https://doi.org/10.3389/fphy.2022.1054796
“Coal resources play a very important role in the energy structure, especially in the field of thermal power generation. However, in thermal power generation, coal resources can’t be used efficiently for various reasons, resulting in a waste of energy. Due to the advantages of many kinds of elements and rapid measurement, X-fluorescence spectroscopy (XRF) can rapid measurement a variety of metal elements in coal. Combined with partial least squares (PLS), the relationship between a variety of elements and ash in coal can be established, and the ash value in the measured coal can be quickly obtained, which can effectively guide the coal combustion process of power plant, so as to improve the utilization rate of coal. The experimental results show that under the PLS model, XRF technology has good measurement results for the ash content of 45 calibration set coal samples, in which the determination coefficient of the fitting curve (R2) reaches 0.946, and the root mean square error (RMSE) is only 1.177%. The accuracy of the model is further predicted under a cross validation. 15 validation set coal samples are brought into the model for prediction. According to the prediction results, the R2 reaches 0.982, and RMSE is only 0.726%. Finally, four of the 60 samples are randomly selected for stability test, and the relative standard deviation (RSD) is less than 1%. Therefore, the quantitative analysis method of XRF method based on PLS model has high accuracy and stability, which can provide guidance for rapid online measurement of coal ash and coal blending.”
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2.2 XRF setup
As shown in Figure 1, XRF experimental device is mainly composed of X-ray tube (rhodium target), Ultra-high performance silicon drift detector (SDD), vacuum chamber, high-voltage power supply, vacuum pump and PC, which belongs to energy dispersion type. After the high-voltage power supply supplies power to the X-ray tube, the X-ray is generated and acts on the sample of the sample table in the vacuum chamber. The signal light generated by the interaction between the X-ray and the sample is detected by SDD and finally input to the PC terminal to obtain the spectrum. During measurement, the vacuum chamber always maintains a vacuum of 150 Pa, which is controlled by the vacuum pump. Here, the current and voltage of the X-ray tube are 0.3 mA and 10 kV respectively, and the measurement time of each sample is 30 s. Because X-ray is sensitive to temperature change, which will affect the accuracy of the final spectral line, the whole experiment is kept under constant temperature control at 25 an.
FIGURE 1. XRF experimental setup, here, 1, high-voltage power supply; 2, X-ray tube; 3, vacuum chamber; 4, sample table; 5, vacuum pump; 6, SDD; 7, PC.
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3.1 Spectrum
As shown in Figure 2, the XRF spectrum of coal sample is shown. The abscissa represents the track number, which corresponds to the energy of each element, and the ordinate represents the intensity. The metal elements related to ash in the coal sample are marked in the figure. Because S also affects the ash value, the strength of element S is also used as an input variable to establish the model. The spectral data are integrated and normalized for subsequent model.
FIGURE 2. XRF spectrum of coal sample.
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