Co-gasification of pretreated palm kernel shell and Mukah Balingian coal / Razi Ahmad

Abundant of biomass in Malaysia such as palm waste has a great potential as renewable energy resource. Utilization of low rank coal offers a good prospective to replace high rank coal in gasification. However, there are restriction in individual gasification and limitation of biomass and low rank coal due to poor characteristics. Therefore, samples pretreatment prior to co-gasification are desirable to overcome the problems. In this research, co-gasification of palm kernel shell (PKS) and Mukah Balingian (MB) low rank coal was carried out in a fixed bed reactor with steam as co-gasification agent. In the first objective, PKS and MB were subjected to two different pretreatments i.e. torrefaction and microwave irradiation. The results showed that the properties of both pretreated PKS and MB were improved, where the mass and energy yield, volatile matter, moisture and oxygen content reduced, while the energy density, calorific value, fixed carbon and carbon content increased with increasing pretreatment temperature and microwave power. Torrefied PKS (PKSTo) at 270 °C, preheated MB (MBPr) at 250 °C and microwave irradiated PKS (PKSMi) and MB (MBMi) at 450 W demonstrated a good quality feedstock to be used in co-gasification. Moreover, at preferred parameters, the kinetic analysis displays low activation energy of 96.11 and 119.6 kJ/mol for PKSTo and MBPr, respectively. In the second objective, the co-gasification parameters were optimized to maximize the gas production using response surface methodology (RSM). The results verified that the effect of the independent variables, i.e. gasification temperature, biomass blending ratio and steam flow rate on response variables i.e. gas, tar and char yield were significant due to p-value of less than 0.05. The optimum conditions for gasification temperature, biomass blending ratio and steam flow rate were at 767 °C, 52 % and 54 ml/min, correspondingly. These optimum conditions produced maximum gas yield of 67.3 % with minimum char and tar yield of 20.8 % and 11.9 %, respectively. In the third objective, the comparison between co-gasification of both untreated (PKSUn/MBUn), PKSTo and untreated MB (PKSTo/MBUn) and pretreated (PKSTo/MBPr) blending were evaluated on product yields and gases composition via optimize conditions. The outcomes revealed that, co-gasification of both pretreated samples produced high gas yield due to characteristic enhancement of pretreated samples. The PKSTo/MBPr sample improved the H2 production by 63.9 % than PKSUn/MBUn at 45 min reaction time. High H2 production is in accordance with the high quantity of carbon content in PKSTo/MBPr compared to the PKSUn/MBUn. In the fourth objective, the optimization parameters of catalytic co-gasification was explored. The gasification temperature of 735 °C, catalyst ratio of 12 % and steam flow rate of 51 ml/min produced maximum gas yield of 67.5 %. The catalytic co-gasification shows minor enhancement of 4 % on H2 composition. As a conclusion, the pretreatment approaches on PKS and MB prior to co-gasification is a promising method in enhancing product distribution, specifically on the hydrogen production. Accordingly, the pretreatment on both biomass and low rank coal prior to co-gasification without the catalyst addition that contributed to positive synergy on gas yield and hydrogen production was a novelty and new contribution in this study.