Based on the results of dissection of Nagoya BF No.1, studies were conducted on the degradation of coke in a large blast furnace. The results of these studies show the following facts. 1) The degradation of coke in blast furnaces is greatly influenced by the temperature at which coke is subjected to CO2 reaction. 2) The lump coke, which begins to degrade due to selective solution loss and to decrease its strength at 1 000°C, does not change its grain size up to 1 400°C but begins to reduce it sharply above 1 400°C. 3) The coke fines depositing between the lower part of the shaft and the tuyeres are generated in the vicinity of the raceway and move there by the kinetic energy of the blast. 4) The increase in the alkali content of coke (by 5% maximum in the present study) does not decrease the strength of coke.
Further, the relationship between the inner volumes of Nippon Steel's dissected blast furnaces and the changes in coke size in these furnaces was studied. It is suggested that the coke particle size reduction ratio is higher and the coke degradation conditions are severer in large blast furnaces than in small ones.
