Optimization of Briquetting Conditions for Groundnut Shells and Maize Stalks Using Response Surface Methodology

Abstract

The quality attributes of briquettes depend on feedstock characteristics and process conditions. This study aimed at optimizing compressive strength and specific energy requirement using Response Surface Methodology (RSM). An RSM based on Central Composite Design (CCD), comprising four factorial, four axial, and six center points, was used to generate different sets of experimental conditions. Each condition was replicated three times, yielding a total of 42 experimental runs. Briquetting temperature (40–110 °C) and compression pressure (34–204 MPa) were treated as independent variables in the response modeling. The model terms included constant, linear, interaction, and quadratic components. The optimum briquetting temperature and pressure were 110 °C and 123 MPa for raw groundnut shells and 97 °C and 108 MPa for raw maize stalks. The corresponding optimum specific energy requirement and compressive strength were 22.5 kJ/kg and 21.4 MPa for groundnut shells, and 11.0 kJ/kg and 42.4 MPa for maize stalks. Torrefaction increased the specific energy requirement for briquetting by 42.2% for groundnut shells and 31.8% for maize stalks. Conversely, torrefaction reduced the compressive strength by 74.8% for groundnut shell briquettes and 18.6% for maize stalk briquettes.