Comparison of Different Optimal Designs of Single Mixed Refrigerant Processes

Improving energy efficiency of natural gas liquefaction processes is the major issue in LNG plant research as the processes consume a large amount of energy. A single mixed refrigerant process, one of the natural gas liquefaction processes, has been modeled and optimized in various literatures for improving process efficiency in terms of specific work (energy consumption per unit mass of LNG production). The direct comparison of the results obtained by the literature, however, is not easy because of the differences of process configurations, natural gas compositions, design bases, and optimization models. This study optimizes a variety of single mixed refrigerant processes for minimizing specific work with an equation-oriented modeling environment, and compares the process efficiencies using the specific works minimized by the optimizations. In addition to these, we analyzes the effects of i) process configurations of compression and multistream heat exchanger stages, ii) natural gas compositions, and iii) design bases such as pressure drops in the equipment, cooling water temperature, and equipment efficiencies on the single mixed refrigeration processes. As a result, we find some variables, which are highly sensitive or have a significant impact on the process efficiency, and discover active constraints preventing further improvement.

 This research was supported by a grant from the LNG Plant R&D Center funded by the Ministry of Land, Infrastructure, and Transport (MOLIT) of the Korean government.