1976 Volume 62 Issue 5 Pages 495-504
In the last period of the 25th campaign, during which coke (B) made from an inferior coal mixture was used, a stagnant stock movement and an increase of pressure drop in the lower region occurred at the times when maximum volume of molten products was accumulated in the hearth. Observations with a fibre or bore-scope showed:
(1) Feeding of flaky coke fines from above into the raceway around the tuyere nose;
(2) Scattering of coke fines in the upper bosh (at the position BIII-1);
(3) Alternative fluidization and rapid descent of flaky coke fines in the furnace center (at the position CII-1);
(4) Rise of slag bath surface to a high level (at position CII-1).
These phenomena together with the results of hot-model experiments made the authors conclude that the flaky coke fines, generated at some high-temperature region above the combustion zone as a result of a degradation of charged coke, accumulated gradually in the bosh and hearth and caused a marked increase of slag hold-up and of resistance to gas flow.
Investigations on the cooled furnace contents after blowing-out suggested that the degradation, or the revelation of defects inherent in coke (B), might start at about 1000°C in the lower shaft and become remarkable in the belly. Though a degradation due to the gasification with CO2 may be supposed, other mechanisms should also be examined in view of a large quantity of alkaline matters adsorped by coke in the region from lower shaft to belly.