Thermogravimetric curves are measured, by means of a flexible home-made (HM) system, of the oxidation of wood chars generated from packed-bed pyrolysis at 800 K. A careful control of the sample temperature and a small mass/size (4 mg mass corresponding to 140micron thick particle layer) allow a kinetic regime to be established for heating rates between 5 and 10 K/min. Good quantitative predictions are obtained based on a two-step mechanism, with activation energies affected by the hardwood or softwood origin of chars (125–143 kJ/mol and 186–207 kJ/mol for the devolatilization and oxidation reaction, respectively). The same conditions applied for a standard commercial (SC) thermogravimetric system result into remarkable self-heating leading to uncontrolled ignition and too slow oxygen diffusion rates. Only extremely small sample masses (≤1mg) and slow heating rates (≤5K/min) permit to completely eliminate heat and mass transfer intrusions but the actual limits are strictly related to the specific char reactivity.
Self-heating effects in the thermogravimetric analysis of wood char oxidation / Branca, Carmen; DI BLASI, Colomba. - In: FUEL. - ISSN 0016-2361. - 276:(2020), pp. 1-8. [10.1016/j.fuel.2020.118012]
Self-heating effects in the thermogravimetric analysis of wood char oxidation
Branca Carmen
Primo
;Di Blasi ColombaSecondo
2020
Abstract
Thermogravimetric curves are measured, by means of a flexible home-made (HM) system, of the oxidation of wood chars generated from packed-bed pyrolysis at 800 K. A careful control of the sample temperature and a small mass/size (4 mg mass corresponding to 140micron thick particle layer) allow a kinetic regime to be established for heating rates between 5 and 10 K/min. Good quantitative predictions are obtained based on a two-step mechanism, with activation energies affected by the hardwood or softwood origin of chars (125–143 kJ/mol and 186–207 kJ/mol for the devolatilization and oxidation reaction, respectively). The same conditions applied for a standard commercial (SC) thermogravimetric system result into remarkable self-heating leading to uncontrolled ignition and too slow oxygen diffusion rates. Only extremely small sample masses (≤1mg) and slow heating rates (≤5K/min) permit to completely eliminate heat and mass transfer intrusions but the actual limits are strictly related to the specific char reactivity.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.