Analysis of the thermal hydraulics of a multiphase oxygen production reactor in the Cu-Cl cycle

Abstract

In the thermochemical water splitting process by Cu-Cl cycle, oxygen gas is produced by an endothermic thermolysis process in a three-phase reactor. In this thesis, the required heat for the thermolysis process is provided by adopting the idea of heating some of the stoichiometric oxygen gas by using a nuclear reactor heat source. Then, the gas is re-injected into the reactor from the bottom, to transfer heat directly to the slurry bed of molten salt and solid reactant. In this thesis, the thermal hydraulics of the oxygen slurry bubble column reactor (SBCR) is investigated experimentally and numerically. In the experiments, lower temperature alternative materials, such as helium gas at 90°C and water at 22°C, are used to mimic the actual materials of the oxygen gas at 600°C and molten CuCl at 530°C. From the experimental studies, new forms of empirical equations are formulated for the overall gas holdup and the volumetric heat transfer coefficient in terms of the design and input parameters of the SBCR, such as; the superficial gas velocity, reactor height, and solid particles concentration. The empirical equations are obtained for both bubbly and churn-turbulent flow regimes. It is also determined experimentally the flow regime transition point between bubbly and churn-turbulent flow regimes. Furthermore, it is found experimentally that the solid particle diameter has insignificant effect on the overall gas holdup. To better understand the thermal hydraulics of the oxygen SBCR, a computational fluid dynamics (CFD) models are developed by using the ANSYS FLUENT software. All CFD simulation results are validated by the experimental results of the alternative materials system with good agreements. From the CFD simulations, it is also found that the gas temperature decreases dramatically near the bottom of the reactor, and the effects of the superficial gas velocity, reactor height, and solid concentration on the gas temperature are negligible. Finally, a simple correlation is obtained to calculate the number of oxygen reactors in terms of the superficial gas velocity of the oxygen gas and the oxygen production rate.