Page 156 - Boiler_Operators_Handbook,_Second_Edition

Special Systems 141

turning, however, lubrication has to be established and
proven.
Maintenance of lubricating oil temperatures dur-
ing a GTs operation is very important because the oil
can be too cool as well as too hot. Other temperatures
that should be monitored closely are compressor exhaust
temperature, burner exhaust temperature, and turbine
exhaust temperature. The first two must be within limits
for continued operation and the last as low as possible for
maximum turbine efficiency.
During operation the pressures, temperatures,
and gas velocities through the GT vary as indicated in
Figure 4-11. Atmospheric air accelerates toward the inlet
of the compressor (1-2) accompanied by a drop in static
pressure created as some of the static pressure of the
Figure 4-10. Gas turbine oil nozzle air is converted to velocity pressure. In the compressor
(2-3) the pressure is increased and velocity decreases as
minimum they must be brought up to a speed that pro- the air is compressed because compression reduces the
duces enough compression of the air to produce a dif- volume of the air. Temperature of the air rises from the
ferential pressure across the turbine that, when combined work of compression just as it does in diesel engines.
with burning of the fuel can generate enough power at Between the compressor and the burner (3-4) some
the turbine shaft to power the compressor and the rotat- pressure is lost as the air is directed through different
ing resistance of anything attached to the shaft of the gas passages with provisions to increase turbulence for
turbine. This is normally done with an electric motor; or, mixing with the fuel. Velocity there can decrease when
the electric generator attached to a gas turbine can func- some of the compressed air is extracted to feed through
tion like a motor to get it started. Before everything starts the turbine blades for cooling them. Inside the burner

Figure 4-11. Gas turbine PTV curves