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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 PM 0.2 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 PM 0.2 particles for the various coal samples. [ABSTRACT FROM AUTHOR]

The high-reserve Zhundong lignite, rich in Alkali and Alkaline Earth Metal (AAEM) elements, causes severe fouling and slagging problems in stationary combustion systems. In this paper, the ash deposition propensity as well as its relation to AAEM-rich fine particulates was investigated in a 25 kW down-fired furnace possessing similar conditions to practical combustors. The high content AAEM (mainly calcium) species in Zhundong lignite results in the molten slag at the vicinity of the burner inlet, differing from other case burning high-ash-fusion (HAF) bituminous coal. The ash deposits were collected at a position with gas temperature of 800 °C, whereas the fine particulates were sampled at the same position by a two-stage nitrogen-dilution isokinetic probe. The deposition tendency of ash particles from Zhundong lignite is apparently higher than those from contrast fuels and even herbaceous biomass. It is then related to the sticky surfaces of both bare deposition tube and bulk fly ash particles, forming from large amounts of AAEM species, which enhances the deposition propensity. [ABSTRACT FROM AUTHOR]