Effect of high temperatures on the efficiency of sub-critical CO2 cycle

Aram Mohammed Ahmed,Attila R Imre

doi:10.1556/606.2021.00310

Abstract

AbstractThermodynamic efficiency is a crucial factor of a power cycle. Most of the studies indicated that efficiency increases with increasing heat source temperature, regardless of heat source type. Although this assumption generally is right, when the heat source temperature is close to the critical temperature, increasing the heat source temperature can decrease efficiency. Therefore, in some cases, the increase in the source temperature, like using improved or more collectors for a solar heat source can have a double negative effect by decreasing efficiency while increasing the installation costs. In this paper, a comparison of the CO2 subcritical cycle and the Trilateral Flash Cycle will be presented to show the potential negative effect of heat source temperature increase.

Highlights

The demand for energy in the world increases; this increase is preferably satisfied by modern power plants using a clean, renewable source
The aim of the study is to demonstrate to engineers and researchers that the efficiency does not always increase with increasing heat source temperature, but sometimes the increasing of the heat source temperature close to the critical temperature leads to decreasing the efficiency
This study focused on the subcritical CO2 power cycle with low heat source temperature close to the critical points

Summary

Introduction

The demand for energy in the world increases; this increase is preferably satisfied by modern power plants using a clean, renewable source. A special class of these power plants is the one operated by low heat sources, using organic Rankine cycles or carbon dioxide power cycle. Integration of the absorption refrigeration system with reheat transcritical power cycle leads to improve the efficiency and maintain stable productivity by keeping the low condensation temperature at all different weather conditions. At the low and high heat source temperature, the transcritical CO2 power cycle using mixed CO2 is better than the cycle that using pure carbon dioxide, thermodynamically, and exergo-economically.

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Conclusion