Update of Coal Dustiness and Dust Extinction Moisture (DEM) Standard AS4156.6

This project involved assessing the accuracy and precision of a proposed revised method of preparation for the Australian Standard AS 4156.6 “Coal Preparation - Part 6: Determination of dust/moisture relationship for coal”.  Three different laboratories/entities conducted testing of the Dust Extinction Moisture (DEM), with each testing five different coal types (five tests per coal). The intent of this work was to investigate the within and between laboratory variability according to the specified revised method.

The main objectives included:

• Verification of the precision of the updated and specified preparation method produces reliable evaluation of dustiness and DEM for coal;
• Ensuring the specified preparation method results in good reproducibility and high precision; and
• Create supporting evidence for a formal update of AS4156.6 through the Standards Australia coal preparation sub-committee MN001-02.

The project has resulted in the following major outcomes:

• The apparatus in one laboratory differed from the other two, notably, a smaller internal pipe diameter that produced significantly different dust number (DN) and moisture content (MC) profiles, demonstrated by a steeper curve.
• The current standard AS4156.6 does not explicitly specify the size of the internal diameter. Further research to investigate the effect of internal pipe diameter appears warranted.
• Within laboratory testing showed:
• Range in DEM (%) of 0.20 to 0.69 with an average of 0.44.
• Standard deviation, si, in DEM of 0.09 to 0.28 with an average of 0.18.
• Error in MC ± (%) ranged from 0.01 to 0.13 with an average of 0.04.
• The average error in MC is higher than the ± 0.2 (%) stated in AS4156.6.
• Error DN ± (%) ranged from 14.45 to 53.45 with an average of 25.66.
• The average error in DN is higher than the ± 6 (%) stated in AS4156.6.
• The high error in MC and DN must be considered in the formal update of AS4156.6.
• Between laboratory testing showed:
• Variation (relative) between average DEM:
• Was within ± 10% between Laboratory 1 and 3 for all coals (identical apparatus).
• Was within ± 10% between all laboratories for coals 2, 3 and 4.
• The AS4156.6 gives a reproducibility value (relative) of ± 10% but does not state a repeatability value.
• The variability of the apparatus must be considered in the update of AS4156.6.
• The precision of the updated revised method was assessed per coal type and produced:
• Within laboratory DEM (%) repeatability,r, from 0.37 to 0.65 with an average of 0.52.
• Between laboratory DEM (%) reproducibility, R, from 1.19 to 2.22 with an average of 1.67.
• Values that are comparable to that given for total MC (%) determination in AS1038.1, where r is 0.5 and R is 1.5.