QUALITY OF CHARCOAL FROM Prosopis laevigata (Humb. & Bonpl. ex Willd.) M.C. Johnst. AND Ebenopsis ebano (Berland.) Barneby & J.W. Grimes PRODUCED IN AN EARTH PIT KILN

Abstract

Approximately two billion of people in the world use biomass to produce heat and prepare food. In the metropolitan area of Monterrey, Nuevo León, the demand of vegetable charcoal for recreational use is 5 500t month-1. The trade of charcoal is regulated by empirical knowledge in relation to species, burning time, and spark and ash production. However, certain quality standards must be met for export purposes. Therefore, this paper compares the yield and quality of charcoal from Prosopis laevigata and Ebenopsis ebano produced in an earth pit kiln. The quality was determined by moisture content, volatile material, ash, fixed carbon and calorific value, according to international standards. The data were analyzed with a factorial arrangement. The results showed highly significant differences (p<0.01) in yields, as well as in ash production and calorific value (p<0.05), between the two species. Yields of 2.8, 2.3 m3 t-1, moisture content of 3.6, 3.5%; volatile material of 22.8, 24.9%; ashes of 2.8, 3.2%; fixed carbon of 70.8, 68.6%, and calorific value of 30 241, 29 725 kJ kg-1 were estimated for P. laevigata and E. ebano, respectively. The yields for both species were high, and moisture and ash content were found to be within the international limits. On the other hand, fixed carbon and volatile material did not meet the values allowed by the international standards.