Coking Pressure and Its Relation to Fissure Formation

The danger excessive coking pressure poses to the integrity and longevity of coke ovens has been recognized for many years [1-7]. During carbonisation in a coke oven fissures in the coke are generated due to stresses that arise from the differential contraction rates in adjacent layers of coke, which are at different temperatures [8]. Typically they are longitudinal, i.e. perpendicular to the oven walls and extending inwards from the oven wall to the charge center. Traditionally any link between the larger structure of the coke in the oven, in terms of fissure network development, and coking pressure was dismissed. This was challenged by the finding that the internal gas pressure measured in a movable wall oven depended on the distance between the nearest fissure and the measuring probe [9.10]. This would imply that gas can penetrate the semi coke to some extent, but with increasing difficulty as the continuous layer of semi-coke grows thicker. Effective gas release would then depend on fissures being present in sufficient number and proximity to the area of gas release. These fissures would need to be in place while gases are being evolved, so that the speed with which fissures form and propagate would be of paramount importance.