Modeling Chemical and Thermal States of Reactive Metal Oxides in a CR5 Solar Thermochemical Heat Engine

“Sunshine to Petrol” is a grand-challenge research project at Sandia National Laboratories with the objective of creating a technology for producing feedstocks for making liquid fuels by splitting carbon dioxide (and water) using concentrated solar energy [1]. A reactor-level performance model is described for computing the solar-driven thermochemical splitting of carbon dioxide via a two-step metal-oxide cycle. The model simulates the thermochemical performance of the Counter-Rotating-Ring Receiver/Reactor/Recuperator (CR5). The numerical model for computing the reactor thermochemical performance is formulated as a system of coupled first-order ordinary differential equations describing the energy and mass transfer within each reactive ring and radiative energy transfer between adjacent rings. In this formulation, each of the counter-rotating rings is treated in a one-dimensional sense in the circumferential direction; supporting circumferential temperature and species gradients with assumed negligible gradients in both the radial and axial directions. The model includes radiative heat transfer between adjacent counter-rotating rings, variations in the incident solar flux distribution, heat losses to the reactor housing, and energy of reaction associated with the reduction and oxidation reactions. An overview of the physics included in this first-generation numerical model will be presented. Preliminary results include the circumferential distributions of temperature and species within each of the reactive rings. The computed overall chemical conversion efficiency will be presented for a range of design and operating parameters; including ring speed, carrier ring mass, reactive material loading, radiative emissivity, and differing incident flux distributions.