CINDECA   05422
Unidad Ejecutora - UE
congresos y reuniones científicas
Analysis of an Adsorption/Desorption Cycle used as a Concentrator for the Catalytic Incineration of VOCs
Simposio; FOA11: 11th internacional Symposium on the Fundamentals of Adsorption; 2013
Institución organizadora:
Internacional Adsorption Society (IAS)
Analysis of an Adsorption/Desorption Cycle used as a Concentrator for the Catalytic Incineration of VOCs María A. Campesi*, Guillermo F. Barreto and Osvaldo M. Martínez PROIRQ, Facultad de Ingeniería (UNLP) 1 y 47, CP: 1900, La Plata, Argentina CINDECA, CCT La Plata (CONICET-UNLP), 47 Nº 257, CP B1900AJK, La Plata, Argentina The growth of industrial production has been one of the principal causes of the significant increase of air pollution. Volatile organic compounds (VOCs) are an important class of air pollutants. Particularly, ethyl acetate and ethanol, employed as solvent in printing processes, are typical VOCs released by the manufacture of packaging. The purification of an airstream containing these substances is taken as the base case for this study. Technologies for removal of VOCs from effluents (mainly air) are classified in destructive and recuperative. The specific purpose and/or the economical analysis of the treatment are key factors in choosing one or the other type of options [1]. Catalytic oxidation is the most widespread choice among destructive alternatives. The use of a catalyst allows much lower operating temperatures than thermal oxidation. Even so, current catalytic materials require temperatures well above ambient levels. Although depending on the type of VOC, typical values are not lower than around 200 °C. Very often a large flow rate of VOC laden air at nearly ambient temperature has to be treated, 5-50 Nm3/s being a typical order of magnitude. As a consequence, catalytic oxidation needs bulky catalyst beds and preheating of the incoming effluent with the clean exit stream requires a large exchange surface area, due to the high flow rates and the low thermal driving force. The latter is virtually fixed by the adiabatic temperature rise ΔTad. Concentration of VOCs by including a thermal swing adsorption cycle as a previous step to catalytic incineration [2], named combined system, is an alternative for reducing significantly the sizes of catalyst bed and heat exchanger. The aim of this study is to analyze by simulation the behavior of the adsorption/desorption system, with the purpose of sizing the system and choosing suitable operating conditions. The study was focused on the desorption flow rate, which determines the stream to be fed to the catalytic incinerator. Then, should be as low as possible for increasing the degree of VOCs concentration. The effect of the desorption temperature (TdesWdesWdes) and the amount of adsorbent on is specifically investigated. desW Based on the characteristics of the adsorption/desorption systems and the properties of the stream to be treated, a monolithic rotary concentrator is adopted using activated carbon as adsorbent material. To carry out the simulation of the system a model is proposed which takes into account the heat and mass transfer resistances inside and outside the adsorbent [3]. To carry out the simulation, operative conditions and geometrical characteristics of the concentrator must be proposed. Then, transient adsorption and desorption stages are simulated until each hemi-stage cycles reach a stable condition (cyclic steady state). This procedure was repeated for decreasing desorption flow rate,, until a limiting value, defined as , is attained. Cyclic steady state can not be reached if values of lower than are employed. desWmindesWdesWmindesW Figure 1 shows the effect of the adsorbent volume (Vads) on the value of for two different TmindesWdes. It can be appreciated from figure 1 that increasing Vads above a certain level allows only a marginal decrease of ; therefore, very large VmindesWads can be regarded as being useless. In contrast, low values of Vads lead to a fast increase in , a fact that brings a loss of efficiency and low capacity to deal with variable operating conditions. Therefore, intermediate values, approximately defined by the range 1.5