Additional criteria for MILD coal combustion
Additional criteria for MILD coal combustion
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DOI：
10.1016/j.proci.2020.06.175
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发表时间：
2020-08
期刊：
影响因子：
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通讯作者：
Hang Zhou;T. Ring;J. Sutherland
中科院分区：
文献类型：
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作者：
Hang Zhou;T. Ring;J. Sutherland
提出了基于湍流标量能谱的中强低氧稀释（MILD）煤燃烧的理论基础。这是由以下假设激发的：最小标量混合长度尺度应该是颗粒尺寸的量级或更小，以确保混合可以发生以防止扩散火焰的形成。我们提出的标准进行评估，使用几个实验数据集从文献中的煤燃烧在温和的和传统的燃烧制度。实验结果证实，在MILD煤燃烧中，要打破颗粒周围的传热传质边界层，最小混合长度尺度应在颗粒直径η mixdp的数量级或更小。结果表明，小颗粒周围的小施密特数的物种混合不良导致反应器中的高发光强度。分析了入口速度和射流直径对混合长度尺度的影响。较高的入口速度和较小的射流直径有望达到MILD区。该判据可用于指导实现煤燃烧MILD工况的试验设计。
We proposed a theoretical basis for Moderate or Intense Low-oxygen Dilution (MILD) coal combustion based on the turbulent scalar energy spectra. This is motivated by the hypothesis that smallest scalar mixing length scales should be on the order of the particle size or smaller to ensure that mixing can occur to prevent formation of diffusion flames. Our proposed criterion is evaluated using several experimental datasets from the literature for coal combustion in both MILD and traditional combustion regimes. The experimental results confirm that the smallest mixing length scales should be of the order of or smaller than the particle diameter,ηmix⪅dp, to breakup the heat and mass transfer boundary layers around particles in MILD coal combustion. Results indicate that poor mixing of species with small Schmidt numbers around small particles leads to the high luminous intensity in the reactor. The effects of inlet velocity and jet diameter on the mixing length scales are analyzed. Higher inlet velocity and smaller jet diameter are expected to reach MILD regime. The proposed criterion can be used to guide experimental design to achieve MILD conditions for coal combustion.