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 fmd 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 ll ooc; 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 of2.83 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
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 will be
reduced.·