Sustainable energy recovery via co-pyrolysis of orange peels and agro-wastes: Generation of hydrogen-rich syngas, bio-oil, and biochar

Abstract

This study explores the pyrolysis and co-pyrolysis of orange peels alongside typical agricultural biomass residues, such as peanut shells and coffee grounds. Based on their equal weight percentage, the cited samples were combined with orange peels in a 50:50 wt% ratio. Two technological configurations were employed: a batch setup at the laboratory scale and a semi-batch setup at the industrial scale. As the experiments transitioned from batch to semi-batch configurations, the yield of volatile byproducts, including bio-oil and biogas, showed a significant increase, peaking at 79 % for the orange-peanuts mixture. The semi-batch setup demonstrated enhanced conversion efficiency for both condensable and non-condensable fractions. As a result, the semi-batch configuration was prioritized because of its potential to produce high-quality biogas. As regards to pure biomass pyrolysis, orange peels yielded the largest gas fraction (38.83 wt%) due to their high volatile matter content. The results of co-pyrolysis further revealed that the addition of orange peels to the other residues significantly influenced the thermochemical behavior, leading to an increased biogas yield. Specifically, gas fractions reached 48.90 wt% for the orange-coffee blend and 54.20 wt% for the orange-peanuts combination. In particular, the orange peels incorporation generated innovative blends that reached maximal hydrogen production earlier than individual biomass processing. In terms of bio-oil composition, the established mixtures led to a higher hydrocarbons concentration. The co-pyrolysis process, notably, improves the viable conversion of orange peels and specific lignocellulosic biomass waste, providing thus a distinctive alternative to their processing in accordance with the circular economy and sustainable waste treatment concepts. This approach can serve as a viable solution to support energy resilience and the socio-economic development of rural communities in developing countries.