What is the necessity and frequency of compressor washing for GE 9E Gas turbines? Is compressor washing effects on reducing erosion, corrosion and pitting on compressor blades? If reduction of performance of Gas turbines that results in reduction of
maximum output power or increase of exhaust gas temperature and fuel consumption, at a given output power and ambient temperature, occurred; is it sufficient to do compressor washing? Are detergents of compressor washing effect on pitting of compressor blades?

 

EshanD,

Ahhh, compressor washing.... Axial compressor cleanliness directly affects power output--a dirty compressor can't flow as much air, so the mass flow-rate through the machine is reduced, and that also increases the heat rate (a lower heat rate is better!). Washing can also help to reduce corrosion, depending on the contaminants in the are which are being ingested into the axial compressor inlet.

Off-line washing of the axial compressor can greatly restore output, and possible hand-washing of the IGVs (Inlet Guide Vanes) may also be necessary and helpful.

On-line axial compressor washing has been proven to be somewhat effective, but it's effectiveness decreases over time--leading to the need to perform an off-line axial compressor wash.

The difference between on-line and off-line is that on-line refers to washing when the unit is on-line, producing power. For units with DLN combustors, the detergent must be water-based; for non-DLN combustor-equipped units, an oil-based detergent (usually more effective than water-based detergents) may be used. Off-line compressor washing means the unit must be shut down, and cooled, to perform the washing procedure. Usually, oil-based detergents are used for off-line washing, again because they seem to be more effective.

It's the shutdown and cooldown periods that cost the most--in terms or production and lost revenue, particularly if the gas turbine exhaust is used to produce steam for some process/plant. No exhaust heat--no steam (from the gas turbine exhaust). No running, no revenue for producing power, either. And, it's the cooldown period (usually several hours, if the unit is force-cooled; more if it's not) that also increases lost production and revenue. (The unit internal temperatures must be reduced before putting water and detergent into the axial compressor or damage can occur--hence the need to cool the unit, or allow it to cool.)

So, while on-line washing can be done without shutdown/cooldown period, over time the effectiveness of on-line washing becomes negligible, forcing an eventual shutdown/cooldown to perform an off-line water wash to restore as much performance/output as possible. On-line washing can prolong the time between shutdown/cooldown outages, but eventually, it will be necessary to shutdown and cool down the unit if it's desired to restore as much performance as possible.

And, lastly, frequency. There's <b>NO</b> one-size-fits-all answer for this question: How often should axial compressor washing be performed. The answer to this question is: How much performance degradation can the operations department and/or management and/or ownership tolerate before it's necessary?

The way to derive the answer to the question--and it's basically necessary to do this at EVERY site, and sometimes, if there are multiple units at a site for every unit, because site conditions can vary, such as if one unit's inlet is near a dusty road; or ingests diesel exhaust because it's near a road with lots of lorries; or nearer to a cement plant; or nearer to a refinery with lots of hydrocarbon vapours being ingested into the unit; or closer to the ocean or a large body of water (natural or not), etc.---and that's to chart output over time, and use the performance correction curves provided by the packager of the unit to correct output for ambient conditions (temperature, mostly). And, when the output drops to an unacceptable level--which varies at EVERY site because no two sites have the same ambient conditions--then it's time to perform a compressor wash (on-line or off-line).

Site conditions will ALWAYS determine how fast the compressor fouls. High humidity and airborne contaminants (dust; exhaust fumes; fine sand; hydrocarbon vapours; even salt (from a salt water body of water); fog; etc.) will all determine fouling--and again, that's different at every site. And, only management/ownership/operations can determine what is and isn't an acceptable level of performance degradation--which is affected by site conditions, which are different at every site, and, again, even different at different locations on the same site. And, if the unit is shutdown for an off-line compressor wash, a visual inspection of the axial compressor inlet (bellmouth and IGVs and first stages of the compressor) should always be performed, and then another visual inspection after the wash procedure to determine if the wash was acceptable or not. (Sometimes, depending on the contaminants and the level of contamination, hand-washing of the IGVs and the bellmouth are necessary.)

A typical water wash performance degradation "trigger" level is 3-4% decrease in output, some sites can tolerate more and others less. Again, it depends on MANY factors, and it NOT the same for every site, or even for every unit on the same site.

Hope this helps!!!

 

EshanD,

I did just recently read that a dirty axial compressor doesn't have as great an effect on the mass flow-rate of air, but it does cause the axial compressor discharge temperature to rise, which also reduces compressor efficiency. I haven't had a chance to research that yet, but I wanted to pass along as further information about the effects of a fouled compressor and the effects of washing.