Development of carbonized rice husks briquettes: Synergy between emissions, combustion, kinetics and thermodynamic characteristics

Vianney Andrew Yiga, Andrew Nuwamanya, Agatha Birungi, Michael Lubwama, Harriet Nalubega Lubwama, Development of carbonized rice husks briquettes: Synergy between emissions, combustion, kinetics and thermodynamic characteristics, Energy Reports, Volume 9, 2023, Pages 5977-5991, ISSN 2352-4847, https://doi.org/10.1016/j.egyr.2023.05.066. (https://www.sciencedirect.com/science/article/pii/S2352484723008090) 

Briquettes uptake continues to be low, despite their ability to offset the negative impacts caused by firewood/charcoal. Possible reason for this is lack of literature towards key parameters of the developed briquettes. In the current study, emissions, combustion, kinetics and thermodynamic characteristics of rice husks agricultural residue carbonized briquettes were obtained. The water boiling test and emissions monitoring system for CO, CO2 and PM2.5 were used to determine fuel and energy consumption, thermal efficiency and emissions while thermogravimetric analysis was utilized in obtaining combustion, kinetic and thermodynamic parameters. The activation energy was determined by employing four different model-free methods. Drop strength and particle density of the briquettes were 67.8% and 548.15kg/m3, respectively. Briquettes‘ moisture, volatile matter, ash content and fixed carbon were 7.2%, 16.6%, 47.4% and 28.8% respectively. Average activation energy attained by the developed briquettes by Kissinger–Akahira–Sunose, Ozawa–Flynn–Wall, Starink and Tang methods were 78.3kJ/mol, 83.3kJ/mol, 78.7kJ/mol and 75.0kJ/mol, respectively. Low energy barrier (5.2kJ/mol) between activation energy and enthalpy changes indicated that initiation occurs easily. The obtained thermodynamic parameters indicated that the thermal degradation process was endothermic in nature. High energetic densities (10,688.9MJ/m3) and Fuel Value Indices (255.5MJ/m3⋅%) were attributable to the higher heating value of the developed briquettes (19.5MJ/kg). Keywords: Briquettes; Combustion; Emissions; Kinetics; Pyrolysis; Rice husks; TGA