The strength of industrial cokes. 7. Further studies of the influence of additives in a coke-oven charge on the tensile strength of coke

The objective of this investigation was to determine if the previously established dependence of the tensile strength of coke on the breeze content and particle size of coke breeze in the coke-oven charge was applicable to different types of breeze additives when used in a size range similar to that of commercial practice. Using a small-scale oven to obtain the desired close control of the charge preparation and carbonization conditions, cokes were prepared from a Yorkshire strongly-caking coal blended with either coke-oven breeze, petroleum-coke breeze, or silica sand. The tensile strength of the cokes was determined by the diametral-compression test and some details of their porous structure were obtained from density measurements and mercury pressure porosimetry. The results confirm that the tensile strength of coke varies systematically with the coke-oven breeze content of the oven charge, and in the present case, for a breeze of the particle size range used in commercial practice the tensile strength is increased at low additions and then progressively reduced at higher levels of addition. Different sources of coke-oven breeze behave in a similar manner and appear to act as an inert filler material. On the other hand petroleum-coke breeze additions progressively increase the coke tensile strength, the additive being bonded into the walls of the coke matrix. The changes in tensile strength are accompanied by systematic variations in apparent density and in porosity.