Civil Engineering Reference
In-Depth Information
Typical values for industrial applications with an electric power ranging
between 500 and 5,000 kW are: inlet pressure 4-10 MPa (580-1,450 psi),
outlet pressure 0.3-1 MPa (43.5-145 psi), ASR 10-15 kg of steam/kWh,
oil consumption in the boiler plant 0.7-1 kg of oil/kWh.
An example of a backpressure steam turbine cogeneration plant is given in
Sect.
9.7
.
9.4
The Gas Turbine
The gas turbine as prime mover associated with a heat recovery boiler or with direct
use of the exhausts in the process is another highly efficient topping cycle. It is
available for both mechanical and electric generator drives in a wide range of sizes
from a few hundreds to hundreds of thousands of kW. One can distinguish between
industrial turbines, in the range from 1 to 400 MW, and aero-derivative turbines in
the range from 2 to 40 MW. The revolution speed is generally 3,000-3,600 r/min
for power higher than 60 MW and 6,000-12,000 r/min for lower power.
Gas turbine power plants may operate on either an open or a closed cycle, generally
the Brayton cycle, as shown in Fig.
9.6
. In the open cycle, which is the commoner,
atmospheric air is continuously drawn into the compressor; then, air at high pressure
enters a combustion chamber where it is mixed with fuel and combustion occurs
resulting in combustion exhaust at high temperature. The combustion products expand
through the turbine and are discharged into the environment. Part of the mechanical
power (typically 60 %) is generally used to drive the compressor and the remainder to
generate electricity or to drive other loads.
Fig. 9.6
Simple gas turbine: (a) open to the atmosphere; (b) closed
