Renewable energy sources are fundamental alternatives to supply the rising energy demand in the world and to reduce or replace
fossil fuel technologies. In order to make renewable-based technologies suitable for commercial and industrial applications, two main
challenges need to be solved: the design and manufacture of highly efficient devices and reliable systems to operate under intermittent
energy supply conditions. In particular, power generation technologies based on solar energy are one of the most promising alternatives to
supply the world energy demand and reduce the dependence on fossil fuel technologies. In this dissertation, the dynamic behavior of a
Concentrated Solar Power (CSP) supercritical CO2 cycle is studied under different seasonal conditions. The system analyzed is composed of
a central receiver, hot and cold thermal energy storage units, a heat exchanger, a recuperator, and multi-stage compression-expansion
subsystems with intercoolers and reheaters between compressors and turbines respectively. The effects of operating and design parameters
on the system performance are analyzed. Some of these parameters are the mass flow rate, intermediate pressures, number of
compression-expansion stages, heat exchangers' effectiveness, multi-tank thermal energy storage, overall heat transfer coefficient between
the solar receiver and the environment and the effective area of the recuperator. Energy and exergy models for each component of the
system are developed to optimize operating parameters in order to lead to maximum efficiency. From the exergy analysis, the components
with high contribution to exergy destruction were identified. These components, which represent an important potential of improvement, are
the recuperator, the hot thermal energy storage tank and the solar receiver. Two complementary alternatives to improve the efficiency of
concentrated solar thermal systems are proposed in this dissertation: the optimization of the system's operating parameters and
optimization of less efficient components. The parametric optimization is developed for a 1MW reference CSP system with CO2 as the working
fluid. The component optimization, focused on the less efficient components, comprises some design modifications to the traditional
component configuration for the recuperator, the hot thermal energy storage tank and the solar receiver. The proposed optimization
alternatives include the heat exchanger's effectiveness enhancement by optimizing fins shapes, multi-tank thermal energy storage
configurations for the hot thermal energy storage tank and the incorporation of a transparent insulation material into the solar receiver.
Some of the optimizations are conducted in a generalized way, using dimensionless models to be applicable no only to the CSP but also to
other thermal systems. This project is therefore an effort to improve the efficiency of power generation systems based on solar energy in
order to make them competitive with conventional fossil fuel power generation devices. The results show that the parametric optimization
leads the system to an efficiency of about 21% and a maximum power output close to 1.5 MW. The process efficiencies obtained in this work,
of more than 21%, are relatively good for a solar-thermal conversion system and are also comparable with efficiencies of conversion of
high performance PV panels. The thermal energy storage allows the system to operate for several hours after sunset. This operating time is
approximately increased from 220 to 480 minutes after optimization. The hot and cold thermal energy storage also lessens the temperature
fluctuations by providing smooth changes of temperatures at the turbines' and compressors' inlets. Additional improvements in the overall
system efficiency are possible by optimizing the less efficient components. In particular, the fin's effectiveness can be improved in more
than 5% after its shape is optimized, increments in the efficiency of the thermal energy storage of about 5.7% are possible when the mass
is divided into four tanks, and solar receiver efficiencies up to 70% can be maintained for high operating temperatures (~ 1200°C) when a
transparent insulation material is incorporated to the receiver. The results obtained in this dissertation indicate that concentrated
solar systems using supercritical CO2 could be a viable alternative to satisfying energy needs in desert areas with scarce water and
fossil fuel resources. / A Dissertation submitted to the Department of Mechanical Engineering in partial fulfillment of the
requirements for the degree of Doctor of Philosophy. / Spring Semester 2016. / February 26, 2016. / Concentrated Solar Power (CSP), Efficiency, Optimization, Supercritical CO2 (sCO2), Thermodynamic
Analysis / Includes bibliographical references. / Juan C. Ordonez, Professor Co-Directing Dissertation; Alejandro Rivera-Alvarez, Professor
Co-Directing Dissertation; Hui Li, University Representative; Kunihiko Taira, Committee Member; Carl Moore, Committee Member; Rob
Hovsapian, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_360416 |
| Contributors | Osorio, Julian David (authoraut), Ordonez, Juan Carlos (professor co-directing dissertation), Rivera-Alvarez, Alejandro (professor co-directing dissertation), Li, Hui (university representative), Taira, Kunihiko (committee member), Moore, Carl A. (committee member), Hovsapian, Zohrob O. (committee member), Florida State University (degree granting institution), FAMU-FSU College of Engineering (degree granting college), Department of Mechanical Engineering (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (170 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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