Potential for improving the energy efficiency of cryogenic air separation unit (ASU) using binary heat recovery cycles

Aneke, Mathew; Wang, Meihong

Abstract

In this paper, the potential of improving the energy efficiency of a conventional cryogenic air separation unit (ASU) was investigated through modelling and simulation using Aspen Plus® v 8.1. It is achieved through converting the heat from the compressor effluent to electricity using organic Ranking cycle (ORC). Two different arrangements of combining compressor and waste heat recovery ORC system were compared with the conventional cryogenic ASU which was used as the benchmark. The benchmark is a conventional cryogenic ASU with 3 stages of compression which uses water for intercooling. In the first arrangement the water used as the cooling fluid of the intercooler/after cooler heat exchanger of a conventional cryogenic ASU process was replaced by R134a which also acts as the working fluid for the ORC system (C3WHR) while in the second arrangement, the 3 stages compressor of the conventional process was replaced with a single stage compressor with the same overall pressure ratio as the conventional process and the hot compressor effluent cooled with R134a which also acts as the working fluid of the ORC system (C1WHR). The simulation results based on a cryogenic ASU capable of processing 100 kg/s of atmospheric air at 30 °C as feedstock show that the specific power consumption for the pure products which was 0.32 kWh/kg, 0.37 kWh/kg and 17.35 kWh/kg for oxygen, nitrogen and argon respectively for the conventional cryogenic ASU process was reduced by the addition of the waste heat recovery ORC system. The C1WHR reduced the specific power consumption by an average of 0.2% across the aforementioned pure products while the C3WHR reduced it by an average of 11%. The net power consumption of the conventional cryogenic ASU which was 21826.19 kW was also found to be reduced by the same percentage.

Citation

Aneke, M., & Wang, M. (2015). Potential for improving the energy efficiency of cryogenic air separation unit (ASU) using binary heat recovery cycles. Applied thermal engineering, 81(April), 223-231. https://doi.org/10.1016/j.applthermaleng.2015.02.034

• Journal Article Type: Article
• Acceptance Date: Feb 16, 2015
• Online Publication Date: Feb 24, 2015
• Publication Date: Apr 25, 2015
• Deposit Date: Jun 18, 2015
• Publicly Available Date: Jun 18, 2015
• Journal: Applied thermal engineering
• Print ISSN: 1359-4311
• Electronic ISSN: 1873-5606
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 81
• Issue: April
• Pages: 223-231
• DOI: https://doi.org/10.1016/j.applthermaleng.2015.02.034
• Keywords: Cryogenic air separation unit, Organic Rankine cycle, Waste heat recovery, Compressor heat recovery
• Public URL: https://hull-repository.worktribe.com/output/375543
• Publisher URL: http://www.sciencedirect.com/science/article/pii/S1359431115001428
• Additional Information: Author's accepted manuscript of article which has been published in: Applied thermal engineering, 2015, v.81.