnace combustion system 10, and a static mixer is installed in the mixing chamber. The mixing elements inside the mixing chamber can promote uniform mixing of the gas and solid 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.

[0066] In this embodiment, in step S2, before starting the drop tube furnace combustion system 10, the air tightness of the entire experimental system is checked to ensure that there is no gas leakage; after connecting the drop tube furnace combustion system 10 with the gas supply system 12, the temperature control system 11, and the data acquisition system 4, the cooling system 3 of the drop tube furnace combustion system 10 is started to ensure that the cooling water flow rate is stable at 2-4 L / min to protect the structural integrity of the drop tube furnace combustion system 10 during high-temperature operation; the gas supply system 12 is opened, and a certain amount of carrier gas is first introduced at a flow rate of 3-5 L / min to purge the drop tube furnace combustion system 10 and remove air and impurities in the system; then, the carrier gas flow rate is slowly increased to the experimental set value, and the combustion-supporting gas (air, oxygen, or a mixture of the two) is gradually introduced; the flow rate and ratio 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 an actual industrial combustion environment, the proportion of the combustion-supporting gas can be adjusted according to the actual excess air coefficient; the heating system of the dropper furnace combustion system 10 is started, and the heating elements of the heating system are arranged around the combustion area of the dropper furnace combustion system 10; the heating system adopts a PID control method, and the temperature of the combustion area is monitored in real time by a temperature sensor, and the temperature signal is fed back to the controller; the controller automatically adjusts the power of the heating element according to a preset heating curve, so that the temperature of the combustion area slowly rises to the initial temperature required for the experiment, the initial temperature is between 400-600 °C, and the heating rate is controlled at 10-20 °C / min; during the heating process, the temperature changes are closely observed to ensure a smooth heating process and avoid excessive temperature fluctuations that affect the experimental results.

[0067] In this embodiment, in step S3, after the combustion zone temperature reaches the initial set value, the power of the heating system is maintained stable, and various parameters during the combustion process are continuously monitored. Temperature monitoring is performed using a platinum-rhodium thermocouple, with the measuring end of the thermocouple inserted into the outer wall of the quartz tube in the combustion zone to obtain accurate temperature data. The temperature data is transmitted in real time to the computer 7 via a data acquisition card, which displays, records, and analyzes the temperature data in real time. During the combustion process, the temperature fluctuation range is required to be controlled within ±3°C. If the temperature fluctuation exceeds this range, the temperature control system 11 will automatically adjust the power of the heating element to maintain temperature stability. In addition to temperature monitoring, the gas flow rate during the combustion process must be monitored in real time. The flow rates of the carrier gas and the combustion-supporting gas are precisely controlled and monitored using a mass flow controller with an accuracy of ±0.5% FS. The flow rate data is also transmitted in real time to the computer 7 and recorded simultaneously with the temperature data to facilitate subsequent analysis of the impact of gas flow changes on combustion characteristics during the combustion process. Simultaneously, a pressure sensor is used to monitor pressure changes within the dropper 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.

[0068] In this embodiment, in step S4, a synchronous acquisition system is used to ensure temporal consistency of the Fourier transform infrared spectrum, ICCD image, and mid-infrared image data. A 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 is capable of simultaneously sending trigger signals to the three devices. At the beginning of each measurement, the synchronous trigger 6 sends a synchronous trigger pulse to cause the Fourier transform infrared spectrometer 5 to begin scanning, the ICCD camera to perform exposure and shooting, and the mid-infrared camera to start image acquisition, ensuring that the three devices begin data acquisition at the same time. 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 captured by the mid-infrared camera are respectively transmitted to the computer 7 via their respective data transmission lines (e.g., optical fiber 2, data line). The computer 7 receives, stores, and manages the data in real time. To ensure the stability and accuracy of data transmission, the data transmission line uses a high-speed, interference-resistant cable, and the computer 7 is equipped with a data check and error correction mechanism to ensure that data is not lost or erroneous during transmission.

[0069] In this embodiment, in step S5, the data acquisition system 4 can efficiently focus the full radiation band spectral information of the biomass combustion flame to the entrance of the optical fiber 2 of the drop tube furnace combustion system 10; the optical fiber 2 selects a full radiation band transmission optical fiber 2 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 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 the two coherent light beams to produce an optical path difference, 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; 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 The number of scans is selected between 16 and 64 times according to the signal strength, and the scanning range covers the entire radiation band (400-4000 cm -1 ).

[0070] Temperature and radiation characteristics calculation:

[0071] According to Planck's radiation law, the spectral radiation intensity I(λ,T) of a black body at wavelength λ and temperature T is:

[0072]

[0073] 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 the Boltzmann constant, 1.380649×10 -23 J / K. The spectral emissivity ε(λ) can be approximately described using a polynomial:

[0074]

[0075] 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.

[0076] The spectral emissivity ε(λ j ) is substituted into Planck's radiation law to obtain the temperature (T) relationship of the polynomial coefficients, and the relationship between λ, T and a0, a1, ..., a is established. m The relationship between:

[0077]

[0078] Solve this equation using the least squares method to minimize the error function:

[0079]

[0080] The error function involves fitting the spectral intensity measurements at different wavelengths λ, where the wavelength measurement points are chosen to minimize the difference between the model and the measured data. The polynomial coefficients a0, a1, …, a m and the best estimate of temperature T, which gives the spectral emissivity and temperature values.

[0081] FTIR spectroscopy only measures solid-phase emission in the visible light band. Since particulate matter radiates energy continuously in the thermal radiation band, the radiation characteristics of solid-phase particulate matter in the ultraviolet and infrared bands can be derived by accurately measuring the radiation intensity and its changing trend in the visible light band, combined with the spectral radiation theory of matter and the emissivity change model.

[0082] In this embodiment, in step S6, the combustion flame image passes through the calcium fluoride optical window of the drop tube furnace combustion system and enters the optical collection system of the ICCD camera. After being split by the dispersion prism of the optical collection system, the light of different wavelengths is separated. Monochromatic filters with specific wavelengths are placed 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. The ICCD camera has high sensitivity and fast response, capable of capturing extremely weak light signals and completing imaging in a short time. During the capture process, the gain of the ICCD camera was adjusted between 10 and 100 according to the flame brightness, and the exposure time was selected between 1 and 100 μs to obtain clear, high-quality images of the free radical radiation intensity distribution. To remove interference from solid particles and background noise, the image processing algorithm for the acquired ICCD image included the following steps: first, a wavelet-based image denoising algorithm was used to denoise the image and remove high-frequency noise. Then, a background subtraction algorithm was used to collect a background image without a burning flame and subtract the background image from the burning flame image to eliminate the influence of background noise. Next, a threshold segmentation algorithm was used to set an appropriate threshold based on the characteristics of the free radical radiation intensity to segment the free radical radiation area from the image. Finally, the segmented image was optimized through morphological processing (such as corrosion and dilation operations) to make the free radical outline clearer. There is a certain relationship between the concentration of free radicals and the radiation intensity, and a quantitative relationship between the two can be established through calibration experiments. It is assumed that the concentration C of free radicals and the radiation intensity I satisfy a linear relationship:

[0083] C=kI+b;

[0084] Where k and b are calibration coefficients, which are obtained by measuring the radiation intensity under conditions of known free radical concentration and fitting using the least squares method.

[0085] In this embodiment, in step S7, a monochromatic filter corresponding to the characteristic wavelength of the smoke component is installed in front of the mid-infrared camera; the mid-infrared camera obtains the infrared radiation image of the smoke component, and the influence of solid phase particles is removed by the image processing algorithm to obtain the radiation intensity distribution of the smoke component; according to the Lambert-Beer law, the absorption intensity of the smoke component is I With incident light intensity I 0 , absorption coefficient α, component concentration c and optical path length l The relationship between them is:

[0086] ;

[0087] By measuring the incident light intensity I 0 and absorption intensity I , the absorption coefficient α and the optical path length are known l , the concentration c of the flue gas component can be calculated:

[0088] .

[0089] Method advantages: This measurement method has many significant advantages. 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, stable and controllable combustion experimental conditions can be achieved, providing a reliable basis for accurate measurement. Secondly, the simultaneous acquisition of Fourier transform infrared spectroscopy, ICCD images and infrared images realizes the in-situ synchronous measurement of multiple parameters. Without interfering with the combustion process, key information such as the temperature distribution, radiation characteristics, free radical and flue gas component concentration changes of the combustion flame can be obtained in real time, fully reflecting the dynamic changes of the combustion process. Furthermore, the use of advanced algorithms and data processing methods to accurately analyze and process the measurement data effectively improves the measurement accuracy and data analysis capabilities, and can extract valuable information from complex data. In addition, this measurement method has good versatility and scalability, and can be flexibly adjusted according to different research needs and experimental conditions.

[0090] The value of free radical and flue gas component measurements: Accurately measuring free radical and flue gas component concentrations is crucial for evaluating the environmental performance of combustion processes. This allows for timely monitoring of pollutant generation during combustion, providing data support for the development of cleaner combustion technologies and contributing to the advancement of environmental protection.

Claims

1. A method for in-situ measurement of biomass combustion based on spectroscopy and flame imaging, characterized in that: The following steps are involved: S1. Pretreatment and placement of raw materials A variety of biomass samples are crushed, sieved and dried and transported to a drop tube furnace combustion system (10) via pneumatic conveying; S2. Start-up and preheating of the dropper furnace combustion system (10) Starting the drop tube furnace combustion system (10) and increasing the carrier gas flow rate to the experimental setting value to complete the preheating of the drop tube furnace combustion system (10); S3. Combustion process parameter stabilization and monitoring Maintaining the power of the heating system stable, the collected radiation image of the burning flame is transmitted to the computer (7) in real time; S4. Build a data synchronization acquisition system; A data synchronization acquisition system is constructed using a synchronization trigger (6) and connected to a Fourier transform infrared spectrometer (5), an ICCD camera of an optical collection system (8), and a mid-infrared camera; S5. Combustion flame spectrum data collection The combustion parameters are continuously monitored to obtain the full-radiation band emission spectrum information of the combustion flame, and the collected full-radiation band is transmitted to a Fourier transform infrared spectrometer (5); by substituting the spectral emissivity polynomial into Planck's radiation law and solving the equation using the least squares method, the true temperature of the biomass surface is accurately measured, and the full-radiation band spectrum information is obtained for measuring the temperature and radiation characteristics of different components in different bands; S6. Combustion flame image acquisition The combustion flame image enters the ICCD camera through the calcium fluoride optical window (9) of the dropper furnace combustion system (10), and after being split by the dispersion prism of the optical collection system (8), the light of different wavelengths is separated; the combustion flame image and the free radical radiation intensity distribution characteristic data are collected and transmitted to the computer (7) in real time; there is a certain relationship between the concentration of free radicals and the radiation intensity, and a quantitative relationship between the two is established through calibration experiments; S7. Combustion smoke image acquisition A monochromatic filter with a characteristic wavelength corresponding to the flue gas component is installed in front of the mid-infrared camera to collect infrared radiation intensity distribution image data of the combustion flue gas component and transmit it to the computer in real time (7); the mid-infrared camera obtains the infrared radiation image of the flue gas component, removes the influence of solid phase particles through image processing algorithm, and obtains the radiation intensity distribution of the flue gas component; S8. Comprehensive data analysis and results presentation The emission spectrum data of the full radiation band of the combustion flame is baseline corrected, smoothed and peak-fitted to extract the spectral characteristic parameters. The edge detection and target recognition are performed 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 the results are presented on a computer (7).

2. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 1, characterized in that: In step S1, a random sampling method is used to select raw materials from a diverse biomass sample, specifically including the following steps: First, the biomass is screened using a vibrating screener with a 0.1-1 mm pore size screen to select particles with a relatively concentrated particle size distribution. The screened raw material is then placed in a vacuum drying oven and dried at 60-80°C for 4-6 hours to remove moisture. The dried biomass is cooled to room temperature and stored in a sealed container for later use. The pretreated biomass pellets are then transported to a pneumatic conveying silo, the bottom of which is connected to a precisely controlled screw feeder. The screw feeder's speed is controlled by a motor, which precisely adjusts the biomass feed rate to a range of 0-2 g / min. During the feeding process, the carrier gas enters from the air 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; a mixing chamber is set between the pneumatic conveying silo and the dropper furnace combustion system (10), and a static mixer is installed in the mixing chamber.

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 drop tube furnace combustion system (10), check the air tightness of the entire experimental system; 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) to ensure that the cooling water flow rate is stable at 2-4 L / min; open the gas supply system (12) at a flow rate of 3-5 A certain amount of carrier gas is first introduced at a rate of 100 L / min to purge the dropper furnace combustion system (10) and remove air and impurities in the system; then, the carrier gas flow rate is slowly increased to the experimental set value, and the combustion-supporting gas is gradually introduced; the flow rate and proportion of the combustion-supporting gas are precisely controlled according to the experimental purpose; the heating system of the dropper furnace combustion system (10) is started, and the heating elements of the heating system are arranged around the combustion area of the dropper furnace combustion system (10); the heating system adopts PID control mode, and the temperature of the combustion area is monitored in real time by the temperature sensor, and the temperature signal is fed back to the controller; the controller automatically adjusts the power of the heating element according to the preset heating curve, so that the temperature of the combustion area slowly rises to the initial temperature required for the experiment, the initial temperature is between 400-600 ℃, and the heating rate is controlled at 10-20 ℃ / min; during the heating process, the temperature change is closely observed.

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, the power of the heating system is kept stable by the temperature control system (11), and various parameters in the combustion process are continuously monitored; the temperature is monitored by 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; the temperature data is transmitted to the computer (7) in real time through the data acquisition card, and the temperature data is displayed, recorded and analyzed in real time by the computer (7); during the combustion process, the temperature fluctuation range is required to be controlled within ±3 °C. If the temperature fluctuation exceeds this range, the temperature control system (11) will automatically adjust the power of the heating element; the flow rate of the carrier gas and the combustion-supporting gas is accurately controlled and monitored by the mass flow controller, and the accuracy of the mass flow controller reaches ±0.5%FS; the flow data is also transmitted to the computer (7) in real time and recorded synchronously with the temperature data; at the same time, the pressure sensor is used to monitor the pressure change inside the dropper furnace combustion system (10), and the pressure fluctuation range is controlled within ±50 Pa; the radiation image of the combustion flame is collected by 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, the data synchronization 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 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 at the same time; at the beginning of each measurement, the synchronization trigger (6) sends a synchronization trigger pulse to start 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; 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; the data transmission line uses a high-speed, anti-interference cable, and the computer (7) is configured with a data verification and error correction mechanism.

6. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 5, characterized in that: In step S5, the data acquisition system (4) is capable of focusing the full-radiation band spectrum information of the biomass combustion flame onto the entrance of the optical fiber (2) of the dropper furnace combustion system (10); the optical fiber (2) is selected as a full-radiation band transmission optical fiber with high transmittance; the optical signal is modulated by a Michelson interferometer inside the Fourier transform infrared spectrometer (5); 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 the two coherent light beams to produce an optical path difference, 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; the resolution of the Fourier transform infrared spectrometer (5) is set to 1-4 cm -1 The number of scans is selected between 16 and 64 times according to the signal strength, and the scanning range covers the entire radiation band.

7. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 5, characterized in that: In step S6, 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. The steps of performing an image processing algorithm on the collected ICCD image include: first, using an image denoising algorithm based on wavelet transform to denoise the image and remove high-frequency noise; then, using a background subtraction algorithm, by collecting a background image without a burning flame, subtracting the background image from the burning flame image to eliminate the influence of background noise; measuring the continuous radiation energy of the particles in the thermal radiation band by infrared spectroscopy, combining the spectral radiation theory of the material and the emissivity change model, the radiation characteristics of the solid phase particles in the thermal radiation band are obtained; then, using a threshold segmentation algorithm, according to the characteristics of the free radical radiation intensity, an appropriate threshold is set to segment the free radical radiation area from the image; finally, the segmented image is optimized by morphological processing to make the outline of the free radical clearer; assuming that the concentration C of the free radical and the radiation intensity I satisfy a linear relationship: C=kI+b; Where k and b are calibration coefficients, which are obtained by measuring the radiation intensity under conditions of known free radical concentration and fitting using the least squares method.

8. The in-situ measurement method for biomass combustion based on spectroscopy and flame imaging according to claim 5, characterized in that: In step S7, according to the Lambert-Beer law, the absorption intensity of the smoke component I With incident light intensity I 0 , absorption coefficient α, component concentration c and optical path length l The relationship between them is: By measuring the incident light intensity I 0 and absorption intensity I , the absorption coefficient α and the optical path length are known l , the concentration c of the flue gas component can be calculated: 。

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