No abstract

The image recognition method was proposed to quantify non-adhesion grain boundaries which were considered as a factor of coke strength besides pores, and the correlation between coke strength and the amount of defects evaluated by the method was investigated in comparison with the one by the marking method. Coke with low-quality coal was fractured by a diametral-compression test, and the fracture crosssections were observed by a scanning electron microscopy (SEM) and a 3D laser scanning microscope (LSM). The marking method and image recognition method were applied to SEM and LSM images, respectively. As a result, the fracture strength measured by the diametral-compression test was linearly decreased with an increase in blending ratio of low-quality coal. In the marking method, most non-adhesion grain boundaries were not detected up to 50% in the blending ratio, and the boundaries increased sharply from 50 to 100% in the blending ratio. On the other hand, in the recognition method, the defects which were composed of both pores and non-adhesion grain boundaries, increased linearly with the blending ratio, and the amount of defects corresponded to coke strength. Therefore, the image recognition method is expected as the quantification technique of defects decreasing coke strength.

To understand the properties of coking coal and coke during carbonization process, changes in stacking structure of carbon and carbon aromaticity were estimated using the XRD and NMR measurement techniques for the different four kinds of coking coals thermally treated at various temperatures. In the XRD measurement, the comparison of the diffraction patterns of the coal samples with and without decalcification indicated the proposed method could successfully eliminate peaks from ash components in the diffraction patterns. After thermal treatment, the average number of stacking layers in all the samples increased around temperature of 400-500 °C and slightly decreased around 500-700 °C. In addition, the average number of stacking layers of each sample tended to be larger for sample with higher carbon content. In the 13 C-NMR measurement, the carbon aromaticity became larger for higher thermal treatment temperature, and the order of the carbon aromaticity almost corresponded with that of coke contraction ratio.