In recent years, with rapid economic development, energy structure transformation, and upgrading, stricter environmental protection policies,
and restrictions on fuel and coal-fired boilers, natural gas consumption has grown rapidly. However, there is an unavoidable problem during the use of LNG filling stations,
which is a problem of BOG recovery. If the filling volume of the filling station is relatively large, the evaporation volume of BOG will be relatively smaller,
but if If the gas volume is not large, then the evaporation volume will be huge. This is a big waste for the gas station, so in order to avoid this waste,
we made a BOG recovery skid to reduce the daily losses of the gas station as much as possible. Without the BOG recovery skid, the gas that evaporates every day is only If it can be discharged, it will only be waste.
BOG refers to the gas that naturally evaporates due to the heating of the cryogenic liquid in the cryogenic liquid system.
The BOG treatment methods selected by LNG stations can be divided into two types:
1. BOG reliquefaction process
2. BOG direct compression process
The BOG reliquefaction process refers to sending BOG to the BOG compressor. After being pressurized by the BOG compressor,
it exchanges heat with the refrigerant in the cooler and then condenses into LNG.
This treatment process is suitable for BOG treatment when a large amount of BOG is produced in LNG storage tanks and needs to be recovered but the LNG export volume is small.
Currently, domestic LNG liquid plants and LNG receiving stations generally use this method to process BOG,
but ordinary gas filling stations Will not use it because the cost is too high and the daily vaporization volume is small.
LNG reserve peaking stations generally use BOG direct compression. The BOG is pressurized by the compressor to the pressure required by the external pipeline network,
and then undergoes pressure regulation, metering, and odorization, and finally enters the gas pipeline network for downstream users.
However, our ordinary gas filling stations do not have such a large amount of BOG gas as in peak shaving stations,
nor do they spend a lot of money on the BOG recovery and re-liquefaction process. At most, the excess evaporated gas can be used for your own use within the station,
such as cooking or floor heating. Especially for gas stations in the north, because it is a relatively cold place all year round, the demand for gas is also relatively large.
During the unloading operation, when all the liquid LNG is unloaded into the storage tank, the liquid inlet valve of the storage tank is closed.
At this time, the tanker is filled with gaseous natural gas; at the end of the unloading operation,
the remaining part of the liquefied natural gas in the liquid phase pipeline cannot fully enter the storage tank,
and the tanker is unloaded. Some natural gas must remain on the booster page;
when the storage tank is filled with liquid, as the liquid phase enters, the tank pressure will inevitably increase,
and the gas phase will be recovered through the bypass valve; during use, the liquefied natural gas in the storage tank will also naturally vaporize to a certain extent. rate;
the temperature of these parts of gaseous natural gas is extremely low when recovered,
and it needs to undergo further heat exchange with the external environment through the BOG vaporizer before it can be recycled and used.
It enters pressure regulation and measurement and is sent to the station for use after pressure regulation, measurement, and odorization.
Because all BOG gases are colorless and odorless, it is difficult to detect leaks during use on the station. Moreover, once leaks occur, they are basically indoors and cannot be well-ventilated,
so all BOG recovery skids must be equipped with An odorizing device that can detect and prevent gas leakage, thus greatly increasing the safety of the equipment.
The BOG recovery skid is indispensable in the energy recovery industry. It not only saves energy waste but also makes ordinary LNG filling stations more convenient in daily life.