OVER VIEW OF LNG SHIPPING SAFETY CONCERNS Presentation by Capt. B.B. Sinha. The Shipping Corporation of India Ltd. 15.02.2010. New Delhi.
Journey of LNG 1917: First commercial natural gas liquefaction plant in West Virginia (USA). 1959: Methane Pioneer,world s s first LNG carrier, carried LNG from Lake Charles, LA to Canvey Island (UK). 1964: British gas council imports LNG from Algeria, making UK the first importer & Algeria the first exporter of LNG. 1984: Japan purchases 72% of world LNG, 75% of which is used for Power generation, dropped to 48% in 2002. This underlines the importance of shipping in transportation of LNG as bulk of LNG is transported across the globe by ships.
Gas Field LNG Storage Tank Consuming Region Liquefaction Facility LNG Tanker (floating pipe) LNG Storage Tank Vaporizers to Pipeline System LNG Value Chain
MOSS TYPE LNG CARRIERS
MEMBRANE TYPE LNG CARRIERS
SCI s s Foray in LNG Shipping SCI along with consortium partners presently owning & managing 3 LNG carriers of which first two LNG carriers SS. Disha & SS. Raahi (1,35,335 cubic capacity) powered by Steam and the 3 rd, M.t. Aseem (1,55,000 cubic capacity) powered by Diesel Fuel Dual Electric (DFDE) propulsion. All three LNG carriers engaged in carriage of LNG from Qatar to India.
Composition of LNG
PROPERTIES OF METHANE
PROPERTIES OF LNG In liquid state LNG is 1/600 th of the volume of its equivalent gaseous state at atmospheric pressure and ambient temperature. Carriage on ships at/near Boiling point. Boil-off off occurs due to evaporation: - 1 st generation vessels: 0.25% per day - 2 nd generation vessels: 0.15% per day. This Boil-off off gas powers propulsion plant (Steam plant/ DFDE). Almost nil solubility in water. High dielectric power, low conduction of electricity. Non toxic, colourless & odourless. Methane is Green house gas and a pollutant.
Inherent Risks associated with LNG Contact with LNG will damage living tissue due to its low temp. Most metals lose their ductility at these temperatures (-160( deg C). Causes brittle fracture of many materials.
Hazards of LNG Sea Transportation Escape of LNG to atmosphere and water. Fire & Explosion. Injury to personnel. Damage to ship structure due to low temperature.
Possible Causes Breach of cargo containment system due to Collision/Grounding. Formation of vapour cloud leading to Fire/Explosion.
Collision & Grounding Resistance of Gas tankers to collision & Grounding: Table indicating indicative speeds & displacement for collision impacts on a stationary LNG carrier of 1,35,000 cbm (at an angle between 30 deg either side of the perpendicular to the hull of struck tanker) that are estimated to penetrate the tanker s s outer hull. In practice, collisions rarely at 30 deg. Angle. Displacement of Impacting ship in Tonnes. Critical Impact Speed - Knots 93,000 3.2 61,000 4.2 20,000 7.3
Risk Assessment/ Mitigation Quantitative Risk Assessment (QRA) - Risk is defined as the product of frequency (F) of an event and the consequences (C) arising from it i.e., R = F x C. In LNG shipping, frequency of incidents are less but consequences are severe. In over 4 decades of LNG shipping, only 3 casualties, one of collision and two of grounding. Safety standards achieved by following: - Double Hull Construction as recommended by IG Code. - Use of special material for construction of cargo tanks (Invar - 36%Ni steel) and other ship structure including Hull, piping etc. - Two layers of insulation spaces (Primary & Secondary Barrier spaces) to inhibit the boil-off off of the gas and segregation of LNG from ship structure.
Cargo Tank Containment
Cargo Tank Layout Cargo Containment System:
Risk Assessment/ Mitigation Gas release to atmosphere: When LNG released, a cloud will develop that will travel horizontally from the spill point under the influence of prevailing winds developing a shape similar to an elongated plume. In practice, the geometry and behaviour of a gas cloud will be determined by the volume & rate at which LNG released. LNG is flammable between 5.3% and 14% by volume in air. Outside these limits the gas/air mixture is either too lean or too rich to support combustion.
Auto ignition Temperature of Liquid Fuels Fuel Auto ignition Temperature deg. F LNG (primarily methane): 1004 (595 `C) LPG: 850-950. Ethanol: 793 Methanol: 867 Gasoline: 495 Diesel Fuel Approx.: 600
Risk Assessment/ Mitigation Consequences of Ingress from the sea: Rapid mixing of LNG at cryogenic temperatures with much warmer sea water will induce the phenomenon of Rapid Phase Transition (RPT),, a forced rate of phase transition much more rapid than that would release into atmosphere. RPT will induce rapid release of energy in the form of violent non n flammable shocks that may threaten integrity of adjacent structure. re. When spilled on water: Boiling of LNG is rapid, due to the large temperature difference between the product and water. LNG continuously spreads over an indefinitely large area; results s in magnification of evaporation rate. No coherent ice formation on the water.
Prevention is better than cure Better ship design & Robust construction Meticulous planning & Execution of Shipboard operations Training of personnel.
Thank You