High-purity hydrogen production from bark mulch via advanced dual fluidized bed steam gasification

Abstract

This study experimentally investigates high-purity hydrogen production via steam gasification of bark mulch pellets. A 100 kW<inf>th</inf> advanced dual fluidized bed gasifier is coupled with a pilot-scale process chain for product gas cleaning, conditioning, and hydrogen purification. The applied water–gas shift unit processes sulfur- and tar-containing product gas downstream of the gasifier. Measuring the gas composition along the catalyst bed height reveals that a catalyst amount reduction by 32 % is reasonable, as the water–gas shift reaction was not kinetically limited. X-ray photoelectron spectra of the unused and spent samples show that small amounts of sulfur and carbon deposited on the catalyst's surface. As carbon deposition from carbon monoxide and hydrocarbons is not possible from a thermodynamic perspective, the presence of tar compounds could have led to a carbon laydown. The obtained hydrogen purity downstream of the pressure swing adsorption unit is ≥99.971 vol-% with a hydrogen recovery and yield of 75.3 % and 48.5 g<inf>H2</inf> kg⁻¹<inf>BM.db</inf>, respectively.