Conventional and Advanced Exergy Analyses of an Integrated LNG Regasification–Air Separation Process

Abstract

Liquefied natural gas (LNG) is being imported in Pakistan to bridge the gap between the indigenous production and demand for natural gas. The calorific value of imported LNG must be lowered to meet the design requirements of the existing gas-fired power plants. This reduction in calorific value requires mixing with high-purity nitrogen, which can be obtained from the cryogenic distillation of air. Because imported LNG has a significant amount of cold energy and must be regasified/vaporized before injecting into the gas pipeline network, there is potential for recovering this cold energy by integrating the LNG regasification process with the cryogenic air separation process. To achieve these objectives, we developed an integrated LNG regasification–air separation process and compared it with the standalone air separation process. Conventional exergy analysis shows that the integrated process is better than the standalone air separation process both in terms of total power consumption and total exergy destruction ratio. The integrated process was further analyzed using advanced exergy analysis to identify the origin and nature of exergy destruction in the process. The results show that 44.3% of total exergy destruction in the process can be classified as avoidable. Moreover, 91.7% of the avoidable exergy destruction is of endogenous nature, showing that improving the efficiency of individual pieces of equipment should be the topmost priority for process improvement.