Dual-effect single-mixed refrigeration cycle: An innovative alternative process for energy-efficient and cost-effective natural gas liquefaction

Typical liquefaction processes are considered to be energy and cost-intensive. The dual mixed refrigerant (DMR) process (with two independent refrigeration cycles for cooling and subcooling) produces liquefied natural gas (LNG) at relatively high energy efficiency. However, it exhibits a high degree of configurational complexity and high sensitivity to operational conditions, and it also incurs a large capital investment. These factors eventually reduce the overall competitiveness of the liquefaction process, particularly for offshore applications. To address these issues, an energy- and cost-efficient dual-effect single mixed refrigerant (DSMR) process is proposed herein, and it employs a single loop refrigeration cycle to generate the dual cooling and subcooling effect, separately. The DMR process and the proposed DSMR process are simulated (with same design parameters) using well-known commercial simulator Aspen Hysys v10. Then, both processes are optimized using modified coordinate descent algorithm. The specific energy consumption of DSMR is 0.284 kWh/kg-NG, which is equivalent to an energy saving of 22.89% when compared to the conventional DMR process. The exergy efficiency of DSMR is 36.62%, which is 29.67% higher than that of the classical DMR process. Furthermore, the economic feasibility of the proposed DSMR process is evaluated in terms of its total annualized cost, which is 18.52% lower than that of the DMR process. Thus, the proposed DSMR process offers remarkable energy and exergy efficiencies with minimal capital investment. Therefore, DSMR could replace the classical DMR process, as well as other complex mixed refrigerant-based liquefaction processes.