LOI in Combustion Residues

Significance of the Topic

Loss on Ignition (LOI) measurement is critical for assessing unburned carbon and volatile content in combustion residues, influencing cement quality, environmental compliance, and resource recovery. Accurate LOI data guide process control in power generation, cement manufacturing, and materials recycling.

Objectives and Study Overview

This application note describes the determination of LOI in combustion residues by thermogravimetric analysis, referencing ASTM D7348. It aims to demonstrate a robust, reproducible procedure for evaluating moisture content and LOI at high temperature using the LECO TGA701 system.

Used Instrumentation

• Instrument: LECO TGA701 thermogravimetric analyzer
• Ceramic crucibles (621-331)
• Oxygen and nitrogen gas supply

Methodology and Instrumentation

The procedure involves finely pulverized samples (<60 mesh) weighed (~1 g) in ceramic crucibles. A three-step thermal program under controlled gas flows is used:

• Step 1: Drying at 110°C under nitrogen to remove moisture (6 °C/min ramp, 5 min hold)
• Step 2: Preliminary oxidation to 500°C under oxygen (6 °C/min ramp, 5 min hold)
• Step 3: Final LOI determination to 950°C under oxygen (8 °C/min ramp, no hold)

Mass changes are recorded to calculate moisture content and LOI using standard equations:

• % Moisture = ((Initial mass – Moisture mass)/Initial mass) × 100
• % LOI = ((Initial mass – LOI mass)/Initial mass) × 100

Main Results and Discussion

Typical analyses of fly ash, coal fly ash, and Portland cement show moisture below 0.5% and LOI ranging from 0.33% to 1.77%. Replicate measurements yield relative standard deviations under 0.04% for moisture and 0.01–0.04% for LOI, demonstrating high precision. These results confirm the method’s suitability for heterogeneous combustion residues.

Benefits and Practical Applications

• High repeatability and sensitivity for quality control in cement and ash utilization.
• Rapid evaluation of unburned carbon, aiding process optimization.
• Compliance with regulatory and industry standards like ASTM D7348.

Future Trends and Potential Applications

Advances in TGA instrumentation may enable real-time process monitoring and automated data integration with manufacturing control systems. Expanding the method to alternative fuels, biomass ashes, and waste-derived materials will improve resource recovery and environmental assessments.

Conclusion

The TGA-based LOI approach using the LECO TGA701 delivers reliable moisture and combustion residue analysis, crucial for industrial quality assurance. Its precision, standardized protocol, and adaptability make it a valuable tool for cement, power generation, and recycling sectors.

Reference

• ASTM D7348: Standard Test Method for Loss on Ignition (LOI) of Solid Combustion Residues