Biochar production and quality optimization using response surface methodology technique

Abstract

The dependency on fossil fuels can be reduced by the use of renewable energy sources like biomass and it can make a remarkable contribution to the reduction of CO2 emissions and as a result reducing the carbon footprint hence eliminating the greenhouse gas effect. Biomass materials that go to waste can be recovered through the pyrolysis process in order to produce biochar which can be used as a source of energy for cooking. The aim of this study was to carry out optimization of biochar production and quality using the Response Surface Methodology technique. The parameters varied were feedstock moisture content (FMC) (10%, 15% and 20%), pyrolysis residence time (PRT) (in minutes) 90, 135 and 180 and chimney inclination angle (CIA) (30o, 45o and 60o). An experimental insulated metallic carbonization kiln (1 m high and 0.5 m diameter) was developed and used. Response Surface Methodology technique by using Box-Behnken Design was used to develop a mathematical equation to predict the production and quality of the biochar with respect to varied parameters which was later optimized to determine the optimal conditions for biochar production and quality. The biochar quality was based on its moisture content (MC), volatile matter (VM), ash content (AC), fixed carbon (FC) and pH. The combined optimal conditions were 10% feedstock moisture content, 126.93 min pyrolysis residence time and 30o chimney inclination angle resulting to production of 44.35%, MC = 3.82%, VM = 23.52%, AC = 2.94%, FC = 67.89% and pH = 9.28. The mathematical equation developed had composite desirability (CD) of 0.9490 at a p-value≤0.05 which made it viable. These research findings are of importance since optimization reduces the wastage of resources resulting into increase in the efficiency of the pyrolysis system. Keywords: Renewable Energy, Pyrolysis, Biochar, Optimization, Response Surface Methodology