Research On Detction Of Concentration Of Ash In Coal Based On LIBS

The concentration of ash in coal is important to evaluating quality of coal.It is also the basis of rational coal application. Fast and accurate On-line measurement is turly important to evaluating and exploiting coal. It is also the procedure which is crucial to solving low energy efficiency and environmental pollution. Traditional method with detecting the concentration of ash in coal cannot meet the demand of modern industry because of complicated procedures and long time. There are some defects with on-line measurement of ash content, such as low accuracy, high cost and security risks. Laser-induced breakdown spectroscopy (LIBS) is based on studying atomic lines which are generated from the ablation of sample with high power laser pulse in the transient plasma emission. With the development of laser technology and spectroscopy equipment, LIBS is becoming a potential industrial process monitoring technique because of the excellent benefits including multi-element detection at the same time,accurate analysis which do not need any sample pretreatment. The LIBS also has great potential for the concentration of ash in coal on-line measurement.Laser plasma generation is complicated process. It is easily influenced by many factors, for example, energy of laser, triggering time of spectrometer, environment, preparing for samples, matrix effect of sample and data acquisition method. These factors will affect the accuracy of quantitative analysis. The traditional method of quantitative analysis for LIBS is calibration. Although calibration method can quantitative analyze target sample relatively accurate,, accuracy is always restricted by self-absorption and matrix effect.Researchers indicated that partial least squares (PLS) method can reduce the influence of matrix effect, furthermore, it can improve the detection accuracy. Compared with other types of modeling methods, PLS has its own advantages, such as less computing tasks, stable and simple, easy to qualitatively explaining.In this thesis, concentration of ash in coal is the investigating objective, quantitative analysis is the technical target, PLS model in processing of spectrum data is discussed using experimental data and simulated data.The begin of the two chapters introduce its background and significance, and take a overview of the necessity and limitations of ash content on-line measurement and several methods of ash content on-line measurement currently. As a rising technology chemical analysis, laser-induced breakdown spectroscopy is introduced by comparing the advantages and disadvantages of the traditional methods. The Chapter2introduces the principle and qualitative analysis of laser-induced breakdown spectroscopy and investigates the formation mechanism and characteristic of the plasma.The Chapter3introduces the quantitative analysis models of laser-induced breakdown spectroscopy, including traditional calibration model, internal calibration model,free calibration model and autocorrelation analysis model, then introduces partial least squares method. The idea and theoretical basis of PLS method are focused on. The description of the character and modeling to PLS is given detailed.The Chapter4and Chapter5are the principal part of full thesis, which utilizes experimental data and simulated data of laser-induced breakdown spectroscopy to investigate quantitative analysis with ash content in coal. Kennard-stone algorithm is used to select training set and predition set. PLS method is utilized to establish quantitative analysis model, and quantitative analysis for prediction set is verified. The result shows that the laser induced breakdown spectroscopy combined with partial least squares method can detect the concentration of ash content in coal.For the experimental data, the average relative errors (REP) are8%mass fraction approximate. For the simulated data, the average relative errors (REP) are1.06%mass fraction approximate. The experiment verifies the applicability of the laser induced breakdown spectroscopy in synchronization measurement of ash content in coal. The Chapter6is a summary of this thesis, and for the practical problems in ash content in coal detection application, Chapter6gives some suggestions。 In the end, prospects for further work is given.