Thermogravimetric analysis of microalgae combustion under different oxygen supply concentrations

Recently, studies of microalgae in China have increased a lot because of their obvious advantages over other biological fuels. In this paper, the combustion behavior of Chlorella vulgaris (a genus of unicellular green microalgae) was investigated in a thermogravimetric analyzer (TGA) from room temperature to 800 °C in O2/N2 atmospheres. The effects of different oxygen concentrations (20, 50, 60, 80 vol.%) and different heating rates (10, 20 and 40 °C min−1) on the combustion processes of C. vulgaris had been studied. The results indicated that the combustion processes of C. vulgaris could be divided into three stages. The oxygen concentrations and heating rates had important effects on the main combustion processes of C. vulgaris. The iso-conversional method involving Flynn–Wall–Ozawa (FWO) and the Kissinger–Akahira–Sunose (KAS) methods were used for the kinetic analysis of the main combustion process. The results indicated that, when the oxygen concentration varied from 20 to 80 vol.%, the value of activation energy increased respectively from 134.03 to 241.04 kJ mol−1 by using FWO method and from 134.53 to 242.33 kJ mol−1 by KAS method. Moreover, the optimal oxygen concentration for C. vulgaris combustion was 25–35 vol.%.