Turbocharger Deposits and Cleaning
The deposits found on turbochargers are:
- Compressor: Oil mist, dust, soot, etc. which are all derived from the atmosphere.
- Turbine: Fuel derived ashes such as sodium/vanadium compounds, metallic ashes such as iron and nickel. If the fuel has a high level of contaminants such as sodium, iron, calcium, magnesium, etc., there may be excessive ash deposits.
Cleaning of Compressor
A small fixed container is provided which is filled with water to clean the compressor. The water is injected using the air from the turbocharger, so the higher the compressor speed, better the cleaning. Cleaning is carried out at full load and performed once per day. Solvents should not be used. The procedure is as follows.
- Open the filler on the tank and fill with freshwater only. Secure filler cap and close vent.
- Open the air supply valve 'A'.
- Open injection valve 'B' and wait for 30 seconds.
- Close valves 'A' and 'B' and open the vent.
- Check to ensure the tank is empty. If not, there may be a blockage, usually at the bottom of the tank, due to rust and scale, or at the injection nozzle.
The engine speed must be reduced to reduce the exhaust temperature and prevent thermal shock of the turbine. Once the exhaust temperature is at or below the manufacturer's limit, the turbocharger drain can be opened and freshwater admitted to the turbine casing. Water should be admitted slowly until water appears at the drain, then the water flow can be increased, then the drain closed. This operation is usually carried out on a weekly basis.
The turbocharger speed does not have to be reduced when dry cleaning. A container is filled with correct amount of cleaning material, either ground nutshells, activated carbon or small grains of rice. The valve from the container should be opened to blow the material into the turbine casing. After a couple of minutes the valve can be closed. This should be carried out every day or at least once in two days.
As with compressor cleaning, no solvents should be used for cleaning turbine, and if the turbocharger has not been cleaned for a long time it should not be cleaned in service. Deposits may not be evenly removed causing a risk of unbalance. The turbocharger must be opened up and cleaned by hand.
Types of deposits formed in turbocharger, procedure for washing both compressor side and turbine side are discussed.
"Operation and Maintenance of Machinery in Motorships" by N.E Chell
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