煤直接化学链燃烧过程中硫的迁移转化规律及脱除机理研究

The efficient control of the sulfur-bearing pollutants from the coal direct chemical looping combustion process is of importance for the purpose of clean utilization of coal. The scope of this project covers the macroscopic transformation pathways of sulfur when several typical Chinese coals, featured by their high sulfur content, serve as the fuel for the coal direct chemical looping combustion process. Beyond that, a variety of sulfur-containing model compounds that represent the various ways the sulfur naturally occur in coal will also be studied. The distribution of sulfur in gas and solid phases will be investigated to determine the main reaction pathways and the mechanisms for the evolution of sulfur when each model compound is processed. The deactivation and regeneration mechanism of oxygen carrier will be measured via monitoring the carrier’s performance during multiple operations. Upon the introduction of desulfurizer, the desulfurization output and its impact on the oxygen carrier will be determined by analyzing the variations in the composition of sulfur-containing gases, the desulfurizer and the oxygen carrier. Such findings will be further used to uncover the paralleling reactions that take place when oxygen carrier and desulfurizer are competing to react with the sulfur-containing species. Finally, we will optimize the Ca/S ratio on the basis of the effect of the parameter on the desulfurization of both high sulfur coals and sulfur-bearing model compounds, and on the capacity of the oxygen carrier, respectively. This project is supposed to elucidate the mechanisms that underlie the transformation and removal of sulfur in coal during the coal direct chemical looping combustion process, thereby providing theoretical guidelines for the oxygen carrier screening and the control of sulfur emission.

煤的化学链燃烧过程中含硫污染物的高效控制对于实现煤的清洁利用意义重大。本项目不仅研究国内典型高硫煤在直接化学链燃烧过程中硫的宏观迁移转化规律，更进一步按照煤中硫的不同赋存形态以典型含硫模型化合物为研究对象，通过研究含硫组分在气固相中的分布规律，确定各含硫模型化合物中的硫在反应过程中的主要反应途径及迁移转化机理，并通过检测多次运行过程中载氧体的性能表现，确定载氧体的失活及再生能力；通过分析钙基脱硫剂添加前后含硫气体的组成及脱硫剂/载氧体组分变化，考察脱硫剂的脱硫效果及脱硫剂的添加对载氧体的影响，并进一步揭示反应过程中含硫组分与载氧体/脱硫剂之间的竞争反应机制；基于钙硫比对高硫煤及模型化合物中硫的脱除效果及对载氧体性能的影响，确定最佳的脱硫钙硫比。通过本项目的研究可以确定煤中的硫在直接化学链燃烧过程中的迁移转化规律及脱除机理，这将为载氧体的筛选优化及含硫污染物的排放控制等研究提供科学依据。

化学链燃烧是一种具有CO2内分离的新型燃烧技术。由于煤中硫不仅可能会危害大气环境，降低CO2纯度，还可能影响载氧体的反应性能及稳定性。本项目围绕煤直接化学链燃烧过程中硫的迁移转化和脱除机制展开研究，旨在掌握气相含硫污染物的排放/控制规律及煤中硫对载氧体的影响机制。首先，针对高硫煤中硫的迁移转化规律进行了热力学分析，深入研究了煤种类型、反应温度、载氧体过量系数、Ca/S摩尔比等运行参数对气固相含硫污染物的存在状态及分布规律的影响，确定了理论上硫的迁移转化规律及脱除效率。其次，选取了国内典型高硫煤，并按照煤中硫的赋存形态选取典型含硫模型化合物，分别研究了各高硫煤/含硫模型化合物中气相含硫化合物的析出规律、存在形态及转化份额，并确定了连续循环反应后的载氧体中的固相含硫物质的物相组成及硫在载氧体表面的富集状况，确定了煤/模型化合物中硫在化学链燃烧过程中的主要反应途径及迁移转化机理。再次，针对硫的析出采用CaO为脱硫剂进行脱除，研究了Ca/S摩尔比对煤/模型化合物中硫脱除效率的影响规律，并考察脱硫剂的添加对载氧体的表面形貌、物相组成的影响，确定了脱硫剂与载氧体之间的相互作用及其在载氧体表面的富集情况。本课题通过以上三个层次的分析，揭示了煤中硫的迁移转化规律及硫的脱除机理，这对煤中硫在化学链燃烧过程的控制及脱除等具有一定的借鉴意义。