Efficiency Study of a Natural Gas Liquefier Using Precooling Driven by Organic Rankine Cycle

Technical and energy analyses of small-scale liquefied natural gas (LNG) plants using a precooling cycle based on the organic Rankine cycle (ORC) were conducted. The first step of the research included modeling and optimization of the natural gas mixed-refrigerant (MR) liquefaction cycle with propane vapor-compression cycle (VCR) precooling. Calculations were used to determine the value of heat and energy flows under various environmental conditions. The second step of the research included a simulation of ORC cycles using values of high-potential heat obtained earlier. The minimum possible cooling temperature was determined as the intersection point between the required cooling capacity and the possible cooling capacity of the ORC–VCR system. Performance data of ORC–VCR-type refrigerators using natural refrigerants were obtained and analyzed, and optimal operational modes were determined. The applicability of the ORC–VCR type refrigerators was considered using obtained data. The potential cost–benefit of the ORC–VCR systems was compared with those of traditional propane VCR systems.

AIMS: Feasibility study of ORC–VCR systems for the preliminary cooling of an autonomous small-scale plant for natural gas liquefaction plants.

MATERIALS AND METHODS: Natural gas liquefaction cycles and ORC–VCR cycles were simulated using the Aspen HYSYS software. Further optimization and parameter selection were performed using the MATLAB module Global Optimization Toolbox.

RESULTS: The cost–benefit value of the ORC–VCR precooling systems compared with the classic propane VCR refrigerators was found to be up to 15%, depending on the type of the Rankine cycle used and the type of working substance.

CONCLUSIONS: The authors analyzed the feasibility of ORC–VCR systems for the preliminary cooling of autonomous small-scale LNG plants. The application of ORC–VCR refrigerators using high-potential heat of exhaust gases from a diesel generator or an electric generator reduced the consumption of natural gas and specific costs of LNG production. The cost–benefit value compared with those of classic propane VCR refrigerators was up to 15%, depending on the type of the Rankine cycle used and the type of working substance.