CFD simulation of methane pyrolysis in plasma reactor for CO₂-free hydrogen

Abstract

Reducing greenhouse gas emissions and slowing global warming are among today’s most pressing challenges, particularly in the industrial, transportation, and agricultural sectors. One promising solution is the transition to hydrogen as a clean energy carrier. Among the various methods of hydrogen production, turquoise hydrogen, generated through methane pyrolysis, offers a promising pathway to reduce carbon emissions. When this process is carried out in plasma reactors powered by renewable energy, it enables the production of CO₂-free hydrogen. This work presents CFD simulations of methane pyrolysis in two types of plasma reactors: gliding arc plasma (GAP) and microwave plasma (MW). The 0D sensitivity analyses revealed that thermal reactions dominate over electron impact reactions due to high plasma temperatures (3000 – 4000 K). Consequently, in more detailed 2D and 3D simulations, plasma was modeled as a heat source to explore the reaction dynamics and optimize reactor design and operating conditions. In these models, the MW plasma was represented by a Gaussian heat peak, while the GAP plasma was modeled as an “artificial arc”. This approach improved methane conversion in the GAP reactor from 35 to 44 %. The simulation also identified the zones of increased by-product formation within the MW plasma reactor. These findings can inform future improvements in reactor design, helping to enhance overall efficiency. Additionally, simulations were conducted for surface dielectric barrier discharge (SDBD) plasma using a gas mixture of oxygen, nitrogen, and hydrogen. Compared to methane pyrolysis, this mixture involved fewer chemical reactions, so no simplification of the plasma modeling was necessary. The focus of the simulation was on the plasma discharge effects, specifically the influence of ionic wind on gas conversion. Since the gas temperature in the SDBD reactor was significantly lower than in the GAP and MW reactors, the simulations clearly demonstrated the difference between cold and warm plasmas.