Influence of High-Temperature Steam on the Reactivity of CaO Sorbent for CO2 Capture
2012
Donat, Felix | Florin, Nicholas H. | Anthony, Edward J. | Fennell, Paul S.
Calcium looping is a high-temperature CO₂ capture technology applicable to the postcombustion capture of CO₂ from power station flue gas, or integrated with fuel conversion in precombustion CO₂ capture schemes. The capture technology uses solid CaO sorbent derived from natural limestone and takes advantage of the reversible reaction between CaO and CO₂ to form CaCO₃; that is, to achieve the separation of CO₂ from flue or fuel gas, and produce a pure stream of CO₂ suitable for geological storage. An important characteristic of the sorbent, affecting the cost-efficiency of this technology, is the decay in reactivity of the sorbent over multiple CO₂ capture-and-release cycles. This work reports on the influence of high-temperature steam, which will be present in flue (about 5–10%) and fuel (∼20%) gases, on the reactivity of CaO sorbent derived from four natural limestones. A significant increase in the reactivity of these sorbents was found for 30 cycles in the presence of steam (from 1–20%). Steam influences the sorbent reactivity in two ways. Steam present during calcination promotes sintering that produces a sorbent morphology with most of the pore volume associated with larger pores of ∼50 nm in diameter, and which appears to be relatively more stable than the pore structure that evolves when no steam is present. The presence of steam during carbonation reduces the diffusion resistance during carbonation. We observed a synergistic effect, i.e., the highest reactivity was observed when steam was present for both calcination and carbonation.
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