Development Of A Coal Quality Analyzer Based On Laser-Induced Breakdown Spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) is a new type of Laser ablation spectrum analysis technology. The technology uses a high power pulse to interact with material, producing the transient plasma, using the optical system to collect the atoms and ions emission spectrum. According to the corresponding spectrum to achieve the qualitative and quantitative analysis of the chemical elements based on the atomic and ion spectrum wavelength one-to-one correspondence with the specific element, the spectral intensity and the content of corresponding element have a certain quantitative relationship. Because of the technology have the advantages of without sample pretreatment, multi-element analysis at the same time, fast speed, no radiation, etc. The technology has gradually been applied to all walks of life. For example, in terms of rapid or on-line coal quality testing. Some units at home and abroad have carried out the LIBS application in coal-fired power plant and achieved some results. But most them are still mainly stay in the laboratory stage, without really realizing the industrial application and promotion.This paper first introduces the status of coal quality testing. LIBS technology advancement, basic principle, the principle of the quantitative analysis and technical characteristics. Then optimized the LIBS experiment device parameters and developed the pulsed laser power stabilization system, guarantying the stability of the measurement for a long time. We develop a reasonable spectrum pretreatment method, and use the support vector machine (SVM) and partial least squares (PLS) to establish the calibration model for coal quality. On the basis of the research, we develop a coal analyzer for quick detection of ash content, volatile matter, calorific value, and apply it to the industrial field test. The test results proved the practicability of the equipment for the practical application. This paper is divided into the following four parts:1. Introduce the application background and current situation of the LIBS, detailed understanding the formation process of plasma and plasma element line,the broadening mechanisms the line and LIBS technical characteristics, etc.2. Establish a LIBS experiment device for coal analysis and optimize the key parameters for the system. For the technology in practical application, the long-time measurement will cause the laser output power to slow drift, we established a closed-loop feedback type laser power stabilization system. It can stabilize the laser power to the pre-set range so as to ensure the stability of the measurement for a long time.3. Build a practical and effective LIBS spectra data pretreatment methods, including the spectrum fitted by Lorentz and linear, normalization and selection. Using support vector machine (SVM) and partial least squares (PLS) establish the calibration model for coal ash industrial analysis.Then use the above two models to forecast the coal ash content. The results of the root mean square error of prediction are 4.4% and 4.4%, respectively.4. An integrated and fully software controlled LIBS-based coal quality analyzer apparatus are developed based on above research, it can perform the ash content, volatile matter, calorific value of coal samples calculation within 120s.