In this paper, the correlations between coal/char fragmentation and fly ash formation during pulverized coal combustion are investigated. We observed an explosion-like fragmentation of Zhundong coal in the early devolatilization stage by means of high-speed photography in the Hencken flat-flame burner. While high ash-fusion (HAF) bituminous and coal-derived char samples only undergo gentle perimeter fragmentation in the char burning stage. Simultaneously, combustion experiments of two kinds of coals were conducted in a 25 kW down-fired combustor. The particle size distributions (PSDs) of both fine particulates (PM_1-10) and bulk fly ash (PM₁₀₊) were measured by Electrical Low Pressure Impactor (ELPI) and Malvern Mastersizer 2000, respectively. The results show that the mass PSD of residual fly ash (PM₁₊) from Zhundong coal exhibits a bi-modal shape with two peaks located at 14 µm and 102 µm, whereas that from HAF coal only possesses a single peak at 74 µm. A hybrid model accounting for multiple-route ash formation processes is developed to predict the PSD of fly ash during coal combustion. By incorporating coal/char fragmentation sub-models, the simulation can quantitatively reproduce the measured PM₁₊ PSDs for different kinds of coals. The sensitivity analysis further reveals that the bi-modal mass distribution of PM₁₊ intrinsically results from the coal fragmentation during devolatilization.

本文研究了煤粉燃烧过程中煤/炭破碎与粉煤灰形成之间的关系。我们通过在Hencken平板火焰燃烧器中进行高速摄影，观察到了挥发分分解早期阶段准东煤的爆炸状碎片。尽管高灰分融合（HAF）沥青和煤衍生的焦炭样品在焦炭燃烧阶段仅经历了轻微的周边破碎。同时，在25 kW下燃燃烧器中进行了两种煤的燃烧实验。细颗粒物（PM _1-10）和粉煤灰（PM ₁₀₊）分别由低压电子冲击器（ELPI）和Malvern Mastersizer 2000测量。结果表明，准东煤的残余粉煤灰（PM ₁₊）质量PSD呈双峰状，在14 µm和102 µm处有两个峰，而HAF煤的PSD在74 µm处只有一个峰。建立了一种考虑多路线灰形成过程的混合模型，以预测煤燃烧过程中飞灰的PSD。通过合并煤/焦炭破碎子模型，该模拟可以定量地再现针对不同种类的煤测得的PM ₁₊ PSD。敏感性分析还表明，PM ₁₊的双峰质量分布本质上是由脱挥发分过程中的煤碎裂引起的。