Hydrogen production through agro-residue gasification and adsorptive separation

Abstract

The present work reports on the characterization of mixed agro-residue pellets and their subsequent use for syngas generation in a laboratory-scale downdraft gasifier utilizing the mixture of oxygen and steam as the gasifying agent (equivalence ratio/steam to biomass ratio: 0.21/2.15). Pure hydrogen is realized in a vacuum pressure swing adsorption system using zeolite 13X adsorbent. Regarding pellets, the high ash content (11.46 ± 0.38 wt%) and the presence of inorganic elements (potassium, silicon, calcium) dictate gasification process level interventions. The key requirement established experimentally is maintaining the reactor temperature under 900 °C for a clinker-free operation. This prerequisite, accomplished through an optimized char-ash extraction rate, enables the consistent production of hydrogen-rich (42.2 ± 0.9 vol%) syngas with a lower heating value of 8.3 ± 0.2 MJ/Nm3 at a gross cold gas efficiency of 78.9%. The cyclic separation system operates at a pressure ratio of 7.5 and continually generates pure hydrogen with minimal contaminants. The oxy-steam gasification of high ash feedstock in a near-ambient fixed-bed reactor and its integration to a low-pressure swing adsorption system for practical multi-specie syngas separation with quality assessment of the produced hydrogen are the main novelty features.