Offline & Online Washing for Gas Turbine 1

[norzul]

Hi,

We'd procured 4 X 25MW gas turbines (GE/NP). Got some question on the washing facilities:
1) Based on your experience, what is the typical & optimum frequency of online and offline washing
2) Water quality?

Thanks

norzul

 

[ahung]

Hi in our power plant we have five gas turbines Siemens Westinghouse model W501D5 100 MW ISO conditions. Actually we running at base load condition in simple cycle. According with our experience the most effective compressor cleaning is off line washing. The optimun frecuency for off line washing is one time every month, but normally its very difficult to us stop and cooldown the machine before off line compressor cleaning.

On line washing is only for maintain the conditions of compressor after we did at effective cleaning with an off line washing. One time every week its a optimun frecuency.

About the water quality its should be demineralised water.

Another point its about the detergent for cleaning the compressor its better use the type RTU (Ready to use) like Zok27 or RMC both of them are Bio Degradable.

Note: Every gas turbines has his own compressor cleaning system.

Regards

Alberto J. Hung C
Caracas Venezuela

 

[norzul]

Hi Ahung,

How long does it take yu to stop the GT from running to actually carry out the off line compressor cleaning?

Next, how many hours to complete the offline compressor cleaning?

Normal operation > shutdown > offline cleaning > Normal operation : Typical duration?

Yu mentioned about simple cycle...do yu have HRSG?

Thanks

norzul

 

[ahung]

Hi norzul, normally when you shutdown the gas turbine before do the off line washing you need to wait cooldown the machine: typical around 24 to 48 hours.

For the off line compressor washing first we need to do the following procedure for W501D5 units:

1. Start the machine at 800 rpm using the starting electric motor

2. Inject water for 3 or 5 minutes using the pump of compressor cleaning system. You don´t use liquid detergent at this moment.

3. Inject a blend of water and liquid detergent using the eductor of cleaning system for 5 minutes.

4. Shutdown the machine and wait around 20 minutes. (Its necessary let the liquid detergent make the "job" removing the dust from compressor blades.

5. Finally you start the unit again at 800 rpm and begin to inject water to remove the detergent from compressor blades. This action can take around 8 or 10 minutes.

We dont have HRSG in our plant. We waiste a lot of energy when we run our machines in base load condition and simple cycle because in Venezuela the natural gas its very cheap

Regards

Alberto J. Hung C
Caracas Venezuela

 

[norzul]

TQ Ahung for a detailed explanation. Btw, what is your NG price. In our case, we have 2 tiers of pricing i.e. for power plant sector and for normal industrial sector.

For power plant = USD 1.7/MMBTU (HHV)
For normal industrial = USD 3.2/MMBTU (HHV)

Another thing...do yu establish some criteria prior to decision to shutdown the GT and do the offline washing i.e. for example based on GT performance, power output, pressure drop across compressor, etc.?

Thanks

norzul

 

[ahung]

Hi norzul Here in Venezuela for Power plant the NG price is 0,78 US$/MMBTU (HHV). This is a reason that you don´t see any Combined Cycle Plant using Gas turbines in Venezuela.

The criteria for do off line washing is based on our own experience. Of course this criteria is according for GT deterioration performance basically for Loss of power output and pressure drop across axial compressor, but its very important consider the site conditions: In our case the plant is locate outside of Caracas the environment and air its very clean, our neighbourhoods are a National park and a Big Public College. We don´t have any industries near our plant.



Regards

Alberto J. Hung C
Caracas Venezuela

 

[toothless]

We operate GE Frame 6 units. We on-line wash (50 gallons) every 12 hours with demin water. I don't think the "soap" additive does any good with the on-line wash. The on-line wash helps "maintain" cleanliness, it really does clean to improve performance.

We perform off-line wash with a solvent and demin wate rmix 2-3 times per year. This cleans very well.

Run an isentropic efficiency calculation on the compressor to determine when it is fouled.

 

[abeltio]

the optimum frequency for OffLWW is determined for each site...

the compressor fouling depends on the site conditions.

the output goes down with time, so does the revenue the cost of shutting down for OffLWW of course increases.

the OffLWW recovers the output but has a cost due to lost revenue...

some sites do OffLWW just before the peak season to have the best output when the prices are the highest.

OnLWW: just delays the need for OffLWW... some units require to unload the unit for OnLWW, other don't.

So if OnLWW needs to unload the unit... there is also an economic equation: the output loss to perform the OnLWW vs. the gain of output...

i.e. there is no technical requirement to do water wash, only commercial.

for some units it is so expensive to do an OffLWW that they only do it during a schedule outage, e.g. a combustion inspection.

for GE units, the use of detergent for OnLWW is not recommended - i.e. water only.

also... OffLWW is performed with HOT water around 85degC while OnLWW is done with the demin water at ambient temperature.

the OffLWW requires manual valving and starting some fans in manual... follow the manufacturer's recommendations to the letter.

the OnLWW is usually fully automatic.








saludos.
a.