Samuel A. Iwarere

3D magnetohydrodynamic modelling of a dc low-current plasma arc batch reactor at very high pressure in helium

This paper deals with a three-dimensional (3D) time-dependent magnetohydrodynamic (MHD) model under peculiar conditions of very high pressures (from 2 MPa up to 10 MPa) and low currents (<1 A). Studies on plasma arc working under these unusual conditions remain almost unexplored because of the technical and technological challenges to develop a reactor able to sustain a plasma at very high pressures. The combined effect of plasma reactivity and high pressure would probably open the way towards new promising applications in various fields: chemistry, lightning, materials or nanomaterial synthesis.A MHD model helps one to understand the complex and coupled phenomena surrounding the plasma which cannot be understood by simply experimentation. The model also provides data which are difficult to directly determine experimentally. The model simulates an experimental-based batch reactor working with helium. The particular reactor in question was used to investigate the Fischer–Tropsch application, fluorocarbon production and CO2 retro-conversion. However, as a first approach in terms of MHD, the model considers the case for helium as a non-reactive working gas.After a detailed presentation of the model, a reference case has been fully analysed (P = 8 MPa, I = 0.35 A) in terms of physical properties. The results show a bending of the arc and displacement of the anodic arc root towards the top of the reactor, due to the combined effects of convection, gravity and electromagnetic forces. A parametric study on the pressure (2–10 MPa) and current (0.25–0.4 A) was then investigated. The operating pressure does not show an influence on the contraction of the arc but higher pressures involve a higher natural convection in the reactor, driven by the density gradients between the cold and hot gas.

Investigation of tetrafluoromethane as a plasma gas in a very high pressure/low current dc batch reactor by means of 3D MHD modelling

This paper deals with 3D MHD modelling of the behaviour of a tetrafluoromethane (CF4) plasma arc in a batch reactor under peculiar conditions of low current (0.35 A) and very high pressure (50 atm).The first part of the manuscript presents results for a horizontal configuration of the reactor, as is undertaken experimentally. The model has led to the understanding of the instabilities observed experimentally for such unusual operating conditions. The curved shape of the arc and the sliding of the anodic arc root along the electrode have been revealed to be the source of the experimental instabilities.The latter part of the manuscript investigates the effect of two vertical configurations of the reactor; with a cathode at the top and cathode at the bottom to overcome the instabilities. In these reactor configurations, the arc is much more stable and stays centred in the middle of the electrodes. These configurations are more suitable for the stability of the arc discharge, but have to be verified experimentally.

Carbon Dioxide to Energy: Killing Two Birds with One Stone

Carbon dioxide (CO2) is regarded as one of the arch villains in the long debate on global warming, or what has now been more correctly termed climate change, as it accounts for approximately 85 % of the total greenhouse gases that are emitted annually. The majority of sources are from the combustion of fossil fuels. With a growing global population and consequently a growing demand for energy, there has been extensive research on alternative fuels and energy sources, as well technologies for the combustion of fossil fuels. In order to mitigate the environmental effects of carbon dioxide, numerous strategies have been proposed which focus on limitation of emissions from sources, capture, and degradation. Carbon dioxide in theory could be a potential feedstock for the production of fuel, energy, and value-added chemicals. In effect, carbon dioxide could be turned from a villain to a hero, i.e. producing energy while reducing greenhouse gases. It is therefore important that researchers continue to look for practically feasible, inexpensive, environmentally friendly, and energy efficient technologies that can utilize CO2 by converting it into energy, liquid hydrocarbon fuels, and value-added chemicals. This review presents the current state of the art in this regard, with emphasis on technological improvements to make carbon dioxide a viable feedstock for energy and value-added chemical production.