Abstract
Fe2O3/Al2O3 and Fe2O3/TiO2/Al2O3 oxygen carriers were fabricated and evaluated for chemical looping hydrogen generation (CLHG) using a TGA system and a fixed-bed reactor. Oxygen carriers were converted to around 33% in a fixed-bed reactor to ensure uniform reduction. The reduced oxygen carrier was tested for steam generation, where in all cases Fe2O3/Al2O3 displayed a better conversion than Fe2O3/TiO2/Al2O3. It was found that increasing the reaction temperature from 800 to 850 °C had little effect for either oxygen carrier, but a further increase to 900°C resulted in an increased steam conversion. A higher steam flow rate caused a lower overall steam conversion but a higher H2 production. A higher feed rate of reduced oxygen carrier let to a higher steam conversion up to a rate of 18.4 and 14.9 g min–1 for Fe2O3/Al2O3 and Fe2O3/TiO2/Al2O3, respectively. A final comparison was performed with up to 50 redox cycles, where Fe2O3/Al2O3 showed superior reactivity in the first cycles but ended at a conversion of 54.6% with Fe2O3/TiO2/Al2O3 ending at a conversion of 64.6%.
Highlights
IntroductionThe ways to produce hydrogen are many, with the steam-iron process (SIP) being used since the early 20th century (Hurst, 1939)
Hydrogen is an environmentally friendly energy option which can address issues such as global climate change, air pollution and energy security
The reactivity of fabricated Fe2O3/Al2O3 and Fe2O3/TiO2/Al2O3 oxygen carriers were examined in a thermogravimetric analyzer (TGA) using syngas as reducing gas for 50 successive redox cycles
Summary
The ways to produce hydrogen are many, with the steam-iron process (SIP) being used since the early 20th century (Hurst, 1939). In this process, iron species are employed to split water molecules by binding to the oxygen atoms, generating iron oxide and hydrogen. Iron species are employed to split water molecules by binding to the oxygen atoms, generating iron oxide and hydrogen This process can be implemented in continuous reduction and oxidation cycles of the iron oxide. The integration of the steam-iron process with chemical looping, termed as chemical looping hydrogen generation (CLHG), generates high-purity CO2 and H2 simultaneously by using an Fe-based oxygen carrier operating in a moving-bed reactor (Tong et al, 2013)
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