Proposal for a high efficiency LNG power-generation system utilizing waste heat from the combined cycle

High-efficiency power-generation with an LNG vaporizing system is proposed: it utilizes the LNGʹs cold energy to the best potential limit. This system can be applied to LNG vaporizers in gas companies or electric power companies and recover the LNGʹs cold energy as electric power. The system consists of a Rankine cycle using a freon mixture, natural-gas Rankine cycle and a combined cycle with gas and steam turbines. The heat sources for this system are the latent heat from the steam-turbineʹs condenser and the sensible heat of exhaust gas from the waste-heat recovery boiler. In order to find out the optimal condition of the system, several factors, such as gas turbine combustion pressure, steam pressure, condensing temperature in combined cycle, composition of mixture freon, and natural gas vaporizing pressure are evaluated by simulation. The results of these studies show that in the total system, about 400 kWh can be generated by vaporizing 1 ton of LNG, including about 60 kWh/LNG ton recovered from the LNG cold energy when supplying NG in 3.6 MPa.. About 8.2 MWh can be produced by using 1 ton of LNG as fuel, compared with about 7 MWh by the conventional combined system. A net efficiency of over 53%HHV could be achieved by the proposed system. In the case of the LNG terminal receiving 5 million tons of LNG per year, this system can generate 240 MW and reduce the power of the sea water pump by more than 2 MW.