{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,23]],"date-time":"2026-01-23T15:15:43Z","timestamp":1769181343847,"version":"3.49.0"},"reference-count":38,"publisher":"MDPI AG","issue":"1","license":[{"start":{"date-parts":[[2026,1,21]],"date-time":"2026-01-21T00:00:00Z","timestamp":1768953600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Entropy"],"abstract":"<jats:p>In cryogenic air liquefaction systems, a major share of the mechanical energy consumption is associated with exergy destruction caused by heat transfer in recuperative heat exchangers. This study investigated the exergetic optimization of cryogenic gas separation systems by focusing on the Claude\u2013Heylandt cycle as an advanced structural modification of the classical Linde\u2013Hampson scheme. An exergy-based analysis demonstrates that minimizing mechanical energy consumption requires a progressive reduction in the temperature difference between the hot forward stream and the cold returning stream toward the cold end of the heat exchanger. This condition was achieved by extracting a fraction of the high-pressure stream and expanding it in a parallel expander, thereby creating a controlled imbalance in the heat capacities between the two streams. The proposed configuration reduces the share of exergy destruction associated with heat transfer in the recuperative heat exchanger from 14% to 3.5%, leading to a fourfold increase in the exergetic efficiency, together with a 3.6-fold increase in the liquefied air fraction compared with the Linde\u2013Hampson cycle operating under identical conditions. The effects of key decision parameters, including the compression pressure, imposed temperature differences, and expander inlet temperature, were systematically analyzed. The study was further extended by integrating an air separation column into the Claude\u2013Heylandt cycle and optimizing its configuration based on entropy generation minimization. The optimal liquid-air feeding height and threshold number of rectification trays were identified, beyond which further structural complexity yielded no thermodynamic benefit. The results highlight the effectiveness of exergy-based optimization as a unified design criterion for both cryogenic liquefaction and separation processes.<\/jats:p>","DOI":"10.3390\/e28010125","type":"journal-article","created":{"date-parts":[[2026,1,21]],"date-time":"2026-01-21T13:59:54Z","timestamp":1769003994000},"page":"125","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Optimization of Cryogenic Gas Separation Systems Based on Exergetic Analysis\u2014The Claude\u2013Heylandt Cycle for Oxygen Separation"],"prefix":"10.3390","volume":"28","author":[{"given":"D\u0103nu\u021b-Cristian","family":"Urduza","sequence":"first","affiliation":[{"name":"Department of Engineering Thermodynamics, National University of Science and Technology Politehnica Bucure\u0219ti, 060042 Bucharest, Romania"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0861-3413","authenticated-orcid":false,"given":"Lavinia","family":"Grosu","sequence":"additional","affiliation":[{"name":"Laboratoire Energ\u00e9tique M\u00e9canique Electromagn\u00e9tisme (LEME), IUT de Ville d\u2019Avray, 92410 Ville d\u2019Avray, France"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alexandru","family":"Serban","sequence":"additional","affiliation":[{"name":"Department of Engineering Thermodynamics, National University of Science and Technology Politehnica Bucure\u0219ti, 060042 Bucharest, Romania"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-5317-5659","authenticated-orcid":false,"given":"Adalia Andreea","family":"Percembli (Chelmu\u0219)","sequence":"additional","affiliation":[{"name":"Department of Engineering Thermodynamics, National University of Science and Technology Politehnica Bucure\u0219ti, 060042 Bucharest, Romania"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Alexandru","family":"Dobrovicescu","sequence":"additional","affiliation":[{"name":"Department of Engineering Thermodynamics, National University of Science and Technology Politehnica Bucure\u0219ti, 060042 Bucharest, Romania"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,21]]},"reference":[{"key":"ref_1","unstructured":"European Commission (2025, August 29). 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