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The effects of particle size and reducing-to-oxidizing environment on coal stream ignition

机译：粒径和还原氧化环境对煤流着火的影响

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摘要

Coal particles experience a transition from a reducing to oxidizing environment in the near-burner region of pulverized coal (pc) boilers. For the first time, we report a fundamental study of ignition of a coal-particle stream experiencing a flame environment that transitions from a reducing to an oxidizing environment (termed reducing-to-oxidizing environment). High-speed videography is used to observe the particles in situ, and scanning electron microscopy is used to characterize the sampled particles. The effects of particle size on ignition are presented for four size bins (63–74 µm, 75–89 µm, 90–124 µm and 125–149 µm) for PRB subbituminous coal at two nominal gas temperatures (1300 K and 1800 K). An oxidizing environment with 20% molar oxygen composition is used as base-case. In contradistinction to single particle studies where particles are reported to ignite heterogeneously at higher temperatures, this study shows that coal streams ignite homogeneously, irrespective of particle size, in the oxidizing environment. By changing nominal gas temperature from 1300 K to 1800 K, ignition time decreases, on average, by a factor of five for each of the particle size bins. For both gas temperatures, the trend in ignition delays as particle size changes is non-monotonic. However, at 1800 K nominal gas temperature, ignition delays are independent of particle size in the reducing-to-oxidizing environment and ignition delays are doubled on average when compared to those in the oxidizing environment. It is more noticeable at the lower gas temperature of 1300 K that homogeneous ignition of coal streams is oxygen-dependent below 90 µm particle size and temperature-dependent above 90 µm. In general, ignition delay is determined by volatile release rate (controlled by the particle temperature) and the local oxygen concentration. Micrographs of particles also confirm that ignition and char burnout times are longer in the reducing-to-oxidizing environments than those in the oxidizing environments.
机译：在煤粉锅炉附近的燃烧器区域，煤颗粒经历了从还原到氧化的转变。我们首次报告了对煤颗粒流着火的基础研究，该煤颗粒流经历了从还原环境转变为氧化环境（称为还原-氧化环境）的火焰环境。高速摄影术用于原位观察颗粒，而扫描电子显微镜则用于表征采样的颗粒。给出了两种标称气体温度（1300 K和1800 K）下PRB次烟煤的四个粒度仓（63-74 µm，75-89 µm，90-124 µm和125-149 µm）对点火的影响。 。具有20％摩尔氧含量的氧化环境用作基本情况。与单颗粒研究不同，在单个颗粒研究中，据报道颗粒在更高的温度下会不均匀地燃烧，这项研究表明，在氧化环境中，无论颗粒大小如何，煤流均能燃烧。通过将标称气体温度从1300 K更改为1800 K，对于每个粒度仓，着火时间平均缩短五倍。对于两种气体温度，随着粒径变化点火延迟的趋势都是非单调的。但是，在标称气体温度为1800 K时，在氧化还原环境中，点火延迟与粒径无关，与氧化环境中的点火延迟相比，点火延迟平均增加了一倍。在1300 K的较低气体温度下，煤流的均质着火在90 µm以下的粒度取决于氧气，而在90 µm以上的温度则取决于氧气。通常，点火延迟由挥发物释放速率（受颗粒温度控制）和局部氧气浓度决定。颗粒的显微照片还证实，在还原至氧化环境中，点燃和炭烧尽时间要比在氧化环境中更长。

著录项

  • 来源
    《Combustion and Flame》 |2018年第9期|282-291|共10页
  • 作者

    Adewale Adeosun; Zhenghang Xiao; Zhiwei Yang; Qiang Yao; Richard L. Axelbaum;

  • 作者单位

    Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis;

    Department of Thermal Engineering, Tsinghua University;

    Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis;

    Department of Thermal Engineering, Tsinghua University;

    Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    Reducing-to-oxidizing environment; Coal; Homogeneous; Ignition; Coal stream;

    机译：还原氧化环境;煤;均质;点火;煤流;

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