At what compressor efficiency ratio is water washing advised to be implemented for GE Frame 5 gas turbines.

 

Ilechie Chiedozie,

Everyone detests the answer, but that doesn't make it any less correct: It's different for every site--because of factors like elevation, type of inlet air filter, ambient contaminants (dust from nearby dirt roads (if any), dust from nearby industrial plants such as cement plants (if any), airborne hydrocarbons from nearby roads and vehicle exhaust (lorries) or refineries or chemical plants, and ambient humidity and the source of ambient humidity (is the plant near a sea or ocean which can mean salty air, etc.).

Every site and operations manager has to trend compressor performance beginning with as clean a compressor and inlet air filters as possible, and monitor performance degradation (compressor pressure ratio decrease; power output decrease), correcting for ambient temperature changes and power levels to the extent possible (using manufacturer-provided performance correction "curves").

And, then, when the cost of shutting down (lost production due to the time required for cooling and performing the off-line compressor water wash) drops below the lost output/efficiency, then it's time to shut down and perform an off-line water wash. This can vary of the course of a year as ambient conditions change, and power requirements change.

Every site I'm aware of that has tried to implement a single value for all conditions and times has eventually abandoned that plan because someone perceives the frequency ("cost", really!) to be too great. What was good for one manager at some time, never proves to be good for another manager at another time--and, to a certain degree, that's okay. Continuous improvement, right?

It really is a dynamic thing. Every site operates their unit slightly differently, under slightly different conditions--environmental as well as ambient as well as economic. And, it's all about what management decides is economically unacceptable output versus the cost of shutting down and performing a compressor wash.

The key is to properly perform the wash--to not take shortcuts with the washing or the rinsing, and to analyze the effectiveness of the washing by visually inspecting the turbine bellmouth and IGVs BEFORE the washing process starts AND after the wash has completed, as well as monitoring the effluent from the water wash- and false start drains. Some sites even test the effluent for contaminants to check for effectiveness of rinsing. Too many sites just "go through the motions" when performing a compressor water wash, trying to complete it in as little time as possible without monitoring the drains or checking to see how much cleaner the compressor inlet is.

Using too much detergent is another problem, and not properly rinsing can cause detergent residue to build up on the compressor which lessens any efficiency gain. (Remember: The detergent manufacturer is already recommending the maximum amount of detergent so as to maximize detergent sales. I always find it easier to cut that recommendation in half at least to begin with, while trying to find what works best for a particular site. Too much detergent can require LOTS of rinse water, which should be demineralized water--which isn't cheap.)

It's all a learning and balancing act--there really are no hard-and-fast rules for any type of turbine at any site. And, when I've made a recommendation (when demanded), site management always questions that recommendation after a few washes and someone comes up with a spreadsheet--or a perception--that the time to perform a wash needs to change.

Every site has to develop their own criteria, based on site conditions and adjust their criteria as necessary and as conditions change to meet site economic goals (maximizing production and revenue while minimizing maintenance costs).

Sorry; but this is the answer. Even sites which have paid tens of thousands of US dollars for software to help with this decision have usually over-ridden the software recommendations to meet economic goals. But the proper way to arrive at the proper point for your site and your turbine is to trend operation and build a site-specific database from which to make a decision about when to shut down to perform a compressor water wash--and then to inspect the compressor inlet BEFORE and AFTER the wash to gauge basic effectiveness and to ensure that a proper rinse has been done to remove detergent and contaminants that can remain and even build up over time to hamper compressor efficiency.