The standard "ASTM D7582-15 Standard test methods for proximate analysis of coal and coke by macro thermogravimetric analysis" developed by the American Society for Testing and Materials (ASTM) describes instrumental test methods including determination of moisture, volatile matter and ash and calculation of fixed carbon in the analysis of coal and coke samples prepared in accordance with the standards "ASTM D2013-01 Standard practice for preparing coal samples for analysis" and "ASTM D346/D346M-11 Standard practice for collecting and preparing coke samples for laboratory analysis". These instrumental test methods cannot be applied to thermogravimetric analyzers using microgram-sized samples.
Moisture determined by instrumental test methods described in ASTM D7582-15 is used to calculate other analytical results on a dry basis using procedures described in ASTM D3180-12 Standard Practice for Calculating Coal and Coke Analyses on Bases Other Than Specified.
Moisture can be used in conjunction with air dry moisture loss determined by the standard “ASTM D3302-07a Standard test method for total moisture in coal” to determine total moisture in coal. Total moisture is used to calculate other analytical results as received using the ASTM D3180-12 standard.
Ash yield is the residue remaining after heating coal and coke samples.
The resulting ash is different in composition and quantity from the mineral components found in the original coal. Combustion results in the expulsion of all water, loss of carbon dioxide from carbonates, conversion of iron pyrite to iron oxides and sulfur oxides, and other chemical reactions. The ash yield determined by this test method may differ from the ash produced in furnace operations or other combustion systems because combustion conditions affect ash chemistry and quantity.
Ash yield is used for the following purposes:
Volatile matter yield, when determined as described herein, can be used to indicate coke yield on carbonization.
In macro thermogravimetric analysis of coal and coke, moisture, ash and volatile matter are the three basic parameters used to evaluate coal quality.
In thermogravimetric analysis, the mass of a sample in a controlled atmosphere is recorded repeatedly as a function of temperature or time or both. In macro thermogravimetric analysis, a sample size of approximately 1 g is used. All mass measurements are performed by the system. In a typical analysis, the temperature is normally increased from ambient temperature to a specified temperature and held at that temperature for a specified time. The mass change is recorded repeatedly throughout the procedure. For thermogravimetric analysis of coal and coke samples, moisture and ash analyses are completed when the sample reaches a constant mass as defined in the instrumental operating parameters. Alternatively, moisture and ash measurements can be considered complete after the sample has been heated for a fixed period of time. In volatile matter analysis, samples are weighed after being heated to 950°C and held at this temperature for 7 minutes.
Moisture is determined by measuring the mass loss of a coal or coke analysis sample when heated under specified conditions of temperature, time, atmosphere, sample mass and equipment specifications.
Volatile matter is determined by measuring the loss in mass of a coal or coke sample when heated under strictly controlled conditions. The measured mass loss is used to calculate the volatile matter after correcting for moisture content.
It is determined by measuring the mass of the residue remaining after burning a sample of ash, coal or coke under specified conditions of sample mass, temperature, time, atmosphere and equipment characteristics.
In these test methods, moisture, volatile matter and ash can be determined sequentially in a single instrumental procedure. Another procedure allows moisture and ash to be determined sequentially. Moisture and ash can also be determined in separate determinations. Robustness tests and past experience have shown that volatile matter values determined in samples without moisture determination (without drying the sample) are always higher than in dried samples.
Good laboratory practice requires checking for deviations between analytical methods for contractual compliance. If only a few types of coal are to be tested routinely, the instrument used in these test methods must be suitable for the coals to be tested.
It must be demonstrated that results are equivalent to those obtained using the standards "ASTM D3173-11 Standard Test Method for Moisture in Coal and Coke Analysis Sample", "ASTM D3174-02e1 Standard Test Method for Ash in Coal and Coke Analysis Sample", and "ASTM D3175-20 Standard Test Method for Volatile Matter in Coal and Coke Analysis Sample". If they are found to be non-equivalent, the instrument used shall be calibrated or the instrument results shall be adjusted to establish and maintain equivalence.
Alternatively, if a wide range of coal types are to be tested, the instrument used in these test methods should be calibrated using certified reference materials of known composition that cover the specified range of parameters.
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