Diesel electric dredger order
Belgium’s Jan De Nul Group has ordered three 3,500 m3 Trailing Suction Hopper Dredgers to be built at Keppel Nantong, and these vessels which will operate in environmentally sensitive areas, will not be LNG powered.
The design of these vessels is based on the 3,400 m3 TSHD Alvar Nuñez Cabeça de Vaca and Sebastiano Caboto, built in 2011, and successfully operating since. The vessels combine a shallow draught with high manoeuvrability, making them very suitable for working in confined areas.
The vessels are diesel-electric propelled: all major drives (thrusters, dredge pump, jet pumps...) are electrically driven, and controlled by means of frequency converters. In this way each system can operate at its optimal speed and power. Power is generated by three diesel generator sets; a control system automatically starts and stops the sets depending on the power requirement, and by means of asymmetric load sharing we ensure that the load is optimally distributed over the diesel generator sets. All these measures result in a low fuel oil consumption, which is the best in its class.
Thanks to the low fuel oil consumption, emissions are lowered, but in addition the vessels are equipped with exhaust gas treatment systems in order to further reduce harmful emissions.
New vessels need to comply with IMO regulations for NOx emissions. As the new dredgers will frequently operate in estuaries and on rivers, or near the coast, and therefore near residential areas, Jan De Nul Group decided to limit the NOx emissions to a level far below the actual requirements, and to reduce other contaminants that are currently not regulated by IMO.
The new vessels will operate with normally available fuel oil, and the exhaust gases are cleaned by means of a Selective Catalytic Reduction (SCR) system, and a Diesel Particulate Filter (DPF). The SCR system lowers the amount of NOx in the exhaust to a level corresponding with the future European (EU Stage V) requirements for inland waterway vessels; this standard is much more stringent than the applicable IMO Tier II and Tier III requirement for seagoing ships.
The DPF removes particulate matter from the exhaust, down to a level in accordance with the future EU Stage V requirement for inland waterway vessels.
Combined with the use of readily available low sulphur fuels, the emissions (NOx, SOx, Particulate Matter, CO and Hydrocarbons) will comply with EU Stage V, which Jan De Nul claims will be better than any other vessel or dredger.
Jan De Nul interestingly opted to reject LNG as a fuel for this new vessel. Liquified Natural Gas, consisting mostly of methane, has a number of advantages: less greenhouse gas CO2 is emitted, and emissions of some contaminants such as NOx, SOx, particulate matter are lower compared to a diesel engine on fuel oil, without exhaust gas treatment system. However, Jan De Nul has justified this decision to go for diesel-electric as it says the same or even better results are achieved by using exhaust gas treatment, and the important environmental and operational downsides of LNG, such as dangers of methane leakage and poorer fuel availability are avoided.
By Jake Frith
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