ABSTRACT
This work investigated and quantified the calorific values of the main branches and trunks of eleven
(11) tropical trees in correlation with their chemical composition in order to assess their suitability
for use as credible sources of wood fuel. The determination of the carbon, hydrogen, nitrogen,
oxygen and sulphur (CHNOS) content of the samples was done using an organic elemental
analyser, while an oxygen bomb calorimeter was used to experimentally determine their corresponding
gross heat values. The experimental gross heat values for the branches examined ranged
from 18,703.37 kJ/kg in Lophira lanceolata to 21,350.35 kJ/kg in Afzelia africana while that of the
trunks ranged from 19,747.74 kJ/kg in Tectonia grandis to 22,408.68 kJ/kg in Prosopis africana. These values were within and about the expected ranges observed for tropical trees and may be
considered adequate for wood fuel. The general trend in both branches and trunks was that the
higher the carbon content, the higher the gross heat value of sample. The absence of sulphur in
almost all the samples except, Prosopis africana, (0.055%) was indicative of the fact that the negative
environmental impact with respect to harmful emissions of oxides of sulphur is practically
non-existent with respect to these species. In the light of the aforementioned variables, the main
branches of Afzelia africana (21,350.35 kJ/kg), Nauclea diderrichii (21,157.30 kJ/kg) and Tectonia
grandis (20,257.13 kJ/kg) could be used as credible sources of firewood and charcoal production.
With respect to the trunks, the timbers in order of preference would ideally be Prosopis africana
(22,408.68 kJ/kg), Nauclea diderichii (21,436.42 kJ/kg) and Brachstigia eurychoma (20,924.7
kJ/kg).