Experimental and Computational Investigation of Algae Biomass Gasification in a Self-Circulating Fluidized Bed Reactor: Effects of Equivalence Ratio on Syngas Yield, Carbon Conversion Efficiency, and Energy Potential

Algae have emerged as a promising renewable bioresource for sustainable energy production due to their high photosynthetic efficiency, rapid growth rate, and ability to thrive in non-arable lands. Unlike conventional biomass sources, microalgae possess higher volatile matter content and lower lignin composition, making them an ideal candidate for thermochemical conversion. This study focuses on the design, fabrication, and experimental analysis of a self-circulating fluidized bed gasifier using dried microalgae biomass as the primary feedstock. The research evaluates syngas composition, gas yield, heating value, carbon conversion efficiency, and cold gas thermal efficiency under three equivalence ratios (ER) of 0.3, 0.4, and 0.5. Experimental trials were conducted with Spirulina platensis and Chlorella vulgaris as feedstocks, which were pre-treated through dewatering, drying, and size reduction (particle size ~ 500 µm) before gasification. Hydrogen yield was highest at 11.8% with 0.3 ER value while 19.6% carbon monoxide concentration was observed at 0.4 ER value. The amount of methane changed from 3.2–4.5% with elevated ER values, showing a decline with higher ER values owing to a rise in oxidation reactions. The optimum ER was observed in the ranges of ER = 0.5 for the maximum carbon conversion efficiency (CCE) of 92.8%. And, ER = 0.4 for the maximum cold gas efficiency (CGE) of 71.4%. The syngas heating value ranged from 4.5 MJ/Nm³ to 5.2 MJ/Nm³, influenced by the H₂ and CO concentrations. Computational Fluid Dynamics (CFD) simulations were conducted using the ANSYS Fluent software, employing a k-ε turbulence model and species transport equations to validate experimental results. The simulated gas composition showed deviations within ± 7.5%, confirming the accuracy of the experimental setup. Despite challenges such as high moisture retention and ash sintering, the study demonstrates that algae-based biomass gasification can serve as an efficient and scalable bioenergy solution. Future research will focus on catalytic gasification, co-gasification with lignocellulosic biomass, and techno-economic feasibility assessments to enhance the commercial viability of algae-derived syngas for power generation and hydrogen production.