Experimental investigation of chemical looping hydrogen generation using iron oxides in a batch fluidized bed

Abstract

Chemical looping hydrogen generation (CLHG) is a promising technology for the combustion of gas or solid fuels with hydrogen production and inherent separation of CO 2. In this paper, experiments on CLHG using iron oxides as oxygen carrier and CO as fuel were carried out in a batch fluidized bed. The effects of reduction time, operation temperature, particle sizes and addition of CO 2 in the reduction gases on hydrogen production were investigated. At 900 °C, the hydrogen concentration on a nitrogen-free base reached 99.3% in the steam oxidation phase. The key process for the redox of hematite for hydrogen generation was the reduction of hematite to wüstite or metallic iron. Iron carbide and carbon deposit occurred in the reduction phase, which released a little amount of CO and CO 2 in hydrogen production phase, while little CO or CO 2 were detected in the air oxidation phase. Longer reduction time favored deeper reduction of the oxygen carrier and increased hydrogen production. When the reduction time decreased from 40 to 20 min, the hydrogen concentration peak lowered from 17.72% to 10.68%. High temperature improved reduction reactivity and elevated hydrogen production. The average hydrogen concentrations were 6.15%, 6.22%, 6.28% and 7.50% for the redox temperatures of 800, 850, 900 and 950 °C, respectively. Particles in smaller sizes with higher BET surface areas and better fluidizability had higher hydrogen production. The rise of the CO 2 partial pressure in the reduction gases decreased hydrogen production. The peak of hydrogen concentration dropped from 12.10% to 3.30% when the inlet CO 2 partial pressure increased from 0% to 45.5%.