Production of Metallurgical Coke from Low Rank Coal Utilizing Wet Oxidation

Japanese steel industries, which are importing all coal resources required, are facing the necessity of increasing usable coal resources due to the recent rapid decrease of high-grade coking coal reserve and increase in its price. Low rank coals such as brown coals and subbituminous coals are promising substitutes for coking coals since they are abundant and cost-effective. However, the low rank coals generally have no thermoplasticity which is required for producing a coke with high mechanical strength using conventional coke ovens. In this work we have proposed to pretreat low rank coals by oxidative degradation reactions with aqueous oxidant such as hydrogen peroxide in order to convert them into thermoplastic coals suitable for coke making. An Australian brown coal was treated with hydrogen peroxide aqueous solution either at room temperature for 4, 8 and 24 h, or at 60 degrees C for 0.5, 1 and 2 h. The treated coals were then pelletized at room temperature and carbonized at 900 degrees C to obtain cokes. It was found that the strength of the resulting cokes increased with increasing the oxidation time at 60 degrees C and reached the level of a commercial coke, indicating that the treatment gave thermoplasticity to the coal. It was thus suggested that the wet oxidation was effective as a pretreatment for producing cokes from low rank coals.