Turbine technology|Maintenance Antifoam injection
Foam–steam manifold
Boiler
Tote tank trial foam rinsing stage
injection Foaming skid Tote tank neutralisation/passivation Air
Waste drains
injection Foam
observed after foam cleaning. This includes the most critical areas of the turbines, like rotor steeples and blade dove tails. Some of these steam turbines have been cleaned several times during their lifetime for the purpose of deposit removal. The technology originally was developed for removal of deposits from steam turbine blades. In the beginning the focus was on copper and on deposits of iron and its oxides. In later years, foam cleaning has been applied to removal of deposits of other compositions. Foam cleaning has also been successfully applied to gas turbines.[7]
The usual method Antifoam Tote tank trial foam rinsing stage antifoam skid Waste-
Chemical tank
Picture 4. Schematic of a foam cleaning system for a gas turbine (image courtesy Ecol [8]
)
some 180 μS/cm (DC). The degas conductivity (Degas turbine cond, blue line) remained more or less stable all the time around 2 μS/cm. Based on these results, it was clear that at least a second wash sequence needed to be executed to reach low concentrations of sodium and low conductivity levels that allow restart of the turbine. Before the second cleaning cycle could be started, the turbine and the boiler needed to cool down again to be able to provide wet steam of sufficient amount and for a sufficient time span.
During the second wash cycle, the conductivities dropped to 8 μS/cm for the direct conductivity, 1.6 μS/cm for the acid conductivity, less than 1.0 μS/cm for the degassed conductivity, and sodium concentration was less than 0.4 mg/l (see picture 3).
The analytical results for conductivity and the sodium concentration in the wet steam condensate were good enough to allow restart of the turbine. The restart of the turbine can be regarded as a third or final washing cycle. After an extended bypass operation, the turbine
went back to service. The overall efficiency had increased from 78% to 87% for the turbine.
Foam cleaning
Removing deposits with the help of active foam is a very elegant method for removal of deposits without having to uncover the machine. The time required for such cleaning, during which the turbine is not available, is about one week including cool-down time. The foam cleaning itself normally needs less than one day. Foam cleaning has proven to be more effective than saturated steam washing and online or offline compressor washing, and is also suitable for removing stubborn deposits that are insoluble in water and steam, as the mixture of the cleaning foam can be adapted to the expected deposit composition. Oil spills in the turbine can also be removed with foam. The method has been used in the United States on steam turbines for more than 40 years and has proven itself several hundred times over without any impairment of turbine operation or corrosive attack on turbine components being
Waste tank
for removing fouling layers on GT compressor blades is online and offline washing. Offline cleaning is done with turning gear in operation and the cleaning mixture is sprayed into the compressor. With this method, the front rows of the compressor can be cleaned very well, but the high-pressure stages of the compressor are only partly cleaned or even not at all. With online washing, the cleaning agent is sprayed into the running machine. This has an additional effect similar to water jet cleaning. However online washing carries the risk that dirt loosened in the low-pressure section of the compressor is transferred to the high-pressure section of the compressor and cakes there due to the high temperatures that occur when the combustion air is compressed.
There is also a risk that some of the loosened dirt will become caked in the burner cans and the turbine section or in the cooling channels of the turbine blades. Clogged cooling channels lead to reduced cooling air flow, overheating of the blades and ultimately to irreparable blade damage.
The foam acts as a gas and liquid, it fills the entire area to be cleaned and is great for cleaning systems not designed to hold the weight of a liquid. The foam enters the smallest spaces for total cleaning and due to its razor-soap-like texture it can carry particles in suspension. A big advantage compared to wet steam washing and water washing is that even though the cleaning volume is large, the generated volume of liquid waste to be disposed of is small.
Depending on conditions and the nature of deposits, the foam composition can be
5a
Foam is injected at the turbine or interior of the machine
Turning gear operation transports the foam through the entire machine
)
5b
Defoaming agent destroys the foam so that only a small amount of liquid waste must be collected at the end
Pictures 5a, 5b and 5c. Foam injection at bellmouth (5a), transportation of the foam through the turbine by turning gear (5b), destruction of the foam with antifoam (5c), (pictures courtesy Ecol[8]
26 | July/August 2025|
www.modernpowersystems.com
5c
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