Statistically optimized charcoal production from Prosopis juliflora for use as alternative fuel in cement factories

Abstract

Prosopis juliflora is an invasive species, which is spreading at an alarming rate in Ethiopia. Cement factories in the country are using fossil fuels contributing to the global greenhouse gas emission. The present study has aimed at utilizing Prosopis juliflora charcoal as a carbon-neutral alternative fuel for cement factories with the objectives of reducing CO2 emission and controlling the spread of the plant to arable areas. The study focused on optimizing the charcoal preparation conditions using central composite design response surface methodology. The independent process variables were carbonization temperature and time, which were investigated in the temperature and time ranges of 300–600 °C and 60–180 min, respectively. The response variables were charcoal yield, calorific value, and volatile matter content. Quadratic model equations were selected for all responses based on analysis of variance. The respective regression analyses have demonstrated that the model equations can be used to predict the charcoal yield, calorific value, and volatile matter content in the investigated range with 99.85%, 99.9%, and 99.9% variability, respectively. For the predicted optimal carbonization condition, charcoal yield, calorific value, and volatile matter content were found to be 47.52%, 24.43 MJ/kg, and 56.58%, respectively. The charcoal prepared at the optimized condition was subjected for elemental and proximate analysis and compared with other alternative fuels that are in use in the industry. Results show that the charcoal has better desirable properties such as less moisture and volatile matter and higher fixed carbon content and calorific value.