Date of Award

2016

Document Type

Open Access Dissertation

Department

Chemical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

John W. Weidner

Abstract

In today's world, alternative clean methods of energy are needed to meet growing energy demands. Concentrating solar thermal power, more commonly referred to as CSP, is unique among renewable energy generators because even though it is variable, like solar photovoltaic and wind, it can easily be coupled with thermal energy storage as well as conventional fuels, making it highly dispatchable. One challenge with concentrated solar power (CSP) systems is the potential corrosion of the alloys in the receivers and heat exchangers at high-temperature (700-1000 °C), which leads to a reduction of heat transfer efficiency and influences the systems durability. The objective of this dissertation is to create a comprehensive mathematical model including thermal gradients and fluid flow to predict corrosion rates and mechanisms observed in state of the art molten salt heat transfer systems.

The corrosion model was designed and benchmarked against a thermosiphon reactor. This thermosiphon reactor exposed the alloy coupons to non-isothermal conditions expected in CSP plants. Cathodic protection was also added to the model as a mitigation strategy for corrosion of metal surfaces. The model compared the corrosion rates for the cases with and without cathodic protection under different operational conditions for different high-temperature alloys (e.g., Haynes 230, Haynes NS-163, and Incoloy 800H). The model is capable of considering the effects of kinetic and mass transfer on the corrosion rate under high temperature fluid flow systems.

The results reveal that temperature has an important effect on the corrosion rate of high-temperature alloys in molten salt systems. For the case with the higher temperature range 800-950 ℃, the corrosion rate is almost twice that of the case with the low temperature range 650-800 ℃. Another important factor is dissolved metal ions (e.g., Cr3+) that diffuse to the surface of the alloy as a result of disproportionation reaction at the more electropositive metals and cause the oxidation\reduction reactions on the surface of the alloy.

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