TORREFACTION AND CHARACTERIZATION OF MAHOGANY SAWDUST FOR SOLID FUEL PRODUTION

Abstract

As interest in biomass utilization into combustion fuels grows, the torrefaction, becomes ever more important. Torrefaction is aimed to maximize energy by removing undesirable components (water, hemicellulose and volatile matter) which cause poor ignition characteristic, excessive smoking and low combustion efficiency when used for energy generation in boilers and blast furnaces. In this research, the effect of torrefaction on the physiochemical and combustion characteristic of tropical biomass (Mahogany Sawdust) were investigated. The proximate and ultimate analyses of the tropical biomass were determined before torrefaction and at different torrefaction temperature (200, 250 and 300 oC). The Sawdust was subjected to thermal degradation test via Thermogravimetric Analysis (TGA). Fourier Transform Infrared Spectroscopy (FT-IR) analyses were also carried out to determine the presence of active functional group in the raw biomass and the resulting torrefied biomass. Electron Microscopy (SEM) analysis was finally carried out to determine the morphologies of the raw and torrefied biomass. The result of biomass weight loss as function of temperature variation revealed that at relatively low torrefaction temperature of 200 and 250 oC the weight loss were very pronounced, whereas at torrefaction temperature of 300oC, the weight loss of the tested biomass becomes relatively negligible. In the fixed bed furnace, the change in sawdust mass yield between 10 min was (21.37%) and 30 min (32.14%) at 200oC was about 10.77% and it increased between 200oC and 300oC. The oxygen-carbon ratio deduced from the ultimate analysis of the torrefied biomass displayed a low and concentrated distribution in the Van Krevelin plot than those of raw biomasses. The thermal stability of the biomass feedstock from TGA were found to be in the decreasing order of 300>250>200OC. TGA curves for raw sawdust and torrefied sawdust showed three main decomposition with the curves of torrefied sawdust shifting to higher temperatures. The energy yield of torrefied sawdust is higher than that of untorrefied sawdust. The optimal heating value of the torrefied SD was found to be 28.2 MJkg-1 against 19.5MJkg-1 of the raw SD depicting 44.62% increase of the heating value. The FTIR showed that torrefied sawdust at 300oC has more C=C than sawdust torrefied at 200oC and 250oC. The plot of conversion against temperature and ln g (α) against 1/T for SD using first order kinetic shows first order kinetic shows a linear relationship with regression coefficient (R2) of 0.7442.The torrefied briquettes strength was in order of: 300OC>250OC>200OC. The finding from this study revealed that the Sawdust from mahogany can be used as a solid renewable and environmentally friendly fuel as an alternative or potential replacement for coal.