Effect of coke contraction on mean coke size

In order to develop a coal blending technology to control the size of blast furnace coke, we investigated the relationship between coke size and the contraction behavior of semi-coke after resolidification which is one of the factors determining coke size. Coke contraction after resolidification was measured successfully by heating the coal sample from room temperature to 1000 °C using a high-temperature dilatometer. The contraction coefficient of coke showed a first maximum near the resolidification temperature (contraction beginning temperature), a first minimum at around 550 °C and a second maximum at around 700 °C. The measurement of contraction characteristics of 15 coals confirmed that the first maximum of coke contraction coefficient varied according to the type of bituminous coals and was independent of coal VM (volatile matter) and Ro (vitrinite reflectance). On the other hand, the contraction coefficient of coke after the first minimum (at around 550 °C) was nearly independent of the type of bituminous coals. The coke contraction ratio between the resolidification temperature and 1000 °C increased with increasing the first maximum of coke contraction coefficient. It was confirmed both in laboratory scale and in commercial scale that mean coke size is strongly associated with coke contraction ratio after resolidification and that mean coke size increases with decreasing coke contraction ratio. In view of the information and data presented in this paper, a practical application of the technology to control coke size by coal blending based on the coke contraction percentage of each coal is expected.