A gas turbine/closed cycle solution for effective recovery in LNG regassifiers

The problem of energy recovery from LNG regasification terminals is attracting scientific as well as industrial attention. Still few LNG regasification terminals are operating (with special reference to Europe), and a substantial margin of performance improvement appears to be possible with respect to current industrial solutions. Advanced research schemes for power recovery have been proposed, which however often entail complicated plant layouts. The idea here developed is to couple a modern gas turbine with an intermediate closed gas cycle, taking care of keeping low values of heat transfer exergy destruction. The closed gas cycle is coupled to the cold-end (LNG) side in two supercritical heat exchangers, that is, the heat rejection at closed cycle turbine exhaust, and the compressor intercooler. The intermediate pressure of the two-stage compressor is matched to guarantee uniform conditions between the two critical heat exchangers, so that the GNL flow is split in two approximately equal separate streams. Two different working fluids suitable for cryogenic operation were considered for the closed cycle: Helium and Nitrogen. The natural gas properties were modeled as a real mixture using Refprop. The performance estimation of the plant includes the calculation of the exergy balance and main environmental indicators. Attractive performance figures appear to be possible, both in terms of efficiency and of carbon footprint.