Oxy-CFB燃烧高钠煤时受热面积灰机理研究

In recent years, the Zhundong coal has attracted great attention due to its unique advantages such as abundant storage, low mining cost and excellent reactivity. However, the high sodium existed in the Zhundong coal may easily cause the ash deposition and corrosion of the heat transfer surface during the combustion process and has negative effects on the equipment operation and efficiency. The oxy-fuel circulating fluidized bed (Oxy-CFB) combustion technology, which combines the advantages of the CFB combustion technology and the oxy-fuel combustion technology, exhibits great potential to reduce the CO2 emission. Based on the tube furnace test and ternary phase diagram theory, this project conducts the research of the sodium migration patterns under the Oxy-CFB combustion atmosphere. Combined with the visualization technology of the ash deposition, an Oxy-CFB hot test facility is established to study the ash deposit mechanism of the heat transfer surface and effects of additives on the ash reduction during the high-sodium coal combustion process. Besides, the Euler-Lagrange approach is adopted to build a comprehensive and experimentally-validated mathematical model for the ash deposition of the heat transfer surface. The density functional theory is used to explore the reactivity of the mineral substance in the ash, the influence of sodium on the phase change rules of different mineral substances, and the micromechanism of the ash fusion characteristics. This project is expected to improve the theoretical research on the thermal conversion of the high-sodium coal and reveal the sodium migration patterns and ash deposition of the heat transfer surface under the Oxy-CFB combustion atmosphere.

准东煤储量丰富、开采成本低、反应活性好，近年来日益受到关注。然而其钠含量高，在燃烧过程中极易造成受热面积灰和腐蚀，影响设备运行安全和效率。循环流化床富氧燃烧（Oxy-CFB）技术结合循环流化床燃烧和富氧燃烧的优势，是一种极具前景的CO2减排技术。项目将基于管式炉试验和三元相图理论研究高钠煤在Oxy-CFB燃烧气氛下的钠迁移转化规律。搭建Oxy-CFB热态试验台，结合积灰过程的可视化技术，研究高钠煤Oxy-CFB燃烧时受热面灰沉积机理，研究添加剂对减轻积灰的影响规律和机制。基于Euler-Lagrange模型，建立经详细实验数据验证的受热面飞灰沉积过程数学模型。运用密度泛函理论探究飞灰中矿物质的反应活性、钠对矿物质间相变的作用规律，揭示影响灰熔融特性的微观机理。期望通过本项目的工作促进高钠煤热转化利用的理论研究，并深入揭示Oxy-CFB燃烧条件下高钠煤中钠的迁移转化规律和受热面积灰机理。

准东煤储量丰富、开采成本低、反应活性好，近年来受到关注。然而其钠含量高，在燃烧过程中极易造成受热面积灰和腐蚀，影响设备运行安全和效率。循环流化床富氧燃烧（Oxy-CFB）技术结合循环流化床燃烧和富氧燃烧的优势，是一种极具前景的CO2减排技术。本项目采用实验和理论研究相结合的方法，开展了对准东煤燃烧过程中受热面积灰机理的研究。.基于管式炉试验台对比了空气气氛和富氧下燃烧准东煤时Na的迁移释放特性。发现三种气氛下温度对Na迁移释放的影响规律基本一致，温度的升高促进煤中Na的释放，使灰中含量明显减少。水蒸气浓度的升高有效地促了煤颗粒中Na的释放。.系统地研究了掺杂添加剂对准东煤燃烧过程中Na迁移释放的影响。高岭土的综合效果最好。掺杂高岭土能有效促进可溶性Na与Al2O3·2SiO2·2H2O反应生成NaAlSi3O8等含Na的硅铝酸盐，增加燃烧过程中不溶性Na的比例。利用基于DFT理论的CASTEP模块计算高岭土层间羟基缺失情况及表面水分子浓度对NaCl吸附能的影响。.系统地研究了流化床条件下燃烧准东煤时，流受热面的积灰特性，并进一步探究了掺杂高岭土对受热面积灰的防控效果。结果表明，温度、水蒸气及受热面表面温度的变化都会影响灰沉积速率。.基于双流体模型模型（TFM），本项目开展了烟气循环方式下循环流化床富氧燃烧过程的数值模拟研究。在烟气循环燃烧工况下，循环烟气份额、压力、温度以及气体排放浓度与试验数据较为吻合，验证所建模型的可行性。基于欧拉-拉格朗日框架下的稠密离散相模型（DDPM），本项目建立循环流化床燃烧CFD综合模型，并研究不同O2/CO2气氛下循环流化床富氧燃烧过程。.基于CFD-DEM方法粘性颗粒碰撞粘附模型，对小型流化床实验台台积灰段积灰过程进行了计算。模拟结果表明，积灰形成于采集管迎风面，其几何形态具有较高的对称性，积灰厚度沿管壁轴向方向中央高而两端低；小粒径颗粒的碰撞率和粘附率随着烟气温度和壁面温度的提升而提升，且粘附率提升更为突出；数值模拟得到的烟气流速等工况参数对积灰特性的影响规律与验证实验结果接近。