Single mixed refrigerant LNG process: Investigation of improvement potential, operational optimization, and real potential for further improvements

Abstract

The single mixed refrigerant (SMR) process is categorized as one of the most promising candidates for LNG-FPSO (floating production storage and offloading) projects as well as small-scale applications, owing to its simple and compact design. Nevertheless, high energy consumption is one of the major issues associated with the SMR processes. This study presents a systematic approach that includes identifying the improvement potentials in the existing SMR process, operational optimization of the system according to those potentials, and uncovering the real potential for further enhancements in the optimized process. To this end, the sources of irreversibilities are identified using an advanced exergy analysis in order to identify further potential of an improvement. The results reveal that 43% of the overall exergy destruction associated with the Base Case (Case I) of the SMR process can be avoided by either optimization or process retrofitting/revamping. Considering this improvement potential, the multivariate Coggins optimization (MCO) approach is applied and specific energy consumption value of 0.35 kWh/kg-NG is achieved leading to 18% energy savings with 77% overall exergy efficiency. The large difference between the exogenous and endogenous exergy destructions indicates that the interconnection between the process equipment is extremely weak, and that the performance of the equipment involved does not have a significant effect on the efficiency of the other equipment. Composite curves analysis is performed to analyze the performance of the LNG cryogenic heat exchanger before and after the application of the MCO approach. To determine economic feasibility and savings, economic analysis is executed that determine the 18% and 16.4% savings for operating cost and total annualized cost, respectively.