Thermal Stability Test of Coal Using Thermogravimetric Analysis (TGA)

Thermal Stability Test of Coal Using Thermogravimetric Analysis (TGA)

Coal industrial analysis includes the determination of moisture, ash, volatile matter, and fixed carbon. Traditional methods require the use of muffle furnaces, ovens, and other equipment, which are cumbersome and prone to significant errors. Thermogravimetric analysis (TGA) is a commonly used method to evaluate the thermal stability of coal, widely applied in coal analysis, particularly in studying coal pyrolysis, combustion characteristics, volatile matter release, ash residue, and reaction kinetics.

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I. Testing Principle

When coal is heated in an inert gas atmosphere, it undergoes a pyrolysis process: volatiles gradually escape, while fixed carbon and ash remain. The thermogravimetric analyzer monitors in real time the mass changes of the coal sample during the heating process, plotting TG (thermogravimetric) and DTG (derivative thermogravimetric) curves to analyze its pyrolysis characteristics.

II. Experimental Testing Steps

1. Sample preparation: Grind the coal sample into a uniform powder. Take 15–30 mg of sample to avoid heat transfer differences caused by uneven particle size.
2. Equipment: TGA1000 Thermogravimetric Analyzer.

3. Instrument parameter settings:
- Atmosphere: High-purity nitrogen (to avoid oxidation reactions, simulating a pyrolysis environment). Gas flow rate: typically 50 mL/min.
- Temperature program: From room temperature to 800 °C (adjustable according to experimental requirements). Recommended heating rate: 20 °C/min.
4. Testing process: Spread the sample evenly at the bottom of the crucible to avoid accumulation, run the TGA program, and record TG changes.
5. Data analysis:
- Drying and dehydration stage (room temperature – 200 °C): Removal of adsorbed and some bound water. For example, between 50 °C and 200 °C, weight loss was 7.64%.
- Volatile analysis stage (200–600 °C): The main pyrolysis stage, where organic matter decomposes and releases volatiles, producing tar, CH₄, etc. Total weight loss ~42.6%.
- Final decomposition stage (600–800 °C): Further decomposition of carbon content, then stabilization.

III. Role of TGA in Measuring Coal Thermal Stability

1. Evaluation of coal thermal stability: TGA measures the mass change of coal samples during heating to assess thermal stability at high temperatures.
2. Analysis of pyrolysis rate and weight loss: As temperature rises, the pyrolysis rate of coal changes. TGA accurately measures mass change rates at different temperatures, i.e., pyrolysis rate. By analyzing these curves, the reaction speed of coal pyrolysis can be understood.
3. Evaluation of additives’ effect on coal stability: To improve coal thermal stability, additives are sometimes added. TGA can be used to evaluate their effectiveness by comparing mass–temperature curves of coal with and without additives.

IV. Precautions During the Experiment

1. Sample uniformity: Uneven particle size may cause fluctuations in test results.
2. Heating rate: The heating rate must be properly adjusted; rates that are too fast or too slow may affect test results and reaction details.