Analysis of moisture, ash, carbon, and volatile content in coal by NIRS

Importance of the topic

Efficient evaluation of coal quality parameters such as moisture, ash, fixed carbon, and volatile matter is essential for energy production, regulatory compliance, and process optimization. Traditional proximate analysis methods require extensive sample preparation, controlled-atmosphere combustion, and several hours per sample, limiting throughput in industrial and laboratory settings. Near-infrared spectroscopy (NIRS) provides a rapid, reagent-free alternative capable of delivering multi-parameter results in under one minute, supporting real-time decision making and cost reduction.

Objectives and study overview

This application note presents the development and validation of Vis-NIR calibration models for simultaneous determination of four key coal quality attributes using the Metrohm NIRS DS2500 Solid Analyzer. A set of 30 pulverized coal samples covering a wide compositional range was measured to build predictive models and evaluate accuracy against standard ASTM reference methods.

Methodology and instrumentation

The study workflow comprised:

• Sample preparation: Grinding of coal to a particle size of 0.2 mm and filling of a rotating large sample cup to minimize pathlength variability.
• Spectral acquisition: Scans recorded in the 400–2500 nm range on the Metrohm DS2500 Solid Analyzer, averaging multiple sub-spectra per sample.
• Software and calibration: Vision Air Complete software for data preprocessing, multivariate model development, and cross-validation.

Used instrumentation:

• DS2500 Solid Analyzer (Metrohm, article no. 2.922.0010)
• DS2500 large sample cup (Metrohm, article no. 6.7402.050)
• Vision Air 2.0 Complete (Metrohm, article no. 6.6072.208)

Key results and discussion

Calibration models exhibited strong correlations between NIR predictions and reference laboratory values:

• Ash content: R² = 0.973; SEC = 0.48 %; SECV = 0.73 %
• Volatile matter: R² = 0.944; SEC = 0.29 %; SECV = 0.38 %
• Fixed carbon: R² = 0.937; SEC = 0.40 %; SECV = 0.52 %
• Moisture: R² = 0.896; SEC = 0.23 %; SECV = 0.28 %

These figures of merit confirm that NIRS can reliably replace time-consuming combustion methods, offering precision suitable for routine quality control.

Benefits and practical applications

• Rapid turnaround: Complete proximate analysis in less than one minute per sample without chemical reagents or nitrogen atmosphere.
• Cost efficiency: Elimination of furnace operation and gas consumption reduces operating expenses.
• Operational simplicity: Minimal sample handling and robust instrument design allow deployment in both laboratory and production environments.

Future Trends and potential applications

Progress in chemometric algorithms and instrument miniaturization is expected to further improve predictive performance and enable inline monitoring of coal feedstock. Integration with process control systems and cloud-based analytics will support adaptive process optimization and remote diagnostics.

Conclusion

The Metrohm DS2500 Solid Analyzer coupled with Vis-NIR spectroscopy provides a fast, accurate, and cost-effective approach for coal proximate analysis. High model robustness and minimal sample preparation make this solution well suited for high-throughput quality control and industrial process monitoring.

Reference

• Metrohm Application Note AN-NIR-117: Analysis of moisture, ash, carbon, and volatile content in coal by NIRS.
• ASTM D3174-04: Standard Test Method for Ash in Coal and Coke.
• ASTM D3175: Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke.
• ASTM D3172: Standard Practice for Proximate Analysis of Coal and Coke.
• ASTM D3173: Standard Test Method for Moisture in the Analysis Sample of Coal and Coke by Drying.