Thermogravimetric and kinetic analyses of the Skeletonema costatum microalgae combustion using the fitting method

Abstract

This work was intended to understand the potential of Skeletonema costatum (S. costatum) microalgae being the solid biofuel feedstock by studying its combustion behavior under a thermogravimetric analyzer (TGA). The following parameters were used during the experiment: about 5 mg of weighed sample was put into a ceramic crucible; the atmospheric air of 100 ml/min was flowed to the chamber to ensure sufficient combustion air; heating was escalated with a rate of 10 °C/min, and combustion was performed at a temperature range from 30 °C to 1200 °C. The results showed that the combustion process of S. costatum microalgae could be divided into four stages of decomposition, including the evaporation stage of moisture content from a temperature of 31.68 °C to 150.93 °C, the devolatilization stage from a 150.93 °C to 505.053 °C, the stage of char combustion from a 505.053 °C to 1018.15 °C and the final stage of ash decomposition from 1018.15 °C to 1200 °C. The kinetic parameters were calculated in the 1st, 2nd, and 3rd stages based on the fitting model of the Coats-Redfern method by selecting reaction mechanisms. The activation energy values for 1st, 2nd, and 3rd stages were 71.18; 39.49, and 56.92 kJ/mol, respectively, and correlation coefficients (R2) of 0.959; 0.988, and 0.978, respectively in the Chemical Reaction Order models.