LAUSR

Abstract Generally speaking, natural cold sources, such as seawater or air, are often used in natural gas liquefaction processes to cool the compressed refrigerant and natural gas. Since both the required refrigeration and the performance of compressors are closely related to ambient temperature, natural gas plants are designed according to summer operating conditions, because the highest ambient temperature in summer results in the highest refrigeration requirement of the system. However, in winter conditions, with the decline of ambient temperature, precooling by natural cold source can reach lower temperature. When the cooling capacity of natural cold sources is fully utilized, the already built natural gas liquefaction plant can not only reduce energy consumption, but also increase production in winter. To realize cleaner production, this paper comparatively investigated the potential of three mixed refrigerant liquefaction processes, which includes the single mixed refrigerant (SMR), dual mixed refrigerant (DMR) and propane precooled mixed refrigerant (C3MR) processes, for energy reduction and production increase in winter. Based on the optimal conditions under different ambient temperature obtained by genetic algorithm, the specific power consumption, heat transfer performance, as well as changes of typical process parameters such as the flow rate and composition of mixed refrigerants are studied to analyze the effect of natural cold source on the process. When the ambient precooling temperature drops from 40 °C to 10 °C, the specific power consumption of the three processes declines by 20.84%–24.97%, and when it drops to −10 °C, the specific power consumption of the three processes can be reduced by 34.31%–40.53%, which means huge benefit of power-saving. While keeping the volume flow of the compressor in winter the same as that in summer, the SMR process and C3MR process have the largest (26.6%–54.6%) and smallest (16.1%–25.4%) production increase potentials, respectively. Further study is conducted to analyze the load changes of key equipment and economic benefits after changing into energy saving mode or production increase mode in winter. The results indicate that both mode in winter is feasible for the processes with the help of natural cold source, and this may bring considerable increase in economic profits.