LNG unloading system

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Once the LNG carrier arrives at the unloading terminal, the LNG is pumped from the pump on the carrier, through the LNG unloading arm, and delivered to the LNG storage tanks via the unloading main pipe. The evaporative gas displaced by the LNG upon entering the storage tank is returned to the LNG hold of the transport ship through a return gas pipeline and a gas-phase return arm, in order to maintain pressure balance in the unloading system. During unloading, the operating pressure of the LNG storage tank is slightly higher than that of the LNG carrier, to ensure that the vapor from the storage tank can return directly to the carrier without the need for pressurization. The vapor pressure returning to the transport ship is controlled by a control valve. During normal operation without unloading, LNG is pumped out by the low-pressure transfer pump inside the LNG storage tank, and circulates at a low flow rate through the unloading pipeline to keep it in a cold standby state. The majority of the cyclic LNG returns to the LNG low-pressure outlet manifold leading to the re-condenser, while the remaining portion returns to each LNG storage tank via the LNG unloading manifold and the bypasses at the top and bottom feed valves of the LNG storage tanks.