Steam Thermal Power Plants: Efficiency and Key Technologies
Steam Thermal Power Plants and Efficiency
Steam thermal power plants are one of the pillars of global electricity production and operate using the Clausius–Rankine cycle. In these facilities, the working fluid is water, which changes its physical state throughout the cycle. The process begins in the boiler, where liquid water is progressively heated until it reaches the saturation temperature, at which point evaporation begins. After this stage, the resulting steam continues to be heated and becomes superheated, reaching high pressures and temperatures. This superheated steam enters the steam turbine, where it expands and produces mechanical work that is converted into electricity by the generator. After passing through the turbine, the steam—now at lower pressure and temperature—enters the condenser, where it is cooled and turned back into water. From there, a feedwater pump pushes it back toward the boiler, thus closing the cycle.
Real-World Losses and Efficiency Factors
The real operation differs from the ideal one due to numerous losses that reduce efficiency. There are expansion losses in the turbine due to irreversibilities; pump losses; pressure losses in pipes, in the boiler, and in the condenser; as well as thermal losses to the environment. To improve efficiency, technologies such as multi-stage steam reheating are introduced, allowing the turbine to operate at higher temperatures without the steam reaching excessive moisture levels. Another fundamental technique is regeneration, which consists of extracting part of the steam from the turbine to preheat the feedwater before entering the boiler. This increases the average temperature at which heat is supplied and therefore improves cycle efficiency. The temperature of the condenser cooling water also plays a decisive role: it is lower when seawater is used, enabling higher efficiencies.
Modern Design Limits and Environmental Systems
Thanks to the development of advanced materials and new boiler and turbine design technologies, modern plants can operate at pressures up to 27–29 MPa and temperatures of 600 °C, achieving efficiencies of 44–47% when using hard coal. In the case of lignite, efficiencies typically range between 41% and 43%. The theoretical efficiency limit of a modern steam plant is estimated at around 50%.
Despite these advances, installing environmental protection systems such as electrostatic precipitators or desulfurization units introduces additional losses that slightly reduce efficiency, although they significantly improve air quality by limiting pollutant emissions.
Water Use and Environmental Impact
The steam cycle is a closed system that requires a large quantity of water for the cooling process. For this reason, many plants are built near rivers or coasts. To avoid excessive water use and reduce thermal impact on the environment, many facilities use cooling towers that allow part of the water to be recycled.
Finally, it is important to highlight that plant efficiency directly affects environmental impact: the higher the efficiency, the lower the fuel consumption and the lower the emissions of carbon dioxide and other pollutants. For this reason, modernization of components and improvement of conversion processes remain key priorities in steam thermal power plant engineering.