Absorber Intercooling in CO 2 Absorption by Piperazine-Promoted Potassium Carbonate Jorge M. Plaza, Eric Chen, and Gary T. Rochelle Dept. of Chemical Engineering, The University of Texas at Austin, Austin, TX 78712 DOI 10.1002/aic.12041 Published online November 5, 2009 in Wiley InterScience (www.interscience.wiley.com). Intercooling was evaluated as a process option in CO 2 absorption by piperazine (PZ) promoted potassium carbonate. The system performance with 4.5 m K þ /4.5 m PZ was simulated by a model in Aspen Plus V R RateSep TM . The absorber was evaluated for use with a double matrix stripper by optimizing the position of the semilean feed and intercooling stages to maximize CO 2 removal. Additionally, a simple absorber system was modeled to observe the effect of intercooling on systems with variable CO 2 lean loading. Intercooling increases CO 2 removal by as much as 10% with the double matrix configuration. With a simple absorber, the effectiveness of intercooling depends on solvent rate. Near a critical liquid/gas ratio (L/G) there is a large improvement with intercooling. This is related to the position of the temperature bulge. An approxi- mation is proposed to estimate the critical L/G where intercooling may maximize removal. V V C 2009 American Institute of Chemical Engineers AIChE J, 56: 905–914, 2010 Keywords: CO 2 absorption, temperature bulge, modeling, intercooling, critical L/G Introduction Carbon dioxide capture and sequestration is a major option to reduce greenhouse gases and address global cli- mate change. Chemical absorption is the most attractive technology to reduce CO 2 emissions from coal fired plants. Intercooling is a common strategy to increase the perform- ance of absorption systems. Jackson and Sherwood 1 showed that intercooling increased absorption up to 37% and even higher during the winter in refinery gas absorbers for absorp- tion of C þ 4 from cracking coal gas. Linhoff 2 reports the use of intercooling in a refinery with vapor recovery by an absorp- tion oil. Sobel 3 introduces the use of a computational method for absorbers which routinely include a feature for modeling intercooling. A number of authors have shown that absorber intercooling can be effective with CO 2 capture by amines. 4–7 Patents have also been filed with more complex intercooling configurations to increase absorber performance. 8–10 Intercooling is especially useful for systems where the heat of absorption (i.e., heat of solution and/or reaction) results in an increase in temperature of the solvent affecting the vapor pressure of the dissolved species. Kvamsdal and Rochelle 11 observed this behavior for the absorption of carbon dioxide from flue gas by aqueous monoethanolamine (MEA). They studied absorber parameters such as liquid/gas ratio (L/G), height of packing, and flue gas composition and its effect on the appearance of a temperature bulge in the absorber. Chen 12 observed similar behavior for systems using piperazine- (PZ) promoted potassium carbonate (K þ ). He developed a rate- based absorber model for the mentioned system. The model was originally generated from work carried out by Cullinane 13 and later translated into Aspen Plus V R by Hillard. 14 Chen used the Data Regression System V R in Aspen Plus V R to simultane- ously regress equilibrium constants and interaction parameters to predict equilibrium and speciation. This work uses the tools developed by Chen to analyze a system using a 4.5 m K þ /4.5 m PZ solvent. Different absorber configurations were studied to evaluate the effect of intercooling on absorber performance. Vapor–Liquid Equilibrium (VLE) and Kinetics Model The K þ /PZ solvent was introduced by Cullinane 13 as an alternative to the widely used MEA. MEA has a high Correspondence concerning this article should be addressed to G. T. Rochelle at Rochelle@che.utexas.edu V V C 2009 American Institute of Chemical Engineers AIChE Journal 905 April 2010 Vol. 56, No. 4