摘要
Biomass energy provides over 70%of the national energy demand in Kenya.Increased demand has contributed to increased environmental degradation through deforestation,contributing significantly to the global emissions of greenhouse gases,loss of habitats,and biodiversity,and increased health risks.Efficient charcoal conversion technologies have been researched and developed.However,no studies have been undertaken to establish the influence of the improved technologies on the quality of charcoal produced and the emission levels of greenhouse gases from each kiln.The study was undertaken(in eastern Kenya)to determine the effect of carbonization technology and tree species on the quality of the charcoal,the emission levels of the kilns,and the energy properties of the charcoal from various selected species.A total of 14 species were sourced for the study and carbonized using the Adams retort,portable metal,improved earth and the traditional earth kilns.The results indicated that Balanites aegyptiaca,Terminalia spinosa,Acacia nilotica and A.tortilis were ranked best indigenous species in terms of calorific values with mean calorific values above 6.0 kcal/g while Prosopis juliflora,Casuarina equistifolia and Eucalyptus camadulensis were the best exotic species with mean kcal/g of 6.430 kcal/g,5.972 kcal/g and 5.633 kcal/g respectively.Analysis of variance on the energy values indicated there was no significant difference in the quality of charcoal produced using the different kilns.The improved earth kiln and the portable metal kiln produced charcoal that was more dense and intact.Charcoal from the preferred indigenous species had also the longest burning time with a mean of 124 minutes compared to 62.4 minutes for the exotics.The highest burning temperature was found in the indigenous species.Results on emission tests were conducted using a portable gas analyzer on the four kiln types.The carbon dioxide emissions were rather high.Methane production in all kilns showed an upward trend at the beginning of the carbonization process and towards the end,the levels declined.The study concluded that a number of species are overexploited for charcoal production with no conservation measures being undertaken thus being threatened with extinction.The types of kiln have significant effect on the energy values(calorific values)of charcoal.The quality of charcoal using improved kilns gave high calorific values.Emission levels for all kiln types were generally high.The study recommends further research on all improved charcoal conversion technologies for reduced emission of greenhouse gases especially retorts since they utilize the flue gases.
