A novel cryogenic power cycle for LNG cold energy recovery

A novel cryogenic cycle by using a binary mixture as working fluids and combined with a vapor absorption process was proposed to improve the energy recovery efficiency of an LNG (liquefied natural gas) cold power generation. The cycle was simulated with seawater as the heat source and LNG as the heat sink, and the optimization of the power generated per unit LNG was performed. Tetrafluoromethane (CF4) and propane (C3H8) were employed as the working fluids. The effects of the working fluid composition, the recirculation rate of the C3H8-rich solution and the turbine intermediate pressure were investigated. In the cryogenic absorber, the C3H8-rich liquid absorbs the CF4-rich vapor so that the mixture exhausting from the turbine can be fully condensed at a reduced pressure. This reduction of turbine back pressure can considerably improve the cycle efficiency. The presented cycle was compared with the C3H8 ORC (organic Rankine cycle), to show such performance improvement. It is found that the novel cycle is considerably superior to the ORC. The efficiency is increased by 66.3% and the optimized LNG recovery temperature is around −60 °C.

► A novel cryogenic cycle with a vapor absorption process for improving the energy recovery efficiency of an LNG (liquefied natural gas) cold power generation is proposed. ► Propane (C3H8) and tetrafluoromethane (CF4) are employed as the working fluid. ► The performance improvement of the power cycle has been compared with that of an C3H8 ORC (organic Rankine cycle). ► The results show that the novel cycle is considerably superior to the ORC. ► The efficiency is increased by 66.3% and the optimized LNG recovery temperature is about −60 °C.