System Description
The exhaust gases from the Gas Turbine are used in a Heat Recovery Steam Generator (HRSG) to produce steam, which is then directed to the Steam Turbine.
After passing through the Steam Turbine, the condensation heat is dissipated in a Cooling Tower.
Several pieces of equipment are cooled through a closed cooling water circuit, which is itself cooled by the main cooling system through heat exchangers.
The Gas Turbine, Generator, and Steam Turbine are arranged on a single shaft line and connected through a synchronous self-shifting clutch (SSS clutch). The generator is located between the two turbines.
GAS TURBINE
The V94.3A Gas Turbine is a single-shaft, single-casing machine operating on natural gas as fuel.
The rotor is supported by two bearings:
The Gas Turbine shaft consists of:
The Hirth serrations maintain the alignment of the disc assembly and hollow shaft sections, allowing:
The annular combustion chamber is connected to the common outer casing of the Gas Turbine.
Gas Turbine provides a uniform exhaust gas temperature profile across the entire diffuser section. This is achieved through the 24 hybrid burners forming a continuous flame ring, thereby eliminating hot and cold spots.
The hybrid burners limit thermal NOx formation without the need for steam or water injection, based on a design and operational experience developed since 1986.
COMBUSTION SYSTEM ADVANTAGES
Low NOx and CO emissions
Low pressure loss
High operational flexibility
Symmetrical design using a reduced number of heat shield shapes
Optimum number and size of burners
Compact design with good accessibility
GENERATOR
The single-shaft mounted generator is a two-pole type, with direct radial hydrogen cooling of the rotor windings and indirect cooling of the stator windings.
The hydrogen-filled generator casing is a gas-tight and pressure-resistant construction, equipped with terminal shields at both ends.
The three-phase winding inserted into the stator core is of a two-layer transposed-bar design. The winding is vacuum impregnated together with the stator core.
The generator rotor shaft is vacuum-forged and fitted with two radial bearings located in the terminal shields.
Hydrogen circulates within the Generator in a closed circuit by means of axial fans located near the radial bearings.
The Generator gas system includes the equipment required for filling, purging, and operating the generator with air, purge gases, and hydrogen.
An excitation transformer is used to supply excitation current for the auxiliary power systems. A static frequency converter is used for starting the Gas Turbine / Generator train, supplying power to the Generator so that it can operate as a motor during start-up.
STEAM TURBINE
The Steam Turbines are modular in design, factory-assembled and transported in modules to enable more efficient installation. They consist of a High Pressure (HP) turbine (H-type) and a combined Intermediate/Low Pressure (IP/LP) turbine (E-type).
In each turbine, the shafts are designed with a single radial bearing arrangement. This means that the shaft has only one bearing located between the two Steam Turbine casings.
The shafts are rigidly coupled through integral flanges. Each Steam Turbine is equipped with a combined stop and control valve for high-, intermediate-, and low-pressure steam admission. These valves are fitted with electro-hydraulic actuators.
A common lubrication system is provided for the Gas Turbine, Steam Turbines, Generator, and Clutch. During normal operation, oil is supplied by an electric pump.
A synchronous clutch is located between the Generator and the High Pressure (HP) Steam Turbine and transmits the torque generated by the Steam Turbines to the Generator.
The clutch increases operational flexibility and allows faster start-up of the generating unit.
CONDENSER
The box-type condenser is located downstream of the Low Pressure (LP) Steam Turbine and forms an integral part of it.
The Steam Space and Condensate Hotwell are constructed of steel.
The condenser is supported by a foundation underneath. The Steam Space has a rectangular shape in order to ensure optimum utilization of the available steam volume.
Extraction of non-condensable gases is carried out by 2 × 100% liquid ring vacuum pumps.
HRSG
The Heat Recovery Steam Generator (HRSG) features a once-through design in the Intermediate and Low Pressure sections and a Benson-type design in the High Pressure section, generating steam at these three pressure levels.
An integrated condensate preheater improves combined cycle efficiency by using the energy from the exhaust gases to preheat the condensate before it passes through the feedwater pump and low-pressure circuit.
The boiler is designed for outdoor installation and does not include a bypass stack between the Gas Turbine and the boiler. The boiler is equipped with an exhaust duct connected to the stack.
INSTRUMENTATION AND CONTROL
To meet the technical, economic, and environmental requirements of modern power plants, the SPPA-T3000 Distributed Control System (DCS) is used for almost all equipment at the Pego Combined Cycle Power Plant.
It is based on open hardware and software technology standards, thereby benefiting from continuous innovations in microelectronics.
