Refers to the BOG storage tank, which contains the heater to heat and liquefy the BOG flash steam.
Since the daily evaporation rate of LNG in the cryogenic storage tank and the cryogenic tank car is about 0.3%, this part of the evaporated gas (lower temperature) is referred to as BOG flash steam (Boil Off Gas), which increases the pressure of the gas phase space of the storage tank.
In order to ensure the safety of the storage tank and the needs of loading and unloading vehicles, a safety pressure reducing valve for the storage tank is set in the design (the BOG can be automatically removed according to the pressure during storage of the storage tank). The generated BOG gas passes through the vent valve to the BOG heater after heating, Then enter the BOG storage tank for storage.
Since the low temperature liquefied natural gas (LNG) storage tank (about -160°C) is invaded by the heat of the external environment, part of the mechanical energy of the submerged pump in the LNG tank is converted into heat energy, which will cause the LNG in the tank to vaporize to produce flash gas. Vapor is BOG gas.
Treatment of BOG Safely Released Gas
BOG mainly comes from the natural gasification of 0.3% per day of LNG tanker return gas and storage tanks. The volume of the commonly used tanker is 40m3. The time for recovering BOG is calculated as 30min. The gas pressure in the tanker after unloading the LNG is about 0.55MPa. It can be calculated according to 0.2MPa.
The return gas of the recovery tanker requires a BOG heater flow rate of 280m3/h, and the BOG heater flow rate can be calculated by adding the natural evaporation of the LNG storage tank. The storage temperature of LNG is -163°C, that is, the temperature of BOG is about -163°C. In order to ensure the safety of equipment, BOG should be heated to 15°C. BOG heaters can be sized based on flow and temperature.
The recovered BOG can directly enter the pipe network after pressure regulation, metering, and odorization. If the user uses non-continuous gas, a BOG storage tank needs to be set up for storage.
