Optimization of mixed refrigerant compositions for the prico natural gas liquefaction process using hysys optimizer

Abstract

To export natural gas to overseas, it has to be liquefied and transported by the LNG tankers. The liquefaction process of natural gas is an energy intensive process as it requires a huge amount of energy to liquefy the natural gas from ambient temperature to -160 oC. Therefore, reduction in energy consumption is highly recommended. The new introduction of Floating Liquefaction Natural Gas (FLNG) Vessels, which provide mobile gas processing, storage and offloading jetty, receives natural gas from different gas reservoirs that leads to the variation of natural gas compositions. The key challenge lies on developing an optimal mixed refrigerant range of the multi-feed gas composition of LNG plants. In this paper, an optimized mixed refrigerant range is introduced based on variation in feed composition in order to minimize the energy consumption. PRICO mixed refrigerant cycle is being adopted as a refrigeration cycle due to its simplicity, compactness and low investment. The feed composition data has been taken from different sources as stated in the literature. Aspen HYSYS software is used to simulate the PRICO process and HYSYS Optimizer tool is used to optimize the cycle. The findings show an overall compression power reduction of 30 % in three different NG compositions. A special case was introduced where the NG contains methane concentration around 67%. The results of the optimized special case show a compression power reduction around 44% and higher LNG liquefaction rate.