减少二氧化碳对LIBS检测飞灰中未燃碳含量影响的研究

Reduction of CO_2 Effect on Unburned Carbon Measurement in Fly Ash Using LIBS

通常热力发电厂将飞灰中未燃碳的含量作为评价锅炉燃烧效率的重要指标,通过测量飞灰中未燃碳的含量来评价煤粉燃烧的充分程度,进而实现优化燃烧、提高机组效率。基于激光诱导击穿光谱技术(LIBS)无接触、快速响应、高灵敏度、可以在线测量等特点,备用来测量飞灰中未燃碳的含量。由于烟气中CO_2气体的存在,碳谱线强度会随CO_2浓度的变化而改变。为了减少CO_2气体对飞灰未燃碳测量结果的影响,提出并设计了具有二级旋风分离器的LIBS测量飞灰未燃碳含量实验系统,飞灰从给粉机流出后通过二级旋风分离器进入测量腔体,脉冲激光经过透镜作用于飞灰样品进而产生等离子体。LIBS系统采用双中心波长光谱仪,可测得飞灰中C,Si,Mg,Fe,Ca和Al等主要元素谱线,同时高分辨率通道可分辨出相邻C和Fe的元素谱线,可以在获得充分的飞灰光谱信息的同时保证了测量的精度。实验结果表明该系统可有效分离和收集飞灰颗粒,减少CO_2气体对测量结果的干扰,为LIBS技术的工程应用提供了更准确的依据。

In thermal power plant ,the measurement of unburned carbon in fly ash becomes increasingly important because unburned carbon contents are usually important factors for the operation of power plants and it can be an indicator of the combustion conditions Thus ,the goal of combustion optimization and efficiency improvement can be achieved .More specifically ,the unburned carbon concentration in fly ash reflects the combustion efficiency of the power generator set .The combustion efficiency decreases with increasing of unburned carbon level in fly ash ,which means a loss of fuel energy .Owing to the noncontact ,fast response ,high sensitivity and online measurement features ,LIBS was used to measure the quantitative contents in fly ash in this research .But the carbon emission intensity changed with the fluctuant amount of CO2 in flue gas .In this study ,dual-channel spectrometer was utilized to analyze the elemental spectra of C ,Si ,Mg ,Fe ,Ca ,Al and so on ,and the neighboring elemental spectra ,such as C and Fe ,can be recognized in the high resolution channel ,which means sufficient fly ash spectrum information can be gained with enough measurement accuracy at the same time .Cyclone was designed and two-stage cyclone system was proposed into the system of LIBS measurement for unburned carbon contents in fly ash .Fly ash particles from the feeder flow through the two-stage cyclone and went into the chamber .The laser shot on the fly ash through the lens .Plasma was acquired and then recorded and analyzed by spectrometer and ICCD camera .The two-stage cyclone system was proven to be detectable for the unburned carbon in fly ash .In addition ,two-stage cyclone system can be able to separate and collect fly ash particles from flow gas to reduce the influence of CO2 in fly ash particle flow ,thus ,exact data can be got to guide the operation of the thermal power plant ,which provide more benefits to the engineering applications of LIBS .