High Enclosure Temperature of MS 5001 Gas turbine

A

Thread Starter

Azee

Hi,

We have a GE frame 5 gas turbine Model MS 5001 R/NT installed at our complex. We are facing issue of high enclosure temperature specially when ambient goes above 50 deg C. Some other observations are as follows

- Both ventilation fans are in continuous operation.

- There is no drop in compartment pressure with both ventilation fans so presumably there is no ventilation air leakage (Delta P data compared to Previous years record with 02 fans in operation).

- All the dampers are in open position and there is no apparent restriction in flow path.

- Turbine high exhaust temperature issue is also faced in conjunction with the enclosure temperature issue and turbine shifts to temperature control mode so load is restricted

- Inlet filters delta P is within range

- Compartment Temperature is around 15 deg greater than recorded during previous years

We suspect that this might be caused by cooling/sealing air piping leakage. This turbine had undergone major overhaul last year and is in service for 6 months after that.

I have following questions to ask,

1. In short term can i devise a method to cool the temperature of ventilation air fed to the compartment by installing a water sparger of sorts?

Will the moisture carried over with the ventilation air have any effect on instrumentation or cause any corrosion?

2. Besides process air leakage can there be combustible gas leakage that could cause this temperature increase?

Regards,
MAz
 
MAz,

Good information, and good questions!

Do the compartment vent fans draw their air from after the turbine inlet air filters?

How old are the vent fans? Could they be worn and/or dirty and not flowing as much air as in the past? Even if you're moving the same or slightly less air, if the incoming air is hotter the effect of cooling is going to be less.

Electric motors also decay in efficiency over time, and are also subject to performance degradations under extreme heat.

Have you checked the current drawn by the motors to see if it's balanced and nearly equal? Do you have any previous operating data for the motors to see if they're working as well as they have in the past?

Yes; leaks from the axial compressor horizontal and vertical joints can cause hot compressor air to enter the compartment and raise the compartment temperature. As can leaks from atomizing air piping/flanges. Leaks from compressor bleed valve piping/flanges can also contribute to high compartment temperatures. It's customary to use a cloth on the end of a long stick to search for leaks at flanges and joints, though that's a real problem for personnel at the other end of the stick when it's so hot....! Combustible gases may leak from combustion cans/fuel nozzles--but they wouldn't generally cause high compartment temperature, but maybe under the right circumstances they could.

High <b><i>compartment</b></i> temperature isn't going to affect exhaust temperature--and load is always restricted when the ambient temperature is high; that's normal and to be expected.

You should be as certain as possible that there are no leaks of high temperature air into the compartment before trying to cool the incoming cooling air. You could certainly try some kind of evaporative cooler for the incoming air--but the increase in humidity is not going to be a good thing for devices and metal, especially if the paint has long since flaked off.... I wouldn't worry too much about most instruments, because they are, or should be, mostly tubed with and constructed with stainless steel or otherwise be impervious to high humidity (that's a presumption, based on the devices provided with most new turbines).

Certainly it wouldn't be advisable to spray water into the path of the incoming air, even if it's highly atomized ("fogged"). But, creating some kind of duct and evaporative cooler is going to be difficult. And, this would really only be a temporary solution, probably.

Can you investigate installing larger fans/motors, or larger fan impellers and motors in the same fan enclosure, to move more air?

Is there a way you can ensure the air entering the compartment isn't heated by, say, some nearby motor or the exhaust ductwork through some unusual air flow pattern, such as from L.O. Coolers? I've temporarily used plywood sheets to block unwanted hotter air from being drawn into compartments during extremely hot ambient conditions caused by unusual site layouts and prevailing winds.
 
Dear MAZ;

Most of time, High enclosure temperature, if instruments are fine, is due to hot air leak. To detect this or those leaks, you need to stop the enclosure ventilation at all, open the door and a volunteer (mechanical) with a flag will try to find any leaks. This task will not be done at 50°C!! Do it earlier morning when ambient temperature is lower. This task will take few minutes and will not affect the gas turbine running. Make risk assessment if necessary..

Hope this is helpful
Regards
Karim
 
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