Improve The Repeatability Of LIBS Measurement And The Application To Coal Analysis

Fast coal online measurement is great important for security, stability, andefficiency of power plant operation. Currently, the online measurement devices on themarket have the shortcomings of expensive and exsitence of potential radiation hazards.However, laser-induced breakdown spectroscopy (LIBS), as a new atomic emissionspectroscopy, because of its rapid detection, capability of analysis all the elements, hasgreat potential for application to coal analysis. Howerver, the major drawback is its poorreproducibility performance. Therefore, improving reproducibility performance becomeone of the most important reseach directions in the field of LIBS.In the dissertation, we present a spectrum standardized method in order to improvethe reproducibility of LIBS measurements. The basic principle is described as below.The characteristic line intensity of the specific element is the fuction of plasmatemperature, electron number density and the total number density of the measuredelement particles according to Shah-Boltzmann equation. Supposing there is a standardplasma state (that is standard plasma temperature, electron density and the standard totalnumber density of measurement element particles). Then, for the multiplemeasurements of the same sample, convert the recorded characteristic line intensity atvarying conditions to the intensity under a standard condition to compensate the lineintsnsity fluctuations resulting from these three plasma physical parameters.However, the spectrum standardization approach needs complex calculations tocompute the electron number density and plasma temperature of each singlemeasurement. In order to overcome the shortcomings of the spectrum standardizationapproach, a simplified spectrum standardization method was proposed, which does notneed large number of calculations to explicitly convert the characteristic line intensity toa standard state, but feature plasma temperature and electron number density withinformation of characteristic line intensity. Then, Taylor expansion is applied near thestandard plasma condition to obtain the standard state value of the characteristic lineintensity from theory, and the simplified spectrum standardization model is establishedthrough theory derivation. In the simplied spectrum standardization appraoch, only one physical quantity isused to characterize plasma temperature or electron number density, so the physicalquantity is vulnerable to self-absorption and elements interference effects. To deal withthis problem, we propose a multivariate spectrum standardization method, namely usingmultiple physical quantities to characterize of the plasma temperature and electronnumber density.The spectrum standardization approach, the simplied spectrum standardizationappraoch, and the multivariate spectrum standardization method are applied todetermine Cu concentration in brass samples respectively. And results show that, notonly in improving the measurement accuracy, but also in reducing the uncertanty ofLIBS measurements, the three spectrum standardization methods achive bettereffectiveness compared to the traditional spectrum normalization method. And themultivariate spectrum standardization method yields the best results.The multivariate spectrum standardization method is applied to determine Cconcentration in coal samples, and results show that, the multivariate spectrumstandardization method can improve the measurement accuracy and reduce theuncertanty of LIBS measurement compared to the traditional spectrum normalizationmethod.