Automatic Start-up of steam turbine driven lube oil pump 2

[CaracasEC]

Hi All,
We have these large process gas compressors on the ongoing construction of our Ethylene Cracker Plant. One of our current issue is about the lube oil pump operation. The main lube oil pump is a steam turbine driven and an auxiliary pump that is motor driven. However, one question arise during our Hazop, that the event of maintenance of the steam turbine driven pump, the motor driven pump will be online. Then after maintenance, the steam turbine driven pump will be the standby pump. However, to have the flexibility of operation, we want these steam turbine driven pump to be on auto-start-up which would modify the lube oil accumulator sizing. The normal start-up of a motor is 4 seconds while on the turbine that we bought is 17 seconds and will have an impact on the accumulator sizing. What is your current design on your plant?

 

[Pumpsonly]

To avoid having to add additional control and bigger accumulator, just switch back to steam turbine driven pump as main after maintenance. The reason to use steam turbine driven as main is because of extra steam availability and its reliability.

 

[CaracasEC]

Thanks Pumpsonly, how about the flexibility of operation?

 

[JJPellin]

We would not normally require auto-starts on both the motor and the turbine drivers. We would run the turbine and auto-start the motor. I see very little value in setting it up for auto-start of the turbine. And, since it would complicate the design of the accumulators, I would not bother.

Johnny Pellin

 

[CaracasEC]

Hi JJPelin, what we are considering on the auto start-up of the turbine is an operator error after the maintenance of the steam turbine driven lube oil pump. The possibility of switching from the motor to the turbine after maintenance will be a possibility and once happened a 1.5 million dollar minimum shutdown cost because of the compressor lube oil system will cost the plant...Hoping for your comments.thank you very much

 

[JJPellin]

I would still not add the auto-start on the turbine. By complicating the design of the accumulators, you could end up causing another problem. If you have run status for the motor driver, set up an alarm that the board operator has to acknowledge once per shift. The board operator will make sure that they switch back to the main pump.

If you try to make the system idiot proof, someone will just come along and invent a better idiot.

Johnny Pellin

 

[CaracasEC]

Hi JJPelin, thanks again for your suggestion. For the accumulators, what would only the change is between a 4 sec start of the motor and the 17 seconds start of the turbine. It will be a matter of additional size of the accumalator. Would there still i'm missing on the lube oil design once we adopt the auto start-up of the steam turbine?