CaO对CaSO4氧载体化学链燃烧中硫释放的抑制机理

As an innovative combustion, Chemical-looping combustion (CLC) has been suggested among the best alternatives to achieve an increase in combustion efficiency simultaneously with low energy penalty for inherent CO2 capture. The research on CLC with CaSO4 oxygen carrier is just in an exploratory stage. The sulfur loss during both the CaSO4 reduction and CaS oxidization leads to the deactivation of CaSO4 oxygen carrier. To prevent the sulfur loss, the additive of CaO was introduced to CaSO4 oxygen carrier in fuel reactor for CLC. The utilization of CaO additive does not bring new materials and new reactions. CaO additive is supposed to react with gas sulfides in the fuel reactor. Then the sulfidation products are expected to be oxidized to CaSO4 in the air reactor, and can be used as oxygen carrier later. The paths of sulfur release from both CaSO4 and CaS, the transformation between the gas sulfides, both the component distributions and the textures of the granules of the oxygen carriers and CaO additive as a function of reaction time, the mechanism of sulfur retention by CaO additive for different gas sulfides, the mechanism of competitive absorptions between gas sulfides and CO2 by CaO additive will be discussed. And the activity,the mechanical strength and the performance of the mixed oxygen carrier of CaSO4-CaO during multicycle tests will be obtained, which would be useful for further research.

CaSO4作为氧载体的化学链燃烧技术目前处于初步探索阶段。本项目针对氧载体的硫释放失活问题，提出了在CaSO4氧载体中添加CaO颗粒的方法，旨在抑制气体硫化物的释放和维持氧载体载氧功能。拟以煤气为燃料、CaSO4为氧载体，对CaO添加剂在化学链燃烧中的固硫机理展开研究，重点揭示氧载体中硫元素的释放途径与规律，气体硫化物之间的相互转换关系，氧载体颗粒和CaO添加剂颗粒成分分布以及颗粒织构时间的演化过程，CaO添加剂在CaSO4氧载体还原反应阶段和再生反应阶段对不同气态硫化物的固化机理以及固硫和固化CO2竞争反应机理，并获得复合氧载体（CaSO4-CaO）反应活性、机械强度、持续循环能力等性能评估数据，为今后的进一步研究提供理论基础和实验数据。

化学链燃烧是一种很有前景的控制温室气体方法。由于CaSO4氧载体具有较高的载氧能力和低廉的价格，将其应用于化学链燃烧的氧载体具有非常广泛的前景。本项目针对CaSO4氧载体使用过程中存在硫释放失活问题，提出了在CaSO4氧载体中添加CaO颗粒的方法，旨在抑制气体硫化物的释放和维持氧载体载氧功能。首先，深入开展复合氧载体CaSO4-CaO还原反应过程中硫元素迁移的热力学分析，获得了CaSO4氧载体中的硫元素释放，气相硫化物之间相互转化和CaO添加剂吸收固化不同气态硫化物的反应机理，获得了当有SO2和COS释放时，CaS和CaSO4以及CaO稳定存在的区域。第二，开展CaO添加剂在CaSO4还原反应过程及CaS氧化再生过程中的固硫机理研究，通过改变复合氧载体制备方法、反应温度、反应时间、CaO/CaSO4摩尔配比、CO浓度、O2浓度和CaO/CaS摩尔配比，考察气体硫化物的释放、CO2生成和固体产物分布，获得较优CaSO4-CaO氧载体颗粒的制备，获得CaSO4氧化还原反应过程和CaS氧化过程中硫的释放途径和规律，获得CaO加入对硫释放的抑制机理。在还原气氛下，添加CaO，不仅有利于CO2生成，还能吸收固化SO2和COS（借助XRD和XRF分析）；虽然SO2不容易被CaO吸收固化，但是当反应气氛中有CO时，SO2会进一步转化成容易被CaO吸收固化的COS，从而被CaO固化成CaS。在氧化气氛下，由于O2的存在，SO2会被吸收固化成CaSO4。第三，开展基于CaSO4-CaO氧载体的化学链燃烧循环反应性能研究，通过改变复合氧载体制备方法、CaO/CaSO4摩尔配比、CO浓度，并引入环境因子以评估燃烧效率与气体污染物释放的关系，从而评估CaO的加载对CaSO4氧载体整体性能的影响效用。本课题通过以上三个层次的分析，揭示了CaSO4中的硫元素释放、气体硫化物之间的相互转化机理、CaSO4-CaO的还原反应机理和CaS-CaO的氧化反应机理，这些对于化学链燃烧脱硫、煤燃烧脱硫及煤气化脱硫等方面有着很强的借鉴意义。并获得如下主要结论：CaO的加入在抑制气体硫化物释放的同时有利于CO2生成，增强了CaSO4氧载体的反应耐久性。