5.2.3.1 Palm Kernel Shells

In the palm oil mill, after the hydrocyclone separation process, the palm nuts are sent to the crushing unit where they are dried and cracked, whilst the PPF are sent to the boiler. The cracked shells without the kernel or seeds are called palm kernel shells (PKS). PKS can be described as the hard endocarps surrounding the palm kernels or seeds which are obtained after the residual nuts from the screw press are mechanically crashed to extract the seeds or kernels.

Presently due to increase in palm oil production, the world’s annual generation of PKS is estimated at 11.1 million tonnes as compared to 2.52 million tonnes and

4.3 million tonnes in 2004 and 2006, respectively (MPOB 2012). Because PKS possess high solid content (with a calorific value of about 22.14 MJ/kg), low sul­phur (about 0.09% dry weight) and low ash (about 3% dry weight) contents, they are often used as fuel for the power plants in the palm oil industry (Yusoff 2006). However, nearly 40% of these wastes are utilised by the oil mill for power genera­tion; the rest are dumped in open space in the crushing unit and sometimes inciner­ated in an uncontrolled manner within the industry contributing to significant environmental pollution.

The proximate and ultimate compositional analyses carried out by Sukiran (2008) show that PKS contains about 30% moisture content by wet weight, 73.74% volatile matter, 18.37% fixed carbon, 2.21% ash, 53.78% carbon, 7.20% hydrogen and 36.30% oxygen. The inorganic composition of PKS expressed in % ash (mois­ture free) includes 2.96% Si2O, 0.60% K2O, 0.48% CaO, 0.83% MgO, 0.08% Fe2O3, 0.24% Al2O3 and 0.59% P2O5 (Chaiyaomporn and Chavalparit 2010). The fuel den­sity of PKS is about 1,430 kg/m3 (Mohammed et al. 2012).

The holocellulose compositions of PKS are about 20.8% cellulose and 22.7% hemicellulose with lignin content of about 50.7% (Saka 2005).