Composite bio-briquettes from bagasse and cotton stalks: Chemical, physico-mechanical and emissions analysis

Biomass selection and characterization are critical in producing briquettes of high quality. The study investigated properties that influence performance of composite carbonized briquettes. Samples were made from cotton stalks, bagasse, bentonite clay, and molasses in proportions of 58.2 wt%, 31.7 wt%, 9.0 wt%, and 1.2 wt%, respectively. Laboratory tests were undertaken using elemental and thermogravimetric analyzers to determine ultimate and proximate analysis of residues and briquettes. A Fourier Transform Infrared spectrophotometer was used to obtain the structural composition of residues and scanning electron microscope to assess the morphology of briquettes. Water boiling test was undertaken following the ISO 19867-1:2018 standard to determine thermal efficiency and emissions of CO and PM2.5. Compounds in the ash were determined using an X-Ray Fluorescence spectrometer. Results showed volatile matter of 83.0, 80.8, and 24.5 wt% for cotton stalks, bagasse, and briquettes, respectively. Fixed carbon of residues was relatively low with cotton stalks at 14.0 wt% and bagasse at 15.5 wt%. The predominant structure was cellulose with 42.7% for cotton stalks and 68.8% for bagasse. Morphological analysis showed a porous heterogeneous structure having non uniform open pores with dimensions between 2 and 20. A high thermal efficiency of 86.4% and low burning rate of 2.66 g/min was registered. The emission rate was 0.14 g/min for CO and 13.29 mg/min for PM2.5. The major compounds found in ash were SiO2 at 51.6 wt% and Al2O3 at 20.5 wt%. The briquettes satisfied the ISO and WHO standards required for cooking and water heating applications using cookstoves.