Enhancing energy efficiency: Design and simulation of air fractionation unit integrated through LNG cold energy and two-stage organic Rankine cycles

Abstract

The study explores air separation processes, proposing an innovative design incorporating liquid natural gas (LNG)'s two-stage Rankine cycles to address traditional approaches' complexity and energy intensity. Significant wastage of energy during air compression in standard units is recuperated for liquefied natural gas regasification, with a focus on enhancing cold energy recovery, emphasizing cryogenic LNG advantages. Aspen HYSYS (12.1) is used for process modelling and simulation evaluating a combined two-stage Rankine cycle integrated into air separation. Specific energy requirements for high-purity oxygen and nitrogen production are reduced to 0.38 and 0.12 kWh/kg, respectively. The integrated Rankine cycle generates 4456.32 kW, which is sufficient for air separation process. Exergy destruction and component efficiency are explored and parametric optimization, revealing LNG variables' significant impact. Economic analysis indicates a fair 5.25-year payback period. This approach aligns with sustainability goals, providing a compelling efficiency-enhancing option for the LNG sector.