Abstract
A new combined supercritical CO2 recompression Brayton/Kalina cycle (SCRB/KC) is proposed. In the proposed system, waste heat from a supercritical CO2 recompression Brayton cycle (SCRBC) is recovered by a Kalina cycle (KC) to generate additional electrical power. The performances of the two cycles are simulated and compared using mass, energy and exergy balances of the overall systems and their components. Using the SPECO (Specific Exergy Costing) approach and employing selected cost balance equations for the components of each system, the total product unit costs of the cycles are obtained. Parametric studies are performed to investigate the effects on the SCRB/KC and SCRBC thermodynamic and thermoeconomic performances of key decision parameters. In addition, considering the exergy efficiency and total product unit cost as criteria, optimization is performed for the SCRBC and SCRB/KC using Engineering Equation Solver software. The results indicate that the maximum exergy efficiency of the SCRB/KC is higher than that of the SCRBC by up to 10%, and that the minimum total product unit cost of the SCRB/KC is lower than that of the SCRBC by up to 4.9%.
Highlights
Global warming, environmental pollution and growing demand for energy have increased attention on the efficient use of energy resources
The values of decision and performance parameters for the thermodynamic and economic optimal design (TOD and EOD) cases are shown in Table 8 for the supercritical CO2 recompression Brayton cycle (SCRBC) and the supercritical CO2 recompression Brayton/Kalina cycle (SCRB/Kalina cycle (KC))
Parametric studies are performed for the cycles to assess the effects on the exergy efficiency and total product unit cost of such decision parameters as compressor pressure ratio, ammonia–water temperature at pre-cooler1 outlet, pinch point temperature difference in pre-cooler1, pump pressure ratio, ammonia concentration at the condenser outlet and minimum temperature difference in the superheater
Summary
Environmental pollution and growing demand for energy have increased attention on the efficient use of energy resources. Having used a low-grade heat source, Cayer et al performed a detailed analysis for a carbon dioxide transcritical power cycle [7] They reported the work in four steps: energy analysis, exergy analysis, finite size thermodynamics and heat exchanger surface calculation. Sarkar performed an exergy analysis for the SCRBC and optimized its performance [9] He reported that the irreversibilities in heat exchangers are higher than those in turbo-machinery and that the high temperature regenerator (HTR) is more effective than the low temperature regenerator (LTR) at raising the cycle efficiency. Hu et al compared the performance of a supercritical gas Brayton cycle for several types of working fluids such as CO2-based binary mixtures and pure carbon dioxide They found higher efficiencies for both CO2-He and CO2-Kr mixtures [22].
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