Analysis of limestone for flue gas desulfurization in a power plant with ARL QUANT’X EDXRF Spectrometer

Significance of the topic

Flue gas desulfurization (FGD) is essential for reducing SO₂ emissions from coal-fired power plants and preventing acid rain. Limestone-based wet scrubbers are the predominant technology, capturing over 90% of SO₂. Ensuring the chemical composition of limestone feedstock is critical for scrubber efficiency and byproduct quality.

Objectives and study overview

This application note evaluates the Thermo Scientific™ ARL™ QUANT’X energy-dispersive X-ray fluorescence (EDXRF) spectrometer for the quantification of major and minor oxide components in limestone used for FGD. The study covers sample preparation, measurement protocols, calibration accuracy, and instrument precision.

Methodology

Sample preparation involves grinding limestone to ~325 mesh and pressing 40 mm pellets under 200 kN. Measurements are performed under vacuum with a total live time of 150 s per sample. Two excitation conditions are employed:

• Low-Z (4 kV, no filter, 120 s) for Mg, Al, Si
• Mid-Z (18 kV, thin Pd filter, 30 s) for Ca, Fe

Tube current is adjusted to maximize count rate without detector saturation.

Instrumentation

The ARL QUANT’X EDXRF spectrometer features:

• Air-cooled Rh end-window tube (0.05 mm Be window), 50 W maximum
• Electrically cooled silicon drift detector (30 mm²)
• Nine primary beam filters for optimized excitation
• Optional 10-position sample changer for unattended operation

Main results and discussion

Calibration curves for Ca, Mg, and Fe display excellent linearity across concentration ranges relevant to limestone (CaCO₃ >95%, SiO₂ <3%, MgCO₃ <2%, Al₂O₃ <1.5%, Fe₂O₃ <3%). Certified reference materials were used to establish calibration. Repeatability tests (10 consecutive runs) yielded relative standard deviations between 0.15% and 0.62% for all oxides, meeting industry reproducibility requirements.

Benefits and practical applications

• Rapid, non-destructive multi-oxide analysis
• High precision at both major (up to ~100%) and trace (<0.25%) levels
• Cost-effective routine quality control for FGD limestone
• Supports regulatory compliance and process optimization

Future trends and opportunities

Advances may include integration with automated sample handling and real-time data analytics, expansion to trace element monitoring for contaminant assessment, and coupling with complementary spectroscopic or mineralogical techniques to enhance speciation insights.

Conclusion

The ARL QUANT’X EDXRF spectrometer provides a fast, accurate, and precise method for limestone characterization in FGD applications, fulfilling stringent industry requirements for oxide quantification and enabling reliable process control.

References

Pascal Lemberge. Application Note AN41960: Analysis of limestone for flue gas desulfurization in a power plant with ARL QUANT’X EDXRF Spectrometer. Thermo Fisher Scientific, 2019.