Coal chemical-looping gasification of Ca-based oxygen carriers decorated by CaO

• CaSO4–CaO/Ben compound oxygen carriers have higher catalytic reactivity.
• CaSO4–CaO/Ben compound oxygen carriers have excellent recycling ability.
• The synergy of CaSO4 and CaO was verified during the coal CLG process.
• The kinetics of CLG are well described by the active site extending model.

Chemical-looping gasification (CLG) for reacting coal with oxygen carriers to yield syngas is a clean and effective coal gasification technology. In the present investigation, a mechanical mixing-impregnation method was used to prepare a CaSO4–CaO/bentonite (CaSO4–CaO/Ben) compound oxygen carrier with excellent catalytic reactivity and stabilizing ability. An investigation on the reaction performance, cyclability and sulfur release of CaSO4–CaO/Ben was performed in a batch fluidized-bed reactor with steam as the gasification–fluidization medium. The results of this study demonstrate that the CaSO4–CaO/Ben compound oxygen carrier has excellent catalytic reactivity. At 900 °C, the carbon conversion rate, cold gas efficiency and syngas content reached 96.84%, 84.28% and 66.98%, respectively. Furthermore, the addition of CaO can inhibit CaSO4 side reactions to improve the stability of the oxygen carrier. The cold gas efficiency, carbon conversion efficiency and syngas content exhibited slight changes during ten redox cycles, which indicates that the CaSO4–CaO/Ben oxygen carrier has excellent reactive stability. SEM images of the oxygen carrier after being recycled in ten redox reactions indicated that the surface of the oxygen carrier became porous, which favored CLG. The coal CLG kinetics could be well explained by an active site extending model, and the synergy of CaSO4 and CaO was verified during the coal CLG process.

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