Effects of minerals containing sodium, calcium, and iron on oxy-fuel combustion reactivity and kinetics of Zhundong coal via synthetic coal

Abstract

The greatly high contents of alkali and alkali earth metals in Zhundong coal have a negative impact on the combustion and utilization of the coal, which results in serious fouling and slagging problems. In the present study, the influences of different minerals on the oxy-fuel combustion of Zhundong coal via synthetic coal were investigated by thermal analysis, and two isoconversional methods were applied to conduct the kinetic analysis. Additive minerals with single metallic elements including sodium (NaCl, NaCO3, NaAlSi3O8), calcium (CaCl2, CaCO3, CaSO4), and iron (Fe2O3, Fe3O4 and FeS2) rather than complex mixtures were added into synthetic coal to avoid the combined catalysis among various minerals. The experimental results show that the thermogravimetric and derivative thermogravimetric curves of synthetic coals under oxy-fuel conditions are similar to those of Zhundong coals. Most of selected additive minerals affect the ignition temperature slightly (less than 10 °C) but tend to lower the burnout temperature (5–25 °C), which narrows the main combustion temperature zone. The addition of CaCl2 raises the burnout temperature from 645.4 to 689.5 °C and drives down the average combustion rate from 4.44 to 3.83% min−1, while other minerals exhibit negative correlation with the maximum and average combustion rates in most cases. The reaction kinetics analysis indicates that the apparent activation energy of coal combustion depends heavily on the category of additive minerals, which varies from 21.31 to 39.05 kJ mol−1 (average values calculated by KAS method). Besides, the apparent activation energy declines with an increase in the conversion rate of samples.