Techno-economic analysis of seawater freezing desalination (SFD) using liquefied natural gas (LNG)

摘要

Natural gas (NG) has been widely used in industries over the world as a high efficiency and low carbon emission fuel to replace the conventional fossil fuel, such as coal and oil. For easy storage and long-distance transportation across the oceans, NG is liquefied by cooling down to -162°C and converting into liquid phase at atmospheric pressure. The liquefied natural gas (LNG) is regasified at the storage terminal by increasing the pressure and temperature for supplying to end users. In the regasification process, a large amount of cold energy, including latent heat and sensible heat, at about 827 kJ/kg-LNG has been lost through heat exchange between LNG and seawater. Considering the increasing worldwide use of LNG, up to 258 MT (Mega Ton) in 2015, the potential power that could be recovered from the cold energy will be approaching to 6.8 GW. The utilization of LNG cold energy has a high potential to become a low cost and sustainable energy for industrial applications such as power generation or desalination. Seawater freezing desalination (SFD) may work due to the lower the temperature, the lower the solubility of salt (NaCl) in seawater. According to the phase diagram, NaCl will be separated out as the temperature decreases to -2°C causing the seawater to turn into freshwater ice and concentrated brine. This article aims to investigate the economic potential of SFD using the cold energy from regasification of LNG.