Upgradation in Physio-Chemical Characteristics and Thermal Behaviour of Thar Coal Subjected to Torrefaction

Abstract

This study explores the improvement in physiochemical attributes, thermal behavior, and combustion characteristics of low-rank Thar coal through torrefaction, a thermal pretreatment process. Thar coal samples were torrefied at five temperatures (200, 225, 250, 275, and 300°C) for two residence times (30 and 60 minutes). The study assessed changes in proximate and ultimate composition, calorific value, energy density and combustion traits of untreated and torrefied coal using thermogravimetric analysis (TGA). Results indicated slight improvement at low torrefaction temperatures (200-225°C), while higher temperatures (275-300°C) significantly enhanced fuel properties. Key findings include increased fixed carbon, reduced moisture and volatile matter, and higher heating value (HHV). The TGA graph demonstrated that torrefied coal has improved fuel properties compared to raw coal samples. The derivative thermogravimetric curve (DTG) shifted upward, signifying a change in peak (Tm) and decomposition temperatures along with an increased torrefaction temperature. The samples torrefied at 300°C for 60 minutes yielded best results, showing improved ignition (Ti) and burnout temperatures (Tb) and reduced emissions. This research focuses on torrefaction as a potential technique for improving the quality of low-grade coals of Pakistan hence opening up opportunities for controlled energy production.