A novel liquid natural gas combined cycle system integrated with liquid nitrogen energy storage and carbon capture for replacing coal-fired power plants: System modelling and 3E analysis

The judicious utilization of cryogenic energy released during the regasification process of liquid natural gas (LNG) is important for enhancing the operational efficiency of combined-cycle power plants utilizing LNG. This study introduces an innovative natural gas combined cycle (NGCC) process, denoted as NGCC-LNES, designed for power generation and carbon capture through the utilization of LNG cryogenic energy, specifically targeting the alleviation of the load on conventional coal-fired peak-shaving power plants. The proposed process lowers the boiling point of liquid nitrogen below the LNG storage temperature through nitrogen pressurization. Subsequently, the cold energy inherent in LNG is harnessed to liquefy nitrogen, and the surplus cold energy is stored for the continuous liquefaction of CO2. Illustrating this concept with an NGCC system featuring a 1 kg/s LNG flow rate, we developed a numerical calculation model employing Aspen Plus for a comprehensive analysis encom-passing energy, exergy, and power peak regulation. Furthermore, this study conducts an in-depth examination of the influence exerted by the peak-to-valley power-price ratio on the payback period of the system. It also explores the prospective applications of this innovative system in China and other major LNG-importing nations world-wide as a replacement for peak-shaving coal-fired power plants. The results show that over a 24-hour operational period, the LNES system can consistently and reliably supply 2722.82 kW of power for 8 h, achieving a round-trip efficiency of 75.26 %. Specifically, the exergy efficiencies of the NGCC-LNES during the energy storage and release phases are determined as 58.50 % and 54.44 %, respectively. Notably, as the peak-to-valley power price ratio escalates from 2.5 to 5, the payback period of the system investment contracts significantly, decreasing from 24.62 years to 4.25 years. Remarkably, the initial investment cost of the LNES technology stands at 947.58 $/kW, positioning it competitively relative to alternative energy storage technologies such as compressed air, sodium-sulfur batteries, and flow batteries, and closely aligns with pumped hydro energy storage solutions. Importantly, this innovative technology has the capacity to reduce carbon emissions by 0.21 % and 1.5 % for major global LNG importers by 2022 and China by 2060, respectively.