Solar Thermochemical Water-Splitting Ferrite-Cycle Heat Engines

TLDR

Thermochemical cycles use high‑temperature heat to generate chemical work, with efficiency governed by temperature and internal irreversibility, and require specific ferrite reactants and construction materials. The paper introduces a counter‑rotating‑ring receiver/reactor/recuperator solar thermochemical heat engine concept and outlines its basic operating principles. The engine uses two counter‑rotating ferrite beds that move in close proximity to enable efficient thermal recuperation between solids. The design concepts for two‑step solar‑driven thermochemical heat engines based on ferrites achieve inherent hydrogen‑oxygen separation, are well suited to high‑concentration solar flux, and preliminary efficiency estimates show promising performance.

Abstract

Thermochemical cycles are a type of heat engine that utilize high-temperature heat to produce chemical work. Like their mechanical work producing counterparts, their efficiency depends on the operating temperature and on the irreversibility of their internal processes. With this in mind, we have invented innovative design concepts for two-step solar-driven thermochemical heat engines based on iron oxide and iron oxide mixed with other metal oxide (ferrites) working materials. The design concepts utilize two sets of moving beds of ferrite reactant materials in close proximity and moving in opposite directions to overcome a major impediment to achieving high efficiency—thermal recuperation between solids in efficient countercurrent arrangements. They also provide an inherent separation of the product hydrogen and oxygen and are an excellent match with a high-concentration solar flux. However, they also impose unique requirements on the ferrite reactants and materials of construction as well as an understanding of the chemical and cycle thermodynamics. In this paper, the counter-rotating-ring receiver∕reactor∕recuperator solar thermochemical heat engine concept is introduced, and its basic operating principles are described. Preliminary thermal efficiency estimates are presented and discussed. Our results and development approach are also outlined.