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

Abstract

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 peatsmoldering 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.

Kinetic investigation on the smouldering combustion of boreal peat

“…. The same phenomena were observed and recorded by other authors, [3], [29], [7]. The figure 2 highlights the interest of studying DTG curves.…”

“…The analysis of the thermal degradation of peat and the understanding of the underlying processes is essential to the development of models of combustion [3] and quantify the risk of peat fires. Chen et al study the decomposition of peat samples from northeast China [7] and observed three main stages, moisture evaporation, organic matter pyrolysis, and inorganic compound decomposition. This mechanism was then used to simulate the smouldering process.…”

“…The present paper is devoted to the study of the thermal degradation of three kinds of peat under air with ThermoGravimetry (TGA) and kinetic analyses of the data. This investigative method is commonly used for this purpose on different materials [8], [9], [10] and the numerous data from the literature show the interest of TGA experiments [7], [11], [12], [13]. Experiments were conducted on peat samples coming from various two boreal regions, Scotland and Siberia, and from different depths.…”

Computational study of critical moisture and depth of burn in peat fires

“…By integrating the heat flow measurements for peat samples (see Bergner and Albano 1993;Chen et al 2011 Huang et al (2015), the weakest ignition protocols required to ignite the dry top layer are 8.3 kW m À2 for 5 min, or 5.0 kW m À2 for 30 min. Based on this result and to ensure a successful ignition, a strong heating source ( _ q 00 e ¼ 30 kW m À2 , similar to a flame) for 5 min is chosen as the ignition protocol.…”

Thick wood particle pyrolysis in an oxidative atmosphere

“…This type of process is called "auto-thermal" and this type of pyrolysis is called "oxidative pyrolysis". In the literature, it is reported that the presence of oxygen greatly affects the behaviour of the pyrolysis (Amutio et al, 2012;Chaos et al, 2012;Chen et al, 2011;Su et al, 2012).…”