Process Compressors Cleaning Systems

• Scaling or precipitation
• Particulate
• Corrosion
• Chemical reaction
• Solidification
• Composite

The four main types of gas turbine compressor cleaning are shown below in the table below along with their advantages and disadvantages. Abrasive cleaning is seldom carried out anymore due to the high potential risks associated with this type of cleaning and modern gas turbines. The other three types are much more common and performed on gas turbines of varying sizes across the world. The two most popular water wash methods performed on gas turbines are offline and online. Rochem best practice recommends both online and offline washing. Online washing helps limit performance deterioration in service while regular offline washing raises baseline performance.

During on-line cleaning, atomised cleaning fluid is injected into the system while the compressor is still running. It reduces the rate at which foulants build up in process compressors and can significantly reduce losses, increase efficiency, and reduce unplanned shutdowns for cleaning.

Fouling consists of deposited airborne particles ingested from the environment. These can include not only salts and minerals or hydrocarbons, but also aggressive gases such as Sox, Nox or Cl2. Once these particles adhere to the compressor blading, an increase in surface roughness is seen affecting the aerodynamic performance and in turn compressor performance. This ingested pollution is also a contributor to blade corrosion.

These chemicals react with moisture from the environment creating acidic compounds, reducing the operational life of the machine, and increasing maintenance costs to the operator.

In 2012, Andrew F Bromley carried out a fouling cost prediction for three engines based on a reduction in energy output over a period of 8000 hours which can be seen below in figure 1. This indicates a huge potential monetary cost to running a fouled turbine, suggesting that the installation and running cost of a turbine wash system is relatively insignificant in comparison and you are likely to see a return on investment within the first year.

Figure 1. Prediction of the cost of fouling - Gas turbine power degradation and compressor washing, tutorial part 2, ASME International gas turbine and aeroengine congress - Andrew F. Bromley

A further issue of fouling is the blocking or partial blockages of cooling passages in hot section stators and blades, as bleed air is contaminated by foulants entering the cooling system. This results in improper cooling and accelerates thermal fatigue on components. This then increases maintenance costs and lengthens shutdown periods.

Although the problems highlighted above will not be eliminated by installing a turbine wash system, it will mitigate the risk and cost incurred from operating in non-ideal environments. By performing a wash, we are removing this build-up of foulant from not only the compressor blades but all internal surfaces.

Many foulants can be simply flushed away with water but not all of them. FYREWASH® chemicals are a range of specialist cleaning chemicals designed for all types of fouling while meeting current manufacturer and environmental standards worldwide. They are mixed with treated water in a ratio of 1:4 and practice has shown that FYREWASH® F1 and F4 are best suited to clean process compressors. Alternatively, where water is prohibited by the process parameters, process compressor cleaner can be used as it contains no water. Other cleaning fluids can be used in the cleaning process.

The onset of performance loss may be rapid commencing soon after start-up or develop more gradually over time.

• 15 - 30% shortfalls in the head are common
• 10% efficiency loss is translated into a 10% increase in power to maintain production
• Power constraints result in a drop in production revenue and profits
• Losses amounting to $4.8M per unscheduled shutdown are not exceptional!

In principle, process compressors with oil seals or self-acting dry gas seals are suited for on-line cleaning. A design verification will be carried out to determine if any modifications are required for each particular case.

These can be manufactured to suit any application, but standard nozzles use 1-1/2" ANSI/DIN flange connections rated to suit the process application.

• Rochem injection nozzle system installed in the process compressor suction pipeline.
• Rochem self-contained wash delivery skid operating at pressures up to 100 barg.

There are two choices to deal with this problem:

• Take the unit out of service, open the casing and manually clean the process compressor internals. This method is a very time-consuming and costly solution
• Or install a Rochem on-line cleaning system that allows the process compressor to be cleaned during normal operation in a matter of minutes.