Influence of Expanded-Air Fraction on Product Distribution and Energy Performance of Turboexpander and Joule–Thomson Refrigeration Systems in Double-Column Cryogenic Air Separation Units

Ratri Puspita Wardani; Mohammad Irwan Fatkhur Rozy; Amani Salsabil Husodo; Alifah Nur Aini Fajrin; Fitria Dwi Andriani; Kharin Nova Ledya Rezkirana; Siti Fatimatus Zahro

doi:10.29017/scog.v49i3.2136

Authors

Ratri Puspita Wardani Universitas Pembangunan Nasional Veteran Jawa Timur https://orcid.org/0009-0009-8715-7660
Mohammad Irwan Fatkhur Rozy Institut Teknologi Sepuluh Nopember https://orcid.org/0000-0002-4810-6141
Amani Salsabil Husodo Universitas Pembangunan Nasional Veteran Jawa Timur https://orcid.org/0009-0005-3282-4586
Alifah Nur Aini Fajrin Universitas Pembangunan Nasional Veteran Jawa Timur https://orcid.org/0009-0001-7800-658X
Fitria Dwi Andriani Universitas Pembangunan Nasional Veteran Jawa Timur https://orcid.org/0009-0002-9727-8756
Kharin Nova Ledya Rezkirana Universitas Pembangunan Nasional Veteran Jawa Timur
Siti Fatimatus Zahro Universitas Pembangunan Nasional Veteran Jawa Timur

DOI:

https://doi.org/10.29017/scog.v49i3.2136

Keywords:

cryogenic air separation unit, Joule–Thomson valve, industrial gas, process simulation, specific power consumption, SDG 7

Abstract

Cryogenic air separation units (ASUs) are the most widely applied technology for producing high-purity oxygen and nitrogen for industrial applications. Conventional double-column ASUs generally employ either turboexpander- or Joule–Thomson (JT) valve-based refrigeration systems, whose refrigeration performance strongly influences product distribution and overall energy consumption. Since the amount of refrigeration generated by a turboexpander depends on the fraction of compressed air directed to the expansion process, optimizing the expanded-air fraction offers a promising approach to improve the energy performance of cryogenic ASUs. This study investigates the effect of expanded-air fraction on the performance of a cryogenic ASU and compares turboexpander- and Joule–Thomson (JT) valve-based refrigeration systems using Aspen HYSYS simulation. The simulation was performed using a feed air flow rate of 12,000 kmol.h⁻¹ at 30°C and atmospheric pressure, while the expanded-air fraction in the turboexpander configuration was varied from 20% to 50% of the total feed airflow. Increasing the expanded-air fraction enhanced refrigeration generation and power recovery, resulting in lower column thermal duties and specific power consumption. Gaseous nitrogen production increased from 2,418 to 5,055 kmol.h⁻¹, while liquid nitrogen production decreased from 7,000 to 4,375 kmol.h⁻¹. Temperature profile analysis of the low-pressure column showed that additional refrigeration lowered the operating temperature and improved vapor–liquid equilibrium, promoting oxygen enrichment in the liquid phase and nitrogen enrichment in the vapor phase. Consequently, oxygen purity increased from 97.4% to 98.0%, while nitrogen and oxygen recoveries remained above 99%. The optimum performance was obtained at 50% expanded air, achieving the lowest specific power consumption of 354.5 kWh.ton⁻¹ GOX. Compared with the JT valve configuration, the turboexpander reduced the specific power consumption by approximately 6.1% owing to simultaneous refrigeration generation and mechanical work recovery. These findings demonstrate that optimizing the expanded-air fraction provides an effective operational strategy for improving both product flexibility and energy efficiency in double-column cryogenic ASUs.

References

Chen, S. J., & Yu, B. Y. (2021). Rigorous simulation and techno-economic evaluation on the hybrid membrane/cryogenic distillation processes for air separation. Journal of the Taiwan Institute of Chemical Engineers, 127, 56–68. https://doi.org/10.1016/j.jtice.2021.08.001

Cheng, M., Verma, P., Yang, Z., & Axelbaum, R. L. (2022). Flexible cryogenic air separation unit—An application for low-carbon fossil-fuel plants. Separation and Purification Technology, 302. https://doi.org/10.1016/j.seppur.2022.122086

Erdöl, H. B., Şahin, F. İ., & Acaralı, N. (2024). Novel Study on Cryogenic Distillation Process and Application by Using CHEMCAD Simulation. ACS Omega, 9(13), 15165–15174. https://doi.org/10.1021/acsomega.3c09490

Huo, C., Sun, J., & Song, P. (2023). Energy, exergy and economic analyses of an optimal use of cryogenic liquid turbine expander in air separation units. Chemical Engineering Research and Design, 189, 194–209. https://doi.org/10.1016/j.cherd.2022.11.030

Klein, H., Fritsch, P., Haider, P., Kender, R., Rößler, F., Rehfeldt, S., Freko, P., Hoffmann, R., Thomas, I., & Wunderlich, B. (2021). Flexible Operation of Air Separation Units. In ChemBioEng Reviews (Vol. 8, Number 4, pp. 357–374). John Wiley and Sons Inc. https://doi.org/10.1002/cben.202100023

Perry, R. H. , & Green, D. W. (2019). Perry’s Chemical Engineers’ Handbook (9th Edition). McGraw-Hill Education.

Piguave, B. V., Salas, S. D., De Cecchis, D., & Romagnoli, J. A. (2022). Modular Framework for Simulation-Based Multi-objective Optimization of a Cryogenic Air Separation Unit. ACS Omega, 7(14), 11696–11709. https://doi.org/10.1021/acsomega.1c06669

Seader, J. D., Henley, E. J., & Roper, D. K. (2024). Separation Process Principle (4th Edition). John Wiley & Sons.

Shingan, B., Vijay, P., & Pandiyan, K. (2023). Cryogenic Air Separation Process Integrated with Cold Utilization of Liquefied Natural Gas: Design, Simulation and Performance Analysis. Arabian Journal for Science and Engineering, 48(12), 16921–16940. https://doi.org/10.1007/s13369-023-08218-5

Smith, J. M., Van Ness, • H C, Abbott, • M M, & Swihart, • M T. (2021). Introduction to Chemical Engineering Thermodynamics (9th Ed). McGraw-Hill Education.

Ye, H., Zheng, J., & Li, Y. (2019). Feasibility analysis and simulation of argon recovery in low oxygen-purity cryogenic air separation process with low energy consumption. Cryogenics, 97, 109–121. https://doi.org/10.1016/j.cryogenics.2018.11.006

Young, A. F., Villardi, H. G. D., Araujo, L. S., Raptopoulos, L. S. C., & Dutra, M. S. (2021). Detailed Design and Economic Evaluation of a Cryogenic Air Separation Unit with Recent Literature Solutions. Industrial and Engineering Chemistry Research, 60(41), 14830–14844. https://doi.org/10.1021/acs.iecr.1c02818