煤粉着火燃烧过程光学诊断研究发展

煤炭储量丰富,尽管新能源和可再生能源快速发展,煤炭资源在未来几十年仍将作为我国一次能源重要组成部分。同时煤炭利用带来很多环境污染问题,因此未来煤炭资源的利用逐渐向高效、低碳、低污染物排放利用方式转变。随着光学技术的不断发展,涌现出多种适用于煤粉燃烧诊断的原位非接触式光学诊断技术,极大地促进了燃烧学的发展,为煤炭清洁高效利用提供了更多试验手段。介绍了国内外煤粉着火、不同方式下燃烧特性的光学诊断研究进展,对煤粉单颗粒和煤粉颗粒流的着火燃烧过程的光学诊断研究进行总结。目前常用的煤粉燃烧光学诊断技术主要包括全光谱成像、CH*/C2*化学发光成像、平面激光诱导荧光(PLIF)、双色/三色高温计、米氏散射、激光诱导白炽光、相干反斯托克斯-拉曼光谱、激光诱导击穿光谱等多种先进的光学诊断技术,可对煤粉单颗粒、颗粒流的着火延迟、脱挥发分、挥发分燃烧、着火模式、环境因素(环境温度、氧浓度、气氛)、富氧燃烧、水-氧燃烧、煤中碱金属释放等多方面关键问题进行光学诊断研究,为煤炭清洁高效利用提供了理论和试验基础。采用OH-PLIF和三色高温计对热解半焦和神华烟煤混合燃料共燃的着火和燃烧特性进行研究。综合考虑着火延迟和混合物的燃尽率,热解半焦的最佳掺混比为20%,为热解半焦的实际工业应用提供了参考。同时采用500 Hz、5 k Hz高时间、空间分辨率的OH-PLIF技术探究煤粉颗粒流中单颗粒挥发分燃烧的发展过程和挥发分着火的时序演变过程,通过二者的结合获得煤粉颗粒流从着火到挥发分燃烧的时间特性。采用OH-PLIF技术对烟煤和褐煤煤粉颗粒流燃烧火焰的脱挥发分和挥发分燃烧行为进行探究,提出采用OH信号径向分布的相对标准偏差探究火焰稳定性的方法。相同燃烧条件下,烟煤煤粉颗粒流燃烧的稳定性高于褐煤。基于OH-PLIF和CH*化学发光诊断技术,提出一种用于探究煤粉颗粒流中颗粒挥发分燃烧振荡特性分析方法——动态模态分解方法(DMD)。随着氧浓度的增加,挥发分火焰振荡增强。颗粒的聚集可能导致煤粉挥发分燃烧的低频振荡。相反,单独或分离的颗粒燃烧会产生较大的振荡频率。但目前取得的成果还不够完善,需要继续深入开展煤粉燃烧的光学诊断试验研究,对污染物NOx的生成及排放、新型水氧燃烧技术中水蒸气作用机理等方面深入探索,开发出新型清洁煤燃烧技术,为我国煤炭资源清洁高效利用做出贡献。

Research progress on the optical diagnostics of pulverized coal ignition and combustion process

Coal,as an important fossil fuel,has abundant reserves.Despite the rapid development of new and renewable energy,coal resources will continue to be an important part of China's primary energy in the coming decades.However,the utilization of coal brings a lot of environmental pollution problems.As a result,the utilization of China's coal resources gradually transforms to the high efficiency,low carbon,and low NO x technology.With the rapid development of optical diagnostics technology,a variety of in situ non-invasive optical diagnostic techniques that is suitable for pulverized coal combustion diagnosis have emerged,which greatly promotes the development of the combustion science and provides more experimental methods for the clean and efficient utilization of coal.In this paper,the research progress of optical diagnosis on ignition and combustion characteristics of pulverized coal in different ways at home and abroad was introduced.The optical diagnostics research progress on ignition and combustion process of pulverized coal for both single particle and particle streams was summarized.At present,the optical diagnostic techniques used for pulverized coal combustion includes:full spectrum imaging,CH*/C*2 chemiluminescence imaging,planar laser induced fluorescence(PLIF),double color/three-color pyrometer,Mie scattering,laser induced incandescence(LII),coherent anti stokes Raman spectroscopy(CARS),laser-induced breakdown spectroscopy(LIBS)and so on.The optical diagnosis research on ignition delay,devolatilization,volatile combustion,ignition mode,environmental factors(ambient temperature,oxygen concentration,atmosphere),oxy-fuel combustion,oxy-steam combustion,the release of alkali metals for both single particle and particle streams was analyzed to provide theoretical and experimental foundation for clean and efficient utilization of coal.The ignition and combustion characteristics of pyrolyzed char and Shenhua bituminous coal blended fuel were studied by using OH-PLIF and three-color pyrometer.Considering the ignition delay and the burnout ratio of the blending,the optimal blending ratio of pyrolyzed char is 20%,which provides a reference for actual industrial application of pyrolyzed char.OH-PLIF diagnostic technology with high temporal and spatial resolution of 500 Hz and 5 kHz were used to investigate the development process of volatiles combustion and the evolution process of volatiles ignition of single particle in pulverized coal particle stream.The time characteristics from ignition to volatiles combustion of pulverized coal particle stream were obtained through the combination of the two.The devolatilization and volatile combustion behavior of pulverized bituminous coal and lignite were investigated with OH-PLIF technology.The relative standard deviation of radial OH signal distribution was used to describe the flame stability.The stability of bituminous coal particle stream combustion is higher than that of lignite under the same combustion conditions.Based on OH-PLIF and CH*chemiluminescence diagnostic techniques,a dynamic mode decomposition method(DMD)was proposed to investigate the combustion oscillation characteristics of volatiles in pulverized coal particle stream.With increase of oxygen concentration,the oscillation of volatile flame is enhanced.The agglomeration of particles may lead to lower frequency oscillation for pulverized coal volatiles combustion.On the contrary,higher oscillation frequency will be produced by individual or separate particle combustion.However,the current achievements are not sufficient.So it is necessary to continue to carry out in-depth research on the optical diagnosis test of pulverized coal combustion,explore the generation and emission of NO x and the mechanism of water vapor in new water-oxygen combustion technology,and develop new clean coal combustion technology,so as to make further contribution to the clean and efficient utilization of Chinese coal resources.