A steam power plant is an open system (control volume) because it features a continuous mass transfer across its boundaries in the form of fuel and air intake, as well as exhaust gases and steam output.
The system’s boundary is represented by the outer rectangle, enclosing all the major components of the steam power plant. The significance of this boundary to the plant is that it defines the system under consideration and established the energy and mass interactions (Wu, Shen & Lee, 2015). The system’s boundary for this case encloses all the major components that include the combustion chamber, steam generator, turbine, condenser, and associated piping as well as auxiliary systems. Several energy transfer mechanisms take place within this boundary, including heat transfer from fuel combustion, work transfer from turbine, and mass transfer of fuel, air, steam, and exhaust gases.
The system comprises of various energy transfer mechanisms such as heat transfer, work transfer, and mass transfer. In regards to heat transfer, there is combustion of fuel in the combustion chamber that releases heat energy (Khaleel, et al., 2022). This heat energy is then transferred to the steam generator, and heats water to steam. This heat is also transferred from the steam to the turbine, causing it to rotate and generate mechanical work. The system transfers waste heat from the condenser to the surrounding environment.
In terms of work transfer, the turbine rotates the generator to convert the kinetic energy from the steam into mechanical work. This results in generation of electric power as output. Energy transfer in the form of work transfer occurs as a result of continuous supply of fuel and air to the combustion chamber (Wu, Shen & Lee, 2015). The steam generator generates steam, which flows through the turbine. Mass transfer also occurs when the system expels exhaust gasses and condensed stem from the plant.
The equation for the steady-flow energy for the stem power plant is as follows:
Where;
is the net heat transfer into the control volume (kJ)
is the net work transfer out of the control volume (kJ)
is the mass flow rate of the exhaust streams (kg/s)
is the mass flow rate of the inlet streams (kg/s)
h is the specific enthalpy of the stream (kJ/kg)
V is the velocity of the stream (m/s)
This equation indicates that heat transfer into the control volume is the difference between the enthalpy flow rates of the exhaust and inlet systems.
References
Wu, X., Shen, J., Li, Y., & Lee, K. Y. (2015). Steam power plant configuration, design, and control. Wiley Interdisciplinary Reviews: Energy and Environment, 4(6), 537-563.
Khaleel, O. J., Ismail, F. B., Ibrahim, T. K., & bin Abu Hassan, S. H. (2022). Energy and exergy analysis of the steam power plants: A comprehensive review on the Classification, Development, Improvements, and configurations. Ain Shams Engineering Journal, 13(3), 101640.
Zabihian, F., & Fung, A. S. (2010). Advanced Power Generation Technologies: Fuel Cells. In Paths to Sustainable Energy. IntechOpen.
