A Method of Estimating the Quality of Fresh Coal from the Analysis of Weathered Outcrop Coal

Abstract

An empirical method of estimating the calorific value and ash content of fresh coal from the analysis of weathered outcrop coal is introduced. The method should be, of course, fully discussed through theoretical treaties on coal-weathering. This is, however, based on many actual data from the analyses of weathered and fresh coal, and may serve to estimate the quality of coals that have only their weathered outcrops in the field. The method is briefly stated as follows:
1. Assumption of the moisture of fresh coals. Approximate value of the moisture can be obtained from the analyses of relatively fresh coals that are in a horizon near to the coal seam in question and are exposed in streams or fresh cuttings.
2. The relation of moisture and calorific value, both on an ash-free basis, of a series of outcroping coals in different stages of weathering is represented in graphs, e.g. Fig. 1. From the graph of the coal in question the calorific value (ash-free) of the fresh coal may be estimated. The graph of a coal in a near horizon or in the same group may be adopted when the data are poor.
3. The relation of moisture (ash-free) and ash content of coals in various stages of weathering, both in the ratio to those of fresh coal, may roughly be graphed as Fig. 2. From this graph the decrease in ash content of the weathered coal is roughly estimated, and the ash content of the fresh coal may be assumed.
4. From 2 and 3 the approximate calorific value of the fresh coal can be obtained.