S.K. Verma - IOCL - Guwahati Refinery
The Delayed Coker unit is basically a tertiary unit for producing value added products such as petroleum coke (PetCoke). The heavy oil along with steam thermally crack in the fuel fire furnace. Essentially the cracking begins at the onset of furnace and ends in the Coke drum. The coke drum overhead vapor flows to the fractionation column where they are separated into LPG, Coker Gasoline (CG), Coker Kerosene (CK), Coker Gas Oil (CGO) and Coker Fuel Oil (CFO). Un-stripped Coker Kerosene is drawn from the fractionation column into the Coker Kerosene side stripper. The level of Coker Kerosene side stripper is maintained with the help of a level controller provided at the CK draw off line and CK from Coker Kerosene side stripper is sent to CK product pumps, where it is pumped through rundown coolers to storage.
A case study has been presented on the repeated failure of Coker kerosene piping circuit from pump casing, control valve, pump suction pining, etc. Detailed root cause analysis was carried out, and included design review of control valve & pump, operation review for temperature /pressure excursion for change in vapor pressure, evaluating historical data, literature survey, etc. The possible explanation of failure in Coker Kero piping circuit and equipment appears to be cavitation/flashing of valve and cavitation swirl in pump suction.
The following paper examines further the reason for cavitation in piping circuit and cavitation swirl, and suggests mitigation measures with respect to process change and hardware modifications to avoid reoccurrence of similar failure.
S.K Verma is the Chief Manager of Inspection for Indian Oil Corporation Ltd. He has a Masters in Metallurgical and Materials Engineering, specializing in welding, corrosion, and failure analysis of static equipment in oil refineries.