煤焦与CO2/H2O共气化过程协同作用机理研究

Introducing CO2 as gasifying agent to char-H2O reaction system to yield syngas is helpful to the utilization of CO2. However, the application is restricted to a certain extent because of the relatively slow char-CO2 reaction rate compared with char-H2O reaction . Through the preliminary study, we occasionally discovered that the synergistic effect in reactivity between H2O and CO2 gasification in the presence of alkali metal and alkaline earth metals (AAEM), and 40% CO2 could leads to the most obvious synergistic effects. Therefore, to obtain the detailed AAEM species, content distribution and temperature range that lead to the synergistic effect, the migration rule of AAEM species during AAEM-rich coal gasification with CO2/H2O mixtures will be first investigated. Then, the AAEM species that cause the synergistic effect will be loaded to ash free coal by physically impregnating method to analyze its effects on char gasification reactivity, and the contribution mechanism of AAEM catalytic effect on synergistic effect will be analyzed by multi-scale characterization of the active metal species as well as its valence state and distribution in both char surface and matrix; coal chars with different conversion level will obtained by incomplete gasification with H2O/CO2 mixtures, and the contribution mechanism of char structural evolution on synergistic effect will be analyzed. Last, the inherent relation between the physical chemistry nature that CO2 lead to synergy and the AAEM as well as char structural evolution will be revealed. The result will provide the reliable theoretical guidance for recycling CO2 to industrial gasifier.

将CO2作为部分气化剂引入煤焦-H2O气化体系可实现CO2的有效利用。由于煤焦-CO2反应速率较煤焦-H2O低，使这项应用在一定程度上受到限制。申请者前期研究中偶然发现在含碱金属及碱土金属（AAEM）的煤焦水蒸气气化中，引入40%CO2作为气化剂时，出现使煤焦共气化反应速率较煤焦-H2O明显增大的协同效应。为探明该协同机理，本研究将以富AAEM煤为对象，考察其与H2O/CO2共气化过程中AAEM迁移规律，获取引发协同效应的金属种类、分布及作用温区等重要参数。将相关AAEM种类用负载法植入无灰煤，通过对煤焦表面及内部活性金属元素的价态及分布等进行多尺度表征， 探明AAEM催化作用对共气化协同效应贡献规律；通过分析不同碳转化率下煤焦结构物理化学特性，获得煤焦结构的演变对协同作用的贡献规律。最终揭示CO2作为气化剂带来协同效应的作用机理，研究成果将为CO2用于工业煤气化过程提供科学指导。

将CO2作为部分气化剂引入煤焦-H2O气化体系可实现CO2的有效利用。由于煤焦-CO2反应速.率较煤焦-H2O低，使这项应用在一定程度上受到限制。申请者前期研究中偶然发现在含碱金属及碱土金属（AAEM）的煤焦水蒸气气化中，引入40%CO2作为气化剂时，出现使煤焦共气化反应速率较煤焦-H2O明显增大的协同效应。为探明该协同机理，系统研究了富AAEM煤与H2O/CO2共气化过程中AAEM迁移规律，获取了引发协同效应的金属种类、分布及作用温区。将相关AAEM种类负载至无灰煤，对煤焦表面及内部活性金属元素的价态及分布等进行了多尺度表征，探明了AAEM催化作用对共气化协同效应贡献规律；分析了不同碳转化率下煤焦结构物理化学特性，获取了煤焦结构的演变对协同作用的贡献规律。结果表明：五彩湾煤气化所得不同碳转化率气化残焦中Na与K主要以水溶态形式存在，Ca主要以可交换离子态存在，Na与K的释放率对气氛变化不敏感，Ca的释放量在CO2气氛下最大，CO2气氛下所得气化残焦中Ca的释放比例达到了29.7%，H2O气氛下的释放比例仅为16.4%。CO2、H2O和H2O/CO2气氛所得气化残焦表面AAEMs类矿物质在煤焦表面分散性差异较大，CO2气氛所得气化残焦表面Ca出现了明显的富集现象，H2O气氛的存在能抑制Ca的烧结现象。钙可催化煤焦与H2O/CO2共气化反应产生协同效应，使煤与共气化剂的反应速率大于同等条件下煤与H2O或与CO2的反应速率，CaO是煤焦与H2O/CO2共气化中发挥催化作用的主要钙存在形式，H2O的存在可促进CaO更好地吸附并解离CO2从而发挥催化作用，H2O/CO2共气化有利于产生CaO发挥催化作用的扩散条件，高温条件下CaO 的严重烧结使得其吸附CO2的能力较弱，导致共气化反应过程中的协同效应程度随温度的升高逐渐减弱。研究成果为CO2用于工业煤气化过程提供了一定理论指导。依托本研究项目，已发期刊论文13篇，其中SCI和EI同时收录13篇。已培养毕业硕士研究生2名，另有3名硕士研究生正在培养。