Performance analysis of a 2.45 GHz microwave plasma torch for CO₂ decomposition in gas swirl configuration

Abstract

Microwave plasmas are a promising technology for energy-efficient CO2 valorization via conversion of CO2 into CO and O2 using renewable energies. A 2.45 GHz microwave plasma torch with swirling CO2 gas flow is studied in a large pressure (20–1000 mbar) and flow (1–100 L min−1) range. Two different modes of the plasma torch, depending on the operating pressure and microwave input power, are described: at pressures below 120 mbar the plasma fills most of the plasma torch volume whereas at pressures of about 120 mbar an abrupt contraction of the plasma in the center of the resonator is observed along with an increase of the gas temperature from 3000 K to 6000 K. The CO outflow is generally found to be proportional to the plasma effective power and exhibits no significant dependence on the actual CO2 flow injected into the reactor but only on the input power at certain pressure. Thermal dissociation calculations show that, even at the lowest pressures of this study, the observed conversion and energy efficiency are compatible with a thermal dissociation mechanism.

Determination of the Conversion and Efficiency for CO2 in an Atmospheric Pressure Microwave Plasma Torch

“…The main differences are the absence of a tubular reactor for the incorporation of membranes for gas separation, a lower position of the heat exchanger and the presence at quasi atmospheric pressure of a pump to suck away the effluent gas. D'Isa reported a maximal efficiency of around 25 % for the quasi‐atmospheric pressure measurements but a maximal conversion of about 15 % 20, 22. Hecimovic et al reported that the CO 2 conversion efficiency at a pressure of 200 mbar is independent of the measurement position along the exhaust gas tube and independent of the position of the heat exchanger 20.…”

“…In the work by D'Isa [22], it is shown that the CO 2 plasma switches at around 125 mbar from an extended mode to a contracted mode. According to the change in plasma mode, the gas temperature increases from ~2800 K up to 6000 K. Wolf et al and Spencer and Gallimore reported the same gas temperature of around 6000 K [4,39].…”

“…A torch similar to the one investigated in the current work, equipped with a different exhaust gas treatment, and that can be operated from 60 mbar up to a quasi-atmospheric pressure around 900 mbar, is located at the IPP Institute in Garching [20,22]. The main differences are the absence of a tubular reactor for the incorporation of membranes for gas separation, a lower position of the heat exchanger and the presence at quasi atmospheric pressure of a pump to suck away the effluent gas.…”

Two-temperature balance equations implementation, numerical validation and application to H2O–He microwave induced plasmas

“…However, as an outlook, implementation of a proper method to keep pressure constant during simulation [17] is necessary, especially for plasmas for which the mode structure is sensitive to pressure changes. Such an example is the transition from diffuse to contracted regime in CO 2 discharges [30,42].…”

A New Stripline-Based Atmospheric Pressure Microwave Plasma Sheet Source Designed for Surface Modification of Materials

“…An overview of the types of atmospheric-pressure microwave plasma sources (MPSs) and ways of supplying them can be found in [ 6 ]. Such discharges can be used for gas treatment or conversion, including: gas purification [ 7 ], decomposition of harmful gases [ 8 , 9 ], hydrogen production [ 10 ], CO 2 decomposition [ 11 ], biomass gasification [ 12 ], and also for surface treatment [ 13 ], disinfection [ 14 ], etc.…”