KV Prasad Rakoti - Gujarat Refinery, IOCL
Sunil Kanti - Gujarat Refinery, IOCL
Delayed Coker Unit of Gujarat Refinery (IOCL) was commissioned in April 2011 having capacity of 3.7MMTPA. Feed (VR+RCO) at 270 deg C from Coker fractionator heated to its thermal cracking temperature and routed to coke drums through Coker valves (Make: Velan) like Switch valves (M-08/09) and Drum Isolation valves (SP-06A/B/C/D) with help of heater Charge Pump. Three Heater charge pumps are installed of capacity 295.4 m3/hr @ 574.74m, 1100KW each. This pump is design features of between bearing, two stages, 1st Stage impeller double suction and double seal with API Plan 32+52.Two pumps running in parallel and third one as stand by for two heater operation for four coke drums. Pump-A is Turbine drive and other two are Electrical drive, Motor.
Since from the commissioning, heater charge pump is unreliable and observed repetitive failures like NDE seal leak, damage of thrust bearing in every once in 2-3 months. After analyzing all different failures, following are the main causes and remedies are as follows.
- High erosion on pump wetted parts, caused by Catalyst carryover through CLO from FCCU (mixed in feed tank), high velocity at wetted areas and low surface hardness.
- Change pump wetted parts material from A487 CA 6NM/A to A532 CL III A (Impellers), applied hard coating tungsten carbide (HVOF- HIGH VELOCITY OXYGEN FUEL) on casing internals and reduced the velocities at landed area by changes in geometry.
- Mechanical seal failure due to low flushing flow after a period of time because of increase in stuffing box pressure over a period of 2-3 months and damage of carbon bellow
- Replaced the primary Caron bellow with SiC (Harder face)
- Set alarm limits on DCS for Plan-32 Flow
- Failure of thrust bearing due to high thrust load during the startup and slippage of lock nut.
- Installed the double lock nut to avoid the slippage.
- Maintained minimum flow during the start up.
- Problem with the parallel operation of turbine driven and motor driven with the action of wear and tear of pump internals
- Maintained the flow based on the load sharing.
After implementation of all above actions MTBF of the pump increased from 3 months to more than a year and reduced the production interruptions and also steam saving of 5Kg/MT due to replacement of pump internals.