Size reduction and enhanced power generation in ORC by vaporizing LNG at high supercritical pressure irrespective of delivery pressure

Abstract

LNG regasification terminals generate power with Organic Rankine cycle (ORC) using LNG as the heat sink. A 3-stage ORC designed for regasification pressure of 70 bar(a) produces the highest net power with appropriate temperature approach in each heat exchanger and it is higher by 108 kW for LNG flow of 30 kg/s compared to the fixed temperature approach of 5 K. For 30 bar(a) delivery pressure, a regasification pressure of 70 bar(a) instead of 30 bar(a) produces about 17% higher net power and 1.9 times reduction of total heat exchanger area. The sizing parameter of the turbine becomes 12.3% lower. The analysis shows that total outlet volume flow rate through turbine, pump inlet and hot side of heat exchangers are 24.5%, 28.2% and 25.0% lower respectively for 70 bar(a) regasification pressure. The total capital investment for 30/30 bar(a) and 70/30 bar(a) systems are 18.8% and 21.8% respectively higher than that of 70/70 bar(a) system. For the delivery pressure of CNG at 30 bar(a), the net present value of 70 bar(a) regasification pressure is 1.7% higher than that for 30 bar(a) regasification pressure. This is over and above the flexibility of operation that the regasification terminal achieves with supercritical LNG.