Abstract
Coal can occur in various natural forms and its quality depends on its various properties. Polish coal mines extract and process various coal types, according to the Polish nomenclature. The paper presents an attempt of determining whether is possible to statistically differ the typical coal types occurring in Polish hard coal mines by means of traditional statistical tests. To this purpose three coal types, namely 31, 34.2 and 35 were selected from three Polish mines located in Upper Silesia. After appropriate preparation of the raw coals selected coal properties were examined, including combustion heat, ash contents, sulfur contents, volatile parts contents and analytical moisture. Then, by means of several statistical tests it was verified whether it is possible to prove statistically that these coal types differ significantly not knowing the type of distribution they represent. To this purpose such tests as Kruskal-Wallis test, test of series, Wilcoxon test and median test were applied. The results were statistically evaluated and the conclusions were made. The presented methodology may serve to compare not only coal types but also other raw materials.
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