Numerical investigation of hydrogen production from low-pressure microwave steam plasma

Hydrogen is recognized as a suitable energy carrier that can facilitate the storage and transport of renewable energy. In this context, hydrogen production from microwave-excited steam plasma is one of the least researched techniques and lacks numerical study due to the complex plasma kinetics and difficullty of the simulation process. Therefore, in this study, a kinetic model is developed for steam plasma, considering forty-one reactions and fourteen species. Two-dimensional microwave steam plasma is modeled using COMSOL Multiphysics software for the first time. At a microwave power of 800 W, plasma formation and hydrogen production from low pressure (1 Torr) and high temperature (150 °C) steam plasma are numerically studied within the time domain of 10⁻¹⁰ to 10⁻⁴ s. The presented results demonstrate that the maximum electron density reaches 5 10¹⁷ m⁻³ at 10⁻⁴s, and 16.8% of the water molecules dissociate to form various species. The conversion rate of water molecules to hydrogen is calculated as 24%. According to the thermodynamic evaluations, the proposed system's energy and exergy efficiencies are 10.31% and 10.14%, respectively, with a hydrogen production rate of 0.68 μg/s. Furthermore, the effect of the applied microwave power on plasma properties and hydrogen production is parametrically studied. Despite the proportional relationship between the input power and hydrogen production, no correlation is found between microwave power and system efficiency.