The Effect of Steam-Oxygen Gasifying Medium on Syngas Upgrading for Nitrogen Reduction

In this work, a promising strategy to achieve nitrogen reduction in syngas produced in small-scale gasification systems is explored. It consists in the substitution of air with steam and oxygen as the gasification medium. The impact of gasifying medium composition on syngas quality was evaluated through both modeling and experimental approaches. A steady-state model of a biomass gasification plant, developed by DTU in Engineering Equation Solver (EES) was adapted to simulate different gasifying media with varying oxygen fractions. The model predictions were then validated against experimental results obtained with steam and oxygen as gasifying agents in an APL Char Pallet, a downdraft gasifier capable of processing 10-25 kg/h of various residual biomasses. The results demonstrated a significant reduction in nitrogen content alongside a concurrent increase in hydrogen concentration in the syngas. Upgrading syngas with low nitrogen content can be a promising carbon-negative alternative pathway for producing green hydrogen, compared to water electrolysis. The experimental findings closely aligned with the model predictions, confirming the effectiveness of switching the gasification medium in enhancing syngas quality for subsequent upgrading.