It takes the ideal combustion reaction to create enough heat to optimally power a gas turbine. Not only do they vary widely from one another—they don’t all use the same fuel to power the reaction—but their inlet air temperature and humidity fluctuate too.
To wrap your head around the factors that affect gas turbine efficiency, consider these elements in the equation.
Inlet Air Temperature
First, the incoming, or inlet, air temperature plays a significant role. As a rule, combustion requires a steady supply of oxygen to continue occurring. That’s why covering a candle extinguishes it. Not only does it require air, but the contents and condition of the air matter too.
One common strategy for manipulating air, inlet cooling, promotes turbine efficiency. Cooling air increases its density, which keeps air molecules together. Because colder air is more compact, it demands less from the compressor. Also, it eases the combustion reaction by ensuring a high ratio of oxygen molecules to facilitate an efficient reaction.
Another modifier of air density is humidity, which is a metric for how much water vapor is in the air. Though it seems counterintuitive given how people describe humid air as “heavy,” humidity actually is less dense than drier air. Thus, humid air decreases gas turbine performance. This is particularly relevant to coastal power plants.
Perhaps the central factor that affects gas turbine efficiency is the fuel involved. Some use natural gas, which has high average efficiency yields, whereas others employ liquid alternatives. Distillate fuel, while it represents a step down in efficiency, is ideal when natural gas is in short supply. The heaviest fuels force industrial plants to operate at lower combustion temperatures and necessitate frequent cleaning.
Exhaust losses from intermediary structures also hamper efficiency. Though silencers provide noise-abatement benefits that outweigh efficiency costs, they do slow the discharge of exhaust gas and, in the process, limit a turbine’s ability to funnel in new air in its place. Gas turbines can also experience losses on the inlet side as chillers and other obstacles impede incoming air flow.