An Optimization Mathematical Model of a nitrogen dual expander process for Liquefied Natural Gas (LNG) production

Abstract

In this work, we address the mathematical modeling of a liquefied natural gas (LNG) production process using a double-expansion refrigeration cycle with nitrogen as the refrigerant. The nitrogen cycle consists of four compression stages, a double expansion, and three multi-stream heat exchangers, which are used to reduce the temperature of the pressurized natural gas. Ultimately, liquefaction is achieved through a rapid pressure drop. To tackle the problem, a Non-Linear Optimization (NLP) mathematical model is proposed and implemented using the GAMS algebraic programming language. The developed model was validated against published results and the commercial simulator Hysys. Finally, the net power required was chosen as the objective function, and the pressure profile of the compression cycle was optimized, resulting in a 2.91% reduction compared to the reference values.