Sangho Lee

Optimal Unloading Procedure for a Mixed Operation of Above-ground and In-ground LNG Storage Tank using Dynamic Simulation

Publisher Summary Natural gas is used as a heating fuel and its usage has increased due to its cleanliness. At the source, natural gas is usually transformed into liquefied natural gas (LNG) to decrease its volume. It is then transported to the demand region by carrier ship. LNG is then transferred from the carrier ship to an onshore storage tank. The process of unloading liquefied natural gas (LNG) from a carrier ship to a storage tank consists of three steps: recirculation, depressurization and unloading. Because LNG is typically maintained at a cryogenic temperature near –160 °C, a recirculation process is needed to keep the unloading pipeline cool and prevent vaporization of the LNG. The unloading line is then depressurized to a pressure valve that lies between the ship and the storage tank. Finally, the LNG in the carrier ship is transferred to the storage tank. There are two different types of LNG storage tanks: above-ground and in-ground tanks. When a single type of tank is used for storage, there are no critical problems encountered between the recirculation and unloading steps. However, for the mixed operation of above-ground and in-ground LNG storage tanks, the depressurization of an unloading pipeline can generate vapor on top of the unloading pipeline of the above-ground tank due to the pressure head. The vapor produced from the above-ground tank can congest depressurization, which can in turn cause excessive BOG(Boil-Off Gas) inflow.

BOG Handling Method for Energy Saving in LNG Receiving Terminal

Abstract Generation of Boil-off gas (BOG) in liquefied natural gas (LNG) receiving terminal affects considerably operating energy costs and safety issue. For that reason, the BOG handling method is determinant for design of LNG receiving terminal. This study proposes the concept of new design for BOG handling and calculates the design variables using sensitivity analysis for minimum send-out case. This design provides 21.9% energy saving and 0.197y payback period.