水蒸气/SO2对钙基CO2吸附剂再生动力学的影响与作用机制

Calcium looping (CaL) is one of the most important technical ways in achieving low-carbon coal utilization. Calcination is the key stage in calcium looping, where sorbents are regenerated using the heat supplied by oxygen-enriched combustion of coal and then ready for CO2 capture. However, most of the existed researches on calcium looping are conducted under the ideal calcination atmosphere of N2/CO2 mixtures, which is far from the real operating conditions. Preliminary studies show that the decomposition process of calcium-based sorbents changes significantly with the presence of steam and SO2 produced in the oxygen-enriched combustion of coal. This project will focus on this issue and study the kinetic characteristics and mechanism in the regeneration of sorbents upon the impact of steam and SO2. The law and the catalytic mechanism on the acceleration of sorbents’ decomposition by steam will be revealed by the combined experiment and molecular simulation using the density functional theory. A changing grain size model will be developed to study the coupling behavior, the key factors and the influences during the simultaneous decomposition and sulfation within a single sorbent particle. Further experiments will be performed to understand the CO2 desorption features of the sorbents and the synergistic and competitive mechanism with the combined effect of steam and SO2, thus properties of sorbent particles and the calcination conditions in calcium looping can be adjusted and optimized. The implementation of the project will provide scientific basis for the development of the CaL-based low-carbon coal utilization technology.

钙循环是煤基低碳利用的重要技术路径之一。煅烧过程是钙循环中的关键环节，需要通过煤的富氧燃烧供热实现吸附剂分解再生进而捕集CO2。然而，目前对钙循环的研究多基于N2/CO2等理想煅烧气氛，而与实际煅烧环境相差甚远。初步研究显示，煤富氧燃烧气氛中的水蒸气和SO2对钙基CO2吸附剂的再生过程有着重要影响。本项目拟针对水蒸气/SO2作用下的吸附剂分解再生动力学特性与机制展开研究。通过实验研究与基于密度泛函的分子模拟，弄清水蒸气加速吸附剂分解再生的规律及催化机理；改进变晶粒粒径数值模型，研究伴随有硫酸化反应的单颗粒吸附剂分解过程中的耦合行为、影响因素及规律；通过进一步的实验研究，揭示水蒸气与SO2共同作用下的吸附剂CO2脱附特性与涉及的协同竞争机制，从而调控与优化钙基CO2吸附剂颗粒结构参数及煅烧过程工况。本项目的实施将为钙循环煤基低碳利用技术的发展提供基础科学依据。

钙循环是煤基低碳利用的重要技术路径之一。煅烧过程是钙循环中的关键环节，需要通过煤的富氧燃烧供热实现吸附剂分解再生进而捕集CO2。而煤富氧燃烧过程中的水蒸气/SO2等组分会对钙基CO2吸附剂的再生过程有着重要影响。基于上述基础问题，1）本项目考察了水蒸气对于钙基吸附剂分解再生的影响规律，发现水蒸气可以降低CaCO3分解温度并加快其分解速率；进一步通过量化计算揭示了H2O在CaCO3表面的吸附活性位点、吸附与解离过程、以及CaCO3分解并释放出CO2的反应路径及反应能垒，从原子层面阐明了水蒸气催化加速CaCO3分解的微观机理。2）针对SO2杂质的复杂影响，基于变晶粒粒径原理建立了耦合碳酸钙分解/氧化钙硫酸化串行反应与热/质传递的颗粒模型，模拟了串行反应间的相互作用与影响因素，结果表明高CO2浓度虽然会降低初始硫酸化速率，但是有利于硫酸化全局反应进行；较大的颗粒与晶粒粒径均会减缓碳酸钙分解及连锁硫酸化反应。3）探究了水蒸气/SO2共存时的CO2吸脱附特性，发现水蒸气在提升吸附剂表面CO2吸附性能参数、优化吸附剂内部孔结构的同时，也为SO2扩散与反应提供了良好的孔隙通道与反应区域，进而呈现出较强的硫酸化促进作用。4）本项目还考察了再生过程煤富氧燃烧灰分的影响特性与机制，研究了钙基CO2吸附剂与煤灰种类、粒径、煅烧条件等关键参数对于煤灰抑制钙材料CO2循环吸附容量的影响规律，揭示了煤灰颗粒在钙基吸附剂表面的物理演变过程及关键矿物元素的迁移规律。上述结果可以为构建高效钙基吸附剂、优化反应工况进而应用钙循环CO2捕集技术提供理论支持和技术支撑。