Optimization of mixed refrigerant system for LNG processes through graphically reducing exergy destruction of cryogenic heat exchangers

Mixed refrigerant (MR) systems are widely employed in natural gas liquefication processes due to the advantage of efficient heat transfer over pure refrigerants. An exergy destruction reduction (EDR) algorithm is proposed to optimize MR composition for energy-efficient natural gas liquefication. Exe...

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Bibliographic Details
Published in:Energy (Oxford) Vol. 168; pp. 200 - 206
Main Authors: Song, Chang, Tan, Shuai, Qu, Fengcheng, Liu, Weidong, Wu, Yong
Format: Journal Article
Language:English
Published: Oxford Elsevier Ltd 01.02.2019
Elsevier BV
Subjects:
Algorithms
Compression
computer software
Destruction
Energy efficiency
energy use and consumption
Exergy
Exergy destruction
Heat exchange
Heat exchangers
Heat transfer
internal temperature
Laws
Liquefaction
Liquefied natural gas
Mixed refrigerant
natural gas
Natural gas liquefaction
Optimization
Optimization main text
Power consumption
Quadratic programming
Refrigerants
Thermodynamics
Optimization main text
Mixed refrigerant
Natural gas liquefaction
Exergy destruction
Heat exchange
ISSN:0360-5442, 1873-6785
Online Access:Get full text
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Summary:Mixed refrigerant (MR) systems are widely employed in natural gas liquefication processes due to the advantage of efficient heat transfer over pure refrigerants. An exergy destruction reduction (EDR) algorithm is proposed to optimize MR composition for energy-efficient natural gas liquefication. Exergy destruction associated with heat transfer is graphically depicted and area of the exergy destruction graph is minimized under the constraint of the minimum internal temperature approach in the heat exchanger. The EDR optimization is performed by directionally regulating individual refrigerant component responsible for decreasing the graphic exergy destruction. The C3MR process is modeled in Aspen HYSYS and the MR systems for the cryogenic heat exchangers are optimized by the programmed EDR solver run in Matlab. The EDR optimization results in 0.2515 kWh·kg−1 specific compression work with 17.7% power consumption savings as compared with the base case. In addition, the exergy destruction rate obtained from the EDR algorithm is 2.9% lower than that from the sequential quadratic programming (SQP) algorithm. The EDR algorithm based on the thermodynamic laws is efficient for optimization of liquefaction processes involving the use of MR system. •Exergy destruction of cryogenic heat exchanger for LNG was graphically analyzed.•Effect of mixed refrigerants on the graphic exergy destruction was evaluated.•Directional regulation of mixed refrigerant minimized exergy destruction efficiently.•The graphic exergy-based optimization resulted in energy-efficient C3MR process.
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ISSN:0360-5442
1873-6785
DOI:10.1016/j.energy.2018.11.105