Design and optimization of multi-component organic rankine cycle using liquefied natural gas cryogenic exergy

In this study, an ORC (organic Rankine cycle) utilizing both low-grade steam from a pulverized coal power plant and LNG (liquefied natural gas) cold exergy is proposed and optimized. The proposed ORC is composed of a pump, a preheater, an evaporator, a superheater, a reheater, a two stage turbine, and a condenser which utilizing LNG as cold sink of the working fluid. The ORC uses R601-R23-R14 ternary mixture as its working fluid and is integrated with a steam cycle as a bottoming cycle. By utilizing the hot and cold exergy of low-pressure steam and LNG that are initially wasted, the ORC is able to generate additional power without consuming fossil fuel. The non-isothermal condensing nature of the ternary mixture working fluid can reduce the exergy loss of the system, and the consequent power generation and efficiency of the ORC are significantly improved. Power generation from the ternary mixture ORC is increased by about 56% and 59% as compared with the pure and binary mixture ORCs, respectively. Important design parameters such as pump discharge pressure, working fluid composition, and turbine inlet and outlet pressure are also optimized to recover the maximum power from the ORC.