Effects of Briquette Blend on Packing Structure of Fine Coal Portion

抄録

Briquette blending aims to increase coke strength by increasing the bulk density of the coal charge by blending in high-density briquettes. This technique tends to decrease the bulk density of the powder coal portion of the coal blend. In this study, we attempted to elucidate the mechanism behind this decrease in the bulk density of the powder coal portion owing to briquette blending. We conducted drop tests of blended coal that included briquettes, observed the behaviour of the dropped coal using a high-speed camera, and then performed quantitative estimation of the change in bulk density by observing the resulting coal packing structure using an X-ray CT system and image analysis. The bulk density of the powder coal portion decreased owing to the formation of localised low-bulk-density regions around the briquettes. Two types of low-bulk-density regions exist. In the first case, the scattering of the powder coal by the impact of the falling briquette forms gaps, which remain in the form of large voids under the briquettes after charging. The second type is presumably due to the large difference in size between the briquette and powder coal, which causes a wall effect between them. We then used a newly developed image analysis process to estimate the widths of the two types of low-bulk-density regions quantitatively as 8–10 mm and 5–6 mm. This study demonstrated how briquette blending creates anisotropic low-bulk-density regions around the briquettes, which leads to a decrease in the bulk density of the powder coal portion.