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Investigations on the emissivity of burning coal char particles: Influence of particle temperature and composition of reaction atmosphere

机译：燃烧煤焦颗粒的发射率研究：颗粒温度和反应气氛组成的影响

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摘要

Radiative properties of burning char particles are one of the key parameters for heat transfer in pulverized fuel boilers. Among the parameters which are suspected to change emissivity of burning char surfaces, particle temperature and the reaction atmosphere (air-fired vs. oxy-fuel) are two factors needing investigation. An experimental campaign is presented which studies the effect of both factors in the spectral range from 1.25 mu m to 5.5 mu m. An in-flight spectrometer test rig measuring thermal radiation emitted by single coal particles was employed. Particle temperature was adjusted by varying the oxygen content in the oxy-fuel atmosphere between 15 and 40%. Average char particle temperatures increase from 1952 to 2582 K with increasing oxygen content. The emissivity drops from epsilon = 0.6 to epsilon = 0.26 (lambda = 2.4-5.5 mu m) and epsilon = 0.33 to epsilon = 0.24 (lambda = 1.25-2.25 mu m) with increasing temperature. The influence of the reaction atmosphere was investigated by performing experiments in a N-2/O-2 atmosphere and comparing to the results to data from an oxy-fuel atmosphere, both containing 20% of oxygen. The difference epsilon(oxy-fuel) - epsilon(N2/O2) is in the range of 0.1 and 0.2 for lambda = 1.25-2.25 mu m and lambda = 2.4-5.5 mu m. Effects of burnout and char structure are discussed to evaluate the results.
机译：燃烧焦炭颗粒的辐射特性是粉状燃料锅炉传热的关键参数之一。在怀疑会改变焦炭表面发射率的参数中，颗粒温度和反应气氛（空气与含氧燃料）是需要研究的两个因素。提出了一项实验活动，研究了这两个因素在1.25μm至5.5μm光谱范围内的影响。使用飞行中的光谱仪测试装置测量单个煤颗粒发出的热辐射。通过在氧燃料气氛中使氧含量在15％至40％之间变化来调节颗粒温度。随着氧气含量的增加，平均炭颗粒温度从1952 K升高到2582K。随着温度的升高，发射率从ε= 0.6降至ε= 0.26（λ= 2.4-5.5μm），ε= 0.33降至ε= 0.24（λ= 1.25-2.25μm）。通过在N-2 / O-2气氛中进行实验，并将结果与​​含氧量均为20％的含氧燃料气氛的数据进行比较，研究了反应气氛的影响。对于λ＝1.25-2.25μm和λ＝2.4-5.5μm，ε（氧-燃料）-ε（N2 / O2）的差在0.1和0.2的范围内。讨论了倦怠和炭结构的影响，以评估结果。

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