基于Langmuir-Hinshelwood动力学解析O2/CO2/H2O气氛下烟煤焦反应机理

流化床富氧燃烧湿烟气循环兼具经济与环保优势。湿烟气循环（O₂/CO₂/H₂O）条件下煤焦与O₂、CO₂及H₂O的反应同时发生。为探究O₂/CO₂/H₂O气氛下煤焦-O₂、煤焦-CO₂、煤焦-H₂O反应间的相互作用机制，在自制高精度热重实验装置上系统考察了O₂、CO₂、H₂O及其混合气氛下，典型烟煤焦在900℃的反应特性。基于吸附和脱附原理的Langmuir-Hinshelwood（L-H）机理性模型分别计算了烟煤焦与O₂、CO₂和H₂O反应的动力学参数。通过采用单独活性位点与竞争活性位点两种假设分析了O₂/CO₂、O₂/H₂O和CO₂/H₂O气氛下烟煤焦-O₂、烟煤焦-CO₂和烟煤焦-H₂O两两反应间的作用机制，揭示了H₂O分子优先吸附于烟煤焦表面活性位点，O₂分子次之，而CO₂分子相对滞后。O₂/CO₂/H₂O气氛下烟煤焦-O₂、烟煤焦-CO₂、烟煤焦-H₂O反应表现出部分竞争反应活性位点，传统的单独活性位点与竞争活性位点假设均无法准确描述其反应速率特性。基于H₂O分子优先，O₂分子次优先吸附的原理，建立了O₂、CO₂、H₂O混合气氛下煤焦反应速率L-H动力学方程，方程计算结果与实验值良好吻合。研究结果为深入分析煤焦颗粒流化床富氧燃烧特性及构建可靠、准确的燃烧反应模型提供了理论支撑。

Langmuir-Hinshelwood kinetic model study of bituminous coal char reaction mechanism in O2/CO2/H2O atmosphere

Wet-recycle oxy-fuel (O₂/CO₂/H₂O) fluidized bed (FB) combustion shows high efficiency of the power plant and low emission of pollutants. In O₂/CO₂/H₂O atmosphere, char-O₂, char-CO₂ and char-H₂O reactions can occur at the same time. To reveal the mechanism of interaction among those reactions, macro-thermogravimetric analysis (TGA) experiments were carried out in mixture of O₂, CO₂ and H₂O at temperature of 900℃ using a bituminous coal-char. The reaction kinetics of char-O₂, char-CO₂ and char-H₂O reactions were obtained through Langmuir-Hinshelwood (LH) model fitting. Assumptions of separate active sites and common active sites were used to analyze the experimental data in O₂/CO₂, O₂/H₂O and CO₂/H₂O atmospheres, results show that H₂O molecules have priority in taking active sites, following by O₂, and finally is CO₂. In O₂/CO₂/H₂O atmosphere, partial competition among char-O₂, char-CO₂ and char-H₂O reactions was experimentally observed, and neither conventional separate active sites nor common active sites models could describe the reaction rate of bituminous char. According to the theory of H₂O molecules primarily and O₂ molecules sub-primarily occupy active sites when O₂, CO₂ and H₂O are present, a new L-H type model was built. The developed model was found to describe well with the measured reaction rate of bituminous char in mixture of O₂, CO₂, and H₂O. The results of this work provide theoretical basis for analyzing of the oxy-fuel FB combustion characteristics of char and developing of reliable char combustion model.