Abstract
The present paper describes the exergy analysis of a Central Receiver System (CRS) power plant. The plant consists of a thousand heliostats with an area of 130 m² each, an external receiver with an area of 59 m² and a height of 70 m, a steam generator, two steam turbines with a reheater in between, two feed water heaters and a condenser. EBSILON®Professional software was used to obtain the exergy efficiency and the irreversibility in each component of the power plant to pinpoint the causes and locations of the thermodynamic imperfection. The model analyzed and tested the effect of two design parameters including the Direct Normal Irradiation (DNI) and the outlet temperature of the Heat Transfer Fluid (HTF) on the exergy performance. The obtained results show at a constant DNI the maximum exergy loss occurs at the Receiver followed by the heliostat field and the power cycle has the lowest exergy loss. The increase of the DNI affects negatively the exergy efficiency of the overall system. The variation of the outlet temperature of the HTF has an impact of the exergy performance of the receiver subsystem as well as the overall system; the increase of the outlet temperature from 450˚C to 600˚C leads to an increase the exergy efficiency of the receiver to about 5% and an increase the exergy efficiency of the overall system to about 1%.
Highlights
Solar exergy is an important alternative exergy source used in many applications, especially in solar power systems which utilize the heat generated by collectors concentrating and absorbing the sun’s exergy to drive heat engines/generators and produce electric power [1]
A theoretical investigation based on the second law efficiency has been conducted for a Central Receiver System (CRS) power plant
The fractional loss at the receiver and the heliostat field increases with the increase the Direct Normal Irradiation (DNI) and as a result the exergy efficiency in both subsystems decreases
Summary
Solar exergy is an important alternative exergy source used in many applications, especially in solar power systems which utilize the heat generated by collectors concentrating and absorbing the sun’s exergy to drive heat engines/generators and produce electric power [1]. Most known types of the solar-thermal systems to produce electricity are trough/steam turbine, tower/steam turbine, and dish/heat engine systems. Out of all these technologies, tower/steam turbine looks like to be the best choice for high power production as it has the largest operating temperature range [2]. The power generation efficiency of the CRS systems are found to be low which directly increase the capital cost of the electricity generation. To investigate the cause of the low generation efficiency in the power generation system an exergy analysis is required. A theoretical investigation based on the second law efficiency has been conducted for a CRS power plant
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