Slide 4 Handling of boil-off gas Use as fuel in boilers Accumulation during voyage Use as fuel in gas engines Use as fuel in gas turbines Re-liquefaction Burn in oxidizer (incinerator)
Slide 5 Means for disposal of boil-off gas Steam turbine propulsion: Two boilers + main and auxiliary condenser Gas engine propulsion: One oxidizer with redundant auxiliaries Diesel engine propulsion: One re-liquefaction unit + one oxidizer Gas turbine propulsion: One oxidizer with redundant auxiliaries
Slide 6 Propulsion alternatives for LNG carriers Steam turbine/dual fuel steam boilers Dual fuel high pressure gas/diesel engine Dual mode low pressure gas/diesel engines Low pressure gas engines and diesel engines Gas turbine & combined gas turbines/diesel engines Diesel engine/boil-off re-liquefaction
Slide 7 Steam Turbine Propulsion - Simplified Furnace Condensate pumps Main Condenser Red gear H.P L.P Shaft Feed pumps Deareator Super- heater Economiser Flue gas uptake Downcomers Boiler casing Water wall
Slide 8 DNV Rules for gas fuelled engine installations The Rules define two concepts for safety against gas hazards in machinery spaces: –Inherently gas safe machinery space The two-barrier concept as known from the IGC Code with an additional requirement for fitting excess flow shut-off in the gas supply –ESD protected machinery space Single wall gas piping accepted. Applicable for low pressure gas engines only
Slide 9 Gas engines - piping Low pressure gas engines have gas supply piping which is difficult to arrange with complete jacketing There are no low pressure gas engines on the market at present having fully jacketed gas piping. However,Wärtsilä, is claiming that they are in the position in the near future
Slide 10 ESD Rule conditions (Emergency Shut Down) Conditions for acceptance of ESD protected machinery space: –Gas supply pressure to be < 10 bar –Automatic de-energising of all sources of ignition on detecting of low concentration of gas and shut-off of gas supply to the engine room –Automatic shut-off of gas supply on loss of engine room ventilation, detection of fire or excess gas flow
Slide 11 ESD protected engine rooms Because of the shut-down requirement for an ESD Protected engine room, the power generation for propulsion and manoeuvring must be divided between two or more engine rooms independent of each other
Slide 15 Re-liquefaction plant for LNG boil-off At present there is experiences only from one shipboard LNG re-liquefaction plant (NYK) Power consumption is high (3,5-5,0 MW) For LNG cargo tanks with permitted filling ratio of 99.5% (spherical) overfill protection arrangements should be considered
Slide 22 Gas emissions from LNG carriers FuelNOxSOxCO2 Steam turbine HFO + LNG 2002.400180.000 Low speed diesel + re-liquefaction HFO3.9501.800120.000 Dual fuel electric LNG only2400100.000 Gas turbines and COGES LNG only8500108.000 Source: ALSTOMEmissions: Tonnes / year / ship
Slide 23 Economics of LNG Re-liquefaction and Slow Speed Diesel Propulsion Low Fuel Consumption for Propulsion, but power required by the re-liquefaction plant adds another 10 – 20 tons of heavy fuel oil Unknown Initial Cost for the Re-liquefaction Plant, but Assumed to be Significant High Power Requirements for Re-liquefaction, in the order of 3-5 MW at max. load
Slide 24 Economics of Dual Fuel Gas/Diesel Engines/Gas Turbines and Electric propulsion Electric Propulsion Plants Require Higher Initial Costs Gas/Diesel Engine Plants Have Lower Fuel Consumption - Thermal Efficiency 42-44% v.s. 31-33% for Steam Propulsion Gas/Diesel Engines Have Higher Maintenance Costs Fuel Cost Savings for Gas/Diesel Plants Increase With Higher Fuel Oil Price
Slide 25 LNG carrier propulsion - Conclusion The traditional steam turbine propulsion has served LNG carriers well for over 30 years Future operating modes will require flexibility and efficient propulsion plants able to accommodate different ship speeds Operating economy and environmental issues have to be considered carefully when selecting propulsion power plant Safety and redundancy are important features required from the propulsion power plant
Slide 26 Offshore re-gasification and discharge
Slide 27 Experienced personnel, - a serious challenge !.. insufficient supply of competent people may have a knock-on effect on other shipping sectors ?
Slide 28 LNG Trade in cold Climate Cold climate: Is this the future environment for LNG carriers? What kind of impact will this have on the Propulsion system?