During the shutdown of the liquefaction plant, why is the LNG stored in large tanks circulated on its own?
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During the shutdown of the liquefaction plant, why is the LNG stored in large tanks circulated on its own?
This shouldn’t be the case. Is it because they want to sell the remaining LNG as soon as possible, but the delivery of tankers to the plant isn’t continuous? Is this done to avoid difficulties in restarting the pumps after they stop? That’s how I understand it
It depends on how long you’ve stopped. If it’s for a short period, you can cycle it to facilitate loading in the near future without the need for pre-cooling. If the shutdown duration is long, it’s sufficient to stop operation; pre-cooling can be carried out again during the next loading process. However, if the shutdown lasts for a long time and there is a large amount of LNG stored in the tank, rolling may occur, and in such cases the pump should be started to initiate circulation.
It’s best to sell most of the LNG, so that there’s no need for pump circulation.
Prevent stratification in large LNG tanks over extended periods of time, as this can lead to mixing over time
Will it roll over over time? Could you explain a bit more? Thank you
The density of LNG is related to temperature; over time, a temperature gradient is created from top to bottom, and the lower temperatures at the bottom mean a higher density
For long-term storage, pump circulation is primarily used to achieve temperature and density equilibrium, as well as to prevent LNG from tumbling
Everything said upstairs is great – it helps prevent stratification caused by uneven temperature changes, which could lead to LNG rolling. The consequence of LNG rolling is intense vaporization, with a large amount of BOG being released. In a foreign country, there was an incident where a large tank rolled over; the entire contents of that LNG tank had to be released immediately, otherwise the tank’s lid would have been pushed off by the pressure.
Each LNG plant has its own measures to prevent the LNG from rolling around inside the storage tanks; regular circulation of the LNG at the bottom helps to prevent this, so the likelihood of such rolling occurring is very low – it generally does not happen.