The exploitation of the physical exergy of liquid natural gas by closed power thermodynamic cycles. An overview

The world trade in LNG (liquefied natural gas) has tripled in the last 15 years and the forecasts are for further rapid expansion. Although the cryogenic exergy of the LNG could be used in many industry processes, it is recognized also as a source for power cycles. When using the low temperature capacity of LNG for power production, several thermodynamic cyc. can be considered. This paper reports the state-of-the art of the most relevant solutions based on conventional and non-conventional thermodynamic closed cycles. Moreover, a novel metrics framework suitable for a fairer comparison among the energy recovery performances of the different technologies proposed. According to the defined indicators the compounds plants with gas turbine and closed Braytc cycles perform really better, with an almost full use of LNG available cold temperature and a fuel con sumption with an efficiency better than that of the current combined cycles. The Rankine cycles wi organic working fluids (pure fluids or non-azeotropic mixtures) using seawater or heat available at low temperature (for instance at 150 degrees C) also perform in a very satisfactory way. Real gas Brayton cycles and carbon dioxide condensation cycles work with very good thermal efficiency also at relatively low maximum temperatures (300 divided by 600 degrees C) and could have peculiar applications. (C) 2015 Elsevier Ltd. All rights reserved.