Kinetic study of thermal degradation of peats by TGA
Résumé
The paper is devoted, for the first part, to the study of thermal degradation of various kinds of peat under air with ThermoGravimetry Analysis. For the second part, thermal data has been analysed under kinetic aspects. Even if peat and humus fires have been extensively studied under biological and ecological aspects, only a few studies dedicated to the chemical and physical aspects of these fires can be found in the literature. To predict the fire risk it is therefore crucial to know the kinetic of thermal decomposition of peat. Investigations were lead on three deposits of peat: two deposits of high-moor peat collected in Edinburgh area (Scotland) and in Tomsk (Russia) and one deposit of transition peat from Tomsk. For temperature ranging from 500 to 950K, TGA curves shows two significant weight losses during the degradation process, which are identified as: (1) emission and oxidation of volatile matters and (2) oxidation of chars. As expected different behaviour were recorded for the different samples. In order to determine the activation energy on the whole process, an isoconversional method was applied. The method has the ability to reveal the complexity of the processes in the form of a functional dependence of the activation energy on the extent of conversion α. In a second step, the knowledge of was used to perform simulations up to heating rates outside the functioning range of the thermal analyser. An algorithm previously developed for plants degradation was applied. This method allows the calculation and the simulation of the solid temperature at different conversion degrees for various heating rates. This preliminary work is an important step for peat combustion modelling since it brings some understanding on the thermal behaviour of peat degradation and it provides kinetic data on the thermal degradation.