Analysis of an efficient liquified natural gas utilization cascade Brayton cycle and an improved cold energy recovery evaluation criterion

Abstract

The cold energy utilization of liquified natural gas is a promising solution for electricity generation systems to raise power output. In order to enhance cold energy recovery performance, here we propose a cascade Brayton cycle, which can efficiently utilize the waste heat from gas turbine and the cold energy of liquefied natural gas. The temperature pinch in natural gas evaporator is successfully reduced by adopting helium as the working fluid. The optimal working condition is determined through parametric sensitivity analysis, and the exergy and economic performance is assessed and compared. The design case outperforming high energy efficiency (68.61 %), competitive exergy efficiency (58.51 %) and excellent levelized cost of electricity (0.0481$·(kW·h)−1). Moreover, the exergy destruction in natural gas evaporator reduced by 4.05 MW, resulting in 23.2 % improvement compared to conventional systems. Simultaneously, a modified criterion of “real specific work contributed per kg/s liquified natural gas” is proposed, which provides a more accurate cold energy recovery evaluation method for cold energy utilization systems. The comparison of reported cold energy utilization systems are conducted based on the modified criterion, and our model delivers the best result among them.