Performance analysis of vaporizer tube with thermoelectric generator applied to cold energy recovery of liquefied natural gas

Abstract

The gasification process of liquified natural gas (LNG) releases a significant amount of cold energy. Traditional vaporizers release cold energy directly into the environment, resulting in energy wastage. In this study, a novel type of vaporizer with a thermoelectric generator (VTEG) that combines an air-heated vaporizer and thermoelectric power generation technology is designed. The heat transfer and generation characteristics of the VTEG are analyzed based on the modeling and calculations. The results reveal that compared with the traditional vaporizer, the outer wall temperature of the VTEG increases by 18.4–35.6 K, which mitigates the frosting problem on the surface of the vaporizer. When the fluid is in the liquid-phase and two-phase region, the generation efficiency is maintained between 1.57% and 2.12%. In the gas-phase region, a gradual decrease in the generation efficiency is observed in accordance with an increase in the natural gas temperature. Moreover, the low generation efficiency of the VTEG can be attributed to the low natural convection heat transfer coefficient outside the tube. An increase in tube length first results in an increase in the output power of the VTEG, which then decreases. An optimal tube length exists at which the VTEG output power is maximum value. In addition, the influence of the flow on the single-phase regions is more significant, wherein an approximately linear increase in the optimal tube length and maximum output power occur in accordance with an increase in the flow. Therefore, suitable selection of tube length of the VTEG is very important.