Rochem Technical Services
ROCHEM FREQUENTLY ASKED QUESTIONS

1. What are the methods of cleaning fouled GT compressors?

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

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2. What is online compressor cleaning?

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.

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3. What are the advantages and disadvantages of online compressor 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)

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4. What is offline compressor cleaning?

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.

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5. What are the advantages and disadvantages of offline compressor cleaning?

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

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6. What are the direct effects of compressor fouling?

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

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7. What causes compressor fouling?

The typical causes of GT compressor fouling are:

  • Passage of oily vapours through filtration system
  • Ingestion of oily vapours through breaches in air inlet plenum
  • Leakage of lubrication oil directly into compressor
  • Leakage of oil form oil-bath type filtration systems
  • Passage of very fine particulate matter through filter system
  • Passage of larger particulate matter through breaches in plenum
  • Re-ingestion of exhaust gasses through filtration system and breaches in air inlet plenum casing
  • Ingestion of saturated salt droplets or dry salt crystals through filters and/or breaches in plenum casings
  • Ingestion of seasonal tree and plant gums
  • Ingestion of wide variety of chemicals and other pollutants generated at site of gas turbine operation

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8. What are the advantages and disadvantages of using plain water for compressor cleaning?

The advantages of using only plain water for compressor cleaning are:

  • Can be used when gas turbine is operating (if injected correctly)
  • Simple to use
  • Relatively inexpensive
  • Can have some cleaning effects if fouling is purely water soluble

The disadvantages of using only plain water for compressor cleaning are:

  • Not effective against oily/greasy contamination
  • Not effective against lacquered or hard carbonaceous deposits
  • May move deposits to hot section of engine to cause corrosion
  • May directly cause corrosion if not inhibited
  • May cause thermal shock/blade stress if not injected correctly
  • Not effective for offline cleaning (unless the deposit is water soluble)
  • Must be high quality water with very low TDS and suspended solids

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9. How many installations have Rochem carried out?

In excess of 4000 nozzle manifold installations world wide on practically every type of gas turbine.

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10. What are the questions to ask when selecting a compressor cleaning system and/or chemical?

Questions to ask regarding the cleaning system:

  • How long has vendor been in business
  • An installation reference list
  • Is the system known to engine manufacturers. Do they approve it or have no objection to its installation and use
  • Is the system a recommended option or installed as standard in new gas turbines by any manufacturers/packagers
  • Does the vendor design, manufacture, install, service and guarantee the system himself. (If not why not)
  • Are the materials of the system good quality
  • How long does the vendor say it should take to install the system. Some can take a few hours to install, others can take weeks to install if it involves drilling thick castings etc
  • Is the design safe? Could it possibly damage the engine or injure those using it
  • Does the vendor have sufficient liability insurance

Questions to ask regarding the cleaning chemicals:

  • Does the manufacturer also manufacture special cleaning chemicals for use with the system and are they tried, tested and approved
  • Was the chemical on offer solely developed for online cleaning or was it originally developed for some other application not directly related to gas turbines
  • Does the vendor offer a choice of chemicals (i.e. solvent-based and water based) to suit particular fouling and/or environmental requirements
  • Is the chemical supplied as a concentrate to save storage and transportation costs. Paying for water in ready-to-use chemical solutions can be very expensive and unnecessary
  • Can the chemical offered also be used safely and effectively for offline compressor washing if need be
  • Does the vendor offer ex-warehouse availability of chemical
  • If the vendor only supplies chemicals are you sure it is safe to use them in your injection system

Recommendation: Be very wary of using any chemical especially for online, fired washing, unless it has been properly tested and approved and has a good long term safety record behind it.

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11. Has there ever been a failure of a Rochem nozzle?

Never in more than 25 years and millions of engine operating hours in every environment.

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12. What does the Rochem Fyrewash system consist of?

The system consists of a uniquely formulated chemical and a specially developed method of application. The cleaning fluid is formulated to remove oil and grease, carbon, salt and general atmospheric fouling from the compressor whether axial or centrifugal type. Complete compatibility with engine materials, including special coatings, is assured by the correct chemical formulation and proven over many thousands of operating hours in a wide variety of engine types. The cleaning fluid has been tested and approved by many of the worlds leading engine builders and also meets stringent U.S. Military Specifications for compressor washing fluids.

The Injection system is designed to deliver the cleaning chemical into the air stream in a highly atomized mist-like form and in every case is specifically designed to suit the particular engine type and air inlet trunking system. For industrial engines a set of specially designed atomizing nozzles connected by a common manifold ring are normally permanently fitted to the air intake plenum chamber and fed from a pressure injection tank or pump system. In all cases the entire system is designed for simple and low cost retrofit.

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13. How does the Rochem Fyrewash system compare in safety and efficiency with other compressor cleaning methods?

Water washing is generally ineffective because it has no power to remove the oily/greasy contamination which is the major problem affecting the loss of compressor efficiency. Even for salt removal purposes – an absolute necessity in marine and many helicopter operations – plain water washing is often of no benefit whatsoever since the salt is usually trapped in and under the layer of oily deposit which the water cannot remove. CRANK-SOAK SOLVENT Cleaning can be effective but it require complete shutdown, is labor intensive, contributes significantly to wear and tear on starting systems, and does nothing to solve the problem of power loss and increased fuel consumption while the engine is becoming fouled in normal operation. ABRASIVE CLEANING METHODS can result in serious blade erosion problems, bearing damage and the removal of very costly blade coatings. Also since abrasive cleaning can only dislodge the contamination back into the air stream, rather than chemically dissolve it, redeposition can occur in the latter stages of the compressor and bearing system.

The Rochem Fyrewash system has none of these disadvantages because it is used while the engine remains in operation, it can be used as frequently as necessary so contamination is not allowed to build up so that output and specific fuel consumption are not affected. The Fyrewash chemical range will keep the compressor clean of any salt, oily and greasy deposits and contamination whilst being fully compatible with blade coatings. It also leaves no residue in the engine nor redesposition of the removed deposits. The Fyrewash patented nozzles apply the wash solution in a highly mist-like form at a controlled flow rate so that there is no danger of blade erosion.

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14. What about cost effectiveness?

The cost of installing and operating a Rochem Fyrewash system is minimal compared to the potential savings in fuel, engine efficiency and output, and the avoidance of downtime to be realized by keeping the compressor clean while the engine remains in normal operation.

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15. How much time is required to install or retrofit a stationary engine?

This depends on to which engine the system is being installed. Some systems can be fitted in a matter of hours whereas others can take a couple of days. Generally the systems are fitted during an engine overhaul or outage.

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16. How much time is required for cleaning the gas turbine?

The time required to clean a gas turbine is dependant upon the size of it. A typical wash takes around 10-20 minutes and consists of a chemical injection followed by a soaking period to allow the chemical to break up stubborn deposits. This is usually around 20 minutes and then will be followed by one or two water only rinses.

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17. Do I need to use cleaning chemicals and detergents?

Rochem suggests the use of cleaning chemicals and detergents for online and offline compressor cleaning. The chemical breaks up the carbonaceous deposits and particulate matter that water alone cannot remove. Think of it as trying to clean a greasy pan with no washing up liquid!

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18. What is the requirement for the water used in the washing process?

The water must be of high quality, i.e. Demineralised or Deionised water.

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19. Is the cleaning procedure safe?

The Rochem Fyrewash system has been designed with safety in mind from conception to build. The patented nozzle design allows for precise atomization of the spray pattern to eliminate erosion to the engine.

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20. How do I go about purchasing the Rochem Fyrewash equipment?

All Rochem Fyrewash systems are available for sale throughout the world. Please use our contact form to send us an enquiry or email sales@rochem.net.

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JUMP TO A QUESTION:

  1. What are the methods of cleaning fouled GT compressors?
  2. What is online compressor cleaning?
  3. What are the advantages and disadvantages of online compressor cleaning?
  4. What is offline compressor cleaning?
  5. What are the advantages and disadvantages of offline compressor cleaning?
  6. What are the direct effects of compressor fouling?
  7. What causes compressor fouling?
  8. What are the advantages and disadvantages of using plain water for compressor cleaning?
  9. How many installations have Rochem carried out?
  10. What are the questions to ask when selecting a compressor cleaning system and/or chemical?
  11. Has there ever been a failure of a Rochem nozzle?
  12. What does the Rochem Fyrewash system consist of?
  13. How does the Rochem Fyrewash system compare in safety and efficiency with other compressor cleaning methods?
  14. What about cost effectiveness?
  15. How much time is required to install or retrofit a stationary engine?
  16. How much time is required for cleaning the gas turbine?
  17. Do I need to use cleaning chemicals and detergents?
  18. What is the requirement for the water used in the washing process?
  19. Is the cleaning procedure safe?
  20. How do I go about purchasing the Rochem Fyrewash equipment?

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