Review of DC and AC Arc Plasma at High Pressures Above Atmospheric Pressure

In light of the adopted green policies and strategies, thermal plasmas are gaining interest as a potential solution to electrify the industry, particularly for endothermic processes, for their tunable enthalpy and the absence of direct CO2 emissions. However, the majority of industrial applications of thermal plasma technologies are at atmospheric or lower pressure, whether for material processing, waste treatment, gasification, assisted combustion or in electric arc furnaces. Very little information exists on thermal plasmas at pressures above 1 bar, with the majority of academic publications using either analytical or numerical methodologies. The main experimental high-pressure plasma studies conducted date back to the 1960s, the 1970s and 1980s mainly in the US and the EU for aerospace applications, in addition to gas blast circuit breaker and underwater welding applications. However, these systems operate only for a few milliseconds to a few minutes at most. The interest in operating plasma systems at high-pressure is on one hand to reduce the volume of the facilities, and therefore, global costs, and on the other hand, is of practical necessity such as the case of underwater welding and in aerospace application where plasma technology plays a role in duplicating the conditions to which a vehicle is exposed to in atmospheric entry/reentry. This paper reports a thorough literature review on all high-pressure plasma arc studies available to date, including journal articles, books, and declassified reports. The findings of the studies are classified into four categories: DC and AC technologies, electrical characteristics, thermodynamics and heat transfer, and electrode erosion. The gaps and limitations are identified, and the main hypotheses are formulated, (re)opening the way for future high-pressure thermal plasma studies. Operating thermal plasma systems at high pressure could have considerable economic benefits, and thus, leading to competitive pricing for electrified high temperature processes, but faces many challenges.