Torrefaction of oil palm frond for enhancing solid fuel properties / Nurhafizah Yaacob

Researches on potential utilization of lignocellulosic biomass from oil palm residues as energy feedstock has increased significantly due to depleting fossil fuel such as coal. However, due to undesired properties of lignocellulosic biomass such as high moisture content, low energy density and energy content, as well as high bulk density, researchers started to find alternative ways to pretreat them into a useful fuel. Torrefaction technology had been considered by researchers and is acknowledged to enhance the fuel properties of biomass towards an efficient renewable energy feedstock. This research investigates the physicochemical properties of oil palm frond (OPF) at torrefaction temperatures of 200°C, 225°C, 250°C, 275°C, and 300°C at 15, 30, 45, and 60 min holding time at a constant heating rate of 10°C/min. The solid torrefied products were characterized in terms of their chemical composition, heating value, mass and energy yield. The color appearances of the solid torrefied products were also reported. Thermogavimetric Analyser (TGA) and elemental analyser were used to determine the chemical composition as well as to investigate the degradation behaviour of the solid torrefied product. Bomb calorimeter was also used to measure the heating value to calculate energy yield of the torrefied products. As a result, OPF with original heating value of 17.8 MJ/kg was improved to 23.42 MJ/kg after subjected to torrefaction at 300°C. The solid yield decreased while the energy yield increased as torrefaction temperature and holding time increases. However, the effect of torrefaction temperature is much more significant while the effect of holding time becomes more prominent at low torrefaction temperature. The degradation behaviour of lignocellulosic constituents; cellulose, hemicellulose, lignin was discussed through TG and DTG analysis. This research also develops an optimum torrefaction parameters; temperature and holding time by using response surface methodology (RSM) based on central composite rotatable design (CCRD). A total of 13 experiments were conducted to optimize the combination effects of the variables. As a result, the regression coefficients of 98.3 and 85.5 for the solid yield and heating value were obtained, respectively. This proved that the RSM based on CCRD is efficiently applicable for the torrefaction study. The result shows that optimum production of solid fuel with enhanced heating value of oil palm frond is obtained at torrefaction temperature of 268°C; holding time of 15 minutes with predicted solid yield and heating value of 70.5% and 21.4 MJ/kg, respectively. This work concludes that a good torrefied OPF can be obtained at a torrefaction temperature higher than 250°C with a holding time 15 minutes.