Determination of halogens in coal using combustion ion chromatography

Importance of the Topic

Coal combustion produces acid gases containing halogens such as hydrogen chloride and hydrogen fluoride. These emissions contribute to environmental acidification and affect mercury speciation in flue gas. Accurate quantification of halogen content in coal is crucial for predicting the performance of emission control devices and optimizing pollution abatement in compliance with regulatory standards.

Objectives and Study Overview

This study demonstrates an automated approach combining high-temperature combustion with ion chromatography (CIC) to measure chloride and fluoride in coal. The aims were to develop a reproducible workflow, establish calibration and validation procedures, and assess method performance against certified reference material.

Methodology and Instrumentation

Coal samples were weighed and introduced into a ceramic combustion tube in a Mitsubishi AQF-2100H furnace. Pyrolysis under oxygen and carrier gases yielded halogen-bearing acid gases absorbed into water. The absorbent was directly injected into a Thermo Scientific Dionex ICS-2100 IC system equipped with an IonPac AS15 anion-exchange column, EGC III KOH eluent generator, CR-ATC trap column, and AERS 500 suppressor. Standards from sodium halide stocks were used to generate calibration curves over 0.1–5.0 mg/L. Moisture and dilution factors were corrected via phosphate tracer injections.

• Mitsubishi AQF-2100H Rapid Furnace with GA-210 gas absorption unit
• Thermo Scientific Dionex ICS-2100 Ion Chromatograph with Integrion HPIC option
• IonPac AG15 guard and AS15 separation columns
• EGC III KOH cartridge, CR-ATC trap column, AERS 500 suppressor
• Chromeleon CDS version 7.2 and Mitsubishi NSX-2100 software

Main Results and Discussion

Calibration curves for fluoride, bromide, and chloride were linear (r2 > 0.9987) across the selected ranges. Analysis of NIST SRM 1635 yielded fluoride at 27.6 mg/kg (certified 25.9 ± 3.3) with 2.1 % RSD, confirming accuracy. Coal samples spanned 60–200 mg/kg fluorine and 30–1400 mg/kg chlorine. Bromine was detected at trace levels below 0.1 mg/L. Precision across replicates ranged from 0.2 to 5.5 % RSD. Sulfur species were observable when absorbent lacked oxidizing agent, highlighting the need for tailored absorption chemistry depending on analytes of interest.

Benefits and Practical Applications

The fully automated CIC approach offers high throughput, reduced chemical waste, and improved reproducibility compared to manual acid digestions or electrode methods. Direct injection of absorption solutions minimizes matrix interferences. Rapid determination of halogen levels helps predict mercury control effectiveness in coal-fired power plants and supports compliance with emission limits.

Future Trends and Potential Applications

Advances in absorbent chemistry and detector technology could extend CIC to multi-elemental speciation including bromine and sulfur oxyanions. Integration with real-time monitoring systems at power plants may offer continuous feedstock characterization. Further miniaturization and field-deployable CIC units could broaden applications to environmental monitoring of solid waste, biomass, and other combustion materials.

Conclusion

Combustion ion chromatography provides an accurate, precise, and automated method for quantifying fluoride and chloride in coal. Method validation against certified material showed excellent agreement and reproducibility. The approach supports emission control strategies by enabling rapid characterization of fuel halogen content.

References

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