FAQs

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!

Never in more than 35 years and millions of engine operating hours in every environment.

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 atomised mist-like form at a controlled flow rate so that there is no danger of blade erosion.

In excess of 10,000 nozzle manifold installations world wide on practically every type of 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.

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.

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.

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 realised by keeping the compressor clean while the engine remains in normal operation.

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

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 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

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 shot blasting 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

There are basically two methods to clean a fouled process compressor; on-line and off-line cleaning.

On-line cleaning

On-line cleaning is the preferred cleaning method for process compressors. The advantage of on-line cleaning is that the process compressor can be cleaned during normal operation. There is no need to shut down the unit and the cleaning operation can be performed in a matter of minutes.

A suitable cleaning chemical will be injected by means of a specially designed nozzle system installed in the process compressor suction line. The atomized cleaning chemical will be entrained by the process gas thereby wetting all the process compressor internals. On-line cleaning will not only clean the gas passages, but also between the impellers and diaphragms.

Depending on the application and fouling level, on-line cleaning can be performed periodically or on a continuous basis. For process compressors where buildup on the diaphragm surface is a problem, continuous flushing with a cleaning chemical may be required.

Given the fact that the atomized cleaning chemical is evenly distributed inside the process compressor casing, there is no risk of flow instability. Any material buildup will be gradually removed thereby minimizing the risk of increased vibration levels and/or accumulation in downstream process equipment.

The positive effect of on-line cleaning will be visible instantly. The process parameters can be monitored and the cleaning operation can be adjusted as required.

Off-line cleaning

To enable off-line cleaning, the process compressor must be shut down and isolated. During off-line cleaning, the process compressor casing will be filled with a suitable cleaning chemical. Care shall be taken not to overfill the casing; the maximum liquid level shall remain below the shaft end seal level. Furthermore, the shaft end seals must remain pressurized to prevent liquid from entering the shaft end seal cavities and bearing areas.

While injecting the cleaning chemical into the process compressor casing, the rotor should be rotated slowly (<20 rpm). The process compressor internals should be soak washed this way for at least 15 minutes. When completed, the liquid can be drained from the casing and a sample should be taken to determine the amount of suspended and dissolved particles. Depending on the results, the procedure should be repeated as required.

Off-line cleaning is an alternative option to on-line cleaning. However, a major disadvantage is that the process compressor must be taken out of service which, in case of no backup, results in a complete plant shutdown. The costs associated with such an unscheduled shutdown could be enormous and adversely affect plant profitability.

Another negative aspect of off-line cleaning is its effectiveness. The process compressor casing can only be filled below the shaft end seal level. The top half of the casing, containing the top half of the diaphragms, cannot be soak washed. Given the fact that any material buildup in this area most likely cannot be removed, off-line cleaning could result in the additional risk of flow instability which potentially could cause increased vibration levels. Furthermore, chunks of dirt may eventually dislodge from the top half and move within the process compressor thereby aggravating the risk of increased vibration. Some will accumulate in the aftercooler inlets or knockout drums resulting in high pressure drops.

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.

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

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.

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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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.

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