Department of Chemical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom.
Environ Sci Technol. 2012 Jan 17;46(2):1262-9. doi: 10.1021/es202679w. Epub 2012 Jan 5.
Calcium looping is a high-temperature CO(2) capture technology applicable to the postcombustion capture of CO(2) from power station flue gas, or integrated with fuel conversion in precombustion CO(2) capture schemes. The capture technology uses solid CaO sorbent derived from natural limestone and takes advantage of the reversible reaction between CaO and CO(2) to form CaCO(3); that is, to achieve the separation of CO(2) from flue or fuel gas, and produce a pure stream of CO(2) 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 CO(2) 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.
钙循环是一种高温 CO2 捕获技术，适用于从电站烟道气中捕获 CO2 的后燃烧捕获，或与燃料转化相结合，用于预燃烧 CO2 捕获方案。该捕获技术使用源自天然石灰石的固体 CaO 吸附剂，并利用 CaO 和 CO2 之间的可逆反应形成 CaCO3；也就是说，实现从烟道气或燃料气中分离 CO2，并产生适合地质储存的纯 CO2 流。吸附剂的一个重要特性，影响该技术的成本效益，是在多次 CO2 捕获和释放循环中吸附剂反应性的衰减。这项工作报告了高温蒸汽（烟道气中约 5-10%，燃料气中约 20%）对四种天然石灰石衍生的 CaO 吸附剂反应性的影响。在蒸汽存在的情况下，这些吸附剂在 30 个循环中表现出明显的反应性增加（从 1-20%）。蒸汽以两种方式影响吸附剂的反应性。在煅烧过程中存在的蒸汽促进了烧结，产生了一种具有大部分孔体积与直径约 50nm 的较大孔相关的吸附剂形态，并且似乎比不存在蒸汽时演变的孔结构更稳定。在碳酸化过程中存在蒸汽会降低碳酸化过程中的扩散阻力。我们观察到了协同效应，即在煅烧和碳酸化过程中都存在蒸汽时，观察到了最高的反应性。
