Water quality for Fogging (GT's)

[Bala0610]

Hi

I have a problem with power not being available at the GT's during hot summer days. Fogging has been suggested to improve the situation.

The required water quality is the (traditional !) DMW with < 10 ppm of TDS, <3 SiO2, pH bet 6.5 to 7.5, conductance < 11x10^(-6) mho/cm.

I have the following water available...
TDS 38 ppms, sulphide 26ppm, hardness (Ca) Nil, pH 3 to 4.5,CO2 100ppm - rarely some traces of light hydrocarbons (evaporatable...) conductnce at about 50 or so...

Normally used fuel gas contains much higher H2S - about 1000 ppms, about 4% CO2.

My query is - (leaving traditional DMW quality specifications aside, which are written around ground water treatment) - can we look at the contaminants in the water (instead of the conventional markers of contamination like TDS / conductance) and evaluate their effect for use in fogging ?

TDS in this supply is due to H2S dissolved...and low pH a result of CO2 / H2S again... There is no conventional scalants (Ca/Mg...). What exactly is the effect on the (initial stages of) air compressor / GT if this quality of water is used for fogging ?

I would prefer not to treat (except for filtration) this water...as some of the treatment options (like de-aeration) is likely to create some additional problems (of disposal of H2S laden air...)

Comments are welcome....

Thanks

 

[davefitz]

you might want to consider an evaporative cooler, if you do not want to treat the fogger water.

There are compact self contained demin stations you can buy, and the power to operate these is easily recovered with the increase in gas turbine output.

fogger water has to be "holy water" to avoid accumulating deposits on the compressor,or imposing a stress-corrosion cracking mechanism on the compressor blades.

There have been a couple of failures of compressors in the last 5 yrs , and you can assume you will lose your OEM warranty on the compressor if you add the fogger. But the capital payback due to the added power is very hard to pass up.

 

[Rich246]

Water has to be pure like the water used for water injection. You should also look at your turbine inlet duct and determine if you will have other problems from using fogging. Our turbine has a double wall inlet duct with insulation for sound. The inside wall is steel which is not solid. Over the year water getting into isulation has madethe inside wall rust away and now you can't walk on it. Our next major outage we need to put in a new liner so we don't risk part of the walls breaking off and going through the turbine. You also need to be able to adjust the fogging, most work based on humidity. If controls over fog you tend to wash dirt into the compressor and you lose load. Online wash helps after fogging but if you carry in lots of dirt from overfogging you will need to do an offline wash to get lost load back.