Hi fellow Gas Turbine experts,

I work in a power plant running 1 Frame 5 and 1 Frame 6b gas turbine.

We did an offline compressor wash using Fyrewash F3 (Detergent), mixed with demineralized water with ratio of 1:5. The washing solution has a pH of 7.07.

Compressor offline wash was done with both GTs cranking for 5 times. The average pH of Frame 5 was 4.1 and Frame 6b was 5.0, which is a little bit too acidic.

I understand that inside the compressor, there are corrosion of metals, carbons, and etc, which causes acidic effluent after mixing with the washing water.

Is pH 4-5 acceptable? Or mitigation steps should be taken?

Thanks and regards.

 

Great question for the OEM/packager of the units at your plant, or perhaps Rochem (manufacturers/distributors of Fyrewash).

What kinds of contaminants do you normally expect to wash out of the compressor and how would you expect them to react with the Fyrewash and demineralized water?

What kinds of fuel do you burn in the units?

Have you measured the pH after the washing before, and if so, was it higher or lower than these readings?

Have you borescoped the compressor to see if there is any unexpected corrosion or metal liberation?

Where were you measuring the pH? At the compressor casing drain? At the combustor "false start" drain? At the exhaust false start drain? From the water wash drains waste tank? Or do the false start/water wash drains drain to a common gas turbine waste tank where oils and fuels might also be present?

When were you measuring the pH of the effluent? During the washing? During the rinsing? After the rinsing?

What were the average temperatures of the samples you were measuring? (Some people use "hot" water for washing/rinsing; greater than 20 deg C.)

You say the wash was performed with the GTs cranking for "...5 times..." Usually, a wash consists of a wash cycle, which usually means the unit is CRANKed and water and detergent are introduced into the inlet.

Then the unit is shut down for some period of time (20 minutes is a typical value; some sites wait more, some less) for a "soak", the purpose of which is to allow the detergent to "do its thing" on the compressor

Then the unit is rinsed of detergent and contaminants by CRANKing again and introducing plain water to rinse the compressor until the drains run clear of soapy residue. Rinses can be very brief (if the compressor wasn't too dirty, and/or if only a small amount of detergent was used), or they can be very long (if the compressor was dirty and/or a large amount of detergent was used--which is usually the case if the manufacturer's recommended ratio is used!).

Having said all of the above, it's still a good question to ask of the turbine manufacturer or the packager of the turbine to see if they have any guidelines. I've never measured the pH of the effluent and don't know about any guidelines.

And, one would think the detergent manufacturer might also have some good ideas on this.

Please write back to let us know what you learn!

 

Hi CSA,

Thanks so much for the reply.

Indeed, I believe mine's a good question for Rochem!

For your questions Sir:

1) I actually expected to wash out metal bits (e.g. nickel) due to corrosion and pitting on the turbine blades. I also thought I'll wash dirt and dust out. After reacting with the Fyrewash and demin water washing solution (which is about neutral), my prediction wash the effluent should be about neutral or alkaline, but it came out quite acidic.

For your info, the to GE GTs at my plant runs about once a week, to generate electricity and steam (Cogeneration).

2) I only use natural gas to fuel the GTs.

3) Initial pH of washing solution was 7.07. After the washing (effluent) was 4(Frame 5) and 5 (Frame 6) respectively, which is a little bit too low.

4) I did a boroscope test last month, but unfortunately, we didn't observe the blades.Even if we did, we were only able to observe the 7th stage (if I am not mistaken).

5) I collect the effluent at the wash waste tank.I am quite sure there are no oil or fuel contaminants there (Good point). However, I measured the pH and the testing lab in the plant. Maybe some slight inaccuracy due to the transfer of effluent?

6) I measured after rinsing.

7) Washing with temperature about 27 degrees C.

You're spot on bout the wash cycle. I will contact Rochem and continue to research about the effluent outcome.

Thanks again CSA

 

Dear all,

Just wanna share that, after changing to Zok 27 or Adrox 6377, it seems the pH improved.

Thanks and regards

 

Crusader,

Thanks for the feedback.

One has to wonder, though, how often did you perform off-line compressor washes before you began measuring the pH, and what has been the compressor washing frequency since you started measuring the pH of the effluent? Is it possible that because of increased washing frequency the contamination has decreased considerably, lowering the pH of the effluent?

Believe it or not, natural gas can and quite often does have liquid contaminants entrained in it. They include lubricating oil and seal oil (from the compressors used to raise the pressure and maintain the flow of natural gas), gasoline (from who knows where, but I've seen gasoline liquids in several natural gas fuel sample reports, and lots of it on more than one occasion, too), various hydrocarbon liquids, glycol, and water.

Yes; contamination during transfer when sampling has definitely been known to occur.

Did you receive any feedback from Rochem?

If the units only run once per week, why is it necessary to wash the compressors so often? Is there some ambient contaminant that necessitates frequent compressor washes?

If you are measuring the effluent from the drains at a common tank, it's likely that the exhaust plenum drains are also directed to that tank when performing a compressor wash (or at least they should be).

Some turbine blade/exhaust plenum contamination will be liberated by a compressor washing and rinsing, but not much if the natural gas is relatively clean and free of contaminants. Most of the washing and rinsing liquids flow out of the compressor discharge/combustion wrapper drains, but a good amount does get through the turbine and into the exhaust.

Lastly, compressor washing isn't really effective on turbine buckets (as GE refers to turbine "blades"). Compressor washing is done to remove dirt from the axial compressor blades (as GE calls them) to improve the efficiency of the compressor which improves the efficiency of the turbine (axial compressor and turbine).

Again, thanks for the feedback!

 

Hi Crusader,

I read your comments with interest and although this was some years ago I wondered if you a.) received a response from Rochem and b.) have you resolved the slightly high pH issue?

Please feel free to contact me directly [email protected] should you require any technical support.

Kind Regards,

<b>Moderator's Note:</b> I usually don't post replies to such old messages. And I don't post messages that could be considered marketing or sales. However, I know people often search our archives for answers to questions, and this poster does give his email in case anyone has similar questions for Rochem.