In Situ Diagnostics on the Dynamic Processes of Ash Deposit Formation, Shedding, and Heat Transfer in a Self-Sustained Down-Fired Furnace

Ash deposition is the most acute problem that hinders safe and efficient operations of coal-fired boilers. In this paper, we investigate the ash deposition process by incorporating in situ observations with standard procedures of ash deposit sampling. A specially calibrated digital camera is used. A sodium-rich Zhundong (ZD) lignite, a Si/Al-dominated bituminous coal, and their blend were burned in a 25 kW down-fired furnace. The deposits were collected at a position with flue gas temperatures of 850 °C. The newly developed RGB pyrometry quantitatively measures the deposit surface temperature in a range of 800–1150 K. During the dynamic deposition process, the deposit surface temperature approaches the local flue gas temperature within 1 h of elapsed time. The heterogeneity of the deposit surface is caused by either the deposition of burning coarse particles or the shedding event of the deposit layer with a low cohesive strength. The deposit structure is characterized by its packing ratio, which positivel...