Anti-icing modules in turbine inlets prevent ice formation on filter elements, the gas turbine inlet bell-mouth, and other gas path components.
The operation of combustion gas turbines in cold climates can present a unique problem: inlet icing. Icing can plug static inlet filtration systems, thereby causing the implosion doors to open and the gas turbine to ingest unfiltered air. Icing can also rapidly increase the pressure drop across trash screens and other inlet components, leading to performance loss and possible damage to ducting from negative differential pressure. In extreme cases, ice can build up on bellmouths, risking foreign object damage and compressor surge. Anti-icing systems are designed to inhibit ice formation on inlet components in order to protect the gas turbine from these hazards.
COMPRESSOR BLEED ANTI-ICING
A compressor bleed anti-icing system increases inlet temperature without affecting absolute humidity by using a portion of the compressor discharge air for this purpose. As a result of compressive forces, this air typically has a temperature of 500°F to 700°F, depending upon the ambient temperature and the gas turbine model.
Pneumafil offers two types of compressor bleed anti-icing systems: low pressure and high pressure.
The low pressure system utilizes one or more low pressure hot air supply duct(s) to which are bolted a series of discharge arms, approximately one meter on center, on opposite sides of the supply duct. Both the supply duct and the discharge arms are of constant (tapered) velocity design. Each discharge arm has a narrow slot running along its top and bottom edges through which the hot air is delivered, at a velocity of about 5,000 fpm, in the form of an unbroken upward and downward overlapping hot air curtain through which the cold, ambient combustion air must pass.
Advantages over conventional unsilenced piccolo high pressure systems:
- No stratification of hot and cold air streams
- Very low noise
- No measurable difference in operating pressure drop whether anti-icing is on or off
This system must, however, incorporate a valve or pressure-reducing orifice to lower the bleed air pressure. Since this process creates noise, we use a large high-temperature silencer to prevent noise bleeding into the low-pressure anti-icing device. Any piping leading to the valve or orifice must be acoustically insulated and the silencers are often located very close to the inlet filter house. The Pneumafil low-pressure anti-icing system is a proven component with wide operator acceptance and experience.
The high pressure system we offer consists of a series of small diameter vertical pipes, welded into a common hot air supply manifold pipe. The vertical pipes are equipped with multiple nozzles or small-diameter orifices, operating at sonic velocity, that deliver the hot gas. However, unlike a conventional piccolo-type system, each opening is equipped with a small silencer to lower the bleed air pressure, attenuate the noise and diffuse the gas. In order to accomplish an even flow of hot air out of each nozzle cluster or orifice, it is necessary to maintain a high pressure behind the nozzle clusters or orifices.
Unlike the low-pressure system, this arrangement is well suited to operate at a range of mass flow rates without causing unacceptable stratification of the hot and cold air streams. However, it must be sized and designed for the "worst-case" scenario in order to cover year-round anti-icing needs. Operational flow is continuously variable, and we have successfully used this system, located immediately upstream of the inlet air filter banks, in many installations. In addition, we have used the system to provide dedicated up-front heating for the gas turbine, in which application it is located in the air duct between the filter house and the inlet silencer.
All components are made from, as a minimum, 300 series stainless steel.