An advanced model was developed in Aspen Plus to simulate and optimize hydrogen-rich syngas production from a PP30-scale downdraft biomass gasifier integrated with Water-Gas-Shift (WGS) and pressure-swing adsorption (PSA). The adiabatic model combines equilibrium RGibbs blocks with corrective RStoic char–gas reactions and was validated against four independent experiments, predicting H₂ and CO within ± 1 % error. Sensitivity analysis identified an optimum “window” of T_pyrol at700 °C, T_gas at 900 °C, and equivalence ratio of 0.25, which double H₂ molar fraction to 40 wt % after a two-stage WGS system (S/C = 3, T_LT = 200 °C). Replacing air with pure O₂ as the gasifying agent effectively eliminates N₂ dilution, increasing H₂ concentration to 59 wt % raising the LHV from 4.5 to 6.7 MJ Nm⁻³. A dual-column, four-step PSA (P_ads = 9.8 bar) delivers 98 % purity at 56 % recovery, while halving the purge stream improves recovery to 64 % with negligible purity loss. The combined interventions provide a realistic pathway for decentralized, biomass-derived clean hydrogen production, which competes with electrolysis on energy density and cleanup requirements. Future work will automate methane correction within Aspen and extend the flowsheet for full techno-economic assessment.