The receiving section consists of the berthing area for LNG carriers, the unloading arms and the transfer line. The berthing area is located at either the primary or secondary jetties which allow LNG carriers with a capacity from 120,000m3 to 265,000m3 of LNG to berth at the primary jetty, and 60,000m3 to 265,000m3 to berth at the secondary jetty. The secondary jetty has been modified to enable it to also reload small LNG ships of 2,000m3 to 10,000m3. The jetties have four mooring dolphins and four breasting dolphins, each of which is equipped with quick release mooring hooks, and four fenders to protect the LNG carrier.
To unload the cargo, the right-hand side of the pier is equipped with four unloading arms, three for liquid, and one, located in the centre, to return the LNG vapour to the LNG carrier. The LNG from the LNG carrier is transferred to three storage tanks through a 40-inch transfer line connecting the unloading arms to the tanks.
The storage section consists of four tanks, three with an operating capacity of approximately 180,000m3 and one with an operating capacity of approximately 260,000m3. They use submersed pumps for the movement of LNG.
The tanks are made up of two coaxial, vertical cylindrical containers. The self supporting inner container is made of 9% Nickel steel and is designed to store the LNG while the outer container is made of pre-stressed reinforced concrete and has the dual function of supporting and protecting the insulating material placed around the inner container and, in the event of an emergency, containing any loss of LNG.
LNG is stored in the tanks at a temperature of approximately -160°C and at a pressure slightly higher than atmospheric pressure.
The SLNG Terminal has the capability to reload LNG back onto a LNG carrier that is berthed at any of the jetties. Using the intank submerged reloading pumps, LNG can be moved from the tanks back to the primary or secondary jetty via the same 40” line used to discharge the LNG into the tanks.
The regasification section consists of High Pressure Booster pumps for the movement and pressurisation of LNG and open rack and submerged combustion vaporisers. The LNG extracted from the storage tanks is pressurised and is then sent to the vaporisers.
The LNG is regasified by means of open rack vaporisers (ORV), three in operation and one in reserve. The heat required to vaporise the LNG within the open rack vaporiser is drawn from the warm seawater as it passes over the surface of the vaporiser.
In the event that the gas grid requires a short term flow increase of regasified LNG injected which is above the capacity of the ORV’s or if an ORV is out of service for maintenance, then the submerged combustion vaporiser (SCV) is placed in operation to meet this need. This fired heater uses regasified LNG as a fuel to heat up the water held within the water bath. The heat that is used to vaporise the LNG within the SCV stainless steel coil is drawn from the heated water as the LNG passes through the system.
Boil-off Gas (BOG) recovery
The BOG recovery system at the SLNG Terminal consists of four reciprocating cryogenic compressors, the suction drum and recondenser. These compressors are used for the continuous recovery of the LNG vapours generated by the heat entering the LNG Terminal’s equipment and pipework during normal operations, and during unloading periods when additional BOG is generated while the LNG carrier is being unloaded. The suction drum is used to allow any entrained liquid that has been carried over with the vapour to be separated from the LNG vapour stream and be returned back into the LNG tanks, thus ensuring that only vapour enters the BOG compressors. Vapour recovery takes place in the recondenser by condensing the LNG vapours with subcooled LNG before it is directed to the suction of the High Pressure Booster pumps.
These systems include all of the activities that support the main process and without which the SLNG Terminal could not function. The most important systems are as follows: the electrical substations and their transmission lines for the supply of power and the transformation of electricity at the SLNG Terminal; fresh water and sea water systems for the disposal of the heat generated by compressors; instrument air systems for the implementation of pneumatic controls; nitrogen systems which allow the flare to be continuously purged; fuel gas system which provides gas to the flare pilots; the metering stations for measuring the quantity and quality of the gas in the outgoing pipelines and the fire and gas protection systems.
Control and safety systems
The SLNG Terminal is monitored and remotely controlled from the Centralised Control Room by means of an automated system. This system is divided into two subsystems:
- Distributed Control System (DCS) whose functions include the acquisition, processing and regulation of the process parameters and the supervision of the LNG Terminal;
- Programmable logic-based automation and blocking system (PLC) which governs the start-up, stopping and blocking of the equipment sequences as well as activating automatic safety procedures in the event of emergency.