Effects of hydrothermal treatment coupled with mechanical expression on combustion performance of Loy Yang lignite

The combustion characteristics and kinetics of hydrothermal treatment (HT) without addition of extra water and of HT coupled with mechanical expression (HT–ME) were investigated using thermogravimetric analysis at various heating rates. The relationships between various physicochemical properties, i.e., amounts of volatile matter and fixed carbon, specific surface area, and pore volume, and combustion performance were also investigated. The activation energy was calculated using the Kissinger–Akahira–Sunose isoconversional method. The results showed that for samples treated using HT and HT–ME, the ignition temperatures and temperatures at which the mass loss rates were at maximum, mainly because of char combustion, were significantly higher than those for raw lignite. They increased slightly with increasing processing temperature, suggesting that HT and HT–ME decrease the reactivity of Loy Yang lignite. The maximum combustion rates of the treated samples were higher than those of raw lignite and the values for the HT and HT–ME samples differed slightly from each other. The higher maximum combustion rates indicate that HT and HT–ME modify the combustion intensity of Loy Yang lignite. Furthermore, the combustion of raw lignite can be described by multistep kinetics, whereas single rate-limiting step kinetics can be used to describe the kinetics of the other samples. Average activation energies of samples treated using HT and HT–ME at 200 °C reached the maximum values.