(8k) Optimal Design and Operation of DMR Refrigeration System for Natural Gas Liquefaction Process

The traditional liquefied natural gas (LNG) processes mainly include cascade (Jensen, et al.; 2006), nitrogen expansion cycle (Remeljej, et al., 2006) and mixed refrigeration cycle (MRC) (Wang, et al., 2007). In this paper, a new methodology for LNG liquefaction process introduced combining turboexpansion, dual mixed refrigeration (DMR), Joule-Thompson expansion targeting energy consumption minimization. It also described thermodynamic analysis-based study of the minimization of the energy consumption of the LNG process. The developed methodology contains three major tasks: (i) modeling and simulation of an existing LNG case (base case); (ii) thermodynamics and mathematical analysis for solution identification; and (iii) modeling and optimization of the newly developed LNG process. In the first stage, based on the modeling and simulation of the base case, the operating status of the refrigerant and natural gas streams of the entire NG liquefaction process are obtained. In the second stage, the energy consumption roadmap is explored through thermodynamic analysis where the temperature and specific enthalpy (T-H) diagram is employed. Based on thermodynamic studies, the energy saving opportunities to improve the base case (i.e., new LNG process) has been identified. In the third stage, a rigorous optimization model is developed to obtain the optimal solution of the new LNG process. The optimization result shows that 18,168 KW of total compressor brake power is saved compare with base case, accounting for near 12.24% savings. It shows that the heat exchanger and chiller duties are also reduced 22,950 KW which accounts for about 5.22% heat exchanger and chiller duties consumption. The COP for base case is 1.42. It increases to 1.56 after optimized, which also indicates the liquefaction process efficiency is improved after optimization. Finally, the energy analysis and economic evaluation between the base and the optimal case will be performed.

References

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