EVALUATION OF COMBUSTION CHARACTERISTICS OF CHARCOAL FROM SELECTED TROPICAL WOOD SPECIES

Abstract

The physical and combustion characteristics of charcoal produced from wood offcuts of some selected tropical wood species (Iroko, Obeche, Afara, and Mahogany) were evaluated. The wood offcuts were collected from different saw-mills in Ibadan metropolis and were converted into charcoal using a portable steel kiln. Physical property such as density and proximate analysis i.e. percentage moisture content (PMC), percentage volatile matter (PVM), percentage ash content (PAC), percentage fixed carbon (PFC) and heating values (HV), of the produced charcoals were determined using the American Standard Testing Method (ASTM D1102-56). The results showed that charcoal produced from Afara wood had the highest heating value of 3.32×104 kJ/kg ; highest PFC of 89.2 % and least value of PMC and PAC of 2.1 % and 3.0 % respectively, while charcoal produced from Iroko wood had the least HV of 3.21×104 kJ/kg; highest PAC value of 6.2 % and PMC and PFC values of 3.8 % and 86.0 % respectively. Obeche species had the highest value of PVM and density of 11.0 % and 0.62 gcm−3 respectively; HV of 3.30×104 kJ/kg, it also had low values of PAC and PMC of 3.5 % and 2.7 % respectively with PFC of 85.5 %. Mahogany species had HV, PMC, PAC, PVM and PFC values of 3.22 ×104 kJ/kg, 3.7 %, 6.0 %. 5.0 % and 89.0 % respectively. Correlation and regression analysis used to develop linear model showed that Ash content had the highest correlation coefficient with heat of combustion. In evaluating the performance of the charcoal samples, they were subjected to three test conditions: water boiling, burn rate of charcoal samples and cooking duration tests. Values obtained as burn rates and water boiling durations were 0.51 kg/hr and 28 mins for Iroko species, 0.58 kg/hr and 24 mins for Obeche species, 0.60 kg/hr and 22 mins for Afara species and 0.54 kg/hr and 28 mins for Mahogany species. Comparative cooking tests were conducted with the charcoal samples using beans as food item. The fastest cook time (45 mins) was recorded with Afara charcoal sample in cook stove. Times taken using other charcoal samples in cook stove were 48, 55 and 58 mins, for Obeche, Mahogany and Iroko wood species respectively. The results from the tests and evaluation of the charcoal samples showed that the best charcoal sample were those produced from Afara wood species which had the best combustion properties among the charcoal samples used. Although other wood charcoal species investigated in this work also had good combustion properties, as they release less or no smoke and can be utilized as a clean and alternative source of energy to firewood for heating purposes.