Evolution of volatile cloud in pulverized coal combustion with high-speed digital inline holographic visualization

Abstract

The coal devolatilization plays a significant role in the combustion of pulverized coal particles. The evolution of volatile cloud during devolatilization of pulverized coal particles (105–125 μm) is studied in a high-temperature flat-flame burner by combining high-speed photography with high-speed digital inline holography (DIH). By the high-speed holographic visualization, the evolution of volatile cloud of pulverized coal from volatile release to soot aggregation generation can be divided into four stages. Effects of coal type on volatile cloud evolution are investigated using three different coals, i.e., Shanxi bituminous coal, Ximeng lignite and Yinni lignite. The results show that both the Shanxi bituminous coal and Ximeng lignite produce soot aggregation during devolatilization, which is rarely observed for Yinni lignite. Moreover, Shanxi bituminous coal has a higher potential in soot cluster formation for its higher coal rank than Ximeng lignite. The high-speed reconstructed image sequences are analyzed to measure the velocity slip between the parent particle and volatile cloud. Compared with Shanxi bituminous coal, Ximeng lignite exhibits a larger slip velocity. This work also demonstrates that high-speed DIH has the powerful capacity of directly observing the evolution of volatile cloud, and helps to gain a deep understanding of pulverized coal combustion.