Cryogenic turbine efficiencies

Abstract

Certain thermodynamic aspects of cryogenic turbines are investigated based on operational data provided by a cryogenic test facility. The cryogenic turbine is intended to produce power by replacing the throttling valve used in natural gas liquefaction plants. The turbine operates at very low temperatures; it admits liquefied natural gas (LNG) at a high pressure and discharges it at a low pressure. The temperature change of LNG in the expansion process through the cryogenic turbine is studied and compared with the temperature change through the throttling valve. It is found that the temperature will be about 2 ^∘C smaller at the turbine exit than that at the throttling valve exit for the same inlet state and exit pressure. To establish a suitable model for the assessment of cryogenic turbine performance, the isentropic efficiency, the hydraulic efficiency, and the exergetic efficiency are studied and compared. The hydraulic efficiency is determined to be the only feasible method to assess the performance of cryogenic turbines.