Influence of fuel ash on the recoverability of copper from the spent material of chemical looping combustion
2020
Dai, Jinze | Hughey, Logan | Whitty, Kevin J.
Chemical looping combustion (CLC) is an advanced energy production technology that inherently separates the CO₂ generated. The oxygen needed for fuel conversion is supplied by the oxygen carrier. When using copper-based oxygen carriers, oxygen carrier attrition is a challenge to the process economics, unless the attrited copper that is mixed with fuel ash in the spent material can be recovered by, for instance, acid leaching. However, fuel ash may transform the attrited copper into certain complexes of low leachability (e.g., CuAl₂O₄), hindering the copper recovery. In this study, the copper content in the spent material was first evaluated. The effects of ash composition and copper content on the occurrence mode of copper in spent material were predicted by thermodynamic modeling. Redox cycles of simulated spent materials based on various coal ashes were performed to reveal the characteristics of CuAl₂O₄/CuFe₂O₄ formation. The CuO-Al₂O₃ reaction was investigated under the temperatures and solid residence times experienced in CLC. The materials were analyzed by X-ray diffraction. The results suggest that the fuel ash with a high Al/Ca ratio may lower the recoverability of copper when the temperature is above 925 °C. The slow formation of CuFe₂O₄ is not expected to affect the copper recovery.
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