Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
DIRECT HEATING OF SUPERCRITICAL CARBON DIOXIDE IN LINEAR FRESNEL COLLECTORS ANALYSIS
Submission Author:
Ricardo Hofer Begrow , SC
Co-Authors:
Ricardo Hofer Begrow, Júlio Passos
Presenter: Ricardo Hofer Begrow
doi://10.26678/ABCM.COBEM2021.COB2021-1962
Abstract
Recent advances in Fresnel technology have made it possible to reach temperatures above 500 °C, enabling the use of a sCO2-based cycle. Both technologies are under development and have great potential for increasing efficiency and reducing costs. The present work aims the analysis of supercritical carbon dioxide (sCO2) direct heating in linear Fresnel collectors for recompression Brayton cycle applications. The direct heating has the advantage of not using intermediate heat exchangers between the solar field and the power block, providing an efficiency increase and cost reduction. In addition, it eliminates the need for heating the molten salt circuit by electrical resistances during shutdowns. Thermal energy storage can still be used by dividing the solar field between CO2 and molten salts, still partially presenting the listed benefits. The use of one or more absorber tubes was evaluated for direct heating, considering the pressure loss, heat loss and estimated cost. For reaching significant values, the pressure loss proved to be decisive in the choice of the receiver. SA-213 tubes with external machining were considered, with a wall thicknesses that support a maximum allowable working pressure (MAWP) above 20 MPa, according to the maximum allowable stresses of ASME Code Sections II and VIII. In several construction aspects, mainly in relation to evacuation, a single absorber tube with a glass tube enclosure, similar to that used in parabolic trough collector, proved to be preferable Considering thermal stress, the operation of an evacuated receiver with a flat glass cover can present significant challenges. In addition, evacuated tubes are commercially available and have high thermal efficiency, considering the selective surfaces available on the market, with an emissivity of up to 9.5% and an absorptivity greater than 94%. High pressures in the absorber requires some modifications to the available commercial evacuated tubes. Due to the corrosive characteristic of wet CO2 and the high operating temperature, the use of a stabilized stainless steel, such as AISI 321, may be the best option. In addition, greater wall thickness is required. As the standard tubes of greater thickness have the same outside diameter as those of less thickness, there is no need for modifications to the glass enclosure, indicating the possibility of an easy adaptation of the industry.
Keywords
Supercritical carbon dioxide power cycle, concentrated solar power, Linear Fresnel Collector, Direct Heating, Absorber Design
