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Liquefied natural gas (LNG) is transported by the sea-ships with relatively low pressure (0.13-0.14 MPa) and very low temperature (about 100 K) in cryo-containers. Liquid phase, and the low temperature of the medium is connected with its high exergy. LNG receives this exergy during the liquefaction and is related with energy consumption in this process. When the LNG is evaporated in atmospheric regasifiers (what takes place in many on-shore terminals as well as in local regasifier stations) the cryogenic exergy is totally lost. fortunately, there are a lot of installations dedicated for exergy recovery during LNG regasification. These are mainly used for the production of electricity, but there are also rare examples of utilization of the LNG cryogenic exergy for other tasks, for example it is utilized in the fruit lyophilization process. In the paper installations based on the Brayton cycle gas turbine are investigated, in the form of systems with inlet air cooling, liquid phase injection, exhaust gas based LNG evaporation and mirror gas turbine systems. The mirror gas turbine system are found most exegetically effective, while the exhaust gas heated systems the most practical in terms of own LNG consumption. [ABSTRACT FROM AUTHOR]

In the paper, a second order thermodynamic analysis of a small scale alpha-type Stirling engine is presented. The developed mathematical model is based on the Finite Time Thermodynamics (FFT) approach and it is derived from the differential time dependent equations of energy and mass conservation. The engine model consists of three spaces: compression, expansion and regenerator. In contrast to available models, the model presented in this paper assumes polytropic processes in the compression and expansion spaces, which corresponds to the non-ideal heat transfer in these spaces. The results, obtained using the developed second order model, were compared with the results obtained using the Computational Fluid Dynamics (CFD) analysis of the same engine. A very good agreement between the second order model and the CFD model was achieved. Finally, the developed model was applied to analyse potential to recover cryogenic exergy of the Liquefied Natural Gas (LNG). The paper presents the results of the dimensional upscaling of the engine and the influence of the average working pressure. It was revealed that increasing the size of the engine or the average working pressure moves the engine to practically unachievable working conditions. [ABSTRACT FROM AUTHOR]

LNG (liquefied natural gas) delivered by means of sea-ships is pressurized and then regasified before its introduction to the system of pipelines. The utilization of cryogenic exergy of LNG for electricity production without combustion of any its portion is analyzed. For the conversion of LNG cryogenic exergy into electricity, the Stirling engine is proposed to be applied. The theoretical thermodynamic model of Stirling engine has been applied. This model is used to investigate the influence of pinch temperature in heat exchangers, engine compression ratio and dead volumes ratios on the thermodynamic parameters of the Stirling engine. The results of simulation represent the input data for investigations of thermodynamic performance of the proposed system. In order to evaluate the thermodynamic performance of the proposed process, an exergy analysis has been applied. The exergy efficiency and influence of design and operational parameters on exergy losses are determined for each of the proposed system configurations. The obtained results represent the background for advanced exergy-based analyses, including thermo-ecological cost. [ABSTRACT FROM AUTHOR]