Information FOULED TURBINES = LOST PROFITS An average GAS turbine of about 46.500 kW with a normal level of deposit, for size and quantity, is subjected: • power decrease of 3% • increase 1% of the thermoelectric ratio The overall performance drop can cost more than 500.000 $ » 440.000 € All year SCALES: the accumulation of unwanted particles ( with variable dimensions between less 1 and 10 mi-crometers) that during the operation settle along the air way inside the gas turbine. The main effects caused by the scales on the palettes are: • increase of surface roughness; • compromising of geometry and volumes, with drop of the aereodynamics performance ; • reduction of the air flow. Between 70% and 85% of overall performance loss can be attributed to the deterioration of the compressor, caused by the scale on the palettes. TYPES OF FOULING Hydrocarbons The worst fouling problems are caused by mixtures of liquids and oils or generally hydrocarbons, that deposit on the blades and form an oily film which catches particulate matter. This could be caused by the burnt fuel exhausts emitted from turbines, and can be particularly severe if less clean fuels such as crude oil are used. Oil leaks are another major problem and even smoke from surrounding industries, cities and vehicles contribute to-ward the fouling. Salt water As the air ingested into the compressor is heated, moisture in the air evaporates, leaving salt and dissolved constituents to deposit on the blades. When subjected to the hightemperatures temperatures inside the compressor, these deposits can become firmly baked onto the compressor surfaces. Salt also causes corrosion and rust, so it should be promptly removed. This is a major problem in coastal areas and offshore. Other causes Dust and sand generally cause erosion and can lead to fouling when combined with other constituents such as oily vapours. The atmosphere also contains numerous other contaminants including farming chemicals, gases from neighbouring industries, plant spores, insects and smog. Even some additives in certain cleaning products, if not rinsed off properly, can contribute to fouling. WASHING IS THE BEST SOLUTION Regular washing is the most effective way to remove fouling and is the method specified by the turbine manufacturers. It involves injecting a cleaning fluid into the compressor to restore performance. Washing will also halt the progression of corrosion which can cause pitting of the blades and encourage further fouling. The fouling however can be made up of many different and often sticky substances, that when subjected to high temperatures become even more resistant to cleaning and hard to remove. To overcome this, proven clean-ing chemicals must be used. Minco’s next generation of cleaning fluids have been specially designed to break-down and eliminate all types of compressor fouling, whilst still com-plying with stringent OEM requirements. Even at low temperatures or with short contact times they will effectively restore any compressor to pristine condition. Our products have been designed to effectively lift dirt and then carry it clear of the compressor. They are free rinsing and will not leave any sticky residue when evaporated, making them ideal for both on-line and off-line washing. They also prove washing can be safe for the equipment, the operator and the environment. WASHING METHODS OFF – LINE (SOAK OR CRANK) WASHING Off-line washing is conducted with the gas turbine in a cooled state, by injecting a cleaning solution into the compressor while it is being turned at cranking speed Once the chemicals are injected into the compressor, the gas tur-bine is shut off and allowed to come to a halt. The chemicals are then left to soak for 20-30 minutes, before being rinsed with de-mineralised or deionised water. The main drawback is the amount of time the turbine must be tak-en out of operation to allow it to cool and be prepared for washing. The efficiency of crank washes however is very high, and the power recovery is close to the original level or the level reached after a major overhaul. ON – LINE (FIRED) WASHING This involves regularly spraying a cleaning solution into a compressor run-ning at full speed. High operating temperatures inside the compressor, the high centrifugal forces on the injected liquid and the short contact time of the wash solution with the fouling all limit the effectiveness of this method. The washing fluid will however reach the inlet guide vanes and first stage compressor blades which will result in some power recovery. This im-proves availability by slowing the rate of loss of output and prolonging the time between off-line washes. Using a suitable detergent will improve the wetting abilities of the wash solution, improving contact with the fouling so improving the cleaning effect, and also reducing the total amount of liquid required per wash. WHEN TO WASH? On-line washing needs to be performed regularly to decrease the fouling rate, but the timing of off-line washing is a more complex proposition and will depend on the following: • Amount and type of Contaminants in the Air Supply. • Acceptable Level of Power Degradation to the user. • Time Constraints owing to demand for availability. • The Level of Air Filtration employed. These variables all mean there can never be one universal cleaning procedure. The most beneficial regime of on-line and off-line washing is usually developed through experience, and needs to be customised for every compressor. Full power can be difficult to regain once significant fouling occurs so we recommend that the compressor is washed regularly to prevent the build-up of fouling deposits and maintain performance. TG Clean Group in collaboration with Minco is happy to work with operators to help them develop the best washing programme for their specific needs.