I
why is it recommended to do online compressor washing at reduced load?
S
sd
The only thing that I could think of is that due to the nature of operation of axial compressors where water injection actually increases air flow through the compressor due to the drop in temperature, it would eventually result in increase in gas turbine generated MW. Therefore reducing the load slightly would actually would make sure that you dont over generate MW when doing online washing. For machines struggling to generate sufficient MWs due to stretching period for offline water washing, online water washing sometimes is the only way to maintain the maximum MW possible 
C
CSA
For several reasons, but the biggest one is probably because when the water wash flow is stopped or is tripped the exhaust temperature can "spike" and possibly initiate a trip on over-temperature.
Air flows are also very high at Base Load (which is when most people want to do on-line water washing). Throw in a bunch of water and stresses on compressor components go up. The lower the ambient, the higher the air flows. (Of course, on-line water washing isn't allowed at temp's that could result in icing of the inlet guide vanes, but that doesn't stop some owners/operators who like to live life on the edge.)
Air flows are also very high at Base Load (which is when most people want to do on-line water washing). Throw in a bunch of water and stresses on compressor components go up. The lower the ambient, the higher the air flows. (Of course, on-line water washing isn't allowed at temp's that could result in icing of the inlet guide vanes, but that doesn't stop some owners/operators who like to live life on the edge.)
N
NLN
As far as I know Online wash, preferably, to be done at base load. The reason being the guide vanes are wide open so as to get the spray to clean initial stages as well the guide vanes. It is not sure about your units and limitations if any!
J
Jason Anderson
Compressor washes should be done offline if possible. Online cleaning is less effective and also will result in a higher wear of the compressor blade coating.
Online cleaning should be done at base load with fully-opened inlet blades. Use demineralized water, an approved cleaning solution, and verify that the compressor intake temperature is certain to remain above freezing. Drain valves should be left closed. Avoid using high pressure jets when cleaning online.
Only one online cleaning should be done between each offline cleaning. Online cleaning is harder on the blading and is less effective on blading stages farther back from the inlet.
Reference: Siemens V84.2 training manual
Online cleaning should be done at base load with fully-opened inlet blades. Use demineralized water, an approved cleaning solution, and verify that the compressor intake temperature is certain to remain above freezing. Drain valves should be left closed. Avoid using high pressure jets when cleaning online.
Only one online cleaning should be done between each offline cleaning. Online cleaning is harder on the blading and is less effective on blading stages farther back from the inlet.
Reference: Siemens V84.2 training manual
A
A. OZTAS
Axial compressor of the GT is so called mass flow compressor. The property of axial compressor is, compressing the sucked air in the mass flow. The volumetric flow is much less then centrifugal compressor (these are volumetric flow compressors, used in process system).
Performing On-Line WW, means adding water (contains oxygen) will increase the mass flow of the GT's axial compressor. Increase of mass flow will lead to increase of GT power output (higher CPD, increase of torque, so as a result the output of the Generator increases). Roughly figure will be about 1MW increase for 0.5kg/s injection (steam). You will ask your self now where does the steam suddenly come from?
As you know, the CTD (axial compressor discharge temp.) of the GT is about 300DEGC (572DEGF) for a GE mid size Frame machine. For a 16 stage compressor, the temperature at the 4th stage is about 100 DEGC (212DEGF). Once you start injecting the water during the ON Line WW, at the 4th stage the water start converting into steam. Steam will become more and intensive once it has reached the last stage of the axial compressor, where as the temperature (CTD) is the highest. It's highly advisable to switch over from base load to part load (lets say, decrease the output by 4MW for GE FR5 and FR6), otherwise you might trip the GT by over firing.
Once you know this, you should ask your self about the efficiency of On Line WW. Is this kind of washing really cleaning all the compressor blades? After the 4th stage, there is no more water (it evaporates to steam), NO WATER NO CLEANING. Ask your wife/partner, no water no clean dishes.
Good Luck
Performing On-Line WW, means adding water (contains oxygen) will increase the mass flow of the GT's axial compressor. Increase of mass flow will lead to increase of GT power output (higher CPD, increase of torque, so as a result the output of the Generator increases). Roughly figure will be about 1MW increase for 0.5kg/s injection (steam). You will ask your self now where does the steam suddenly come from?
As you know, the CTD (axial compressor discharge temp.) of the GT is about 300DEGC (572DEGF) for a GE mid size Frame machine. For a 16 stage compressor, the temperature at the 4th stage is about 100 DEGC (212DEGF). Once you start injecting the water during the ON Line WW, at the 4th stage the water start converting into steam. Steam will become more and intensive once it has reached the last stage of the axial compressor, where as the temperature (CTD) is the highest. It's highly advisable to switch over from base load to part load (lets say, decrease the output by 4MW for GE FR5 and FR6), otherwise you might trip the GT by over firing.
Once you know this, you should ask your self about the efficiency of On Line WW. Is this kind of washing really cleaning all the compressor blades? After the 4th stage, there is no more water (it evaporates to steam), NO WATER NO CLEANING. Ask your wife/partner, no water no clean dishes.
Good Luck
