New Mærsk Triple-E ships worlds largest and most efficient; waste heat recovery and ultra long stroke engines contribute to up to 50% reduction in CO2/container moved

Rendering of the Triple-E. Click to enlarge.

Mærsk Line has signed a contract with Korea’s Daewoo Shipbuilding & Marine Engineering Co., Ltd. to build 10 of the world’s largest and most efficient vessels—the Triple E (Economy of scale, Energy efficient and Environmentally improved)—with an option for an additional 20 vessels. The newbuilds are scheduled for delivery between 2013 and 2015.

Four-hundred metres long, 59 meters wide and 73 meters high, the Triple-E is the largest vessel of any type on the water today, according to Mærsk. Its 18,000 TEU (twenty-foot container) capacity is 16% greater (2,500 containers) than today’s largest container vessel, Emma Mærsk. The Triple-E will produce 20% less CO2 per container moved compared to Emma Mærsk and 50% less than the industry average on the Asia-Europe trade lane.

In addition, it will consume approximately 35% less fuel per container than the 13,100 TEU vessels being delivered to other container shipping lines in the next few years, also for Asia-Europe service.

Each vessel will cost US$190 million. Besides its size, which provides superior economies of scale compared to other vessels (more cargo means less CO2 per container moved), the efficiency of Triple-E comes from its innovative design.

The Triple-E vessels have a 26% slot cost advantage compared to the 13,100 TEU vessels sailing on today’s oceans considering a full roundtrip from Asia to Europe (based on a bunker price of US$600 per metric tonnes). Slot cost is a consolidated figure from several costs; bunker fuel, vessel costs (operational and capital) plus port and canal fees.

Two ‘ultra-long stroke’ engines turn two propellers, and specially optimized hull and bow forms guide the vessel through the water at the speeds typical in the industry today. An advanced waste heat recovery system captures and reuses energy from the engines’ exhaust gas for extra propulsion with less fuel consumption.

To reduce the environmental impact of the vessels beyond their lifecycle, Mærsk Line is setting a new standard for the way vessels are recycled. All the materials used to build the Triple-E class will be documented and mapped in the vessel’s ‘cradle-to-cradle passport’. This means that when the vessel is retired from service, this document will ensure that all materials can be reused, recycled or disposed of in the safest, most efficient manner.

Propulsion system. The top speed of the Triple-E was capped at 23 knots, two knots lower than Emma Mærsk’s top speed. This meant a power requirement of 65-70 megawatts compared to Emma’s 80 megawatts—about a 19% reduction. A slower max speed also enabled Mærsk Line to consider engines that could operate at slower revolutions—‘ultra-long stroke’— which provides the greatest fuel efficiency.

To retain the efficiency created by the slower revolutions of an ultra-long stroke engine requires a larger propeller diameter. However, the size of the propeller is limited by the dimensions of the vessel and the available space beneath the keel.

To mitigate these restrictions and achieve the desired efficiency, Mærsk Line research determined that a two engine/two propeller ‘twin skeg’ system was superior to the one engine/propeller setup. The Triple-E’s two propellers are 9.8 metres in diameter with 4 blades each, compared to Emma’s single propeller, which is 9.6 metres in diameter with 6 blades. The combined diameter of the propellers provides greater pushing power in the water and the fewer number of blades creates less resistance.

All together, the Triple-E’s twin-skeg propulsion system consumes approximately 4% less energy than Emma Mærsk’s single engine/single propeller propulsion system.

The MAN diesel engines weigh 910 metric tonnes each, and deliver output of 43,000 hp (32,065 kW). Fuel consumption is 168 grams bunker oil per kWh produced.

Waste heat recovery. The Triple-E is the latest in a succession of Mærsk Line vessels (20 vessels, including the 8 Emma Mærsk class vessels) to be equipped with an energy saving advanced waste heat recovery system. For the Triple-E, the effect of the waste heat recovery system is a reduction in the engine’s fuel consumption and CO2 emissions by approximately 9%.

When exhaust gas leaves the engine, it has a very high heat potential. Utilizing this potential in an exhaust gas boiler, it is possible to generate steam. The waste heat recovery system then supplies the steam into a turbine connected to a generator which then recovers electrical energy.

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