Roberto L. Romero

Radiation field modelling in photoreactors. I: Homogeneous media

Abstract The present work reports an analysis of the existing models for the description of the radiation field inside photochemical reactors for homogeneous systems. With this purpose incidence and emission models are critically analysed and the contributions of the main research groups are presented. The review classifies the results known up to the present in a methodological way and, as a logical consequence, projects those areas where further work is needed.

A cylindrical photoreactor irradiated from the bottom—I. Radiation flux density generated by a tubular source and a parabolic reflector

Abstract The present work studies the radiant energy field generated by a system made up of an ultraviolet radiation source located at the focal axis of a cylindrical reflector of parabolic cross-section. This system allows us to irradiate a cylindrical photoreactor from the bottom, avoiding the introduction of the source in the reaction space. The equations governing the energy transfer were formulated and solved numerically; to do so, three emission models were applied: the line source model with emission in parallel planes, the line source model with spherical emission, and the extense source model with volumetric emission. The behaviour of each one of these models was comparatively analysed to establish their ability to predict the radiant energy flux density within the reacting space of the photoreactor. A very simple experimental check of the model predictions showed very good agreement only when compared with those of the extense source model with volumetric emission.

Modeling of a fluidized-bed photocatalytic reactor for water pollution abatement

Abstract A system consisting of a fluidized bed of quartz-support particles impregnated with titanium dioxide in a UV-irradiated annular arrangement is presented as an efficient reactor configuration for the photocatalytic oxidation of diluted trichloroethylene in water. A mathematical scheme is developed to analyze the fluidized bed, including a detailed radiation field representation and an intrinsic kinetic scheme. The model is used to predict operating conditions at which good mixing states and fluid renewal rates are accomplished throughout the bed, and to compute contaminant decay. Systems analyzed include a high-pressure Hg lamp, 0.3 m long setup, and an “actinic”, low-pressure lamp in a 1 m long reactor. For relatively high flow rates, per-pass oxidation conversions between 9 and 35% are reached depending on the reactor system considered, and on the titanium oxide concentration in the bed, ranging between 0.1 and 0.5 kg m −3 . Results indicate a strong dependence of reactor performance upon the radiation energy available at each point in the annulus. This availability, in turn, is a fraction of both lamp power and UV-radiation penetration within the bed. For the selected contaminant, the kinetic scheme shows that the low-energy disadvantage in the low-pressure lamp reactor can be compensated by the fact that the radiation field is more evenly distributed throughout the fluidized particle bed.

A cylindrical photoreactor irradiated from the bottom—II. Models for the local volumetric rate of energy absorption with polychromatic radiation and their evaluation

Abstract This study of the radiation field generated in a cylindrical photoreactor irradiated from the bottom presents the theoretical foundations of a method for the experimental verification of three different radiation models. The expressions representing the local volumetric rate of energy absorption (LVREA) were formulated and applied to the prediction of the rate of an actinometric reaction. This reaction takes place inside a microreactor operated in a batch recycling system with polychromatic radiation. The values obtained portray the same behaviour as that of the energy densities calculated previously (Part I), thus becoming a valid, accurate method for the experimental measurement of the absolute values of the radiation field that are sought after (volumetric rate of energy absorption). The proposed approach is able to produce quasi-point values of the absolute values of the VREA at the microreactor as an excellent approximation to the absolute values of the LVREA (local measurements). The present work also points out the qualitative and quantitative discrepancies of the results predicted by the line models when compared with those of the extense source model with volumetric emission.

Modelling and parametric sensitivity of an annular photoreactor with complex kinetics

Abstract This paper reports the behaviour of a continuous annular reactor irradiated with a tubular ultraviolet source placed at its axis, and analyzes the case of a chemical reaction occurring in the homogeneous phase with complex kinetics. The reacting system is analyzed without resorting to the kinetic steady state hypothesis, thus allowing the computation of concentration profiles for the intermediate activated species. Three different models of radiation sources are considered: the line source model with emission in parallel planes, the line source model with spherica We have investigated and evaluated the influence of all significant parameters of the system on the reactant, intermediate species and product concentr