Temperature Measurements and Submicron Ash Formation in Oxy-Coal Combustion

CBET-0755431LvendisOxy煤燃烧是一种很有前途的清洁煤技术，可能会减缓全球变暖。尽管探索可再生能源很重要，但在任何可以想象到的未来能源情景中，煤炭可能仍将是一种重要的能源。为了减缓全球变暖，应该通过提高发电、传输、分配和使用的效率以及通过二氧化碳捕获和封存来限制二氧化碳排放。废气中低浓度的氮气稀释二氧化碳是从传统的风吹式煤粉燃烧中捕获二氧化碳成本高的主要驱动力。在纯氧或与循环烟气混合的氧气中燃烧煤炭可以产生富含二氧化碳的流出物，从而降低直接压缩和储存烟气的成本。为了充分发挥氧煤燃烧技术的潜力，本研究对在相关条件下使用单一煤粉的燃烧过程有了基本的了解。煤在O2/CO2气氛而不是O2/N2气氛中的燃烧动力学很重要，因为CO2可以(1)与煤反应，(2)通过其传输性质和热容相对于氮的差异影响温度，以及(3)通过可逆反应MO+CO=M+CO2抑制灰烬中难熔氧化物的蒸发，其中M可以是铁、镁或二氧化硅。这项工作将多年来在常规煤/空气燃烧中开发的所有实验和分析工具应用于氧煤燃烧领域，并解决了重要的基本问题：在氧煤燃烧中，煤颗粒燃烧得更热、更快，是增加还是减少了污染物排放。用多色光学高温法观测了煤粒的燃尽史，并由此推算出燃烧温度和反应速率。由于煤颗粒的最高温度可能比最高气体温度高出数百度，因此颗粒温度的知识对于评估整体炉膛效率、炉膛出口气体温度以及锅炉内灰渣的堵塞和结垢倾向非常重要。此外，在这项工作中，监测了氧煤燃烧废气中燃烧生成的颗粒物和其他污染物，并将其与传统燃烧过程中的颗粒物和其他污染物进行了性质比较。由于处理含氧煤电厂污染物排放的策略仍处于形成阶段，这些数据将特别有价值。

CBET-0755431LevendisOxy-coal combustion is a promising clean-coal technology that may reduce global warming. Coal is likely to remain a vital source in any conceivable future energy scenario despite the importance of exploring renewable sources of energy. To mitigate global warming, CO2 emissions should be constrained by improving efficiency of power generation, transmission, distribution, and use, as well as through CO2 capture and sequestration. The low, nitrogen-diluted CO2 concentration in the exhaust gas is a major driving force for high costs of capturing CO2 from conventional air-blown pulverized-coal combustion. Burning coal in pure oxygen or in oxygen blended with recycled flue gases can produce a CO2-rich effluent, thereby lowering the costs of the direct compression and storage of the flue gas. For technology development in oxy-coal combustion to reach its full potential, this study provides a fundamental understanding of the process using single coal particles, under pertinent conditions. Combustion kinetics of coal in an O2/CO2 atmosphere rather than O2/N2 is important because CO2 can (1) react with coal, unlike N2, (2) influence temperature through the differences in its transport properties and heat capacity relative to nitrogen, and (3) inhibit vaporization of refractory oxides of ash through the reversible reaction MO + CO = M + CO2, where M might be Fe, Mg, or SiO. This work applies all of the experimental and analytical tools developed over years of study in conventional coal/air combustion to the domain of oxy-coal combustion, and addresses important fundamental questions: Do coal particles burn hotter and faster in oxy-coal combustion Are pollutant emissions enhanced or reduced. Burnout histories of individual coal particles are observed, with multi-color optical pyrometry, and combustion temperatures and reaction rates are deduced. Because maximum coal-particle temperatures can exceed maximum gas temperatures by as much as several hundred degrees, knowledge of particle temperatures is important for evaluation of overall furnace efficiencies, furnace exit gas temperatures, as well as slugging and fouling tendencies of ash in a boiler. Furthermore, in this work, combustion-generated particulates and other pollutants are monitored in the effluent gases of oxy-coal combustion and are compared in character to those from the conventional combustion process. Because the strategies for handling pollutant emissions from oxy-coal plants are still in their formative stages, these data will be especially valuable.