mining engineering: Coal Sampling

Why do we sample? (organise picture of ship, coal preparation, stockpile, sample container)

Monitor quality
Control quality
Commercial
Efficiency

Sampling Standards

ISO 1988 – Hard coal - Sampling
ISO 9411 – Solids mineral fuels – Mechanical sampling from moving streams
BS 1017 – Sampling of Coal and Coke
ASTM D2234 – Practice for Collection of a Gross Sample of Coal

Seven Golden Rules

A number of increments are required to make up the sample.
Increments must be “cuts” which traverse or intersect the whole width and thickness of the coal stream, usually at a transfer point or through a falling stream.
The mass of the increment to be taken must be known.
The sampling implement must intersect the falling stream of material at constant velocity.
The width of the sampling implement or cutter must be at least 3 times the nominal top particle size of coal being processed.
The increment must never over fill the sample collection container.
During subdivision to produce a representative sub-sample, size reduction by crushing must always precede sample division and a minimum mass must be retained.

Precision and Bias

Precision – a term used to indicate the capability of a person, an instrument, or a method to obtain repeatable results; specifically, a measure of the chance error as expressed by the variance, the standard error, or a multitude of the standard error.

Bias – an error that is consistently negative or consistently positive. The mean of errors resulting from a series of observations which does not tend towards zero.

Imprecise and Inaccurate