Optimum Expanded Fraction for an Industrial, Collins-Based Nitrogen Liquefaction Cycle

Area of Science:

• Thermodynamics
• Chemical Engineering
• Cryogenics

Background:

• Industrial nitrogen liquefaction commonly employs Collins topology with variations.
• Optimizing these cycles requires minimizing specific power consumption over maximizing liquid yield.

Purpose of the Study:

• To determine the optimal expansion flow share in industrial Collins-based nitrogen liquefaction cycles.
• To analyze the thermodynamic performance and exergy efficiency of the optimized cycle.

Main Methods:

• Process simulation using Unisim Design R451 with Peng Robinson Equation of State for nitrogen.
• Calculation of optimal expanded flow percentage and specific compression work.
• Exergy analysis to identify exergy destruction points and overall efficiency.

Main Results:

• An optimal expanded flow of 88% was identified, exceeding conventional cycles (75-80%).
• The optimized cycle achieved a specific compression work of 430.7 kWh/ton of liquid nitrogen.
• Exergy analysis indicated a 40.3% exergy efficiency, with significant destruction in post-compression cooling.

Conclusions:

• The study provides an optimized design for industrial nitrogen liquefaction, improving energy efficiency.
• Significant exergy destruction in cooling stages presents opportunities for waste heat recovery and secondary applications.
• The findings challenge conventional assumptions regarding liquid yield versus power consumption.