We have two frame 5 gas turbines (equipped with dual fuel nozzles but currently turbines operate on gaseous fuel) MS 5001P with Gardner Denver Atomizing Air compressor model SMAD/1. This is a screw compressor with timing gears so that screws do not come in contact during operation.

Previously there had been oil leakage from this compressor thru seal vents.

Recently during shutdown oil was observed from false start drain valve before startup of gas turbine. Upon further checking oil leakage was observed from atomizing air precooler drain and atomizing air manifold.

When gas turbine was started it tripped on overspeed and also fir was observed at gas turbine exhaust

Although these turbines are equipped with dual fuel system, these have been operating on gaseous fuel for a very long time. Also we do not have any paln to operate these turbines on liquid fuel.

We have no experience of any maintenance on atomizing air compressor.

to prevent oil leakage we have seal welded atomizing air and liquid fuel passages of fuel nozzle and atomizing air compressor discharge is currently being vented which causes a lot of noise

Can we operate compressor with suction and discharge blinded?
What will be the procedure for removal of compressor from accessory gear box?

Any supplier who can provide spares for this compressor? Gardner Denver says its obsolete

 

You've welded the fuel nozzles...!! I don't believe. Overspeed trip & fire in the exhaust....!! I do believe it. Please tell me where you are so I can stay well away

 

Dear we had seal welded the dual fuel nozzles at atomizing air, liquid fuel and purge air inlet after discussion with OEM and experience sharing from a couple of other sites who had done so. Also we have no standby power source and this was an emergency situation.

Excessive oil leakage was observed from exhaust plennum, atomizing air precooler drain and atomizing air manifold.
Therefore we had no other option at that time

Any suggestion on atomizing air compressor removal procedure/precautions will be helpful

 

Please check your PnID drawing to check whether the MAAC air is supplied to. Only then you could safely decide on the removal. If the liquid fuel is not used and causing leakages and fire hazard, I don't foresee any reason to weld the liquid fuel nozzles. Why don't you just isolate and drain the liquid fuel line? This can be done at the liquid fuel forwarding pumps. Every problem has a simple solution. Please don't alter any as designed flow of gas, liquid or air without a comprehensive analysis and study of the systems. Mere discussion would not be sufficient. Lack of experience on the maintenance of MAAC should not be a reason not to repair/service it. Get the OEM to assist and I'm sure it can be done.

Good luck and keep us posted!

 

Our turbines are only equipped with accessory gear box drive atomizing air compressor. (No motor driven atomizing air compressor) To boost the atomizing air compressor to proper level during start up a blower is provided which is belt driven from Diesel Engine used for starting gas turbine.

I had mentioned earlier that we operate the turbines on gaseous fuel. Major portion of atomizing air compressor during normal operation is recycled back to suction. A small portion is used to pressurize/purge liquid fuel and atomizing air passages.

Previously during normal operation oil had been observed from atomizing air compressor shaft end seals vents. This indicated worn shaft as well as bearing seals. (Lube oil is supplied to atomizing air compressor bearing from gas turbine main lube oil header). Probably because of high atomizing air compressor suction and discharge pressure oil can not flow into compressor suction or discharge lines.

During last shut down, initially oil leakage was observed from false start drain valve. Then keeping in view the previous problem, atomizing air precooler drain was checked and oil was observed coming out of it.

Also oil leakage was observed from atomizing air manifold inlet and exhaust plennum. We suspected that due to worn atomizing air compressor seals at suction and discharge ends, oil supplied to bearings leaked into compressor suction and discharge lines.
When a start attempt was made gas turbine tripped on overspeed and also fire was observed at gas turbine exhaust probably due to lube oil leaking into combustors as well as exhaust plennum. (Gas Turbine compressor discharge air is supplied to exhaust plennum up stream of atomizing air compressor).

It is not possible to isolate L.O. supply to compressor without discoupling {uncoupling?} it from accessory gear box.

OEM has told that compressor manufacturer (GARDNER DENVER) had discontinued the production of this compressor and offers no replacement for this line. (Same has been confirmed by GARDNER DENVER). The installation of new compressor requires modification in atomizing air piping. This will be carried out in next planned outage.

Temporarily we want to discouple {uncouple?} this compressor from accessory gear box.

 

you have to check the coupling (type) between gear box and AA compressor. It could be a quell shaft, finger/spider coupling or belts. Remove that coupling and install the compressor again. you can blind the in/out of compressor. but prior to doing this once check the system after AA compressor that any other utilization of that air for any purpose (for instrumentation or sensing of pressure etc. and its effects after blinding).

Which type of shaft sealing is there in Screw compressor. Review the drawing, may you can rectify this without any major spare parts. may be some consumable items (O ring or gaskets required for maintenance.

I also agree that turbine original condition should not be modified prior to proper study and analysis.

 

I fully agree that turbine original configuration should not be modified with out proper review. Currently we only need temporary solution till next planned outage when we will replace the compressor.

This compressor is driven by accessory gear box through quill shaft. Drawing suggests that quill shaft is coupled with atomizing air compressor shaft by a hub which is engaged with quill shaft through splines and with atomizing air compressor shaft through key.

space available to slide the compressor in straight line away from accessory gear box (towards inlet plennum) is approximately 40mm.
Is it possible to discouple the compressor from accessory gear box with out removal of accessory gear box cover?

Since this is a screw compressor with screws equipped with timing gears so that during operation there is slight clearance between screws (screws do not come in physical contact) can we leave this compressor coupled to accessory gear box and blind its suction and discharge?

 

Now I'm confused.

Lube oil system and liquid fuel system are two different system all together. Observing oil coming out from false start drain valve is definitely liquid fuel. If lube oil is seen to come our from the false start drain valves, something is seriously wrong somewhere.

 

Due to leakage from atomizing air compressor seals, oil incressed into both suction and discharge lines of atomizing air compressor. The oil entering discharge line of atomizing air compressor reached atomizing air manifold. from atomizing air manifold oil entered into atomizing air passages of dual fuel nozzles and finally into the liners. Probably oil leaking into combustor no 5 liner was visible from false start drain valve.

Similarly atomizing air compressor takes suction from main compressor discharge. Upstream of atomizing air compressor (before atomizing air precooler) main compressor discharge is provided to exhaust plennum. Oil was also observed leaking from atomizing air precooler drain and exhaust plennum probably because of oil leaksge into atomizing air compressor suction

 

Very well feedback FSX,

Oil observed in liquid fuel nozzle may agreed but oil leak in atomizing air pre-cooler drain is strange as NRV is there between pre-cooler and suction of MAAC which will allow air /(fluid) only from pre-cooler to suction.

Please make sure??

Take care
G.Rajesh