Combustion Gas Turbines - The Variable-Angle Nozzles Load Turbine PDF Print E-mail
Written by Norrie   
Wednesday, 13 January 2010 10:12
Article Index
Combustion Gas Turbines
Principles and Operation
The Air Compressor
The Combustion Chamber
The Compressor (HP) Turbine
The Variable-Angle Nozzles Load Turbine
Turbine/Compressor Lube Control Oil System
Turbine Hydraulic Oil Trip System
Turbine Overspeed Trip Mechanisms
Turbine System Details
All Pages

4. THE VARIABLE-ANGLE NOZZLES & LOAD (L.P.) TURBINE

After driving the H.P. Turbine, the hot gases now pass to the separate, second stage, or L.P. Turbine. The gases are directed on to the rotor blades by twenty-four (24) ‘Variable Angle Nozzles‘. The L.P. Turbine is connected by the second shaft to the ‘LOAD’ - i.e. Gas compressor, Pump, Generator…Etc..
THE L.P. TURBINE IS ALSO CALLED THE 'LOAD TURBINE'.

As the load on the L.P. turbine changes, the speed will tend to change. The control system will adjust the Fuel Gas Control Valve which changes the fuel supply to the combustion chamber. The change in energy of the air will maintain the speed of the L.P. Turbine. However, the change in energy will also tend to change the speed of the H.P. Turbine. The H.P. speed control system will adjust the angle of the 2nd-Stage nozzle-vanes. (Figure. 20). The change in nozzle-vane angle increases or decreases the back-pressure on the H.P. Turbine and thereby controls the H.P. turbine speed. The speed control system links the H.P. turbine, the L.P. turbine, the Fuel Gas Regulator and the Nozzle Regulator into a complex control system which maintains the speed and stability of the machine and will be discussed shortly. The speed control system is operated hydraulically by the ' Turbine Control Oil ' which is produced by the Fuel Gas Regulator that takes a supply from the lube oil system and boosts the pressure to 300 psi; called Constant Control Oil (CCO). This is the control oil which produces two (2) variable oil supply pressures as below : -

1. From the Fuel Gas Regulator oil goes to the Fuel Gas Control Valve - This is called ' VCO ' - Variable Control Oil.

2. 300 psi CCO goes to the Nozzle Regulator, which produces another variable oil pressure that goes to the Nozzle Control Cylinder which hydraulically adjusts the Nozzle control ring and thereby the nozzle-vane angles. This is called ' NCO ' - Nozzle Control Oil.
The speed control system maintains the H.P turbine at about 6,900 R.P.M. and the L.P. turbine at about 5,900 R.P.M. The turbine Control Oil system is discussed in a later section.


Figure. 20
From the Load Turbine, the hot exhaust gases are vented to atmosphere (at about 900 °F). In some installations, this exhaust is put to further use for steam generation or other processes.
Figure. 21 - Shows the layout of the main parts of the turbine.




Last Updated on Wednesday, 24 February 2010 20:06