Co-gasification of Turkish lignite and three plastic wastes in a lab-scale updraft gasifier: case-study equilibrium (gibbs free energy), openfoam CFD, analytical validation, and experimental-range benchmarking

• Geometry–specific downdraft reactor (Ø160 body, Ø80 throat, three air rings, 4×Ø15 mm nozzles per ring) tested for two lignites (Çan, Göynük) and three plastics (LDPE, PP, PET), both individually and in co–gasification. • Gibbs free–energy minnimization (GEM) applied for equilibrium compositions; OpenFOAM CFD simulations provide spatially resolved flow, reaction, and radiation fields. • Analytical 1D downdraft model adds closed–form validation, enabling a triple check (GEM ↔ CFD ↔ 1D). • Co–gasification with plastics increases H 2 and CH 4 yields and reduces CO 2 ; PET shows milder H 2 enhancement due to oxygen content. • Peak temperature zone identified above ring–2; reduction zone at the throat shows CO increase and tar cracking. • Mesh independence and uncertainty analysis included for SCI–Q1 level reporting. This study investigates the co-gasification of lignite and plastic waste with the aim of producing hydrogen-rich syngas while simultaneously addressing waste utilization challenges. A comparative modeling framework was developed by integrating one-dimensional analytical calculations (1D), Gibbs free energy minimization (GEM), and computational fluid dynamics (CFD) using OpenFOAM. The results demonstrated that blending plastics with lignite enhanced hydrogen yield and syngas quality, with a 20 % plastic fraction identified as the optimum operating condition. The authors validate the modeling framework using literature-based experimental data, with deviations normally within ±10 %. The results demonstrate not just the technological viability of co-gasification, but also their real-world implications for sustainable hydrogen production and waste-to-energy applications and represent a cleaner alternative to straight combustion.