Simulation of Methane Pyrolysis Using Direct Current Thermal Plasma with Computational Fluid Dynamics Incorporating Chemical Kinetics

Abstract

Methane (CH₄) pyrolysis using thermal plasma is considered as a leading technology for hydrogen (H₂) production. In particular, the direct current (DC) plasma torch has attracted significant attention for this application due to its advantages over other plasma sources, including lower system cost and simpler operation. Despite growing interests, there are a lot of challenges in optimizing and scaling up the process. A reliable computational fluid dynamics (CFD) simulation is essential to address these challenges. In this work, the CFD model coupled with chemical reactions was developed to analyze the pyrolysis process and particularly estimate the pyrolysis performance like CH₄ conversion and species selectivity. The experimental work was conducted to demonstrate the validity of the developed simulation method. CH₄ flow rates of 10, 30, and 50 L/min were examined under fixed plasma operating conditions, which consisted of an N₂ plasma gas flow rate of 15 L/min, a discharge current of 200 A, and a voltage of 84 V at atmospheric pressure. The simulation results showed good agreement with experimental data across all flow rates, particularly in predicting CH₄ conversion, when accounting for discrepancies in the energy delivered by the plasma flame to the reactor. Moreover, H₂ selectivity at 10 L/min has little difference between simulation and experiment. However, larger differences observed at 30 and 50 L/min are attributed to limitations in the current chemical mechanism, which considers only the reaction pathway from CH₄ to C₆H₆. Despite these limitations, the developed simulation approach offers a useful tool for process optimization, enabling the prediction of CH₄ conversion under various plasma operating and CH₄ injection conditions.