Different analyses and tests use different preparations of coals, usually recorded in the results as some type of “basis.” The following standard coal analysis bases can be converted to each other for standard reporting (ASTM method D3180-12; American Society for Testing and Materials, 2013, p. 515–517). Knowing the basis in which results are presented for correct correlation to parameters or use in equations is important.

Different recording standards are used for different measurements of coal components (modified from Ward, 1984).

 

Common recording standards (in alphabetical order):

  • Air-dried basis: Data or results are calculated to the moisture condition of the coal after being allowed to air-dry (at room condition humidity). Usually denoted as “ad” or “AD.”
  • As-determined (air-dried) basis: Usually denoted as “adm” or “ADM.” Even after air-drying, coal typically contains some moisture, which is referred to as residual moisture.
  • As-received basis: Data or results are calculated to the moisture condition of the coal sample when it arrived at the testing facility. Usually denoted as “ar” or “AR.”
  • Dry basis: Data or results are calculated to a theoretical base as if there were no moisture in the coal sample. This basis is commonly used in testing laboratories because of issues related to measuring moisture. Usually denoted as “dry” or “DRY.”
  • Dry, ash-free basis: Data or results are calculated to a theoretical base as if there were no moisture or ash in the coal sample. A calculation is made as if the coal was only composed of volatile matter and fixed carbon (Thomas, 1992). Usually denoted as “daf” or “DAF.”
  • Dry, mineral matter-free basis: Data or results are calculated to a theoretical base as if there were no moisture or mineral matter in the coal sample (ASTM method D388-12; American Society for Testing and Materials, 2013, p. 390–396). For this basis, a calculation is needed to determine mineral-matter content rather than ash yield. In the United States, that equation uses the Parr formula:
    Mineral matter (weight %) = (1.08 x ash yield (weight %)) + (0.55 x total sulfur (weight %))

    Usually denoted as “dmmf” or “DMMF.”
  • Equilibrium-moisture basis: Data or results are calculated to a moisture level of a coal sample established at equilibrium moisture conditions according to ASTM method D1412 (American Society for Testing and Materials, 2013, p. 425–429).
  • Moist, ash-free basis: Data or results are calculated to a theoretical base as if there were no ash, but there is moisture, in the coal sample. Usually denoted as “maf” or “MAF.”
  • Moist, mineral-matter-free basis: For some low-rank coals, this basis is used to calculate calorific value. It uses a theoretical base as if there were no mineral matter, but includes the moisture content of the coal sample. For this basis, a calculation is needed to determine mineral-matter content rather than ash yield (see Parr formula above). Usually denoted as “mmmf” or “MMMF.”

 

Reference

 

 


Last Modified on 2017-11-01
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