Biomass is an important new energy source because it is indigenous to every part of the world, inexpensive and renewable. Malaysia’s ability to produce and consistently export a large quantity of high quality palm oil has made it one of the major vegetable oil exporters in the world. By-products and waste from the palm oil mills are generated in significant amounts and mainly consist of empty fruit bunches, oil palm stone, oil palm shell, palm kernel cake and palm oil mill effluent. Some of this waste is currently used as fuel for boilers with low energy efficiency, as a soil conditioner, or in furniture making. There is a significant interest in recovering energy from oil palm shells and extensive research has been carried out in this area in other studies. However, research on energy production from oil palm stone (OPS) and palm kernel cake (PKC) is very limited. Waste from the oil palm industry, especially OPS and PKC, is abundant and could help to meet the energy demand if properly managed.
The main objective of this PhD study was to investigate the main characteristics of the thermo-chemical conversion of OPS and PKC. A series of combustion and pyrolysis tests were carried out using OPS and PKC as the raw materials in fixed bed and pilot-scale fluidised bed reactors. In addition, the FLIC modelling code was used to predict key parameters including theoretical solid temperature and gas composition, and to validate the experimental results from fixed bed combustion tests. Pelletisation was also carried out on PKC due to the loose nature and small size of the particles.
In the series of pyrolysis tests using OPS and PKC carried out in a fixed bed reactor, the effects of heating rate at the temperature of 700°C on the yields and properties of the pyrolysis products were investigated. The calorific values of the chars obtained from the OPS and PKC were approximately 28 MJ/kg. The properties of the chars produced were similar to bituminous coal in terms of their calorific value and carbon content. The pyrolysis liquids obtained from the OPS and PKC had calorific values of 21-38 MJ/kg. The pyrolysis liquids obtained from OPS were in the form of a homogeneous liquid, whilst that derived from PKC contained more than half as an aqueous fraction.
The results from the fixed bed combustion tests showed that the burning rates increased with an increase in the air flow rate. In addition, results from the FLIC code used to simulate the fixed bed combustion of the oil palm stone showed good agreement with the experimental data in terms of predicting the dynamic temperature profiles along the bed height and the flue gas composition. The effect of primary air flowrate and initial bed temperature were the main parameters investigated in the pilot-scale fluidised bed combustion tests. Both the internal temperature and the surface temperature were found to decrease as the primary air flowrate increased. In all tests CO emissions were less than 0.2%. The emissions of SO2 and HCl ranged from 0.02 ppm to 0.05 ppm, significantly below the levels set by legislation. Stable combustion was observed at a bed temperature of 950°C. The most abundant elements found in the ash were Al, Ca, Fe, K, Mg, Mn, P, S and Si.
The variables explored in the pelletisation of PKC were pressure, temperature, fuel moisture content and the effect of binders, which all had significant effects on density and tensile strength. The most favourable conditions for pellet production were found to be a pressure of 9338 psi/64.38 MPa, a temperature of 80-100°C and a fuel moisture content of 7.9%. These pellets had densities of 1184-1226 kg/m3 and tensile strengths of 930-1007 kPa. Adding small amounts of caustic soda (1.5-2.0wt %) to the PKC under these conditions increased the tensile strength to 3055 kPa, whereas starch additives were not found to be effective binders.
