Dominique Cancellieri

Thermal degradation of pinus pinaster needles by DSC, part 2: kinetics of exothermic phenomena

Fire behavior prediction models required for controlling wildland fires can be calculated from a mathematical approach, taking the thermal and chemical properties of forest fuels into account. There is a need for a better understanding of the thermal decomposition of forest fuels. Two steps have been observed during the thermal degradation of Pinus pinaster needles under air sweeping. The two corresponding exothermic peaks showed by DSC curves are superimposed. An original and simple method is proposed to separate each peak from the global exotherm then the kinetic analysis is performed using single peak method (1 scanning rate) and isoconversion method (at least 3 different scanning rates).

Sampling and Quantitative Analysis of Smoke during a Fire Spreading Through a Mediterranean Scrub

This work consists in sampling and analyzing volatiles and smoke released by a typical Mediterranean vegetation during a fire. On an experimental burning plot, we used two original devices to collect volatiles and smoke. Thanks to air sampling pumps, atmosphere samples were taken, into cartridges filled with an adsorbent and into tedlar bags. The test site was instrumented with different other sensors (thermocouples, fluxmeters, anemometers, IR and visible cameras) in order to get the maximum data [1]. Analyses were performed at the laboratory by gas chromatography one day after the field experiment. Samples were thermally desorbed from the cartridges in the GC column coupled to a MS detector. We aim to characterize the risks related to the toxicity of smoke in actual conditions. Benzene, Toluene and Xylene (BTX) are highly toxic compounds that we propose to quantify in the smoke sampled during the fire. Quantification of such compounds was done with an external calibration using commercial mixtures of BTX.

Thermal Degradation of Lignocellulosic Fuels: Biopolymers Contribution

Every year, thousands hectares of forest do burn in southern Europe. The Mediterranean area is especially affected during the dry season. Nevertheless, in spite of considerable efforts in fire research, our ability to predict the impact of a fire is still limited, and this is partly due to the great variability of fire behaviour in different plant communities (De Luis et al., 2005). The combustion of forest fuels is partially governed by their thermal behaviour since this step produces a flammable gas mixture. Therefore, the analysis of the thermal degradation of lignocellulosic fuels is decisive for wildland fire modelling and fuel hazard studies (Dimitrakopoulos, 2001; Balbi et al., 2000; Stenseng et al., 2001). We propose in this work to focus on the thermal degradation of different forest fuels and their main components. Following a literature survey, we noticed that there is a lack in the description of the thermal degradation of forest fuels concerned by wildland fires (Grishin et al., 1983; Larini et al., 1998; Sero-Guillaume & Margerit, 2002; Linn & Cunningham, 2005). Even if these models are very different, it’s well known that the energy emitted remains a crucial data. Classic approaches are based on the consideration of the low heat content value obtained by bomb calorimeter (Rothermel, 1983; Andrews, 1986; Nunez-Regueira et al., 2005). The experiments are led in constant volume what bring about a strong temperature raising, and with an excess of pure oxygen. These conditions are far from those met during a wildfire at atmospheric pressure in the air. DSC seems to be a convenient tool in order to follow the thermal degradation at the laboratory (Liodakis et al., 2002). The degradation of forest fuels begins with the pyrolysis process from 373K to 773K (Simeoni et al., 2001; Shanmukharadhya & Sudhakar, 2007; Tonbul, 2008; Yuan & Liu, 2007). Non-combustible products, such as carbon dioxide, traces of organic compounds and water vapour, are emitted between 373K and 473K. Above 473K, the pyrolysis breaks down the fuels components into low molecular mass gases (volatiles), and carbonaceous char. Around 773K all the volatiles are gone; the remaining char is oxidized in a glowing combustion (Beall & Eickner, 1970). Wood is a complex organic material, composed of cellulose (40 to 45% for coniferous trees and 38 to 50% for leafy trees), lignin (26 to 34% for coniferous trees and 23 to 30% for leafy trees), hemicellulose (7 to 15% for coniferous trees and 19 to 26% for leafy trees), extractives (<15%), ashes (< 1%) water and mineral matter (Orfao et al., 1999; Weiland et al., 1998). The chemical composition varies from species to species and within the same variety it varies with the botanical origin, age and location in the tree (trunk, branches, crown and roots). In

New experimental diagnostics in combustion of forest fuels: microscale appreciation for a macroscale approach

In modelling the wildfire behaviour, good knowledge of the mechanisms and the kinetic parameters controlling the thermal decomposition of forest fuel is of great importance. The kinetic modelling is based on the massloss rate, which defines the mass-source term of combustible gases that supply the flames and influences the propagation of wildland fires. In this work, we investigated the thermal degradation of three different fuels using a multi-scale approach. Lab-scale experimental diagnostics such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), use of the cone calorimeter (CC) or Fire Propagation Apparatus (FPA) led to valuable results for modelling the thermal degradation of vegetal fuels and allowed several upgrades of pyrolysis models. However, this work remains beyond large-scale conditions of a wildland or forest fire. In an effort to elaborate on the kinetic models under realistic natural fire conditions, a massloss device specifically designed for the field scale has been developed. The paper presents primary results gained using this new device, during large-scale experiments of controlled fires. The mass-loss records obtained on a field scale highlight the influence of the chemical composition and the structure of plants. Indeed, two species with similar chemical and morphological characteristics exhibit similar mass-loss rates, whereas the third presents different thermal behaviour. The experimental data collected at a field scale led to a new insight about thermal degradation processes of natural fuel when compared to the kinetic laws established in TGA. These new results provide a global description of the kinetics of degradation of Mediterranean forest fuels. The results led to a proposed thermal degradation mechanism that has also been validated on a larger scale.

Chapter 5 – Modeling Peat-Fire Hazards: From Drying to Smoldering

Peat is an organic and flammable material used for energy generation and involved in wildfires. Smoldering fires do not have the visual impact of flaming fronts but are an important aspect of wildfires because of the associated large carbon emissions and damage to valuable ecosystems. Moreover, in the case of extreme dry conditions or strong winds, smoldering fires develop easily into scrub or forest flaming fires. An advanced knowledge on the mechanisms and kinetic parameters controlling the drying process and the thermal decomposition of peat is of importance for understanding smoldering peat fires and quantifying the associated risks. In this context, the present chapter proposes a contribution to determine kinetic parameters to model peat-fire hazard. Three main topics were developed: thermal behavior, kinetic analysis, and fire hazard modeling. 1. Investigations were conducted on boreal peat samples from two regions (Scotland and Siberia) and for three depths: two high-moor peat types collected in Edinburgh and in Tomsk, and one transition peat from Tomsk. For each sample, the botanical composition, degree of decomposition, ultimate analysis, and moisture content were determined and correlated to the thermal behavior obtained using two thermal apparatuses: a Thermogravimetric Analyzer and a Differential Scanning Calorimeter, along with a humidity analyzer. The complementary use of these thermal techniques provides details about the partial processes and reaction kinetics. The peat samples were submitted to thermal stress from the ambient temperature to 773 K with heating rates of 10, 20, and 30 K/min. A significantly different degradation behavior was observed for the different peat types. However, three main degradation steps can be isolated. The first one consists of a drying step between ambient temperature and 473 K, the second one is a devolatilization step between 473 and 650 K, and last one is a combustion step from 650 to 773 K. A large part of this chapter is dedicated to the description of these phenomena and their correlations with the various physicochemical, botanical, and physiological parameters of the peat previously determined. 2. Based on the experimental results, another part of the chapter is devoted to the determination of kinetic constants. The kinetic triplet of each reaction involved during thermal degradation was estimated. Water evaporation is known to be an important mechanism that dictates the ignition and spread of peat fires. In this context, the thermokinetic constants for drying were determined using two different methods: the Inverse Kinetic Problems and Kissinger Akahira Sunose methods. Moreover, it is well known that devolatilization conditions have a major bearing on the yield of char and its reactivity in the process. This evidence, together with the need to develop models that predict peat behavior when it is subjected to a heating process, confers a great interest on the kinetic study of smoldering and combustion. For these two complex exothermic phenomena, the kinetic triplets of each reaction were estimated using a more detailed Hybrid Kinetic Method. This method has the advantage of eliminating errors caused by the ambiguity of the phenomenon. 3. Despite the negative impact of peat fires, a science-based system has not yet been developed for the prediction of their occurrence. Such a method would allow one to assess the probability of occurrence of peat fire, taking into account the natural and anthropogenic pressure, weather conditions, terrain characteristics, and dynamics of the moisture content of the peat layer. Therefore, the description of peat drying is a major parameter in the prediction of fire danger. The last part of the chapter devoted to the development of a mathematical model of the drying of a peat layer is based on a single temperature. The iteration–interpolation method was used to numerically solve the mathematical model. The thermokinetic constants previously obtained were used to implement the simulations. The model allows one to obtain the time variation of the volume fraction of water, gas phase, and temperature of the peat layer. To conclude, an accurate set of mathematical models that can be used for predicting peat-fire hazard is presented. These models take into account all known reasons for ignition of natural fires. The specific meteorological conditions, anthropogenic pressure, and simulation of the dynamics of the moisture content of the peat layer are included in the analysis.

Investigation of organic wastes from Mediterranean plants to produce biogas by anaerobic digestion

The University of Corsica is contributing to the research of both efficiency and integration of renewable energy in the main electrical grid. Since 2013, a scientific program concerning the valorization of biomass energy has been developed to investigate the methane potential through the anaerobic digestion process of lignocellulosic resources. In Corsica, due to the clearing brush policy to prevent forest fires, cellulosic wastes are generated. Besides, Corsica is an important producer of essential oil from Mediterranean species thanks to a process generating an important amount of dried vegetation as waste every year. The aim of this preliminary study on biomass as renewable energy was to characterize and to select the most appropriate substrates for the anaerobic digestion process. Fiber contents and Biochemical Methane Potential (BMP) were performed on five substrates. Heather, rockrose and strawberry tree were chosen as representative of forest fuels. Water distillation residues of laurel and immortelle were considered as natural resource wastes. On this work, we focus on the three species which had the best BMP. Rockrose, dry residue of immortelle and strawberry tree produced 139, 124 and 87 Nm3 CH4 per grams of volatile solids, respectively. The ratio holocellulose: lignin, thanks to the Van Soest method of fiber determination, was determined for those species: 3.8, 3.4 and 1.7. This parameter is a key factor to take into account for the correlation of the BMP with the compositional characteristics. Further work will be performed on these chosen substrates to optimize the anaerobic digestion process in 15 L-reactors.