In GE gas turbines, lub oil heat exchanger cooling water will enter first in generator & generator outlet cooling water (hot water)will enter in lub oil heat exchanger. What is the reason behind it?

 

We really don't have much information here. What Frame size machine (and we're presuming it's a heavy duty machine, not an aero-derivative or some other machine)? Is the cooling water coming from a plant cooling water system, or is it from a self-contained cooling water system that is specific to the turbine-generator?

This is something I've never given much thought to or researched; it's one of those things that's always just worked. Are you having problems maintaining L.O. header temperature? Or any other temperature that is maintained by the cooling water system?

Have you measured the temperature of the water entering and leaving the generator heat exchangers?

I think you'll find that the temperatures in the generator are lower than the temperatures in the L.O. heat exchanger, and that the designers have had this in mind. The cooling water encounters successively higher temperatures as it flows from one heat exchanger to the next and finally to the water-to-air heat exchanger before returning to the turbine-generator.

Even more interesting, have you measured the temperature of the cooling water entering and leaving the cooling water module water-to-air heat exchangers (water-to-air "finned" heat exchangers, usually with some kind of forced air (fans) over the heat exchanger tubes/fins)? I'm always amazed when I do that, because sometimes, even on the hottest days, there's only a 1 or 2 deg C temperature drop across the heat exchanger! And, yet, everything works fine.

I've seen sites where they have not re-installed the orifice between the cooling water module and the turbine, or they haven't properly adjusted the butterfly valve used in place of the orifice, and they have problems maintaining temperature(s).

I wish I had a better answer. I'm not a thermodynamics engineer and, again, with but one exception in almost 30 years I've never had a problem with the cooling water system provided with a GE-design heavy duty gas turbine being able to control temperatures as required.

Maybe otised can shed some more light on the subject.

 

thank u for your reply..i am talking about heavy duty turbine only. i have seen both 9E & 9FA frames, both are designed in a same fashion. we are using a plant cooling water system (DM water). till now we haven't faced any problems with lub oil temperatures. i haven't measured the temperatures at any time. i will measure & come back to you.

 

Have a read of the P&IDs for the Cooling Water Systems of the units. You will likely find expected heat rejection values, pressures, and flow-rates.

And, not being a thermodynamics engineer nor having ever had to deal with any heat rejection issues (except once) I can't make any analysis or recommendations.