激光诱导击穿光谱法测量煤中碳含量的基体效应及其消除

发布时间：2018-05-23 09:09

本文选题：激光诱导击穿光谱 + 基体效应　；参考：《清华大学》2014年博士论文

【摘要】：研制开发煤质在线检测装置,对于电厂提高运行效率、降低污染排放和提高运行安全性等方面都十分重要。激光诱导击穿光谱技术(LIBS)由于具有检测速度快、几乎无需样品制备和能够同时进行多元素测量等优点,在煤质在线检测上极具应用潜力。实现LIBS在煤质在线检测上的应用,关键之一在于实现LIBS对煤中碳含量的准确测量。然而,由于煤的化学组成和结构十分复杂,LIBS对煤中碳含量的测量会受到复杂的基体效应的影响,导致测量的准确性较差。本文研究了基体效应对LIBS测量煤中碳含量的影响及其产生原因。研究表明,煤中挥发分和灰分含量的变化是产生基体效应的主要原因。当挥发分含量较高时,等离子体中烧蚀产生的碳原子数量偏低,导致碳原子谱线强度偏低。随着灰分含量增加,等离子体温度升高,从而影响碳原子谱线强度。对此,本文研究了消除LIBS测量煤中碳含量受到的基体效应的数据处理方法。首先,本文建立了用于光谱数据预处理的光谱标准化方法。该方法采用碳双原子分子(C2)和碳氮双原子分子(CN)的谱线强度补偿在测量高挥发份含量的煤时出现的碳原子谱线强度降低。对于补偿后的碳原子谱线强度,该方法又利用光谱数据消除了由于等离子体的总粒子数密度、温度和电子密度变化对其造成的影响,从而有效提高了LIBS测量煤中碳含量的准确性和精度。然后,本文建立了基于光谱标准化的偏最小二乘(PLS)定标模型。该模型利用光谱标准化后的碳原子谱线强度提取碳含量的主要信息,利用PLS方法修正残差,使得LIBS对煤中碳含量测量的准确性进一步提高。本文进一步利用空间限制作用方法提高基于光谱标准化的PLS定标模型的性能。首先,本文通过等离子体在不同尺寸圆柱型坑洞的空间限制作用下辐射强度的时空分布实验,证明了空间限制作用的机理在于反射激波与等离子体中烧蚀物质蒸气的相互作用。实验表明,当坑洞直径的尺寸适中,并且坑洞的高度与等离子体高度相近时,圆柱型坑洞具有最优的空间限制作用效果。然后,本文设计了尺寸适中的圆柱型坑洞,用于煤中碳含量的测量。结果表明,在坑洞限制作用下应用基于光谱标准化的PLS定标模型,能够进一步提高LIBS测量煤中碳含量的准确性和精度。
[Abstract]:It is very important for power plant to improve operation efficiency, reduce pollution emission and improve safety of operation. Laser induced breakdown spectroscopy (LIBS) has the advantages of high detection speed, little need for sample preparation and multielement measurement at the same time, so it has great application potential in on-line coal quality detection. One of the key points to realize the application of LIBS in on-line coal quality detection lies in the accurate measurement of coal carbon content by LIBS. However, because the chemical composition and structure of coal are very complex, the measurement of carbon content in coal will be affected by complex matrix effect, which leads to the poor accuracy of the measurement. In this paper, the effect of matrix effect on the measurement of carbon content in coal by LIBS and its causes are studied. The results show that the change of volatile matter and ash content in coal is the main cause of matrix effect. When the content of volatile matter is high, the number of carbon atoms produced by ablation in plasma is low, which leads to the low intensity of the spectrum line of carbon atom. With the increase of ash content, the plasma temperature increases, which affects the intensity of carbon atom line. In this paper, the data processing method for eliminating the matrix effect of carbon content in coal measured by LIBS is studied. Firstly, a method of spectral standardization for spectral data preprocessing is established. In this method, the spectral line strength of carbon diatomic molecule (C2) and carbon nitrogen diatomic molecule (CN2) is compensated for the decrease of the intensity of the carbon atom line in the measurement of coal with high volatile content. For the compensated spectral line strength of the carbon atom, the influence of the total particle density, temperature and electron density of the plasma on it is eliminated by using the spectral data. Therefore, the accuracy and accuracy of LIBS measurement of coal carbon content are improved effectively. Then, a partial least square (PLS) calibration model based on spectral standardization is established. In this model, the main information of carbon content is extracted by the intensity of carbon atom spectral line after spectral standardization, and the residual error is corrected by PLS method, which makes the accuracy of the measurement of carbon content in coal further improved by LIBS. In this paper, the performance of the PLS calibration model based on spectral standardization is further improved by using the spatial limiting action method. Firstly, the spatiotemporal distribution of the radiation intensity of the plasma under the space limitation of different size cylindrical potholes is proved to be due to the interaction between the reflected shock wave and the ablative material vapor in the plasma. The experimental results show that when the diameter of the hole is moderate and the height of the hole is close to the height of the plasma, the cylindrical hole has the best effect of space restriction. Then, a cylindrical hole of moderate size is designed to measure the carbon content in coal. The results show that PLS calibration model based on spectral standardization can further improve the accuracy and accuracy of LIBS measurement of carbon content in coal.
【学位授予单位】：清华大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM621

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