Properties of atmospheric pressure plasmas in packed bed reactors

摘要

Summary form only given. Atmospheric pressure dielectric barrier discharges (DBDs) sustained in packed bed reactors (PBRs) are being investigated for remediation of toxic gases, CO2 removal and conversion of waste gases into higher value compounds. Though investigated extensively in experiments, few computational studies of PBRs have been performed to date [1]. For applications involving chemical reprocessing which require a high degree of reactant selectivity, the ability to control plasma properties is particularly important. In this paper, we report on the results of a computational investigation of PBR-DBD properties using the multi-fluid plasma hydrodynamics simulator nonPDPSIM [2].PBRs were simulated in 2-dimensions using coplanar electrodes with dielectric beads (rods in 2D) having different configurations. The base case gas is humid air at ambient temperature and atmospheric pressure. The reaction mechanism includes 33 species and 147 reactions. Electrons were seeded near the cathode, and a negative pulse was applied, forming an anode-seeking streamer. The influence of packing geometry, filler gas and bead material on discharge properties was investigated. We found that increasing the rod dielectric constant or decreasing inter-rod separation increases regional electric field enhancement, and therefore electron densities, temperature, and discharge propagation velocity. Propagation mechanisms were also examined. It was found that photoionization plays an important role in discharge propagation around the beads, as it serves to seed charges across regions of low electric field, and in areas of high field enhancement. In plasmas where ionizing radiation has a short penetration distance, discharge propagation around rods is significantly reduced. Upon breakdown in regions of high electric field, electron impact (as opposed to photoionization) was the primary ionization source. Formation of inter-rod, cathode-seeking restrikes, reminiscent of the experimentally-observed filamentary microdischarges [3], was seen. Positive and negative surface ionization waves were also observed. Preliminary results indicate that radical generation takes place near rod surfaces and is largely influenced by these ionization waves. This is likely due to characteristically high electric fields and electron energies in the ionization front, which lead to increased reaction rates.