(616h) Modeling CO2-Free Hydrogen Production Via Microwave-Driven Methane Pyrolysis in a Fluidized Bed of Carbon Particles

Hydrogen is expected to play a crucial role in the transition to a net-zero emissions future by 2050. It is a carbon-free energy carrier that is widely used in many industrial applications such as oil refineries, steelmaking, and chemical production. Therefore, hydrogen is a promising vector for supplying global energy demand, and its demand is projected to double by 2030. Currently, only 0.5 Mtonnes/year is provided by clean technologies of hydrogen production, while the global demand for hydrogen is 70 Mtonnes/year. Thus, it is imperative to explore CO₂-free technologies for hydrogen production. Despite the increasing interest in hydrogen via electrolysis, this method is highly energy-intensive and not scalable enough to meet the demand. Alternatively, methane pyrolysis can produce hydrogen without direct CO₂ emissions and with modest energy inputs, making it a potential stepping stone from fossil fuels to renewable energies. Abundant resources of natural gas and the need for CO₂-free hydrogen production methods have made methane pyrolysis a promising area of research and technological development.

Provided by renewable electricity, microwave energy is a sustainable and efficient method of providing energy for methane pyrolysis. In comparison to electrolysis, the use of microwaves significantly reduces electricity consumption by 80%. The current study presents a novel modeling approach to study the sustainable production of CO₂-free hydrogen through non-plasma methane pyrolysis using microwave energy and carbon particles in a fluidized bed reactor (FBR). We have validated this technology through experimental means, with results showing that over 95% of methane is converted into hydrogen with a selectivity of over 90% and pure solid carbon as a by-product. In this technology, carbon particles, with an average size of 350 microns, in FBR absorb microwave energy and create a hot medium (>1200℃) in contact with flowing methane. As a result, methane decomposes into its constituents of matter, namely, hydrogen and solid carbon. Currently, the chemical and energy industry lacks a proper model that can simultaneously describe the nature of microwave heating and fluidization. Modeling such a complex phenomenon requires the multiphysics combination of electromagnetic (EM) simulations, fluid flow, and particle dynamics. To this end, the interaction of microwaves with carbon particles in the FBR is modeled by solving EM equations, otherwise known as Maxwell’s equations, in a 1 kW-unit microwave cavity. Firstly, the FBR is assumed to be a uniform medium with a porosity of 0.4. The uniform medium approximation method divulges that the FBR of carbon particles only absorbs ~ 18 W out of 500 W of microwave input power, contradicting the absorbed power of ~ 100 W obtained from the experimental data. Hence, this finding emphasizes the fact that the FBR of carbon particles cannot be considered as a uniform medium due to their considerable electrical conductivity. Therefore, the microwave heating of the FBR is studied at a particle scale for the very first time. The simulation results reveal that electric charges are formed on each individual particle inside the FBR, contributing to the absorption of microwave energy mainly due to Joule heating rather than dielectric heating. A one-way coupling algorithm is then developed where the distribution of the electric field inside the FBR is imported into a CFD-DEM model. The developed CFD-DEM model will shed insights into the effect of fluidization mixing on the temperature distribution due to non-uniform microwave heating. Given this, the proposed model can serve as a valuable tool to study any chemical production processes that utilize electrification and fluidization, improving the efficiency of energy usage and reducing costs within the chemical production sectors.