Separation Science and Technology, 49: 2105–2113, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 0149-6395 print / 1520-5754 online DOI: 10.1080/01496395.2014.907316 Energy and Exergy Evaluation of an Air Separation Facility: A Case Study Emin Açıkkalp, 1 Hasan Yamık, 1 Necmettin Caner, 2 and Erol Açıkkalp 2 1 Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Bilecik S.E. University, Bilecik, Turkey 2 Department of Chemistry, Faculty of Arts and Sciences, Eskisehir Osmangazi University, Eskisehir, Turkey In this study, an air separation plant working according to the principle of separation of two columns and producing argon, nitro- gen, and oxygen with a daily capacity of 250 tons was analyzed in detail with respect to the first and second laws of thermody- namics and the results were evaluated. The energy and exergy values for each point defined in the system were obtained. By using these values, thermodynamic evaluations for both the whole sys- tem and also its components were made. The efficiency values of energy and exergy, the values of energy losses and exergy destruction rates, the EIP (energetic improvement potential rate), ExIP (exergetic improvement potential rate), and the produc- tion of entropy values were found as 0.453, 0.79, 4368.475 kW, 10535.875 kW, 2391.535 kW, 3800.485 kW, and 35.347 kW/K, respectively. The energy and exergy efficiencies of the plant were found to be 45.3% and 13.1% respectively. Keywords air separation; energy analysis; exergy analysis; energy efficiency; exergy efficiency INTRODUCTION The separation of air into its components is carried out for industrial and medical use. The widest use of nitrogen is as an inert blanking gas and as a reactant in chemical processes. Oxygen is used both for industrial and medical purposes. There are three methods of air separation commercially available: the cryogenic distillation process, the pressure swing adsorp- tion (PSA) process, and the membrane separation process. The cryogenic distillation is used when high purity of the products is needed. The PSA process becomes interesting from a com- mercial point of view when a nitrogen flow between 10 and Address correspondence to Emin Açıkkalp, Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Bilecik S.E. University, Bilecik, Turkey. E-mail: eacikkalp@ gmail.com Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsst. 100 m 3 /h is needed with a purity of 98 to 99.5 vol%. Membrane separation is used for small flows, less than 10 m 3 /h, and low purity, lower than 98.5 vol%. Cryogenic distillation is required when the products are needed in a liquid form (1). The first steps in a cryogenic air separation facility are compressing the feed air and removing water, carbon dioxide, and other hydrocar- bon contaminants. The resulting mixture consists of nitrogen, oxygen, argon, and some traces of other noble gases. Then, the cleaned air is cooled to cryogenic conditions in the MHE (main heat exchanger) and subsequently fed to the distillation unit. The distillation unit separates the air into an oxygen stream and a nitrogen stream but sometimes an argon stream is pro- duced as well. The product streams are passed again through the MHE and compressed or pumped to pressures that are required downstream of the air separation facility. There exists a wide variety of process designed for the cryogenic separation of air. The main differences are related to the method used for pro- viding refrigeration, to the method used for pressurizing the products, to the operating pressures, and to the column con- figuration in the distillation section. The type of process chosen depends usually on the feed and product specifications of the specific application (2). Although there are a lot of studies in the literature about air separation units, evaluation of their performance using energy and exergy analyses are limited. The papers about exergy analysis at air separation units can be seen at (1-6). As referred to above, this study is all the more important because air separation units are mostly used as utility plants in most industries. Energy and exergy analyses are the most convenient methods to assess the performance of any system. In this study, energy and exergy analysis of an air separation plant which produces nitrogen, oxygen and argon with a capac- ity of 250 tons/day at Turkey was made and the results were evaluated. There have not been any studies about energy and exergy assessment of an air separation facility at Turkey as of yet. In addition to that, it is the most comprehensive research in the literature about evaluating performance of an air separation facility. 2105