Natural Gas Power Plants

General Structure of Natural Gas Combined Cycle Plants
► Combined cycle plants make use of both gas and steam turbines. Alongside with electricity generated by gas turbines that use natural gas as fuel, additional electricity is also generated by steam turbines using steam that is produced by transferring the waste heat of high-temperature exhaust gas of turbine exhaust to the boiler.
► In such plants, combined cycle efficiency can be achieved at around 50 to 60% to operate under the designed conditions by combining the benefits of high upper temperature of gas turbine cycles and low lower temperatures of steam turbine cycles.
Parts of A Natural Gas Combined Cycle Plant
► Heat Recovery Steam Generator (HRSG)
► Steam Turbine Generator (STG)
► Condenser
► Cooling Tower
► Gas Turbine
► Generator
1) Heat Recovery Steam Generator (HRSG)
The heat recovery steam generator has three pressure levels:
♦ HP: High pressure is about 45 bars (400 °C).
♦ IP: Intermediate pressure is about 12 bars (224 °C).
♦ LP: Low pressure is about 4 bars (120 °C).
♦ HP is used directly in the steam turbine. This turbine is supported by IP, when necessary.
♦ IP is also sold to neighboring factories.
♦ LP meets the need of the facility and also feeds the degasifier unit.
2) Steam Turbine Generator (STG)
♦ The role of the STG is to convert the energy of IP and HP steams that are coming from the HRSG into electricity by means of the generator that is connected to the same rotor. The control system employed in the plant has limited control over the STG.
♦ STG has a structure that widens moving from steam inlet to steam outlet and has 16 stages. Blades that are placed on the rotor and stator blades that are fixed on the outer body between the blades form the foundation of this system.
3) Condenser
♦ The steam that passes through all stages of the STG and whose properties change heavily is sent to the condenser that is connected to the STG. The condenser contains a bundle of pipes that circulate water at 24°C that is coming from the cooling tower. The steam passing through these pipes condenses and becomes ready for reuse.
♦ The water passing through the pipes in the condenser engages in heat exchange with the steam and gets quite hot. This water is sent to the cooling tower for cooling.
4) Cooling Tower
♦ The water is poured from the top, propellers at the top suck the air leading to a heat exchange between water and air. After this process, the cooled down water pours into the pool. And from here, it is pumped again into the condenser.