Chemical looping gasification of Chlorella: Parametric optimization, reaction mechanisms, and nitrogen-containing pollutants emission

Abstract

Chemical looping gasification (CLG) can realize the effective utilization of microalgae’s energy. In this work, the CLG of Chlorella based on NiFe2O4 oxygen carrier (OC) was studied. Optimal parameters of Chlorella CLG were obtained as temperature at 800 °C, OC to biomass ratio (O/B) at 1.0, respectively. Under such conditions, the gasification efficiency could reach 84.67%. After 5 redox cycles, the gasification efficiency could still maintain higher than 70.49%, indicating the good stability and activity of NiFe2O4. The comparative TG-FTIR-DSC analyses were conducted for CLG and control group. With the detailed investigations on the weight loss, products emissions and heat transfer, the in-depth mechanisms of CLG were revealed. Additionally, the variation of activation energy (E) was investigated by Flynn-Wall-Ozawa method. In low-temperature range, CLG had higher E due to energy absorption by OC. But in elevated temperature range, OC could promote gasification and tar cracking, leading to the lower E and more fuel gases production. Moreover, CLG showed obvious suppression of nitrogen-containing pollutants emission due to the catalytic effects of NiFe2O4. This study performed a fundamental understanding of the CLG, and it is hoped to provide a theoretical basics for the clean and efficient utilization of algal biomass.