Development of Upgrading Method of Low Rank Coal for its Utilization in Cokemaking Process

Japanese steel industries, which are importing all coal resources required, are facing the necessity of increasing usable coal resources. They are to increase the kinds and amounts of usable coal and to develop the technologies for upgrading low rank coals such as subbituminous coal and brown coal as substitutes. In this work we have developed methods for upgrading brown coal. The methods involve the fractionation of brown coal using sequential thermal solvent extraction, dewatering and upgrading of brown coal using hydrothermal treatment, and co-pyrolysis of upgraded brown coal and plastic derived wax. The fractionation method successfully fractionated an Australian brown coal into six fractions, some of which are expected as binders for cokemaking because of their thermal plasticity. The hydrothermal upgrading/extraction method can not only removes water from brown coal but also separates the coal into extract of low molecular mass compounds and upgraded coal having lower hydrophilicity and spontaneous combustibility and higher calorific value than the raw coal. Addition of the upgraded coal to the coking coals was found to enhance the gasification reactivity of the resulting coke. Co-pyrolysis of the upgraded coal and waxes formed from waste plastics was also investigated as one of the methods for further upgrading the hydrothermally upgraded coal. It was found that the waxes effectively removed oxygen atoms from the upgraded coal and tended to be retained as a solid carbon in the coke through co-pyrolysis. It is shown that these methods enable to produce binders for cokemaking and substitute of slightly/noncaking coal.