Dual Reflux PSA Process Applied to VOC Recovery as Liquid Condensate
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Dual Reflux PSA Process Applied to VOC Recovery as Liquid Condensate REIKO WAKASUGI∗ Department of Applied Chemistry and Biochemistry, Kumamoto University, Kumamoto, Japan [email protected]
AKIO KODAMA Department of Human & Mechanical Systems Engineering, Kanazawa University, Kanazawa, Japan MOTONOBU GOTO AND TSUTOMU HIROSE Department of Applied Chemistry and Biochemistry, Kumamoto University, Kumamoto, Japan
Abstract. A new pressure swing adsorption process was proposed for treatment of low-VOC-concentration air streams. Feed gas is supplied to the high pressure column at some intermediate position to divide it into an enriching and a stripping sections. A part of air stream leaving the high pressure column is returned to the low pressure column as stripping reflux while air stream leaving the low pressure column is returned totally to the high pressure column as enriching reflux. With this dual reflux policy, VOC vapor can be enriched in the enriching section up to a concentration high enough to be condensed in liquid state as well as VOC free air is produced in the stripping section. High efficiency of the dual reflux PSA was confirmed experimentally in a lab-scale unit with a model system of ethanol-activated carbon for various parameters such as half cycle time, feed rate, feed inlet position etc. The optimum feed inlet position was found experimentally and its behavior was interpreted based on an analytical simulation by short cycle time approximation. Keywords: pressure swing adsorption, volatile organic compounds, dual reflux PSA
1.
Introduction
Accumulation of volatile organic compounds (VOCs) in the human body and environment has become a subject of discussion even if very low concentration since VOC emission is one of the major sources of air pollution. Laws and regulations of VOC treatment have been stringent in every country and the technology development in high efficiency removal and recovery is an immediate issue. Now several kinds of treatment method are available in the thermal oxidation, the catalytic combustion and the electron beam decomposition as well as alternatively adsorption technology by thermal swing adsorption (TSA). ∗ To
whom correspondence should be addressed.
Pressure Swing Adsorption (PSA) has been widely utilized for purification and separation of gases by developing various kinds of processes. In recent years PSA has been applied to solvent elimination (Liu et al., 2000) and its demand has increased from viewpoints of compact apparatus, economical energy and so on. To separate and recover very low concentration organic vapor we propose here a new Dual Reflux PSA (DR-PSA) process accompanied with liquid condensation. The DR-PSA has both stripping and enriching processes by setting the feed inlet position at some middle point of an adsorption column (Diagne et al., 1995; Mc Intyre et al., 2002). Concentration of product gas from the adsorption column can be reduced in a stripping section, and at the same time solvent vapor can be enriched in an enriching section to a
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