Optimization of the briquette production process from the composition of bagasse and walnut shell using the response surface methodology (RSM) and its calorific value

Densification of biomass materials such as briquette improves the management properties of materials for transportation, storage, and so on. This study aimed to determine the optimal conditions of the briquette production process using a hydraulic press from the combination of bagasse and walnut shell using response surface methodology. The effects of independent variables including bagasse particle size (PS), process temperature (PT), bagasse moisture content (MC), and the composition ratio percentage of the walnut shell to bagasse (CR) were evaluated at three levels on the response variables of the density and tensile strength. The calorific value of the briquette was determined through validated linear and nonlinear equations of the high heat value using the proximate analysis of volatiles, fixed carbon, and ash. The results showed that by decreasing the moisture content of bagasse particles, the density and tensile strength of the briquette increased. Adding walnut shell particles to the briquette produced with the size of fine particles reduces tensile strength. The briquette production significantly reduced the percentage of volatile materials relative to their biomass and increased the percentage of fixed carbon. The calorific value of the raw material sample relative to the briquette produced increased from 16 to 22 MJ/kg. The optimal values of the density and tensile strength of briquettes were equal to 867.847 kg/m3 and 1.356 MPa, respectively at the CR of 5%, PS less than 1.18 mm, MC content of 7%, and PT of 360 °C. At this condition, the calorific value of 22 MJ/kg was obtained.