Power Plant Engineering

Fig. 9.20. Splash Plate Type Injector.
Fig. 9.21. Duplex Nozzle.
9.6.4.2 Injector
There are various types of injectors in current use. Fig. 9.20 shows a splash plate type injector. In
this case, the fuel at pressure about 40 bar is deflected into a cone by a splash plate, without spin. The
conical fuel film thins with increasing radius and surface tension breaks the film into droplets of about
50 to 100 µm diameter. The included cone angle of the spray is typically about 80° to 100°.
Fig. 9.21 shows a duplex nozzle with single feed. It successfully atomises the fuel varying over a
flow range of 50 to 1.
9.7 CONTROL OF GAS TURBINES
The purpose of gas turbine controls is to meet the specific control requirements of users and safe
operation of the turbine. There are basically two types of controls. They are as follows:
(A) Prime control and
(B) Protection control
9.7.1 PRIME CONTROL
The objective of the prime control is to ensure the proper application of the turbine power to the
load. The users of the gas turbines have specific control requirements according the use of gas turbines.
The requirements might be to control:

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GAS TURBINE POWER PLANT
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(1) The frequency of an a.c. generator,
(2) The speed of a boat or ship,
(3) The speed of an aircraft,
(4) The capacity or head of a pump or compressor,
(5) The road speed of a vehicle.
Power turbine speed
97% 100%
100%
0
Fuel
flow
Main fuel
control
Other inputs
Fuel
supply
Net
fuel
Fuel
valve
Lin
ka
ge
am
pli
fie
d
er
ro
r s
ign
al
Relay
Governor
H.P.
oil
Error signal
Speed sensor
Load
Exhaust
Intake
air
C
C C
Required
fuel
through
distributer
Ped
Fig. 9.22. Prime Control (Hydro-mechanical).
On a gas turbine a.c. generator set the prime objective of the control is to maintain the constant
electrical frequency irrespective of the load. This is achieved by selecting the primary controller as a
speed governor (a speed sensing device), which maintains the constant electrical loads. On a gas turbine
driven pipeline compressor, the prime objective of the control is to maintain a constant pipeline pressure
downstream of the driven compressor. In this case, the pipeline pressure is sensed and turbine power is
varied to maintain a constant pipeline pressure for varying flow conditions. There is relatively constant
relationship between turbine power and fuel flow, so in the prime control, the position of fuel valve is
controlled.
In Hydro-mechanical Speed Governing System (Prime Control), the governing loop is similar to
that discussed in the case of steam turbine. The system uses a centrifugal governor (mechanical) to sense
the speed of the turbine and the reference is set for rated speed of the turbine (Fig. 9.22). The governor
senses the speed through the accessory drive shaft and flyweights. Internally, the governor hydraulically
amplifies the error signal and provides an actuator output position that can be linked to a fuel valve. The
fuel valve either throttles or by passes the metered fuel from the main fuel control. The speed-sensing
device may be electrical or hydraulic.