Sol–Gel-Derived NiO/NiAl₂O₄ Oxygen Carriers for Chemical-Looping Combustion by Coal Char

Abstract

Chemical-looping combustion (CLC) is a very promising technology to combine the energy-utilization situation in China and CO2 zero-emission in situ allowing for CO2 sequestration by efficient and energy-saving ways and without nitrogen oxide (NO x ) formation. Having an oxygen carrier with sufficient reactivities in reduction and oxidation and enough recyclability and strength for long-term operation is one of the key issues of the CLC process. This paper focuses on the investigation of Ni-based oxygen carriers for CLC by coal char. First, Al(OC3H7)3 and Ni(NO3)2 are selected as the main raw materials to prepare sol–gel-derived NiO/NiAl2O4 oxygen carriers. The oxygen carrier with a mass content of 60% NiO, a sintering temperature of 1300 °C, and a sintering time of 6 h performs comparatively well. Second, the reduction reaction of the NiO/NiAl2O4 oxygen carriers with char and the circular reduction/oxidation reactions of the NiO/NiAl2O4 oxygen carriers with char/air or hydrogen/air are carried out in a thermogravimetric analysis (TGA) instrument to investigate the reactivities and chemical life of the prepared NiO/NiAl2O4 oxygen carriers. The experimental results show that (a) when the TGA temperature is higher than 850 °C, NiO/NiAl2O4 starts to react with coal char rapidly, which indicates that CLC of coal char using NiO/NiAl2O4 as oxygen carriers is a feasible technology of energy utilization in principle; (b) NiO/NiAl2O4, which maintains its activity over single-cycle reduction/oxidation reactions with char/air or multiple-cycle reduction/oxidation reactions with hydrogen/air, exhibits extremely good recyclablity; (c) the porous beehive structure of the NiO/NiAl2O4 particle is maintained, and the sintering behavior between different particles is not observed during cyclic studies. Those experimental results prove the sol–gel-derived oxygen carrier NiO/NiAl2O4 is capable of being used in chemical-looping combustion fueled by coal char or H2.

Progress in Chemical-Looping Combustion and Reforming technologies

“…The direct solid-solid reaction between char and oxygen-carrier has been observed in TGA apparatus using Cu-, Ni-, Mn-, Fe-and Co-based oxygen-carriers [227,229,306,307]. However, the solid-solid reaction could be disguised when a gasifying agent is used as fluidization gas, which is the case for CLC.…”

Chemical-Looping Combustion and Gasification of Coals and Oxygen Carrier Development: A Brief Review

“…The reactivity of single cycle reduction-oxidation reactions for coal char and NiO/NiAl2O4 oxygen carriers were tested using TGA [74]. NiO/NiAl2O4 oxygen carrier with 60%NiO by mass (N6AN1306) and particle sizes of 125-180 µm was prepared using a sol-gel method.…”

Characterization of a sol–gel derived CuO/CuAl2O4 oxygen carrier for chemical looping combustion (CLC) of gaseous fuels: Relevance of gas–solid and oxygen uncoupling reactions

“…The CuO/CuAl 2 O 4 oxygen carrier material was prepared through the sol-gel technique which was usually used for preparing catalyst [35] and sometimes for the preparation of oxygen carrier particles being used for CLC technologies [28,[36][37][38][39][40] [28] where a similar material containing 60 wt.% CuO and 40 wt.% CuAl 2 O 4 was prepared. After crushing and sieving, the particles being sized to 125-180 μm were selected as oxygen carrier to be used in this work.…”