Causes Leading to Formation of Shot Cokes and Measures for Its Prevention in Super Viscous Oil Delay

Shot cokes are frequently formed in the delayed coking unit treating the super viscous oil at PetroChina's Liaohe Petrochemical Company. Considerable work has been carried out to avoid the formation of shot cokes. The test results obtained have shown that the property of super viscous oil has played a key role in the formation of shot cokes. After adjusting and optimizing the process indices the operating regime of the delayed coking unit at a throughput of 118t/h of the super viscous oil is specified as follows: a reaction temperature of 498-502℃, a reaction pressure of 0.17-0.25 MPa, a recycle ratio of 0.5-0.6 and a fractionation tower bottom temperature of 355-365 ℃. In the meantime,the delayed coking process has adopted measures to enhance pre-fractionation of the feedstock to rationally remove light fractions and maintain a steady gas velocity in order to avoid the formation of shot cokes.