Calcium-looping for post-combustion CO2 capture. On the adverse effect of sorbent regeneration under CO2
Calcium-looping for post-combustion CO2 capture. On the adverse effect of sorbent regeneration under CO2
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DOI：
10.1016/j.apenergy.2014.03.081
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发表时间：
2014-08
期刊：
影响因子：
11.2
通讯作者：
J. Valverde;P. E. Sánchez-Jiménez;L. Pérez-Maqueda
中科院分区：
文献类型：
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作者：
J. Valverde;P. E. Sánchez-Jiménez;L. Pérez-Maqueda
CaO固体颗粒在高温下的多循环碳化/焙烧(C/C)是最近出现的钙环(CAL)技术的基础，该技术已被证明具有潜在的实现高和可持续的燃烧后CO2捕获效率的潜力。尽管试点工厂项目在兆瓦级取得了成功，但将Cal技术扩大到商业水平(到GWth级)的一个令人担忧的问题是，当吸收剂在高温(约950摄氏度)下通过焙烧再生时，只能部分恢复CaO碳化反应活性，因为焙烧炉中的二氧化碳浓度较高。为了重新激活吸附剂，提出了一种新的CAL概念，其中在高温/高CO2浓度下运行的再碳化器反应器在进入焙烧炉进行再生之前会导致固体进一步碳化。多循环热重分析(TGA)测试表明，由于加热/冷却速率低的技术限制，在高温焙烧而在极低的CO2分压下再生的脱硫剂可以通过重碳化来重新激活。我们报告了多循环C/C和碳化/重碳化/焙烧(C/R/C)热重分析在高升温/冷凝速率下的结果，以及在高CO2分压下在干燥大气中再生的结果。结果表明，在此条件下，CaO转化率在短短几个周期内急剧下降到很小的残留值。此外，引入重碳化阶段实际上也有不利的影响。理论研究表明，在富CO_2气氛中，CaCO_3的分解是由反应性CaO(1~1~1)表面的CO_2动态吸附/脱附控制的，这将阻止再生的CaO晶体结构沿这些反应性表面生长，而重碳化会增强这种作用。然而，焙烧炉中H2O的存在，也是在CaO反应面上动态吸附/解吸的，它将屏蔽CO2的吸附/解吸，从而缓解CO2对再生CaO结构碳化反应活性的严重不利影响。氧气燃烧会产生大量的水，目前正在中试工厂中使用，以提高焙烧炉的温度。人们正在探索辅助技术，以帮助加热部分碳化的固体，因为氧燃是对加州技术的重大惩罚。我们的研究表明，如果脱硫剂在高CO2分压下再生，那么在干燥的焙烧炉环境中注入蒸汽是必要的，以避免CaO转化率的急剧损失。
The multicyclic carbonation/calcination (c/c) of CaO solid particles at high temperature is at the basis of the recently emerged Calcium-looping (CaL) technology, which has been shown to be potentially suitable for achieving high and sustainable post-combustion CO2capture efficiency. Despite the success of pilot plant projects at the MWthscale, a matter of concern for scaling-up the CaL technology to a commercial level (to the GWthscale) is that the CaO carbonation reactivity can be recovered only partially when the sorbent is regenerated by calcination at high temperatures (around 950 °C) as required by the CO2high concentration in the calciner. In order to reactivate the sorbent, a novel CaL concept has been proposed wherein a recarbonator reactor operated at high temperature/high CO2concentration leads to further carbonation of the solids before entering into the calciner for regeneration. Multicyclic thermogravimetric analysis (TGA) tests demonstrate the feasibility of recarbonation to reactivate the sorbent regenerated at high calcination temperatures yet at unrealistically low CO2partial pressure mainly because of technical limitations concerning low heating/cooling rates. We report results from multicyclic c/c and carbonation/recarbonation/calcination (c/r/c) TGA tests at high heating/coling rates and in which the sorbent is regenerated in a dry atmosphere at high CO2partial pressure. It is shown that at these conditions there is a drastic drop of CaO conversion to a very small residual value in just a few cycles. Moreover, the introduction of a recarbonation stage has actually an adverse effect. Arguably, CaCO3decomposition in a CO2rich atmosphere is ruled by CO2dynamic adsorption/desorption in reactive CaO (1 1 1) surfaces as suggested by theoretical studies, which would preclude the growth of the regenerated CaO crystal structure along these reactive surfaces, and this effect would be intensified by recarbonation. Nevertheless, the presence of H2O in the calciner, which is also adsorbed/desorbed dynamically in CaO reactive planes, would shield CO2adsorption/desorption thus mitigating the deeply detrimental effect of CO2on the carbonation reactivity of the regenerated CaO structure. Oxy-combustion, which produces a significant amount of H2O, is currently used in pilot-scale plants to raise the temperature in the calciner. Auxiliary techniques are being explored to help heating the partially carbonated solids since oxyxombustion represents an important penalty to the CaL technology. Our study suggests that steam injection would be necessary in a dry calciner environment to avoid a sharp loss of CaO conversion if the sorbent is regenerated at high CO2partial pressure.