Thermal Analysis and Decomposition Kinetics of Chinese Forest Peat under Nitrogen and Air Atmospheres

The mechanism of forest ground fire is thermal decomposition and smoldering combustion of forest peat or duff. The availability of oxygen is believed to influence the processes. This paper aims to investigate the thermal decomposition of peat under inert and oxidative atmospheres. Experiments were monitored under nitrogen and air atmospheres, using the non-isothermal thermogravimetric (TG) and differential thermal analysis (DTA) methods. The pyrolysis curves of peat showed three main stages, i.e., the stage of moisture evaporation (together with low stability of organic compounds) (315-432 K, with the heating rate of 10 K/min), organic matter pyrolysis (432-805 K), and inorganic compound decomposition (805-1075 K). The stage of organic matter pyrolysis also contained three steps, corresponding to hemicellulose, cellulose, and lignin pyrolysis. Because the temperature of inorganic compound decomposition was higher than the peat-smoldering temperature, this stage of inorganic compound decomposition was not important for peat pyrolysis. Therefore, the peat pyrolysis processes were simulated using reactions of four fractions: moisture, hemicellulose, cellulose, and lignin. In the combustion curves, the inorganic compound decomposition stage was not distinct, while the organic matter pyrolysis stage became two consecutive stages, i.e., the stage of organic matter decomposition (427-575 K) and char oxidative combustion (575-800 K). A scheme containing moisture evaporation (together with low stability of organic compounds) and two consecutive reactions was proposed to simulate the combustion processes. The good agreement between the experimental and simulated curves validated the proposed models for pyrolysis and combustion of peat. The kinetic parameters of main components/steps were compared to those reported for lignocellulosic biomass.