Liquid nitrogen pre-cooling method for the unloading manifold pipe at Shandong LNG terminal

Pre-cooling of unloading manifold pipes is the key to ensure the smooth commissioning of LNG terminals. Because it can not only prevent pipes from being damaged by the fast change of pipe temperature, but also test the quality and performance of low-temperature devices. In order to cut down the berthing time of LNG ships and reduce the operation cost of Shandong LNG terminal. Therefore, it was proposed to pre-cool the unloading manifold pipe by using liquid nitrogen before gas receiving of the first ship. In Shandong LNG terminal, the unloading manifold pipe is fairly long, so it is divided into three sections (A, B and C) for progressive pre-cooling. When the temperature difference between pipeline top and bottom is more than 10 ℃, it shall be eliminated by blowing the pipe explosively after the pressure is built up to 0.2 MPa by turning off the shutdown valve. In order to facilitate the operation and control, the working conditions of the vaporizer shall be adjusted on the basis of temperature nodes of 0 ℃, －30 ℃, －60 ℃, －90 ℃, －120 ℃ and －150 ℃ so as to control the pre-cooling rate. Results show that this method is highly safe and operable. During the pre-cooling process, the temperature difference between pipeline top and bottom shall be kept below 30℃ and the pre-cooling rate shall be less than 10 ℃/h. This method is favorable for decreasing the temperature difference between pipeline top and bottom, reducing the pre-cooling time, improving the pre-cooling efficiency and shortening LNG ship berthing time by about 7 days.