What Happens to Cleaning Fluid During a Gas Turbine Compressor Wash?

There’s more to compressor washing than just spraying cleaning fluid into the compressor. While from the outside it seems like that’s all that’s happening, the fluid must be precisely delivered, transported, distributed, make contact with fouled surfaces, remain there long enough to interact with deposits, and then rinse away.

…And all this must happen in the extreme conditions of a gas turbine compressor, often under full load during on-line washing!

Understanding the journey of gas turbine compressor cleaning fluid can help improve your practices and achieve better overall performance.

The Cleaning Circle

The theory behind the cleaning circle, also known as Sinner’s Circle, shows us that cleaning is reliant on four things:

• Time
• Chemical action
• Temperature
• Mechanical action

You can read more about it here, but the basic principle is that all four factors affect each other and are needed to achieve a clean.

When relating the cleaning circle to gas turbine compressor washing, the wash fluid must:

• contact the fouled surface and retain contact for a sufficient period of time for chemicals to work
• consist of relevant, effective chemicals to break down foulants
• be delivered at an effective temperature (to react with foulants but also prevent thermal shock)
• physically wash away the debris

Keep the cleaning circle in mind as we look at what happens to cleaning fluid during a gas turbine compressor wash.

1. Injection

Once the wash fluid has been prepared, which can be done automatically to precise specifications using a wash skid, it is injected into the gas turbine compressor. Specialist wash nozzles are crucial at the injection stage, delivering fluid droplets into the high-airflow environment.

However, simply spraying wash fluid into the compressor does not guarantee an effective clean. There are many factors that affect coverage, wetting, foulant penetration and rinsing, including:

• Nozzle position
• Spray direction
• Droplet characteristics
• Injection velocity
• Compressor airflow
• Inlet geometry
• Wash-system configuration

Getting the injection stage right is key to the whole cleaning process.

2. The wash fluid’s journey

Once injected, the wash fluid interacts with the fast-moving air within the gas turbine compressor; the trajectory is not the same as spraying liquid onto a stationary surface. Injection location, droplet mass and velocity all play a part in where and how effectively cleaning fluid is distributed.[i]

It’s important to ensure the wash fluid makes it from the nozzle to the blade surfaces and achieves useful coverage. After all, the fluid can only clean a surface it actually touches.

3. Does all the cleaning fluid reach every compressor stage?

Wash fluid enters the front of the compressor and travels downstream. However, its behaviour changes on its journey; turbine configuration and operating conditions influence liquid distribution.

Keep in mind that while cleaning fluid does not simply pass through every stage in the same way, spray distribution at the inlet affects what happens downstream. The amount of liquid reaching different areas can vary, and it’s important to ensure effective coverage where it's needed.

4. Where does mechanical action fit into the process?

Thinking back to the cleaning circle, we need to consider mechanical action: how gas turbine cleaning solution reaches and interacts with the blades.

The same detergent will produce different results if the delivery system provides poor coverage.

5. What happens when a droplet reaches a fouled blade?

Once the cleaning liquid reaches a surface, the next two things to think about are contact time and chemical action (remembering the cleaning circle). The fluid must spread over the surface rather than simply hit it and move away.

Surfactants in cleaning chemicals reduce the surface tension of water and improve the fluid’s ability to spread across a surface, i.e. making contact with contaminants.

6. What happens to the fouling once the fluid makes contact?

Once initial foulant/wash fluid contact is achieved, time and chemical action are then the key factors. It’s essential that the wash solution contains the right chemicals and the correct dilution to target the specific foulant composition. E.g. a gas turbine compressor operating in a forest area is likely to present sticky sap deposits, while an offshore site will have high proportions of salt in the compressor.

While achieving contact is the first step, you need to make sure the fluid that reaches the fouled blades is chemically capable of cleaning the foulants there and given enough time to do so. OEM guidelines help determine how long to conduct soaks during offline washes for this reason.

The right wash chemicals can also help:

• Wet the contaminated surface (surfactants are key here)
• Loosen deposits
• Interact with oil/grease
• Disperse and emulsify suitable contaminants
• Keep dislodged material suspended and prevent it from immediately redepositing (foam is important for this)

7. What role does foam actually play?

It’s easy to overlook foam as simply a standard feature of cleaning products. However, it’s standard for a reason, as it plays a crucial role: it helps cleaning chemicals ‘stick’ to a surface for longer. This assists the ‘time’ factor in the cleaning circle, allowing the cleaning chemicals to do their job.

The downside of foam can be that excessive quantities increase rinse requirements, especially as it floats on the surface of effluent. Getting the balance right is essential for effective, efficient cleaning.

Read more about the role of foam here.

8. What happens to the loosened contamination?

Removing foulants is all very well, but what happens next is just as important. The released material must be removed from the compressor to prevent it redepositing and/or interfering with the turbine’s airflow and productivity.

Following the wash stage, rinsing removes residual detergent and contaminants, and the effluent is flushed out for disposal. This is the end of the journey for our cleaning fluid:

Nozzle → airflow → blade surface → foulant → rinse → drain

Summary

We’ve looked at what happens to cleaning fluid when it enters a gas turbine compressor and how the cleaning circle is key to achieving effective results. Compromising on any factor has implications for the whole process, which is why the chemical and the wash hardware cannot

be considered in isolation.

Carefully selected and correctly diluted cleaning chemicals must be delivered, transported, contact fouled surfaces, given the time and conditions to interact with deposits, then be rinsed away.

While it’s easy to think about that initial injection of wash fluid and presume the job is done, what happens next is crucially important and worth reviewing.

If you’d like to find out more about how we can help adjust cleaning practices at your gas turbine site, please get in touch.

[i] Mund, F.C. & Pilidis, P. (2005) Online compressor washing: A numerical survey of influencing parameters (2005). Published in Proceedings of the Institution of Mechanical Engineers, Part A: Journal