Why rinse time is often the longest part of a compressor wash

During a , the cleaning phase takes a relatively short amount of time. In contrast, rinsing wash effluent with water often monopolises the wash time, usually taking much longer than the initial clean.

While it’s potentially surprising to learn that wash time is dominated by rinsing, understanding ‘why’ can help you make important, profitable decisions about your .

Example gas turbine compressor wash procedure

Each gas turbine will have OEM procedures and offer guidance on wash/rinse cycles. Even if the cleaning phase is completed relatively quickly, rinse cycles can significantly extend total wash duration.

As an example, GE pulse rinse procedures are as follows:

• Wash cycles may include 8–9 one-minute injection pulses before rinsing begins.
• Approximately 29 rinse pulses are then required.
• Plus up to 5 additional rinse pulses if conductivity is not within specified limits (operators often report needing more than the minimum number of rinse pulses).

Rinse times when using traditional/high foam detergents have been reported lasting as long as 12 hours on General Electric 7F and 7HA units. Extreme cases reported 16–20 hours total rinse duration on certain units. That’s a long wait to get the gas turbine back into normal operation.

Why does rinsing take so long?

for effective cleaning. In gas turbine compressor washing, foam maximises the coverage of blades with active cleaning chemicals and increases chemical contact time for an effective clean. Once the cleaning chemical has done its job by breaking down and lifting away foulants, it’s essential that the foam is rinsed away according to OEM specified conductivity levels.

However, because it floats on the surface of water, foam can take a long time to rinse away – think of rinsing the washing-up bubbles down your plug hole at home. If you have a lot of foam, it requires a lot of rinsing. In a gas turbine compressor, it can take several rinse pulses and a relatively long time.

Choosing the right chemical for your needs is the best way to maximise cleaning power while producing only the necessary levels of foam.

Water and waste

While downtime due to wash duration represents lost revenue, another important factor to consider is water usage and effluent production. Most gas turbine sites use demineralised water for washing (recommended), and there is an associated cost with this, not to mention some sites have a limited supply. At the other end of the process, effluent must be responsibly disposed of according to local legislation.

Simply put, it’s beneficial to minimise water use in gas turbine compressor washing to reduce costs and effluent production.

Looking at the figures, a typical off-line wash uses up to 3,500 gallons on large units. This potentially doubles with high foam cleaners, and there have been reported cases where sump overflow has required vacuum truck removal.

How to reduce foam levels

High foam chemistry requires more flushing; more flushing means more rinse cycles, i.e. more water and longer outages. Some operators try to get around high foam levels by double-diluting their wash chemicals. However, this is false economy as although rinse time is reduced, the cleaning efficacy is also reduced, meaning another costly off-line clean will be needed sooner rather than later.

There’s no getting around the fact that a certain level of foam and rinsing is required. It’s simply a case of finding the right cleaning chemical that balances cleaning efficiency with foam production.

Choosing the right cleaning chemicals is key

While compressor on-line washes can be carried out during normal operation, off-line washes require the turbine to be shut down, i.e. no longer productive/profitable. While are essential to the long-term health of a gas turbine compressor, operators are interested in two things:

• Ensuring the compressor is thoroughly cleaned to maximise time between offline washes
• Getting the turbine back online as quickly as possible

Choosing the right cleaning chemical can help with both these things by:

• Thoroughly cleansing away foulants
• and only producing the necessary levels of foam to complete the clean without necessitating excessive rinsing.

Rinse time with low foam detergents

Compressor water wash time is dependent on many variables, including fouling severity and environment. However, operators have reported General Electric 7FA units rinsed in approximately 90 minutes, with many completing the rinse stage in 1.5–2 hours (15–20 pulses) when using low foam detergents.

Low foam cleaning chemicals also often reduce water usage by 1/3 and sometimes up to 50%.

Next steps

Understanding what happens during a gas turbine compressor wash is the best way to make informed decisions and implement improvements. Knowing that the rinse stage is by far the longest part of the process can help guide your cleaning chemical choice, striking the right balance between foam production and cleaning efficiency.

We’ve spent over 40 years developing cleaning equipment and chemicals for gas turbine compressors and our line of are chosen at sites around the globe for their outstanding performance.

We look at every aspect of the cleaning cycle, including the implications of foam production on rinse time, to create optimum products for our customers. If you’re interested in improving cleaning efficiency at your site, , and please if you have any questions.

References: all data supplied by Rochem.