Thermogravimetric Analysis of Flue Gas Desulfurization (FGD) - TGA801

Importance of the Topic

Thermogravimetric analysis (TGA) is a versatile technique for monitoring mass changes in materials under controlled temperature and atmosphere. It is crucial for characterizing decomposition, dehydration, oxidation, and volatilization processes in diverse samples, particularly heterogeneous solids.

Flue gas desulfurization (FGD) solids, a byproduct of coal-fired power plant scrubbers, find widespread use as additives in the building materials and cement industries. Accurate determination of moisture content, gypsum, calcium sulfite, lime, and carbonate fractions in FGD solids is essential for product quality control and process optimization.

Study Objectives and Overview

This application note describes a macro‐TGA method, aligned with ASTM D8339, to quantify key constituents in FGD solids using gram-scale samples. The goals are to define a robust temperature program for sequential mass loss steps, validate repeatability on reference materials, and demonstrate suitability for industrial QC workflows.

Methodology and Instrumentation

Samples are ground to below 0.5 mm and weighed at approximately 1 g in ceramic crucibles. A six-step temperature profile under nitrogen and oxygen atmospheres separates free moisture, gypsum decomposition, calcium sulfite conversion, dehydroxylation of lime, carbonate decomposition, and final ash determination. Each step combines controlled ramp rates, hold times, and gas flow settings to isolate specific mass change events.

Used Instrumentation

• TGA801 macro thermogravimetric analyzer
• Ceramic crucibles (621-331) and sample spoon (611-844)
• Nitrogen and oxygen gas supplies with mass flow controllers

Main Results and Discussion

Analysis of NIST SRM 2429 and high-purity gypsum demonstrates excellent repeatability (<0.1 % RSD for major components). Typical data yield free moisture near zero, gypsum at ~97.6 %, calcium sulfite around 2.4 %, minor Ca(OH)₂ and CaCO₃ under 0.5 %, and consistent ash content (~79.2 %). Calculated ash matches measured values within 0.2 %, confirming method accuracy.

Benefits and Practical Applications

• Enables reliable QC of FGD solids in cement and construction additive production
• Supports process control by tracking moisture and reactive phases
• Reduces sample size requirements for heterogeneous materials

Future Trends and Potential Applications

• Integration of evolved gas analysis (e.g., FTIR or MS) for enhanced phase identification
• Automation of sample handling and data processing for high-throughput QC
• Extension to other industrial byproducts and complex composites

Conclusion

The described macro-TGA method, following ASTM D8339, provides a precise, repeatable protocol for quantifying key phases in FGD solids. Its adaptability to gram-scale samples and clear stepwise decomposition profile make it a powerful tool for routine quality assurance in industrial settings.

Reference

• ASTM D8339 – Standard Test Method for the Analysis of Flue Gas Desulfurization Solids by Macro Thermogravimetric Analysis