Parametric characterisation of air gasification of chlorella vulgaris biomass

Abstract

The gasification of green algae Chlorella vulgaris in air was investigated using both a thermogravimetric analyzer (TGA) and a bench scale horizontal axis quartz tube reactor (HQR). The full range of solid state kinetic models produced best fits with TGA results varied for the 5 subzones of conversion vs. temperature, with the nucleation and nuclei growth ‘A2’ followed by ‘A3’ or contracting volume models producing close matches for T ≤ 367 °C, zero order model between 358 and 468 °C, and contracting surface models for T ≥ 458 °C, each model yielding their set of apparent activation energy (E 0.04 s¯¹) corresponding to rate constants in the range 0.001 to 0.005 s¯¹. The HQR was used to investigate the effects of microalgal biomass loading, temperature and equivalence ratio (ER) on CnHm/CO/H₂ gas yield and composition, carbon conversion efficiency (CCE) and lower heating value (LHV) of syngas under air gasification conditions. Increasing microalgal biomass loading from 1 to 2 g led to a decrease in H2 content (24.2 to 19.5 vol. %) in the gases. An optimal temperature of 950 °C resulted in the highest H₂, CO and CH₄ yields at 2.9, 22.8 and 10.1 wt. % of biomass from a maximum gas yield of 76.1 wt. %, and highest H₂/CO ratio (1.75) and CCE of 56.3 %. The effect of ER was measured in two phases 0.1 to 0.26 and 0.26 to 35, respectively. During the first phase, the positive effect of ER performed a major part compared to second phase, so as the H₂ content, H₂ yield, CCE and LHV were increased