Experimental and numerical study on degradation behavior of coke with CO₂ or H₂O gasification reaction at high temperature

Coke undergoes gasification reactions of CO₂ and H₂O in the blast furnace, and the gasification reactions degrade the coke and affect the operation of the furnace. In this study, to evaluate the factors that govern the strength of coke in the furnace, the fracture behavior of coke under blast furnace conditions was examined both experimentally and numerically. The three-point bending test was performed on coke subjected to the gasification reaction under conditions similar to those inside a furnace. It was found that coke gasified with CO₂ is more likely to fracture than that with H₂O since the conversions at fracture of the samples gasified with CO₂ and H₂O were 0.71 and 0.78, respectively. X-ray computed tomography images of coke taken before and after the gasification reactions showed that increase rate of porosity was almost uniform from the central part to the external surface in the case of CO₂ gasification reaction, while it increased from the sample center towards the external surface in the case of the H₂O gasification reaction. In addition, the finite element analyses using an isotropic damage model were performed. As a result, the damage spread in the analytical object in which the pore structure after the CO₂ gasification reaction was reflected, while the damage was localized in the analytical object in which the pore structure after the H₂O gasification reaction was reflected. These results suggested that the difference in the spatial distribution of the porosity increase rate within the coke samples owing to the differences in the rate-limiting steps of the gasification reactions greatly affected the strength of the coke samples.