One-dimensional numerical study of thermal performance of an organic Rankine cycle system using liquefied natural gas as a cold source for cold energy recovery

A hybrid liquefied natural gas vaporizer system using an organic Rankine cycle for cold energy recovery is proposed for a typical liquefied natural gas (LNG) receiving terminal. Seawater and LNG are used as the hot and cold sources, respectively. A one-dimensional numerical model is established to formulate the conjugated heat transfer and thermodynamic characteristics for the evaporator, condenser, thermolator, and other components of the system. A solution algorithm for the coupled problem is developed, and the temperature distribution profiles for the three working fluids, namely, seawater, propane, and LNG, are obtained. The effects of five typical operating parameters, namely, the inlet temperatures of seawater and LNG, the inlet mass flow rates of seawater and LNG, and the propane condensation pressure, on the system are investigated. In the evaporator, the major thermal resistance occurs in the tube side of propane, and the peak values for the inner side and total heat transfer coefficients are found in the two-phase zone. An inner-side peak heat transfer coefficient for LNG is located near the pseudo-critical temperature in the condenser. The heat transfer coefficients are distributed uniformly on both the inner and shell sides of the thermolator. The seawater inlet temperature and propane condensation pressure are the two most sensitive factors for thermal efficiency. The inlet LNG mass rate and inlet LNG temperature have opposite effects on the thermal efficiency and the organic Rankine cycle output power.