(201d) Thermodynamics Analysis Based Optimal Design and Operation of Dmr Refrigeration System for Natural Gas Liquefaction Process

Mozammel Mazumder, Qiang Xu*, and Srinivas Palanki

Dan F. Smith Department of Chemical Engineering

Lamar University, Beaumont, Texas 77710, USA

Abstract

The liquefied natural gas (LNG) supply chain has diversified the global gas market previously dominated by pipeline gas suppliers and improved the security of energy supply of many consuming nations. The traditional 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. Aspen HYSIS version 8.8 with PENG-ROB equation of state is employed for the modeling. 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. Certainly, the optimization results will be validated through rigorous process simulation and thermodynamic analysis. Finally, the energy analysis and economic evaluation between the base and the optimal case will be performed.

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