Preliminary Drying of Oil Palm Fronds Using Concentrated Solar Thermal Power

Biomass is an important renewable energy source. Malaysia has a great potential for biomass stock and especially oil palm wastes. The fact that oil palm fronds contain high moisture content makes it unsuitable to be used directly as a biomass fuel, neither for direct combustion nor gasification. In addition, conventional and costly drying methods make the fronds a non-attractive fuel. The objective of this paper is to find a cheap, sustainable and efficient way of drying oil palm fronds. A new design is proposed that utilizes concentrated solar thermal energy for drying the biomass. A solar dryer rig has been designed and fabricated. The system’s target is to maximize the thermal energy received into the system and to minimize energy loss out of it. The rig consists of three main components. A 49 inch Fresnel lens with a concentration ratio of 8 is used for concentrating the solar energy onto a receiver. The second component is the lens holder that provides the needed elevation for the lens according to the required temperature inside the drying chamber, having the maximum temperature at an elevation equals to the focal length. The third component is the drying chamber. It consists of a sheet of aluminum painted in black and a glazing made of 12 mm acrylic sheets. The aluminum sheet which acts as the receiver is designed to receive solar radiation at different times of the day; thus eliminating the need for a sun tracking system. The glazing is used for trapping the heat energy inside the drying chamber, and minimizing conduction of the heat to the surrounding environment. The chamber contains perforations in order to provide air flow inside the chamber; for a faster removal of humidity. Experiments have been performed on samples of oil palm fronds at a drying temperature not exceeding 110°C; in order not to affect the organic material of the biomass. Results have been compared with another experiment that used an electric oven for drying at the same temperature. Using the proposed system, the samples were completely dried in 6.5 hours with an average efficiency of 55.4%, compared to 10.5 hours when using the electric oven. The proposed system achieved an average drying rate of 4.75 g/hr compared to an average drying rate of 2.83 g/hr using the electric oven. These results were achieved since relative humidity value inside the drying chamber was lower compared to that inside the oven. One drawback of the system is its heavy dependence on the weather. Cloudy conditions affect the results severely. It is recommended to combine another source of heating to the current one. By converting the proposed system into a hybrid one the problem of inconsistent solar radiation can be reduced.