 |
A gas turbine is basically two sets of fan blades attached
to a single shaft. In between the two sets of blades, a fuel is burned.
The expanding gases that result from the combustion push on the blades,
causing them to spin. |
- The modern gas turbine consists of three sections:
- compressor,
- hot section (combustion), and
- power turbine (expansion).
There are two basic configurations for these sections:
- Two Shaft - the compressor and hot section can be on one
shaft, while the power turbine is on a second shaft, or
- Single Shaft - all three sections can be on one shaft.
Two Shaft
With the two shaft configuration, the compressor and
hot section spin at about 10,000 rpm, while the power turbine spins at about
3,600 rpm (60Hz). One of the most common examples of a two shaft turbine is
General Electric's LM2500.
Single Shaft
One shaft turbines operate at around 3,600-6,000 rpm.
A gear reducer is used between the gas turbine and the generator. A common
example of this type of turbine is the Rolls Royce RB211.
Simplified Schematic
Here is a simplified schematic representation of a single shaft gas turbine.
Compressor (Compression Stage)
Air enters from the left and is compressed by the first
set of blades (to about 25 times its original volume, in some of the newest
models). As it moves to the right, the air is forced through the ‘compression
stage’, into a smaller and smaller volume (darker and darker blue) by
the shape of the turbine (represented as a yellow cone).
Hot Section (Combustion Stage)
The fuel (typically it’s natural gas) is burned in the combustion chamber
at about 2,000°F, causing the expanding gases to push against the second
set of blades (in the ‘expansion' or 'power' stage).
Power Turbine (Expansion Stage)
Both sets of blades are connected by a single shaft, so the energy which compressed
the air at the beginning (at the ‘compression’ blades), was actually
created by the force on the back set of blades (the ‘power’ blades).
The shaft is also connected to a generator, which generates
the electricity when it spins. In modern gas turbines, the hot gases that
are exhausted from the power turbine leave at about 1,000°F.
Let's take a look at some typical uses for the gas turbine. |
