Gas Turbine Anti-Icing Systems

Gas turbines ingest the same volume of air for a given rotational speed.  In very low ambient air temperatures water droplets can freeze and cause blinding of the inlet system.  Therefore, the gas turbine is very susceptible to icing.   Ice build up in a gas turbine inlet can have catastrophic results.  Ice particles with sufficient size and mass can severely damage the rotating components.

In addition, ice or snow build up on a filter face will quickly and dramatically increase the operational resistance of the inlet system.  This will, at a minimum, increase the fuel consumption, decrease the thermal efficiency, and result in a power reduction.   The gas turbine can and will trip out of service unless something is done to reverse the ice build up.

Freezing of airborne water droplets on objects colder than 32°F is a very difficult type of icing to prevent.  The ice formed by this process may be classified as clear, rime, or hoar frost.  Clear ice occurs when water droplets have sufficient time to spread into a film before freezing.  This type of ice usually occurs at temperatures near 32°F, but can form at lower temperatures depending on droplet velocity and the frequency of droplet impaction.  When droplets freeze before they completely lose their shape, an amorphous frost or rime ice forms.  If each droplet freezes immediately on contact with a surface, a true crystalline ice or hoar frost forms.

All three types of ice may result from either condensation or precipitation.  Icing caused by water droplets, which exist in the airstream of a gas turbine inlet, is known as precipitation icing.  The usual source of these droplets is fog or rain.  Icing caused by water droplets, which condense from the vapor phase because of the presence of the inlet, will be called condensate icing.  The condensation can be caused by a temperature decrease which typically occurs when the air is accelerated to a higher velocity or merely by turbulence in the case of a super saturated air water vapor. There are many types of Anti-Ice Systems available. They each cause a parasitic load on the gas turbine by taking energy generated by the machine and by introducing a heat source to the inlet.  Basically, the heat can originate from the high pressure compressor or from the gas turbine exhaust.  It can then be either directly injected into the inlet airstream or passed through a heat exchanger. The chart shows some of these alternatives.

Anti-Ice Systems can only prevent ice build up during gas turbine operation. They are normally designed to raise the air inlet temperature by  9° F and prevent condensate ice from forming.  They are not to be confused with De-Ice Systems. De-Ice Systems are designed to remove formed ice and snow from an inlet while the machine is off line.  An external power source is required which is not normally available on turbomachinery.