Process compressors are critical equipment items, fouling will adversely affect the compressors reliability and availability. Any machinery downtime or even reduced capacity will negatively impact on your profits. The performance of your process compressors can be radically reduced by fouling carried in the medium being processed or by accumulation inside the process compressor itself resulting from the polymerization or seal oil contamination.
The Rochem on-line nozzle and delivery system allows the process compressor to be cleaned during normal operation. The PC range uses Rochem’s proven washing technology offering the user a simple and effective method to ensure maximum performance from your process compressor.
What are the options when cleaning a gas turbine?
The four main types of turbine cleaning are shown below in table 1 along with their advantages and disadvantages. Abrasive cleaning is seldom carried out anymore due to 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. The online washing helps limit performance deterioration in service while regular offline washing raises baseline performance.
||A high level of performance recovery at a low cost
||Can clog cooling holes in blades increasing thermal fatigue and likely to cause erosion to surface coatings
||Restores turbine to "as new" condition offering maximum performance recovery
||Lengthy shutdown and large amount of man hours required
||Performed in service, no need to reduce speed or lower output
||Extra loading of the turbine and increased erosion risk from large droplets
||Deep cleans turbine resulting in significant performance recovery without shutdown
||Requires a reduction in operating speed and multiple rinse cycles
Table 1: Advantages and disadvantages of different cleaning regimes
What is the on-line cleaning process?
On line washing is a process that reduces the rate at which foulants build up in process compressors. While the turbine is still running, atomised cleaning fluid is injected into the system. Online cleaning can significantly reduce losses, increase efficiency and reduce un-planned shutdown for cleaning.
Why do we need to clean the compressor?
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 accelerated 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.
Do I need to use chemicals for cleaning?
Water alone cannot remove all the foulant types. FYREWASH® chemicals are a range of specialist cleaning chemicals with outstanding performance designed for all types of fouling and meeting current OEM & environmental standards world-wide. They are mixed with treated water in a ratio of 1:4. Practice has shown that FYREWASH® F1 and F4 are best suited to clean process compressors. Where water is prohibited by the process parameters process compressor cleaner can be used as it contain no water.
Will the cleaning chemical damage process compressor seals?
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.
What is the process connection size and form?
These can be manufactured to suit any application, but standard nozzles use NPT or 1-1/2” ANSI/DIN flange connections rated to suit the process application.
What are the foulant types?
- Scaling or precipitation
- Chemical reaction
- Solidi cation
What is the scale of associated losses?
Onset of performance loss may be rapid commencing soon after start-up or develop more gradually over time.
- 15 – 30% shortfalls in 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!
The solution to process compressor performance recovery
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
What equipment is required?
- Rochem injection nozzle system installed in the process compressor suction pipeline
- Rochem self-contained wash delivery skid operating at pressures up to 100 barg