LNG Power Recovery

Abstract

The thermal efficiency of a Carnot cycle is limited by the maximum and minimum temperatures available. The construction of LNG (liquid natural gas) terminals and the need to vaporize LNG offers a cooling source at a very much lower temperature than sea water. By using the cold sink and by adapting the waste heat available from a combined cycle plant, it is possible to recover power from the vaporization of LNG. This is done by the use of a reverse cascade refrigeration process where energy is extracted by expanders instead of energy input by compressors. The paper explains how the hot and cold processes can be integrated to produce a compound cycle with an overall efficiency of some 55 per cent or more depending on the quantity of LNG to be vaporized. Special reference is given to the features needed for the rotating equipment and how equipment selection is critical to the realization of a practical working power station.