Components and Configuration of Combined Cycle Power Plants
– Gas turbines for primary power generation
– Heat recovery steam generators (HRSG) to capture waste heat
– Steam turbines for additional power generation
– Condensers to convert steam back into water
– Cooling systems to maintain optimal temperature
– Combined-cycle systems can have single-shaft or multi-shaft configurations
– Unfired heat recovery steam generator (HRSG) with modular components is most fuel-efficient
– Supplementary-fired and multishaft systems chosen for specific fuels or applications
– Single-shaft system has one gas turbine, one steam turbine, one generator, and one HRSG
– Multi-shaft system has one steam system for up to three gas turbines
Advantages and Applications of Combined Cycle Power Plants
Advantages:
– Higher efficiency compared to traditional power plants
– Reduced greenhouse gas emissions
– Flexibility to use different fuel sources
– Ability to provide both electricity and heat
– Cost-effective operation and maintenance
Applications:
– Large-scale power generation for cities and industries
– Cogeneration for combined heat and power (CHP) systems
– Integration with renewable energy sources like solar or wind
– Backup power generation for emergencies or grid stability
– Distributed generation for remote areas or islands
Challenges and Limitations of Combined Cycle Power Plants
– High initial capital investment
– Dependence on natural gas availability and prices
– Limited efficiency during start-up and shutdown processes
– Environmental concerns related to gas emissions and water usage
– Technological constraints for bottoming cycles and small temperature differences
Fuel and Efficiency in Combined Cycle Power Plants
– Natural gas is the most common fuel used
– Supplementary fuel can be natural gas, fuel oil, coal, or biofuels
– Integrated solar combined cycle power stations combine solar energy with another fuel
– Next-generation nuclear power plants can utilize higher temperatures for better efficiency
– Small-scale combined cycle plants in remote areas can use renewable fuels
– Combining gas and steam cycles achieves high input temperatures and low output temperatures
– The electric efficiency of a combined cycle power station can be over 60%
– Combined cycle units may deliver low-temperature heat energy for industrial processes
– Most combined cycle units have peak efficiencies of 55 to 59%
– Efficiency of the turbine is increased by running hotter combustion
– Cooling and materials research are ongoing to improve turbine blade durability
– Pre-cooling combustion air increases turbine expansion ratio and power output
– Combustion technology research focuses on complete fuel burn up and pollution reduction
– Improving thermal conductivity and using corrosion-resistant materials can enhance steam generator efficiency
Notable Combined Cycle Power Plants and Other Technologies
– Archimede combined cycle power plant in Italy (2010)
– Martin Next Generation Solar Energy Center in Florida
– Kuraymat ISCC Power Plant in Egypt
– Yazd power plant in Iran
– Hassi Rmel in Algeria and Ain Beni Mathar in Morocco
– Integrated gasification combined cycle (IGCC) uses synthesis gas (syngas) produced from sources like coal and biomass
– IGCC can raise electricity generation efficiency to around 50%
– Integrated solar combined cycle (ISCC) integrates a solar thermal field within a combined cycle plant
– ISCC plants increase generation capacity or reduce fossil fuel use
– Daily steam turbine startup losses are eliminated in ISCC plants
– Load output of a combined cycle power plant is limited by pressure and temperature transients and steam chemistry conditions
– Active competition exists to achieve higher efficiencies in combined cycle power plants
– Efficiencies of nearly 60% have been reached in some power plants
– Siemens achieved 60.75% efficiency with a gas turbine
– The Chubu Electrics Nishi-ku power plant is expected to have 62% efficiency
– The Électricité de France plant in Bouchain holds the Guinness World Record for the most efficient combined cycle power plant at 62.22% Source: https://en.wikipedia.org/wiki/Combined_cycle_power_plant
A combined cycle power plant is an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy. On land, when used to make electricity the most common type is called a combined cycle gas turbine (CCGT) plant. The same principle is also used for marine propulsion, where it is called a combined gas and steam (COGAS) plant. Combining two or more thermodynamic cycles improves overall efficiency, which reduces fuel costs.
The principle is that after completing its cycle in the first engine, the working fluid (the exhaust) is still hot enough that a second subsequent heat engine can extract energy from the heat in the exhaust. Usually the heat passes through a heat exchanger so that the two engines can use different working fluids.
By generating power from multiple streams of work, the overall efficiency can be increased by 50–60%. That is, from an overall efficiency of the system of say 34% for a simple cycle, to as much as 64% net for the turbine alone in specified conditions for a combined cycle. This is more than 84% of the theoretical efficiency of a Carnot cycle. Heat engines can only use part of the energy from their fuel, the remaining heat (i.e., hot exhaust gas) from combustion is wasted.
