In recent years, turbine inlet air chilling (TIAC) has become a highly reliable method of enhancing power plant performance by increasing the output and efficiency of combustion turbines during periods of high ambient temperature. This is typically achieved either through mechanical or absorption chilling and involves supplying chilled water (or an alternative fluid) to the heat exchanger in the filter house of the combustion turbine, thereby cooling the inlet air which raises its density and increases mass flow rate through the compressor.
Not Just More Megawatts, Better Megawatts: The Case for Combined Cycle Output Augmentation in a Low Power Price Environment
Currently, the fragmented U.S. wholesale power markets do not face a scarcity of megawatts, as evidenced by the North American Electric Reliability Corporation’s (NERC) recent Summer Reliability Assessment and reported by Public Power Daily here.
However, this does not suggest turbine inlet air chilling (TIAC) is not a valuable resource for U.S. power generators. TIAC quickly elevates a combined cycle unit’s productive capacity during challenging ambient conditions. The benefits of the additional megawatts produced from low-heat rate/low-cost generation resources may be evaluated on a relative (better) or absolute (more) basis.
Ambient conditions have a significant impact on the operation of natural gas power plants. This is largely due to the fact that as temperature and humidity rise, air becomes less dense and mass flow rate through combustion turbines decreases.
Inlet cooling has become a popular method for boosting power output by lowering the temperature of air before it enters the turbine’s compressor. Plant operators today have the option of using any number of cooling/chilling techniques for reducing air inlet temperature – two of the most common of which are turbine inlet air chilling (TIAC) and wet compression.
Both TIAC and wet compression offer distinct advantages that make them more or less suitable for use depending on the specific needs of the facility. Understanding what those advantages are is essential to making the right decision when choosing which method to employ, thus ensuring optimal use of capital budgets.
While both Supplementary or Duct Firing and Turbine Inlet Air Chilling (TIAC) are solutions to offset the megawatt output degradation of gas turbines when ambient temperatures rise, the two technologies take very different approaches. With TIAC, the combustion gas turbine inlet air is chilled. In the case of duct firing, injection of fuel is utilized to increase the temperature and mass flow rate of the exhaust gases.
Rather than competing, the two technologies – duct firing and turbine inlet cooling – can actually complement each other when used correctly.
For maximum power output, power plant owners can utilizing the reliable power augmentation provided by TIAC, and balance the requirements with duct firing. This scenario allows them to produce the required power at the lowest possible heat rate.