Fig. 1. Experimental NIRS-XRF setup for analyzing calorific value of coal

Fig. 2. Three-dimensional structure of experimental NIRS-XRF setup for analyzing calorific value of coal

Fig. 3. Typical XRF spectrum of coal

Fig. 4. XRF spectra of calibration samples

Fig. 5. Typical NIRS spectra for coal

Fig. 6. NIRS spectra of calibration samples

Fig. 7. Typical XRF pretreatment spectra of coal

Fig. 8. Typical NIRS pretreatment spectra of coal

Fig. 9. Regression coefficient of NIRS spectra

Fig. 10. Normalized spectrum

Fig. 11. Comparison of predicted and certified calorific values of coal by using single NIRS and NIRS-XRF

Fig. 12. Comparison of measurement repeatability of calorific value of coal between single NIRS and NIRS-XRF