Investigation and thermodynamic analysis of hydrogen liquefaction cycles: Energy and exergy study

The use of hydrogen as a clean fuel has drawn the attention of many scientists due to the problem of energy and environmental pollution caused by fossil fuels. One of the important requirements for expanding the use of hydrogen is the investigation and thermodynamic analysis of liquefaction cycle; this includes the thermodynamic investigation of different cycles of hydrogen liquefaction in pre-cooling and cryogenic cooling. Thermodynamic analysis comprises an examination of the cycle's energy and exergy, as well as the equipment employed. In this research, three liquefaction cycles with different pre-cooling cycle and cryo-cooling cycle have been evaluated. The use of organic Rankine cycle ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>O</mml:mi> <mml:mi>R</mml:mi> <mml:mi>C</mml:mi></mml:mrow> </mml:math> ) and liquefied natural gas ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>L</mml:mi> <mml:mi>N</mml:mi> <mml:mi>G</mml:mi></mml:mrow> </mml:math> ) has also been applied in the cycles and the arrangement of the equipment. Simulations and analyzes have been done in Aspen HYSYS V12. The results show that in the pre-cooling process of cycles 1, 2, and 3, the amount of useful exergy is 49.87 %, 58.87 %, and 61.21 %, respectively, which means that the third cycle uses the input exergy better. Also, in the pre-cooling process of cycles 1, 2, and 3, the amount of exergy loss is 33.86 %, 26.77 %, and 19.73 %, respectively, which means that the third cycle has less exergy loss in the pre-cooling process. The findings indicate that in each of the three cycles, over 50 % of the input exergy is wasted in the cryo-cooling process. Value of specific energy consumption ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>SEC</mml:mi></mml:mrow> </mml:math> ) for cycle 1,2, and 3 is equal to 6.605 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>k</mml:mi> <mml:mi>W</mml:mi> <mml:mi>h</mml:mi> <mml:mo>/</mml:mo> <mml:msub><mml:mrow><mml:mi>k</mml:mi> <mml:mi>g</mml:mi></mml:mrow> <mml:mrow><mml:mi>L</mml:mi> <mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , 6.601 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>k</mml:mi> <mml:mi>W</mml:mi> <mml:mi>h</mml:mi> <mml:mo>/</mml:mo> <mml:msub><mml:mrow><mml:mi>k</mml:mi> <mml:mi>g</mml:mi></mml:mrow> <mml:mrow><mml:mi>L</mml:mi> <mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> and 6.618 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>k</mml:mi> <mml:mi>W</mml:mi> <mml:mi>h</mml:mi> <mml:mo>/</mml:mo> <mml:msub><mml:mrow><mml:mi>k</mml:mi> <mml:mi>g</mml:mi></mml:mrow> <mml:mrow><mml:mi>L</mml:mi> <mml:msub><mml:mi>H</mml:mi> <mml:mn>2</mml:mn></mml:msub> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , respectively. The three cycles under examination had COP values of 0.19945, 0.19936, and 0.19884, in that order. Also, the values for EXE cycles 1, 2, and 3 are 45.816 %, 45.883 %, and 45.797 %, respectively. Analyzing the energy and exergy of liquefaction cycles is a good step toward increasing cycle efficiency, identifying weak places, and altering cycles to improve efficiency.