When compressor washing and rinsing gas turbine engines at low temperatures, antifreeze will need to be added to the fluid to prevent the formation of ice which can cause blade damage.
It is necessary to add antifreeze as soon as the ambient temperature drops below +5°C, this is due to the air pressure drop at the intake lowering the air temperature.
Some compressor wash fluids are not compatible with certain antifreeze agents. Separation of the mixture can occur. If this happens, there is a risk that pure antifreeze could be injected into a running engine which could aid combustion.
ZOK recommends the use of Mono Propylene Glycol as an antifreeze agent as it is less flammable, is less toxic and possesses a higher biodegradation profile than Methanol and Isopropyl Alcohol, which are other alternatives.
ZOK does not recommend the use of Ethylene Glycol as it can leave sticky deposits on the blades and after thermal degradation this may form glycolic acid, which can attack turbine materials. Although some operators do use Methanol and Isopropyl Alcohol, ZOK does not suggest the use of either. This is because Methanol is toxic and both Methanol and Isopropyl Alcohol are highly flammable.
The addition of an antifreeze agent should be in line with the recommendations of the gas turbine OEM; however where no recommendation is given the table below can be used.
RECOMMENDED DILUTIONS FOR ZOK 27® OR ZOK MX® CONCENTRATE (TO MAKE 100 LITRES TOTAL MIX)
Concentrate (to make 100 litres total mix):
|Outside air temp (C)||ZOK 27 or ZOK mx (litres)||Water / Methanol
|Water / Methanol||Water / IPA
|+5 to -5||20||60/20||60/20||60/20|
|-5 to -20||20||40/40||50/30||30/50|
|-20 to -30||20||30/50||40/40||10/70|
|-30 to -40||20||20/60||30/50||Not Suitable|