Modeling of a Solar Receiver for Superheating Sulfuric Acid

Abstract

A volumetric solar receiver for superheating evaporated sulfuric acid is developed as part of a 100 kW pilot plant for the hybrid sulfur (HyS) cycle. The receiver, which uses silicon carbide foam as a heat transfer medium, heats evaporated sulfuric acid using concentrated solar energy to temperatures of 1000 °C or greater, which are required for the downstream catalytic reaction to split sulfur trioxide into oxygen and sulfur dioxide. Multiple parallel approaches for modeling and analysis of the receiver are used to design the prototype. Focused numerical modeling and thermodynamic analysis are applied to answer individual design and performance questions. Numerical simulations focused on fluid flow are used to determine the best arrangement of inlets, while thermodynamic analysis is used to evaluate the optimal dimensions and operating parameters. Finally, a numerical fluid mechanics and heat transfer model is used to predict the temperature field within the receiver. Important lessons from the modeling efforts are given, and their impacts on the design of a prototype are discussed.

Thermodynamic Model of a Solar Receiver for Superheating of Sulfur Trioxide and Steam at Pilot Plant Scale

“…However, the option to increase the thermal efficiency by a closed geometry was rejected, since the cylindrical shape features better mountability and a higher degree of flux homogeneity. This configuration also exhibits a satisfactory robustness against changes in the fraction of solar irradiation incident the absorber [13]. An even mass flux distribution was confirmed by CFD methods with a cavity length of 0.2 m [13].…”

“…This configuration also exhibits a satisfactory robustness against changes in the fraction of solar irradiation incident the absorber [13]. An even mass flux distribution was confirmed by CFD methods with a cavity length of 0.2 m [13]. With this geometric configuration and at nominal conditions, outer heat transfer coefficients above 50 W/m²K yielded window temperatures below 800 °C, which is a conservative design limitation for fused silica [25].…”

“…Variation of the diameter while keeping a cylindrical shape has already been shown and discussed in [13] naturally showed a more pronounced impact on temperatures and receiver efficiency. However, the option to increase the thermal efficiency by a closed geometry was rejected, since the cylindrical shape features better mountability and a higher degree of flux homogeneity.…”

“… Predict required heliostats during the solar tests for desired intercept power  Optimize receiver geometry and positioning  Analyse and set design parameters for the secondary concentrator  Check adequateness of heliostat selection algorithm at different power levels and times  Provide realistic boundary conditions for the thermodynamic receiver model (v.s.) and CFD model [13] The DLR Solar Tower in Jülich [7] is located at 50.913° latitude north (longitude 6.388°). Its heliostat field including optical properties based on deflectometric data and the tower geometry are available as libraries for STRAL; the raytracing can thus be processed for an arbitrary flat shaped aperture at any position on the tower and tilt angles.…”

“…The methodology and results of these models are presented and discussed in this paper. A complementary CFD analysis of the receiver has already been reported in [13] and a summary of the receiver design applying CAE tools has recently been presented in [14].…”