Application of Gy's sampling theory to coal: A simplified explanation and illustration of some basic aspects

Abstract

Gy's sampling theory (Gy, 1982) can be applied to coal sampling problems to calculate the dependence of sampling variance on both the intrinsic coal properties (size distribution and washability) and the variations in coal stream properties with time (characterised by the corrected variogram). The theory has not been widely used by the coal industry in Australia, perhaps because of a lack of understanding of Gy's exposition. An explanation of the theory is given in simple terms, and equations useful to the coal sampler are presented and their use illustrated. Further, the application of the theory to the handling of data from on-line ash measurement instrumentation is discussed and illustrated. It is demonstrated that an on-line ash gauge can be used to characterise the time variations in coal properties in terms of a variogram which can, in turn, be corrected for gauge accuracy and then used in design calculations for a mechanical sampling system.