A study on boiling characteristics of direct contact LNG evaporator
摘要
Existing Liquefied Natural Gas evaporators use the indirect contact heat transfer mode where LNG of extremely low temperature of -162 degree C flows inside of tubes and 20-30 degree C sea water flows on the outside of tubes. However these indirect contact heat exchangers provide a relatively low heat transfer efficiency and have many problems in their applications, such as, material fatigue in the tubes caused by high differential temperature between the two fluids, material corrosion, erosion by the chloride of sea water and micro-biologic attacking, etc. In order to solve these problems, direct contact heat exchanger is proposed as a new design concept direct contact heat exchanger does not have any structures within the column so that it is totally free from the problems of the conventional ones. It may also be expected to give very high heat transfer performance. In the present investigation, in order to make sure of the feasibility for the direct contact LNG evaporator, experimentations have been carried out for the fluid dynamic characteristics such as bubbling, icing, sudden expansion phenomena and water content of the produced natural gases. Throughout the investigation, the water flow rate was fixed to be 10 1/min with water height 500 mm in the column. The LNG flow rates were 0.12 1/min, 0.36 1/min, 0.6 1/min and the pressures considered were 100 kPa, 300 kPa, and 500 kPa. The results show that as the pressure increased, the bubbles becomes small and uniform throughout the column, and the frequency becomes high with less mile % of water contents in the produced gas. It is also observed that the increase of the LNG flow rates gives less mole % of water contents in the gas. (author). 20 refs., 17 figs.