Potassium interactions with copper slag and magnetite fines in chemical-looping processes

Abstract

Using oxygen-carrying bed materials is a promising alternative to conventional fluidized bed combustion. Biomass-derived fuels contain ash rich in K and P, which might react with the oxygen carrier, leading to agglomeration and other problems. This study investigates the performance of copper slag (Järnsand, Fe-Si-oxide) and magnetite fines (MAF, Fe 3 O 4 ) as oxygen carriers in a lab-scale fluidized bed reactor with subsequent material analysis. The conversion of methane and the fluidization was monitored, as K 2 CO 3 or KH 2 PO 4 was added as ash model compound. The fuel conversion was mainly unaffected by K-salt addition, apart from when K 2 CO 3 was added to MAF at 950 °C and the conversion increased, along with increased porosity. Järnsand captured K from K 2 CO 3 . Mg and Al inherent to Järnsand participated in the interaction, contributing to increasing the melting point of the formed K-silicates. In MAF, the uptake of K was low: thermodynamic calculations suggested the formation of KFe 11 O 17 and small amounts of slag. KH 2 PO 4 always caused agglomeration by a melt-induced mechanism. The K-P-melt absorbed Fe in MAF or Ca in Järnsand. In conclusion, Järnsand seems like a promising oxygen carrier for biomass-derived fuels, while MAF might suffer from poor particle integrity in the presence of K-rich ash species. • A novel method was used to mimc the conditions in a biomass-fired boiler • MAF (Fe-oxide) captured less K than Järnsand (Fe-Si-oxide) • K 2 CO 3 increased porosity and fuel rectivity of MAF at 950 °C • Järnsand captured K in Mg/Al-K-silicates, solid at 850 °C but slag at 950 °C • Addition of KH 2 PO 4 caused a melt-induced agglomeration in MAF and Järnsand

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