Torrefaction of a mixture of animal waste and wood chips to produce sustainable bio coal: Kinetics and implications
No Thumbnail Available
Date
2024
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
Perennial energy demands globally and the need to cut on fossil fuel based emissions has paved way for alternative energy sources such as raw biomass. However, raw biomass has faced challenges as a source of energy due to its low energy density and high moisture content compared to fossil coal. Consequently, pre-treatment of raw biomass has been deemed necessary to improve the aforementioned properties. The torrefaction process has been identified as an effective means to produce a sustainable solid fuel in the form of bio-coal from raw biomass. It is a promising technology that can be used to achieve a closed carbon cycle and mitigate greenhouse gas emissions. Characterization of bio-coal has shown comparative physical and chemical properties to fossil coal which can be synthesized by subjecting biomass to high-temperature thermo-chemical processing Biomass derived bio coal has shown excellent potential as a partial replacement for coal to achieve a closed carbon cycle and mitigate carbon dioxide emissions. Several drawbacks are associated with using animal waste as the sole feedstock for torrefaction processes. These issues encompass suboptimal energy yield, elevated ash levels and subpar bio coal quality. To counter these drawbacks, in this study, torrefaction on wood waste, animal waste and a mixture of the aforementioned materials at a ratio of 50: 50 by mass was investigated. The process conditions investigated included temperature and residence time intervals of 200 C to 500 C and 30 to 120 minutes respectively. The results showed that a positive adjustment in temperature and residence time increased the higher heating value (HHV) primarily due to release of moisture and volatile material. Wood and animal waste higher heating values were increased to 23.7 MJ/kg and 19.87 MJ/kg respectively from 17.9 MJ/Kg and 16.7 MJ/Kg respectively. Wood had a higher heating value upon treatment as the decomposition of hemicellulose and cellulose enhanced the thermal stability, fixed carbon content and calorific value. Whereas, animal waste had the least incremental increase in heating value due to a high initial content of volatile substances. The study showed that to overcome the drawbacks of having a low mass yield and heating value for animal waste, mixing animal waste with wood chips was effective in producing a product with a higher mass yield and calorific value. The kinetic analysis indicated that wood torrefaction is easily achievable compared to that of animal or mixed torrefaction as it had the lowest activation energy.
Description
Keywords
Citation
Tshuma, N., Moyo, L.B., Danha, G., Mamvura, T., Geoffrey, S. and Artur, D., Torrefaction of a Mixture of Animal Waste and Wood Chips to Produce Sustainable Bio Coal: Kinetics and Implications. Available at SSRN 4727846.