Interaction of Swine Manure Ash-Oxygen Carrier Particles under Chemical Looping Conditions

The interaction between biofuel ashes and the oxygen carrier in chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) processes will be a key factor for the future implementation of these processes on an industrial scale. This is important if the biofuel used is a waste product with a high ash content, as much as 30 wt %, as is dry swine manure. The main components of swine manure ash are Ca (17 wt %) and P (13 wt %). The present work studies the interactions between three different oxygen carriers, two synthetic magnetic Cu-based CLOU oxygen carriers (Cu30MnFekao7.5 and Cu30MnFe_Mag) and ilmenite, and swine manure ash. CLOU and CLC cycles were performed in a batch fluidized-bed reactor under harsh conditions using up to 33.3 wt % ash. For both CLOU oxygen carriers, the concentration of O₂ released depended on rates of carrier conversion, although no agglomeration problems were found after 20 h of CLOU and CLC redox cycles with 25 wt % ash, and their CLOU reactivities also increased. However, the ilmenite sustained hard agglomeration after 20 h of CLC cycles with 25 wt % ash. After 20 h of CLC/CLOU redox cycles at 900 °C, all of the oxygen carriers showed ash particles adhering to their surface, with a higher degree of ash cover on Cu30MnFekao7.5 and ilmenite, both with minerals in their composition. Therefore, the presence of minerals in the oxygen carrier, either as a support or in the form of impurities (mainly Si and Al as kaolinite), could be related to a greater interaction with the ashes. Interaction with some ash elements resulted in ilmenite agglomeration, and the diffusion of K inside Cu30MnFekao7.5 particles was observed by using scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX), particularly on the kaolin-rich areas inside the oxygen carrier.