EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

Coal weathering is regularly surveyed by cokemakers in order to avoid coke quality deterioration as a result of coal rheological properties decrease. Usual Gieseler fluidity and dilatation rheological tests are sensitive to weathering, but require values of initial and oxidized coal, which makes these tests difficult to be used. For this reason, three promising weathering detection tests were selected and studied. ASTM D 5263-01 Alkali extraction test is normally used to detect coal weathering before its extraction and is recognised by coal suppliers. It was shown the ASTM test detects oxidation after coal extraction at approximately 80% of rheological properties loss (without taking into account oxidation before coal delivery). Besides, the test is not sensitive to thermally weathered coals, and coals that contain clays. In abrasion drum test coal weathering is detected as evolution of dilatation within coal grains, i.e. progression of weathering front. This test is sensitive to oxidation but is rather time-consuming. Petrographic stain test developed by Gray et al. (1976) was proved to be sensitive to weathering before and after extraction. The advantages of this test are that it can be an addition to the standard petrographic analysis used at coke plants.