Evaluation of a charcoal production process from forest residues of Quercus sideroxyla Humb., & Bonpl. in a Brazilian beehive kiln

Abstract

Carbonization process from Brazilian beehive ovens and quality of charcoal from residues of branches and cracked firewood from Quercus sideroxyla were evaluated. Oven temperature and time, charcoal yields, quality and calorific value were also assessed. In addition, charcoal quality was determined using proximate and elemental analysis. Moreover, charcoal was classified according to its size. Since values for immediate and elemental analysis were expressed as percentage, data were transformed using the arcsine square root function for each studied variable. The relationship between temperature and time process for cracked firewood and branches were R2=0.99; p<0.0001 and R2=0.98; p<0.0001, respectively. The carbonization of cracked firewood was slower (131.6h), oven temperature reached 975°C and had higher yield (5.4m3t−1), compared to branches (86.7h, 1007°C and 9.2m3t−1, respectively). The best charcoal quality was obtained from the middle section of the oven when using cracked firewood; with a mean calorific value of 32,000Jg−1, moisture content 3.3%, volatile materials 19.0%, ash 5.2%, fixed carbon 72.2%, and carbon 89.41%. Elemental analysis had the following mean values: H=2.95%, O=2.93%, N=0.2%, and S=0.01%. The quality size of the charcoal of branches was acceptable according to France and Belgium standards. The quality of charcoal produced from branches can be improved by controlling air intakes to prevent increments in temperature.