In previous post (typical process flow diagram of small scale LNG regasification facility), I explained that LNG storage tank played important part in the facility. It is used to stored LNG for certain duration (usually in term of round trip). In small scale LNG regasification facilities, vacuum insulated tank is usually used because the capacity if small. But when the capacity is high, LNG flat bottom tank is used.
In this post I want to share you difference and comparison between LNG flat bottom tank and vacuum insulated tank and give some advice what to choose.
Table below shows comparison of flat bottom storage tank and vacuum insulated tank.
We can see that each tank has its own pros and cons. Flat bottom is preferable when required tank volume is high and space are relatively large. On the other hand, vacuum insulated tank is preferable when volume is low. In one source, for storage with quantity of less than 250 m3, vacuum insulated tanks are the best option. But for volume larger than 50000 m3, flat bottom tank are the best option. But, how in between?
Figure below shows economic comparison of vacuum insulated tank and flat bottom tank.
- When capacity is lower than 4500 m3, vacuum insulated tanks is recommended (use multiple tanks)
- When capacity is between 4500 m3 and about 20 000 m3, we can use vacuum insulated or flat bottom. Further economic evaluation on piping system, valve, instrumentation, boil-off gas handling, and required space must be done
- When capacity is larger than 20 000 m3, it is recommended to use flat bottom tank
When we choose several vacuum insulated tank
When we choose vacuum insulated tank for relatively large volume of LNG, for example 5000 m3, we need to evaluate overall cost roughly to see which one is the best configuration (500 m3 x 10 unit, 600 m3 x 4 unit, or other combination). We need to consider:
- Piping cost
- Instrumentation cost
- Valve cost
- Tank cost
- Required area
The evaluation will give us better justification of which combination is the cheapest.