Plasma and Flow Dynamics in Gliding- and Transferred-ARC Reactors for Hydrogen Production from Polyethylene

Hydrogen, due to its high energy density and sustainability potential, is considered a leading chemical energy storage alternative to fossil fuels. Given the absence of natural sources of hydrogen, hydrogen has to be procured from substances such as water, fossil fuels, biomass, or plastics. Nonthermal plasma-based hydrogen production approaches have the potential to be more energy efficient, selective, and environmentally-benign than thermochemical methods. In this study, gliding arc and transferred arc nonthermal plasma reactors have been designed, built, and characterized through the production of hydrogen from low-density polyethylene (LDPE) using nitrogen as auxiliary gas at atmospheric pressure and temperature conditions. These reactors have complementary operational characteristics, making their parallel evaluation compelling to reveal the mechanisms by which nonthermal plasma enables the extraction of hydrogen from solid feedstock. In both reactors, the dynamic characteristics of the plasma affect its interaction with the solid LDPE feedstock, and hence the production of hydrogen. Concurrently, the interaction between the hydrogen emanating from LDPE and the impinging nitrogen flow can significantly affect the plasma dynamics, affecting its stability and the gas and particulate flows throughout the reactors. Visualization of the plasma and gas flow are conducted using long-exposure photography, high-speed photography, and high-speed Schlieren imaging. Visualization results together with current and voltage signals and gas chromotography analyses are used to correlate the plasma and flow dynamics to the production of hydrogen as function of the reactors’ main operation parameters, namely inflow rate, driving voltage, and electrode-feedstock spacing. The experimental diagnostics are complemented with Computational Fluid Dynamics simulations to assess flow and thermal characteristics across the reactors. Residence time, arc stability, gliding velocity, plasma volume, and plasma-feedstock interaction area as function of the operational parameters are also determined and analyzed.