Research On The Measurement Of Organic Elements In Coal Using Laser Induced Breakdown Spectroscopy

There is a great diversity of coals in China and coal property varies everywhere.Meantime,most Chinese power plants use coal as dominant fuel for electricity generation,resulting in inevitable change of coals put into boilers.Therefore,it is very important to do coal property measurement,especially measuring the content of organic elements.Organic elements are the main elements in coal,with C、H、O、S determine coal’s calorific value and N、S burned to be pollutants.The traditional techniques of coal property measurements take too much time and effort to be used for in-situ analysis.Laser induced breakdown spectroscopy(LIBS),as a brand-new atomic emission spectroscopy and its capability of rapidly measuring multiple elements at the same time,has been seen as a promising technique for coal analysis.But the measurement accuracy is still a problem due to matrix effect of coal and difficult ionization of organic elements.15 different coals are used to build calibration models of organic elements in coal.Single spectral line is often used for direct calibration,whose accuracy is terribly bad for organic elements measurement.Research shows that the matrix effect of coal and the fluctuation of plasma temperature contribute to the low precision.A new data correction method,based on local spectral normalization and plasma temperature compensation,is developed from the theoretical formula of spectral line intensity.Partial least squares regression(PLS)is also used for calibration.The R2 value of each calibration model of organic elements is improved to around 0.9,the root mean square error of calorific value is 1.716 MJ/kg,and the average relative error is 6.89%,which is totally derived from the LIBS measurement of organic elements.LIBS is proved to be able to measure coal property online in future.For elements of less content in coal,like H、O、N、S,it is hopeful to build a easier calibration model if line intensity enhancement can be acquired.Microwave-assisted LIBS(MA-LIBS)is a newly-developed technique for signal enhancement,and is used to coal analysis in this paper.With different microwave power applied to LIBS,spectral line gain and plasma temperature is studied to choose the best power.When microwave of optimized power is coupled to LIBS,how the line intensity varies with laser energy is also investigated.Results show that MA-LIBS enables line intensity enhancement in coal analysis,but further steps must be taken to get better signal enhancement.