Abstract
Propane-Precooled Mixed Refrigerant (C3MR) and Single Mixed Refrigerant (SMR) processes are considered as optimal choices for onshore and offshore natural gas liquefaction, respectively. However, from thermodynamics point of view, these processes are still far away from their maximum achievable energy efficiency due to nonoptimal execution of the design variables. Therefore, Liquefied Natural Gas (LNG) production is considered as one of the energy-intensive cryogenic industries. In this context, this study examines a single-solution-based Vortex Search (VS) approach to find the optimal design variables corresponding to minimal energy consumption for LNG processes, i.e., C3MR and SMR. The LNG processes are simulated using Aspen Hysys and then linked with VS algorithm, which is coded in MATLAB. The results indicated that the SMR process is a potential process for offshore sites that can liquefy natural gas with 16.1% less energy consumption compared with the published base case. Whereas, for onshore LNG production, the energy consumption for the C3MR process is reduced up to 27.8% when compared with the previously published base case. The optimal designs of the SMR and C3MR processes are also found via distinctive well-established optimization approaches (i.e., genetic algorithm and particle swarm optimization) and their performance is compared with that of the VS methodology. The authors believe this work will greatly help the process engineers overcome the challenges relating to the energy efficiency of LNG industry, as well as other mixed refrigerant-based cryogenic processes.
Highlights
The continuous growth of human society will adversely affect the world energy requirements in the near future [1]
It can be observed that there is a larger gap between the temperature-heat flow composite curves (THCC) of base case and the Vortex Search Optimization (VSO)-optimized Single Mixed Refrigerant (SMR); especially in a temperature range of −70 to 40 ◦ C
This large gap indicates the exergy destruction inside the cryogenic Liquefied Natural Gas (LNG) heat exchanger, which leads to low energy efficiency
Summary
The continuous growth of human society will adversely affect the world energy requirements in the near future [1]. The optimal execution (i.e., via determining the optimal operating pressures and composition of the mixed refrigerant) of the liquefaction processes is minimized by the overall compression power [11,12] This eventually enhances process efficiency by exploiting economic advantages with low energy requirements. The proposed selection criteria were applied to the MR used in SMR and C3MR system; and a decrease in energy consumption for compression was observed In another similar study, Xu et al [29] developed a correlation between the ambient temperature and mixed refrigerant composition to evaluate energy utilization for PRICO LNG process. The major contribution of this study is the implementation and evaluation of the single-solution based Vortex Search (VS) [31] methodology to find the optimal design variables (corresponding to minimal energy consumption) of the SMR (for offshore applications) and C3MR (for onshore applications) processes.
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