Chemical looping
combustion (CLC) is a promising technology for
fuel conversion with inherent carbon capture. Because sulfur is an
integral part of coal, the existence of sulfur contaminants in coal
may degrade the purity of CO2 and deteriorate the performance
of the oxygen carrier in the CLC process. To uncouple the complex
behavior of inorganic sulfur in coal, sulfur release of three inorganic
sulfur-containing compounds (FeS2, FeSO4, and
CaSO4) mixed with activated carbon during the temperature-programmed
process and the CLC process using iron ore as an oxygen carrier were
investigated in a batch fluidized bed reactor at 950 °C. The
results showed that, in the temperature-programmed process, the initial
decomposition temperatures of FeS2, FeSO4, and
CaSO4 were about 400, 500, and 650 °C, respectively.
During the reduction and oxidation stages of CLC, SO2 was
the main sulfur-containing gaseous compound. The sulfur stability
of CaSO4 was higher than those of FeS2 and FeSO4. The fractions of sulfur converted to gaseous species in
the reduction stage (X
S,g,red) of FeS2 and FeSO4 reached 90.38 and 87.42%, respectively,
within 20.5 min, while the corresponding value was 53.97% for CaSO4. During 5 cyclic redox experiments at 950 °C, the fraction
of sulfur converted to gas species was almost maintained stable, while
the energy-dispersive X-ray spectroscopy analysis showed the accumulation
of sulfur after the cyclic reaction.
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