A Study of the Effects of Potassium Vapour on Carbonised Materials

Metallurgical coke in the blast furnace provides a permeable matrix through which reducing gases may ascend and molten materials descend. The coke bed matrix permeability is thus an important property of the coke for blast furnace operations. A lack of permeability will inevitably lead to a poor gas distribution and result in a reduction of the furnace output and efficiency. A decrease in the permeability of the carbonaceous coke matrix arises when changes, induced by the blast furnace environment, occur in the properties of the material and affect the matrix voidage by causing a reduction of coke strength. A major influence of change within the blast furnace is the presence of recirculating alkali, particularly potassium, which is known to induce considerable microstructural change (enhanced localised ordering), within the metallurgical coke. These microstructural changes, lead to structural weakening and the subsequent degradation of the coke structure as a consequence of a variety of factors 1. The formation of an intercalated material that results in expansion of the carbon lattices. This structure would thus be more accessible and susceptible to degradation by chemical and mechanical attack. 2. Structural ordering by single or repeated intercalation orders the structure by the removal of crystallographic defects. This would create interfaces between ordered and disordered carbon and thus weaken the material. 3. The occurrence of different microstructural forms within the carbon would affect degradation through differential volume expansion and give rise to localised stresses. The resulting degradation and structural weakening of the coke has a detrimental affect on the coke bed matrix by reducing the coke mean size and voidage of the material and ultimately coke strength. The present research has been orientated towards investigating the affect and susceptibility of different carbon structures to alkali attack. The structural changes occurring within these carbons being studied as a model for the more heterogeneous coke system. Knowledge of the induced structural changes and affects of the parameters involved would allow conclusions to be drawn as to the most suitable methods or treatments for reducing or eliminating the destruction of metallurgical coke, in the blast furnace, by alkali vapours. The majority of this work has involved analysis of the microstructural aspects of the different carbons and the changes induced therein. The work can be divided into two parts 1. The carbonisation of the parent materials, under various conditions, up to 800 and 110