Proceedings magazine is a communication tool for the Coast Guard's Marine Safety & Security Council. Each quarterly magazine focuses on a specific theme of interest to the marine industry.
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48 Proceedings Fall 2015 www.uscg.mil/proceedings Liquefed Gas Barges Bunker and cargo considerations. by LT cristinA nElson Staff Engineer U.S. Coast Guard Hazardous Materials Division Mr. roy blEibErg Director of U.S. Gas Development American Bureau of Shipping Liquefed Gas Production, Transportation, and Use An example of an LNG bunker barge. Image courtesy of GTT North America. Liquefed natural gas (LNG) has arrived on the maritime stage as a viable fuel, due in part to increasing regulatory pressure for cleaner air emissions. For this reason as well as long-term economic benefts and the desire for environ- mental leadership, the maritime transportation sectors have begun to evaluate LNG as a fuel option. LNG is a unique cryogenic liquid stored at temperatures of about -162°C. It can't be delivered to many destinations that need it via existing fuel supply networks, so suppliers must develop new infrastructure to form a liquefed natural gas supply network. Further, this new infrastructure must include liquefaction, storage, transportation, and distribu- tion capabilities. As much of the developing infrastructure will be project- and end user- specifc, the typical maritime LNG consumer requires an option that can store liquefed natural gas as well as transport and distribute it to vessels. Options Three liquefed natural gas bunkering options seem most likely: • trucks, • pier-side storage facilities, • barges. There are advantages and challenges with each method. For example, trucks can transport LNG to various ports, but they cannot accommodate large quantities, and transfer rates are relatively slow. Depending on the size of the ship, small loads will require multiple transfer operations. This raises risk, since it increases the number of times person- nel interface with the cryogenic cargo. Additionally, trucks travel along roadways, which increases land transportation risk. Pier-based storage tanks can accommodate large quantities, but they are capital-intensive and lack mobility. Barges have many desired capabilities, including: • mobility, • relatively high loading rates, • suffcient capacity for most gas-fueled ships. Barges could potentially bunker liquefied natural gas, shuttle liquefied natural gas cargo along coastal routes, meet deep-draft vessels for ship-to-ship transfer at sea, and deliver LNG cargo to whichever port has the best commer- cial opportunities. Tank Design Today, Coast Guard personnel are frequently in conversa- tion with industry members, barge designers, owners, and investors who ask about what requirements LNG barges must meet to be granted Coast Guard approval. Given LNG's unique properties, designers need comprehensive guidance before they can move forward. LNG bunker barge designers must frst decide which containment system will be employed. This will have a wide-rang- ing impact on many elements of the barge design, including the vessel arrangement, inspection access, and what operating equip- ment will be required. Additionally, there are several differ- ent types of liquefed natural gas fuel storage tanks. LNG tanks can be inde- pendent tanks, which include Type A,