Thermodynamic analysis of an LNG fuelled combined cycle power plant with waste heat recovery and utilization system

Abstract

SUMMARYThis paper has proposed an improved liquefied natural gas (LNG) fuelled combined cycle power plant with a waste heat recovery and utilization system. The proposed combined cycle, which provides power outputs and thermal energy, consists of the gas/steam combined cycle, the subsystem utilizing the latent heat of spent steam from the steam turbine to vaporize LNG, the subsystem that recovers both the sensible heat and the latent heat of water vapour in the exhaust gas from the heat recovery steam generator (HRSG) by installing a condensing heat exchanger, and the HRSG waste heat utilization subsystem. The conventional combined cycle and the proposed combined cycle are modelled, considering mass, energy and exergy balances for every component and both energy and exergy analyses are conducted. Parametric analyses are performed for the proposed combined cycle to evaluate the effects of several factors, such as the gas turbine inlet temperature (TIT), the condenser pressure, the pinch point temperature difference of the condensing heat exchanger and the fuel gas heating temperature on the performance of the proposed combined cycle through simulation calculations. The results show that the net electrical efficiency and the exergy efficiency of the proposed combined cycle can be increased by 1.6 and 2.84% than those of the conventional combined cycle, respectively. The heat recovery per kg of flue gas is equal to 86.27 kJ s À1 . One MW of electric power for operating sea water pumps can be saved. The net electrical efficiency and the heat recovery ratio increase as the condenser pressure decreases. The higher heat recovery from the HRSG exit flue gas is achieved at higher gas TIT and at lower pinch point temperature of the condensing heat exchanger.

Review on recent liquefied natural gas cold energy utilization in power generation cycles

“…There have been a lot of researches focusing on improving the efficiency of the power generation cycles, and many advanced power generation cycles utilizing LNG cold energy were proposed. In this review, only the researches after the year of 2010 is discussed, and some previous research can be referred to (Griepentrog et al, 1976;Angelino et al, 1978;Krey, 1980;Najjar et al, 1991;Najjar et al, 1993;Wong, 1994;Kim et al, 1995;Chiesa et al, 1997;Hisazumi et al, 1998;Miyazaki et al, 2000;Deng et al, 2004;Kaneko et al, 2004;Wang et al, 2004;Zhang et al, 2006;Shi et al, 2007;Bai et al, 2008;Lu et al, 2009;Shi et al, 2010;Tsatsaronis et al, 2010).…”

Effect of supplementary firing options on cycle performance and CO2emissions of an IGCC power generation system

“…Constant polytropic efficiency for the compressor and isentropic efficiencies for the gas turbine and the steam turbine are assumed and a value of 85% is used [16,17].…”

Exergy recovery during LNG gasification using ambient air as heat source

“…Shi and Che [6] used a conventional water vapor Rankine cycle, the generation of steam is carried out by the exhaust gas of a gas turbine. LNG is gasified at the condenser by condensing Rankine cycle steam and hot water extracted from the steam generator.…”