磁场环境下铝电解熔融铝液成分激光诱导击穿光谱原位测量分析

铝电解车间具有高温、强磁、多粉尘等环境特点,当前生产过程中熔融原铝的成分检测主要是人工取样然后离线分析,化验过程及结果具有较大的滞后性,故将激光诱导击穿光谱(LIBS)技术应用于铝电解车间铝液成分原位、实时测量具有重要意义。实验采用Nd:YAG脉冲激光器,多通道光纤光谱仪和电感耦合器件(CCD)探测器组成的激光诱导击穿光谱测量系统对电流为400kA电解槽中熔融铝液的主要成分铁、硅进行了探测,对原铝中部分元素的特征谱线进行了归属分析。考察了激光能量在磁场环境下的衰减变化及谱线梯度变迁规律,结果表明,距离电解槽边缘约2m处激光能量衰减达最大。分析了磁场对测试系统的影响,并建立了定标曲线,铁和硅两种元素按照内标法建立的定标曲线拟合度分别为93.50%和97.10%,采用该模型进行了测试实验,并用国标GB/T 7999—2015中光电直读发射光谱(OES)测试的相关指标验证测试结果的重复性与允许差。实验证明,LIBS技术在电解铝行业在线检测方面具有较好的应用前景,但是测试的稳定性与重复性也是面临的一个重要问题。

In-situ measurement and quantitative analysis of molten aluminum liquid ingredient by laser-induced breakdown spectroscopy under magnetic field condition

The aluminum electrolysis workshop has the environmental characteristics of high temperature, strong magnetism and heavy dust. In the current production process, the composition of molten raw aluminum is usually analyzed offline after manual sampling. The detection process and results are greatly lagging. Therefore, the application of laser induced breakdown spectrum (LIBS) technology for the in-situ and real-time measurement of aluminum liquid composition in electrolysis workshop has important significance. The laser-induced breakdown spectroscopy system composed of Nd: YAG pulsed laser, multichannel fiber optic spectrometer and charge coupled device (CCD) detector was used. The main composition including iron and silicon in molten aluminum liquid in 400kA electrolytic cell was detected. The attribution analysis of characteristic lines for some elements in molten aluminum liquid was carried out. The attenuation and gradient evolution laws of laser energy in the magnetic field were investigated. The results showed that the maximum attenuation of laser energy was at the position with distance of 2m to the edge of electrolytic cell. The effect of magnetic field on the test system was analyzed. The calibration curve was also established. The fitness of calibration curves for Fe and Si based on the internal standard method was 93.50% and 97.10%, respectively. The proposed model was used for testing experiments. The repeatability and admissible error of measurement results were verified using the related indexes in optical emission spectrometry (OES) in GB/T 7999-2015. The results showed that LIBS technology had good application prospects in online detection in electrolytic aluminum industry. However, the stability and repeatability in measurement were also important problems.