The Phenomena of Secondary Weight Loss in High-Temperature Coal Pyrolysis

Abstract

Studies on coal pyrolysis via a thermogravimetric analyzer (TGA) are typically performed under a variety of temperature increases beginning at ambient temperature. A main limitation in these procedures is that the reaction temperatures (generally lower than 1000 °C) are typically lower than those met in pulverized coal boilers and ash flow temperatures (AFTs; generally higher than 1100 °C). In this paper, five Chinese coals are clarified to low- or mid-AFT coals as their AFTs increase. They were then prepared in TGA at several temperatures below or above their AFTs under N2 atmosphere for approximately 30 min after a heating procedure at a rate of 80 °C/min. The coal and residual char samples were collected and analyzed via X-ray diffraction and compared to the chemical thermodynamic calculation. The secondary weight loss appeared between 1200 and 1450 °C in the TG curves of four mid-AFT coals but not the low-AFT coal. The results showed that this secondary weight loss was caused by the carbothermal reduc...