Improvement of Coking Property of Low-Grade Coals by Mild Reduction Treatment

Abstract

With the recent concern over the depletion of high-quality coking coal used for coke production, it is desirable to develop a simple method to convert low-grade coals with poor coking properties into high-quality coking coals. In this study we have focused on the possibility that polymerization reactions caused by the recombination of coal-inherent radicals may occur when coal is heated, which can deteriorate the softening and melting properties of coal. Aiming at removing such radicals, we have proposed a pretreatment method for improving coking property of low-grade coals, in which low-grade coals are treated with a reductant such as formic acid at around 60°C. It was shown that the treatment by either aqueous formic acid or formic acid vapor significantly improved the coals’ thermoplastic performance and enhanced the strength of the resulting coke even though consumption of the reductant formic acid was small enough to hardly change the elemental composition of the coals. We have also succeeded in restoring the coking property of weathered coking coal.