Effect of the primary oxidizer stream jet velocities on the ignition and combustion characteristics of pulverized coal under MILD oxy-coal combustion conditions
Effect of the primary oxidizer stream jet velocities on the ignition and combustion characteristics of pulverized coal under MILD oxy-coal combustion conditions
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DOI：
10.1016/j.fuel.2023.128876
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发表时间：
2023
期刊：
影响因子：
7.4
通讯作者：
Yuegui Zhou;Ting Zhang;Bo Zhou
中科院分区：
文献类型：
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作者：
Yuegui Zhou;Ting Zhang;Bo Zhou
MILD富氧煤燃烧技术是一种具有前景的CO2捕集和封存技术，其特点是通过氧化剂或燃料喷射的高速作用，进行强烈的烟气再循环来预热燃料并稀释氧化剂。在 O2/CO2 和 O2/N2 气氛下，在氧气浓度为 5%-21%、气体温度为 1473–1873 K 的平焰煤粉燃烧器上，实验研究了 1.7 m/s 至 11.2 m/s 范围内的初级氧化剂流射流速度对煤点火和燃烧特性的影响。通过数码相机记录煤火焰图像，分析不同一次氧化剂流射流速度和热协流条件下煤颗粒的火焰结构演变和着火延迟时间。通过光纤光谱仪监测煤燃烧辐射光谱，并通过双色高温测定法得出煤颗粒温度。结果表明，当CO2替代N2时，随着O2浓度的降低，亮黄色烟灰火焰逐渐消失。当一次空气射流速度在 1473 K 和 5% O2 下从 1.7 m/s 增加到 11.2 m/s 时，O2/CO2 气氛和 O2/N2 气氛之间的点火延迟时间差从 2.8 ms 减少到 0.2 ms。这意味着提高射流速度有利于抵消CO2物理化学性质对煤点火的延迟效应。由于 O2 加速扩散到煤颗粒流中，在具有最高喷射速度的 O2/CO2 气氛下，煤颗粒峰值温度在 1873 K 和 5% O2 下增加了 68 K。此外，提出了无量纲煤颗粒温度参数η来表征高射流速度下协流与煤颗粒之间的传热和质量传递改善引起的峰值煤颗粒温度的变化。在 O2/CO2 气氛下，在 1873 K、21% O2、射流速度为 11.2 m/s 下，η 的最大值为 1.053，表明在高气体温度和 O2 浓度下，射流速度的增加对峰值颗粒温度的升高有主要影响。
MILD oxy-coal combustion technology is a prospective technology with the potential for CO2capture and storage, and it is characterized by the intense flue gas recirculation to preheat the fuel and to dilute the oxidizer due to the oxidizer or fuel jet with high velocity. The effect of the primary oxidizer stream jet velocities ranging from 1.7 m/s to 11.2 m/s on the coal ignition and combustion characteristics were experimentally investigated on a flat flame pulverized coal burner at various oxygen concentrations of 5%-21% and gas temperatures of 1473–1873 K under O2/CO2and O2/N2atmospheres. The coal flame images were recorded by the digital camera, and the flame structure evolution and ignition delay times of coal particles were analyzed at different primary oxidizer stream jet velocities and hot coflow conditions. The coal combustion radiation spectrum was monitored by an optical fiber spectrometer and the coal particle temperatures were derived with the two-color pyrometry. The results showed that the bright yellow soot flame gradually disappeared with the decrease of O2concentration when CO2replaced N2. The difference of ignition delay times between O2/CO2atmosphere and O2/N2atmosphere decreased from 2.8 ms to 0.2 ms when the primary air jet velocity increased from 1.7 m/s to 11.2 m/s at 1473 K and 5% O2. This meant the elevated jet velocity was beneficial to offset the delayed effect of the physicochemical properties of CO2on coal ignition. The peak coal particle temperature increased by 68 K at 1873 K and 5% O2under O2/CO2atmosphere with the highest jet velocity owing to the accelerated diffusion of O2into coal particle stream. Moreover, a dimensionless coal particle temperature parameterηwas proposed to characterize the variation of the peak coal particle temperature caused by the improved heat transfer and mass transport between the coflow and coal particles under high jet velocity. The maximum value ofηwas 1.053 at 1873 K and 21% O2under O2/CO2atmosphere with the jet velocity of 11.2 m/s, indicating the increased jet velocity had the predominant effect on the increase of peak particle temperature at high gas temperature and O2concentration.