Observations of anomalous mass-loss behavior in SRM coals and cokes on drying.
The determination of moisture content in coal and coke is required for the accurate reporting of physical and chemical constituents on a dry mass basis. Interlaboratory comparisons are reported on a dry mass basis and require reproducible assessments of moisture content to minimize differences among laboratories. Comparability between laboratories is necessary to ensure equity in trade and to avoid costly disputes between buyer and seller. Moisture loss was measured as mass (M) loss as a function of time (t) at constant temperature in a dynamic inert nitrogen atmosphere on 10 SRM coals (7 bituminous and 3 subbituminous) and 4 SRM cokes. Three different patterns of mass-loss were observed-ideal (dM/dt = 0), and two anomalous behaviors, negative deviation (dM/ dt < 0) and positive deviation (dM/dt > 0). Bituminous coals with lower moisture (1-4%) and volatile content (33-38%) tend to display either ideal or positive behavior while subbituminous coals with higher moisture (12-17%) and volatile content (41-47%) display negative behavior. The identification of these different mass-loss patterns demonstrates the potential for method bias depending on the drying end-point definition (ASTM and LECO) used.
Mann
Jacqueline L
JL
Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899-8391, USA. jmann@nist.gov
Kelly
W Robert
WR
MacDonald
Bruce S
BS