What are the preparations for LNG storage tanks before they are used?

What are the preparations for LNG storage tanks before they are used?

The liquefied natural gas storage tank and combined pipeline are installed in place, and after passing the inspection and acceptance, the pre-use preparation work will be carried out. Tanks must be purged with dry nitrogen and pre-cooled with liquid nitrogen before first use. The purge pressure should not be less than 0.2 MPa.

Before purging, should loosen the differential pressure (liquid level) gauge two ends of the joint, thoroughly open differential pressure (liquid level) gauge combination valve. Check for moisture in the discharged air stream. If there is moisture, continue to purge until there is no moisture to stop purging. Tighten the joints at both ends of the differential pressure (liquid level) meter and close the balance valve of the LNG storage tank to make the differential pressure (liquid level) meter in a normal working state.

Before the tank is filled with LNG for the first time, LNG gas is used to replace the liquid nitrogen or nitrogen in the tank. Turn over the discharge valve first to evacuate the nitrogen, and then close the discharge valve. Turn over the exhaust valve, and pass through the unloading platform to introduce the LNG gas in the LNG tank into the LNG storage tank. The pressure in the tank rises to 0.1-0.2 MPa, close the exhaust valve, stabilize for 3 minutes, and open the exhaust valve to evacuate. Repeat this 2-3 times, and the replacement is completed. Use a combustible gas detector or a sample of exhaust air to do ignition tests to check the degree of replacement.

When filling LNG for the first time, it is necessary to pre-cool the LNG storage tank or check the pre-cooling situation of the storage tank before, and the liquid inlet speed should be strictly controlled and the operation should be slow. First slowly open the upper inlet valve, and introduce the LNG in the tank car into the storage tank through the unloading table. Since there is a gasification lag process in the LNG into the storage tank, it is necessary to carefully observe the speed of the pressure increase in the tank, and the liquid inlet The amount must be small. When the pressure rises to 0.3 MPa, turn over the gas exhaust valve to reduce the pressure, and close the upper inlet valve if necessary.

The lng tank is pre-cooled after continuous liquid intake and exhaust. After a period of liquid inlet control, the pressure in the tank is stable, and the liquid level gauge shows that there is a certain liquid level in the LNG storage tank, the upper liquid inlet valve can be gradually opened, and the lower liquid inlet valve can be opened.