Numerical and experimental study of a packed bed plasma reactor for environmental applications.
20 June 2017
Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerpen (route: UAntwerpen, Campus Middelheim
Organization / co-organization:
Department of Chemistry
Koen Van Laer
Public defence of the PhD thesis of Mr. Koen Van Laer - Faculty of Science - Department of Chemistry
Climate change is happening and is caused by human activity! Throughout Earth’s history, the planet has been warming and cooling over and over, but never before did the temperature change occur so quickly. The rise of the atmospheric CO2 concentration caused by the burning of fossil fuels can be seen as the major contributor. If we wish to mitigate the rise of sea level and minimize the amounts of extreme weather events, it is high time that we start acting. The research performed in this thesis very much fits in this context, because it contributes to increasing our knowledge about packed bed plasma reactors (PBPRs) which are being investigated to be used in environmental applications in general, and for the splitting of greenhouse gas CO2 in particular.
By experimental study, we show that introducing a packing in a dielectric barrier discharge (DBD) reactor can simultaneously increase both the conversion and energy efficiency compared to a non-packed reactor. This makes the PBPR a promising tool for CO2 conversion. However, the plasma behaviour in a PBPR is not well known. Since experimental plasma diagnostics is not straightforward with a packing present, a modelling study is very much of interest.
To oppress the calculation time, approximations had to be made. The resulting 2D axisymmetric model with helium as discharge gas, however, already provides us with interesting insights.
It is shown that a packing enhances the electric field strength at the contact points of the dielectric material due to polarization by the applied potential. At low applied potential the discharge exist locally, while at higher potentials the plasma gains the ability to propagate in between the beads filling the full gap. When the dielectric constant of the packing is changed to higher values (ε ≥ 100), the plasma can again switch from full gap discharge, to localised plasma. Depending on the gap distance between electrodes and the size of the packing beads, this localisation can take place at lower dielectric constants, namely when the gap distance is decreased, or when the packing diameter is smaller.
Next, the discharge gas was changed to dry air, to pave the road for future research with CO2. It is shown that the typical filamentary discharge of a non-packed reactor operated with a molecular gas, changes to a combination of standing filamentary microdischarges and surface discharges.
There is still a long way to go before a PBPR can be fully modelled with CO2 as discharge gas, as it is used in experiments. Our work paves the road for future research by increasing the understanding which will help to optimize the PBPR to, ultimately, make it suitable for industrial implementation.