Performance analysis and comparison of gas liquefaction cycles

Gas liquefaction cycles are an important application of cryogenics and liquefied gases are used in variety of industries and processes. Gas liquefaction cycles are massive energy consumers. Therefore, their design and operation should be optimized thermodynamically and economically to minimize the energy consumption and cost. In this thesis, thermodynamic and economic assessment of commonly used gas liquefaction cycles including simple Linde-Hampson, precooled Linde-Hampson, Claude and Kapitza cycles were performed. The cycles were modeled in computer environment for various gases including air, nitrogen, oxygen, argon, fluorine, and methane. Thermodynamic performance parameters including liquid yield, liquefaction work, COP, and second law efficiency; and economic parameters including specific product cost and specific energy cost were calculated for all considered cycles and gases. The fraction of the gas that was liquefied (i.e., liquid yield) is determined to be in the range of 0.07 - 0.20, 0.13 - 0.33, 0.22 - 0.26, and 0.09 - 0.1 for simple Linde-Hampson, precooled Linde-Hampson, Claude and Kapitza cycles, respectively. The second law efficiencies are determined to be 0.12 - 0.27, 0.22 - 0.45, 0.76 - 0.82 and 0.43 - 0.46 for the same cycles, respectively. Parametric studies are carried out to investigate effects of compressor inlet temperature, compressor outlet pressure, compressor isothermal efficiency, minimum temperature difference in heat exchanger, and turbine isentropic efficiency on the thermodynamic and economic performance parameters. An economic comparison of the cycles indicates that Kapitza cycle has the highest specific product cost followed by simple Linde-Hampson cycle, precooled Linde-Hampson cycle, and Claude cycle. It also appears that for large scale applications, Claude and precooled Linde-Hampson cycles are most suitable options both thermodynamically and economically. Key words: Cryogenics, gas liquefaction, thermodynamic analysis, economic analysis, Claude cycle, Linde-Hampson cycle