Gas Turbine Not Cooling

T

Thread Starter

Thomas

We are operating a GE MS9001E Gas Turbines. recently one of the machine is running with two BT (Ventilation) fans due to high temperatures in the turbine compartment. The inlet air flow rate started to drop as compared to the other Gas Turbine. We constantly running two BT fans, so we don't have redundency on those BT fans. If one BT fan trips, the Gas turbine trips as well due to the high temperature in the compartment. Previously we had couple of trips due to these fan failures.

We found some holes on the compartments and sealed them but still the problem is not going away. The Inlet air flow sensor were also checked and found to be okay.

What else can we check?
 
Thomas,

Some turbine compartments are under a positive pressure by the turbine compartment vent fans, and some are under a negative pressure (few mm of water vacuum). Ventilation problems can be the result of many things, including leaks of axial compressor discharge air from casing joints, leaks of combustion gases from combustors, etc.

It's not likely that ambient air leaking into the turbine compartment is going to cause high compartment temperatures--unless the "holes" are very large.

GE and packagers of GE-design heavy duty gas turbines frequently use reverse tangential centrifugal fans (look it up on the Internet using your preferred Internet search engine). These fans actually need to rotate in the opposite direction of what one would expect them to rotate in by looking at the angle of the fan blades in order to produce rated air flow. If they are rotated in the reverse direction, they will still produce some air flow, but very little in relation to what they would produce when rotating in the proper direction. And, when they are run in the wrong direction the motors also draw excessive current--which most technicians/electricians "resolve" by making changes to the thermal overload relay setting of the motor starters. (Which isn't the proper resolution, and leads to premature motor failures, also.)

So, look for leaks from the axial compressor or turbine casing joints, etc. Make sure all the dampers/louvers are working properly (review the Diagram, Flow-Heating and Ventilation and the Fire Protection P&ID). Many times some dampers/louvers are latched open and unlatched when fire extinguishing agent is discharged--and never get relatched, or don't get re-latched after a maintenance outage, or just vibrate loose and close, restricting ventilation air flow.

Check the current drawn by the vent fan motors; that's the best indication of how "hard" the vent fans are working. Compare the measured current against the motor nameplate current values; a properly working fan will draw current at or very near rated current. If the current is much less than rated, it's not working properly (restricted suction or discharge; etc.). Or, if the current is much more than rated then it might be rotating in the wrong direction (see above).

Sometimes I've even seen redundant vent fans not properly isolated from each other, and when both are running less air actually flows than when one fan is running. (This is usually caused by improperly working dampers/louvers.) So, running both fans can actually lead to higher compartment temperatures than if just one is running. Or, if one is running and can draw air in through the other fan because the dampers/louvers are not working properly then compartment temperatures may be higher than normal.

Use the P&IDs to check all the dampers/louvers to make sure everything is working properly.

And write back to let us know what you find and how you resolve the problem.
 
A

Abdur Rehman

Thomas,

R u having online monitoring of turbine compartment temperature? if so than can you share the amount of pressure build by pressurizing fan in turbine compartment, normal temperature in turbine compartment along with alarm and trip temperatures?

Moreover kindly share the types of thermocouples you have for online monitoring of Turbine compartment temperature? Which type of fire detectors you have in your GT?
 
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