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The most common types of coal (lignite, bituminous and anthracite) are distinguished by their different chemical and physical properties. The calorific value of coal can be determined by analysing its carbon content, for example by using combustion analysers. In addition, efficient management of the desulfurisation plant requires control of the sulfur content. Compared to the large amount of coal a typical laboratory sample consists of – a 10 l bucket or even more – the sample volume required for analysis is fairly low, only approximately 1 g. The German industry standard (DIN 51701) defines the sample amount to be tested, as this relates to the particle size: the bigger the particles are, the more sample material is required. However, a small amount needs to represent a large quantity. Therefore, an important step to take before analysing coal is sample preparation with laboratory crushers and mills to obtain a representative sample. For more inhomogeneous coal samples, such as brown coal, the sample preparation step becomes even more important in ensuring reproducible analysis results. The fineness of the sample can influence the standard deviation of the analysis results, as will be shown in this article using brown coal as an example. In general, using a sample divider to produce a representative part sample and a final grind size of the sample of 100 μm help to obtain results with high reproducibility.

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