Adsorption (2008) 14: 399–413 DOI 10.1007/s10450-008-9102-4 Heavy reflux PSA cycles for CO 2 recovery from flue gas: Part I. Performance evaluation Steven P. Reynolds · Amal Mehrotra · Armin D. Ebner · James A. Ritter Received: 30 April 2007 / Revised: 3 January 2008 / Accepted: 16 January 2008 / Published online: 31 January 2008 © Springer Science+Business Media, LLC 2008 Abstract This study evaluated nine stripping PSA cycle configurations, all with a heavy reflux (HR) step, some with a light reflux (LR) step, and some with a recovery (REC) or feed plus recycle (F+R) step, for concentrating CO 2 from stack and flue gas at high temperature (575 K) us- ing a K-promoted HTlc. Under the process conditions stud- ied, the addition of the LR step always resulted in a bet- ter process performance; and in all cases, the addition of a REC or F+R step surprisingly did not affect the process per- formance except at low feed throughputs, where either cy- cle step resulted in a similar diminished performance. The best cycle based on overall performance was a 5-bed 5-step stripping PSA cycle with LR and HR from countercurrent depressurization (CnD) (98.7% CO 2 purity, 98.7% CO 2 re- covery and 5.8 L STP/hr/kg feed throughput). The next best cycle was a 5-bed 5-step stripping PSA cycle with LR and HR from LR purge (96.5% CO 2 purity, 71.1% CO 2 recov- ery and 57.6 L STP/hr/kg feed throughput). These improved performances were caused mainly by the use of a very small purge to feed ratio (γ = 0.02) for the former cycle and a larger one (γ = 0.50) for the latter cycle. The former cycle was good for producing CO 2 at high purities and recoveries but at lower feed throughputs, and the latter cycle was use- ful for obtaining CO 2 at high purities and feed throughputs but at lower recoveries. The best performance of a 4-bed 4-step stripping PSA cycle with HR from CnD was disap- pointing because of low CO 2 recoveries (99.2% CO 2 purity, 15.2% CO 2 recovery and 72.0 L STP/hr/kg feed through- put). This last result revealed that the recoveries of this cycle S.P. Reynolds · A. Mehrotra · A.D. Ebner · J.A. Ritter ( ) Department of Chemical Engineering, Swearingen Engineering Center, University of South Carolina, Columbia, SC 29208, USA e-mail: ritter@engr.sc.edu would always be much lower than the corresponding cycles with a LR step, no matter the process conditions, and that the LR step was very important to the performance of these HR cycles for this application and process conditions stud- ied. Keywords Pressure swing adsorption · Dual reflux · Stripping PSA · Rinse step · Recovery step · Feed plus recycle step · Heavy reflux · Light reflux · Carbon dioxide capture · Global warming 1 Introduction The production and subsequent release of carbon dioxide into the atmosphere, no matter the source, is becoming an increasingly serious issue with respect to its affect on global warming (White et al. 2003). As one of the more familiar greenhouse gases, carbon dioxide has the ability to warm the planet by trapping energy radiated from the surface of the earth that would otherwise be released to space. One of the major sources of carbon dioxide release into the at- mosphere is through the burning of fossil fuels for energy, which unfortunately makes it ubiquitous. A considerable effort is underway worldwide to curb CO 2 emissions from coal fired and other fossil fuel based power plants, because these plants are responsible for over 40% of the carbon dioxide emissions in the USA alone (Ebner and Ritter 2007). The goal is to capture CO 2 from stack or flue gas, concentrate it to around 90 to 95 vol%, and sequester it somewhere in the Earth. Viable CO 2 capture options include absorption, cryogenic condensation, adsorp- tion, and membrane technologies. To date, however, none of these technologies is economically feasible; so, considerable