Now that the end of this year nearby when the coal stock was checked by the surveyor there always seems some shortage of coal stock even though the raw coal weighers for the coal mills and also fine coal weighing systems are calibrated regularly all through the year.How and why this shortage.? what % age you give for tranportation loss? How to make up the loss.Pl reply.
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re Coal Stock.
Surveyors measure volume not tonnes and must rely on an accurate bulk density value to convert the surveyed volume into tonnes. The bulk density of the stockpile may be different at various locations in the pile depending also on whether the stockpile is loose or has been compressed ( by driving heavy machinery over it) to prevent spontaneous combustion etc.
Are you sure that the bulk density figure used by the surveyors is representative of the whole stockpile?
re Coal Stock.
Loose coal will have a lower bulk density than the coal in the stockpile. The bulk density of the coal in a stockpile increases with depth because the coal at the bottom of the pile is compacted by the weight of coal above it. To get a more accurate estimate of the bulk density you should perform two different bulk density tests on the loose coal taken from the stockpile. The first is a loosely packed bulk density which represents the lowest bulk density at the top of the stockpile and the second is a packed bulk density which represents the density of the coal at the bottom of the pile. By averaging the two results, you get a closer estimate of the real bulk density of the coal in the whole stockpile.
ASTM D6347 is a standard method for determining coal stockpile bulk density using Nuclear Backscatter Depth Density Methods. See: http://www.astm.org/Standards/D6347.htm
Also described in this presentation;- http://www.google.com.au/url?url=http://arippa.org/presentations/Fuel%2520Stockpiles%2520KIMBLE%25202009.pptx&rct=j&frm=1&q=&esrc=s&sa=U&ei=_a-HVIiTGIeG8QW1wICIBA&ved=0CB8QFjAC&sig2=C9Q1B70upq8Kocu5yv8RoA&usg=AFQjCNHyPo0xoH0ImMTTPr3qgscK5IiLUg
It's less likely, but one other thing could be free moisture content. If the raw coal is delivered at a certain free moisture content and loses some moisture while being stored before use, the raw coal weighfeeders would weigh a lower amount. Of course in wet weather the opposite would be the case, if it's stored outside. Just a thought.