Design and optimization of a photocatalytic reactor for air purification in ventilation systems
4 June 2019
Stadscampus, Kapel van de Grauwzusters - Lange Sint-Annastraat 7 - 2000 Antwerpen (route: UAntwerpen, Stadscampus
Organization / co-organization:
Department of Bioscience Engineering
Jeroen Van Walsem
Siegfried Denys, Silvia Lenaerts & Bart Modde
PhD defence Jeroen Van Walsem - Faculty of Science, Department of Bioscience Engineering
Photocatalysis has been labeled for decades as a promising technique for air purification. The principle seems straightforward and requires a photocatalyst that is immobilized on a substrate, and UV sources to activate the photocatalyst. Yet it seems that the commercialization of photocatalytic systems does not break through on the global market. The aim of this thesis is to identify and tackle the bottlenecks that impede commercialization from an application-oriented approach.
The problem of indoor air pollution is enhanced by the fact that people spend more and more time indoors and that ventilation is kept to a minimum as an energy-saving measure. This inevitably leads to an accumulation of volatile organic compounds (VOCs). Human exposure to VOCs is related to the sick building syndrome leading to complaints such as headache, fatigue and lack of concentration. In addition, exposure to VOCs is related to serious long-term health effects such as cancer or respiratory diseases. Therefore, the integration or retrofitting of a photocatalytic air purifying unit into heating, ventilation and air conditioning (HVAC) equipment has been chosen as an interesting approach.
These ventilation systems are characterized by high flow rates and the necessity of minimal pressure losses. Therefore, the permeability and the available exposed surface were selected as main selection criteria for photocatalytic substrates. After a quantitative analysis of potential substrates, borosilicate glass tubes were selected. Glass tubes can be stacked to constitute a transparent monolithic multi-tube reactor. Moreover, borosilicate glass is relatively inexpensive and has excellent UV-A light transmitting properties.
Since the operation of photocatalytic reactors is based on a complex interaction of physical and chemical processes, mathematical models were developed, supported by experimental data, that include all these phenomena as a tool for reactor design and optimization. Intrinsic kinetic parameters provide the fundamentals for these models as they describe the photocatalytic reaction rate, independent of fluid dynamics, reactor geometry and radiation field. In this work they were estimated by means of a Computational Fluid Dynamics (CFD) study, based on FTIR experiments with a lab scale multi-tube reactor.
Finally, the aforementioned CFD approach was used to obtain insights for the light source configuration in upscaled multi-tube reactors. After taking all these insights and some practical implications into account, a final upscaled multi-tube reactor design was proposed and converted into a first built prototype. Subsequently, it was evaluated according the CEN-EN-16486-1 standard for VOC removal by the external scientific research center ‘CERTECH’.