Power plant based on three series Rankine cycles combined with a direct expander using LNG cold as heat sink

The research work aims at the efficient extraction of electric power using the cold available as heat sink in the regasification process of LNG. To this end, the article proposes and analyses an efficient power plant composed of series Rankine cycles combined with a direct expansion based turbine, where the rejected heat from each cascade power unit is used to heat the liquefied natural gas in a regasification plant. Some recent contributions have been compared with the results achieved from the analysis of the proposed power plant which is based on cascaded Rankine cycles in which argon and methane are used as working fluids and a direct expansion turbine serving as direct power generation, is applied as heat sink for a Rankine cycle operating with methane. As the result of the optimisation of an objective function, taking the ratio of the obtained power to the mass flow rate of LNG as the performance criteria, the cascaded Rankine cycles operating with argon and methane, combined with a direct expander working with regasified LNG, yield the highest possible exergy efficiency (approaching 300 kW/kg-LNG) when compared with the most recent contributions carried out in this field.