Oil palm shell

The shell produced from cracking the palm seeds is known as oil palm shell. It is a hard endocarp which surrounds the palm seeds or kernels. It is obtained when the residual nuts from the screw press are crushed mechanically to extract the kernels or seeds. The oil palm shell is a lignocellulosic biomass. Lignocellulose materials have a massive potential as a feedstock to produce electrical power, heat and fuels (Hoekman et al., 2011; Liu et al., 2013). Because of the rapid increase in the oil palm production, the world’s annual generation of oil palm shell also has increased up to 11.1 million tons. Previously its amount was 2.52 and 4.3 million tons in 2004 and 2006 respectively (Lee and Ofori-Boateng, 2013).
Oil palm shell is characterized by proximate analysis and ultimate analysis (Unz, et al., 2010). Meanwhile, these properties may vary with changing the environment and time (Christian, et al., 2006; Lewandowski and Heinz, 2003; Pordesimo, et al., 2005).
The ultimate analysis, proximate analysis, chemical composition, inorganic composition and HHV of oil palm shell (Abnisa et al., 2013; Abnisa et al., 2011; Abubakar and Ani, 2013; Arami-Niya et al., 2010; Asadieraghi and Wan Daud, 2014; Asadullah et al., 2013; Aziz et al., 2012; Aziz et al., 2011; Basiron and Weng, 2004; Chaiyaomporn and Chavalparit, 2010; Hasegawa, et al., 2004; Hussain et al., 2006; Jamaluddin et al., 2013; Kean et al., 2013; Kongab et al., 2013; Lee and Ofori-Boateng, 2013; Mohammed et al., 2012; Mohammed et al., 2011; Özçimen; Salema et al., 2013; Singh, 1999; Uemura et al., 2010; Uemura et al., 2011; Yang et al., 2004; Yusoff, 2006) are listed and compared to those of EFB (Asadieraghi and Wan Daud, 2014; Butler et al., 2011; Chew and Bhatia, 2008; Jamari and Howse, 2012; Lim et al., 2014; Minowa et al., 1998; Nhuchhen and Abdul Salam, 2012; Tye, et al., 2011; Yang, et al., 2004), oil palm trunk (Kelly-Yong, et al., 2007; Varman and Saka, 2011; Yuliansyah et al., 2010), oil palm fronds (Wan Rosli et al., 2004; Yuliansyah, et al., 2010) and oil palm fibers (Asadieraghi and Wan Daud, 2014; Goh, et al., 2010; Luangkiattikhun et al., 2008; Mazaheri et al., 2010; Tye, et al., 2011; Werther et al., 2000; Yang, et al., 2004) in Table 2.2.
Proximate analysis incorporates the quantifiable determination of FC, VM, ash and moisture content (Khan, et al., 2009). The main purpose of proximate analysis is to determine the energy content of biomass or fuel by finding the ratio of combustible substances (FC and VM) to noncombustible constituents (ash and moisture content). On the other hand, an ultimate analysis defines the elemental composition in terms of hydrogen, carbon, nitrogen, oxygen and sulphur contents (Khan, et al., 2009). The ultimate analysis aims to determine the composition and quantity of the gas emitted during combustion, as well as the amount of oxygen needed for burning of biomass or fuels (Chang, 2014).
As shown in Table 2.2, the oil palm shell contains a higher amount of VM, about 66-78 %, which reveals its ease of ignition (Omar et al., 2011). Although, it is less than that of oil palm fronds and trunks. The presence of FC in a large quantity, 13-23 %, points out that a significant amount of heat generation from burning the oil palm shell can be obtained compared to other wastes of the oil palm industry. It also can be noticed the amount of ash present in the oil palm shell is in a small quantity. The oil palm shell has a higher FC to VM ratio and a lower moisture to ash content ratio. This heightens the ratio of combustible to the noncombustible substances resulting a higher HHV of oil palm shell (15.9-22.14 MJ/kg). The HHV of the oil palm shell is comparable to that of hardwood (17.63-20.81 MJ/kg) and softwood (19.66-20.63MJ/kg) (Garcia-Perez et al., 2007; Telmo and Lousada, 2011).