Energies (Oct 2024)
Optimizing S Chemical Looping Combustion with Cu-Fe Combined Oxygen Carriers: Performance and Mechanistic Insights
Abstract
This study focuses on the S-to-H2SO4 industry by investigating the chemical looping combustion (CLC) process utilizing Fe-based and Cu-based oxygen carriers (OCs), which are widely applied in CLC technology. The primary objective is to conduct combined CLC reactions of these two metal carriers in a three-zone temperature tube furnace, aiming to achieve a higher SO2 yield than what is attainable by reacting a single metal carrier with S. The investigation reveals promising industrial applications, offering potential benefits in terms of reducing equipment costs, enhancing energy efficiency, and lowering the emissions of the H2SO4 production industry. Through a series of experiments, the study examines the effects of reaction temperature and material molar ratios on SO2 generation. The solid reaction products were characterized using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). The experimental results indicate that the combined Cu-based and Fe-based OCs exhibit a higher SO2 yield during the reduction stage compared to using either Fe-based or Cu-based OCs independently. Under optimal conditions, with a carrier gas flow rate of 300 mL/min, an Fe2O3/S molar ratio of 6:1 in the second temperature zone, and a reaction temperature of 900 °C, the total SO2 yield in the third temperature zone reached approximately 85%. This was achieved at a reaction temperature of 850 °C, with an Fe2O3/S molar ratio of 6:1 in the first half of the zone and a CuO/S molar ratio of 12:1 in the second half of the zone. SEM-EDS analysis further revealed that the combined OCs showed no significant signs of agglomeration or sintering after 10 cycles of the reaction. However, Cu-based carrier particles increased in size by 50%, while Fe-based carrier particles remained relatively stable. Additionally, the low mass-to-atom ratio of S on the surface of OCs after the cyclic reaction suggests that the reduced-state OCs can be fully oxidized and regenerated following the release of SO2 during oxidation.
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