高碱金属煤O2/CO2燃烧的积灰结渣机理研究

Xinjiang Zhundong coalfield has a superhuge reserve, while its combustion utilization has given rise to serious fouling problems on heat-exchanger surfaces due to high content of alkali metals. O2/CO2 combustion technology can realize large-scale CO2 capture and significantly reduce NOx emission, which is one clean coal-fired power-generation technology and is worth being applied for utilization of Zhundong coal. However, understanding on the deposition and slagging mechanism induced by alkali metals during O2/CO2 combustion of coal is still lacking, which severely restricts the large-scale clean utilization of Zhundong coal. In this study, several typical Zhundong coals are selected, and the thermal migration of alkali metals and relevant microscopic reaction mechanisms will be probed through experiment, molecular modelling and reactive force field (ReaxFF) molecular dynamics simulation. A novel double-pipe sampler with continuous varing temperature along flue flow will be employed to investigate the condensation of alkali metals and deposition of ash. A single-pipe heat-exchanger with controllable surface temperature will be utilized to explore the slagging growth and mechanism induced by alkali metals during O2/CO2 combustion of coals. The chemical thermodynamic equilibrium simulation will also be employed to probe the transformation of mineral components during coal combustion. Ultimately, the deposition and slagging mechanism during O2/CO2 combustion of high alkali metal coal will be elucidated. This study will provide scientific basis for solving the fouling problems during O2/CO2 combustion of high alkali metal coal, and also provide theoretical value and engineering guiding significance for promoting the clean, efficient and safe utilization of Zhundong coal.

新疆准东煤储量丰富，但其碱金属含量高造成在燃烧中易发生换热面严重沾污的问题。O2/CO2燃烧技术作为一种清洁的燃煤发电技术，能实现大规模捕集CO2并显著降低NOx排放，值得应用于准东的燃烧利用中。但目前对高碱金属煤O2/CO2燃烧积灰结渣的机理依然缺乏足够的认识，严重制约了准东煤的大规模清洁利用。本项目以准东煤为主要研究对象，通过实验、分子建模和ReaxFF模拟研究O2/CO2燃烧中碱金属迁移过程及微观反应机制；利用沿烟气流动方向温度连续变化的套管式采样器研究碱金属凝结与积灰特性；采用可控壁温的单管换热器研究换热面结渣过程以及碱金属诱发结渣沾污机理；采用化学热力学平衡方法模拟分析各种矿物组份在煤燃烧中的转变规律，最终阐明高碱金属煤O2/CO2燃烧的积灰结渣机理。本项目研究将为解决高碱金属煤燃烧的换热面沾污问题提供科学依据，对推动准东煤的清洁、高效、安全利用具有重要的理论价值和工程指导意义。

研发高碱金属煤O2/CO2燃烧技术，能够实现燃煤电站污染物的近零排放，促进新疆准东煤的高效、清洁和安全利用。本项目针对高碱煤O2/CO2燃烧的积灰结渣机理开展研究工作，通过实验研究和分子模拟阐明O2/CO2燃烧过程中的碱金属迁移规律以及碱金属诱发的换热面沾污特性。本项目研究的主要成果和结论包括：. 首先，基于大数据分析获得了高碱煤煤质参数间的定量关系，准东煤中钠钙铁硫对煤灰熔融过程有耦合作用，定量关系分析能够进一步深化对煤反应过程中反应性及矿物质迁移内在关系的理解。硅铝系添加剂主要影响准东煤峰值燃烧速率，而添加剂比例对燃烧特性的影响非单调。与空气燃烧相比，相同氧浓度下，O2/CO2燃烧会促进准东煤中钙的释放，却有利于铁的固化，对Na释放的影响与温度相关。煤灰中晶体物质的种类主要受到燃烧温度的影响，而燃烧气氛的影响很小。. 其次，本文基于HRTEM图像数据，提出了一种快速耦合堆垛和孔径分布的高碱煤焦大分子建模方法。基于Perl语言开发了相应的建模自编程序Fringe3D和Vol3D，实现了构建具有特定孔径分布和多种赋存形态Na分布的煤焦大分子模型。相同氧气浓度下，O2/CO2燃烧条件下的积灰要弱于空气燃烧，而O2/CO2燃烧中O2浓度的升高加剧积灰现象，准东煤中Fe、Ca元素与铝硅化合物反应生成低温共熔体，在高温下出现粘性较强熔融相。管壁面温度对积灰趋势的影响非单调，积灰机理随着积灰时长会发生变化。. 最后，空气和O2/CO2气氛下准东煤灰熔融温度几乎没有差别，但煤灰的微观理化特性存在差异。O2/CO2气氛主要影响到熔融煤灰表面Ba、Na和Ca元素的分布，而O2浓度是影响准东煤熔融灰表面微观形貌的主要因素。O2/CO2燃烧气氛下，随着温度的升高灰渣中各矿物质相的特征峰强度逐渐降低，灰渣中的晶相向玻璃态或非晶态物质转变。灰渣中石英、钙黄长石和尖晶橄榄石承受高温能力较强。. 本项目的开展能够为控制高碱煤O2/CO2燃烧积灰结渣问题提供理论基础。.