Thermodynamic Analysis of Microalgae–Plastic Co-Gasification: Impacts on Syngas Composition and Combustion Potential

Abstract This study addresses the challenge of high ash content in microalgae, which negatively affects gasification efficiency and reactor performance, by blending microalgae with plastic waste. This approach mitigates the ash-related issues while leveraging the benefits of plastic's low ash content, high volatile matter, and rich hydrogen content during gasification. A blend of microalgae (Nannochloropsis oculata) and polypropylene is proposed, and the gasification reaction is analyzed using an equilibrium model. The model evaluates the effects of blending ratio, steam-to-feedstock ratio, temperature, and pressure on gas composition. Key performance indicators are syngas composition, syngas combustion quality, and overall exergy efficiency of the process. Results show that the H2 yield increased by 12.5% with a higher steam-to-feedstock ratio (0.5–2.5) and by 3.89% when biomass content is reduced from 100% to 80%. The H2/CO ratio rose 210.1% at a higher steam-to-feedstock ratio and 100% biomass, while heating value and exergy efficiency improved by 8.68% and 12.08%, respectively, at lower steam-to-feedstock ratio and 80% biomass. Maximum H2 yield (60.8 mol%) was achieved at 900 °C, and highest H2/CO ratio (2.73) at 750 °C. Peak heating value (11.69 MJ/m3) and efficiency (58.13%) occurred at 1000 °C and 80% biomass. At 1 atm gasification pressure, H2 yield hit 60.03 mol% with 49.73% efficiency, while 20 atm gasification pressure increased the H2/CO ratio by 12.24% and the heating value by 28.89%.