Reflector design for the optimization of photoactivated processes in tubular reactors for water treatment

Abstract

Photoactivated advanced oxidation processes have excellent performance in removing recalcitrant pollutants from water. However, the high operating cost associated with the energy consumption of UV lamps is a big drawback. In this work, the design and optimization of the reflector in a tube-in-tube membrane photoreactor were carried out using a ray tracing methodology to maximize the light deployed to the reactor. Simulations were carried out using different lamps/reactor arrangements with 1, 2 and 3-sided flat reflectors and with circular and parabolic geometries. Results showed that direct radiation is maximized when the distance reactor-lamps is minimized, increasing optical efficiency. On the other hand, it was observed that for the flat reflectors, the closer the furthest point of the reflector to the center of the reactor, the higher optical efficiency is achieved due to the reduction in the number of bouncing rays in the reflector. In the case of parabolic geometries, some additional considerations are necessary, since not only the distance at which the reflector is placed matters, but also its geometrical focus. The best performance is achieved for those in which the distance from the furthest point of the reflector to the center of the reactor was lower and the lamps placed near the focus of the parabola. For the studied reflector geometries, the calculated optical efficiencies when using anodized aluminum were 46.1%, 56.5%, 60.0%, 41.8%, and 65.9% for reflectors of 1, 2, and 3 sides, cylinder, and parabola, respectively. Model predictions were successfully validated using experimental ferrioxalate actinometry data, confirming the huge potential of this simple simulation methodology for photoreactor design purposes.