Title

Thermoeconomic and Optimization Analysis of Advanced Supercritical Carbon Dioxide Power Cycles in Concentrated Solar Power Application

Date of Award

1-1-2018

Degree Name

Ph.D. in Mechanical Engineering

Department

Department of Mechanical and Aerospace Engineering and Renewable and Clean Energy

Advisor/Chair

Advisor: Andrew Chiasson

Abstract

Various supercritical CO2 Brayton cycles were subjected to energy and exergy analysis for the purpose of improving calculation accuracy; the feasibility of the cycles; and compare the cycles' design points. With respect to improving the accuracy of the analytical model, a computationally efficient technique using constant conductance (UA) to represent heat exchanger performances. Three parametric analysis were conducted: total conductance, maximum and minimum operating temperature, and pressure ratio for appropriate optimization. Recompression sCO2 Brayton cycle based on three parametric analysis achieves the highest thermal efficiency and power output at different operating condition. Also, the findings show that the simple recuperated sCO2 Brayton cycle has the highest specific power output in spite of its simplicity. Then a novel combined power cycle based on the recompression configuration were proposed for the purpose of improving overall thermal efficiency of power cycles by attempting to minimize thermodynamic irreversibilities and waste heat as a consequence of the Second Law. The power cycle concept comprises an advanced recompression sCO2 Brayton configuration as a topping cycle and a split flow tCO2 Rankine configuration as a bottoming cycle. The topping sCO2 recompression Brayton cycle used a combustion chamber as a heat source, and waste heat from a topping cycle was recovered by the tCO2 Rankine cycle due to an added high efficiency recuperator for generating electricity. The combined cycle configurations were thermodynamically modeled and optimized using an Engineering Equation Solver (EES) software. Single and multi-objective optimization techniques conducted in this research is developed using a genetic algorithm (GA). The findings show that the higher thermal efficiency was obtained with recompression sCO2 Brayton cycle - split flow tCO2 Rankine cycle. Also, the results show that the combined sCO2 cycles is practical and promising technology compared to conventional cycles.To produce an ecologically justifiable energy along with cost-competitive, concentrated solar power tower plant model is conducted. The aim of concentrated solar power (CSP) system modeling was to assess the system viability in a location of moderate-to-high solar availability. A case study is presented of a city in Saudi Arabia. To achieve the highest energy production per unit cost, the heliostat geometry and thermal energy storage (TES) dispatch are optimized. Solar power tower (SPT) is one design of CSP technology that is of particular interest here because it can operate at relatively high temperatures. The present SPT-TES field comprises heliostat mirrors, a tower, a receiver, heat exchangers, and two molten-salt TES tanks. The main economic indicators are the capacity factor and the levelized cost of electricity (LCOE). The findings indicate that SPT-TES with sCO2 power cycles is economically viable. The results also show that integrating TES with an SPT has a strong positive impact on the capacity factor at the optimum LCOE.

Keywords

Energy, Engineering, Mechanical Engineering

Rights Statement

Copyright 2018, author

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