It is very important to have Anti-Icing Systems for ground-based gas turbines located in humid climates (where air relative humidity can be more than 80% and dense fog can cause air temperatures to drop below 5 0C). Such climatic conditions lead to ice formation. This ice can plug the inlet filtration system causing a significant drop in pressure in the inlet system, which in turn leads to performance loss. In extreme cases, there is even a possibility that the ice pieces get ingested into the compressor (first blade stage) which may cause foreign object damage. Ice may also cause the disruption of compressor work because of excessive vibration, or surging by decreasing the inlet flow. The major factors that lead to the ice formation in gas turbines are ambient temperature, humidity and droplet size. So, under the climatic conditions which are prone to ice formation, an anti-icing system is employed which heats the inlet air before entering the compressor. Let us discuss some important aspects of Anti-Icing Systems.
The objective of an Anti-Icing System is to prevent or limit the ice formation in the gas turbine inlet path.
Gas Turbine Anti-Icing Systems (GT-AIS) can be categorized in two groups.
- Inlet heating systems
- Component heating systems
Inlet heating systems operate by transferring heat from a heat source (exhaust gases can be used) to the cold ambient air at the entrance of the gas turbine. If the temperature of inlet air raises sufficiently by this heat transfer, icing cannot form in the gas turbine intake.
AxCYCLE™ is a tool, which provides the flexibility and convenience to study various parameters and understand the performance of thermodynamic cycles.
This is especially important in the design of gas turbine plants equipped with anti-icing systems. Anti-icing systems can significantly affects the overall efficiency of the gas turbine. Therefore, it is important to:
- Choose the most optimal configuration of the scheme at the design stage; and
- Analyse the scheme parameters for GT off-design regimes with a functioning AIS.
With the help of AxCYCLE™, one can model different cycle schemes for GT-AIS by using different arrangements for heating by:
- Combustion products;
- Air taken after the compressor or from intermediate stages of the compressor;
- A mixture of air and flue gases;
- Air heated in the oil coolers, etc.
To conveniently simulate the gas turbine cycles with an Anti-Icing system, a specialized “ANTIICING” component is available in AxCYCLE™. This component simulates the mixing of ambient airflow with a hot flow of air or gases.
The main purpose of this simulation is to determine the heating air/gas flow rate to ensure:
- Required temperature of mixed flow at the outlet of Anti-Icing System.
- Required overheating of the mixture (ambient wet air and admixing flow of air or flue gases) above the dew point temperature at the outlet of the Anti-Icing System.
For example, Figure 1 below shows the scheme of heating, by air taken from an intermediate stage of the compressor and additionally heated by flue gases in a surface heat exchanger.
In the above scheme, heating air is not taken after the compressor but from an intermediate stage. This is because the Anti-Icing system does not need the heated air to be at high pressure therefore no additional energy is required. Thus taking air from the intermediate compressor stage helps to increase the overall efficiency of GT. Before entering the “ANTIICING” component, this air is additionally heated in a heat exchanger by the turbine exhaust gases.
In the component heating system, heat is applied to a certain area of the inlet to eliminate or prevent the formation of ice. This heat evaporates or prevents supercooled water droplets from freezing. Two different kinds of heat sources could be used in this system to warm up the icing surface: 1) Electro-thermal system and 2) Compressor bleed air. These two types of component heating systems are mostly used in aeroderivative Gas Turbine engines, a topic for a different article.
Calculation of GT-AIS operating modes determines the behaviour of the gas turbine and the control system, for different loads and for various weather conditions. Such off-design calculation can be performed in AxCYCLE™ as shown for the example in Figure 2 below. The variation in air temperature at the outlet of the AIS can be observed when different conditions (like ambient air humidity, ambient air temperature, generator power, presence or absence of fog) change.
With the help of AxCYCLE™, it is also possible to analyze (even in the automatic mode) various situations (i.e. a combination of different weather conditions and loads of the power plant) and understand whether in all situations the anti-icing system will operate adequately while ensuring a high overall efficiency of the cycle.
Interested in learning more about anti-icing systems and system modeling? Join us on on September 6th at 10:00AM EDT for a one-hour webinar discussing how to design the most optimal anti-icing system, while ensuring high gas turbine efficiency in all operating modes. Register here - http://www.softinway.com/en/education/webinars/anti-icing-system-modeling-and-simulation-for-gas-turbines/ or get in touch at Info@Softinway.com to schedule a demo!