Carbon dioxide torrefaction of oil palm empty fruit bunches pellets: characterisation and optimisation by response surfa
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ORIGINAL ARTICLE
Carbon dioxide torrefaction of oil palm empty fruit bunches pellets: characterisation and optimisation by response surface methodology Bemgba B. Nyakuma 1 & Syie L. Wong 1 & Hasan M. Faizal 2 & Hambali U. Hambali 1,3 & Olagoke Oladokun 1 & Tuan Amran T. Abdullah 1,3 Received: 5 July 2020 / Revised: 1 October 2020 / Accepted: 9 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The carbon dioxide (CO2) torrefaction of oil palm empty fruit bunch (OPEFB) pellets was investigated at various temperatures from 250 to 300 °C and residence times from 15 to 60 minutes. The objective was to investigate the effects of CO2 torrefaction on the yield and characteristics of the torrefied products. The optimal conditions for maximum mass yield (MY) of CO2 torrefaction were also examined by response surface methodology (RSM) using full factorial design. Results revealed that temperature and time significantly influenced the mass (MY), liquid (LY) and gas (GY) yields. The MY and energy yield (EY) decreased with increasing severity of torrefaction, whereas the LY, GY, energy density (DE) and higher heating value (HHV) increased during the process. Characterisation revealed substantial improvements in the microstructure, pH, hydrophobicity and grindability of the torrefied pellets compared with the raw pellets. The thermal ignition and degradation characteristics of the OPEFB pellets were also significantly transformed after torrefaction. The liquid torrefaction products contained an acidic, turbid and pungent mixture of water and organic compounds. RSM optimisation revealed the optimal conditions: temperature of 275 °C and residence time of 35 minutes with the predicted MY of 50.54%, mass loss of ML = 49.46% and HHV = 24.47 MJ/kg. The findings revealed that CO2 torrefaction is a practical approach to clean energy recovery. Keywords Carbon dioxide . Torrefaction . Oil palm . Empty fruit bunch . Pellets . Optimisation
Nomenclature AAEM AC AIM ANOVA CO2 CPKO CPO DE EY
Alkali and alkali earth metals Ash content Agency for innovation in Malaysia Analysis of variance Carbon dioxide Crude palm kernel oil Crude palm oil Energy density Energy yield
* Bemgba B. Nyakuma [email protected] 1
School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia
2
School of Mechanical Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia
3
Centre of Hydrogen Energy, Institute of Future Energy, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia
FBT FC GNI GY HHV KFT LY MC ML MY O2 OOC OPEFB OPEFB pellets OPT OPW PKS RM RSM SEM SF
Fixed bed tubular Fixed carbon Gross national income Gas yield Higher heating value Karl Fischer titration Liquid yield moisture content Mass loss (%) Mass yield (%) Oxygen Optimal operating conditions Oil palm empty fruit bunch Oil palm empty fruit bunch pellets Oil palm trunks Oil palm wastes Palm kernel shells Residual mass (%) Response surface method
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