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Modelling of air treatment by solar photocatalysis in semi-pilot compound parabolic collector (CPC) reactor

Solar photocatalysis, as an advanced oxidation process with titanium dioxide (TiO2) as most used photocatalyst is listed as emerging best available technique (BAT) in the reference document for common wastewater and waste gas treatment/management systems in the chemical sector. Widespread research has been made into the photocatalytic properties of TiO2 because of its ability to break down and destroy many types of pollutants. Over the years, application of solar photocatalysis has been widely research as a method for improvements of air quality [1, 2]. Air pollutants, such as ammonia (NH3) and nitrogen oxides (NOx), which emissions are related with human activities in rural and urban areas (industry, traffic, agriculture), are causing environmental and health issues, such as production of tropospheric ozone, acid rains, global warming and human diseases relevant to respiratory and immune systems [2, 3]. Hence, application and intensification of photocatalytic pollutant’s degradation raised importance about the appropriate photocatalytic reactor design. Consequently, due to the multiphysics approach, faster data processing and reducing number of the experiments, computational fluid dynamics modelling (CFD) gained on the importance [4]. Therefore, in this work multiphysics approach of modelling was applied when air pollutants (NH3 and NOx) were photocatalytically degraded in a compound parabolic collector (CPC) reactor with immobilized TiO2 on a rubber pads under simulated solar irradiation. A tool for assessing the degradation performance of the semi-pilot reactor was designed in the CFD software (COMSOL) and compared with predictive model consisted of sub- models: radiation emission, fluid-dynamics and the reaction kinetics coupled with irradiation absorption and combined with the appropriate mass balance. For the comparation and validation of the CFD model, experimental results were used. Experiments were carried out in a semi-pilot CPC reactor which was chosen as a state-of-the-art in reactor design. Simulated solar irradiation with different portions of UVB and UVA light was used. Commercially available materials were used for the preparation of photocatalyst, namely TiO2 P25 and rubber pads obtained from industry. Air pollution was introduced into CPC reactor in air stream reach with NH3 or NOx. The stream of NOx was represented nitrogen dioxide (NO2), nitrogen oxide (NO) and nitrous oxide (N20). Obtained CFD models contributed to the optimization of the process parameters and reduced the number of the experiments. As well, it represents a good basis for the pilot reactor scaling and modelling of the photocatalytic degradation of different pollutant concentrations and species.

titanium dioxide (TiO2), ammonia (NH3), nitrogen oxides (NOx), compound parabolic collector (CPC) reactor, modelling

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