4E Assessment and Optimization of a Biomass Gasification Combined Cycle System Featuring a Novel Parameter

Biomass has gained attention as a promising alternative energy source due to its environmental and economic benefits. This study presents a comprehensive 4E analysis—covering energy, exergy, economic, and environmental aspects—of a biomass-based gas turbine combined cycle system. To fill the gap in evaluating the quality of syngas produced from different biomass feedstocks, a novel metric called the Syngas Quality Index (SQI) is introduced. Defined as the ratio of reducing gases (H₂ + CO) to non-reducing gases (CO₂ + CH₄), SQI serves as a practical and comparative indicator for assessing syngas effectiveness. This index helps identify the most suitable biomass type to maximize syngas quality and overall system performance. Multi-objective optimization was conducted using heuristic algorithms within a Python-based framework to enhance efficiency and reduce emissions. The model was validated across various gasifier types and operating conditions, and response surface methodology confirmed high prediction accuracy. The system achieved energy and exergy efficiencies of 36.6% and 19.03%, respectively, with the highest exergy destruction occurring in the gasifier. Hardwood biomass produced the best syngas composition (SQI = 2.64), and the most efficient optimization results were obtained with minimal CO₂ emissions. Overall, the proposed approach provides a practical decision-making tool for selecting optimal biomass feedstocks and improving the design of sustainable energy systems.