Abstract
To overcome the degradation of the cycle efficiency of a supercritical carbon dioxide (S-CO2) Brayton cycle with dry cooling, this study proposes an improved design of an S-CO2 centrifugal compressor. The conventional air centrifugal compressor can achieve higher efficiency as backsweep angle increases. However, the structural issue restricts the maximum allowable angle (−50~−56°). In this study, an S-CO2 centrifugal compressor performance was examined while changing the backward sweep angle at impeller exit to study if the previous optimum backsweep angle for an air centrifugal compressor is still valid when the fluid has changed. It is shown through an analysis that an S-CO2 centrifugal compressor can achieve the highest efficiency at −70° backsweep angle, which is greater than the typical design value. The S-CO2 centrifugal compressor is less restricted from a structural integrity issue because it has low relative Mach number regardless of the low sound speed near critical point (Tc = 304.11 K, Pc = 7377 kPa). It is also shown in the paper that the variation of compressibility factor does not impact on its total to total efficiency since its Mach number is still lower than unity. Finally, it is also shown that a backward sweep impeller can achieve higher pressure ratio and operate stably in wider range as the mass flow rate is decreased. As further works, the suggested concept will be validated by the structural analysis and the compressor performance test.
Highlights
A supercritical CO2 (S-CO2 ) Brayton cycle is a promising power technology for the generation heat to power conversion systems due to its high cycle efficiency at moderate turbine inlet temperature (550~750 ◦ C), compact cycle configuration, and alleviation of turbine blade erosion in comparison with the steam Rankine cycle [1]
The characteristics of a dry cooling system relate to disadvantage of a higher compressor inlet temperature (CIT) than the water cooling system, which results in the power plant efficiency deterioration
The desire to minimize water consumption led to the power plant integrated with a dry cooling
Summary
A supercritical CO2 (S-CO2 ) Brayton cycle is a promising power technology for the generation heat to power conversion systems due to its high cycle efficiency at moderate turbine inlet temperature (550~750 ◦ C), compact cycle configuration, and alleviation of turbine blade erosion in comparison with the steam Rankine cycle [1]. The characteristics of a dry cooling system relate to disadvantage of a higher compressor inlet temperature (CIT) than the water cooling system, which results in the power plant efficiency deterioration. An S-CO2 Brayton cycle operating near the critical point is relatively insensitive to the compressor efficiency on the cycle performance because of its small compression work. As the cycle moves further away from the critical point and requires more compression work, higher compressor efficiency becomes very important to the system performance. Institute and Jinsol Turbo Machinery in Korea are examples of such collaboration [7,8,9] These experimental studies have mostly focused on applying existing accumulated air compressor technologies to the S-CO2 compressor since an S-CO2 Brayton cycle is not yet mature power generation technology. Performance of S-CO2 Brayton cycle relative to CIT and compressor isentropic efficiency variations
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