Storage of small samples of coking coal for thermal rheological tests

A study was undertaken with the aim of finding the best practical way of storing small coal samples in a laboratory setting to limit their extent of oxidation for maintaining good thermal rheological properties. Samples of a Canadian medium-volatile bituminous coal of Cretaceous age (‘as received’ and < 0.42 mm sizes) were stored under various media (open trays in laboratory, in an oven, under water and under vacuum) and temperatures (− 15, 4, 20 and 40 °C) for up to 60 weeks. Samples were analyzed for Chemical changes including O content, O / C, H / O, H / C, Volatile Matter, and Calorific Value; Thermal Rheological changes in Fluidity, Plastic range, Dilatation, Free-Swelling Index and Alkali Light Transmittance. Coke Quality changes in Coke Cake Contraction, Coke Reactivity and Coke Strength indices as well as Coke Optical Textures were also examined. For chemistry related changes, the most obvious ones due to oxidation are in atomic oxygen, which increases, and calorific value, which decreases. Concerning thermal rheology changes, fluidity and dilatation were found to decrease the most whereas Free-Swelling Index and Alkali Light Transmittance do not appear to be sensitive indicators of early stages of oxidation for the examined coal. Pertaining to coke quality, coke cake contraction remains essentially unchanged, Coke Strength after Reaction decreases and Coke Reactivity Index increases, and textures reveal a significant increase in coke inerts.This work has found coal oxidation to be mainly influenced by the storage temperature, with rate of oxidation increasing with temperature, and to a lesser extent by particle size, with oxidation being more likely the smaller the particle size.Of the different storage conditions tested in this investigation, keeping coal at cold temperatures (< − 15 °C) was found to be the most favourable for limiting its oxidation and thereby maintaining good thermal rheological properties.