The Effects of Particle Size on CO2 reduction in Packed Bed Dielectric Barrier Discharge Plasma Reactors

Utilisation of CO2 emissions for production of synthetic fuels as an energy storage vector has the potential to be an economically viable mechanism to assist in the mitigation of anthropogenic climate change. Packed bed plasma reactors (PBRs) are a potential technology that could be utilised for reduction of CO2 to CO as one of the steps in the fuel production process. Current understanding of the behavior of plasma discharges within PBRs is very poor, and the effects of many of the parameters that can be varied are still unknown.
This thesis aims to investigate the effects of particle size (180 μm to 2000 μm - random shape) of two different commonly used packing materials (Al2O3 and BaTiO3) on the conversion of CO2 in PBRs. The reactor behavior is observed through determination of product gas composition and plasma power consumption in order to determine CO2 conversion and reactor efficiency. Electrical characterisation techniques are used to determine reactor burning voltage, and capacitances. These capacitances are subsequently used to quantify the occurrence of reactor partial discharging over a range of different operating conditions.
The results indicate that smaller particles (down to 180 μm) can significantly increase CO2 conversion by up to 70%, provided that the voltage applied is sufficiently high to generate a discharge in the void spaces of the packing material. However, with decreasing particle size, the reactor burning voltage is found to increase exponentially, as well as the tendency of the reactor towards partial discharging. Consequently, there are two recommendations:
I. Higher electric field strengths should be used by researchers working with packed bed reactors
II. Reactor capacitances, including the effective dielectric capacitance, should be reported for all packed bed reactor experiments in order to determine whether partial reactor discharging behavior is occurring