(550g) A Numerical Model of Ambient Air Vaporizer and Its Validation with Pilot Scale Data

Recently, new types of liquefied natural gas(LNG) receiving terminals have emerged, and the number of projects they are involved in is gradually increasing [1]. These terminals are expected to be built in the equatorial and subequatorial regions, such as Indonesia, Mexico and Brazil. In the countries, the site conditions and environment factors such as ambient temperature and relative humidity are favorable conditions for the performance of ambient air vaporizer(AAV) [2]. Using ambient air as heat source will not only save the fuel used in traditional regasification process and the operating cost but help in reducing emissions detrimental to the environment [3].
 In AAV, LNG which passes through a number of interconnected tubes absorb heat from ambient air. One of main problems that occurs in the equipment is frost formation due to condensation and freezing of water-vapor contained in the ambient air. The frost deposited at the surface of tubes will lower the heat transfer rate because the thermal conductivity of ice is less than one-fortieth that of aluminum alloy which was used as material of the tubes.
 The objective of this study is to predict the effect of frost to the performance of AAV over time and analyze effects of external factors. Information of the equipment geometry and time dependent input data such as air conditions and LNG temperature at inlet is used to build numerical model of AAV. The model which provide frost thickness and density and LNG-related variables at overall length of the tube was calibrated and validated with pilot scale data. The dynamic heat transfer performance of AAV is also studied from the model. This study is expected to contribute to cryogenic-related processes whose performance is affected by frost.

[1] Egashira S. LNG Vaporizer for LNG Re-gasification Terminal. Kobelco Tech Rev. 2013;32:64-9.
[2] Patel D, Mak J, Rivera D, Angtuaco J. LNG vaporizer selection based on site ambient conditions. Proceedings of the LNG. 2013;17:16-9.
[3] Dendy T, Nanda R. Utilization of Atmospheric Heat Exchangers in LNG vaporization processes: a comparison of systems and methods. SPX Corporation, Houston, Texas. 2008.