My assessment lead me to a point where i think the compressor discharge air is leaking through a gland packing underneath the combustion chamber (From where Lubrication pipe connects with bearing#02).

Please help me in finding the possible reasons. And if someone had faced such a situation then please share.

 

Hi,

The air leak you mentioned could be repaired by opening the flange (bearing#2 lubrication) and replace the gasket.

From my knowledge, air leak from that part has no noticed effect on compressor efficiency. What might actually affect compressor efficiency are:

1. Inlet air filters dirty
2. IGV not working properly
3. deformation on compressor blades
4. stages sealing in compressor are leaking
5. compressor water wash is needed

regards,
Maythem

 

Maythem,

Excellent reply.

 

Thanks for the reply Mathew.

Well our efficiency loss is around 0.8% and during base load I physically verified the leakage of air from Bearing#02. I am much convinced that if that gland packing is passing then 11 bar air will be leaving at much higher flow rate resulting in less efficiency.

Also we have checked compressor blades, inlet filters and anti surge valve. No abnormal condition was visible. Although our evaporator cooler water channels were blocked. After its maintenance we regain 0.2%.

 

Sir,

Theoretically how much % improvement in compressor efficiency was observed after offline wash provide all other conditions are good. like inlet filter dp with in the good range, etc...

 

hello,

in where i work we off-line wash both turbine and compressor every 10 days because we are running on crude oil. that is why unfortunately i do not possess such data (efficiency improvement by water wash).

even in dusty weathers the compressor efficiency will not be dropped out in 10 days.

regards,
Maythem

 

Maythem,

Dust/dirt by itself isn't really the problem when it comes to axial compressor cleanliness and throughput (though eventually it will become a problem). It's the combination with humidity that results in the "coating" of the axial compressor blades (rotating and stationary) that causes the decrease in throughput.

If the machines at your site are running crude, and you're also performing off-line turbine washes then it's likely that site management has just decided to perform off-line axial compressor washes at the same time as the off-line turbine washes (since the unit's shut down anyway).

Off-line turbine washing isn't normally done on machines running on natural gas (or other "clean" gases), but is done more commonly on crude-fired machines--to help remove the heavy metals which plate out on (coat) the turbine nozzles and -buckets and reduce the efficiency of the turbine section as well as reduce the parts life of the nozzles and buckets.

If the axial compressor weren't washed during the off-line turbine washings it's a good bet that eventually the axial compressor throughput (and CPD) will drop over time, even with a relatively dry ambient environment. Turbine inlet air filters are not capable of removing all dust and debris from the air entering the axial compressor. And, eventually that dirt is going to deposit (coat) the stationary and rotating turbine compressor blading and reduce the axial compressor throughput and decrease CPD for the same operating conditions when the compressor is clean--which decreases performance.

Hope this helps!

 

Dear Maythem, CSA,

Here where I'm working, SAHARA of North Africa, we never ever performed the water washing on both GT and Axial compressor. Because the burnt fuel gas is a clean natural gas So there is no need to wash the turbine (as explained by CSA).

For the axial compressor and regarding our experience, if we are not performing this water washing, it's because each time the machines are opened (Major Inspection or boroscope inspection,..) axial compressors are found clean and in good shape (no dust/dirt, no fouling, no erosion/corrosion). The only times the axial compressors have been found dirty are when there was an oil leak (oil arrived to the axial compressor) and when cracks happened on the air inlet panels and sand went through to the axial compressor.

At this period of year (October to February), weather is nice but the humidity is a little bit higher and the air filters begin to suffer a little bit (increase of the air filters diff. pressure) due to the mixture of humid air and dust.

The hottest period is between June and September, the ambient temperature is over 40°C which make the GTs operating on CPD Biased exhaust temperature Control the most of time.

<b><i>For people</i> not for GTs</b>, the worse and windy and hot period with sand storms is, let's say, between February and June but gas turbines don't suffer as much as people.

Here, Sahara, <b>DUST is everywhere</b> and the climate is dusty but with a <b>clean dust</b> I mean with a very very low humidity. So if the air filtration is adequate only <b>small</b> and <b>dry</b> particles of dust or sand (about a micron) will pass through the filter media. And these CLEAN particles of DUST or sand are going to clean up or wash our axial compressors therefore no need to make the water wash.

This is my <b>own opinion</b> and I would like and hope read Mr CSA comment about this.

Best Regards
Karim

 

Dear CSA,

Thank you for the input. that is exactly what i meant. we stop the unit anyways for washing, so we wash both turbine and compressor and it is become a routine thing.

regards,
MAYTHEM