Optimization of the Substitution of Ethylene by Ethane in the Refrigerant Mixture for Energy Saving in a Natural Gas Liquefaction Plant

Authors

Manrique, Herbert

Pretell, Victor

Ramos, Williams

Lujan, Cesar

Abstract

Natural gas is an energy source less contaminant than oil or coal and it is transported through pipes or as liquefied natural gas (LNG). PERU LNG directs the first LNG plant in South America, which has a capacity of 4.45MTPA and uses the technology C3MR for the liquefaction. This technology employs a refrigerant mixture formed by ethylene and other light compounds due to the ratio ethane/methane ratio in the feed is not enough to make a refrigerant that achieve a good performance of the process. However, ethane molar composition is highly enough for a correct separation and its use as pure component preparing the mixed refrigerant could generate a significant reduction in power consumption. The present work has as objective to determinate the mixed refrigerant composition (with no ethylene) that minimizes the power consumption of liquefaction process. To meet that goal, this work models the liquefaction process using a spreadsheet to estimate the thermodynamics properties and the software MATLAB to solve the optimization of refrigerant composition with the genetic algorithm. Finally, the energy consumption of the process was reduced in 26.9MW, that is equivalent to 15.5% respect to the base case, without modifying the initial operational conditions.