Offline cleaning methods:

• Crank-soak chemical washing using in-built chemical injection/water rinsing systems
• Crank-soak chemical cleaning using hand held hose or lance
• Partial hand cleaning (e.g. Struts, IGV’s, 1st stage rotor & stator blading) using chemicals, rags, brushes and water rinse
• Full hand cleaning with compressor covers removed using chemicals, various types of abrasives or even light shotblasting techniques
• Steam cleaning

Online cleaning methods:

• Injection of abrasives (e.g. crushed nutshells) into the compressor air stream to displace blade deposits by high velocity impingement
• Injection of plain water to remove water soluble deposits
• Injection of special chemical solutions (solvent & aqueous based) to chemically dissolve and remove surface deposits from the blades

The compressor can be chemically cleaned on a frequent basis while the gas turbine remains in normal operation. Again, if done properly, on-line cleaning can be very effective in preventing – or at least significantly reducing – the fouling of the compressor with the additional and most vital advantage being that there is no shut down involved nor any interruption to operation or production of the plant which it serves.
With the continued development and improvement of on-line cleaning processes and chemicals – which Rochem has specialized in for over 20 years – one of the most efficient and popular ways of maintaining compressor efficiency is to now use a combination of on-line and off-line washing procedures.
If a properly designed on-line cleaning system and chemical is used this procedure should, at the very least, significantly reduce the rate of build up of compressor fouling and thus considerably extend the running time of the machine before shut down is required for off-line cleaning.

Lets start with the disadvantages:
Can have limited effect if chemical is not properly formulated
Can have limited effect if chemical is not injected properly
Some online cleaning chemicals are quite expensive and results may not justify the costs in some cases
Some online cleaning systems are very expensive and are priced against what the customer may save in operation costs rather than what it actually costs to develop and manufacture the equipment
Now the advantages:
No engine shutdown required
Can arrest or slow down the rate of compressor fouling while the gas turbine remains in operation thus maintaining heat rate and saving large amounts of money by avoiding additional fuel burn
Helps maintain power output to avoid loss of production revenue and unnecessary use of standby machines
There is no interruption to production or operation routines as washing can be carried out at full speed and load
The cleaning process usually takes only a matter of minutes
There is no waste chemical or water to deal with after the wash
Assuming the chemical is properly formulated and injected it should not contribute to any additional atmospheric pollution
By avoiding shutdowns for offline washing thermal cycles are also considerably reduced thus extending the life of the engine
No erosion, thermal shock, bearing damage, cooling system blockage (if properly designed system is used)

The gas turbine can be completely shut down on a regular basis for so-called crank-soak washing. If done properly this form of cleaning can be effective in restoring most of the lost performance. However, as all turbine operators know, it is very time consuming and laborious and, overall, a very costly exercise – especially when the shut down of the gas turbine means the total loss of revenue for the whole period of the shutdown from the sale of electricity and/or steam or costly interruption to the production of the factory which the gas turbine serves.

Let’s start with the disadvantages:
Gas Turbine must be shut down completely
Time consuming process
Labour intensive process
Costly problems in disposing of waste chemical and rinse water
Lost power output cannot be recovered
Shutdown/Startup thermal cycles for offline wash are damaging
Extra wear and tear on starting system during offline wash
Can wash salt and corrosives into inaccessible parts of the engine
Only a short term cure and not a prevention for compressor fouling
Now the advantages:
When carried out correctly can effectively clean compressor and restore majority of lost performance.

On day to day operating costs:
Higher fuel costs due to increased heat rate
Reduction in power output and loss of related production revenue
Use of more expensive external power supplies to make up shortfall
Higher cost of operating standby plant to make up shortfall
On longer term operating and maintenance costs:
Reduction in life of all hot section components due to higher EGT’s
Higher maintenance costs in more frequent replacement of components
On safety:
Possibility of compressor stall and subsequent engine damage
possibility of rotor imbalance, vibration and catastrophic breakup
On capital expenditure:
More frequent replacement of expensive hot section components
Greater investment in non-productive standby plant and redundancy
Shorter amortization periods for gas turbine