Anti-icing or inlet heating are used either to reduce the risk of ice formation and turbine bellmouth or to avoid filter clogging from icing or snow formation.
Anti-icing mechanisms are generally used on gas turbine inlets when the air temperature is between -5 to 5°C and the relative humidity is above 70%. Icing on the filter is also influenced by the velocity of air.
Icing on the filters raises the pressure drop of the system, diminishing the power output and can lead to the turbine shutting down. As pressure drop increases, turbine efficiency and power output drops. A differential of 100 Pa (0.40’’ water) lowers power output by 0.2% and raise fuel consumption by 0.1%. Raising the inlet air temperature also diminished the risk of ice formation in the turbine bell mouth. Icing in the compressor could damages the turbine internals.
Pulse filter media velocities are usually lower than static filter media velocities and the pulsing mechanism helps dislodging the snow and ice. This can diminish the requirement for anti-icing protection on the filter, but won't help for the risk on the turbine bellmouth.
In order to offer a viable defence against static filter icing inlet, air must be heated by at least 7-8°C. There are usually various ways of achieving this depending on the situation: Anti-icing by mixing the ambient air with hot air
The hot air can be taken from:
• hot air from the gas generator compressor bleed, hot air from the GT enclosure cooling air exhaust, Anti-icing with electric resistance