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.
The purpose of this blog is to help operators make that decision by providing an overview of both methodologies.
Wet compression, or over fogging as it’s sometimes called, involves injecting demineralized water into the intake stream, where it evaporates, lowers the temperature of the air, and increases mass flow rate. This is in contrast to traditional fogging or evaporative cooling in that the amount of water injected is more than what can be evaporated before entering the low pressure compressor. Excess water is carried over into the compressor and evaporates as heat of compression is generated (similar to a SPRINT system).
Wet compression systems can be easily turned on and off, which allows for power output to be increased rapidly during times of peak demand. They also can be retrofitted to existing frames without the addition of support infrastructure such as generators and transformers. Doing so, however, may require adding protective measures to plant equipment to prevent damage from water, which increases cost.
Additionally, because spray systems have to be placed in close proximity to the inlet to allow droplets to enter the compressor, there is a higher risk of causing damage to equipment if a part breaks or becomes loose. Controlling the amount of water being injected is also critical to avoid the formation of large droplets, which can lead to casing distortion caused by uneven water distribution, damage to blades, and electrostatic charge build-up.
Wet compression can be utilized alongside other inlet cooling technologies in most environments; however, it is particularly well suited for applications in hot, dry climates where an adequate supply of water is readily available.
Turbine Inlet Air Chilling (TIAC)
TIAC uses refrigeration – either through mechanical or absorption chilling means – to supply chilled water (or brine) to a heat transfer device. The air entering the gas turbine filter house is cooled as it passes through the device and then flows into the gas turbine, thereby increasing mass flow rate and improving power plant efficiency.
One of the biggest advantages of TIAC is that it provides the operator with very precise control of the turbine’s inlet air temperature, so output is highly predictable. This makes it ideal for use in any environment (dry, humid, etc.); however, with superior flexibility, TIAC is especially advantageous in very volatile power markets, where prices can shift dramatically in short periods of tim
Unlike wet compression, TIAC is not limited by the availability of water because it can be done in a closed cycle that runs dry. In recent years, this has become particularly relevant due to growing concerns of excessive water usage in energy production operations. In very arid regions with high electricity demand, such as the Middle East or parts of California, the use of methods that require substantial volumes of water like wet compression or evaporative cooling may not be feasible.
One of the biggest deterrents that so often keep operators from using TIAC at power generation facilities is up-front cost. However, by having enhanced control over output and being able to maximize revenue during times of peak demand, any cost to implement the system is easily recouped and additional savings can be gained throughout the lifecycle of the facility.
So Which Option is Right For Your Application?
While TIAC continues to be one of the most economical ways to improve turbine efficiency and reliably increase output at natural gas power facilities, the decision of which cooling technology to implement largely depends on the individual needs of the operator.
In some applications, it may be advantageous to augment an existing wet compression system with TIAC in order to maximize power output and improve reliability. However, this will ultimately depend on the specific needs of the facility.
In the end, local climate, availability of water, market volatility, and CAPEX/OPEX limitations will all play an important role in choosing the right option – and as such, they should be carefully evaluated in order to ensure maximum value generation for the plant in the long-term.