LNG Terminal Operations

There are four marine loading arms that can be used to connect the LNG carrier berthed at the jetty to the terminal. Each jetty is equipped with four loading arms - two liquid, one vapour and one hybrid. The vapour arm is important in ensuring that gas flows freely back to the ship and maintains a positive pressure into the ship.

The BOG compressors are used to control the pressure in the storage tanks by recovering the boil-off gas and sending it to the recondenser, which recondenses the gas into liquid using LNG. The liquefied gas is subsequently transferred to the high pressure booster pumps. Gas enters the BOG compressor at -135°C, causing ice to form around the inlet to the compressor.

This is where LNG is transformed into its gaseous state by warming the liquid using heat from sea water, before being delivered into the pipeline system. The LNG travels upwards through the ORV at around -135oC and as it travels, heat is exchanged with the seawater flowing down from the top. Regasified LNG comes out from the top of the ORV at about 25oC.

Each ORV can take about 180 tonnes of LNG. The amount of seawater required to vaporise 180 tonnes of LNG in the ORV is approximately 4,000 tonnes per hour. This is to make sure that reduction in the temperature of the returning seawater is no more than 10°C, so that it has minimum impact on the surrounding marine environment.

If the ORV cannot be used (e.g. due to a loss of power to run the seawater pumps), the SCV serves as a backup to turn LNG into gas.

Currently, there are three LNG storage tanks, each with a capacity of 180,000 cubic metres. Each tank can fit two Airbus A380s stacked on top of one another. LNG is stored in these tanks at just above atmospheric pressure and at approximately -161°C. The tanks are about 88 metres in diameter and 52 metres tall.

Flaring of gas is used as a last resort in situations where the pressure is rising in the tanks and the available capacity of the BOG compressor is insufficient to reduce the tank pressure. Some of the gas will then be diverted into the flare system to prevent over-pressurisation of the tanks and to maintain the pressure within an allowable range.