Non-thermal plasma and air treatment

The quality of the air we breathe has always been a major concern, both from a health point of view and in terms of living comfort. Historically, the "beaux quartiers" have always developed to the windward side of cities (in Paris, for example, to the west) in order to benefit from the "pure air" of the countryside. Similarly, convalescents and even the sick (tuberculosis, for example) were advised to spend time in the mountains (sanatoriums) or by the sea. These associations between health and presumed air quality were not really based on precise scientific data, but rather on empiricism, often associating odor and dust with a pathogenic role.

The development of analytical sciences has made it possible to quantify the notion of polluted air and to identify the presence of toxic compounds in the air, in conjunction with epidemiological studies showing the pathogenic effects of these compounds. This has led to the enactment of standards governing emissions of these toxic compounds and, consequently, to the development of air treatment methods to eliminate them.

At present, a distinction must be made between effluents intended for discharge outside (industrial effluents) and the treatment of indoor air (air coming directly from outside and possibly polluted or recycled air). This is due, on the one hand, to the concentrations to be treated (higher in the case of industrial effluents) and, on the other, to the more stringent standards for indoor air.

In the case of industrial effluents, the nature of the pollutants (volatile organic compounds – VOC – possibly chlorinated and/or sulfurated, nitrogen oxides) will, of course, depend on the industrial activity concerned. In general, the number of different pollutants to be treated is small, they are well identified or easily identifiable, but the treatment corresponds to a significant total gas flow (from a few thousand to several hundred thousand m ³ /h). These pollutants are often associated with solid (dust, soot) or liquid aerosols, which need to be treated in a specific way.

The most commonly used processes are based on high-temperature thermal oxidation (catalytic or purely thermal) in continuously operating units. Given the high flow rates to be treated and the temperature required for total oxidation of the VOCs, energy expenditure is considerable, but can be greatly reduced by heat recovery and if the concentration of VOCs to be eliminated is sufficient to ensure energy autonomy by using the heat from the exothermicity of the total VOC oxidation reaction.

The concentration required to achieve process autothermy can be achieved by concentrating effluents or, more cleverly, by judiciously capturing...