摘要 |
<p>lmproved oxygen recovery in the operation of a pressure swing adsorption system for air fractionation is obtained by passing the air, freed of water and CO2, through an adsorbent bed maintained at elevated temperature throughout the cycle and which is selective for retention of nitrogen, and consequent withdrawal of any oxygen-rich primary effluent product. Each adsorbent bed of a group of parallel main beds (1, 2, 3, 4), in turn, undergoes the steps of adsorption at highest pressure followed by at least two stages of counter-current desorption by pressure let down and, at the achieved lower pressure level, purging of the bed with part of the primary oxygen-rich effluent. The purged bed is then re- pressured in several stages, first with desorbed gas rich in nitrogen introduced into the bed at the initial air inlet, and then brought to the high adsorption pressure level by introduction in opposite direction of oxygen-rich primary effluent product. In a preferred embodiment ambient air (10) is passed through a pretreater section providing an adsorbent bed (A, B) for removal of water and carbon dioxide. The thus purified air is compressed with consequent rise in temperature and then only partly cooled down by exchange with cooler desorbed and purged nitrogen-rich gas products withdrawn from the main adsorbent beds. These nitrogen-rich products thus heated by the exchange are employed in regenerating a water and carbon dioxide laden bed of the pretreater section. While the adsorption-desorption is operated in a pressure swing cycle, the pretreater section is operated in an independent thermal swing cycle. Alternatively, the feed air may be compressed prior to its introduction into the pretreater and the thus generated heat utilized by heat exchange for heating the purified air effluent to be fractionated.</p> |