A Study on Causes of Formation of Shot Coke in Delayed Coking Units

The study on how shot coke is generated started only in recent years both within and outside China.The deep mechanism has not yet been extensively studied.In China,most relevant studies are known from media reports on production of refining enterprises and little laboratory study has been carried out.No mature theoretical system has been developed.Based on the shape and properties of shot coke,this article describes the dynamic process of vapor nucleation of shot coke and concludes that the fundamental cause of formation of shot coke is the high gas velocity inside the coking drum,which will result in high concentration and long residence time of coke particles(or predecessors) in the vapor.The coke particles will eventually form shot coke after blending,friction and other processes.Based on this understanding,various factors affecting the formation of shot coke can be well explained.According to that theory,gas velocity in the coking drum is the function of multiple factors including feedstock properties and operational conditions and is one of the key factors contributing to the formation of shot coke.That mechanism can well explain various phenomena and affecting factors regarding the formation of shot coke.Gas velocity in the coking drum is a comprehensive crite-rion for judgment and the function of feedstock properties and operational conditions.Fitting the critical gas velocity with regard to the formation of shot coke through hydrodynamic calculations based on the working conditions of units and feedstock properties will provide a substantial guidance to the operation of the units.