Enhancing the COP of Natural Gas Liquefaction via Mixed Refrigerants: A Comparative Study of Propane-Based Blends with NH₃, SO₂, and CO₂

The increasing global demand for natural gas as a cleaner energy alternative has intensified the need for more energy-efficient liquefaction technologies. One of the key components in natural gas liquefaction is the refrigeration cycle, where the choice of refrigerant significantly influences system performance. Propane is widely used due to its favorable thermodynamic properties. However, there is growing interest in optimizing its performance through refrigerant blending. This study investigates the impact of different propane-based refrigerant mixtures, namely propane-NH₃, Propane-SO₂, and propane-CO₂ on the coefficient of performance (COP) in a natural gas liquefaction cooling cycle. Simulation results at two operating temperatures (-15.11°C and -20°C) demonstrate that refrigerant composition plays a crucial role in determining system efficiency. At -15.11°C, pure propane exhibited a COP of 2.79, while mixtures with NH₃ and SO₂ significantly improved performance, achieving peak COPs of 6.25 and 6.42, respectively, at a 1:9 mixing ratio. Similar trends were observed at -20°C, where the highest COP values for propane-NH₃ and propane-SO₂ mixtures were 5.79 and 5.96, respectively. In contrast, the propane-CO₂ mixture consistently yielded the lowest COP values, indicating inferior energy efficiency. These findings suggest that incorporating NH₃ or SO₂ into propane-based refrigeration cycles can substantially enhance the energy performance of natural gas liquefaction processes, whereas propane-CO₂ blends may increase energy consumption and operational costs.