Influence of calcium chloride on the fine particulate matter formation during coal pyrolysis.

[Display omitted] • The PM 0.5 yield drop then rise with CaCl 2 loading, the bottom at 1.5 wt% Ca. • Soot inhibition and CaCl 2 condensation cause the two-stage trend of PM 0.5 yield. • The release rate of Ca into PM 0.5 increases with temperature and CaCl 2 loading. • CaCl 2 -impregnation reduces the sizes of the soot primary particles and aggregates. • The interaction mechanisms between CaCl 2 and soot are proposed. This study investigated the influence of CaCl 2 on fine particulate matter (PM 0.5) formation during coal pyrolysis. Two acid-washed coals were loaded with different amount of CaCl 2 by physical impregnation. Pyrolysis experiments were conducted in a flat-flame burner at 1400 K, 1600 K, and 1800 K. The PM 0.5 yield was evaluated through the size-segregated sampling with a low pressure impactor (DLPI+). Then, the transformation properties of CaCl 2 was analyzed with X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). Finally, the soot properties were analyzed with transmission electron microscopy (TEM), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The results show that PM 0.5 yield is affected by coal type, CaCl 2 loading level, and pyrolysis temperature. Loading small amount of CaCl 2 can reduce the PM 0.5 yield through soot inhibition, while high loading of CaCl 2 increases the PM 0.5 yield by forming mineral particles, the lowest PM 0.5 yield occurs at 1.5 % Ca content. The PM 0.5 reduction rate of CaCl 2 increases then decreases with temperature from 1400 K to 1800 K. On all tested conditions, the PM 0.5 yield of low-rank Zhundong subbituminous coal was lower than Shenhua bituminous coal. The release rate of Ca into PM 0.5 is positively related to pyrolysis temperature and CaCl 2 loading level. Ca loading decreases the sizes of soot primary particles and agglomerates, and leads to smaller amorphous cores and more disordered graphitic shells in the soot primary particles. CaCl 2 loading also causes the dealkylation and deoxygenation of soot. The influence of CaCl 2 on soot formation can be summarized as the catalytic effect on soot precursor formation, the enhancement of soot nucleation, and the inhibition of soot coagulation. [ABSTRACT FROM AUTHOR]