Mineral manipulation of Zhundong lignite towards fouling mitigation in a down-fired combustor

Abstract

With the increasing use of low-grade lignite for energy production, ash related problems have received renewed attention due to their detrimental effects on power plant equipment. This study investigates the fuel effect on the ash deposition in a 25 kW self-sustained down-fired furnace, with practical implications to the efficient utilization of a sodium-rich Zhundong (ZD) lignite. The active fouling control methods include co-firing with Si/Al-dominated HAF-2 bituminous coal and pretreatment using water leaching. Both manipulation methods reduce the propensity to form ultrafine PM0.2 particles and ash deposition for simulated furnace exit conditions compared with combustion of only ZD lignite. While the deposits formed by HAF-2 bituminous are prone to shed, blending with ZD lignite increases the ash collection efficiency and prevents massive deposit collapse. The morphology of the ZD ash deposits is characterized by a smooth shape with wide spreading angle, whereas those formed by the blended samples with ≥33 wt% bituminous coal have sharp and pointed shapes with smaller spreading angles. Deposits by samples with ≥67 wt% ZD lignite have an inner layer of micro-size particles. The local basic to acid ratio of the deposits gradually decreases from the inner to the outer layers. The apparent particle sticking probability due to the fuel effect derived from the experimental and theoretical results positively correlates with the yield of ultrafine PM0.2 particles for the various coal samples.