1. Pre-cooling with low-temperature nitrogen gas first:
1. Check the unloading crane pipe is in good condition, and there is no rainwater, garbage and other sundries in the pipe. Connect the crane pipe to the tank truck and check whether the connection is firm.
2. Turn on the tank truck self-supercharger (or use a dump truck supercharger) to increase the tank truck pressure to 0.3MPa. Slowly open the gas phase valve of the tanker and check for leaks at the hose connection.
3. Slowly pour low-temperature nitrogen into the storage tank until the pressure of the storage tank rises to about 0.2MPa. Close the unloading valve of the unloading platform, and after the storage tank is kept cold for 15 minutes, open the full test valve of the storage tank to discharge nitrogen, and the process is repeated.
4. Determine the internal temperature of the storage tank, release the gas through the full valve, and measure it with a thermometer. When the gas temperature reaches the expected value (-70°C～-100°C), the gas pre-cooling work is completed.
2. Liquid nitrogen pre-cooling:
1. Vent the pressure of the storage tank to slightly positive pressure, and close the lower inlet valve. Close the balance valve of the level gauge and use the level gauge.
2. Slowly open the tanker's liquid phase valve to a smaller opening, and slowly close the small tanker's gas phase valve to allow liquid nitrogen to enter from the upper part of the storage tank. Control the opening of the unloading platform valve to keep the pressure at 0.3MPa. When the pressure of the storage tank rises to 0.2 MPa ~ 0.3 MPa, the unloading platform valve should be closed in time, and the gas phase of the storage tank should be manually vented and relieved. Repeat this operation.
3. Listen carefully to the sound in the storage tank and observe the pressure of the storage tank at the same time. When the sound decreases and the pressure no longer rises, slowly open the front and rear valves of the emergency shut-off valve at the lower part of the storage tank to feed liquid up and down at the same time. Closely observe and record the pressure of the storage tank during the liquid filling process to prevent the pressure from rising. When the pressure rises, the outlet valve of the tank truck should be closed in time, and the gas phase of the storage tank should be opened to manually vent the pressure.
4. When the liquid level gauge of the storage tank reaches a certain value (usually 20% of the storage tank), the liquid inlet ends.
5. After the liquid inlet task is completed, close the liquid phase valve of the tanker, open the gas phase valve of the tanker, and purge the unloading pipeline to the storage tank.
6. Close the tanker valve and the unloading valve of the unloading platform, and unload the hose. After closing the unloading platform valve, the liquid between the valve and the check valve should be vented.
7. Close the gas-phase manual vent valve of the storage tank and the front stop valve of the emergency shut-off valve for the liquid in the lower part of the storage tank. The upper liquid inlet valve of the storage tank will be closed after the unloading truck LNG pipeline returns to normal temperature.
8. Use the liquid nitrogen in the storage tank to pre-cool the supercharger, air-bath vaporizer and other low-temperature pipelines.
9. Venting low-temperature nitrogen using liquid nitrogen pre-cooling requires venting low-temperature nitrogen through the gas phase pipe. These low-temperature nitrogen can be pre-cooled to other storage tanks through gas phase pipes connected to other tanks, which can save liquid nitrogen.
