Coal weathering study to predict oxidation, improve coke properties and protect coke oven operation (COWEST) : final report

The progression of fluidity loss due to oxidation emerges as a coal property that correlates with the CSR loss of the coke from weathered coal. Coal transportation and storage must be carried out under low relative humidity levels (< 20 %) to avoid coke quality deterioration. The by-products plant operation will be affected by the lower tar yield per tonne of coal and the higher phenol content of the tar when carbonising oxidised coals. The coke yield will be reduced when using coals oxidized at high temperatures (50°C) and under high relative humidity levels (90 %). Weathering usually reduces coking pressure but in some cases coking pressure increases due to the faster drop in fluidity than in dilatation. The alternative stain and abrasion drum tests can determine the extent of coal oxidation but the stain test is not quantitative and the abrasion drum test is rather time-consuming. Pristine high fluidity coal can be added to weathered high rank coal to produce a blend with optimum fluidity. Blending oxidised low and high rank coals also improve the cold mechanical strength of the coke. Mild oxidation of low/medium rank coals improve coke quality and reduce the fluidity to optimum levels. Coal tar improves the JIS index of oxidised coals but impairs the CSR of high rank coals. Crushing and pre-heating of weathered coals cannot recover the coking properties. Higher bulk density of weathered coals leads to better coke quality but coking pressure also increases at high bulk densities.