Economic Feasibility of Power Generation by Recovering Cold Energy during LNG (Liquefied Natural Gas) Regasification

Liquefied natural gas (LNG) has emerged as the leading option for global natural gas trade. Imported LNG must be regasified at the receiving terminal. The practice of using seawater as the heat source for regasification is a sheer waste of the available cold energy in LNG. In this study, power generation from LNG cold energy is investigated to reverse this wastage. We have developed a superstructure for this power generation process (PGP) that includes direct expansion of LNG and organic Rankine cycle (ORC) with simultaneous selection of the working fluid components and their compositions. Using a simulation-based optimization paradigm, the economic viability of the PGP is investigated by maximizing its net present value (NPV). Our results show that although a PGP with both direct expansion and ORC has a higher exergy efficiency, its NPV is nearly 64% lower than that of a PGP with ORC only. We present case studies for various combinations of process parameters and found that LNG regasification pressure has the maximum impact on NPV of the PGP followed by LNG feed temperature and composition. The maximum-NPV PGP uses only ORC and produces a net power of about 0.5-12.9 kW/t(LNG) after satisfying the power demand of the LNG regasification process. The NPV is about $6.87-2.45 million; thus, power generation by recovering cold energy in an LNG regasification terminal is economically viable. We also present a robust process design strategy to handle uncertainties in LNG composition.