Chapter 27
Combined Cycle Power Plant


Thermal Power Plants are power plants operating on carbon-based fuel such as coal, natural gas, and petroleum products. There are five major types of thermal power plants in use on the power grid today:

Steam Turbine Power Plants produce electric power by creating steam at high pressure and temperature (superheated steam at 2000 psia/138 bars and 1500°F/815°C) in boilers, which is then expanded through a steam turbine causing the turbine to drive a generator, which then produces electric power. The steam leaving the turbine is usually sent to a condenser, which maintains a vacuum and where the steam is condensed back to a liquid condensate (water). The steam turbine follows the Rankine Cycle. Steam turbine power plants can produce up to 2000 MW of power and are most widely used plant types in the world. These plants have a thermal efficiency between 28% and 35%.

Simple Cycle Gas Turbine Power Plants are plants that follow the Brayton Cycle; in gas turbines, the air is compressed in the compressor section of the turbine to a high pressure (580 psia/40 bars) and temperature (1300°F/704°C), and in the combustor the air is further heated to a higher temperature (2600°F/1426°C) at constant pressure. The gas leaving the combustor is at a high pressure and high temperature and is then expanded through the turbine section. The gases leaving the turbine are at a pressure of about (15.0 psia/1.03 bars) and a temperature of about (1200°F/649°C). The turbine drives the gas turbine's compressor and the generator, which produces electric power. These gas turbines can produce up to 300 MW of power. The gas turbine power plant can be installed in 12–18 months, and thus have been used widely in developing nations where energy requirements change rapidly. These plants have a thermal efficiency between 25% and 45% depending on the size of the plant.

  • 27.1 Introduction
  • 27.2 Typical Cycles
  • 27.3 Gas Turbine
  • 27.4 Gas Turbine HRSG Systems
  • 27.5 Steam Turbine
  • 27.6 Combined Cycle Plants
  • 27.7 Availability and Reliability
  • 27.8 References

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