Liquid Natural Gas (LNG) is becoming increasingly important for global trade. It can be flexibly transported between any pair of exporting and receiving LNG terminals. The LNG process includes liquefaction, transportation, storage and regasification of LNG.
Boil off gas (BOG) compressors are installed at LNG terminals (export & import) to transport and compress the boil off gas from the storage tanks. Re-condenser will liquefy again the gas and pumps are transporting the LNG back to the storage tanks. At import terminals the BOG compressors are also designed for the unloading case when a new load from a LNG carrier is delivered to the receiving terminal. Unloading arms transfer the cargo safely from the ship and connect the ship’s manifold system to the terminal. These arms are protected by a Power Emergency Release Coupler (PERC) and allow a rapid disconnection of the system to protect the ships manifold system and the terminal’s hard arms. During such ship unloading the flow conditions is significantly higher than under normal operation.
Under normal operating conditions the amount of BOG can be regulated by vaporizers. Such systems are designed to control the amount of BOG to the designed requirements. The amount of reserve capacity from a terminal will depend on expected shipping delays, seasonal variations and consumptions and strategic reserve requirements.
Send-out compressors will either transport the gas into a fuel gas line towards gas power plant or into a NG pipeline system for users. Send-out compressors are installed at LNG import/receiving terminal to transport and compress further the gas from the discharge header of the Boil off gas compressors into the distribution pipe line.
The send out compressors which are compressing into a transportation grid are operating in a range of typically 40-80bar pressure. Therefore the compressor discharge pressure is 80bar. The grid has exit points of transmissions with regional networks, storage infrastructures and key consumer areas.
Send out compressors which are compressing into the distribution network are operating in a range at 20-50bar discharge pressure. Therefore the compressor discharge pressure is 50bar.The gas will be supplied to industrial consumers, power plants and local distribution companies.
Gas power plants with high efficiency gas turbines will tolerate only very low gas pressure fluctuations to remain high efficient. For this reason fuel gas booster compressors are required to stabilize the feeding pressure to the gas turbine.
Floating storage and regasification unit (FSRU) are permanently moored near shore. LNG carriers supplying the FSRU with liquid natural gas for storage. The onboard storage capacity will increase the supply flexibility if the FSRU concept is designed for bunkering (see attached picture)??. The onboard regasification plant produce the gas to supply the onshore users such as process or power plants. High performance gas turbines have a higher efficiency than 40%. Therefore the gas power plant need an inlet pressure of ~50bar which will require often a fuel gas booster compressor.
Floating production storage and offloading unit (FPSO) and Floating liquefied natural gas facility (FLNG) are both moored directly above the natural gas field and is connected to a subsea system and/or drilling platforms. The onboard facility produce natural gas, LPG and natural gas condensate. The gas treatment remove impurities and followed by liquefaction stored the product in the hull. The carrier will distribute towards the import terminals. Boil off gas compressors transport the boil of gas form the LNG and LPG storage tanks further.
The term Liquefied Petroleum Gas (LPG) refers to gases, such as propane or butane, which remain liquid at room temperature and under low pressure. In natural gas and oil production, LPG is often flared on site because it is not economical to process. It is produced during exploration as well as a byproduct of petroleum refining. However, LPG can also be used as a fossil fuel for heating or cooking. In addition, LPG is used as a fuel for vehicles with gasoline engines, which is why the energy source is also known as autogas.