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Research Papers

Exergy Analysis of Different Cold End Configurations for Helium Liquefiers

[+] Author and Article Information
Rijo Jacob Thomas

Cryogenic Engineering Centre,  Indian Institute of Technology Kharagpur, Kharagpur 721302, Indiarijojthomas@gmail.com

Parthasarathi Ghosh

Cryogenic Engineering Centre,  Indian Institute of Technology Kharagpur, Kharagpur 721302, Indias.partha.ghosh@gmail.com

Kanchan Chowdhury

Cryogenic Engineering Centre,  Indian Institute of Technology Kharagpur, Kharagpur 721302, Indiachowdhury.kanchan@gmail.com

J. Thermal Sci. Eng. Appl 4(2), 021009 (Apr 20, 2012) (11 pages) doi:10.1115/1.4005730 History: Received August 09, 2011; Revised December 16, 2011; Published April 19, 2012; Online April 20, 2012

Cold end in helium liquefiers, where finally the gas is converted to liquid, may have different alternatives in configuration to achieve maximum exergy efficiency. Apart from high exergy efficiency, which also means low specific power consumption, reliability of operation and complexity of equipment design are also some of the concerns for designers. In this work, various cold end configurations are compared at different operating conditions to help arrive at appropriate choices during design and operation. When single Joule–Thomson valve is replaced by more efficient cold ends with expanders, it allows reduction of the number of Brayton stages in precooling section as well as the total heat exchanger size. Cold end with expander and Joule–Thomson valve combination has been found to be a good compromise between reliability, liquid production, specific power consumption, and exergy efficiency. However, for such a configuration, it is important to fix the intermediate pressure at appropriate level so as to avoid liquid formation at the exit of the expander.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

A typical large-scale helium liquefaction cycle showing the functional sections (GHe, gaseous helium; LHe, liquid helium; GN2 , gaseous nitrogen; LN2 , liquid nitrogen; COMP, compressor unit; HX, heat exchanger; EXP, expander; JT, Joule–Thomson valve; SEP, phase separator; CV, control volume; HP, high pressure; LP, lower pressure; IP, intermediate pressure)

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Figure 2

Large-scale helium liquefaction cycle without liquid nitrogen precooling

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Figure 3

T-s diagram for the helium liquefaction cycle without liquid nitrogen precooling

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Figure 4

Schematic and T-s diagrams of different cold end configurations used in helium liquefaction cycles (CE, cold end; HP, high pressure; LP, low pressure; L, liquid; G, gas)

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Figure 5

Effect of variation in inlet temperature on fraction of liquefaction for isentropic expansion (Process “A-B”) and isenthalpic (Process “C-D”) expansion

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Figure 6

Effect of inlet temperature on cold end exergy efficiency for different configurations

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Figure 7

Exergy expenditure for different cold ends (expander efficiency = 70%, stage inlet pressure = 22 bar, SEP pressure = 1.013 bar, intermediate pressure = 4.66 bar)

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Figure 8

Optimum intermediate pressure for Double JT for different inlet temperatures (JT1 inlet pressure: 22 bar, JT2 discharge pressure: 1.013 bar, HX effectiveness = 0.97)

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Figure 9

Optimum intermediate pressure for Double EXP (EXP1 Inlet pressure: 22 bar, EXP2 discharge pressure: 1.013 bar, Heat exchanger effectiveness =0.97)

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Figure 10

Optimum intermediate pressure for EXP + JT (EXP inlet pressure: 22 bar, JT discharge pressure: 1.013 bar, Heat exchanger effectiveness = 0.97)

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Figure 11

Variation in exergy efficiency of cold ends with nondimensional effective UA

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Figure 12

Exergy expenditure for different cold ends (Expander efficiency = 70%, Stage Inlet pressure = 22 bar, SEP pressure = 1.013 bar, optimum intermediate pressures and saturated effective UA condition)

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Figure 13

Cold box exergy efficiency as a function of total heat exchanger area with different cold ends as parameter

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Figure 14

Variation of cold end inlet temperature for the different cold ends attached to Config.4-1

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Figure 15

Comparison of different cold ends on the basis of different objective functions

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