Abstract
sCO2 power cycle is the most investigated and most promising technology for replacing conventional steam cycle in CSP plants. Nevertheless, the efficiency of sCO2 power cycle is strongly penalized by high ambient temperatures which are typical of favourable CSP locations. This paper focuses on a new working fluid for power cycles which consists of CO2 blended with C6F6. The addition of C6F6 increases the fluid critical temperature allowing for a condensing cycle for ambient temperatures up to 45 °C. The calculated gross mechanical efficiency of the innovative cycle is around 42% when adopting a typical Peng Robinson equation of state with van der Waals mixing rules for a maximum operating temperature of 550 °C and a minimum cycle temperature of 51 °C. This performance varies just of ±0.1% if the prediction of the binary interaction parameter of the Peng Robinson is over- or under-estimated by 50%, but more significantly if other equations of states are adopted (up to 1% points). Moreover, a detailed analysis on the operating conditions of the cycle components highlighted that components design is affected by the adopted EoS. A sensitivity analysis is then performed to identify where the largest differences in predicting the efficiency of the cycle occur.
Highlights
Power generation from high temperature concentrating solar power (CSP) plants is a promising technology [1], it is still characterized by significant capital cost and a resulting Levelized Cost of Electricity (LCOE) higher than competitive renewable and fossil fuel technologies [2]
Performance and costs of steam cycle are negatively affected by the limited power output of solar plants and limited maximum temperatures (550 C) as well as the high ambient temperatures of optimal CSP location
This paper discusses the performance of an innovative working fluid for the exploitation CSP plants: the innovative fluid consists of CO2 blended with C6F6
Summary
Power generation from high temperature concentrating solar power (CSP) plants is a promising technology [1], it is still characterized by significant capital cost and a resulting Levelized Cost of Electricity (LCOE) higher than competitive renewable and fossil fuel technologies [2]. Previous works on CO2 mixtures for power cycle identified some potential candidates as organic compounds, noble gases or inorganic compounds, depending on different heat source applications If organic compounds, such as hydrocarbons or refrigerants, are selected as blending components, the limiting factor becomes the thermal stability of the compounds themselves. Inorganic compound such as TiCl4 or N2O4 are suitable for blending the CO2 when high temperature heat sources (above 550 C) are available leading to thermodynamic efficiencies of the resulting transcritical cycles in the range of 49% with a maximum temperature equal to 700 C This efficiency is higher than the corresponding one calculated for pure CO2 cycles [4,25,26]. PCeSAFT can describe phase equilibria for a large variety of including binary CO2 mixtures, using a single system dependent interaction parameter [47,48]
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