Simultaneous production of biochar and thermal energy using palm oil residual biomass as feedstock in an auto-thermal prototype reactor

• Published in: Journal of cleaner production 2020-09, Vol.266, p.121804, Article 121804
• Main Authors: Heredia Salgado, Mario A., Coba S, Jonathan A., Tarelho, Luís A.C.
• Format: Article
• Language: English
• Subjects: Agro-residues; Auger reactor; Biochar; Kernel shell; Palm oil; Pyrolysis
• ISSN: 0959-6526; 1879-1786
• DOI: 10.1016/j.jclepro.2020.121804

In developing countries, the technology used for biomass carbonization requires major retrofits for an efficient conversion of the residual biomass produced in the palm oil mills into biochar. This study analyzes a prototype of a small and modular auger reactor (P-SMART) that uses untreated kernel shells as feedstock to produce biochar and thermal energy. The P-SMART does not require inert gases during operation, neither diesel nor natural gas for the initial heating process. This study shows that the carbonization process can be driven by the energy generated during pyrolysis gas combustion (auto-thermal conditions) from a biomass load capacity of 30 kg/h. During the auto-thermal operation, the thermal energy generated by pyrolysis gas combustion is higher than that required by the carbonization process. The carbon monoxide concentration in the flue gas during the auto-thermal operation was 197 mg/Nm3 which is lower than the European eco-design requirement of 500 mg/Nm3 (both measured at 11% vol. O2, dry gas). The biochars produced during auto-thermal operation have a macro-porous structure with a pore radius that ranges from 0.42 to 12.48 μm. The carbon content and the molar H/Corg and O/Corg ratio of the analyzed biochars are in accordance with the European guidelines for the sustainable production of biochar of less than 0.7 and 0.4 respectively. Moreover, relevant soil nutrients were observed in the KS ash, namely: silica (30 wt%), potassium (8.2 wt%) and phosphorous (3 wt%). •No external sources as diesel or natural gas were used for heating or operation.•No inert gases were used to promote an inert atmosphere or drag the pyrolytic gas.•The carbonization process is autothermal for biomass loads over 30 kg/h.•The characteristics of the biochars produced are within the European guidelines.•The kernel shell ash is rich in silica, potassium, and phosphorous.