Kinetic studies on combustion of microalgae under different oxygen concentrations

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.%) in the heating rates 20°C-min^-1 on the combustion processes of Chlorella vulgaris had been studied. The results indicated that the combustion processes of Chlorella vulgaris could be divided into three stages. The oxygen concentrations had important effects on the main combustion processes of Chlorella 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 Chlorella vulgaris combustion was 25-35 vol.%.