Pollutant formation during oxy-combustion of coal

化石燃料燃烧产生的二氧化碳排放是全球变暖的一个重要问题。发电厂正在考虑的一种碳捕获和封存技术是氧煤燃烧。因此，需要对氧煤燃烧的运行和环境影响进行评估。与空气燃烧相比，氧气燃烧也可以减少二氧化硫的排放，因为烟道气中含有高浓度的三氧化硫，导致飞灰和炉膛中的火山灰沉积物上的硫保留。飞灰颗粒上较高的固硫率降低了二氧化硫的排放量，另一方面也带来了将飞灰用于水泥和混凝土生产的问题。需要对氧气燃烧条件下的二氧化硫排放进行进一步的研究，特别是调查飞灰的滞留情况。与氮氧化物和硫氧化物的排放相比，富氧燃烧中痕量金属排放的问题在文献中并没有得到太多的关注，关于富氧燃烧条件下汞的转化的报道也很少。令人担忧的一个领域是，汞和三氧化硫等污染物会导致二氧化碳压缩机和再循环管道的腐蚀。氧气燃烧和空气燃烧的特性有很大不同，这导致了污染物在烟气中的行为发生变化，从而产生了排放。随着这一领域的研究开始增长，对污染物形成的基本理解仍有待阐明，在开发去除技术之前，需要了解这些污染物在氧化燃烧条件下的形态和行为。该项目的目的是调查空气和氧气燃烧条件下污染物行为的差异。这项研究的独特之处在于，它将首次在基础水平上全面调查富氧燃料燃烧过程中污染物的形成，将小试实验、动力学模拟和分子模拟相结合。该项目完成后的两个主要里程碑是：1)通过小试实验和动力学模拟，阐明了硫氧化物和微量金属的气相化学，以及其他烟气成分的影响和回收利用；2)通过小试实验和分子模拟，研究了硫氧化物和微量金属在飞灰上的非均相化学，确定了飞灰的固硫机理。本研究将为燃煤电厂了解与烟气中污染物相关的腐蚀风险以及对飞灰的污染提供有用的信息飞灰上的硫磺滞留程度可能会阻止他们将飞灰出售给混凝土生产商。除了实践知识外，它还将提供对烟道气和飞灰表面发生的污染物化学的基本了解。将从该项目产生的实验数据将在文献中提供，并可用于验证文献中现有的模型。此外，从事该项目的研究生和本科生将获得燃烧化学的深入知识以及出色的实验和建模技能。

Carbon dioxide emissions from combustion of fossil fuels is of great concern for global warming. A technology being considered for carbon capture and sequestration in power plants is oxy-coal combustion. Thus, the operational and environmental impacts of oxy-coal combustion need to be evaluated. Sulfur dioxide emissions can also be reduced with oxy-firing compared to air combustion due to high concentrations of sulfur trioxide in the flue gas resulting in sulfur retention on fly ash and ash deposits in the furnace. Higher sulfur retention on the ash particles reduces the sulfur dioxide emission rates, on the other hand it creates problems utilizing the fly ash for cement and concrete production. Further research regarding the sulfur dioxide emissions under oxy-firing conditions needs to be performed, specifically to investigate the fly ash retention. In comparison to the emissions of nitrogen and sulfur oxides, the subject of trace metal emissions in oxy-fuel combustion has not received much attention in the literature and little information has been reported on the mercury transformations under oxy-fired conditions. One area of concern is that the pollutants such as mercury and sulfur trioxide cause corrosion in carbon dioxide compressors and recirculation lines. The characteristics of oxy-combustion and air-combustion are fairly different and this results in changes in the behavior of pollutants in the flue gas, thus the emissions. As research in this area is beginning to grow, the fundamental understanding of pollutant formation remains to be elucidated and before developing removal technologies, one needs to understand the speciation and behavior of these pollutants under oxy-fired conditions. The objective of this project is to investigate the differences in pollutant behavior under air- and oxy-fired conditions. This research is unique in the fact that it will be the first comprehensive investigation of pollutant formation during oxy-fuel combustion at a fundamental level combining bench-scale experiments, kinetic modeling and molecular modeling. Two major milestones that will be achieved by the end of this project are the following: 1) Gas phase chemistry of sulfur oxides and trace metals will be elucidated by both bench-scale experiments and kinetic modeling and effects of other flue gas constituents and the recycling will be determined 2) Heterogeneous chemistry of sulfur oxides and trace metals on fly ash will be investigated by bench-scale experiments and molecular modeling and the mechanism of sulfur retention on fly ash will be identified.This research will provide useful information for the oxy-fired power plants regarding the risk of corrosion associated with the pollutants in the flue gas as well as the extent of sulfur retention on fly ash that could prevent them selling the fly ash to concrete producers. Besides the practical knowledge, it will also provide a fundamental understanding of the pollutant chemistry that is taking place in the flue gas and on the fly ash surface. Experimental data that will be produced from this project will be made available in the literature and could be used to validate the existing models in the literature. Additionally, the graduate and undergraduate students working on this project will gain an in-depth knowledge of combustion chemistry as well as excellent experimental and modeling skills.