In GE gas turbines DLN system water wash should be done at what load? Whether it is in base load or reduced load? Why?
In GE 7Fa we are doing online water wash at a reduced load approximately by 3%. Machine should be out of temperature control, transitioning to speed control. This is done to avoid peaking of the machine during the water washing.
I would like to add one more point that online washing should not be conducted when the Inlet bleed heat is open. This valve should not be forced to close to carry out the water wash.
Turbine should be in running condition and not to be in shutting down period.
IGVs preferably can be 3 to 4 deg less than full load (base load).
Dear GE Gas Turbines,
We perform an online rinse/wash to our GE7EA DLN 1.0 turbines daily. GE specifies that the online wash should be done at base load only with IGV's at maximum angle and IBH the inlet bleed heat valve closed. Keeping the IGV's at or near maximum angle reduces chances of water droplets hiding out in low pressure zones of the IGV blades and contributes to a better wash.
If you do not keep the unit on temp control you should watch your IGV angle, since you can expect a 3-5% rise in power output during a wash, which could cause the IGV's to close down in an attempt to maintain exhaust temperature. You do not specify the model of turbine you are using, but I can tell you that on the 7EA inlet bleed heat is closed with IGV angle greater than 61 deg, so IBH should never be a problem if the unit is at or near base load.
As a sidenote we have modified logic to monitor the secondary flame detector intensity and stop the wash if 2 flame detectors fall below a set threshold. We have noted in colder ambients that the increased moisture from the wash seems to fog over the flame scanners at times.
It was the problem of fogging with some DLN systems. But in DLN 2.6 we did not face this problem.
However it was recommended by GE to reduce the load. It might be mentioned in your GE manual also to whether do the water wash at reduced load or at base load.