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Article

Optimum Expanded Fraction for an Industrial, Collins-Based Nitrogen Liquefaction Cycle

1
ETSI Industriales, Universidad Politécnica de Madrid (UPM), José Gutiérrez Abascal 2, 28006 Madrid, Spain
2
Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Cerámica y Vidrio. Kelsen 5, Campus de Cantoblanco, 28049 Madrid, Spain
*
Authors to whom correspondence should be addressed.
Entropy 2020, 22(9), 959; https://doi.org/10.3390/e22090959
Received: 1 August 2020 / Revised: 21 August 2020 / Accepted: 28 August 2020 / Published: 30 August 2020
(This article belongs to the Special Issue Thermodynamic Optimization of Complex Energy Systems)
Industrial nitrogen liquefaction cycles are based on the Collins topology but integrate variations. Several pressure levels with liquefaction to medium pressure and compressor–expander sets are common. The cycle must be designed aiming to minimise specific power consumption rather than to maximise liquid yield. For these reasons, conclusions of general studies cannot be extrapolated directly. This article calculates the optimal share of total compressed flow to be expanded in an industrial Collins-based cycle for nitrogen liquefaction. Simulations in Unisim Design R451 using Peng Robinson EOS for nitrogen resulted in 88% expanded flow, which is greater than the 75–80% for conventional Collins cycles with helium or other substances. Optimum specific compression work resulted 430.7 kWh/ton of liquid nitrogen. For some operating conditions, the relation between liquid yield and specific power consumption was counterintuitive: larger yield entailed larger consumption. Exergy analysis showed 40.3% exergy efficiency of the optimised process. The exergy destruction distribution and exergy flow across the cycle is provided. Approximately 40% of the 59.7% exergy destruction takes place in the cooling after compression. This exergy could be used for secondary applications such as industrial heating, energy storage or for lower temperature applications as heat conditioning. View Full-Text
Keywords: large-scale Collins cycle; thermodynamic analysis; exergy analysis; optimisation; nitrogen liquefaction; exergy efficiency; optimum expander flow; specific power consumption; liquid yield large-scale Collins cycle; thermodynamic analysis; exergy analysis; optimisation; nitrogen liquefaction; exergy efficiency; optimum expander flow; specific power consumption; liquid yield
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MDPI and ACS Style

Arnaiz-del-Pozo, C.; López-Paniagua, I.; López-Grande, A.; González-Fernández, C. Optimum Expanded Fraction for an Industrial, Collins-Based Nitrogen Liquefaction Cycle. Entropy 2020, 22, 959. https://doi.org/10.3390/e22090959

AMA Style

Arnaiz-del-Pozo C, López-Paniagua I, López-Grande A, González-Fernández C. Optimum Expanded Fraction for an Industrial, Collins-Based Nitrogen Liquefaction Cycle. Entropy. 2020; 22(9):959. https://doi.org/10.3390/e22090959

Chicago/Turabian Style

Arnaiz-del-Pozo, Carlos, Ignacio López-Paniagua, Alberto López-Grande, and Celina González-Fernández. 2020. "Optimum Expanded Fraction for an Industrial, Collins-Based Nitrogen Liquefaction Cycle" Entropy 22, no. 9: 959. https://doi.org/10.3390/e22090959

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