Development of a novel multi-loop refrigeration cycle for offshore low-temperature distillation

Refrigeration systems are well-established for natural gas liquefaction operating at cryogenic temperatures. However, refrigeration in the intermediate cryogenic temperature range required for low-temperature distillation (LTD) has received significantly less attention. LTD has emerged as a promising technology for separating CO 2 from CO 2 -rich natural gas, particularly when high methane purity is required. Despite this potential, the development of refrigeration systems specifically designed to support LTD under offshore constraints remains limited. This study proposes a novel process scheme based on multi-loop nitrogen expansion cycle to support LTD for offshore CO 2 removal from natural gas. Nitrogen is selected as the refrigerant due to its inert, non-flammable, and single-component nature, which offers advantages in terms of safety and operational simplicity for offshore installations. Several nitrogen expansion cycles (NEC) are modelled in Aspen HYSYS, including single NEC, dual NEC, and a precooling cycle incorporating CO 2 as the refrigerant. The proposed multi-loop single NEC allocates separate loops to meet different cooling demands within the distillation process, enabling improved temperature matching in heat exchangers. Simulation results show that the multi-loop configuration achieves the highest COP of 0.826 among the evaluated cycles. The proposed configuration also offers practical advantages for offshore applications, including simplified refrigerant inventory, improved operational safety, and compatibility with potential integration into LNG liquefaction facilities. The results demonstrate that nitrogen-based expansion cycles can provide an effective and practical refrigeration solution for supporting low-temperature distillation in offshore CO 2 -rich natural gas processing. • Identified suitable nitrogen cycle for safe and compact offshore application. • Refrigeration cycle modelled with feasible range for low-temperature distillation. • Proposed a novel multi-loop nitrogen expansion cycle for improved efficiency. • Novel refrigeration cycle achieved COP twice the base case.