研究目的
To study the evolution of volatile cloud during devolatilization of pulverized coal particles and investigate the effects of coal type on this evolution using high-speed photography and high-speed digital inline holography.
研究成果
High-speed DIH effectively visualizes the four-stage evolution of volatile cloud in pulverized coal combustion, from volatile release to soot aggregation. Coal type significantly influences this evolution, with Shanxi bituminous coal showing higher sooting potential and Ximeng lignite exhibiting larger velocity slip between parent particle and volatile cloud. Yinni lignite does not form soot aggregation. The technique provides deep insights into coal combustion dynamics, aiding in cleaner coal utilization.
研究不足
The residence time of coal particles is short (less than 100 ms), limiting the observation of char burning period. The field of view in high-speed DIH is limited due to magnification, making it challenging to capture the entire devolatilization process. The study focuses on specific coal types and conditions, which may not be generalizable to all coals or combustion environments.
1：Experimental Design and Method Selection:
The study uses a high-temperature flat-flame burner to simulate combustion conditions. High-speed photography and high-speed digital inline holography (DIH) are employed for direct observation and 3D imaging of burning coal particles and volatile clouds. The DIH system includes a laser, spatial filter, collimator, and high-speed camera for recording holograms, which are processed using wavelet reconstruction and image fusion algorithms to extract particle and cloud information.
2：Sample Selection and Data Sources:
Three types of pulverized coal particles (Shanxi bituminous coal, Ximeng lignite, Yinni lignite) with a size range of 105–125 μm are used. They are ground and sieved, with properties detailed in proximate and ultimate analyses.
3：List of Experimental Equipment and Materials:
Equipment includes a water-cooled sintered bronze McKenna burner (Holthuis & Associates), mass flow controllers (Alicat/MCV, ±1%), screw feeder, K-type thermocouples, continuous wave laser (Oxxus LCX-532S, 50–500 mW), attenuator, spatial filter, collimator, high-speed camera (Phantom V2512), camera lens (Nikon AF 50 mm, 1:1.8D), extension tube, and 3D motorized linear stage. Materials include O2, N2, CO2, methane, and the coal samples.
4：8D), extension tube, and 3D motorized linear stage. Materials include O2, N2, CO2, methane, and the coal samples.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The burner generates a stable flat flame with controlled gas flows. Coal particles are fed into the flame, and their combustion is recorded at 6000 fps with an exposure time of 10 μs using the high-speed camera for both photography and holography. Holograms are denoised, reconstructed slice by slice, and fused into extended focus images for analysis of particle and cloud properties.
5：Data Analysis Methods:
Reconstructed images are analyzed to measure velocity, size, and morphology of particles and volatile clouds. Statistical analysis is performed on soot cluster frequency and velocity slip differences between coal types.
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