Parametric Characterization of Air Gasification of Chlorella vulgaris Biomass

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 five 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 degrees C, a zero-order model between 358 and 468 degrees C, and contracting surface models for T >= 458 degrees C; each model yielding their set of apparent activation energy (E < 41 kJ mol(-1)) and pre-exponential factors (A > 0.04 s(-1)) corresponding to rate constants in the range 0.001-0.005 s(-1). The HQR was used to investigate the effects of microalgal biomass loading, temperature, and equivalence ratio (ER) on CnHm/CO/H-2 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 H-2 content (24.2-19.5 vol %) in the gases. An optimal temperature of 950 degrees C resulted in the highest H-2, 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 H-2/CO ratio (1.75) and CCE of 56.3%. The effect of ER was measured in two phases 0.1-0.26 and 0.26-35, respectively. During the first phase, the positive effect of ER played a major part compared to second phase, so the H-2 content, H-2 yield, CCE, and LHV were increased.