Influence of High-Temperature Steam on the Reactivity of CaO Sorbent for CO2 Capture

American Chemical Society
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Journal Article
Environmental Science & Technology, 2012, 46 (2), pp. 1262 - 1269
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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 510%) 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 120%). 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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