Effect of solution loss reaction on coke degradation rate under sheer stress

Abstract

The degradation behavior of spherical coke samples was measured under sheer stress. The samples underwent the solution loss reaction until various degrees in several reaction temperatures (10-30 wt% and 1 273-1 573 K). A sample is settled between two horizontal boards with parallel grooves like washboard. The sheer stress was applied to the sample by sliding upper board at a certain cycle with a constant vertical load. The generated powder was sieved and weighed, and the appearance of the coke sample was observed. From the measurement of the powder generation rate and discussion on the reaction mode of the solution loss reaction, the degradation behavior can be explained by the distribution of local reaction degree within a coke particle. The powder generation rate from the samples reacted in lower temperature increases with increase in overall reaction degree because the reaction of coke substrate with carbon dioxide, namely the strength deterioration, proceeds in entire particle. The high temperature samples show little increase in the powder generation with the overall reaction degree since the surface reaction mode increases local reaction degree in the vicinity of particle surface and this reacted layer is also consumed from the surface. This dependency of the powder generation behavior on the reaction mode of the solution loss reaction measured in this study corresponds to the previously reported behavior in the raceway zone regardless of grinding mechanism. Therefore, it is considered that the single-particle degradation test of coke is an appropriate method to measure the degradation behavior of a coke particle under sheer stress.