Process knowledge based opportunistic optimization of the N2–CO2 expander cycle for the economic development of stranded offshore fields

• A novel opportunistic optimization algorithm was developed for the N2–CO2 system.
• The optimization method was inspired by process knowledge.
• Energy savings and process understanding were achieved simultaneously.
• The proposed optimization makes the N2–CO2 expander system more competitive.
• The methodology can be generalized easily for any expander process.

Several small scale natural gas (NG) liquefaction processes, such as N2–CO2 expander processes, are attracting considerable attention. The inherent safety of operation and the smaller footprints make this process suitable for the economic development of stranded offshore NG fields. Unlike the mixed refrigerant process, a higher energy demand is an unusual concern with N2–CO2 expander processes. Therefore, optimization of this process is carried out to make it competitive with other technologies. This paper presents an opportunistic optimization algorithm inspired by in-depth process analysis coupled with a rigorous simulation. The optimization method shows an energy saving of 15% compared to the base case and provides process understanding. The strong point of the proposed optimization methodology is that it can be modified easily and generalized for any expander-based NG liquefaction process.