Calcium
sulfate (CaSO4) has attracted a great amount
of attention as a potential oxygen carrier (OC) to be applied in chemical
looping combustion (CLC) due to its high oxygen transfer capacity,
wide distribution, and easy accessibility, but its low reactivity
and sulfur emission from side reactions of CaSO4 should
be well resolved. In this research, the CaSO4–CuO
mixed OC was prepared using the template method combined with the
sol–gel combustion synthesis (SGCS). Its reaction characteristics
with a selected lignite (designated as YN) were investigated and the
greatly enhanced reactivity of this mixed OC was confirmed relative
to the single CaSO4 and CuO. Meanwhile, the comprehensive
heat effect showed the desired exothermic characteristics for this
mixed OC reaction with YN when the mass ratio of CaSO4 to
CuO was fixed as 6:4. Furthermore, morphological analysis indicated
that the solid products from YN reaction with the CaSO4–CuO mixed OC were porous without discernible sintering, mainly
because the CaSO4 included not only provided the lattice
oxygen involved for oxidation of YN coal, but also acted as the temporary
inert support to improve the resistance of the reduced Cu to sintering.
Finally, the gaseous and solid products formed were systematically
investigated and clearly indicated that the gaseous sulfur species
formed from the side reactions of CaSO4 were effectively
fixed with solid Cu2S formation; as such the potential
harms incurred could be eliminated. Overall, this preliminary research
revealed the greatly enhanced reactivity of this mixed OC as well
as its good fixation capacity for sulfur emitted from the side reaction
of CaSO4, which is much desired in the real CLC system.