Knowledge base
A gas turbine is a machine that moves air: its output depends on the mass of air the compressor can swallow, and hot air is thin air. On a 40 °C afternoon a heavy-duty turbine typically delivers 15 to 25 % less than its rating at the ISO condition of 15 °C, and its heat rate gets worse - exactly when the grid needs the power most. Inlet air cooling cools the air before the compressor and wins much of that output back. This guide explains the methods, the role of the finned inlet coil, and what such a coil must survive.
Why Temperature Costs Output
The compressor runs at a fixed speed and draws a fixed volume of air per second. When the air is hotter, that volume weighs less, the turbine burns less fuel at the same firing temperature, and the shaft power falls - roughly half to one percent for every kelvin above 15 °C, depending on the machine. The efficiency falls too, because the compressor spends more of the work on hot air. A turbine rated 100 MW at 15 °C may therefore deliver around 80 MW at 40 °C, and the 20 MW that are missing are the most valuable megawatts of the year.
Evaporative, Fogging Or Coils
Evaporative coolers and fogging systems spray water into the intake air; the water evaporates and cools the air towards its wet-bulb temperature. They are cheap and effective in dry climates, but they cannot cool below the wet-bulb temperature, they lose most of their effect in humid air, and they consume treated water. Mechanical inlet cooling uses finned coils in the air intake, fed with chilled water or a glycol mixture from a chiller or a thermal storage tank: the air can be cooled to 10 °C or less whatever the humidity, at the cost of a chiller plant and its power.
The same coils run in reverse in winter. In cold, humid air, ice can form in the inlet filters and on the first compressor stages; warm glycol in the inlet coil - often heated with recovered heat - lifts the air a few kelvin above freezing and keeps the turbine running. Many plants use one coil bank for both duties.
What An Inlet Coil Has To Withstand
An inlet coil sits in the full air stream of the turbine, so its air-side pressure drop costs output directly: every extra pascal at the inlet is lost power and efficiency, which is why inlet coils are designed for low face velocity and low pressure drop rather than for compactness. When the air is cooled below its dew point, water condenses on the fins; droplet eliminators downstream of the coil and drain pans under it keep that water out of the compressor. The coil must also not shed anything into the intake - fin material, corrosion products, coating flakes - so materials and coatings are chosen for the site's atmosphere and the cleaning regime.
TECS builds gas turbine inlet coils for cooling and anti-icing duty, with the coil geometry, materials, drain pans and eliminators designed for the turbine's airflow and the site. Send the turbine model, the inlet airflow, the design ambient and humidity and the chilled or heated fluid available, and the proposal shows the coil bank that fits.
In Short
- A gas turbine loses roughly 0.5-1 % output per kelvin above 15 °C
- Evaporative and fogging systems: cheap, limited by the wet-bulb temperature and humidity
- Chilled-water or glycol coils: cool below wet bulb, independent of humidity
- The same coils heat the intake air in winter against icing
- Low pressure drop, drain pans and droplet eliminators are part of the design
- TECS builds inlet coils for cooling and anti-icing duty
What To Send With An Enquiry
- Gas turbine model and the inlet airflow
- Design ambient temperature and humidity, summer and winter
- Target inlet air temperature and the allowed pressure drop
- Cooling and heating fluid: chilled water, glycol, temperatures and flow
- Inlet house dimensions and the space for the coil bank
- Site atmosphere and the corrosion class
Questions We Are Often Asked
How much output does inlet cooling recover?
It depends on the turbine and the climate; cooling from 40 °C to 15 °C can recover most of the 15-25 % a heavy-duty turbine loses on a hot day. The turbine maker's performance curves give the figure for a specific machine.
Is evaporative cooling enough?
In a dry climate it gives a good gain cheaply. In humid air it can only reach the wet-bulb temperature and the gain shrinks; mechanical coils are chosen where the air is humid or the target temperature is low.
Does the inlet coil reduce output?
Its pressure drop does, a little, all year round. That is why inlet coils are designed for a low pressure drop and why the net gain is calculated with the coil's resistance included.
Can the same coil prevent icing?
Yes. In winter warm glycol runs through the coil and lifts the inlet air above freezing; many plants use one coil bank for summer cooling and winter heating.
What happens to the condensate?
It is collected in drain pans under the coil and droplet eliminators downstream stop carry-over into the compressor. Both are part of the coil bank design.
Contact Us
Send us the heat duty, the fluid temperatures and flow rates, the ambient conditions and the installation limits. We answer with a design proposal - or write to us on WhatsApp.
