Burning Dynamics of Straw Chars under the Conditions of Thermal Analysis

Burning is investigated, by means of thermogravimetry, of 17 straw chars produced from packed-bed pyrolysis at moderate temperatures, using wood chars for comparison. The exothermic process always consists of an oxidative devolatilization stage followed by actual burning, generally leading to almost complete conversion for temperatures around 750 K. The majority of straw chars exhibits two-stage burning taking place, first in a catalytically (alkali) activated kinetic regime, with peak rates at temperatures around 650-690 K, and then in a thermally activated kinetic regime, with peak rates at temperatures around 700-730 K. In the other cases, burning is a one-stage process occurring either in a catalytically activated regime, with temperatures of the peak rates around 675-685 K, or in a thermally activated regime which also includes wood chars (temperatures of the peak rates again around 700-730 K). Moreover, burning of the residual char is completed at temperatures above 750 K (in a very few cases with further local peak rates around 825-875 K) in a diffusive regime.