Thermal Transport Phenomena in Carbonate Particles Undergoing Chemical Looping

Abstract

Thermochemical processes, and specifically those processes which involve heterogeneous solid--gas thermochemical looping of metal oxides, are important technologies with applicability to many research fields and industries. One emerging field is solar thermochemistry, in which concentrated solar thermal energy is used to drive thermochemical reactions. Realization of a solar thermochemical technology requires understanding of heat and mass transfer characteristics and chemical kinetics of the reacting system.

In this thesis, intra-particle thermal transport phenomena in particles undergoing cyclic chemical transformations are studied, with the goals of (1) advancing understanding of intra-particle thermal transport phenomena inhibiting chemical reactions and (2) guiding process and reactor design. Intra-particle thermal transport phenomena are studied by developing a detailed numerical model of heat and mass transfer in a single particle undergoing thermochemical looping in Part I of this thesis and using the model to investigate the transient rate and extent of reactions in particles undergoing thermochemical cycling in Part II. Understanding these intra-particle thermal transport phenomena supports the design and operation of better chemical reactors and advances the fields of thermochemical looping and solar thermochemistry.

Calcium oxide looping is chosen as the model reaction cycle. The cycle consists of the endothermic calcination of calcium carbonate into calcium oxide and carbon dioxide, and the exothermic carbonation of calcium oxide with carbon dioxide to form calcium carbonate. The analyzed system is a single, porous particle undergoing calcium oxide looping in an idealized, reactor-like environment. Transient changes in spatial gradients of temperature and composition of the solid and fluid phases are considered.

The developed model is used in two application investigations. In the first investigation, directly irradiated particles are configured for carbon dioxide capture. Cycle time, magnitude of irradiation, particle size, and ambient gas temperature are varied, and evaluation metrics are used to compare the effect of varying each parameter. In the second investigation, furnace heated particles are configured for carbon dioxide capture and thermochemical energy storage. Experimental results are obtained by thermochemically cycling single sorbent particles of varying sizes in a furnace in different carbon dioxide atmospheres. Adjustments to the numerical model produce numerical results in agreement with experimental data for the first thermochemical cycle.

Investigations and model predictions are used to assess the relative importance of operational parameters via evaluation metrics. These metric trends can be extrapolated to help address particle-based reacting medium level practical considerations and choice of compromises when designing a reacting medium and system process. Show more