ZOK Frequently Asked Questions

If you require any further information regarding ZOK gas path cleaners, please take a look at our FAQs below. If you need further help then please contact us by mail, phone or email.

Q.WHY DO I NEED TO WASH?

The compressor of a gas turbine ingests a large amount of air. This air (even when filtered), contains contaminants which are deposited on the compressor blades and stators.

These deposits build up, eventually leading to a reduction in compressor efficiency.

Compressor washing removes this deposited fouling, restoring the aerodynamic profile and compressor efficiency.

A reduction in compressor efficiency causes an increase in fuel consumption; an increase exhaust gas temperatures (EGT) and reduced power output.

Q. HOW OFTEN SHOULD THE COMPRESSOR BE WASHED?

It very much depends on engine usage and environmental factors.

It seems to be generally accepted that an off-line clean should be undertaken when compressor performance has reduced by a maximum of 5%.

The basic objectives of on-line (or ‘Hot’) cleaning are to maintain the cleanliness of a gas turbine compressor after off-line (Crank or ‘Cold’) washing, to maintain power and efficiency by minimizing ongoing losses, and to extend the operating period between planned shutdowns required for off-line washing.

Q. HOW DOES ONLINE ‘HOT’ WASHING COMPARE WITH OFFLINE ‘COLD’ WASHING?

Online cleaning (‘HOT’Washing)
Performed with the gas turbine operating and under load. It maintains compressor efficiency after offline washing, minimizing power losses. Online cleaning also extends the operating period between shutdowns.

Online cleaning is generally recommended every three days to weekly.

Operating and local environmental factors will determine the appropriate wash regime.

Offline cleaning (‘COLD’ Washing)
Performed with the engine shutdown. Restores maximum power and efficiency.
Off-line cleaning is a more thorough process than on-line cleaning due to both the greater volume of cleaning solution that is passed through the engine and the much greater dwell (soak) time for the cleaner to work.

Offline cleaning is generally recommended three to four times per year.
Operating and local environmental factors will determine the appropriate wash regime.

On-line Washing – PROS

  • Increases operating periods between Off line washes
  • No waste disposal required (fully consumed during cleaning)
  • No shutdown required – No loss of revenue

On-line Washing – CONS

  • May not fully clean all compressor stages
  • Must use pure water for wash and rinse

Offline Washing – PROS

  • Maximum power recovery
  • Cleans entire compressor section
  • Good Quality water (potable) may be used for wash and rinse

Offline Washing – CONS

  • Requires complete engine shutdown and cooling period.
  • Potential loss of revenue
  • May not be convenient (availability)
  • Waste requires careful disposal, according to local regulations

Compressor wash fluid is commonly heated (especially for on-line washing). Heating specifications can be obtained from the engine manufacturers’ maintenance manual.

Q. WHAT SHOULD BE USED TO WASH THE COMPRESSOR?

Solvent-based cleaners are being replaced by aqueous (water) based cleaners for both environmental and health & safety reasons.

All ZOK products are water based, detergent cleaners. Standard dilution is a 20% solution (1 part ZOK to 4 parts demineralised water).

ZOK products are available with and without a corrosion inhibitor package (ZOK 27 & ZOK mx respectively).

Q. WHY DO WE NEED TO USE DEMINERALISED WATER FOR GAS TURBINE WASHING AND RINSING?

Demineralised or de-ionised water is used in gas turbine engines during on-line compressor washing and rinsing.It is essential that this water meets the very demanding specifications of the gas turbine engine manufacturers so that it does not damage the turbine during its passage through the engine by depositing alkali metals or hard water scale.

The demineralised water manufactured by ZOK complies fully with the following specifications:

NATO S-1739 (WTA)
Rolls-Royce MSRR9435
General Electric GEI 41042
Solar Turbines ES 9-62

ZOK manufactures Demineralised Water using the reverse osmosis (RO) process.
Typical Specification, to Defence Standard 68/253:

Conductivity @ 20°C                               10 µS/cm max.
Silica content (mg/L)                                3 max.
pH                                                              5.0 – 7.5
Dissolved solids (mg/L)                           10 max.

Q. HOW MUCH COMPRESSOR CLEANING FLUID SHOULD I USE?

Quantities, flowrates and (possibly) wash fluid temperature requirements for compressor cleaning can be obtained from the engine manufacturers’ maintenance manual.

Q. IS CORROSION INHIBITION NEEDED?

ZOK 27 contains a separate corrosion inhibitor package to control corrosion. Maximum performance is achieved at the standard (20%) dilution ratio. During the cleaning process the corrosion inhibition package coats the blade surfaces protecting them from corrosion.

Optimum corrosion protection is achieved by off-line washing with ZOK 27, followed by an unfired spin on the starter to remove excess wash fluid. Ideally, blanks should be fitted to the air inlet and turbine exhaust.

Offshore operators of industrial gas turbines have found that they can wash an engine with ZOK 27 before shutdown and then just leave it, without having to use dewatering fluids. If the engine is shut down for more than a week, the operator simply gives it another ZOK 27 wash, not to clean it again but to “freshen-up” the corrosion inhibition effect of ZOK 27.

Q. CAN I USE ANTIFREEZE?

When compressor washing and rinsing gas turbine engines at low temperatures, antifreeze will need to be added to the cleaning fluid to prevent freezing.
ZOK recommends the use of Mono Propylene Glycol (MPG) as an antifreeze.
In general, glycols are non-corrosive, have very low volatility and very low toxicity.
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 Dilution for ZOK Concentrate (for 100 litres total mix):

Outside air temp (°C)

ZOK (Litres)

Water / MPG (Litres)

Above +5

20

80 / 0

+5 to -5

20

60 / 20

-5 to -20

20

40 / 40

-20 to -30

20

30 / 50

-30 to -40

20

20 / 60

Q. IS ZOK BIODEGRADABLE AND CAN I DISCHARGE IT INTO DRAINS OR WATERCOURSE?

ZOK products are biodegradable.

The question regarding discharge into drains / watercourse is a matter for your local jurisdiction.

You MUST check with your local environmental agencies before discharging effluent into any drains / watercourses.

Q. CAN I PASS THE EFFLUENT INTO AN OIL / WATER SEPARATOR?

Because ZOK products contain surfactants which, by their very nature hold oils suspended in an emulsion. It is highly likely that an oil / water separation system will NOT operate satisfactorily with ZOK products.

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