we have on line wash past day, and i have record data before and after before (mw=105, cpd=10.4, compressor discharge temp=369).

at online wash time (mw=107, cpd=10.5, compressor discharge temp=356).

after (mw=105, cpd=10.4,compressor discharge temp=362).

this online wash my be the tenth one after off line wash. what is your opinion?

and i need paper from GE determine the factor that made online wash necessary

 

To the best of my knowledge, GE hasn't produced any recommendations for on-line washing. I don't think they really like on-line washing--or they haven't in the past.

Based on the data you provided, there was NO change in load or CPD after the wash. Therefore the wash was ineffective for all intents and purposes.

When performing any axial compressor washing--particularly on-line washing--it's really important to have meaningful data from before and after the wash (at steady state conditions!) to evaluate the effectiveness of any wash. If there was no improvement in output/CPD, then the wash was ineffective (presuming the instrumentation used to gather the data is calibrated properly and working properly).

Data, gathered with good instruments and in a consistent manner, provides the answer to the question. (As for the drop in CTD--that could be due to the cooling effect of the water during or immediately after the washing. We don't know when that last data point was taken, and it really isn't very relevant--if CPD doesn't increase for the same fuel flow, and load doesn't increase for the same fuel flow, then the compressor wasn't effectively cleaned.

And, as has been said before, the performance improvement after successive on-line washes degrades to negligible on almost every turbine. On-line washing really only cleans the first few stages of the axial compressor; after that the water has flashed to steam and is not as effective in removing dirt and contaminants. At that point the unit needs to be shut down to perform an off-line axial compressor water wash to try to gain back more performance.

If CPD and output don't increase after an on-line wash, then it was not effective. And the data as presented shows no improvement in CPD or output.

Compressor washing decisions have to be driven by the amount of performance degradation the site management/ownership can tolerate. And since the amount and type of contaminants varies from site to site, and sometimes even on the same site (based on the proximity of units to sources of contaminants) it's very difficult to say with any certainty precisely when a unit should be washed (off-line or on-line) based strictly on time. There are sites that NEVER wash--on-line or off-line. They don't worry so much about performance degradation or improvement. Other sites do worry about efficiency and performance degradation and improvement. But, even if GE published specific criteria there are sites which would say, "Well, or site/conditions are different and we can't follow those criteria!"

As with washing automobiles, or dishes, or clothes--the simple application of water, and even detergent, will not remove all dirt and contaminants. Sure; a car can be sprayed with water and even detergent, but sometimes to get it clean one has to scrub certain areas more than others. Axial compressors are no different. And, when on-line washing really only cleans the first few stages of the entire axial compressor it's effectiveness is necessarily going to be less than off-line washing even for the first wash. That is, if you washed a compressor off-line, and then did another off-line compressor wash, then did an on-line wash and compared the results of all of the washes you would most likely find that the on-line wash did produce a performance improvement/CPD increase, but not exactly the same amount as was achieved by successive on-line washes. And successive on-line washes will produce less and less improvements--until there's virtually no discernible difference (as in the data you provided).

 

ibr2016,

I'm wondering if one of the things which is causing confusion is the data you provided as "at online wash" showing an increase in output. That would be the TEMPORARY result of increasing the mass flow through the axial compressor and turbine when water is flowing during the on-line wash. If it was possible to monitor the actual fuel flow difference to several decimal places (high degree of accuracy) you would also see that during the time water was flowing during the on-line wash the fuel flow also increased (slightly), and then decreased (slightly)--particularly if the unit was operating at Base Load (CPD-biased exhaust temperature control). This would be because the water slightly decreases the exhaust temperature and the control system would slightly increase the fuel flow to raise the exhaust temperature.

A LOT of operations managers and plant owners see these "performance gains" (output increases) during on-line washing, and then start "on-line washing" on a daily basis when the revenue-per-MW is highest (and likely the output is slightly lower due to a high ambient temperature) to increase the power output to make more revenue. This is NOT GOOD for either the compressor or the hot gas path components--it increases stresses on the compressor components (rotating and stationary blading), and at the same time it artificially depresses the firing temperature which depresses the exhaust temperature. If the unit is operating on Base Load exhaust temperature control, the control system will increase the fuel which will increase the firing temperature above the design value, which leads to increased thermal stress on the hot gas path parts, particularly turbine nozzles and buckets.

So, while it may seem an innocuous thing to on-line wash for several hours per day, it's really not. I've even seen site management use the off-line water wash spray nozzles when the unit was running, which means a LOT more water is flowing into the axial compressor while the unit is running. At one site, the compressor was catastrophically damaged in less than three months of this practice, which meant the unit was out of service and not producing any electricity or revenue for about three months while it was being repaired. Amazingly enough, even though the management personnel told the technicians to force logic to allow this to occur, they blamed the turbine control system for allowing this to occur--blaming the damage on the turbine control system and saying the damage was covered under the OEM's warranty.

Again, it's not clear exactly why daily on-line washes are being performed, it may not just be for cleaning the compressor. And, if it's not just for cleaning the compressor, then it's also not good for the machine--especially if it's done for more than ten (10) minutes or so (which is a good indicator of ulterior motives for on-line washing).

Lastly, you've never really answered the question about the type of contaminants ingested into the axial compressor at your site. This is the largest factor in determining the need to wash, and the frequency of washing--both on- and off-line.

Hope this helps!