Thermal design of intermediate fluid vaporizer for subcritical liquefied natural gas

• Thermal design method is established for an IFV vaporizing subcritical LNG.
• Heat transfer coefficient and temperature profiles along tube lengths are estimated.
• Effects of operating parameters on thermal design results are investigated.

The re-gasification process plays an important role in the liquefied natural gas (LNG) supply chain. The advantages of an intermediate fluid vaporizer (IFV) include the better energy efficiency, less sensitivity to ambient conditions and no icing or frosting problem. In this paper, the thermal design method has been established for the IFV when vaporizing the subcritical LNG. The typical heat transfer characteristics in the different sections and flow boiling zones have been predicted. The effects of the operating parameters such as the inlet mass flow rate and pressure of LNG and the inlet seawater temperature on the heat transfer coefficients and the required heat transfer areas of the thermolator, evaporator, condenser and the whole IFV have been investigated. The results indicate that the increase in the LNG pressure not only changes the heat transfer coefficient in each flow boiling zone but also influences the transition from one flow boiling zone to another, and ultimately leads to a profitless increase of the required heat transfer area of the condenser. The results reported here would provide insight into the vaporization process of subcritical LNG and give guidance to the potential design optimization of an IFV.