Abstract
Supercritical carbon dioxide (S-CO2) Brayton cycles (BC) are soon to be a competitive and environment friendly power generation technology. Progressive technological developments in turbo-machineries and heat exchangers have boosted the idea of using S-CO2 in a closed-loop BC. This paper describes and discusses energy and exergy analysis of S-CO2 BC in cascade arrangement with a secondary cycle using CO2, R134a, ammonia, or argon as working fluids. Pressure drop in the cycle is considered, and its effect on the overall performance is investigated. No specific heat source is considered, thus any heat source capable of providing temperature in the range from 500 °C to 850 °C can be utilized, such as solar energy, gas turbine exhaust, nuclear waste heat, etc. The commercial software ‘Aspen HYSYS version 9’ (Aspen Technology, Inc., Bedford, MA, USA) is used for simulations. Comparisons with the literature and simulation results are discussed first for the standalone S-CO2 BC. Energy analysis is done for the combined cycle to inspect the parameters affecting the cycle performance. The second law efficiency is calculated, and exergy losses incurred in different components of the cycle are discussed.
Highlights
Gas turbines (GT) are inevitable in modern power generation
It is worth that Kim al. et the amount of pressure loss that could occuroccur in a printed circuitcircuit heat exchanger (PCHE)
As expected, the S-CO2 recompression Brayton cycle (RBC) thermal efficiency declined with the pressure drop
Summary
Gas turbines (GT) are inevitable in modern power generation. The simple GT cycle has poor efficiency due to the elevated temperature of flue gases. Wang et al investigated the t-CO2 cycle to exploit low-grade geothermal sources for electricity production [19] They used liquefied natural gas (LNG) as a low-temperature heat sink to allow low back pressure of the CO2 turbine, greatly improving the overall performance of the cycle. We consider various working fluids, including CO2 , in the bottoming cycle, utilizing low-grade heat energy from S-CO2. The selection of appropriate working fluids depends on many factors and properties, such as critical temperature and pressure, chemical stability at the operating temperature, environment friendliness, economic convenience, and allows a high utilization of the energy available from the heat source. The potential improvements in the overall efficiency with the bottoming cycle utilizing addresses the results of the exergy analysis. This analysis could help in selecting the working fluids suitable for the bottoming cycle
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