Primary Fragmentation Behavior Investigation in Pulverized Coal Combustion with High-Speed Digital Inline Holography

摘要

Comprehension on the primary fragmentation of coal particles is important in understanding and optimizing practical coal combustion and creating credible combustion models. High-speed digital inline holography (DIH) at 6000 Hz is employed to investigate the primary fragmentation of China Ximeng lignite (90-154 mu m) during coal devolatilization. The particle morphologies, 3D trajectories, and size evolutions of the parent coals as well as the corresponding fragments are captured by time-resolved holographic visualization. Three fragmentation modes, fragmentation at the particle center, exfoliation/fragmentation at the outer zone, and a hybrid fragmentation mode of both, are observed in this study. The particle morphologies show distinct appearances under the three different fragmentation modes. It is found that the pressure resulted from the volatile products inside particle under the mode of fragmentation at the particle center will accelerate or decelerate the fragments. Statistical result on particle sizes on the recorded 26 coal particles undergoing fragmentation indicates that small particles formed because of coal fragmentation, which occupy 17.1% in the range of 26-40 mu m. It is also concluded that the flame temperature and particle residence time during coal devolatilization have an obvious influence on the possibility of coal fragmentation in the operating condition and target research region. Digital inline holography is demonstrated to be capable of in situ three-dimensional (3D) measurement of particle fragmentation during coal devolatilization.