Power Plant Engineering

286 POWER PLANT ENGINEERING

The high-pressure system consists of main fuel pump, relief valve, strainer, fuel control, shut-off
valve, flow distributor and nozzles. The main fuel pump generates the oil pressure sufficient to be
injected in the combustion chamber. The relief valve installed around the main fuel pump is to protect
the fuel system from excessively high pressure created by the shut-off valve or clogging of the passage
in the fuel system by transferring the excess fuel to the pump inlet. The function of shut-off valve is very
simply to interrupt the supply of the fuel to the combustion chamber and affect a shut down of the
turbine automatically or manually. It is also used for interrupting the flow of other fluids such as the gas
supply pressure to the pneumatic starter, the flow to the pneumatically driven pumps and the supply to
auxiliary fuel lines such as the starting fuel injector. Generally, the shut-off valve is of solenoid type. The
gas turbine requires that the fuel should be well distributed in the various fuel injectors. Flow divider
accomplishes the work. 1t is a pressure sensitive valve which positions the valve opening determined by
the pressure at inlet to the flow divider.

Fuel

Air

Air

Fuel spray

Splash

plate and

heat shield

Air

Main fuel

Primary

Fuel

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: