Advanced Exergy Analysis Based on the Parametric Study of the Regasification of LNG Integrated Into an Air Separation Process

Abstract

The growing demand for natural gas leads to an increasing LNG market. The amount of traded LNG has more than doubled during the last decade. This trend is intensified by the rising number of liquefaction plants (export terminals) and regasification plants (import terminals). At the end of the year 2013 there were 86 liquefaction plants in 17 exporting countries and 104 import terminals in 29 importing countries. Also the number of floating regasification plants is growing. It is expected that the LNG market will grow with 7 % per year until 2020. In comparison, the market for gaseous natural gas only will increase with approxematly 1.8 % per year. The difference could be led back to the several advantages, when using LNG. Thus LNG enables the extraction of natural gas in offsite areas and leads to a flexible gas market. Especially with improving the efficiency of each part of the LNG chain — liquefaction, transportation, storage and regasification — and its fallen prices the LNG market will continue to grow. For the regasification of LNG different processes have been used, while mainly the vaporization via direct or indirect heating is applied. Due to their location at the coast of the importing country, seawater, air or the combustion gases coming from natural gas are used as thermal energy. A further possibility is the combination of regasification of LNG with generating electricity. Additionally, the regasification of LNG could be integrated into chemical processes (oil refinery and petrochemical plants), where low temperature refrigeration is required. The authors have already reported a concept for the integration of the regasification of LNG into an air separation and liquefactions process, i.e. into a cryogenic processes. In previous publications, an evaluation of the conventional air separation unit in combination with the LNG regasification has been reported. It was emphasized that the integration of LNG leads to a lower power consumption for the entire system. This paper deals with an improved concept for integrating the regasification of LNG into an air separation process. Due to structural changes, comparing the first design and the new design, the system can be further improved from the thermodynamic point of view. The aim of this paper is to discover the potential for improvement by the parametric study. The results obtained from the sensitivity analysis (energetic and exergetic) are reported as well as the results obtained from the advanced exergetic analysis. Some options for new designs of this system are be developed.